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Running 1.5 HP 3 phase motor on a 12V SLA battery
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P E Schoen
Apr 2, 2012, 3:32:04 AM4/2/12
to
I'm working on a project to use a three-phase motor on an electric tractor.
As a proof-of-concept, I have replaced a 10 HP B&S gas engine on a Craftsman
riding mower, with a 2 HP 3450 RPM three-phase motor, and I was able to
drive a short distance on an extension cord to single phase 240 VAC and a 2
HP Fuji/GE motor controller. I have some youtube movies that show some of my
progress, but they don't show my more recent better results.
http://www.youtube.com/v/kYaDbyAzdnA&hl (2 years before I bought it for $40)
http://www.youtube.com/v/SGd8i6dp4SY&hl
http://www.youtube.com/v/DdvscTp3thw&hl
My next step was to power it from batteries. A previous post about using an
iron-core toroid to generate 350 VDC at 1.5 kVA or more was to be the DC-DC
converter for this, and I still may build a more practical version. But for
now, I wanted something simple, so I decided to use an ordinary automotive
inverter. I used a full wave bridge to a pair of 3300 uF 400 V capacitors in
series, with the common to one side of the AC, which generated about 320
VDC. It was able to power the VF drive, but the 175 watt inverter was not
enough to run a 1.5 HP 1725 RPM motor. A 300 watt inverter worked for a
short time, but the 6 amp power supply kept tripping. So I replaced it with
a 12 year old 17 A-H SLA battery and it was able to run the motor under no
load, with only an occasional complaint from the inverter. Here are the
results:
RPM Vbatt Ibatt Freq Imotor Vmotor
0 12.4 1.0 0 0 0
300 12.1 7.0 10.0 2.41 42
450 12.1 7.0 15.0 2.32 62
900 11.8 8.0 30.0 2.35 121
1200 11.9 9.5 40.0 2.22 152
1930 12.1 7.0 61.0 1.35 164
2500 12.0 7.0 83.3 1.00 164
The RPM values are based on synchronous speed. The motor seemed to have good
torque, but I didn’t have a way to load it properly, and I didn't want to
load the inverter too much. It seemed to complain when the battery current
reached about 10-12 amps during start-up, especially at 1200 RPM.
I plan to buy a larger inverter for the last phase of this project. The best
deals at Harbor Freight are as follows:
750W $50 $0.067/watt
1000W $80 $0.08/watt
1200W $100 $0.083/watt
2000W $160 $0.08/watt
But I found some much cheaper on eBay
3000W $100 $0.033/watt
1000W $55 $0.055/watt
1000W (220V) $43 $0.043/watt
Those prices include shipping and are "buy it now" prices. If these will do
the job, there's no way I can build one myself for anywhere near that unless
I don't count my time and use surplus/junk box parts. And one facet of my
project is to make the system modular and easily built anywhere in the
world.
But I want to use at least two batteries to get reasonable run time. This
proof-of-concept phase is only for a utility cart which will probably need
only about 1 HP average, so a single 100 A-H deep cycle battery should give
at least one hour, which is fine. Even my 17 A-H SLA might give me 15
minutes, and I have another small battery I could add. But since these are
12V inverters, I need to consider what is the best way to get the needed
link voltage. My best guess is to use one inverter for each battery, connect
the AC through a FWB to get 160V, and then connect two in series for 320V.
The batteries will be "hot", however, since the inverters are not isolated.
So I just need to put them in plastic containers and use isolation
techniques to monitor voltage and current.
I plan to make a datalogger to keep track of the power and energy used under
various load conditions (mostly going up and down hills), to get an idea of
efficiency. I want to compare my results to other electric tractors which
usually use brushed DC motors or BLDCs, and relatively simple controls.
OK, enough of a "brain dump" for now. I'll post more when I have more to
tell. Please feel free to comment and make suggestions.
Thanks,
Paul
As a proof-of-concept, I have replaced a 10 HP B&S gas engine on a Craftsman
riding mower, with a 2 HP 3450 RPM three-phase motor, and I was able to
drive a short distance on an extension cord to single phase 240 VAC and a 2
HP Fuji/GE motor controller. I have some youtube movies that show some of my
progress, but they don't show my more recent better results.
http://www.youtube.com/v/kYaDbyAzdnA&hl (2 years before I bought it for $40)
http://www.youtube.com/v/SGd8i6dp4SY&hl
http://www.youtube.com/v/DdvscTp3thw&hl
My next step was to power it from batteries. A previous post about using an
iron-core toroid to generate 350 VDC at 1.5 kVA or more was to be the DC-DC
converter for this, and I still may build a more practical version. But for
now, I wanted something simple, so I decided to use an ordinary automotive
inverter. I used a full wave bridge to a pair of 3300 uF 400 V capacitors in
series, with the common to one side of the AC, which generated about 320
VDC. It was able to power the VF drive, but the 175 watt inverter was not
enough to run a 1.5 HP 1725 RPM motor. A 300 watt inverter worked for a
short time, but the 6 amp power supply kept tripping. So I replaced it with
a 12 year old 17 A-H SLA battery and it was able to run the motor under no
load, with only an occasional complaint from the inverter. Here are the
results:
RPM Vbatt Ibatt Freq Imotor Vmotor
0 12.4 1.0 0 0 0
300 12.1 7.0 10.0 2.41 42
450 12.1 7.0 15.0 2.32 62
900 11.8 8.0 30.0 2.35 121
1200 11.9 9.5 40.0 2.22 152
1930 12.1 7.0 61.0 1.35 164
2500 12.0 7.0 83.3 1.00 164
The RPM values are based on synchronous speed. The motor seemed to have good
torque, but I didn’t have a way to load it properly, and I didn't want to
load the inverter too much. It seemed to complain when the battery current
reached about 10-12 amps during start-up, especially at 1200 RPM.
I plan to buy a larger inverter for the last phase of this project. The best
deals at Harbor Freight are as follows:
750W $50 $0.067/watt
1000W $80 $0.08/watt
1200W $100 $0.083/watt
2000W $160 $0.08/watt
But I found some much cheaper on eBay
3000W $100 $0.033/watt
1000W $55 $0.055/watt
1000W (220V) $43 $0.043/watt
Those prices include shipping and are "buy it now" prices. If these will do
the job, there's no way I can build one myself for anywhere near that unless
I don't count my time and use surplus/junk box parts. And one facet of my
project is to make the system modular and easily built anywhere in the
world.
But I want to use at least two batteries to get reasonable run time. This
proof-of-concept phase is only for a utility cart which will probably need
only about 1 HP average, so a single 100 A-H deep cycle battery should give
at least one hour, which is fine. Even my 17 A-H SLA might give me 15
minutes, and I have another small battery I could add. But since these are
12V inverters, I need to consider what is the best way to get the needed
link voltage. My best guess is to use one inverter for each battery, connect
the AC through a FWB to get 160V, and then connect two in series for 320V.
The batteries will be "hot", however, since the inverters are not isolated.
So I just need to put them in plastic containers and use isolation
techniques to monitor voltage and current.
I plan to make a datalogger to keep track of the power and energy used under
various load conditions (mostly going up and down hills), to get an idea of
efficiency. I want to compare my results to other electric tractors which
usually use brushed DC motors or BLDCs, and relatively simple controls.
