How to increase amperage of a variable DC output circuit?

Discussion in 'General Electronics Chat' started by cmavridis, Apr 28, 2015.

  1. cmavridis

    Thread Starter New Member

    Apr 28, 2015
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    Hello people!

    I am new to this forum but i couldn't find any specific information easily. Let me describe you what i want to do.

    I have a wheel gaming controller for a pc, which provides feedback information to the wheel through 2 simple DC motors that turn a larger gear which is 1:1 with the wheel.

    The motors voltage is controlled by a board which simply takes usb information from games, and translates it to -24 to +24VDC as output for the motors.

    Here is the board controlling the motors, in red the 2 mosfets (9977GM and 4951GM), 3 diodes (P6KE27CA) and motor connections (parallel):

    [​IMG]

    The motors on the circuit are in parallel. As you add motors you increase the performance of the wheel, all aspects (torque wise). I modded the wheel and added 2 more motors, and i only have tested the 3 of them because i am afraid of the mosfer amplifiers capacity.

    It has 2 amps, the 9977GM for the positive supply and the 4951GM for the negative. They are rated to 60V - 3A approximately. The motors are 24V - 0,7A each and by default it uses 2. I also replaced the stock 24V power supply with a factory grade 24V - 5A one.

    As far as specs go, the fets and surrounding diodes seem to handle 4 motors but i don't feel good pushing them to their limits. I added a large heatsing to the mosfets also.

    My question before i risk connecting the 4 motors... Is there a simple circuit i can make that replicates the boards output but can provide more amperage? (board output -> circuit that gives same voltage but more amps -> motors)

    I know i can swap the mosfets with better ones, if someone can provide specific info it will also be great,
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Without a schematic of the board's output section it is almost impossible to say, and I doubt that Logitech is going to give you one. Without it, it would take a lot of probing with a scope to reverse-engineer the output stage, the first step in designing an external current booster.

    ak
     
  3. cmavridis

    Thread Starter New Member

    Apr 28, 2015
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    hey. thanks for the reply.

    while i understand this logic, why do you say that its impossible? i mean since the output is continuous (not pulsed) voltages from -24V to +24, is it that complicated to take that output voltage as reference/input and replicate it with simple transistors that can handle more amps?
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    It still depends. You can add transistors that can handle more current, but can the power source provide it?

    For example, suppose you have a power supply that can provide 1A at a certain voltage. There's no way you can increase it above 1A; even by replacing the pass transistors with ones with a higher current rating. The person who figures out how to do this will win a Nobel Prize.
     
  5. cmavridis

    Thread Starter New Member

    Apr 28, 2015
    4
    0
    oh sorry i didn't mention i already have a power supply that can give 5A and another one at 10A to use instead of the stock 24V 1.7A

    I have already tested the device with 2 motors @28V (doesn't drop even with the 5A psu) and i added a heatsink on the mosfets that becomes warm after many tests. risky but it worked.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,804
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    Are you sure? If you used a simple meter to measure the voltage at the motor terminals then the meter is too slow to register PWM pulses and will have measured an average voltage. The motor presence will tend to smooth the reading. I'd be surprised if the FETs were operating in a linear mode rather than PWM mode.
     
  7. cmavridis

    Thread Starter New Member

    Apr 28, 2015
    4
    0
    No i didnt even measure there, i know it would average the voltage to display. I only had it on the power supply to check for dropping. I am just assuming it would be constant but you might be right.

    i will measure the output with an oscilloscope to be sure.

    To sum up, can someone share a simple circuit to do the job -if- it is not pulsed?
    Why would it be different than pulsed?

    Also, i played a little bit a game to stress it over time. Forces there are continuous and usually really high. Since nothing blew up, i assume i am within amperage of the mosfets etc (i will measure the total amperage drawn soon also) and they just get warm (the heatsink i mean). If i add a fan, do you think it would be ok for now? Ok i will share the amperage measurement later for this.
     
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