Reversed leads to the HV pack (Solved)

[kiev]

Moving PM messages from Inbox so everyone can read and learn and benefit from the experience of others:

Hi,

I reversed the polarity on my HV wires when switching the HV Battery and now got a P1A15 error.
You got an idea on what got damaged or a trouble-shooting plan on how to fix the car?
It's a 2012 ION.
Thank you in advance
luci
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Howdy Luci,

sorry to hear about your car. i would think that the large capacitor in the MCU may have been damaged by the reverse polarity. Also the DC/DC converter in the lower plenum of the On Board charger could be damaged. It would be interesting to trace out the damage just to understand all the items that get taken out by reverse polarity.

If you are comfortable to measure HV, then you could open the MCU cover to measure if there is any HV present on the input terminals.

If there is none, then you could remove the cover of the MCU, then take out the big black rectangular capacitor and test it on an LCR meter to see if it still reads 800uF. If it is okay, then put it back in.

If you have a Scan Tool that can reset the fault codes then do that, then see what happens with Starting to READY.

Then measure the MCU input terminals to see if the voltage holds up on the HV input to the MCU when you turn the key. Using a scope would be better in that you could capture the turn-on transient to see the HV rise, how high it goes, etc. There is a photo of this in one of the threads, maybe the P1A15 thread.

Where are you located, i'm in Alabama USA.

kenny
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Hello kiev, thanks for your answer.

What i did so far:
Read and clear dtc, after clearing I can hear the Contactors switching, but after ~1s I can hear another click, and after that I have to clear the code to get them switching again.
EMCU Capacitor Voltage reads 2V - Service manual advises to change HV battery if so.
Accessible fuses are checked.
I checked HV with a HV multimeter with the main wires connected to the inverter and without.
I am not sure about the speed of it, I think it should sense some Voltage though. I will test it with a scope soon.
Today I checked the isolation on HV+ and HV- with 50V to check if the voltage sensing is still working. It read 19kOhms and voltage slowly rised on the isolation tool and in the data list read from the EMCU.
So voltage sensing is wworking fine - not so sure about the 19kOhms though.
Have to recheck it with the main wires disconnected again.
Contactors and dtc are exactly the same when charging with AC.
I cannot connect with my Scan Tool to the OBC.
I am not sure if I was able before though.
Will check the condenser, good idea!

I am from Germany, btw.

Thank you for your help.
Luci
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[kiev]

Hi Kiev,
just lo tet you know, car is fine again.
I tested the capacitor and it was good.
Tested the voltage mesauring circuits - everything was working.

So I went to the battery.
The precharge resistor was toast.
Suprisingly it did not show any dmg. Resistance was o.L. though.
It was 24 ohms, 80W - I think because of the IONs higher Voltage.
I bought 2 47 ohms 100W resistors and connected them parallel.

All good.

So just to let you know - if you switch polarity on main battery the precharge resistor is gonna blow.

 

[coulomb]

if you switch polarity on main battery the precharge resistor is gonna blow.

With the massive advantage of hindsight, that makes sense. The motor controller full bridge looks like two very large diodes in series to a reversed battery. If the battery was connected directly across those diodes, they'd explode.

But of course, the pre-charge resistor connects first. The capacitors will be held to about two volts by the diodes conducting, and the current will be limited by the pre-charge resistor to about 15 A, which the diodes in the IGBTs can handle comfortably. But the pre-charge resistor can only handle it for a fraction of a second. It would normally fail open circuit, preventing the pre-charge from completing, protecting everything else from damage.

I have to admit, when I first read about the reversal, I was fearing much, much worse. Thanks to Luci and Kiev for the final report.