OK, enough of a "brain dump" for now. I'll post more when I have more to
tell. Please feel free to comment and make suggestions.
Thanks,
Paul
Winston
Apr 2, 2012, 9:36:44 AM4/2/12
to
P E Schoen wrote:
(...)
> But I want to use at least two batteries to get reasonable run time. This proof-of-concept phase is only for a utility
> cart which will probably need only about 1 HP average, so a single 100 A-H deep cycle battery should give at least one
> hour, which is fine.
Were that the case, yes. :)
1 HP at 100% efficiency is 746 W or 62.2 A.
Figure 30% efficiency and that number goes up to 207 A.
So figure about *6 minutes* at 1 HP, for a 100 AH battery, not an hour. :)
See the data for the '121000' battery here:
http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/Constant_Current-Power_Discharge_Ratings_PS__PSH_Series_10_Dec_14.pdf
Read "the small print" about lead acid batteries here:
http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/20110920-TechManual-Lo.pdf
--Winston<-- "The Large Print Giveth and the Small Print Taketh Away."
Tom Waits "Step Right Up", _Small Change_ (1976)
(...)
> But I want to use at least two batteries to get reasonable run time. This proof-of-concept phase is only for a utility
> cart which will probably need only about 1 HP average, so a single 100 A-H deep cycle battery should give at least one
> hour, which is fine.
1 HP at 100% efficiency is 746 W or 62.2 A.
Figure 30% efficiency and that number goes up to 207 A.
So figure about *6 minutes* at 1 HP, for a 100 AH battery, not an hour. :)
See the data for the '121000' battery here:
http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/Constant_Current-Power_Discharge_Ratings_PS__PSH_Series_10_Dec_14.pdf
Read "the small print" about lead acid batteries here:
http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/20110920-TechManual-Lo.pdf
--Winston<-- "The Large Print Giveth and the Small Print Taketh Away."
Tom Waits "Step Right Up", _Small Change_ (1976)
NT
Apr 2, 2012, 11:13:21 AM4/2/12
to
On Apr 2, 8:32 am, "P E Schoen" <p...@peschoen.com> wrote:
> I'm working on a project to use a three-phase motor on an electric tractor.
> As a proof-of-concept, I have replaced a 10 HP B&S gas engine on a Craftsman
> riding mower, with a 2 HP 3450 RPM three-phase motor, and I was able to
> drive a short distance on an extension cord to single phase 240 VAC and a 2
> HP Fuji/GE motor controller. I have some youtube movies that show some of my
> progress, but they don't show my more recent better results.
>
> http://www.youtube.com/v/kYaDbyAzdnA&hl(2 years before I bought it for $40)http://www.youtube.com/v/SGd8i6dp4SY&hlhttp://www.youtube.com/v/DdvscTp3thw&hl
> I'm working on a project to use a three-phase motor on an electric tractor.
> As a proof-of-concept, I have replaced a 10 HP B&S gas engine on a Craftsman
> riding mower, with a 2 HP 3450 RPM three-phase motor, and I was able to
> drive a short distance on an extension cord to single phase 240 VAC and a 2
> HP Fuji/GE motor controller. I have some youtube movies that show some of my
> progress, but they don't show my more recent better results.
>
3kVA is too small. 1.5hp - 1.12kW. Guesstimate another 20% onto the
current for lagging pf -> 1.34kVA. Even 6x run current during startup
would be 8kVA. If you use a 3kVA invertor, you'll need a way to cope
gracefully with excess demand by reducing Vout to limit i.
NT
P E Schoen
Apr 2, 2012, 4:32:10 PM4/2/12
to
"Winston" wrote in message news:jlca1...@news7.newsguy.com...
> P E Schoen wrote:
>> But I want to use at least two batteries to get reasonable run time.
>> This proof-of-concept phase is only for a utility cart which will
>> probably need only about 1 HP average, so a single 100 A-H deep
>> cycle battery should give at least one hour, which is fine.
> Were that the case, yes. :)
> 1 HP at 100% efficiency is 746 W or 62.2 A.
> Figure 30% efficiency and that number goes up to 207 A.
> So figure about *6 minutes* at 1 HP, for a 100 AH battery, not an hour.
> :)
I can't see where efficiency can be that low. The motor is about 85%
efficient, and there will also be some inefficiencies in the transmission,
differential, and rolling friction of the tires on the ground. But I can't
easily measure those, so I'm just assuming that 1 HP as measured by motor
draw will be sufficient. The VF controller is rated to be about 94%
efficient. The conversion from AC to DC is probably about 95% efficient. And
the inverter is supposed to be about 90% efficient. So the overall
efficiency (not counting the battery itself) is 0.94*0.95*0.90 = 80%. Thus
for 1 HP motor draw, the battery would need to provide 1.24 HP or 928 watts
or 77 amps. The battery you mention below would provide that for 30-45
minutes. Or the same based on a constant 155 watts per cell.
Yes, my 1 hour figure was too optimistic, but within a binary order of
magnitude. Now, to determine the actual power needed, I have an access road
which is approximately 300 feet long and a rise of about 80 feet. I would
like my tractor to be able to carry its own weight and me this distance at
about 5 MPH, which is about 400 pounds in 36 seconds. The actual work is 400
lb * 80 ft / 36 seconds or 392 lb-ft/sec. 1 HP is 550 lb-ft/sec. So it's in
the right ballpark. I figure that the motor efficiency of 85% and mechanical
efficiency of drive train at 80% will be 68% which means 392/0.68 or 576 HP.
Close enough for "gummint work"!
> See the data for the '121000' battery here:
> http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/Constant_Current-Power_Discharge_Ratings_PS__PSH_Series_10_Dec_14.pdf
> Read "the small print" about lead acid batteries here:
> http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/20110920-TechManual-Lo.pdf
There have been many tractor conversions that seem to indicate that a
sustained draw of about 3 HP is needed for actual mowing work that was
originally done with an 8 to 10 HP gas engine. It is generally accepted that
there is a 3:1 ratio of equivalent power for gas/electric, so that seems
about right. IIRC the tractor used three 100 A-H batteries and they lasted
for about 1/2 hour of mowing, so again my optimistic estimate is not far off
the mark. But the proof is in the pudding (or the "putting" of a datalogger
on the system and actually trying it).
There is a website dedicated to one person's three-year electric mower
project, using a larger tractor which happens to be essentially the same as
my other one, which I plan to electrify with a 5 HP electric motor and a 7.5
HP 480V VF controller, using three or four batteries:
http://www.diyelectricmower.com/
And here are videos of my tractor:
http://www.youtube.com/watch?v=mF24Sict-MM (walk-around)
http://youtu.be/xPO9Xo8EHUw (engine test, removal, electric motor and
controller)
And my diesel tractor:
http://youtu.be/6KbZc0WLq4Q (walk-around)
http://youtu.be/t-j3O06ExVg (start and run)
http://youtu.be/BgXon0J15as (ride)
I'm having some fun with these projects, and I hope to learn a lot about
electric vehicles in general. Eventually I may want to make my own
street-legal electric car, as some guys in Canada did for less than $1000
(including the car!):
http://forkenswift.com/index.htm
Thanks,
Paul
> P E Schoen wrote:
>> But I want to use at least two batteries to get reasonable run time.
>> This proof-of-concept phase is only for a utility cart which will
>> probably need only about 1 HP average, so a single 100 A-H deep
>> cycle battery should give at least one hour, which is fine.
