Discussion in 'General Electronics Chat' started by kdcouture200, Jul 28, 2014.

1. ### kdcouture200 Thread Starter Member

May 22, 2010
17
2
i'm making a power supply for a motor which requires 24Vdc at 8 amps.
so i made the circuit in the photo. the problem is that the simulation is saying i'm drawing 17 or so amps through the transformer is this right or is multisim mistaken? also i'm not sure but is the I p-p really 103 amps because that seems way off to me. thanks for you help.

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2. ### PaulEE Member

Dec 23, 2011
423
32
I'm not sure how the simulation is setup, but the 103 amps might be the current flowing into that 50 mF capacitor bank you've got there (at startup)...perhaps run the simulation for several seconds of time and see if that current stabilizes at a lower value?

3. ### PaulEE Member

Dec 23, 2011
423
32
Alternatively, perhaps you can impose an initial condition on the capacitors to see if that current is closer to 8 amps.

You might also consider a different topology for the circuit, but that would be another thread altogether

4. ### kdcouture200 Thread Starter Member

May 22, 2010
17
2
what kind of other technology would give the desired output?

5. ### PaulEE Member

Dec 23, 2011
423
32
Well, often times, when somebody wants to drive a motor that takes any appreciable amount of power to run, they will often use a switching circuit to generate a square wave. Then, adjusting the duty cycle (the amount of time the square wave is in the "on" position with respect to the total square wave period), you can adjust the amount of power the motor gets, therefore allowing throttling of RPM.
Things to look up are pulse-width modulation, half-bridge, h-bridge, output filter, etc etc. There is a lot of information on this website and on google about such things The advantage to this method is that the power-throttling is done by adjusting duty-cycle instead of feeding a power transistor with a constant power supply and "burning away" what isn't needed. Make sense?