simple 24V DC brushed motor driver circuit with relays help

[guskenny83]

Hi,

I have a 60A, 24V DC geared, brushed motor taken off an electric wheelchair that i want to use to help my friend build a pottery wheel.

to this end, all i need it to do is rotate with variable speed (controlled by a foot pedal) in the one direction, so i think a proper digital motor driver with bi-directional, full PWM speed control might be a bit overkill (and expensive)..

does anyone know of any good resources where i can learn about simple DC motor driver circuit design using relays? or have any advice on where to start with what i want to achieve?

i found this site (http://www.robmeyerproductions.com/bows.html) which seems okay, but it doesnt mention anything about controlling the speed. i have only had experience with DC motor control using digital PWM signals; with the relay circuit, would the speed be controlled by using a potentiometer to adjust the supply voltage to the motor?

also because it draws so much current, does anyone have any ideas about power supply to the motor? it doesnt need to be battery operated..

anyway, any help would be greatly appreciated
thanks
gus

 

[hzuiel]

I think your situation might actually be easier than mine. There are circuit boards on sale on ebay that are dc motor controllers with a potentiometer on them. Like http://www.ebay.com/itm/24V-60A-DC-...564?pt=LH_DefaultDomain_0&hash=item27b36cffbc You could cut their potentiometer off and splice one of these http://www.ssccontrols.com/homepage-potentiometercontrols.htm on and there you go. I wouldn't put the table directly on the drive shaft of the motor, wobbling back and forth will probably break the motor over time, you'll probably need to get a dedicated shaft and bearing for the table, and a couple of pulleys. This is also safer if something gets caught in the wheel the belt can slip.

 

[guskenny83]

I think your situation might actually be easier than mine. There are circuit boards on sale on ebay that are dc motor controllers with a potentiometer on them. Like http://www.ebay.com/itm/24V-60A-DC-...564?pt=LH_DefaultDomain_0&hash=item27b36cffbc You could cut their potentiometer off and splice one of these http://www.ssccontrols.com/homepage-potentiometercontrols.htm on and there you go. I wouldn't put the table directly on the drive shaft of the motor, wobbling back and forth will probably break the motor over time, you'll probably need to get a dedicated shaft and bearing for the table, and a couple of pulleys. This is also safer if something gets caught in the wheel the belt can slip.

thanks a lot for your help.. i was planning to use a separate shaft and pulley mounted with bearings for the table..

ive seen those motor controllers on ebay before, but they are a bit too expensive.. i was hoping there would be a cheaper solution that didnt involve PWM control.. but if not then i suppose that might be the best way to go..

what kind of power supply would you suggest to use for this controller?

also, i wont need the full power from the motor, im sure i will probably only need a quarter of the power, as it only needs to spin some clay, and not a human and heavy steel frame, so would it be possible to run it at 12V and 30A? or will the motor draw 60A regardless of what is being supplied? and i would need to run it at 6V and 60A? i have a very limited knowledge of how ohms law works sorry..

thanks again for your help
cheers

 

[hzuiel]

Come to think of it, there wasn't anything on that page that said what the input voltage was for that controller. You could use something like this. http://www.ebay.com/itm/9-40V-40A-1...994?pt=LH_DefaultDomain_0&hash=item3cd4de9a1a and I'm not sure about the power input. It looks like it takes dc input, 9-40v. Ac adapters seem expensive too.

You might be able to use this but i'm not sure what ohm potentiometer you need. http://www.ebay.com/itm/Marquardt-F...388?pt=LH_DefaultDomain_0&hash=item43be704834

Where are the electronics from the wheelchair? Surely some of that is re-useable.

 

[duke37]

Why DC?
Consider using a washing machine universal motor running on AC. Control it with a dimmer control. this may need amplifying to supply the current. The drum assembly may also be useful.

 

[guskenny83]

Why DC?
Consider using a washing machine universal motor running on AC. Control it with a dimmer control. this may need amplifying to supply the current. The drum assembly may also be useful.

im using DC because i have a motor already, but i might be able to get a hold of an AC motor from a washing machine too, so i will have a look into that.. do you think it would be easier? then just wire the foot pedal into the dimmer switch?

i worry a bit about working with 240V AC.. but i suppose 24V 60A DC is pretty bad as well.. hehe

 

[guskenny83]

Come to think of it, there wasn't anything on that page that said what the input voltage was for that controller. You could use something like this. http://www.ebay.com/itm/9-40V-40A-1...994?pt=LH_DefaultDomain_0&hash=item3cd4de9a1a and I'm not sure about the power input. It looks like it takes dc input, 9-40v. Ac adapters seem expensive too.

You might be able to use this but i'm not sure what ohm potentiometer you need. http://www.ebay.com/itm/Marquardt-F...388?pt=LH_DefaultDomain_0&hash=item43be704834

Where are the electronics from the wheelchair? Surely some of that is re-useable.

the electronics for the wheelchair are dead, my friend was playing around with them and connected the battery without grounding the controller properly and 24V went through the 5V circuit, frying everything.. thats why i got the motor from them for free..

if i was to use a relay circuit similar to one from this site:
http://www.robmeyerproductions.com/bows.html
and then put a variable voltage regulator in series with the DC power supply, would that work alright to control the speed?

 

[Fish4Fun]

Supplying//Controlling 60A @ any Voltage is a non-trivial business. You would be MUCH better off to go with a motor designed for 1) Speed Control 2) to be driven from line power. Assuming the wheelchair motor is a large brushed 24Vdc motor, @ 60A this would be 1.4kW. This is likely WAY more than you need to spin a pottery wheel, and likely has a great deal more value to someone who needs that kind of power; that is, you can likely sell your motor on ebay and get more than enough to buy all the bits you need for your project and end up cash positive. If you feel you must use this massive DC motor, I would suggest you investigate Golf Cart speed controllers, while I am certain they will be expensive, they are the closest thing to a mass-market solution you will find.

Fish