> Were that the case, yes. :)
> 1 HP at 100% efficiency is 746 W or 62.2 A.
> Figure 30% efficiency and that number goes up to 207 A.
> So figure about *6 minutes* at 1 HP, for a 100 AH battery, not an hour.
> :)
efficient, and there will also be some inefficiencies in the transmission,
differential, and rolling friction of the tires on the ground. But I can't
easily measure those, so I'm just assuming that 1 HP as measured by motor
draw will be sufficient. The VF controller is rated to be about 94%
efficient. The conversion from AC to DC is probably about 95% efficient. And
the inverter is supposed to be about 90% efficient. So the overall
efficiency (not counting the battery itself) is 0.94*0.95*0.90 = 80%. Thus
for 1 HP motor draw, the battery would need to provide 1.24 HP or 928 watts
or 77 amps. The battery you mention below would provide that for 30-45
minutes. Or the same based on a constant 155 watts per cell.
Yes, my 1 hour figure was too optimistic, but within a binary order of
magnitude. Now, to determine the actual power needed, I have an access road
which is approximately 300 feet long and a rise of about 80 feet. I would
like my tractor to be able to carry its own weight and me this distance at
about 5 MPH, which is about 400 pounds in 36 seconds. The actual work is 400
lb * 80 ft / 36 seconds or 392 lb-ft/sec. 1 HP is 550 lb-ft/sec. So it's in
the right ballpark. I figure that the motor efficiency of 85% and mechanical
efficiency of drive train at 80% will be 68% which means 392/0.68 or 576 HP.
Close enough for "gummint work"!
> See the data for the '121000' battery here:
> http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/Constant_Current-Power_Discharge_Ratings_PS__PSH_Series_10_Dec_14.pdf
> Read "the small print" about lead acid batteries here:
> http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/20110920-TechManual-Lo.pdf
sustained draw of about 3 HP is needed for actual mowing work that was
originally done with an 8 to 10 HP gas engine. It is generally accepted that
there is a 3:1 ratio of equivalent power for gas/electric, so that seems
about right. IIRC the tractor used three 100 A-H batteries and they lasted
for about 1/2 hour of mowing, so again my optimistic estimate is not far off
the mark. But the proof is in the pudding (or the "putting" of a datalogger
on the system and actually trying it).
There is a website dedicated to one person's three-year electric mower
project, using a larger tractor which happens to be essentially the same as
my other one, which I plan to electrify with a 5 HP electric motor and a 7.5
HP 480V VF controller, using three or four batteries:
http://www.diyelectricmower.com/
And here are videos of my tractor:
http://www.youtube.com/watch?v=mF24Sict-MM (walk-around)
http://youtu.be/xPO9Xo8EHUw (engine test, removal, electric motor and
controller)
And my diesel tractor:
http://youtu.be/6KbZc0WLq4Q (walk-around)
http://youtu.be/t-j3O06ExVg (start and run)
http://youtu.be/BgXon0J15as (ride)
I'm having some fun with these projects, and I hope to learn a lot about
electric vehicles in general. Eventually I may want to make my own
street-legal electric car, as some guys in Canada did for less than $1000
(including the car!):
http://forkenswift.com/index.htm
Thanks,
Paul
Winston
Apr 2, 2012, 5:57:49 PM4/2/12
to
P E Schoen wrote:
(...)
(...)
> I can't see where efficiency can be that low.
You are right. It'll be lower.
> The motor is about 85% efficient, and there will also be some
> inefficiencies in the transmission, differential, and rolling friction of the tires on the ground. But I can't easily
> measure those, so I'm just assuming that 1 HP as measured by motor draw will be sufficient. The VF controller is rated
> to be about 94% efficient. The conversion from AC to DC is probably about 95% efficient. And the inverter is supposed to
> be about 90% efficient. So the overall efficiency (not counting the battery itself) is 0.94*0.95*0.90 = 80%.
> Thus for 1
> HP motor draw, the battery would need to provide 1.24 HP or 928 watts or 77 amps. The battery you mention below would
> provide that for 30-45 minutes. Or the same based on a constant 155 watts per cell.
wildly optimistic, IMHO. Figure about half the energy you put into the battery
will be available on discharge.
The terminal (!) voltage at that rate is 1.85 V per cell (or discharge to about
10% of capacity).
This'll wreck your battery muy pronto. Industry practice is to limit discharge to
40% of capacity, worst case (1.98 V per cell).
This is assuming that you want more than a couple runs off each battery
you buy.
Have fun Paul! :)
--Winston
bw
Apr 2, 2012, 8:42:14 PM4/2/12
to
"Winston" <Win...@Bigbrother.net> wrote in message
news:jld7c...@news7.newsguy.com...
>P E Schoen wrote:
>>
> Even if you have a bottomless pocketbook for batteries, your estimate is
> still
> wildly optimistic, IMHO. Figure about half the energy you put into the
> battery
> will be available on discharge.
>
> The terminal (!) voltage at that rate is 1.85 V per cell (or discharge to
> about
> 10% of capacity).
> This'll wreck your battery muy pronto. Industry practice is to limit
> discharge to
> 40% of capacity, worst case (1.98 V per cell).
>
> This is assuming that you want more than a couple runs off each battery
> you buy.
>
Yes, exceeding rated discharge by a factor of 10 will severely impair the
>>
> Even if you have a bottomless pocketbook for batteries, your estimate is
> still
> wildly optimistic, IMHO. Figure about half the energy you put into the
> battery
> will be available on discharge.
>
> The terminal (!) voltage at that rate is 1.85 V per cell (or discharge to
> about
> 10% of capacity).
> This'll wreck your battery muy pronto. Industry practice is to limit
> discharge to
> 40% of capacity, worst case (1.98 V per cell).
>
> This is assuming that you want more than a couple runs off each battery
> you buy.
>
number of cycles. Also, mass produced sealed LA batts have a discharge
rating over a specified time, such as 8 hours or 10 hours, or until some
voltage end point such as 1.9 volts per cell.
Some designs are tested to determine engineering limits, thermal
characteristics, internal resistance, etc.
SLA discharge curves for SLAs made by Johnson show curves for 0.1, 0.3, 0.5
on up to 7 times capacity. That design showed the 10 hour rating to 1.6
volts/cell. The 2C curve ended after 10 minutes at 1.2 volts per cell. There
is a 7C curve that ends at 1.0 volt/cell which was reached in 1 minute.
There are many pages of such testing in Linden's Handbook of Batteries.
The OP could increase the capacity to avoid over 50 percent discharge. Just
increase the size by a factor of 10, for example using high capacity tractor
starting batteries in parallel.
P E Schoen
Apr 2, 2012, 9:13:13 PM4/2/12
to
"NT" wrote in message
news:7ea9fd32-fa96-483f...@x17g2000yqj.googlegroups.com...
> I wouldnt even contemplate any of the under 3kVA invertors, and
> really 3kVA is too small. 1.5hp - 1.12kW. Guesstimate another
> 20% onto the current for lagging pf -> 1.34kVA. Even 6x run current
> during startup would be 8kVA. If you use a 3kVA invertor, you'll
> need a way to cope gracefully with excess demand by reducing
> Vout to limit i.
