Hold my beer & watch this ...
Bob Engelhardt
also have a VFD that will go to 400 Hz. The recent discussion about the
rpm limits of motors prompts me to see what happens.
So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
But I thought that I'd give you guys a chance to make predictions. What
do you think will happen?
Bob
Oh - the motor is 1755 rpm @ 60 Hz => 10500 @ 400. It is older & dirty
inside. The bearings? I dunno - it spins pretty easily.
Ignoramus15568
> I have a 1 HP 3 ph motor that I don't want & nobody else does either. I
> also have a VFD that will go to 400 Hz. The recent discussion about the
> rpm limits of motors prompts me to see what happens.
>
> So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
> But I thought that I'd give you guys a chance to make predictions. What
> do you think will happen?
My prediction:
The memory card will get full just as the motor spectacularly self
destructs.
i
Wes
>So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
>But I thought that I'd give you guys a chance to make predictions. What
>do you think will happen?
I bet it never spins as fast as calculated. I'll even venture it doesn't explode.
Wes
Jon Anderson
a video camera? <G>
Jon
Jim Stewart
I bet that it will spin to close to nameplate x 6.6
and doesn't explode.
Ignoramus15568
I think that the bearings will overheat and fail
Jim Wilkins
> I have a 1 HP 3 ph motor that I don't want & nobody else does either. I
> also have a VFD that will go to 400 Hz. The recent discussion about the
> rpm limits of motors prompts me to see what happens.
Did you get the VFD from Bob Neidorff?
jsw
Bob Engelhardt
trouble. And at no load it runs 1800 rpm @ 60 Hz. Bob
Buerste
"Bob Engelhardt" <bobeng...@comcast.net> wrote in message
news:hli04...@news4.newsguy.com...
I'll bet you rip a hole in the time-space continuum. GOOD, then I don't
have to visit relatives Sunday.
Paul Hovnanian P.E.
>
> I can add: I've run it at 180 Hz (5400 rpm) without any signs of
> trouble. And at no load it runs 1800 rpm @ 60 Hz. Bob
If its well enough balanced so as to run well at that speed, it'll
probably make 400Hz. If not, the rotor vibration might cause the rotor
to hit the stator, whereupon it will shatter. The case might contain the
pieces, but there will be smoke and sparks.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Who is General Failure and why is he reading my hard drive?
Karl Townsend
> have to visit relatives Sunday.
This would really help me out too. I didn't call the MIL when my honey went
to the hospital.
Karl
Jim Stewart
But I'd still stay out of the plane of rotation.
Joseph Gwinn
Bob Engelhardt <bobeng...@comcast.net> wrote:
Well, it could well burst at six times design rpm. I would put sandbags
around it, just in case, because the stored energy will be quite large
at near synchronous speed. Energy varies as the square of speed.
What may also happen is that eddy current losses at 400 Hz are very
large in a motor designed for 60 Hz, so it melts instead.
Or both.
Joe Gwinn
DoN. Nichols
> also have a VFD that will go to 400 Hz. The recent discussion about the
> rpm limits of motors prompts me to see what happens.
>
> So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
> But I thought that I'd give you guys a chance to make predictions. What
> do you think will happen?
I think that the shading coils will fly out of the slots in the
rotor -- assuming that you start it at 60 HZ and then take the speed up
at a rate that it can track. I suspect that *starting* it at 400 Hz
would leave it not able to spin up - but I could easily be wrong.
> Bob
>
> Oh - the motor is 1755 rpm @ 60 Hz => 10500 @ 400. It is older & dirty
> inside. The bearings? I dunno - it spins pretty easily.
I think that the bearings will be fine -- at least until the
rotor spins apart.
Enjoy,
DoN.
--
Email: <dnic...@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Ignoramus15568
I would highly recommend to tape a video for such a test. I have not
had a motor shitty enough to not feel sorry about destroying it, but I
personally would love to see the video if Bob does it.
Bob, if you do this, give the motor some time. I do think that it
should self destruct from one cause or another. I think that bearings
should melt if the motor does not disintegrate before.
Higher speed means more pressure on bearings from centripetal force,
and at higher linear speed, so the heat generation in bearings should
be speed squared, I think. This means that at 6.5 times design speed,
the bearings will generate 44 times more heat.
i
John
The bearings should hold up to at least 6000rpm above that speed motors
use a higher precision bearing. It also depends on how well the rotor
is balanced. Higher rpm would require better balancing or the rotor and
bearings will eventually self destruct.
