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

 

[jiripolivka]

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

You can have complex and expensive solution as well as a simple one.
For your case, to drive the rotating table, it will be good to know if you really need he high full power of the motor, 1440 Watts (two horse power). I think a quarter of it may make it, but you must try how much power the user really needs.
For the tests and to design the electric drive I would borrow two 12V car batteries and run a test. If 12 V is too much, you can try two or three 6V batteries connected in series, and use the foot switch to select 6 or 12 V to run the spindle. If more that 12 but not 24 V are needed, you can try three 6V batteries and use the switch to add or remove the voltage in stages, 6-12-18 V.

If you determine the useful range of voltages, then you can decide how to design either a charging circuit for the batteries, or how to operate the motor from AC power.
There are various battery chargers on the market and obtainable as surplus for a low cost but most will not be able to directly feed the motor. A 1.5 kVA transformer from 120 or 220 V to 6-12-18-2 V may be needed but it is expensive. Switching power supplies are available but also expensive.

Several 6 or 12 V batteries with a charger may be the cheapest but good solution.

 

[guskenny83]

You can have complex and expensive solution as well as a simple one.
For your case, to drive the rotating table, it will be good to know if you really need he high full power of the motor, 1440 Watts (two horse power). I think a quarter of it may make it, but you must try how much power the user really needs.
For the tests and to design the electric drive I would borrow two 12V car batteries and run a test. If 12 V is too much, you can try two or three 6V batteries connected in series, and use the foot switch to select 6 or 12 V to run the spindle. If more that 12 but not 24 V are needed, you can try three 6V batteries and use the switch to add or remove the voltage in stages, 6-12-18 V.

If you determine the useful range of voltages, then you can decide how to design either a charging circuit for the batteries, or how to operate the motor from AC power.
There are various battery chargers on the market and obtainable as surplus for a low cost but most will not be able to directly feed the motor. A 1.5 kVA transformer from 120 or 220 V to 6-12-18-2 V may be needed but it is expensive. Switching power supplies are available but also expensive.

Several 6 or 12 V batteries with a charger may be the cheapest but good solution.

thanks for your advice, i dont need to run it from batteries, i can use a DC power supply directly from AC.. so if i only want maximum 1/4 of the power of the potential power of the motor, can i run a 30A, 12V power supply?

sorry, i only have a pretty limited knowledge of ohms law..

thanks again

 

[Venkadesh_M]

If you are doing wired, then you can use the above website circuits, and a regulator (like one used for fan but not just a pot) series with the motor....

 

[jiripolivka]

Yes, you can try the AC/DC 12 V, 30A power supply. Make sure it is well cooled, the motor with the spindle may become overloaded for a short time. Batteries usually handle better the overload.
And PLEASE,learn the Ohm's Law. It is so simple, U = RI and you can understand any electric circuit! Next remember that the power is P=UxI. This is almost all you need for working with electric circuits.

Good luck!