Actually the current limit of the inverter seems to limit its output during
startup which involves charging the two 3300 uF capacitors. Once charged,
they should be able to handle a motor current surge of 3 HP (2200 watts or 7
amps at 320 VDC) for about 75 mSec. If I used 12,000 uF 200 V capacitors
instead, they would give about 300 mSec surge. The motor controller would
handle the overload stuff.
I just did a bit of testing on the tractor, and it seems that maybe the
automotive type inverters are not the way to go. I could only run the motor
in neutral and at 600 RPM it drew 10.5 to 11.5 amps. At about 850 RPM it
drew 12.5 amps at a battery voltage of 11.5 volts, and at 1080 RPM it
reached a peak current of about 15 amps at which point the undervoltage trip
on the VF drive shut it down. I checked the bus link voltage, and it was
only about 250 VDC with no load other than the drive, and it dropped to 203
VDC under load. This was with 3.36 amps per phase and 43 volts according to
the drive display. When I released the clutch the battery current rose to
about 15 amps and the tractor started to move but then the drive kicked out.
This was not really surprising, but the low bus link voltage makes me think
it may not be practical to use the automotive inverters, especially the 120
VAC type in a voltage doubler configuration as I have. The stepped sine wave
is really a rectangular waveform with 180 volt peaks at about 35% duty
cycle, which is 106 VRMS. I did an LTspice simulation which showed 325 volts
out into 150 ohms, for 707 watts, but this requires 20 amp peak current
pulses from the inverter, and it is probably limited to something like 9.5
amps which is 600 watts (peak) / (180V * 0.35). The actual input power at
shut-down is about 11.5V*15A = 172 watts, but the power factor of the load
is probably causing a higher output current draw. The motor is drawing 43 *
3.36 * sqrt(3) = 250 VA according to the VFD display.
My simulation shows 8.15 amps RMS at 89.3 VRMS (30% duty cycle and 1 ohm
source resistance), which is 727 VA. But I have a pure resistive load of 707
watts.
Anyway, maybe I should go back to my original plan to make my own DC-DC
converter. And I'm wondering if I might be able to modify the 600 watt UPS I
described in another post. I already have a PIC circuit that will drive the
MOSFETs in push-pull configuration, although I probably need to add gate
drivers to get 10 volts for good results (they probably are not logic
level). If I drive the transformer with 49% duty cycle, and a somewhat
higher frequency (probably 180-240 Hz), I should be able to get a solid 160
volt square wave which should drive my doubler to 320 VDC. Probably worth a
try, since otherwise I was going to scrap it.
Stay tuned...
Paul
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WIRE 0 592 -64 592
WIRE 64 608 64 544
FLAG 64 608 0
FLAG 32 240 out
FLAG -416 240 in1
FLAG -416 432 in2
SYMBOL diode -144 400 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value MUR460
SYMBOL diode -208 336 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D3
SYMATTR Value MUR460
SYMBOL polcap -16 272 R0
WINDOW 3 24 64 Left 2
SYMATTR Value 3300µ
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=600 Irms=2.9 Rser=0.018 Lser=0
SYMBOL res 48 352 R0
SYMATTR InstName R1
SYMATTR Value 150
SYMBOL diode -208 256 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value MUR460
SYMBOL diode -144 512 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value MUR460
SYMBOL voltage -464 256 R0
WINDOW 3 -212 392 Left 2
WINDOW 39 33 83 Left 2
SYMATTR InstName V1
SYMATTR Value PWL repeat for 10( (0 0) (+7m 0) (+1u 180) (+3m 180) (+1u 0)
(+7m 0) (+1u -180) (+3m -180) (+1u 0) ) endrepeat
SYMATTR SpiceLine Rser=1
SYMBOL polcap -16 480 R0
WINDOW 3 45 31 Left 2
SYMATTR Value 3300µ
SYMATTR InstName C2
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=600 Irms=2.9 Rser=0.018 Lser=0
SYMBOL res -80 272 R0
SYMATTR InstName R2
SYMATTR Value 25k
SYMBOL res -80 448 R0
SYMATTR InstName R3
SYMATTR Value 25k
TEXT -464 472 Left 2 !.tran 1 startup
news:7ea9fd32-fa96-483f...@x17g2000yqj.googlegroups.com...
> I wouldnt even contemplate any of the under 3kVA invertors, and
> really 3kVA is too small. 1.5hp - 1.12kW. Guesstimate another
> 20% onto the current for lagging pf -> 1.34kVA. Even 6x run current
> during startup would be 8kVA. If you use a 3kVA invertor, you'll
> need a way to cope gracefully with excess demand by reducing
> Vout to limit i.
startup which involves charging the two 3300 uF capacitors. Once charged,
they should be able to handle a motor current surge of 3 HP (2200 watts or 7
amps at 320 VDC) for about 75 mSec. If I used 12,000 uF 200 V capacitors
instead, they would give about 300 mSec surge. The motor controller would
handle the overload stuff.
I just did a bit of testing on the tractor, and it seems that maybe the
automotive type inverters are not the way to go. I could only run the motor
in neutral and at 600 RPM it drew 10.5 to 11.5 amps. At about 850 RPM it
drew 12.5 amps at a battery voltage of 11.5 volts, and at 1080 RPM it
reached a peak current of about 15 amps at which point the undervoltage trip
on the VF drive shut it down. I checked the bus link voltage, and it was
only about 250 VDC with no load other than the drive, and it dropped to 203
VDC under load. This was with 3.36 amps per phase and 43 volts according to
the drive display. When I released the clutch the battery current rose to
about 15 amps and the tractor started to move but then the drive kicked out.
This was not really surprising, but the low bus link voltage makes me think
it may not be practical to use the automotive inverters, especially the 120
VAC type in a voltage doubler configuration as I have. The stepped sine wave
is really a rectangular waveform with 180 volt peaks at about 35% duty
cycle, which is 106 VRMS. I did an LTspice simulation which showed 325 volts
out into 150 ohms, for 707 watts, but this requires 20 amp peak current
pulses from the inverter, and it is probably limited to something like 9.5
amps which is 600 watts (peak) / (180V * 0.35). The actual input power at
shut-down is about 11.5V*15A = 172 watts, but the power factor of the load
is probably causing a higher output current draw. The motor is drawing 43 *
3.36 * sqrt(3) = 250 VA according to the VFD display.
My simulation shows 8.15 amps RMS at 89.3 VRMS (30% duty cycle and 1 ohm
source resistance), which is 727 VA. But I have a pure resistive load of 707
watts.
Anyway, maybe I should go back to my original plan to make my own DC-DC
converter. And I'm wondering if I might be able to modify the 600 watt UPS I
described in another post. I already have a PIC circuit that will drive the
MOSFETs in push-pull configuration, although I probably need to add gate
drivers to get 10 volts for good results (they probably are not logic
level). If I drive the transformer with 49% duty cycle, and a somewhat
higher frequency (probably 180-240 Hz), I should be able to get a solid 160
volt square wave which should drive my doubler to 320 VDC. Probably worth a
try, since otherwise I was going to scrap it.
Stay tuned...