Another point is as the frequency is increased the motor reactance
increases which caused a drop in current in the windings. If you really
want to go for broke, set the current limiting for the rating on the
motor but connect the motor for 220 and run it on 440 so that at the
higher frequencies you will still have full current in the windings. The
drive must have at least twice the rated hp of the motor. The motor
will now theoretically put out twice its rated hp. at double the rpm.
I predict that the motor with no load will spin up to the less than
the calculated rpm because of the increased reactance at the higher
frequencies.
John
dav19...@nowhere.invalid
<bobeng...@comcast.net> wrote:
>So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
>But I thought that I'd give you guys a chance to make predictions. What
>do you think will happen?
>Bob
A quark-gluon plasma will form which will condense into a micro black
hole which will begin growing in mass as it consumes the Earth's core.
All of we global elites could care less about this, however, as we
have made plans for our evacuation from planet Earth aboard super
secret Nazi designed flying saucer evacuation pods that we have based
in Neuschwabenland in Antarctica (except for Bill Gates who has his
own Space Shuttle gassed up and parked in a silo on the MicroSoft
corporate campus).
I personally, due to my stature amongst the global elites, have
boarding pass number 3, so I will be sure to escape this catastrophe
and flee to our pre-built enclave on Alpha Centauri.
Dave
sta...@prolynx.com
The magic smoke will remove itself from inside as the speed exceeds
what the winding ties will take and they start rubbing on the stator.
Had the same happen to a badly rebuilt starter motor, was sparky, for
awhile! If it's got ball-bearings, they might exceed rated speed,
could be interesting if that happened. Make sure you've got a good
breaker on the circuit when the inevitable happens. Not sure what
happens to a VFD if it starts delivering power into a dead short.
Stan
dav19...@nowhere.invalid
<bobeng...@comcast.net> wrote:
>So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
>But I thought that I'd give you guys a chance to make predictions. What
>do you think will happen?
>
>Bob
Something similar to this gas engine maybe?
http://www.liveleak.com/view?i=fee_1266466975
Dave
Richard J Kinch
> But I thought that I'd give you guys a chance to make predictions. What
> do you think will happen?
The Euro will collapse and the Dow will sink to 6000 by June.
Oh, wait. What predictions did you have in mind?
Robert Roland
<bobeng...@comcast.net> wrote:
>So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
>But I thought that I'd give you guys a chance to make predictions. What
>do you think will happen?
I'm pretty sure the bearings will not fail. Model airplane engines run
at 15,000 RPM or more for hundreds of hours on ordinary, hardware
store bearings.
I think the copper parts of the rotor will deform, contact the stator
and break. There will be some sparking and smoking before the motor
just stops.
I did the same thing to a 12V DC motor once. It got 300 VDC when an
output transistor in the power supply shorted. Remnants of the rotor
windings were wrapped around the motor in the direction of rotation.
--
RoRo
Pete Snell
>
> Something similar to this gas engine maybe?
>
> http://www.liveleak.com/view?i=fee_1266466975
>
> Dave
Ouch! That turned into a bad day for someone.....
Pete
--
Pete Snell
Department of Physics
Royal Military College
Kingston, Ontario,
Canada
-----------------------------------------------------------------------
Either this man is dead or my watch has stopped.
Groucho Marx (1895�1977)
Stormin Mormon
power, can you do it?
--
Christopher A. Young
Learn more about Jesus
www.lds.org
.
"Buerste" <bue...@wowway.com> wrote in message
news:fQ0fn.27$BD2...@newsfe14.iad...
Randy
would love to see that at 5000 frames/sec.
Thank You,
Randy
Remove 333 from email address to reply.
basilisk
I've actually done this with a 50hp, 1750 motor, but I dialed the speed up
from 0hz, when I got to 180hz, the motor refused to run any faster
and the of the speed of the motor was rising and falling on its on,
no damage to drive or motor.
The drive was an AB 1336 and was located about 100 feet from
the motor, if the drive had been within a few feet of the motor
the results might have been different.
Possibly it wouldn't run any faster due to core saturation.
basilisk
Mark Rand
wrote:
>So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
>But I thought that I'd give you guys a chance to make predictions. What
>do you think will happen?
