Another electrical issue.

[Kaktus 0]

Hi guys.

 

For some reason my alternator doesn't charge my battery. I had my alternator at one of local auto electricians and it tested ok. I saw with my own eyes that it charges at 13,2V on theire machine... but when i put the alternator in my car my battery only shows 11.8V when the car is idling.

Last night i even went so far as to run a jumperlead directly from the alternator to the battery (bypassing the starter) and it made no difference.

 

I'm sure this is something very small, yet very frustrating.

 

All help would be gratefull apreciated.

Hugo

[davidwort 0]

battery? how old, has it ever been completely discharged, does it hold charge left disconnected

[Kaktus 0]

Ta for the quick response David.

 

Battery has just passed a year now. I had it at the shop where i bought it from a couple of months ago, and they said it's fine.

 

What i can mention is that i have a constant drain on my battery aswell. It's about 0.1A ( if i remember correctly) and it is the electrical windows/central locking unit that draws my battery flat over 3 or 4 days. I never found the problem as to why it's draining so much, but i doubt it very much that that is the reason for the 11.8v reading over my battery at idle.

 

Or am i wrong?

[Kevin Bacon 5]

Might be worth checking your earths.

 

There's a couple of big gauge straps by the battery, these often corrode on the body connection due to the exposure to water.

 

The alternator has one heavy guage wire, which shares a connection with the starter motor, check this too. There's also a thin blue wire on the alternator which is for your dash warning light. I would check this wire isn't shorting on something.

 

I say this because that's exactly what happened to mine. The battery wouldn't last and the reverse lights came on without the gearbox switch connected and the engine would run on with the key taken out! Fun and games tracing that I can tell you. One new fuse board, all new relays and fuses later, it turned out to be both reverse light wires and the alternator dash wire had rubbed together over 13 years and eventually shorted together.

 

This part of the loom is down by the starter motor, so it's worth checking for peace of mind.

[Kaktus 0]

Thanks for the tips guys.

I'll check out the earth and blue wire aswell. :D

[Kaktus 0]

Thanks Guys.

I think i found the problem. Maybe you guys can assist.

What i did last night was i first tried a different battery, and the alternator didn't charge it. So before putting my old battery back in i removed the earth wire that runs from the batery to the body and then to the starter. I thoroughly cleaned and sanded all contact. Put it back with my old battery and now on first start the battery reading gives me just over 12V. When i blip the throttle slightly to about 2000-2500rpm's the Voltage jumps up to 13.8V and then slowly drops to 13.5V and stays there, untill i switch the car off. If i start it up again the results stay the same. I have to blip the throttle before it starts to charge over 13.5V.

 

So i assume it's still not 100%.

Any ideas? Should i look into buying a new earth wire?

 

Ta

Hugo

[davidwort 0]

sounds like alternator diodes to me, similar thing happened to my old alternator, I could see from my dash mounted voltmeter that it read low until the engine was revved then it came up to near normal for the rest of the drive. It eventually went altogether though. Worth trying a new brush pack first.