Paul
======================== VoltageDoubler.asc ===========================
Version 4
SHEET 1 2340 720
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FLAG -416 432 in2
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SYMATTR Value MUR460
SYMBOL diode -208 336 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D3
SYMATTR Value MUR460
SYMBOL polcap -16 272 R0
WINDOW 3 24 64 Left 2
SYMATTR Value 3300µ
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
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SYMBOL res 48 352 R0
SYMATTR InstName R1
SYMATTR Value 150
SYMBOL diode -208 256 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value MUR460
SYMBOL diode -144 512 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value MUR460
SYMBOL voltage -464 256 R0
WINDOW 3 -212 392 Left 2
WINDOW 39 33 83 Left 2
SYMATTR InstName V1
SYMATTR Value PWL repeat for 10( (0 0) (+7m 0) (+1u 180) (+3m 180) (+1u 0)
(+7m 0) (+1u -180) (+3m -180) (+1u 0) ) endrepeat
SYMATTR SpiceLine Rser=1
SYMBOL polcap -16 480 R0
WINDOW 3 45 31 Left 2
SYMATTR Value 3300µ
SYMATTR InstName C2
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=600 Irms=2.9 Rser=0.018 Lser=0
SYMBOL res -80 272 R0
SYMATTR InstName R2
SYMATTR Value 25k
SYMBOL res -80 448 R0
SYMATTR InstName R3
SYMATTR Value 25k
TEXT -464 472 Left 2 !.tran 1 startup
P E Schoen
Apr 2, 2012, 10:09:38 PM4/2/12
to
"bw" wrote in message news:jldh15$ch7$1...@dont-email.me...
> Yes, exceeding rated discharge by a factor of 10 will severely
> impair the number of cycles. Also, mass produced sealed LA
> batts have a discharge rating over a specified time, such as
> 8 hours or 10 hours, or until some voltage end point such as
> 1.9 volts per cell.
> Some designs are tested to determine engineering limits,
> thermal characteristics, internal resistance, etc.
> SLA discharge curves for SLAs made by Johnson show curves
> for 0.1, 0.3, 0.5 on up to 7 times capacity. That design showed
> the 10 hour rating to 1.6 volts/cell. The 2C curve ended after 10
> minutes at 1.2 volts per cell. There is a 7C curve that ends at
> 1.0 volt/cell which was reached in 1 minute.
> There are many pages of such testing in Linden's Handbook of
> Batteries. The OP could increase the capacity to avoid over 50
> percent discharge. Just increase the size by a factor of 10, for
> example using high capacity tractor starting batteries in parallel.
From the chart supplied on the PowerSonic 100 A-H battery, the actual A-H
capacity to 1.85 volts/cell is 93 A-H at 4.65 A (about 1/20 C), 80 A-H at 10
A (1/10 C), and 44 A-H at 58 A ( 0.6 C ). And in the technical data sheet it
says that a deep cycle battery can be discharged at a 1 Hr rate for an
effective capacity of 62% of the rated capacity based on 20 hr discharge.
And at high discharge rates, 1.75 V/cell represents about 50% of capacity,
and the battery "easily recovers" from such a discharge.
Discharging to 50% of capacity should give a total of 400-500 cycles, and
even discharging to 100% will still give about 200 cycles. The 100 A-H
battery I was considering costs $85. So if I get 400 cycles from it, that is
not even 25 cents per cycle. I can live with that. The energy from the grid
adds about 10 cents per charge. If I can run this vehicle at 5 MPH for 1/2
hour, that's 2.5 miles at about $0.12/mile. Not bad.
An equivalent gas powered vehicle might get 50 MPG so 1/20 gallon for 2.5
miles, at $5/gallon, is actually about the same. But electric has
advantages: quieter, cleaner, less maintenance, and can be obtained from
renewable energy sources. And, hey, I just like it!
Paul
> Yes, exceeding rated discharge by a factor of 10 will severely
> impair the number of cycles. Also, mass produced sealed LA
> batts have a discharge rating over a specified time, such as
> 8 hours or 10 hours, or until some voltage end point such as
> 1.9 volts per cell.
> Some designs are tested to determine engineering limits,
> thermal characteristics, internal resistance, etc.
> SLA discharge curves for SLAs made by Johnson show curves
> for 0.1, 0.3, 0.5 on up to 7 times capacity. That design showed
> the 10 hour rating to 1.6 volts/cell. The 2C curve ended after 10
> minutes at 1.2 volts per cell. There is a 7C curve that ends at
> 1.0 volt/cell which was reached in 1 minute.
> There are many pages of such testing in Linden's Handbook of
> Batteries. The OP could increase the capacity to avoid over 50
> percent discharge. Just increase the size by a factor of 10, for
> example using high capacity tractor starting batteries in parallel.
capacity to 1.85 volts/cell is 93 A-H at 4.65 A (about 1/20 C), 80 A-H at 10
A (1/10 C), and 44 A-H at 58 A ( 0.6 C ). And in the technical data sheet it
says that a deep cycle battery can be discharged at a 1 Hr rate for an
effective capacity of 62% of the rated capacity based on 20 hr discharge.
And at high discharge rates, 1.75 V/cell represents about 50% of capacity,
and the battery "easily recovers" from such a discharge.
Discharging to 50% of capacity should give a total of 400-500 cycles, and
even discharging to 100% will still give about 200 cycles. The 100 A-H
battery I was considering costs $85. So if I get 400 cycles from it, that is
not even 25 cents per cycle. I can live with that. The energy from the grid
adds about 10 cents per charge. If I can run this vehicle at 5 MPH for 1/2
hour, that's 2.5 miles at about $0.12/mile. Not bad.
An equivalent gas powered vehicle might get 50 MPG so 1/20 gallon for 2.5
miles, at $5/gallon, is actually about the same. But electric has
advantages: quieter, cleaner, less maintenance, and can be obtained from
renewable energy sources. And, hey, I just like it!
Paul
Tim Williams
Apr 3, 2012, 12:35:52 AM4/3/12
to
If you hack off the FWB and chopper inside the inverter and rewire it as a
full wave doubler, and shove that straight into the VFD (wired for 240VAC
input, which should work on 320VDC just fine assuming there isn't some hunk
of iron providing control voltages). Voila, now the only power factor you
have to worry about is the inverter switching supply's -- which is an
important concern with cap-input filters, but they're made pretty brutally
so it's not really going to notice the difference.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"P E Schoen" <pa...@peschoen.com> wrote in message
news:jldirl$l1h$1...@dont-email.me...
full wave doubler, and shove that straight into the VFD (wired for 240VAC
input, which should work on 320VDC just fine assuming there isn't some hunk
of iron providing control voltages). Voila, now the only power factor you
have to worry about is the inverter switching supply's -- which is an
important concern with cap-input filters, but they're made pretty brutally
so it's not really going to notice the difference.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"P E Schoen" <pa...@peschoen.com> wrote in message
news:jldirl$l1h$1...@dont-email.me...
josephkk
Apr 9, 2012, 10:56:09 PM4/9/12
to
On Mon, 2 Apr 2012 21:13:13 -0400, "P E Schoen" <pa...@peschoen.com> wrote:
>"NT" wrote in message
>news:7ea9fd32-fa96-483f...@x17g2000yqj.googlegroups.com...
>
>> I wouldnt even contemplate any of the under 3kVA invertors, and
>> really 3kVA is too small. 1.5hp - 1.12kW. Guesstimate another
>> 20% onto the current for lagging pf -> 1.34kVA. Even 6x run current
>> during startup would be 8kVA. If you use a 3kVA invertor, you'll
>> need a way to cope gracefully with excess demand by reducing
>> Vout to limit i.
