51 volts DC!

[stinger912]

I have some weird electrical gremlins. I bought a E91 from COPARTS. The vehicle was totaled out by insurance. Nothing has power. Not even a map light. Nothing! I pulled the trunk battery and its leaking blue juice alllllll over the place and the battery reads 2.4Vdc (it looks to be a BMW brsnd GEL battery). I took a known good battery reading 13V and hooked it up to the under-hood jump start terminals. I took a volt meter to the Jumpstart terminals and they read 13V. I took the voltmeter to the trunk and read the terminals clamp as 51Vdc! I didn't have any wires crossed in the trunk and the battery didn't spark when I touched the negative to the jump battery which is normal to see.

The car appears to have hit an animal, probably a deer or elk. It has damage to front driverside. The air filter box was pushed aft into the alternator. As well as the radiator and fan into the serpentine belt.

Can anyone come up with an idea for me of why the car's voltage is 51Vdc when hooked to a 12V battery? I'm guessing there are some wires crossed but why isn't the fuses protecting the system? At some minimum I'd love to have 12V to the car so I can open the wagon tailgate and hook a OBD reader to the car. OFFLY WEIRD TO ME. Seems like it'll be hard for me to trouble shoot. Thank you much.

[JDStrickland]

Disconnect the battery, connect your donor battery to the B Post in the engine bay, then go to the trunk and read the volts on the battery terminals in the car. You should see the same voltage as the donor is providing. Now connect the battery in the trunk and leave the donor battery connected in the engine bay, you should still see the donor battery voltage.

51 volts is very odd, I would say impossible. Do you have an auto-ranging volt meter and it's showing you 51 millivolts, that's entirely possible. If you connect a donor battery to the posts in the engine bay, then this will give you the power you need to open the tailgate, assuming you have the donor battery voltage at the terminals that should be connected to the battery (but that you have removed to test the system).

[marvinstockman]

When you read 51 volts, was the car running. Also, do you have another voltmeter to test with?

[zellamay]

I agree: impossible. Use another meter.

[stinger912]

Ugh!!! I just typed up a long reply and update and it got lost when I hit reply.

- - - Updated - - -

The short of what I typed out was. I got the trunk to pop open giving me easier access to battery box. And the map lights all lit up cus the doors were open. But the wires get unusually warm. Very warm! I don't want to try to start the engine. Even for half a second. Because the accident impact has the fan and radiator pushed up against numerous pulleys and the alternator. I did disconnect the two wires off the alternator. The thick gauge battery cable and a sensor clip wire. Also headlight wires and fog light wires and headlight washer nozzle motor thinking maybe there was a short in those components because of the impact accident. But disconnecting those didn't help with my 51Vdc reading. I checked all 30A or higher fuses in my glove box. All were just fine. Super weird. I do need to try a second voltmeter to rule out the voltmeter as the issue.

[stinger912]

TO JDSTRICKLAND

Well I did exactly what you mention to do. I connected a known really good battery to the engine jump start terminals near the coolant reservoir tank. Then took a voltmeter to the battery clamps in the trunk and they read 51V. Then unhooked the donor battery and took the battery to the trunk. But didn't have the right size to fit in the box tray. So set the battery on the tailgate floor and used two 2AWG wires to connect to the battery clamps. Lights came on and was able to pop open tailgate door. I raced to the engine and checked the Jumpstart leads by the coolant reservoir and they also read 51V. Fricking weird man.

[JDStrickland]

The battery positive terminal has an explosive charge -- similar to an airbag or seat belt retractor -- that disconnects the cable from the battery in an accident. The idea is to disconnect the car from any electrical source that can cause something to happen that the first responders are not expecting.

So, you connected a donor battery to the jumper terminals and see 51 volts at the trunk, and connect the same donor at the trunk and see 51 volts at the jumper terminals. And, you get 51 volts with Engine OFF? Something is boosting the juice inside of the car. You have your meter set to DC, not AC, right? (It pains me to ask that...)

But your initial issue, no power, is the explosive charge that's actually a component of the SRS system, it's an airbag thingy. You know what, the explosive charge might be the trouble, I don't know. There is a cover-thing on the top of the battery that has several fuses built in, and stuff plugged into it. You can connect your jumper cables to a terminal on this cover-thing that will energize the Power Distribution by going around the positive terminal on the battery. Looking at the actual battery terminal, the cable that connects to the terminal is the one with the charge.

In this picture, I think that the terminal at the bottom of the black thing -- this thing is a fuse pack -- is where the cable that goes to the B Post in the engine bay is connected. The red part is just a cover, the black part is the business end of this part. Use a thin screwdriver to pry the metal clips away from the case of the battery, then you can lift the whole thing off. There is a black 2-pin connector that that fits into a channel on the red cover, and the wires go into a cylindrical thing on the positive terminal, this cylinder is the explosive charge that separates the power distribution from the battery itself.


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