Info about the BK 9920 on 6s
 

I know that there are better escs than the 9920, but I have one and would like to get some feedback from the guys running them. I have a new emaxx center chassis with tranny coming (thanks Sike!) and will be trying out my KB45 8xl on it. Do you think that the 9920 can handle that motor (1700kv) on 6s lipo? Motor speed is less than 40k rpm, but I intend on gearing for about 70 with the 2 speed. I can imagine that this will draw alot of current. What kind of ratings can the 9920 handle? It says 99 amps, but can it do that?

If it's a 2 pole motor, then it should work fine. 6s is 25.2v max (4.2v/cell) and 18 NiMH cells are 25.2v right off the charger (~1.4v/cell), so you should be fine. Not sure how much current you'll be drawing since you're geared that high, so I'd watch your temps at first to be sure...

I only paid 40 bucks for the 9920, brand new! My batteries can only put out 100amps cont (on a good day, with a tailwind, going downhill). We shall see if it can do it. Mainly for speed runs, I will gear down to play with it. Much over 45mph is too fast for my play area.

i ran mine with 5s2p of a123 on that same motor. it worked perfect with no heat issues. i know that a bit less voltage, but just to give you an idea. also my batteries could supply much more that the esc was rated. this was all on a heavy ext flm maxx on a 26t pinion buggy diffs and maxx sized tires.

I only ran a 9920 for a few runs because it would not work with my LVC but on 6S it ran pretty hot with a Lehner 1950/7

The german manual can be found here. I know this won't be of much use for you. But there is a note concerning using the BK ESCs at their maximum rated voltage:

Basic translation:
Be carefull when using the max cell count (20 cells) that you won't use them fresh from the charger. Those cells could be above 1.2V.

So the max voltage should not exceed 20x1.2V = 24v. A 6s lipo is at 25,2v fresh from the charger. This could mean trouble. As they also state that they can determine the max voltage the ESC was subjected to when you send it back to BK. Guess it's at your own risk. I know at least of one guy in germany who fried his BK 9920 with 6s lipos. Not on his firt run, but after a while. If i were you i would only use it with 5s max. It's never a good idea to push Esc to their voltage and/or amp limit.

Thanks othello, I am happy with the 9920 in my emaxx on 5s, so I may leave it there!

where did you get the 9920 for $40 ?????

yeah i want one for $40 too. That would tide me over until MMM came out easily I think.

A friend of mine traded something for it. He had it for a while and never used it, still brand new when I got it. He gave it to me and said if I could sell it we would spilt whatever I got for it. I had a guy that would pay 80 for it and my fiend was happy, so I gave him 40, problem was the other guy backed out of the deal. I did not really want the bk, but I gave it a try and have to say that for 40 bucks it is a great controller. Not many features, but that is ok! It runs my 15l in the 2wd emaxx just fine on 5s, barely gets warm. I am probably only pulling 50-60 amps thru it.

I picked one up for 75 lightly used on fleabay. Waiting for it to get here. I have just smoked ANOTHER quark, so at least it might hold me till i get something back from RMA to S&T.

J.

That sucks, how is quark's service? I need to send a 125b back, what do they require in the way of paperwork for a return? I have emailed them, but no reply.

yeah, i get no reply either. someone is sending me their new addy, i'll pass it on to you once i get it. supposedly their service is pretty good. You just write a little note about where/when it was purchased and what happened and send it on it's way to them.

Just off the phone with S&T, here's their new address. The one on their website is wrong.

Sky & Technology
3954 W 182nd Street
Torrance, CA 90504

Thanks 83gt.