Capacitors

[Marvin]

Hi
I was just wondering if there is any benefit in using capacitors on the MMM whilst racing? I see many people use them on lower spec ESCs...

Simon

[BrianG]

It can't hurt. They just help filter out ripple current. Having more of them will simply lessen the load on the built-in ones. As to exactly how much it will help? Hard to say. Depends on the quality of the batteries mostly I would say.

However, adding capacitance will also increase the spark when you hook up your batteries, which will pit your connectors faster.

[Marvin]

So with high quality Flightpower packs (25C continuous, 35C burst, 50C peak) there probably isn't much point?

[BrianG]

I wouldn't think so. But like I said, it can't hurt to add more (except for the extra spark).

[Marvin]

Got any suggestions as to what sort of spec I'd need? (I'd prefer not to use the ones Mike sells - pound is weak at the moment so shipping would be nasty)

[BrianG]

Voltage: Get caps with a voltage that is equal to or greater than the ones currently on the ESC. I usually use 25v up to 5s, 35v up to 6s, 50v up to 8s, and 63v up to 10s. You want around 25% headroom on cap voltage. You can use higher voltage caps on a lower voltage setup, but they get bigger as voltage goes up, so placement might be an issue.

ESR: Unless you get caps that are specifically stated to be low-ESR (equivalent series resistance), just get caps that are 105*C temperature rated or higher. The run-of-the-mill 85*C caps are not low-ESR and they tend to overheat trying to deal with the ripple currents.

Capacitance: I usually go no higher than double the ESC ratings. If an ESC has three 330uF caps (990uF total), get another ~1000uF. Obviously more helps, but the "return on investment" is smaller if you go too crazy. Also, using several smaller caps is better than one large one. So, instead of getting one 1000uF, look for two or three 330uF or 470uF caps.

And as far as installing them in a neat little package, I've done this:

[Marvin]

Thanks, just what I was after