How to test for phase wire failure?

[ClintBX]

Hi ESFMs,

I had the most frustrating experience with a bad phase wire the other day.

After a one hour charge, I was getting no response from the motor. I was already suspecting one of my phases was corroding near the connector but with heat shrink covering it up, I couldn't know for sure.

So i got out my multimeter and tested for continuity on every phase wire from below the point (well below) I suspected and also on the controller end. Buuut, it all tested positive for continuity. I went ahead and changed a connector on the controller as it looked somewhat worse for wears. That didn't fix the issue. Tested for continuity on all the phases once more. Again, all positive.

I started worrying that it might have been either way lower down the line of wiring or worse, in the motor. I got sporadic wheel spins after moving the wires slightly but still had no clue.

I was just about to just go home and pull the motor apart until I decided to just chop back and replace the portion of green phase wire (I suspected all along). And yep! Sure enough that fixed it.

Anyway, my question is;
Is there a reliable way to test for faulty wires or breaks that won't yield false positives like I had with the continuity setting?

Clinton

 

[MadRhino]

It is impedance that you had to test. A very thin connection is enought to give a positive result to a continuity test, but resistance would be very high if a phase wire can't deliver enough current to make a motor spin.

There is another situation thst could have produced a false test result. It is a bad connection that you re-connected by chsnce when moving the wire to test.

 

[ClintBX]

Ok, what is Impedance?And How do I test that?

 

[MadRhino]

Impedance is resistance
Generally marked Ohm or Ω on a multimeter.

A wire that is almost cut or a bad connection will show continuity, but resistance will be high.

 

[biggy]

I experienced the symptoms you are describing on my ebike one day after a hard ride on some steep hills in a trail it felt like my controller was turning on and off and the wheel was getting jumpy and then I would get nothing and if I smacked the bag that my controller was in then it would work and then not work for a couple days I routed through the wiring and i found that my negative wire to my battery on the controller side had melted the solder inside my connector and the wire was barely hanging on so if you moved it in a certain position it would power up and if it moved it would lose power. really has me re thinking to switch to crimp connectors but idk if they can handle the amps, a solution I was also thinking of is potting my crimp connectors in RTV silicone. But anyways yes finding wiring problems can be a hassle sometimes and I'm glad you solved your problem I will have to keep an eye on my phase wires as well.

 

[MadRhino]

Crimping is better than solder, when it is done right of course. High power applications especially, do require crimped connectors.

 

[ClintBX]

Yeah, I prefer crimping because soldering is a big hassle and when your down on the side of the road, pulling out a solder kit is the last thing you want to do. ... And also, I suck big time at it. I keep get weak solders that brea break or cold solders.

Crimp connectors can handle the amps if you pick the right ones but what you have to watch out for is how much heat damage is effecting the wire around that crimp connectors.

Hasn't been an issue for my power wires but those phases have been dying many heat deaths since I upgraded to 48v.

I've started butt splicing thicker gauge wire to the phases and I've found that they are running a lot cooler. The green phase was the last man standing that hadn't been butt sliced yet.

 

[ClintBX]

Impedance is resistance
Generally marked Ohm or Ω on a multimeter.

A wire that is almost cut or a bad connection will show continuity, but resistance will be high.

Thanks MadRhino. This makesa lot of sense.

 

[amberwolf]

i found that my negative wire to my battery on the controller side had melted the solder inside my connector

If it got hot enough to melt solder, that means it was at least a few hundred degrees or more, depending on the type of solder used. Most likely the connector shells are damaged or melted as well. (if they are not damaged at all, then the solder probably did not melt, but instead was never really soldered in in the first place).

Typically that means a very very poor connection at or extremely close to that point, usually arcing across the connection, but at least a very high resistance (compared to the wire itself).

So you should check your connectors for such arcing marks (burns, pits, etc), and for high resistance. If there is any voltage drop across the connection itself during high current draw, the connection is faulty and needs to be replaced.

 

[biggy]

thank you i will have to double check my power line with the multi meter. have been using a spool of solder i found in my grandfathers stuff and i didnt know there are different grades of solder.

 

[amberwolf]

If it's not labelled, can't say for sure, but if it's that old it's probably just common 60/40 tin/lead rosin-core solder, which melts around 370F. That's hot enough to destroy a lot of plastic things, and damage most others noticeably.