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Old 08-03-2007, 01:32 AM   #16
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Quote:
Originally Posted by QuickRC View Post
2 caps in SERIES increases voltage but capacitance remains the same. In PARALELL the capacitance is doubled but voltage remains the same.
Not quite true, for the same values of capacitor, the capacitance in series will be halved.

Equation for capacitors in series: 1/Ct = 1/C1 + 1/C2 + ...
Equation for capacitors in parallel: Ct = C1 + C2 + ...

To answer your original question, I'm not sure that you would gain any advantage by having 2 capacitors in parallel as apposed to having a capacitor of the same overall capacitance.

As for the purpose of capacitors across the battery, I believe it is to smooth out the drops in voltage when under hard acceleration and the voltage of the battery drops due to a large current draw.
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Old 08-03-2007, 07:39 PM   #17
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[QUOTE=Skill;3546109]Not quite true, for the same values of capacitor, the capacitance in series will be halved....

Son of a gun - you're right. I don't feel too bad, it's been 20 years since I had formal education - this is probably the first time I actually used that since then.
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Old 08-04-2007, 02:24 AM   #18
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It's ok, I've just finished an electronics course at A level so it's all quite fresh in my mind at the momen
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Old 08-07-2007, 11:31 PM   #19
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can someone advise what is the optimum cap capacitance i should look for? im planning to buy one... any generic capacitor from electrical shop will do?

im using a Futaba MC230R which has output amp of 90A and will soon change to a 23T motor...

thanks in advance!!
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Old 08-08-2007, 12:42 AM   #20
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Bud from experience suggested cap values are :
caps from a 1000mfd to 3300mfd and fron 16v to 25v also the lowest ESR you can get.
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Old 08-12-2007, 09:07 PM   #21
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Bud from experience suggested cap values are :
caps from a 1000mfd to 3300mfd and fron 16v to 25v also the lowest ESR you can get.
what is the range of the 'lowest ESR' are u referring to? whats the Ohm value?

is >3000uF ok? what about 1 F?
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Old 08-12-2007, 09:28 PM   #22
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Skill, not to nit pick here, because my knowlege is strictly real world acquired, not from a book or formal school, but you said

Quote:
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Not quite true, for the same values of capacitor, the capacitance in series will be halved.
But if my understanding of capacitors in this instance is correct, I believe this to be true:

capacitors in parallel (given the same voltage etc) = ESR or capacitor resistance is the same a a single cap, but capacitance (or volume) is doubled

capacitors in series = capacitance is the same as a single cap, but ESR (internal resistance) is halved (not doubled)

To be clear, you stated the capacitance of said caps in series are halved, but in fact overall capacitance (in realation to just one cap) stays the same.

If you were saying that the cap's volume (capacitance) in series is halved meaning the two together are equal to only one, then I can see your point, but I think you failed to mention the advantage of having them in series.

Again, I'm not formally educated in this area sp feel free to correct me anyone.
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Old 08-13-2007, 02:51 AM   #23
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I'm not saying my way is definitely correct but this formula is what I have been taught and been examined on recently.

Equation for capacitors in series: 1/Ct = 1/C1 + 1/C2 + ...

If you sub in the same value for C1 and C2, say x then you get:

1/Ct = 1/x + 1/x = 2/x
Ct = x/2

Therefore, half the capacitance of one of the capacitors.

As I said, I'm not saying this is 100% correct but this is what I've been taught and have used on a practical basis so I can't see it being wrong.
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