Intermittant charging problem

[MrMCI]

Hi all,

Sorry to post with another problem....at the moment if feels like every time I use my car I end up with something else to fix.

Anyway, this one.

When out driving voltmeter occassionally really drops, as if the car isn't charging. I have driven around with a multimeter onto the battery and charge is usually about 13.5 to 14V but occassionally drops down to 12.5V. This doesnt seem to be rev dependant (i.e. slipping belt). I have tried measuring the voltage on the back of the alternator but it seems to be all over the place, is it AC? I have never had any problems with the car running out of charge but I would say that the problem only happens 20% of the time that I am driving.

Anyone have any ideas? if I need an alternator is the pre-serp the same as a Land Rover?

Thanks in advance.

Mark

[TimJM]

MrMCI said:

Hi all,

Sorry to post with another problem....at the moment if feels like every time I use my car I end up with something else to fix.

Anyway, this one.

When out driving voltmeter occassionally really drops, as if the car isn't charging. I have driven around with a multimeter onto the battery and charge is usually about 13.5 to 14V but occassionally drops down to 12.5V. This doesnt seem to be rev dependant (i.e. slipping belt). I have tried measuring the voltage on the back of the alternator but it seems to be all over the place, is it AC? I have never had any problems with the car running out of charge but I would say that the problem only happens 20% of the time that I am driving.

Anyone have any ideas? if I need an alternator is the pre-serp the same as a Land Rover?

Thanks in advance.

Mark

Not an expert but have you tried testing the output from the alternator? Couldn't voltage drop at the battery be something else in the system using/dropping it? Also, do these alternators have a regulator that could be faulty?

Tim.

[Warbbby]

Is it when the cooling fans cut in? The drop on my voltmeter is similar. My car is at D&C Trim at the moment so I can't check the actual drop.
Mark

[paulathome]

Mark, if your alternator voltage is all over the place I would be checking the 100 amp fuse if you have one, or the wiring between the alternator and the battery.
The reason the voltage on the back of the alternator is all over the place is because the load on the alternator must be changing. (unless the alternator is faulty of course)
The load being the battery which it is trying to charge. When the batery is running low (like after starting) the load will be high (drawing lots of current) and the votage will tend to drop, as the battery gets charged and draws less current the voltage will tend to rise.
So if your alternator output is up and down the load must be changing in sympathy which would tend to suggest an intermittant connection between the load (the battery) and the alternator.
If you have a 100 amp fuse inspect it carefully for corrosion and make sure it's not cracked and the connections are clean and bright.
Hope you get my drift.
Good luck.
Paul.

[MrMCI]

Unfortunately it isn't the fans, if the voltage is low when they come on I am down to about 11 volts :-(

I would like to drive along with the voltmeter connected to the alternator but can't work out what terminals to attach to, I have tried every combo of terminals and keep getting what I assume must be AC voltage (I dont have AC on my voltmeter). Does anyone have any suggestions on where I could measure the output from?

[Loubaruch]

No you will not be measuring AC as the internal circuit in the alternator will convert it (or should do) to DC before it reaches the output terminals. Your alternator could be faulty of course!

Disconnect your battery and take off the alternator cables and give the terminals a good clean up with emery cloth.

Also the 100 Amp fuse is another likely culprit as as been suggested above. THe local TVR garage told me they change the 100A fuse at each main service as they cause so much trouble.

[PeteGriff]

MrMCI said:

Hi all,

Sorry to post with another problem....at the moment if feels like every time I use my car I end up with something else to fix.

Anyway, this one.

When out driving voltmeter occassionally really drops, as if the car isn't charging. I have driven around with a multimeter onto the battery and charge is usually about 13.5 to 14V but occassionally drops down to 12.5V. This doesnt seem to be rev dependant (i.e. slipping belt). I have tried measuring the voltage on the back of the alternator but it seems to be all over the place, is it AC? I have never had any problems with the car running out of charge but I would say that the problem only happens 20% of the time that I am driving.

Anyone have any ideas? if I need an alternator is the pre-serp the same as a Land Rover?

Thanks in advance.

Mark

Hi Mark, unless you have already done so take the output connections of the back of the alternator and then check using a multimeter whilst the engine is running. If the output voltage is all over the place the alternator is probably faulty, as it might be a failing voltage regulator module. If it is a non-serp type earlier engine the modules are only about £11 and are easy to replace. If it is more than that the alternator is only about £65 from Land Rover online parts outlets. Hope that has been helpful, Pete

[MrMCI]

Superb....thanks chaps....part of the reason I bought a Griff :-)