mten3 beeps, doesn't balance after getting caught in the rain

[bobpaul]

About 3 weeks ago I got caught in a heavy downpour with my mten3. I probably rode a couple of miles before I was able to take shelter. Everything was going fine while I was riding, but after I found a roof to stop under it refused to balance. I've left it to dry and opened the case to look inside.

There is some dirt up on the heatsinks up top. All of the connectors are covered in some sealant/glue. At first I thought maybe I'd unplug everything and plug it back in, but when I saw the sealant everywhere and I took a step back.

Both the buttons seem to work. The LED strip works. The bluetooth works and I can connect to my phone app. But when I turn it on, the wheel twitches and then it beeps 5 times. It does not balance. I've tried holding the reset button and pressing the power button 5x to enter/exit shipping mode. When it's in shipping mode the wheel doesn't twitch and it beeps 5 times on start up. So I know it's not just stuck in shipping mode.

Anyone know have ideas on what I should look for or know what's likely wrong?

[bobpaul]

Whelp, there's some corrosion on the through-hole parts

So maybe I can clean this up and touch up those solder joints.

Edited August 23, 2021 by bobpaul

[.....]

can't see the pictures, but the mten is a pretty simple wheel to see everything. It doesnt hurt to check all connections and solder joints. Be careful about any conformal coatings. You may want to recover with some clear nail polish when done, if you find yourself having to break a coating to rewet a solder joint. good luck, let us know how goes...

[The Fat Unicyclist]

What @ShanesPlanet suggests is good...

In addition I would suggest discursive the battery then turning the wheel on (to drain the capacitors) then wait a bit and technetium the battery. 

this will "reboot" your wheel fully and may clear any rain related glitch. 

[mrelwood]

10 hours ago, bobpaul said:

Whelp, there's some corrosion on the through-hole parts

It does look like there’s some water damage on the board.

What I would do if this wheel was brought for me to fix, I’d first unplug the batteries and make sure that there aren’t any crevices where water could’ve entered inside the wrapping. Then I’d flush the mainboard caps by holding the power button for 30 seconds, and leave it be for 30minutes or more. If necessary, I’d then remove the mainboard to have a peek and access to the underside. Then I’d use an ample amount of electronics cleaner or isopropanol, and carefully brush all affected areas clean. Then try to power it up, and if it works, I’d unplug and flush the caps again for applying a coating lacquer on the board.

[bobpaul]

So I pulled the 3 motor cables and measured the drain to BATT+ resistance in the top gates (left in the photo) and the drain to BATT- on the bottom gates (right in the photo).

The FET that the probe is on in the photo (and it's pair right above it) measures short to BATT-. So either one or both of those FETS and/or the gate driver chip is blown. The fets certainly don't look blown and I haven't yet had a chance to locate the driver chip yet. But all of the other fets measure megaohms from drain to their appropriate battery lead.

I ordered a new controller board from ewheels and will have that on Friday. But I still intend to fix this so I have a spare on hand.

[.....]

Wow, you are already beyond anything I could suggest. Please keep us posted as to how you fixed this board and where do you think the problem came from. Did you notice any water ingress on the parts anywhere? I hope the new board wasnt expensive. I would have figured a new board, just because I dont trust my circuit repair skills much.

[bobpaul]

Controller board was $180. They gave me free shipping, which was a pleasant surprise. I got some help from one of the EEs I work with.

It had sat for almost 3 weeks since the rain storm. There was dirt on the heat sink that was clumped in a manner that I think it was wet before it dried, but anything there had dried. I haven't opened the battery; hadn't considered that.

I'm pretty sure that cloth heat shield on the middle motor phase wire (blue motor wire) held water against the pins on that nearest FET.

My initial attempts to "clean up the solder joints" failed. I could not get the solder to flow at all! Never experienced that, but I've never done rework on a board with conformal coating. I'll probably bug one of the EEs again when I'm ready to pull FETS.

Edited August 26, 2021 by bobpaul

[RagingGrandpa]

If that much water got in, be sure to disassemble your battery box and check for moisture in there... water-related corrosion has led to battery fires for multiple EUC's.

Edited August 26, 2021 by RagingGrandpa

[bobpaul]

5 hours ago, RagingGrandpa said:

If that much water got in, be sure to disassemble your battery box and check for moisture in there... water-related corrosion has led to battery fires for multiple EUC's.

