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Discussion Starter · #1 ·
I'm re-doing the batteries in my Mini conversion, and that means all new wiring for everything. When I connected the HV wires to my contactors, I got sparks. So now I have everything connected except the HV +. The pack is 48 Leaf modules, measuring 370V from + to -. I have all the BMS wires connected, and each cell is reading ~3.8V.

The weird bit is this: When I measure + to the chassis, I read a voltage that quickly descends to about 246V. This freaked me out, so I disconnected everything and tried it again using a 12V source to the HV wires that run the length of the car to the Nissan Leaf inverter. The behavior is the same, but with a lower voltage (it descends to about 4-5 volts). It seems that the chassis voltage is coming from those wires running to the inverter. Each is individually routed and bound by rubber clamps to prevent any chafing or a short.

I've seen this behavior before, before I redid the batteries...When the contactors switch off, the voltage at the inverter bleeds down over time. I'm guessing something in there holds a charge for a while, and when denied power, it bleeds away. I just...remember it dropping to 0V.

What I don't understand is why there would ever be a high voltage reading from the chassis, and why it would stay at 246V or 4-5v. When I was reading 4-5V, my test light didn't light up at all. The voltage was there, but the bulb stayed unlit. What could cause that? I don't think there is any kind of short from a battery module to the chassis, since I was seeing the same thing with the pack out of the equation.

Anyone have any clue as to what might be going on or how to troubleshoot further?
 

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Discussion Starter · #2 ·
Bonus issue: My Leaf contactors are behaving strangely. When I connect one side of each to a battery, the other side of the contactor is connected as well...as if the contactor was fused together internally. The power just...always goes through.

The weird bit is that this is true of both contactors. I connect one side of each, and when I test voltage across the other side of each, the full voltage is there, and my test lights shines. Both contactors still "click" prominently when I trigger them, so there's something inside still moving. I never explicitly tested the behavior of these contactors before, since they were behaving as expected, so maybe I'm misunderstanding the design...It just seems weird that power would jump across them when they're "off". Maybe I melted one bit with my messing around, but there's another bit that's still moving around inside?? They don't seem easy to disassemble to check...

The Leaf "Junction Box" has the precharge relay and resistor all wired together. Maybe the precharge bit is letting the power leap...?

I am boggled.
 

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Leaf contactors like to weld -- I've killed a few that way, they generally came back after about 20-25 power cycles. But they may not be reliable anymore.
Disassembly is not possible, there's a sealed module inside that's probably full of hydrogen.

I'm not sure how to deal with the chassis voltage - it's clearly some sort of isolation problem, but I don't know how to deal with that. Does the voltage appear when the inverter is disconnected?
 

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Discussion Starter · #4 ·
With the inverter disconnected, there's no voltage on the chassis when the HV wiring that runs the length of the car is connected to a 12V battery. With the inverter connected, there is a measured voltage that swiftly drops below 0.1V from the inverter case to inverter HV negative. It seems like this is either: 1) a red herring, or 2) the inverter is damaged. There was the tiniest of sparks when I connected the inverter HV + to 12V.

The root of all this was: I hooked everything up, and when I installed the service disconnect (barely touching), there was some fanfare near the contactors. After disconnecting them, and checking the voltage from + to - (with the service disconnect installed), I read 370V, as expected. Both contactors have continuity no matter what, so they've indeed welded.

I just don't understand how the inverter could have been damaged in the first place...If the issue is the inverter not being isolated, it would have manifested before I took the car apart. If the issue is bad wiring, why would my voltage readings on the battery be as expected? I don't understand what would weld (both) contactors together, unless they formed some kind of short in the system. If there was a short, I can't find where it could have been (be?).

Perhaps when I completed the circuit, there was a short that welded the contactors, and also did something bad to the inverter...I just...If the contactors were good (they were before I changed things), then the inverter wouldn't ever have been in the equation...and even with welded contacts, the inverter shouldn't just short out because there's voltage across the HV posts, right?? Maybe the lack of precharge melted something??

Shouldn't my fuse have blown through all this...? The "incident" was a fraction of a second, but if the heat was enough to melt contactors, I'd expect the fuse to go first.

