F01 N57 overcharging issue, hot battery jumper terminal

[pesik]

Hello everyone,

I recently did a timing chain job on my F01 730d 2010, and since the car had not been started in about 10 days, the battery was dead. I jump started it, the car runs and drives perfectly, and about a week later I got a message "battery not being charged". The next time I went to start the car - the battery was dead again. I opened the hood and I saw that the positive jumper terminal nut is loose and all the red plastic around it was slightly melted. I cleaned the remains of the plastic, sprayed a bit of contact spray and I tightened the nut (not with a torque wrench, but its pretty tight). Jump started the car again and it has been okay since then, no messages, no dead battery issue, but it is charging 15.3V since then, I dont know if it was lower before. And the plastic cap on the jump terminal is still getting hot, you can not touch the nut with your hand.
Is 15.3 volts too high, or is the intelligent battery system compensating for the dead battery? What could be the issue with the hot jumper terminal? Its hot all the time while the car is running.

Thanks in advance.

[Qsilver7]

Where are you placing the negative cable? Are you using the dedicated negative terminal that is outlined in the owners manual...or did you select something else that you figure is grounded?

[pesik]

Originally Posted by Qsilver7

Where are you placing the negative cable? Are you using the dedicated negative terminal that is outlined in the owners manual...or did you select something else that you figure is grounded?

I used the negative terminal which is placed behind the passenger side headlight. But the positive terminal is getting hot all the time while the car is running, not only when I jump started it.

[pesik]

Bump, as I still have this problem.

[dpatters20]

Hey pesik, you may have already figured this out, but I'm wondering if there could be a low resistance short from your positive terminal to ground, somehow. I can't think of any other reason the jumper post would be getting hot (temperature), as this should be an end of line terminal, with no current through it normally unless jump starting. Seems like this might also explain the relatively high charging voltage.
I looked at mine, and the positive jumper terminal is mounted on an insulated plastic or fiber composite post. If that plastic melted away, maybe you're shorting to ground somewhere there?
I'm curious - is this post hot even after sitting for hours, not running?
By the way, kudos to you for tackling the timing chain job yourself - how long did that take you? Good luck.

[pesik]

Originally Posted by dpatters20

Hey pesik, you may have already figured this out, but I'm wondering if there could be a low resistance short from your positive terminal to ground, somehow. I can't think of any other reason the jumper post would be getting hot (temperature), as this should be an end of line terminal, with no current through it normally unless jump starting. Seems like this might also explain the relatively high charging voltage.
I looked at mine, and the positive jumper terminal is mounted on an insulated plastic or fiber composite post. If that plastic melted away, maybe you're shorting to ground somewhere there?
I'm curious - is this post hot even after sitting for hours, not running?
By the way, kudos to you for tackling the timing chain job yourself - how long did that take you? Good luck.

Hello there,
Unfortunately I havent figured it out yet.
The red plastic cover is melted, not the whole assembly and it still does its job insulating the terminal. And it only gets hot while the car is running, which does make sense as this is the main connection where the alternator and the battery cable join together, I just cant find out why it gets so hot. The contact surface is properly sanded and cleaned. Maybe something to do with the alternator charging 15.3 volts?
It would be nice if you could check if your car is also charging around 15 volts? (i guess you also have a f01/f02)
And regarding the timing chain, this was the second time I did a timing chain job in my life, and it took me about a week to do it, as I was working by myself and only 5-6 hours daily (18:00 - 00:00).

[dpatters20]

Mine is a 2014 F02 750li. I checked just now, started it up and got steady 15.1 volts at the underhood terminals. Let it finish warming up to check the oil level, and then got 14.97V steady. My terminal is barely warm to the touch - I can press a finger to it indefinitely. Sorry you're dealing with this. It seems like it has to be a high resistance spot in the current path at or very near the terminal. You've checked the terminal itself, so wondering if one or the other cable could be going bad. But the fact you're seeing 15V at the jumper terminal makes it unlikely there's much voltage drop between alternator and this terminal. So maybe it's the cable on the other side of terminal from alternator connection. It would help if I had a wiring diagram, but I don't. Sorry.