High torque electric golf cart using high farad capacitors

[swanztech]

I'm wondering if I can convert an electric golf cart to use four 2 farad 12v capacitors wired in series to provide power to a 48volt 4HP electric golf cart motor.
In audio systems the rule of thumb is 1 farad for 1000 watts.
How would I calculate how much capacitance required for maximum torque output for three seconds? My figuring is 4HP = 2400watts x 3 seconds = 7200watts. In that case 8 farad should cover it.

My idea is to drive a 200amp x 12v alternator with a 5HP petrol engine and have the alternator charge the capacitor bank. The alternator should be able to output 2400watts (4HP) at full output.
The 200amp alternator should be able to produce enough energy to power the cart motor, but producing full torque to get all the weight moving could wear out the alternator pretty quick.
When full torque is needed then the capacitor bank should have plenty of juice to give the motor as much as it can consume.
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Is it possible to wire the 12v alternator in parallel to all four 12v capacitors and wire the capacitors in series to the motor? I'm hoping that possible for easy conversion from 12volt to 48 volt.

Thanks for any help on this.

Steven

 

[Sharkbiteattack]

So the vehicle isn't going to use any batteries? Something you have to keep in mind is that a capacitors capacitance (farads) adds inversely in series. So four 2 farad caps in series would not have a total capacitance of 8 farads. The total charge may still be 4x though. The energy stored in the plates of a capacitor is measured in joules and there's a way to convert that to watt-hrs. As for charging a circuit in parallel but then using it in series, this may be able to be done but would have to require some complex circuitry. It would at least need diodes (which constantly rob power mind you)

I'll let others chime in, I am by no means an expert on electronics, just sharing some knowledge from what I remember in college.


Also just for fun google "Chinese capacitor buses" china has some public busses that run off of ultra capacitors. They have a very short range but can rapidly charge (through induction) at every bus stop

 

[LiteYear]

Please don't try this until you've done a lot more research. The components you're talking about could easily create an explosion that could kill you and the method you propose would definitely not work.

Forget about your rule of thumb. That's a very different problem. Think instead of basic units - energy, power and capacitance. For example:

Watts x seconds = joules, not watts.

Energy (joules) stored in a capacitor = (1/2)*C*V*V. So 1F charged to 12V contains 144J, which at 2400W would be used up in 60ms. Not only that, as you start to deplete the capacitor, its voltage will also drop.

Hopefully you've realised by now that series/parallel wiring is the least of your problems. Not to put too fine a point on it, but reconsidering whether your electrical engineering degree covered 1st year electronics in enough detail would be a decent starting point.

 

[Paulusgnome]

According to the textbooks, the energy stored in a capacitor is calculated as E (joules) = 1/2 CV[sup]2[/sup]

If we assume that you intend to drive you cart with an 8F cap charged to 48V, then E = 0.5 x 8 x 48[sup]2[/sup] = 9216J

If your 4HP motor only draws 1000W (= 1000J/s), it will empty your cap in less than 10 seconds.

And as others have said, 4 x 2F caps in series does not equal 8F, it comes out at 1F, again using the standard textbook formula.

Perhaps a little more thought and calculation are required here?

 

[wayne440]

FWIW, my experience is that a typical 5 horsepower "lawnmower" engine is far from adequate to drive a 200A, 12V alternator.