>
I suspect that the motor will get up there without major issues. May get a
quite a bit of noise from the cooling fan. More so assuming that the blades
stall due to flow constriction. if ball bearings, I'd expect them to cope
quite well for a while. May split an end ring on the rotor, but unlikely to
throw a bar, unless it's a very old design.
Bear in mind that if a bearing seizes, it splits an end ring or throws a bar,
it'll jump a way and start spinning in the direction of rotation. Be prepared
for the cables to pull off their connections if possible.
Otherwise, it could be quite boring :-)
Mark Rand
RTFM
DoN. Nichols
> On Feb 17, 5:03�pm, Bob Engelhardt <bobengelha...@comcast.net> wrote:
>> I have a 1 HP 3 ph motor that I don't want & nobody else does either. �I
>> also have a VFD that will go to 400 Hz. �The recent discussion about the
>> rpm limits of motors prompts me to see what happens.
>>
>> So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
>> But I thought that I'd give you guys a chance to make predictions. �What
>> do you think will happen?
>>
>> Bob
>>
>> Oh - the motor is 1755 rpm @ 60 Hz => 10500 @ 400. �It is older & dirty
>> inside. �The bearings? �I dunno - it spins pretty easily.
>
> The magic smoke will remove itself from inside as the speed exceeds
> what the winding ties will take and they start rubbing on the stator.
This is a three-phase induction motor, so there are no winding
ties on the rotor. Just the welded in copper shorted turns which I
expect to fly out of their slots.
> Had the same happen to a badly rebuilt starter motor, was sparky, for
> awhile!
That's a DC motor with real windings on the rotor. A different
game.
> If it's got ball-bearings, they might exceed rated speed,
> could be interesting if that happened. Make sure you've got a good
> breaker on the circuit when the inevitable happens. Not sure what
> happens to a VFD if it starts delivering power into a dead short.
The VFD will sense the condition and shut down.
Bob Engelhardt
couldn't run to an end.
So far
- with VFD putting out 360 Hz (its max, not 400 as previously stated)
the motor spins to 10,700 rpm easily & "smoothly". 10,800 is nominal
- ran for 10 minutes before losing battery
- drew .35A
- the closed end bearing warmed somewhat. Maybe to 80F
- running at 10,700 is kinda scary so I bolted it down. I kept thinking
about the rotor jamming & transferring its rotation to the case.
- at 10 sec decel time I was getting over voltage on the VFD's DC bus &
had to increase to decel time
The VFD is rated 2 HP (8A) & the motor is 1 HP, so I should be able to
force it into regions that it won't like <G>.
I'm going to decrease the accel time as short as I can to see if DoN's
thought about not starting is true. 'Course short accel time is still
not same as applying 360 HZ.
Stay tuned,
Bob
Larry Jaques
<bobeng...@comcast.net> scrawled the following:
>I have a 1 HP 3 ph motor that I don't want & nobody else does either. I
>also have a VFD that will go to 400 Hz. The recent discussion about the
>rpm limits of motors prompts me to see what happens.
>
>So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
>But I thought that I'd give you guys a chance to make predictions. What
>do you think will happen?
>
>Bob
>
>Oh - the motor is 1755 rpm @ 60 Hz => 10500 @ 400. It is older & dirty
>inside. The bearings? I dunno - it spins pretty easily.
I'll bet it self-destructs at something like double speed for any
length of time. Flames are likely.
--
"Just think of the tragedy of teaching children not to doubt."
-- Clarence Darrow
cavelamb
Larry Jaques
<bobeng...@comcast.net> scrawled the following:
>I have some preliminary results, but my camera battery ran down so I
>couldn't run to an end.
>
>So far
>- with VFD putting out 360 Hz (its max, not 400 as previously stated)
>the motor spins to 10,700 rpm easily & "smoothly". 10,800 is nominal
Absolutely amazing. How did you measure rpm?
>- ran for 10 minutes before losing battery
>- drew .35A
>- the closed end bearing warmed somewhat. Maybe to 80F
And that was probably from the armature/rotor shaft.
>- running at 10,700 is kinda scary so I bolted it down. I kept thinking
>about the rotor jamming & transferring its rotation to the case.
Yeah, think "what's in its path?"
>- at 10 sec decel time I was getting over voltage on the VFD's DC bus &
>had to increase to decel time
>The VFD is rated 2 HP (8A) & the motor is 1 HP, so I should be able to
>force it into regions that it won't like <G>.
True.