Is there some way there could be a mistake in my battery wiring that would still allow it to show the correct voltage from B+ to B-?

This is frustrating.
 

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Lack of precharge will definitely weld the contactors. It usually leaves the fuse though, since the time is incredibly short.
I'd say a short circuit is unlikely, because you'd be seeing melted wires.

Now, in your first post you said:
When I connected the HV wires to my contactors, I got sparks.
You've shown that your contactors are welded shut, so what you did there was skipping precharge altogether - hooking HV straight to the inverter. That may have been the event that caused the problem -- maybe capacitors exploded or something? That could lead to some of the HV leakage.
 

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Discussion Starter · #6 ·
Interesting. Yeesh. I reeeally don't want to replace the inverter. I don't even want to open it up.

I just can't get my head around what order of events could have caused this...If the contactors were good, nothing would get across them...so why would a lack of precharge enter the equation?

I don't want to replace stuff and then have them pop again because the real issue is still lurking, unbeknownst to me...
 

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Right - the contactors must have died somehow. The question is how. I welded mine by powering up my VCU with 5V and then turning on 12V power - so the precharge delay finished before 12V power got to the precharge relay.

Is it possible that something similar happened? Contactors went on simultaneously without the precharge sequence?
 

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Discussion Starter · #8 ·
I have yet to turn the car on since changing the battery setup. My only thought is that they were mounted vertically, such that maybe they flopped closed...but I assumed they're using a spring and orientation doesn't matter. I checked the trigger circuits and they don't have power to them. I'm trying to remember if I, like, dropped them or something inane...
 

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Dropping won't weld them. Ask me how I know.
Could something have happened previously? They may have been welded for quite some time, and you wouldn't notice unless you checked with a meter, since as you said they still click just fine.
 

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Discussion Starter · #10 ·
There is a chance I did something ignorant when disconnecting stuff, though I recall no sparks or pops...Bugger.

I guess the real question is, how can I verify everything with certainty for when I hook stuff back up this next time? I'll certainly test the contactors and fuse...The inverter, ugh. I can open it up and check for burnt caps and dubious smells...It would be painful to replace.
 

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I'm no expert
...but, if your contactors were welded (shorted) the precharge circuit would have been "bypassed"
...& as a result, the HV "inrush" could have damaged the capacitors in the controller (invertor)

I've heard that most "factory" EV's have a built in discharge circuit
...this could be why you saw the voltage dropping

Here is some info on precharge & discharge (it's for racing but, the same concepts apply)
 

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If the contactors in the HV Junction Box came out of a wrecked car, then they may have welded at that time.

What i have found useful over the years is the concept of commissioning. Anytime you build up a device (especially a motor-driven actuator), or change its configuration, it is a good idea to go thru a commissioning procedure to inspect, check and verify the operation of each item before installation. Wires, cables, connectors, fuses, contactors and relays, motor controller and motors, gearbox and transmission, etc. The least little thing that is bad can wreck the whole train.

Recently i was troubleshooting a failed motor driven actuator that had not been thru a proper commissioning. The feedback sensor cables and connectors were advertised as "waterproof" to IP67, but they were never checked and verified as waterproof before installation. Then later while operating out in the field, the actuator failed--well you could guess it, the connectors leaked and shorted out the feedback so that the motors wouldn't run. POS plastic connector-- no way it was waterproof.

i hope you can get to the bottom of this to determine what happened.

As far as lack of isolation from the pack, do you have continuity from the pack (-) to the chassis?

It may be that the inverter failed due to high inrush into the big capacitor on the front end without pre-charge, but that needs ringing out to determine why there is a path from chassis to pack (-).
 

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It may or may not help but this chap is doing a leaf conversion and has loads of info on YouTube, it might help.


Sent from my moto g(8) power lite using Tapatalk
 

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"there was some fanfare near the contactors."

If the contactors closed in the wrong sequence because whatever you have controlling them isn't right then there could have been an inrush current to the inverter that blew the capacitors and welded the contactors. Especially if the contactors opened and closed with the high load a few times back to back
 
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