Alright, I hear ya =D. Just now I opened up the black plastic housing for protecting the battery. It was just a few screws and some sealant. It does not look like water got in there. The actual battery pack is sealed in blue shrink wrap with sealant around where the wires protrude, and that looks well done. I think it's ok.

I think the issue I ran into is that while the board is conformally coated, the FETs aren't. I can touch anywhere on the legs of the FETs with a multimeter and take measurements. Apparently we have some conformal coating touch-up solution at the office, so I plan to take a q-tip and slather some of that around on the new board anywhere that appears to still be conductive.

I also plan to add sealant between the two halves of the chassis when I reassemble it. I think most of the water that got in sprayed up from the wheel chamber, so sealing that edge is important. Any reason to not just put sealant all the way around? Is there any need for air exchange between inside and outside the chassis for cooling purposes or anything?

[RagingGrandpa]

16 hours ago, bobpaul said:

I think most of the water that got in sprayed up from the wheel chamber

Really? Seems like anything that wicked past the seam in the fender area would have a labyrinth between it and the controller... I've been comfortable riding my MTen3 on wet surfaces with tire spray anyway.

 

16 hours ago, bobpaul said:

Any reason to not just put sealant all the way around?

Only that it makes it a pain to disassemble for a tire change later

[mrelwood]

17 hours ago, bobpaul said:

I plan to take a q-tip and slather some of that around on the new board anywhere that appears to still be conductive.

Beware though: The legs of the mosfets can get extremely hot, so sealing them in plastic doesn’t sound like the best off ideas to me. If the legs stay hot longer than expected, the heat could increase the already high temperatures of the mosfet chassis.

Sealing the chassis is where I’d use all my energy and concentration.

[bobpaul]

On 8/27/2021 at 9:42 AM, mrelwood said:

Beware though: The legs of the mosfets can get extremely hot, so sealing them in plastic doesn’t sound like the best off ideas to me. If the legs stay hot longer than expected, the heat could increase the already high temperatures of the mosfet chassis.

So I asked 2 of the EEs I work with and both of them weren't too concerned about the heat BECAUSE the mosfets are all attached to a heat sink that's larger than the circuit board itself. With the big heat sink, any heat that dissipates from the legs to the air should be negligible. But to paint the legs with coating, I would have had to remove the heatsink and there's a small risk of damaging the heat conductive material. I wanted to get back on the road and not risk additional downtime, so when the new board came, I re-assembled everything and used some caulk and electrical tape to seal up the shell a bit.

[bobpaul]

On 8/27/2021 at 8:32 AM, RagingGrandpa said:

Really? Seems like anything that wicked past the seam in the fender area would have a labyrinth between it and the controller... I've been comfortable riding my MTen3 on wet surfaces with tire spray anyway.

Well, what I know for sure is that that cloth heat shield they put over the wires got damp and held water against the circuit board near the middle top-gate FETs. I really have no way of knowing where that water came from, but definitely dust came up from the wheel well and got on the board/heatsink. I really don't think much of any dirt would ever come from above. If dust gets up from the wheel, I'd imagine fine water droplets could, too.

I think it's plausible that some water from wheel sprayed straight up against the top of the wheel well. There is a vertical air gap on either side of the battery; water droplets with a vertical trajectory that made it past the crack in the wheel well could get up to the top I think.

But you're right... I have no reason to think that water didn't come down from the top. I didn't follow Marty's suggestion of taping the center of the handle, and maybe that was my fatal mistake.

Here's how I ended up sealing things up. A little bit of bathtub caulk before closing the shell along the top of the wheel-well, a little bit of caulk after closing the shell under the LED strip, and electrical tape along remaining seams after putting that final, translucent piece of shell on. The caulk along the wheel-well was before I closed the shell because there's no other option there. Hopefully that doesn't make it too hard to open back up. The rest of the caulk I added after closing the shell and I think I should be able to scrape that off next time I open it up.

[bobpaul]

After another couple hundred miles I had to replace the tire. Taking it apart was not a problem. I don't think the caulk in the wheel well was perfect, but I do think it helped. It's winter so I've been riding in snow, slush, and salt and using a hose at the office mop sink to spray it out. I think from above the electrical tape is more important than the caulk, so I only caulked the wheel well this time and taped all the seams as before.

[yloc88]

This same problem just happened to my mten3 :[