>I'm going to decrease the accel time as short as I can to see if DoN's
>thought about not starting is true. 'Course short accel time is still
>not same as applying 360 HZ.
Then try short accel + 360Hz.
Bob Engelhardt
> Absolutely amazing. How did you measure rpm?
I have a "laser" tach. E.g.,
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66632
Bob Engelhardt
> Did you get the VFD from Bob Neidorff?
I don't think - I don't recognize the name. I got it on eBay a couple
of years ago. Bob
Bob Engelhardt
Here's a short video of it spinning up to 10,700 rpm (some pucker
involved the first time I did this). My previous post said that it spun
up "smoothly" & it was quoted cause smooth is relative. Well, it really
is smooth & here's a video with a jigger of water sitting on the motor
(wmv file, 1.2MB, 10 sec):
http://home.comcast.net/~bobengelhardt/MotorVibe.wmv
I let it run 10 minutes & checked the temp (with my finger tip
thermometer) - the warmest part was the closed end bearing & it was just
a little warm. After another 10 minutes the bearing was a little
warmer. And after 45 minutes it wasn't much warmer than after 20. Note
that the fan did not stall & was doing its job nicely. The case was not
noticeably warmer.
After 15 minutes, the current had *dropped* from .35A to .25A & the
speed increased from 10,690 to 10,715. To me that means that there was
less friction in the bearings as it warmed. By 45 minutes, it hadn't
changed any more.
I keep referring to the 45 minute mark cause that's as far as I got
before my camera battery ran out (it's not a video camera, but a stiil
camera that has video). I'm going to try to find another camera, so
it's not over yet.
Bob
David Billington
got about 80k RPM of head room with that tachometer. It's likely to fail
before that is reached but a concrete blockhouse might be useful for
viewing the test.
Mark Rand
wrote:
>On Wed, 17 Feb 2010 19:03:32 -0500, the infamous Bob Engelhardt
><bobeng...@comcast.net> scrawled the following:
>
>>
>>Oh - the motor is 1755 rpm @ 60 Hz => 10500 @ 400. It is older & dirty
>>inside. The bearings? I dunno - it spins pretty easily.
>
>I'll bet it self-destructs at something like double speed for any
>length of time. Flames are likely.
Most reasonably modern (<=25 years) motors tend to use the same rotor for 1800
as for 3600 nominal speeds. There's no cost benefit for making custom rotors
for variants of little motors.
regards
Mark Rand
RTFM
Robert Swinney
Bob Swinney
"Bob Engelhardt" <bobeng...@comcast.net> wrote in message news:hlmqn...@news7.newsguy.com...
rangerssuck
This is far & away the most interesting stuff I've read in this group
in many years. Thanks.
Wes
>This would really help me out too. I didn't call the MIL when my honey went
>to the hospital.
How is she, not the MILstone, doing?
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller
Wes
If yours is like mine, you had to stand next to the gren^H^H^H^Hmotor.
Wes
Wes
>Oh - the motor is 1755 rpm @ 60 Hz => 10500 @ 400. It is older & dirty
>inside. The bearings? I dunno - it spins pretty easily.
Just out of curiosity, what does it really spin at when the frequency is 60 Hz?
Wes
Bob Engelhardt
>
> Just out of curiosity, what does it really spin at when the frequency is 60 Hz?
At 60, 120, & 180 Hz it as spot-on at 1800, 3600, & 5400 rpm. I didn't
check again until 360 Hz.
Bob
Karl Townsend
"Wes" <clu...@lycos.com> wrote in message
news:K%Dfn.234577$er1.1...@en-nntp-07.dc1.easynews.com...
She's much much better. Well, but not quite full strength. We went fishin'
this morning and Julie pulled up about 20 groupers. She was wearing the
custom "Grouper Girl" Tee shirt I had made for her.
Karl
Wes
Cool. So at 360Hz, you got a bit less than calculated. I just wanted to point out my
prediction was correct. (Just barely on rpm) ;)
Wes
Wes
>
>"Wes" <clu...@lycos.com> wrote in message
>news:K%Dfn.234577$er1.1...@en-nntp-07.dc1.easynews.com...
>> "Karl Townsend" <karltown...@embarqmail.com> wrote:
>>
>>>This would really help me out too. I didn't call the MIL when my honey
>>>went
>>>to the hospital.
>>
>> How is she, not the MILstone, doing?
