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Old 10-20-2010, 06:10 PM   #3871 (permalink)
MPaulHolmes's Avatar
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Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000
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Forget the capacitors for a second. Where does the future 1200 amps go that will be flowing through the mosfets, once they shut off? It's going to go through your resistor and diode. It WILL be the same current for a short period of time, because current can't change instantaneously. So, if you are suddenly forcing the current to go through a resistor and the freewheel diode, you are still stuck with Ohms law. V = I*R.

I = 1200amp (let's say).
Was the resistor like 20 Ohms or something? I forgot. Let's say 20 Ohms.

V = 1200*20 = 24000v. You should see 24000v drop from Drain to Battery + for an instant. So, the voltage that the mosfet will see from Drain to Source would be 24000v + Pack voltage. The mosfets are rated for 300v.

Am I missing something?

Let's see if we can come up with an analogy for this... Oprah, a very very large land mass, is moving at 100 mph. Suddenly, she is forced to go into a bog instead, since the path that her wheelchair is on is closed off. Then she starts singing the theme song to the Phantom of the Oprah... I hope that clears it up.

Actually, it's like a whole army of "people", marching in unison. The motor is like a human mass production plant. Putting out 1200 people per second. They need to be notified ahead of time to reduce production. Right now, while the mosfets are ON, the people have no problem just being shoved right out to their ultimate goal in life, B-. (In high school my ultimate goal was a D-, but we won't talked about that). So, now that the "doorway to heaven" (mosfet) is closed, the people have to still keep marching onward, but they have to go through the resistor and diode. The diode ain't nothin, but there are still 1200 people per minute being pumped out of the factory, now being squashed to death (increased pressure means higher voltage) trying to desperately make it across the terrible bog, which is filled with Malaria. They can't slow down either! There are people pushing on their backs, forcing them to move! This causes them to become very angry. Basically, a big fight breaks out, and they start breaking stuff, like the mosfets.

kits and boards

Last edited by MPaulHolmes; 10-20-2010 at 06:26 PM..
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