Sputtering 9920 and hot caps

[giftacrylic]

Converted a Jammin Truggy to brushless a few weeks ago and ran it on 12 cells without any problems. Yesterday, dropped the gearing down a tooth and ran it on 14 cells. Ran great for 5 minutes, then most of my power subsided. Thought my batts were drained so I recharged and tried again. This time, it sputtered violently then took off. The 9920 was not hot but the caps were very hot but not bulging. Switched batts, reprogrammed controller and checked wires. What else can cause this problem?

[neweuser]

it sounds like the controller may not be running properly, or, your batts are sending surges into the esc for some reason...the capacitors may not be all functiioning. It's a touch and go with that one. What motor are you running? Are you using a ubec? check that as well.

[giftacrylic]

Seems as all 4 caps are hot. Running a 7XL w/ a reciever pack, no UBEC. The caps get HOT only after 20 seconds of running. I know this because after every change that I do, I hook it up to see if the problem is fixed.

[neweuser]

Have you checked your wire connections through out the truck? What gearing are you running?

[giftacrylic]

Took the 9920 off and it smells burnt on the top and bottom of the middle of the unit. None of the wires were grounding out or shows wear. This controller never thermalled (shut down) or got hot....Also, I know for a fact that I never shorted out the controller.

[squeeforever]

I think you fried the internal BEC with 14 cells...Any more than 12 and you should run a UBEC...

[giftacrylic]

I have the black jumper removed and am using a reciever pack.

[BrianG]

I wonder how caps can get hot. All they do is filter/couple AC or store a DC charge and unless you are charging and discharging them with large currents (which shouldn't happen if the batteries are any good), they should never get hot. Maybe the circuit board traces are transferring the heat to the caps?

At any rate, lots of heat anywhere means lots of current and a relatively high voltage drop on the ESC, which should not occur with all those FETs paralleled the way they are. I would think several FETs are burned out increasing the circuits total output resistance which then generates more heat.

More heat could also be caused by low output batteries forcing the ESC to supply more current to compensate (in a way).

[squeeforever]

Try another set of batteries. Like Brian said, it might be because the batteries aren't putting out enough power.

[giftacrylic]

That was the first thing that I tried, using GP3700's. Kind of a mute point now that the controller has a burnt electronics smell. It is possible that the motor windings could be touching and shorting out the controller?

[squeeforever]

It's possible. You might have fried some fets.

[neweuser]

My 9920 had hot caps when i ran the 20T pinion with my 10xl. went back to 18T and it's fine now. My 12020, the caps went up like a mountain and the heat was real bad! I use the same batts on my 9920 now and it's fine as long as i don't use my 20T pinion. Electronics are weird!

[BrianG]

Well, like I said, caps should never get hot. Assuming they are still in working order, I can only assume the rest of the circuit is quite hot and the caps are heating up simply because the leads are on the same circuit traces.

They could also warm up if they are charging and discharging at high currents. The batteries charge them up, but then extremely high currents cause the battery voltage to sag and the caps will discharge as fast (and with as much heavy current as the circuit will allow) as possible to compensate. Then, when the load goes away, the batteries continue to supply the load and charge the caps again. This high current charge/discharge could heat them up.

Sometimes, it may seem that electronics are weird, but it all makes sense once the mystery is solved.

[auto2]

my 9920 did the same thing. CAPS were 160 degrees F when the rest of it was 130. one of my caps was hotter than the other 3. I had a motor go bad on me and it ruined the controller. A new controller fixed everything.