>
>Actually the current limit of the inverter seems to limit its output during
>startup which involves charging the two 3300 uF capacitors. Once charged,
>they should be able to handle a motor current surge of 3 HP (2200 watts or 7
>amps at 320 VDC) for about 75 mSec. If I used 12,000 uF 200 V capacitors
>instead, they would give about 300 mSec surge. The motor controller would
>handle the overload stuff.
Geez Paul, typical induction motor start times are about 5 seconds at that
>"NT" wrote in message
>news:7ea9fd32-fa96-483f...@x17g2000yqj.googlegroups.com...
>
>> I wouldnt even contemplate any of the under 3kVA invertors, and
>> really 3kVA is too small. 1.5hp - 1.12kW. Guesstimate another
>> 20% onto the current for lagging pf -> 1.34kVA. Even 6x run current
>> during startup would be 8kVA. If you use a 3kVA invertor, you'll
>> need a way to cope gracefully with excess demand by reducing
>> Vout to limit i.
>
>Actually the current limit of the inverter seems to limit its output during
>startup which involves charging the two 3300 uF capacitors. Once charged,
>they should be able to handle a motor current surge of 3 HP (2200 watts or 7
>amps at 320 VDC) for about 75 mSec. If I used 12,000 uF 200 V capacitors
>instead, they would give about 300 mSec surge. The motor controller would
>handle the overload stuff.
power level, not milliseconds. Make no mistake the VFD helps a lot, but
does not remedy everything.
>
>I just did a bit of testing on the tractor, and it seems that maybe the
>automotive type inverters are not the way to go. I could only run the motor
>in neutral and at 600 RPM it drew 10.5 to 11.5 amps. At about 850 RPM it
>drew 12.5 amps at a battery voltage of 11.5 volts, and at 1080 RPM it
>reached a peak current of about 15 amps at which point the undervoltage trip
>on the VF drive shut it down. I checked the bus link voltage, and it was
>only about 250 VDC with no load other than the drive, and it dropped to 203
>VDC under load. This was with 3.36 amps per phase and 43 volts according to
>the drive display. When I released the clutch the battery current rose to
>about 15 amps and the tractor started to move but then the drive kicked out.
>
>This was not really surprising, but the low bus link voltage makes me think
>it may not be practical to use the automotive inverters, especially the 120
>VAC type in a voltage doubler configuration as I have. The stepped sine wave
>is really a rectangular waveform with 180 volt peaks at about 35% duty
>cycle, which is 106 VRMS. I did an LTspice simulation which showed 325 volts
>out into 150 ohms, for 707 watts, but this requires 20 amp peak current
>pulses from the inverter, and it is probably limited to something like 9.5
>amps which is 600 watts (peak) / (180V * 0.35). The actual input power at
>shut-down is about 11.5V*15A = 172 watts, but the power factor of the load
>is probably causing a higher output current draw. The motor is drawing 43 *
>3.36 * sqrt(3) = 250 VA according to the VFD display.
I agree, direct conversion to 360 V(dc) is a better choice, you can even
>I just did a bit of testing on the tractor, and it seems that maybe the
>automotive type inverters are not the way to go. I could only run the motor
>in neutral and at 600 RPM it drew 10.5 to 11.5 amps. At about 850 RPM it
>drew 12.5 amps at a battery voltage of 11.5 volts, and at 1080 RPM it
>reached a peak current of about 15 amps at which point the undervoltage trip
>on the VF drive shut it down. I checked the bus link voltage, and it was
>only about 250 VDC with no load other than the drive, and it dropped to 203
>VDC under load. This was with 3.36 amps per phase and 43 volts according to
>the drive display. When I released the clutch the battery current rose to
>about 15 amps and the tractor started to move but then the drive kicked out.
>
>This was not really surprising, but the low bus link voltage makes me think
>it may not be practical to use the automotive inverters, especially the 120
>VAC type in a voltage doubler configuration as I have. The stepped sine wave
>is really a rectangular waveform with 180 volt peaks at about 35% duty
>cycle, which is 106 VRMS. I did an LTspice simulation which showed 325 volts
>out into 150 ohms, for 707 watts, but this requires 20 amp peak current
>pulses from the inverter, and it is probably limited to something like 9.5
>amps which is 600 watts (peak) / (180V * 0.35). The actual input power at
>shut-down is about 11.5V*15A = 172 watts, but the power factor of the load
>is probably causing a higher output current draw. The motor is drawing 43 *
>3.36 * sqrt(3) = 250 VA according to the VFD display.
get some regulation done at that stage. Don't know if the VFD will accept
that input though. Much better efficiency to be had though.
P E Schoen
Apr 30, 2012, 3:52:51 AM4/30/12
to
"josephkk" wrote in message
news:r087o7h91lv6umpg7...@4ax.com...
[generous snip]
> I agree, direct conversion to 360 V(dc) is a better choice, you can
> even get some regulation done at that stage. Don't know if the VFD
> will accept that input though. Much better efficiency to be had though.
I finally built a DC-DC converter that should handle up to about 2 HP. It
uses a toroid transformer made from a 500 VA powerstat, with two primaries
of 8 turns each of #10 AWG, and a secondary of about 100 turns of about #18
AWG. I am driving it push-pull using MOSFETs driven by a 500 Hz square wave
generated by a PIC16F684, and it has some current limiting to throttle down
the PWM over about 50 amps. It draws about 2 amps from the 12 VDC SLA
battery (17 A-H), with no load, and produces 320 VDC on the two 3300 uF 400
V capacitors in series, using a doubler circuit as previously described.
This connects to the VFD DC link and the output drives a 3450 RPM 2 HP
induction motor.
This was installed, rather crudely, on a stripped-down riding mower, and I
took it for a ride. I was pleasantly surprised that the battery draw was
only 15-30 amps, and the VFD input was about 250 VDC and 1-2 amps. These are
analog meters and not very steady or accurate, but this calculates to
180-360 watts total battery draw, and 250-500 watts into the VFD. Rough
efficiency about 72%, but probably better. Here is a video I made of the
battery powered vehicle's maiden voyage on battery power:
http://youtu.be/y0qWY4bVnEA
These power figures correlate pretty well to another battery vehicle project
posted here:
http://www.mytractorforum.com/showthread.php?t=218367
His figures were 100 watts coasting, 250 watts on flat ground, and a maximum
of 1114W on a 36% grade and 700 watts on a 17% grade, towing 200 kg. All at
low speed, of course. It's all about torque, then HP if you want to get it
done quicker.
news:r087o7h91lv6umpg7...@4ax.com...
[generous snip]
> I agree, direct conversion to 360 V(dc) is a better choice, you can
> even get some regulation done at that stage. Don't know if the VFD
> will accept that input though. Much better efficiency to be had though.
uses a toroid transformer made from a 500 VA powerstat, with two primaries
of 8 turns each of #10 AWG, and a secondary of about 100 turns of about #18
AWG. I am driving it push-pull using MOSFETs driven by a 500 Hz square wave
generated by a PIC16F684, and it has some current limiting to throttle down
the PWM over about 50 amps. It draws about 2 amps from the 12 VDC SLA
battery (17 A-H), with no load, and produces 320 VDC on the two 3300 uF 400
V capacitors in series, using a doubler circuit as previously described.
