Audio amp as a motor driver?

[jrz126]

I was thinking, if I have a somewhat high (50-60 volts) voltage DC (or maybe even an AC motor) motor, would it be possible to use an audio amp to drive it (put it through a bridge rectifier and filter cap of course)

Then I would be able to use a 12V car battery and also be able to vary the power going to the motor by controlling the input to the amp.

I cant think of anything wrong with doing this, but maybe Im missing something. If this does seem like it would work, which class of amps would be better to use?

I probably wont do something like this, but Im just kinda curious as to if it would work or not

 

[Dr.EM]

I think it would work, it'd be a linear motor driver essentially. It would thus waste a lot of power. A class D amp might be interesting though :?:

 

[Nigel Goodwin]

It could certainly work, but it seems a VERY roundabout way of doing it?, there are plenty of easier solutions. Basically all you are doing is using the inverter in a high power car amp to generate a higher voltage than 12V - so why not throw the amp away and just use an inverter?.

 

[jrz126]

I've never really looked into motor drivers before, so I dont know what is available. My thinking behind this was if I had an old audio amp lying around, why not put it to use, and it would save me from having to buy an inverter and whatnot.
(I was also thinking that it would give some justification for buying some new amps for my car)

how much do the inverters usually run? say for about 500-700 watts?
And what kind of efficiency would I expect from a Class D?

 

[audioguru]

Hi Jeff,
You need a high power, high voltage motor driver circuit that controls a DC motor with PWM or an AC motor with frequency.
An inverter usually doesn't have a variable output voltage and it or an audio amp would curl-up and die if it tried to start or drive a high power stalled motor.

 

[Nigel Goodwin]

As with many questions, so far this is much too vague - we really need to know what he wants to do, and why.

An obvious question is why not use a 12V motor?.

 

[jrz126]

Hi Jeff,
You need a high power, high voltage motor driver circuit that controls a DC motor with PWM or an AC motor with frequency.
An inverter usually doesn't have a variable output voltage and it or an audio amp would curl-up and die if it tried to start or drive a high power stalled motor.

What if I just drive the amp into clipping and then vary the freqency, that would give me a PWM in a round-a-bout sorta way...err...I think... I cant really think straight at the moment, finals are coming up and school is kicking my butt right now.
Most audio amps have a built in short curcuit protection too, so I would think that it would just put it into protect mode?

As with many questions, so far this is much too vague - we really need to know what he wants to do, and why.

An obvious question is why not use a 12V motor?

I'm not really planning on doing this, I was just wondering if it work or not. I was planning on buying this broken subwoofer amp and trying to fix it. I didnt really have a need for it, so I was trying to come up with another use for it. I have a nice 60Vdc motor that I would like to use for something, and I have no way of providing the 60vdc, so I thought I could use the amp for it.

I know its a kinda odd way to drive a motor, but I'm all about the odd projects as see here:

 

[audioguru]

What if I just drive the amp into clipping and then vary the freqency, that would give me a PWM in a round-a-bout sorta way.

No. PWM works by varying the duty-cycle of high to low.

 

[jrz126]

What if I just drive the amp into clipping and then vary the freqency, that would give me a PWM in a round-a-bout sorta way.

No. PWM works by varying the duty-cycle of high to low.

oh yeah, higher frequency would still give me a 50% duty cycle.
What if I put a pwm signal on the input to the amp?

 

[audioguru]

What if I put a pwm signal on the input to the amp?

Few audio amps have DC coupling. Max speed or zero speed would last only 50ms on a capacitor-coupled amp. The amp would probably shutdown anyway when it senses the offset voltage at its output.

 

[Styx]

Yes you "could" use an audio amp as a motor-drive, just like you can use a motor-drive as an audio-amp

The difference? it will be extreamly shite and you run the potential to destroy something.