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# Help Charging my Capacitor Bank Without Tripping The Breaker. Answered

Hello. I need help with charging a capacitor bank I have. It consists of 10 capacitors: 4 4700uf capacitors and 6 6800uf capacitors. All are wired in parallel. I have been charging them with 110AC rectified to DC. The only problem is that whenever I flip the switch to start charging, it trips our shop's 20A breaker and you have to flip it back to start charging again. It trips our breaker every time and dims the lights making my dad angry. So I need some tips on what wattage resistor i need to use to keep from tripping the breaker. I experimented with a 10W resistor and that was way too much resistance. I am not allowed to experiment anymore until someone credible can tell me what to do. Thanks for your help.

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## 1 Replies

steveastrouk (author)2010-10-30

You can stll charge this lot in only a few seconds, but you MUST use a current limiting resistor (and that's selected by RESISTANCE, not power rating).

The worst case current flows at the instant you swithc the supply into an empty capacitor bank, so, for 110V, lets limit the charging current to half your breaker rating, say 10A. So R=V/I, and 110/ 10 = 11, so get a 12 Ohm resistor. Get a fat resistor, say 200W, and you can charge in well under 1 second, without popping the breaker.

Putting a more realistic charging time, say 5 seconds, as a parameter, and taking your capacitor bank as 60,000 uF.

Since R x C = ~63%of the charging time, 5= 0.06 x R > 5/0.06, and R= 83 Ohms, and maximum dissipation = 145 W, but that'll be for a fraction of a second, so a 100W , 83 Ohm resistor will work nicely.

Steve