>> --
>She's much much better. Well, but not quite full strength. We went fishin'
>this morning and Julie pulled up about 20 groupers. She was wearing the
>custom "Grouper Girl" Tee shirt I had made for her.
>
Hospital and loved ones is a discordant combination. It gets worse as we age.
I don't want to hear the combination of my mom and hospital at her age if you get my
drift.
I am glad your Grouper Girl is doing well. Sounds like you got a good catch many years
ago. :)
Wes
Ed Huntress
"Karl Townsend" <karltown...@embarqmail.com> wrote in message
news:4b7f169e$0$77551$892e...@auth.newsreader.octanews.com...
WOW! 20 groupers is a lot of grouper fingers, eh?
That's good; she must be feeling better to do that.
--
Ed Huntress
cavelamb
> Good video, Bob. Thanx for sharing.
>
> Bob Swinney
> "Bob Engelhardt" <bobeng...@comcast.net> wrote in message news:hlmqn...@news7.newsguy.com...
> Another update.
>
> Here's a short video of it spinning up to 10,700 rpm (some pucker
> involved the first time I did this). My previous post said that it spun
> up "smoothly" & it was quoted cause smooth is relative. Well, it really
> is smooth & here's a video with a jigger of water sitting on the motor
> (wmv file, 1.2MB, 10 sec):
> http://home.comcast.net/~bobengelhardt/MotorVibe.wmv
>
Def-i-nut-ly.
BTW, was there a real wager on this?
Karl Townsend
> WOW! 20 groupers is a lot of grouper fingers, eh?
>
> That's good; she must be feeling better to do that.
>
> --
> Ed Huntress
You haven't kept up with the FWC regulations. New this year, closed season
on grouper Jan 1 to May 1. So, strictly catch and release. Julie's not real
happy about the new law.
Record cold in the Gulf pushed groupers on to the reef. If you have "the
knack" you can pull 'em up all day long.
Karl
Ed Huntress
>
>> WOW! 20 groupers is a lot of grouper fingers, eh?
>>
>> That's good; she must be feeling better to do that.
>>
>> --
>> Ed Huntress
>
> You haven't kept up with the FWC regulations. New this year, closed season
> on grouper Jan 1 to May 1. So, strictly catch and release. Julie's not
> real happy about the new law.
You're right, I don't keep up with grouper laws. <g> I was surprised at the
large number your wife caught because I've heard that the pressure on
groupers has been very high, and that they're getting protection.
I *love* grouper -- not in the Biblical sense, but in the deep-fryer sense.
It would be hard to catch a bunch of them and have to toss them back.
>
> Record cold in the Gulf pushed groupers on to the reef. If you have "the
> knack" you can pull 'em up all day long.
I've never seen that. The last time I caught any was 20years ago, up around
Venice, on a head boat, and I think I caught three. I counted it a good day.
--
Ed Huntress
Larry Jaques
<bobeng...@comcast.net> scrawled the following:
>Larry Jaques wrote:
Cool. So, did you expect it to hang in there up to that RPM?
(the gren^H^H^H^Hmotor, not the tach)
Larry Jaques
<ra...@internettie.co.uk> scrawled the following:
OK. Evidently, they're much better balanced than I'd imagined, too.
11Krpm is a whole lot more than plate-rated speed, innit?
Larry Jaques
<karltown...@embarqmail.com> scrawled the following:
I saw grouper in the frozeded food section of a local market last
month and tried it a couple weeks ago. It's not bad, but their
breading was excruciatingly bland. I dosed it with butter, salt,
pepper, and tons of garlic. That was -much- better.
So, what'd the tee say?
Bob Engelhardt
uneventful & inconsequential except for a little warming of the rear
bearing. As reported yesterday.
So I've been thinking - what's the point of continuing like this? It's
been shown to run without exploding & while that could happen yet, I'd
say probably not. And I could run till the bearings got so hot as to
seize, but still, so what. Also, this test is too abstract in that
there's no load on the motor. A torque load will be more real, but
still not do much except warm it more. And how the hell would I put a
torque load on a 10,700 rpm shaft? (OK, I could make a fan, but it
would have to be very precisely balanced.)
A better test would be a radial load. That would show bearing weakness
& model real world use better.
So I put a bearing on the shaft & loaded it with a 35 lb* bucket of lead:
http://home.comcast.net/~bobengelhardt/LoadedMotor.jpg
Spinning that up to 10,700 was another pucker moment, but it was uneventful.
