Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: Bajanick on August 04, 2007, 08:25:33 PM

Title: Easiest way to find stall current of DC motors?
Post by: Bajanick on August 04, 2007, 08:25:33 PM

I should know this by now.....  ::)
I need to find out the stall current of a couple DC motors so i know if my controller is underpowered or not. The max amps the controller can handle is 20 amps per side, and 60 intermittent, I am using 2 wheelchair motors.

Thanks.

Title: Re: Easiest way to find stall current of DC motors?
Post by: Soeren on August 04, 2007, 09:23:36 PM

Hi,

Errr, like stall them and measure the current of course.
Just do it very quickly, to avoid burnt out motors.

Title: Re: Easiest way to find stall current of DC motors?
Post by: Bajanick on August 04, 2007, 09:42:57 PM

Ammeter in series with motor and battery? If I remember correctly thats what I did before but it was several years ago.

Title: Re: Easiest way to find stall current of DC motors?
Post by: Soeren on August 04, 2007, 09:51:16 PM

Hi,


Yes, if you're sure the stall current is below what your meter can handle, otherwise use an external shunt of known resistance and measure the voltage drop over that - method doesn't really matter, as long as you get the numbers without harming the motor.

If this is for a protection circuit, to cut the power at stall, perhaps make it so that it cuts way before stalling, since a "semi-stalled" motor might still be ruined - that's why some motors have temp. sensors installed.

Title: Re: Easiest way to find stall current of DC motors?
Post by: Bajanick on August 04, 2007, 10:18:12 PM

Its so I know if the Controller I have will work without blowing up, lol. Installing some kind of breakers is not a bad idea also.

Title: Re: Easiest way to find stall current of DC motors?
Post by: Soeren on August 04, 2007, 10:36:01 PM

Wheel chair motors are usually made to withstand a lot of abuse (and some amount of stalling), since a wheel chair user depends so heavily on their functionality.

If the motors are anything like the one I used a couple of years ago (www.CupSucker.dk hasn't been updated, but do have pics of the chassis and motor), I'd definitely not control it with a 20A controller, unless perhaps if it has got forced cooling.

Title: Re: Easiest way to find stall current of DC motors?
Post by: Bajanick on August 04, 2007, 11:24:10 PM

Unfortunately I cannot find any specs or info on the motors for this wheelchair.
I have the book "Build your own all terrain robot" and in it they use wheelchairs with aftermarket controllers that can whithstand only 30 amps. I have to assume the stall current of the motors is probably a minimium of 50 amps, but If I place a 20 amp breaker on each motor that would be some protection, actually there is a built in breaker on the wheelchair but I forget what amps it trips at.