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Also, can someone either provide a wiring diagram for this BMS, including where the LIN line terminates? wungun, I'd also like you to check the voltage between the purple wire on the BMS to battery +. That would be at the BMS monitor wire to bat +. Thanks Ray
 

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Discussion Starter #42
Also, can someone either provide a wiring diagram for this BMS, including where the LIN line terminates? wungun, I'd also like you to check the voltage between the purple wire on the BMS to battery +. That would be at the BMS monitor wire to bat +. Thanks Ray
Ray, I've made all these measures already...
It's posted in this thread...

Battery - to chassis ground, 0V
Battery - to engine ground, 0.03V
Purple wire from Battery + shows full battery voltage
Purple wire FROM BMS metered with battery + shows 11.5V
Green wire to battery + shows 9V

What I need is someone to take these BMS measurements on their Rover. I doubt it matters which model car.

Please find attached BMS wiring diagram View attachment batt1.pdf

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It appears to me as if the purple wire is the cause of the voltage drop. From battery, 12.2or 3 to BMS connection is 11.5. Thats almost a 1 volt drop, through a wire with a fusible link. That sounds fishy to me. Ray
 

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wungun, Suggestion: can you check any and all of the wiring going to the + side of the battery, especially those on the BMS. My suspicion here is an issue relating to the wiring to the +side of the battery, based on your testing. Pls take the time to untape, or otherwise expose the connectors, and their related wiring. Anything wrong here may lead to a voltage drop. I don't know how many wires/ connectors are there, but I suspect something wrong here. Taking the necessary time here may expose an issue, or remove it from suspicion. These computers, whether you swear by them or swear at them, their troubleshooting depends on voltage drops. Troubleshoot issues as they do will reveal the problem. Ray
 

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Discussion Starter #46
It appears to me as if the purple wire is the cause of the voltage drop. From battery, 12.2or 3 to BMS connection is 11.5. Thats almost a 1 volt drop, through a wire with a fusible link. That sounds fishy to me. Ray
This wire would seem suspect... You and me both. Please note that this measurement is with the Connector unplugged from the BMS, and the meter place in between the BMS and battery +.
I know for a fact that the purple to the + is indeed reading full voltage.

Why I'm not overly concerned about this 11.5V is because the BMS probably uses a resistor of a known value (100 Ohm?) or a small load to calculate the voltage? Hence the voltage drop?

Also, the purple wire at the BMS is entirely internal as well! All I can say is the ground to the BMS seems solid and its getting full + voltage.
Only way to be certain is to have a donor vehicle to test the same conductors....

And maybe the alternator output is suspect... Actually, I'm pretty sure it is suspect. Weeks ago I was seeing over 14V at idle. But weird that I still had charging fault with new battery and charging at 14+ volts!

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wungun Let's try something. If your DMM has an AC option, let's check across the battery for that. Let me know what you read. If there is a defective or dying diode in the alternator, the ripple voltage may trigger the code as well. I am not sure of the resistor in the BMS line, but you might check the voltage on that line without disconnecting it. You moght be checking this voltage open circuit by disconnecting it. Without current flow through it, you may be getting a false or misleading reading. Ray
 

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Discussion Starter #48
wungun Let's try something. If your DMM has an AC option, let's check across the battery for that. Let me know what you read. If there is a defective or dying diode in the alternator, the ripple voltage may trigger the code as well. I am not sure of the resistor in the BMS line, but you might check the voltage on that line without disconnecting it. You moght be checking this voltage open circuit by disconnecting it. Without current flow through it, you may be getting a false or misleading reading. Ray
Right, right...
Thanks for the input. Good idea....
If the rectifier is dying, I'd likely see flickering lights as well/all sorts of other issues? Worth a check though for sure.
I'll report back...

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If a diode is simply "leaking" and not creating AC voltage, it is still possible for the diode to create enough "hash" to trigger the light, or just lower the voltage enough to be outside the "threshold" of the "pass" indicator. One other thing that comes to mind here is the possibility of being able to "recalibrate" the BMS to the slightly different chemistry battery. If you enter some of the subroutines in either the system or your hand-held, are there options regarding battery chemistry options? One thing to consider here is the "normal" alternators of last century had six diodes, two for each "leg" of the alternator stator. As the requirements for more charging current for higher loads and bigger batteries became commonplace, some of these alternators have four "legs" in the stator, requiring eight diodes. Many alternators have what are called diode trios, or quartets, which monitor each "leg" for correct output. If that diode array is the issue, it will create issues as well. Have I reached the point of TMI yet? I have 25+ years of teaching vehicle electronics experience, and can easily saturate someone with info. Don't want to do that. Ray
 

