bombadero
10 mW
- Joined
- Jun 19, 2019
- Messages
- 32
Hey, I had a similar problem to one seen in a few other threads here on ES, but mine is slightly different, so wanted to get everyone's take on it. I have a dual-motor, dual-battery, wired in parallel setup with components purchased from Grin. The wiring setup is basically two Y-cables plugged into each to form an 'x' between the batteries and two controllers to achieve a parallel wiring harness; works great. Initially, everything was stock as ordered from Grin, with APP connectors. I had issues with connectors out of one of the batteries melting and fusing one day while hauling a heavy load on a warm day. I discovered this is sometimes an issue with APP's (from ES, general web search and confirmed by a Grin employee), so I resoldered all 10 connectors with XT-90's, and have been riding it that way for several months. A few days ago I was taking the dog to the vet and then to the dog park; on the way to the vet, I experienced a sudden loss of power heading up a hill. The bike is 1.1 kW nominal power from both motors combined, so it usually crushes this hill, even towing a 55 lb. dog. I pulled over and power cycled and it went away, so I thought nothing of it. Later in the evening as I was coming home from the dog park, after cresting another hill and resting at a light for a minute or two, when I proceeded through the intersection I heard a brief 'pzzt' noise and the bike died shortly after starting out across. I has some momentum, so I was able to coast to the other side and pull over. After another power cycle, the bike seemed fine again and I finished the trip home without incident, although the bike smelled strongly of an electrical fire. It wasn't actually on fire or smoking, just had that smell.
After some troubleshooting, I narrowed it down to one of the Y-cables, one leg of which only registered ~8.5V on a multimeter, verified with a LunaCycle Power Meter. All other connections read ~58V, which is normal for this bike. The conditions on that night were humid and cold, but it didn't rain that day. Moreover, I covered all of my connections with cable repair tape, which if you're not familiar, sticks to itself like glue once you wrap it on; it's pretty much impossible to unwrap it, you have to cut it off. I have that wrapped from one half of the XT-90 on either side until it meets shrink wrap that had been applied by Grin. I call it 'poor-man's heat shrink', because the seal is easily as tight as shrink wrap. It's also extremely thick. As expected, when I cut that off, there was no moisture inside. What I did not do is apply any dielectric grease or liquid tape. The cables were burnt for a couple inches on the short cable leading to the Baserunner in the rear of the bike; on the Y-cable end, it was much worse, with gold-colored flecks on the outside of the cable insulation from the electrodes in the connector getting so hot they melted, and the carbonization from what appears to be a very small, very brief fire, extended several inches. Fortunately the cable repair tape and the Y-cable contained it. Back on the controller side, the connector had been damaged a little and the little nylon apron that clicks in to protect the solder points was going in at an angle. I was reminded on inspection that I had stripped my cables too much and about 5mm of exposed cable was sticking out of the apron for both hot and neutral. I repaired the connector for now as it reads correctly, supergluing it back into the right orientation with Loctite gel superglue clamped together, and reapplied two layers of tape this time, both high temperature electrical tape and a fresh layer of repair tape on top of that to seal it. I also wedged a piece of rubber between the two wires and taped them separately with electrical tape to insulate them from each other.
After some research, I will probably open that controller connector again and coat that exposed wire with Plastidip Liquid Tape, and grease them liberally with Permatex dieclectric as well for good measure, and do the same with all other connections on both sides. I ordered some new Y-cables to convert to XT-90 (a replacement and some back-up inventory) to replace the fried one. Going forward, I will never strip my cables too long and plan to always make liberal use of liquid tape and dielectric grease.
So here's my question though: does it seem like the 5mm of exposed wire on both hot and neutral was definitely the culprit, or does it seem like moisture may have played a factor? As I said, everything I examined was dry inside, but given how hot that tiny fire burned from the arc/short, if there was any moisture it was probably vaporized instantly. I don't like to use shrink wrap for the end of these XT-90 cables because the connector is so much wider than the cable, and it's not convenient to take apart and inspect when things like this happen. If you do that, to re-apply heat shrink you now need to de-solder and re-solder the whole thing, and then re-shrink it. So that second question is, does Plastidip + Permatex dielectric grease + high temp electrical tape + cable insulation repair tape seem like sufficient insulation against moisture? It seems like overkill to me, but I'd like to hear other folks' opinion. I live in San Francisco, so extreme winter weather is mostly not a concern, apart from the record-breaking bomb cyclone we had recently, but obviously I wouldn't be riding in that! Just light amounts of rain and extremely high humidity on some days.
