fourbanger said:
Motor makes a quick ka-tunk back and forth when throttle is applied then nothing.
Hall sensors disconnected, same thing.
If the controller is sensorless, then the latter means something is probably wrong with the FETs in a phase or more, or a wiring fault in the phases or actual windings, anywhere from the cotnroller PCB to the inside of the motor.
If the controller is not sensorless-capable, then the latter doesn't mean anything, because a hall sensor problem (or complete lack of them) would make the controller unable to spin the motor correctly (or at all).
What he didn't tell me until I got there was it had been running fine until recently.
Then you must find out from him EXACTLY what he changed, or what happened to the unit, JUST BEFORE it stopped working, because that is the cause of the problem. Hardly anyone will ever admit to such changes or accidents or whatever, but whenever such have occurred, it is virtually always the source of the problem. :/
I'd recommend having him make a complete list of all changes made to the system, in the order they were done, and any accidents, bumps, fall-overs, etc., including tire changes, flats, etc, because any or all of them could lead you to the problem, and making the list may make him think of something else he hasn't told you, and may also may make him realize how important information like this is to people helping him fix things.
Another point of interest I discovered was that someone had told him some time ago that the reason the battery/controller connection sparked was because he didn't have the controller chassis "grounded". So I guess he did that and everything was fine, disconnected the battery then parked it under cover for a couple of months and now this. I told him wiring the controller to the Batt- was totally unnecessary and why. I also said that I couldn't think of a reason off hand why that would cause any damage but I certainly wasn't making any promises about it.
Grounding the controller case to battery negative means that anything else that touches the controller case (bike frame, axle, etc) is then also grounded. That means that any short of a signal, power, etc., to the grounded objects will result in damage or destruction to the source of those signals, power, etc.
For instance, if there is wire damage at the axle exit (very common) from an unadmitted crash/etc, then a phase wire shorting to the axle's sharp exit edges is shorting out the FET(s) attached to that, and can blow them up (which can also blow the gate drivers, etc). Since there are two phases active at any moment, a short like that can blow both of them up, and sometimes even damage the third one depending on conditions and operational mode at the time.
To be perfectly honest, there are a couple tests I've picked up from reading this thread that I've yet to try and I really didn't feel like cracking open the controller at the time, and in fact I still don't. Not my pig, not my farm if you catch my drift. It's entirely likely that I'll end up selling him a controller of my own but still, it's against my nature to swap out major components until I know for sure that that's what it's going to take because a) money and b) in my books that only barely qualifies as having "fixed" something as the mystery still prevails. Something went wrong and I still don't know what or why and until I do it's still going to bother me.
That's something I sympathize with...though I usually don't ahve time/energy to pursue it to much depth anymore.
In general, finding the true root cause of failures (failure analysis, somethign I'm reasonably good at in systems I'm familiar with, and have some fun doing) typically requires reasonably detailed knowledge of the system in question, how it works, what kinds of failures are caused by what types of events in such a system, etc., and the ability and willingness and time to carefully disassemble a system one little bit at a time and document and measure things as you go, etc. It can take a long time to do, and even longer when you're not more or less a specialist in that kind of system, as you may have to research how various things work and what their failure modes are.
But in general, there are a few basic causes that happen most of the time for most failures of most systems. The first one is always "somebody messed with it".
WIth electrical stuff, the next one is connectors and wires. (fluid systems it's connectors and hoses, other systems it's connections and materials). Then it's the stuff connected to the connector or wire that failed, etc, etc.
Sometimes so many things failed in a system "at the same time" that it's tough to tell whcih actually caused the others in the complete chain, but it's usually still "somebody messed with it" at the very very root.
The systems that just "randomly fail", at root, are often caused by insufficient original specification limitation, meaning not overspecifying the ability of one or all of the parts to handle the expected loads, not enough margin.
Etc.
That's my philosophy anyway. But I guess sometimes (often) the thing to do is swallow your pride and just do what you gotta to get the damn thing running.
Very often that's the only alternative, due to time limitations. Sometimes you can keep the system down for however long it takes...but that's rare.