This connects to the VFD DC link and the output drives a 3450 RPM 2 HP
induction motor.
This was installed, rather crudely, on a stripped-down riding mower, and I
took it for a ride. I was pleasantly surprised that the battery draw was
only 15-30 amps, and the VFD input was about 250 VDC and 1-2 amps. These are
analog meters and not very steady or accurate, but this calculates to
180-360 watts total battery draw, and 250-500 watts into the VFD. Rough
efficiency about 72%, but probably better. Here is a video I made of the
battery powered vehicle's maiden voyage on battery power:
http://youtu.be/y0qWY4bVnEA
These power figures correlate pretty well to another battery vehicle project
posted here:
http://www.mytractorforum.com/showthread.php?t=218367
His figures were 100 watts coasting, 250 watts on flat ground, and a maximum
of 1114W on a 36% grade and 700 watts on a 17% grade, towing 200 kg. All at
low speed, of course. It's all about torque, then HP if you want to get it
done quicker.
amdx
Apr 30, 2012, 9:56:44 PM4/30/12
to
a skip all the conversion. Like this,
http://www.youtube.com/watch?v=5MKjbXltAew
Not exactly a lawn mower but the details are there.
Mikek
P E Schoen
May 1, 2012, 3:34:25 AM5/1/12
to
"amdx" wrote in message news:28a70$4f9f46ee$18ec6dd7$18...@KNOLOGY.NET...
> I didn't read the whole thread, but why don't you just get a
> DC motor a skip all the conversion. Like this,
> http://www.youtube.com/watch?v=5MKjbXltAew
> Not exactly a lawn mower but the details are there.
Or this: http://www.youtube.com/watch?v=Rfac9zxzZT0 :)
Well, if all I wanted was a utility vehicle or a go-cart or riding mower, I
would just buy one or take the easiest route by using stock components that
are available for conversion. And then I would have the end product but not
the learning experience and thrill of the design and prototyping process.
Also, I claim that standard three-phase motors and controllers with a DC-DC
converter close to the batteries is potentially more efficient, and there
are other advantages of low maintenance, high reliability, ruggedness, and
low cost. The control is also more precise.
As I go through the design process, I am considering and trying various
approaches, and I think I have a concept for something that may be
competitive with many other technologies that tend to become "fixated" on
certain parameters. At one time I thought it would be a great idea to rewind
an induction motor for much lower voltage and higher current, so that it
could be run directly on 24 to 48 VDC batteries, and also overclock it to
get possibly as much as 6 to 8 times the nominal 60 Hz horsepower. It's
possible, but not really practical, yet it was a valuable experience to have
taken a 1/2 HP single phase 120 VAC PSC motor, and rewinding it as a 12 pole
three phase motor at 8 VAC nominal at 60 Hz. I verified that it ran at about
600 RPM at 60 Hz, and then I ran it up to about 240 Hz where it ran at about
2400 RPM.
The thing is that the small size and weight of high frequency motors for
vehicles, particularly tractors, is not a significant advantage. Tractors
often add dead weight just for traction, and lead-acid batteries are perfect
for that. A practical small tractor needs three or four batteries at about
50 pounds each, and a very capable 2 HP motor as I used on my contraption
weighs only about 30 pounds. Even a 5 HP motor, which I plan to use in a
larger tractor, is only about 100 pounds, and it will need probably 300
pounds of batteries.
Part of my "research" is to determine just how much power is really needed
for garden tractors and riding mowers. My old 1967 Simplicity Broadmoor GT
had an 8 HP B&S engine, and it was fully capable of running a 36" mower
deck, or a dozer blade. My "toy" riding mower is much smaller and lighter,
yet it had a 10 HP engine. And most riding mowers now are at least 16 HP.
But I think the actual power needed is closer to 2 HP, and it seems that
lawn mowers as well as cars have incorporated ever more powerful engines
mostly for bragging rights and micro-penile compensation.
Anyway, that was a long answer to a short question. But mainly I make my
choices for my own reasons of enjoying the process more than the end result.
Much like life itself.
Paul
> I didn't read the whole thread, but why don't you just get a
> DC motor a skip all the conversion. Like this,
> http://www.youtube.com/watch?v=5MKjbXltAew
> Not exactly a lawn mower but the details are there.
Well, if all I wanted was a utility vehicle or a go-cart or riding mower, I
would just buy one or take the easiest route by using stock components that
are available for conversion. And then I would have the end product but not
the learning experience and thrill of the design and prototyping process.
Also, I claim that standard three-phase motors and controllers with a DC-DC
converter close to the batteries is potentially more efficient, and there
are other advantages of low maintenance, high reliability, ruggedness, and
low cost. The control is also more precise.
As I go through the design process, I am considering and trying various
approaches, and I think I have a concept for something that may be
competitive with many other technologies that tend to become "fixated" on
certain parameters. At one time I thought it would be a great idea to rewind
an induction motor for much lower voltage and higher current, so that it
could be run directly on 24 to 48 VDC batteries, and also overclock it to
get possibly as much as 6 to 8 times the nominal 60 Hz horsepower. It's
possible, but not really practical, yet it was a valuable experience to have
taken a 1/2 HP single phase 120 VAC PSC motor, and rewinding it as a 12 pole
three phase motor at 8 VAC nominal at 60 Hz. I verified that it ran at about
600 RPM at 60 Hz, and then I ran it up to about 240 Hz where it ran at about
2400 RPM.
The thing is that the small size and weight of high frequency motors for
vehicles, particularly tractors, is not a significant advantage. Tractors
often add dead weight just for traction, and lead-acid batteries are perfect
for that. A practical small tractor needs three or four batteries at about
50 pounds each, and a very capable 2 HP motor as I used on my contraption
weighs only about 30 pounds. Even a 5 HP motor, which I plan to use in a
larger tractor, is only about 100 pounds, and it will need probably 300
pounds of batteries.
Part of my "research" is to determine just how much power is really needed
for garden tractors and riding mowers. My old 1967 Simplicity Broadmoor GT
had an 8 HP B&S engine, and it was fully capable of running a 36" mower
deck, or a dozer blade. My "toy" riding mower is much smaller and lighter,
yet it had a 10 HP engine. And most riding mowers now are at least 16 HP.
But I think the actual power needed is closer to 2 HP, and it seems that
lawn mowers as well as cars have incorporated ever more powerful engines
mostly for bragging rights and micro-penile compensation.
Anyway, that was a long answer to a short question. But mainly I make my
choices for my own reasons of enjoying the process more than the end result.
Much like life itself.
Paul
amdx
May 1, 2012, 10:26:51 AM5/1/12
to
On 5/1/2012 2:34 AM, P E Schoen wrote:
> "amdx" wrote in message news:28a70$4f9f46ee$18ec6dd7$18...@KNOLOGY.NET...
>
>> I didn't read the whole thread, but why don't you just get a
>> DC motor a skip all the conversion. Like this,
>> http://www.youtube.com/watch?v=5MKjbXltAew
>> Not exactly a lawn mower but the details are there.
