MMP fried in a weird way, what could the cause be?

[dna4engr]

Hey guys, I've run mmp on many rigs for a few years.

Today we ran a g6 style event and I ran my 1.9 scx based rig. Fried the esc after the event was over.

Specs:
Mmp, holmes hobbies bls540, over/under gears, 3s, castle bec, futaba 4pls, 12/56 spur pinion

We ran the entire event and were waiting for everyone else to finish. Puddled around a little and and was hanging out when someone noticed the truck was smoking. Immediately I thought lipo fire and threw the body off and grabbed the battery wire to unplug it. As I did this I noticed it wasn't the battery and the smoke was coming from the esc. It got hot enough to unsolder the battery cables from the pcb.
There was water on the course but I did not go in anything deep enough to get up around the esc.
I'm not expecting any warranty from castle and won't even send it in as I've put conformal coating on it.
It's run in wet conditions before but never submerged.

So I'm looking for ideas here. A complete run (probably 20+ hours on this combo this summer) and just idling and it smokes out of no where. As I took it apart tonight, little beads of solder dropped out from the heat that fried it today.









Thanks for the help.

Dna


Sent from my iPad using Tapatalk

[djjiz]

DAMN.

What software was on it?

[dna4engr]

V1.32 firmware. Been running it this way for 10 months.

You're lucky you weren't there to have to smell this thing. It was nasty.

Dna

[Postclanker]

Wow, that got good and hot. If it wasn't the water it probably was a fet on the board that went south. Will be hard to tell in the state it's in now for sure. That think is Krispy.

[CD13]

After you ran it in wet before this event, had you cleaned out the the box the board sets in? I took mine apart after no water run and it was full of crap.

[dna4engr]

Originally Posted by CD13

After you ran it in wet before this event, had you cleaned out the the box the board sets in? I took mine apart after no water run and it was full of crap.

I've never cleaned it out after a run. I put two coats of urethane conformal coating on it. It's been 3 months since this rig has even seen wet terrain. We had a g6 style event that had some puddles but no submersion so all it saw was splashes of water back then.
Since then it's been at crawling comps and a trail event that was on a dry sunny day.

I'm actually afraid to plug the motor into another esc as I'm concerned it could be the culprit. I can check the battery but I don't know what to check on a brushless motor to know if there is a problem. Any hints?

Dna

[Johnnysplits]

How do you have the esc mounted in your rig? If you mount it horizontal, water will lay on the board and find it's way in eventually...even through some conformal coating. Mounting the esc vertically or inverted will ensure complete water runoff.

[djjiz]

Plug the motor directly to the battery. Make sure you got a lot of beers in you. More cells the better.

[dna4engr]

Originally Posted by Johnnysplits

How do you have the esc mounted in your rig? If you mount it horizontal, water will lay on the board and find it's way in eventually...even through some conformal coating. Mounting the esc vertically or inverted will ensure complete water runoff.

It is mounted horizontally, but the likelihood any water has been in there since June is little to none.
I wouldn't rule out water but I'm concerned it's something else. My buddy smoked a brxl by accidentally letting the two motor wires touch with a battery connected and hit the throttle (its a long story, but it was cutting a corner that caused it).
I've lost a mmp to water before and it never fried. It just malfunctioned. To get this much current, it must be a short to ground. Either caused by a motor or something on the pcb.

Dna

[thurayt]

Use an ohmmeter and check all your motor leads against each other and the outside of the motor. If any of them shows no resistance then you have a short in the motor. Which, as you have found will turn an ESC into charcoal. Of you need any clarification on how to test I can tale some pictures

[dna4engr]

So I've measured the motor and battery.

Motor. I checked resistance and continuity of each wire to the motor case. None of the three wires has any resistance when measured against the case, nor do any of the wires have continuity to the case. If I measure any of the 3 wires to each other I have continuity and resistance, is this normal for a brushless motor? I would guess so?

Battery. Overall voltage measures at 11.5v (after 1 hour of running in the g6). Each cell is about 3.7 and some change.

I'm still skeptical that the motor or battery are still good. Is there any chance that the bec could back feed through the rx to the esc? I have the bec powering the rx and the esc is plugged in without the red power wire.

Thoughts ?

Dna

[djjiz]

Never heard of a bec frying anything but itself, servos, and the occasional rx.

Battery sounds healthy. I'll run it if you don't.

[micro racer]

Originally Posted by dna4engr

Motor. I checked resistance and continuity of each wire to the motor case. None of the three wires has any resistance when measured against the case, nor do any of the wires have continuity to the case. If I measure any of the 3 wires to each other I have continuity and resistance, is this normal for a brushless motor?

Dna

Brushless motors should not ground to the case. The motor sounds like it is still good though.

[thurayt]

Motor sounds fine.

[dna4engr]

Originally Posted by micro racer

Brushless motors should not ground to the case. The motor sounds like it is still good though.

Originally Posted by thurayt

Motor sounds fine.

Yea I emailed holmes hobbies and they gave me the same tests to confirm it was good. I'll probably send the motor in for rebuild since it's been through some tough conditions this summer. Plus they can make sure it's all good.

Dna