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Discussion Starter #50
If a diode is simply "leaking" and not creating AC voltage, it is still possible for the diode to create enough "hash" to trigger the light, or just lower the voltage enough to be outside the "threshold" of the "pass" indicator. One other thing that comes to mind here is the possibility of being able to "recalibrate" the BMS to the slightly different chemistry battery. If you enter some of the subroutines in either the system or your hand-held, are there options regarding battery chemistry options? One thing to consider here is the "normal" alternators of last century had six diodes, two for each "leg" of the alternator stator. As the requirements for more charging current for higher loads and bigger batteries became commonplace, some of these alternators have four "legs" in the stator, requiring eight diodes. Many alternators have what are called diode trios, or quartets, which monitor each "leg" for correct output. If that diode array is the issue, it will create issues as well. Have I reached the point of TMI yet? I have 25+ years of teaching vehicle electronics experience, and can easily saturate someone with info. Don't want to do that. Ray
So it's obviously (probably) full wave rectification...
I don't have a hand held capable of looking that deeply into the car... But the dealer did do a couple of resets on it.

Would love to find a used BT Tool for the OBD

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It is full wave rectification, for two reasons: 1. It controls the amount of noise in the system, and 2. It allows the maximum current to the battery, with the least amount of ripple. Ray
 

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Discussion Starter #52
It is full wave rectification, for two reasons: 1. It controls the amount of noise in the system, and 2. It allows the maximum current to the battery, with the least amount of ripple. Ray
... And you don't need as large a capacitor.

So, home from work...

Engine off, 12.12V (still only partial charge, but started this morning at - 22 degrees without hesitation)
Engine on, 14.0V
Using OBD scanner, it reads 13.7V with engine on (red flag?)

Measured + feed to BMS (while connected); reads full battery voltage.

Measured A/C with motor on, initially reads 0.5V but quickly drops to 0.01V.
Its a crap DMM, so....

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wungun: I suspect that the scanner is reading ECM voltage, which will have a small drop simply due to the number of connections it runs through. Suggest loading the alternator with everything: A/C on high, high beams, windshield heater if equipped, everything you can turn on... Then recheck AC with engine running... Let me know. Any possibility of reprogramming charging system for AGM battery? Ray
 

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One more thing you might try is trickle charging the battery overnight. I would like to see something like 12.6-12.8 volts fully charged. Trickle charging prevents the battery from overheating, and may fully charge it. This may "tell" the ECM and BMS to expect higher voltages, and push the charging system a little harder. AGM batteries are good at delivering instant power, even when not fully charged. Let's try that for grins. Ray
 

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Discussion Starter #55
wungun: I suspect that the scanner is reading ECM voltage, which will have a small drop simply due to the number of connections it runs through. Suggest loading the alternator with everything: A/C on high, high beams, windshield heater if equipped, everything you can turn on... Then recheck AC with engine running... Let me know. Any possibility of reprogramming charging system for AGM battery? Ray
AGM battery came out of it... No OEM though... An Interstate. So if was obviously replaced already before I bought the car

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Discussion Starter #56
One more thing you might try is trickle charging the battery overnight. I would like to see something like 12.6-12.8 volts fully charged. Trickle charging prevents the battery from overheating, and may fully charge it. This may "tell" the ECM and BMS to expect higher voltages, and push the charging system a little harder. AGM batteries are good at delivering instant power, even when not fully charged. Let's try that for grins. Ray
I live in an apartment... Can't really do the trickle charge.
This morning, car acted like battery was disconnected.... TPMS reset and so did clock on radio. OBDII is showing 14V charging now....
This is with everyoon and at max!

Maybe I can pull the battery out of the car to charge it this weekend.

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That may be a good thing. If the battery was discharged, and with everything on, the alternator is keeping up with all of the demand. This may have been a BCM response to a low battery. If the voltage drops below a certain level, the BCM will send a disconnect command to protect the battery, and will send a reconnect command when it receives a signal from your fob. Let's see what this situation precipitates. Ray
 

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Discussion Starter #58
That may be a good thing. If the battery was discharged, and with everything on, the alternator is keeping up with all of the demand. This may have been a BCM response to a low battery. If the voltage drops below a certain level, the BCM will send a disconnect command to protect the battery, and will send a reconnect command when it receives a signal from your fob. Let's see what this situation precipitates. Ray
Interesting...
They really put a lot of engineering into these cars, and it shows everywhere you look.

I can imagine the load the car/charging system is being put thru, with this weather! Heavily loaded...

So, battery is out and being charged as we speak.


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If this is the reading on the charger, I am curious where it will stop charging. I am also curious as to the battery voltage when completed. Ray
 

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Discussion Starter #60
If this is the reading on the charger, I am curious where it will stop charging. I am also curious as to the battery voltage when completed. Ray
It monitors the voltage, and if it keeps going up, I assume it keeps charging. When the voltage levels off, it's finished...

It's a charger for my RV model car. It can charge/discharge/balance/storage LiPo, Lead Acid, NiCd, Nickle metal hydride batteries...

According to my meter, the display voltage is a tenth and a half higher on the charger...

Stopped charging and the battery read 13.07V...
13.06V

Im assuming a small surface charge showing...
Tossing it back into the car this morning...
Will report back...

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