>
> Or this: http://www.youtube.com/watch?v=Rfac9zxzZT0 :)
>
> Well, if all I wanted was a utility vehicle or a go-cart or riding
> mower, I would just buy one or take the easiest route by using stock
> components that are available for conversion. And then I would have the
> end product but not the learning experience and thrill of the design and
> prototyping process. Also, I claim that standard three-phase motors and
> controllers with a DC-DC converter close to the batteries is potentially
> more efficient, and there are other advantages of low maintenance, high
> reliability, ruggedness, and low cost. The control is also more precise.
>
> As I go through the design process, I am considering and trying various
> approaches,..
> "amdx" wrote in message news:28a70$4f9f46ee$18ec6dd7$18...@KNOLOGY.NET...
>
>> I didn't read the whole thread, but why don't you just get a
>> DC motor a skip all the conversion. Like this,
>> http://www.youtube.com/watch?v=5MKjbXltAew
>> Not exactly a lawn mower but the details are there.
>
> Or this: http://www.youtube.com/watch?v=Rfac9zxzZT0 :)
>
> Well, if all I wanted was a utility vehicle or a go-cart or riding
> mower, I would just buy one or take the easiest route by using stock
> components that are available for conversion. And then I would have the
> end product but not the learning experience and thrill of the design and
> prototyping process. Also, I claim that standard three-phase motors and
> controllers with a DC-DC converter close to the batteries is potentially
> more efficient, and there are other advantages of low maintenance, high
> reliability, ruggedness, and low cost. The control is also more precise.
>
> As I go through the design process, I am considering and trying various
> Paul
If you want to see some others designing 3 phase converters, check
out the DIY electric car forum. You'll need to look through it to find
the guys doing the 3 phase stuff.
http://www.diyelectriccar.com/forums/
Mikek
P E Schoen
May 1, 2012, 5:59:19 PM5/1/12
to
"amdx" wrote in message news:bd3c8$4f9ff2ae$18ec6dd7$73...@KNOLOGY.NET...
> If you want to see some others designing 3 phase converters, check out
> the DIY electric car forum. You'll need to look through it to find the
> guys doing the 3 phase stuff.
> http://www.diyelectriccar.com/forums/
Thanks. I joined and posted. There was a thread on DC-DC converters and I
might be able to help with that. It seems like most of those guys are into
high power vehicles, looking for 40-50 kW motors and pushing them to several
times rating for Tesla-like acceleration. And some of them are using
hundreds of small batteries to get the voltage and current they need (or
want).
Paul
> If you want to see some others designing 3 phase converters, check out
> the DIY electric car forum. You'll need to look through it to find the
> guys doing the 3 phase stuff.
> http://www.diyelectriccar.com/forums/
might be able to help with that. It seems like most of those guys are into
high power vehicles, looking for 40-50 kW motors and pushing them to several
times rating for Tesla-like acceleration. And some of them are using
hundreds of small batteries to get the voltage and current they need (or
want).
Paul
josephkk
May 4, 2012, 10:36:42 PM5/4/12
to
On Mon, 30 Apr 2012 03:52:51 -0400, "P E Schoen" <pa...@peschoen.com>
wrote:
Hmmm. Works better than i expected.
?-)
wrote:
?-)
P E Schoen
May 4, 2012, 12:48:09 AM5/4/12
to
"josephkk" wrote in message
news:mg49q7t5tiavb8orq...@4ax.com...
> Hmmm. Works better than i expected.
> ?-)
Shows that sometimes you just have to put something to the test. :)
It will be interesting to take some more accurate measurements and run at
higher power. There seems to be about 24 watts with no load at 12 VDC, at
500 Hz. I had thought there was a problem at higher frequencies, but I found
later that I had a wiring error and I need to try again. I'd rather run it
at about 2 kHz or even 4 kHz, if only to reduce the annoying audible noise
at 500 Hz.
The ultimate test will be at 24 VDC and 1200 watts, which I think will be
more than enough to operate this simple vehicle at useful (and fun) speeds
on moderate slopes. The no-load power will probably go up to about 50 watts.
I estimate the primary winding to be about 8 milliohms, so at 50 amps that
will be about 20 watts. The secondary will draw about 4 amps and the
resistance is about 0.6 ohms, so about 10 watts there. The MOSFETs
(HUF75645) have about 0.014 ohms each, and now I have two in parallel but I
plan to use four, which will add another 10 watts. So optimistically I'll
have 1200 watts with 90 watts of losses, or 92% efficiency.
I have found some interest in such a DC-DC converter on the forum:
http://www.diyelectriccar.com/forums/showthread.php/dc-dc-converter-best-set-upi-73181.html
They were discussing the conversion of the main battery pack voltage
(144-300 VDC or so) to 12 VDC for accessories, including a cab heater! I
suggested using ordinary 120 and 240 volt electric fin-strip heaters
directly, or a heat pump to extract the waste heat from the motors and drive
electronics, which also gives the option of running it in reverse for A/C.
I was impressed with some of the motor controllers they were using. There is
a "Soliton 1" which is rated for 300 kW (340 VDC and 1000 amps), for $3300.
They even have a 1.2 MW unit for 10 grand! I question the need for such
power in a passenger vehicle, but apparently these are used on electric
dragsters and super-high-performance vehicles. And these controllers are for
brush type series wound motors. But it's still awesome to consider a 1500 HP
electric motor, which is equivalent to something like a 5000 HP ICE! See:
http://www.evnetics.com/products.php
Stay tuned...
Paul
news:mg49q7t5tiavb8orq...@4ax.com...
> Hmmm. Works better than i expected.
> ?-)
It will be interesting to take some more accurate measurements and run at
higher power. There seems to be about 24 watts with no load at 12 VDC, at
500 Hz. I had thought there was a problem at higher frequencies, but I found
later that I had a wiring error and I need to try again. I'd rather run it
at about 2 kHz or even 4 kHz, if only to reduce the annoying audible noise
at 500 Hz.
The ultimate test will be at 24 VDC and 1200 watts, which I think will be
more than enough to operate this simple vehicle at useful (and fun) speeds
on moderate slopes. The no-load power will probably go up to about 50 watts.
I estimate the primary winding to be about 8 milliohms, so at 50 amps that
will be about 20 watts. The secondary will draw about 4 amps and the
resistance is about 0.6 ohms, so about 10 watts there. The MOSFETs
(HUF75645) have about 0.014 ohms each, and now I have two in parallel but I
plan to use four, which will add another 10 watts. So optimistically I'll
have 1200 watts with 90 watts of losses, or 92% efficiency.
I have found some interest in such a DC-DC converter on the forum:
http://www.diyelectriccar.com/forums/showthread.php/dc-dc-converter-best-set-upi-73181.html
They were discussing the conversion of the main battery pack voltage
(144-300 VDC or so) to 12 VDC for accessories, including a cab heater! I
suggested using ordinary 120 and 240 volt electric fin-strip heaters
directly, or a heat pump to extract the waste heat from the motors and drive
electronics, which also gives the option of running it in reverse for A/C.
I was impressed with some of the motor controllers they were using. There is
a "Soliton 1" which is rated for 300 kW (340 VDC and 1000 amps), for $3300.
They even have a 1.2 MW unit for 10 grand! I question the need for such
power in a passenger vehicle, but apparently these are used on electric
dragsters and super-high-performance vehicles. And these controllers are for
brush type series wound motors. But it's still awesome to consider a 1500 HP
electric motor, which is equivalent to something like a 5000 HP ICE! See:
http://www.evnetics.com/products.php
Stay tuned...
Paul
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