I've attached a photo of the connection in question. BTW, in that photo there is a layer of automotive cable loom on top of the cable repair tape. I'm going to stop using that on cables because it holds moisture, but in this case there was the thick repair tape underneath it. Unlike the repair tape, the automotive loom can unravel a little, although usually it also has very good adhesion to itself once applied, which is why I use it on bikes for various things.

After some troubleshooting, I narrowed it down to one of the Y-cables, one leg of which only registered ~8.5V on a multimeter, verified with a LunaCycle Power Meter. All other connections read ~58V, which is normal for this bike. The conditions on that night were humid and cold, but it didn't rain that day. Moreover, I covered all of my connections with cable repair tape, which if you're not familiar, sticks to itself like glue once you wrap it on; it's pretty much impossible to unwrap it, you have to cut it off. I have that wrapped from one half of the XT-90 on either side until it meets shrink wrap that had been applied by Grin. I call it 'poor-man's heat shrink', because the seal is easily as tight as shrink wrap. It's also extremely thick. As expected, when I cut that off, there was no moisture inside. What I did not do is apply any dielectric grease or liquid tape. The cables were burnt for a couple inches on the short cable leading to the Baserunner in the rear of the bike; on the Y-cable end, it was much worse, with gold-colored flecks on the outside of the cable insulation from the electrodes in the connector getting so hot they melted, and the carbonization from what appears to be a very small, very brief fire, extended several inches. Fortunately the cable repair tape and the Y-cable contained it. Back on the controller side, the connector had been damaged a little and the little nylon apron that clicks in to protect the solder points was going in at an angle. I was reminded on inspection that I had stripped my cables too much and about 5mm of exposed cable was sticking out of the apron for both hot and neutral. I repaired the connector for now as it reads correctly, supergluing it back into the right orientation with Loctite gel superglue clamped together, and reapplied two layers of tape this time, both high temperature electrical tape and a fresh layer of repair tape on top of that to seal it. I also wedged a piece of rubber between the two wires and taped them separately with electrical tape to insulate them from each other.
After some research, I will probably open that controller connector again and coat that exposed wire with Plastidip Liquid Tape, and grease them liberally with Permatex dieclectric as well for good measure, and do the same with all other connections on both sides. I ordered some new Y-cables to convert to XT-90 (a replacement and some back-up inventory) to replace the fried one. Going forward, I will never strip my cables too long and plan to always make liberal use of liquid tape and dielectric grease.
So here's my question though: does it seem like the 5mm of exposed wire on both hot and neutral was definitely the culprit, or does it seem like moisture may have played a factor? As I said, everything I examined was dry inside, but given how hot that tiny fire burned from the arc/short, if there was any moisture it was probably vaporized instantly. I don't like to use shrink wrap for the end of these XT-90 cables because the connector is so much wider than the cable, and it's not convenient to take apart and inspect when things like this happen. If you do that, to re-apply heat shrink you now need to de-solder and re-solder the whole thing, and then re-shrink it. So that second question is, does Plastidip + Permatex dielectric grease + high temp electrical tape + cable insulation repair tape seem like sufficient insulation against moisture? It seems like overkill to me, but I'd like to hear other folks' opinion. I live in San Francisco, so extreme winter weather is mostly not a concern, apart from the record-breaking bomb cyclone we had recently, but obviously I wouldn't be riding in that! Just light amounts of rain and extremely high humidity on some days.
I've attached a photo of the connection in question. BTW, in that photo there is a layer of automotive cable loom on top of the cable repair tape. I'm going to stop using that on cables because it holds moisture, but in this case there was the thick repair tape underneath it. Unlike the repair tape, the automotive loom can unravel a little, although usually it also has very good adhesion to itself once applied, which is why I use it on bikes for various things.