The load bearing was one that I had in my box & it wasn't up to the
task. It was something I had salvaged & was worn. So about 3 minutes
into a run it made a couple of gritch sounds & I stopped it.
Now I need to get a good 7/8" bore bearing or go to the considerable
trouble of turning down the shaft to 3/4" so I can use some other (good)
bearings that I have.
I love doin' shit like this,
Bob
* - why 35 lbs? How much to load it was something I had no idea about.
I found a formula on the web, but it didn't make any sense - it gave
me a few pounds. So I went to my table saw, which has a 1 HP motor & is
tensioned by the weight of the motor. I disconnected the belt & put a
rope in its place. That rope went over the pulley and held a bucket
that I added lead to, until the motor was suspended at the right angle.
It took 35 lbs, which seemed to me to be quite a lot.
Ignoramus30516
i
Bob Engelhardt
> I wish you were my neighbor
Yeah, me too. It's a lot more fun when there's a neighbor into the same
stuff. Bob
Robert Roland
<bobeng...@comcast.net> wrote:
>And how the hell would I put a
>torque load on a 10,700 rpm shaft?
A model airplane propeller.
>(OK, I could make a fan, but it
>would have to be very precisely balanced.)
If you put it on a shaft and lay the shaft on top of a couple of hard,
horizontal edges, you can balance it plenty precisely.
--
RoRo
Bob Engelhardt
To put a radial load on the motor I either needed to buy a 7/8 bore
bearing, or turn the shaft down. I decided to do the shaft, as it was
Sunday and also I'm cheap.
Instead of turning, I figured grinding it down would be just as fast -
given I would have to get the rotor out to turn it. So I turned on the
motor, took my angle grinder & had at it. Tip - if you ever do this, a
7" grinder is MUCH faster than a 4-1/2" one. I had a "Oops" - I thought
the bearing was 3/4" & rough ground to .760, but the bearing was .780!
Must be metric.
Got a smaller bearing, rough ground for it, then finish ground using an
air grinder held in a x-y drill press vise:
http://home.comcast.net/~bobengelhardt/ShaftGrind.jpg
Worked nice. Loctite'd the bearing for good measure.
_Boorrriing_
With the new, good, bearing, I set up the motor with the 35 lb load as I
had before:
http://home.comcast.net/~bobengelhardt/LoadedMotor.jpg
and cranked it up.
Nothing happened! After an hour the motor bearings were barely
detectable as being warmer. The load bearing was warmer, but not hot.
I only ran an hour cause my camera battery only lasted 45 minutes and it
didn't look like anything was going to happen. If it wasn't even warm
after an hour, how long would it take to overheat & fail? Too long.
And what would that show? That running at motor at 6x normal speed will
cause it to fail in, say, 6?, 8?, 10? hours. Not worth it.
_Conclusions_
It has not escaped my attention that there are real world implications
from this testing. Albeit that it was only one motor that I tested, it
is reasonable to assume that this motor was typical.
So, how is this useful? For my drill press, and maybe yours. I have a
3 phase motor and VFD on my drill press. VERY useful - the only way to
power a drill press, IMHO.
I have the VFD configured for 5 - 90 Hz. With the pulleys I'm using
this gives 65 - 1100 rpm spindle speed. The 65 rpm speed is good for
tapping and large hole saw use. But the torque is a little low. But if
I go down one step on the pulleys to get more torque at low speed, I
loose rpms at high speed, which at 1100 is already too slow for small
bits. (BTW - changing the belts is no longer something I do.)
The 90 Hz upper limit I'm using was chosen because the motor's natural
speed is 3450 rpm and I didn't want to go over 5200 rpm. After my
testing I'm not worried about that and even if I don't go to 10,700 rpm,
something in excess of 5300 is not going to bother me.
So if I increase the VFD's max output to 150 Hz I can go lower on the
pulley setup, giving me more low speed torque (about 75% more) and loose
a little high speed (max about 1060 rpm). Or if I keep the current
pulley setup, I'll get a max rpm of 1800. If I suck it up and set the
VFD max to 180 Hz (10,700 motor speed) I could get a spindle speed of
2200 rpm.
I'm not sure what I'll do - I'll have to try different things. The real
point is that I don't feel so constrained as to how fast I can run the
motor.
Thanks for listening and for your comments,
Bob