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Charging and Electrical Problem

1K views 8 replies 5 participants last post by  therapy23 
#1 ·
Having an electrical issue with a Volvo 2003 diesel... the panel is dead. no instruments, warning lights, or starter works. The engine will start by shorting the starter to battery voltage (bypassing panel and starter panel).

I've replaced alternator and starter relay... it did not help.

The start panel is getting battery voltage but I think there is a ground fault. I ran separate ground wire from the battery "-" to the ground wire at the panel. When I did this, the RPM backlight came on and I'm able to start the engine. But the other guages are dead and I don't appear to be charging the batteries from the alternator.

The alternator is an isolated ground alternator. I'm wondering if I have a flakey ground or a harness short somewhere...

I wish I had a good boat wiring diagram / schematic. I suppose I could check the resistance between the alternator B- and the negative battery terminal... I've checked it to the negative master switch terminal but not back to the actual battery terminal. But if it were the master switch causing problems, you'd think I'd be having problems will also of the boat's electrical systems. I'm only having trouble with the panel and starting circuit...

Any thoughts?
 
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#2 ·
To troubleshoot this, you will probably want to at least do a basic wiring diagram of the major components of your electrical system. Without knowing how the system is wired, troubleshooting is impossible.
 
#3 ·
Thanks. I have a basic diagram that came with the engine manual. I've found some mistakes with it and it's not as complete as I'd like. I've been sketching up additional diagrams as I go.

I've been reading Calder's book. The electrical fault tree in the book is leading me to believe there is a problem on the ground side. I suspect it may be the engine ground strap or other negative cable back to battery.

Although the negative terminal on the alternator is isolated, it's not big enough to carry all the current (the guage of the wire is much smaller than what's on the B+ terminal). So there must be a redundant ground path through the alternator housing to engine ground.

I haven't checked the impedance between the engine block and negative battery terminal, but I think I'll check there next. The engine sensors are single wire, so the block must be grounded. I assume the alternator's isolated ground is simply to minimize the amount of current that actually goes through the block (alternator, starter, sensors only).
 

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#7 ·
I think I'll try a jumper cable between battery ground and engine block.
I've diagnosed a lot of problems with jumper wires when I didn't have my multimeter with me. Bad grounds make for some interesting troubleshooting too.
 
#8 ·
Found the problem tonight... I missed connecting a short wire to the engine block when I hooked up the new alternator (B- to engine block). Seems silly to have an isolated ground alternator and use a 6" cable to connected it to the engine block. Oh well. We also had a problem with the start panel electronics. Thanks to the schematic that was sent above, I was able to diagnose that the Vbatt diode had gone somehow. I jury rigged a bulb between panel power and the alternator D+ line. Voila, bulb extinguished and alternator was charging the batteries.

This will work for now, but I still don't have water temp and oil pressure warning circuits working yet. I need to order a new electronic board for the starter panel.

The Mac is in 2 weeks. It's going to be tight. But at least we can generate power now.

Thanks to all the above for the help.
 
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