MMX & PP2200 Smoking Batteries - How to test?

[stimpy]

Hello folks,

Running into a bit of an issue currently... My set up:

Toyzuki
HH PP 2200kv
Mamba Micro X - Bec runs receiver
Castle BEC - Runs Servo
Hitec 7950
3S Batteries

Last time I was out - around 2 weeks ago - my steering got sloppy and at the end of the morning stopped altogether and smoke poured out! Disconnected battery and found the servo had burnt through its casing... ( This was its 3rd time out)

Anyway, sent it off and got a replacement back and whilst that happened I tidied some of the electrics but did not try driving the truck.

Last night I finished the truck off ready for today and thought id best do a quick test run.... Plugged in, steering worked but motor seemed to cog a bit then go mental in reverse!?... Next thing the ESC lights go out... I pull the battery and its red hot!!

Tested the battery and its a cell down and showing insane numbers on the other 2... Balls!..

Checked my wiring; ABC, Swapped the sensor lead, power connections etc. Motor spins freely. So I figured well maybe it was a poor battery so I grabbed an older unit and plugged in. Motor was still cogging then I smelled heat so pulled the battery which again was hot...

At that stage I desoldered the bEC just incase but was still getting red hot battery issues..

So.... Either I've messed something up when soldering - perhaps I put too much heat into the posts? - or when the servo went down it somehow switched polarity for a mo and killed the esc?

Really not sure at this stage but wondered if anyone has had a similar issue or how best to test these components - I have an ohmmeter and an insulation resistance tester...

Any help appreciated "thumbsup"

 

[stimpy]

Just been out to the garage and got the ohmmeter on it..

Esc Battery plug + to - = 3.55 kohm
Esc
A-B post 165 kohm
A-C post 215 kohm
B-C post 335 kohm
These post readings were rising.

Motor
A-B , A-C, B-C all 0.1 ohms

I’m an electrician but know nothing of electronics... Anyone got any ideas!??

 

[Zondar]

First, you have a very dangerous situation here! Only mess with this outdoors in a safe area! A LiPo battery getting "red hot" is insane enough, you don't want a lithium fire indoors! :shock::shock::shock:

Next, you need to isolate the problem by trying only one thing at a time, with everything else disconnected.

It would be good if you could run a DVM in series with your battery or ESC outputs to measure Amp draw. But note that a "red hot" battery indicates that a heck of a lot of amps are being drawn - maybe not a dead short circuit, but for sure something close to that.

The burning of your servo would hint that it's associated with that side of the circuit, so start there, with your motor's ESC, etc., disconnected.

Good luck and BE SAFE!

(Those numbers don't look unreasonable, but then again your motor is on a different circuit than your servo anyway. I wouldn't worry about the non-uniform ESC resistances, since the off-values are basically irrelevant. The ESC would have vastly lower output impedance when actually in use.)

 

[ferp420]

i had a similer situation with my mamba monster x servo fried and took out the ground all the way back to the esc i havent been able to fix it but castle has a good repair/trade in program if they cant fix it they will give you a good deal on a new one

 

[stimpy]

Thanks chaps.

Just been chatting with an electronics buddy of mine and he’s erring towards motor but may pop over in the week and we’ll do some swapping with some cheap stuff he’s got.

I’ve had the esc and the BEC on the castle link and certainly there all looks fine. But then I guess it would either respond or not, but atleast that’s another thing ruled out.

As for attaching an ammeter, I can tell you already it’s a shit load of amps being pulled! My multi meter is only rated to 10A so no point blowing that fuse trying....

Glad to know I’m not the only one. And if anyone else has any other ideas how to test then let me know

 

[stimpy]

So, just took the rig outside....

With the motor disconnected I plugged the esc in.... I know I probably shouldn’t but sod it. First with the ex disconnected, and was fine. Next with the rx connected and was fine. Just a load of warning LEDs.

Of course it has no load so this doesn’t prove much but atleast that didn’t smoke another battery

 

[Voodoobrew]

If only one cell is down on the battery that's where you need to start looking. Each cell should drain evenly. So either your battery was bad before you plugged it in, or there is so thing connected to the balance leads incorrectly. Possibly a bec or a break in the insulation on the wire.

I'm not saying there aren't other problems, but one cell should never be dead if amps are only leaving the battery from the main leads.

If it's not related to the balance leads then (and also because it got hot and low voltage) your one dead cell has a higher internal resistance then the other 2 cells. This causes it to heat up and die faster then the other 2 cells.

Next

If your esc is functioning correctly (which it probably isn't) it will not place an high enough amp draw on the battery unless it's trying to drive the motor (this would make your motor hot also if it's not able to turn).


So my guess is your servo died, which created an electrical surge or short that also wrecked your esc. You then connected the wrecked esc to a battery with a sub par cell in it which was exposed by the high amp draw.

Just guessing though.

Also
Don't try to test the resistance of your battery with an ohm meter.

__________________________
Handy gearing spreadsheet

 

[Voodoobrew]

Check everything metal and conductive for shorts or power where it shouldent be.

My guess is the battery wasn't the only thing that got hot. The other thing that got hot probably has a leak in it.

__________________________
Handy gearing spreadsheet

 

[stimpy]

So, a quick update...

A buddy of mine came round yesterday with some cheapo Chinese offerings that we could play with to work out what was faulty. First up was test the motor, which I was sure was fine as I took it apart and looked 100%. Connected to the cheapo esc and .... spun nicely and caused no issues whatsoever...

Next up... We attached the cheapo motor to my MMX and tentatively plugged the battery in.... Immediately heat started crawling up the leads so pulled her..

So. MMX is screwed... As above, it was either that smoking servo or I put too much heat in soldering. From the sounds of it, it was probably the servo issue but either way I at least know the facts now and have placed an order...

Thanks for all your ideas folks.