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Originally Posted by KISA
Sorry for this questions if it's already been asked, I've looked through a fair number of this forums pages (not all 327 of them) and couldn't see it. But Murphy's law will say it was probably on the next page  |
Probably considering this question was just asked last week. See page 325.
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I'm just wondering what is the need for so many capacitors. I understand they add when in parallel so it affectively 16 x 820uF, roughly a 200V 17mF Capacitor. Is the high capacitance needed to successfully smooth out the voltage swing caused by the mosfet switching frequency or am I completely off the path?
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It's not just the capacitance. There is also the issue of effective series resistance (ESR) and heat dissipation, because the ESR causes the caps to heat up.
The best explanation that I've read so far is Lee Hart's discussion on motor controller capacitance. You can find it here:
Yahoo! Groups
Talks about ESR, ripple current, heat, the whole nine yards. The short of it is that more is more is better to a point, and that the specs of the caps in terms of ESR and temperature are very important. Finally he has an empirical way of determining the correct amount, which measures the ripple current to determine the appropriate amount.
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The reason I ask it that I'm trying to determine what capacitance I will require for a controller I wish to build/test for an electric motorbike and what are the contributing factors?
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See above. Everything you need is there.
Welcome.
ga2500ev