Differances in bk 12020 Warrior and 9920

[RC Fan 4 Life]

topic says it all. would eather one be good for a e-maxx on dual battery packs?

120 can handle 120 amps, 99 can handle 99

120 has 3 circuit boards, 99 has 2

120 has 4 capacitors, 99 has 2 (new ones)

[coolhandcountry]

They can handle it Unless you put some big amp hungry motor on it. But for the most part either can handle a emaxx and daul batteries.

[mmdooley]

120 has 4 capacitors, 99 has 2 (new ones)[/QUOTE]


I just got a 9920 and it has 4 caps and it's not new. I got it from a nice member of this forum. It has 9918 on it so I ask why? He said they(BK) tested the 9918 and was able to get 99 amps. Maybe that's why it has 4 caps?

yer i've got 4 caps on mine, just the latest ones have 2.

[mmdooley]

I wonder why they are running only 2 caps?? would 4 not be better??

[Nick]

2 larger caps, rather than 4 small caps.

[mmdooley]

:007: That makes since lol

[BrianG]

Anyone know what those caps are for? They're a bit small for load filtering, maybe they are there to filter noise/spikes?

By the way, using smaller caps that total the same capacitance as one cap is better because they can produce quicker transient response. Of course, if the circuit doesn't need that feature, it's a moot point.

And speaking of caps, I wonder if using say, a 500,000uF cap on the batteries would help reduce voltage lag when high current draw is being pulled. Of course, this size cap would be somewhat large and relatively heavy, so this is just for speculation.

[maxxdude1234]

lol, good luck fitting a 0.5F cap on a battery pack, I think a cap this big would be a bit over the top for an rc. Some cheap battery packs on ebay do have caps fitted to them, claiming they give a more punchier response. Personally I think its rubbish. If your really that worried about it, just get lipo's - problem solved.

[coolhandcountry]

The supposed to smooth out the voltage in the system. It don't work very will with out them.

[BrianG]

maxxdude: Yeah, I know it's not very practical, but I was just musing really. Something lighter like a couple of 100,000uF caps might make a difference and still be light and relatively small. I don't think it's rubbish really. They will supply a very quick and large amount of current, which is something a battery has a hard time doing. The net effect is a smoother and more steady current drain from the batteries with less voltage drop (as long as the high current is short duration). I guess the only way to verify this is to get one of those current/voltage recording modules and see what the current and voltage drop is with and without the cap(s). At only $13 per cap, I think it's worth a try...

[maxxdude1234]

Even a 100,000uF cap is very large. A 10,000F electrolytic cap is roughly the size of a D size cell.
Anyway even a 0.1F cap, with say 20volts (roughly 16cells) passing through it - it will only hold 2 coulombs of charge. If your motor is pulling 100A+ under hard acceleration, that 2C of charge will last you all of 0.02seconds. Even this would be an overestimate, you would probably get no more than 0.01secs of high current (100A+) from the cap. Its a nce idea but I don't think it would work practically.