Question for electronics majors.
Andrew VK3BFA
very little torque. If I substituted a higher voltage feed supply, and
kept the same (presumably) PWM original control, and taking note of
controller ratings, would this give more torque considering more
energy (from the higher voltage) is being transferred to the motor
where it does more "work" - (not sure of the right techo word here)
Andrew VK3BFA.
Tim Wescott
Probably not. I haven't been tracking the whole saga -- what are you
trying to do?
If you have infinite design freedom, for more torque at low speed you
want to gear the motor down more (assuming you don't also want high speed).
For full motor torque at a controlled low speed you probably need a
speed controller.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Bill Noble
"Tim Wescott" <t...@seemywebsite.now> wrote in message
news:b9SdnYsZ4IDsNV3W...@web-ster.com...
> Andrew VK3BFA wrote:
>> Hey all - the cordless drill saga continues. At low RPM, they have
>> very little torque. If I substituted a higher voltage feed supply, and
>> kept the same (presumably) PWM original control, and taking note of
>> controller ratings, would this give more torque considering more
>> energy (from the higher voltage) is being transferred to the motor
>> where it does more "work" - (not sure of the right techo word here)
>
short answer "no", longer answer, "not for long",
stall torque is based on motor current and magnetic flux - you can increase
current by higher voltage but motor can't tolerate it for long. low speed
is close to stall, so for a first approximation, same argument applies. PWM
control will not increase torque, may burn out with higher current, but most
likely the weak link is the motor.
cavelamb
Keep in mind . . .
Power - Current x Voltage
or
Power = Current SQUARED x Resistance
--
Richard Lamb
http://www.home.earthlink.net/~cavelamb/
Stu Fields
"cavelamb" <""cavelamb\"@ X earthlink.net"> wrote in message
news:6fednVGlzdDOel3W...@earthlink.com...
Another handy formula Power = (Torque x rpm)/5252
In PWM it is possible to increase the pulse width to get more energy into
the motor. Yes if you hold the rpm constant by an external load, you will
increase the torque per the above equation. You can also burn up the motor.
The way torque was obtained in my old Triumph was to put a larger sprocket
on the back wheel which reduced the rpm of the wheel for the same engine rpm
which still produced the same power being provided to the rear wheel. Lower
wheel rpm with same power had more torque.
cl...@snyder.on.ca
wrote:
>Andrew VK3BFA wrote:
>> Hey all - the cordless drill saga continues. At low RPM, they have
>> very little torque. If I substituted a higher voltage feed supply, and
>> kept the same (presumably) PWM original control, and taking note of
>> controller ratings, would this give more torque considering more
>> energy (from the higher voltage) is being transferred to the motor
>> where it does more "work" - (not sure of the right techo word here)
>
>Probably not. I haven't been tracking the whole saga -- what are you
>trying to do?
>
>If you have infinite design freedom, for more torque at low speed you
>want to gear the motor down more (assuming you don't also want high speed).
>
>For full motor torque at a controlled low speed you probably need a
>speed controller.
Higher voltage on a PWM WILL provide more torque - PWM gives much
better torque than a linear control like a rheostat because it allows
the full current to flow
cl...@snyder.on.ca
wrote:
MOST PWM drill controllers (at least both of my Craftsman ans my
Ryobi) have speed feedback - the thumbswitch sets the SPEED of the
motor and the controller provides whatever current is required to
provide the speed called for by the trigger setting (within reason)
Don Foreman
A DCPM motor's max torque is determined by its max current,
independent of speed unless speed affects cooling by internal fan.
Aside from cooling, max torque at max rated current is the same from
stall to the highest speed where it can draw max rated current.
A wound-field series-connected DC motor (unusual in cordless tools)
can deliver significantly greater torque at low speeds.
If your motor's torque droops at low speeds, the problem is in the
controller.
Jim Wilkins
Sure, you can get more torque by increasing cost and complexity, but
perhaps not as much as with a bigger motor or multispeed transmission
for the same price.
In a similar application relays close faster with a higher voltage and
a series resistor. Initially the relay inductance limits the pull-in
current, which rises faster from the higher voltage. The resistor
limits the holding current to the lower value of the normal rated
voltage. The costs are a larger power supply, more electricity used
and a higher voltage driver. In this case more money generally
wouldn't buy a faster relay.
For the motor you risk burning it out and have no way to know when you
have approached that point, even an infrared camera watching the
armature won't show the buried wires.
jsw
cl...@snyder.on.ca
So you burn out a drill that was useless anyway? Big loss, right?
Artemus
"Stu Fields" <e...@iwvisp.com> wrote in message
news:UcWdneHzNdX5v1zW...@linkline.com...
>
>
> Another handy formula Power = (Torque x rpm)/5252
>
and torque in Foot-Pounds.
Art
Andrew VK3BFA
You nailed it, right on. The salvaged motor is to drive a power feed
on my mini mill. Will use the original PWM motor - the rating plate of
which says 14v 20 amps. On a 9.6v drill. Interesting trivia - pulled
the battery charger to pieces - plug pack was 18v open circuit,
dropped down to 12 under charging load....constant 300 ma current -
the "turn the LED" on circuit was more elaborate than the charge
control. Now, I know they have got better - my latest one has a timer
in it, so gross overcharging is avoided. My conclusion - many a
battery pack has been stuffed by people not remembering they were on
charge - even overnight would be too much.....
(Whack a $5 charger on it, turn it off after ...you choose....hours)
None of it owes me a cent, its all junk that would otherwise be thrown
out, so it doesnt matter if I blow it up......
If its got enuff torque at slow feeds when its in place, fine, dont
need to do anything. If it hasn't - then crank up the voltage, see
what happens...
(Will post pictures of the fire if there is one)
Andrew VK3BFA.