Battery or alternator?

[Busiboy]

Hi guys, after this weekend of disasterous 4x4 ing. I now know I have a charging problem. Without getting bent over a barrel by someone wanting to charge me for something what do you reckon the problem could be?

I bought my FJ40 with the chev V8 conversion. Don't knwo how much of an issue these things were previously but they seem to be now. I am onto my 3rd battery and have had my alternator reco-ed as well.

When driving along the alt meter reads anywhere between 0 and 15ish on the positive side depending on revs, at night it goes 0 and lower when running lights. Idling with lights drops to about 15 -ve.

I thought this sort of fluctuation wasn't an issue but als I fear I am gravely mistaken.

Ont eh weekend I developed a very flat battery, not running huge amounts of stuff. Radio and that was it, battery now doesn't hold charge, after 2 hours of high revs driving I still get nothing. Was this just a dud battery or do I have something killing my batteries slowly?

I don't know what else to say, all work was done by a sparky but I think he has stuffed something. Where should I start?

[drivesafe]

Hi Busiboy, what sort of time span are talking about when you say you are on your third battery.

If you hadn’t said that you have had your alternator reconed, I would have considered getting it tested to see if you haven’t done a diode.

There is also the obvious, have you check that all your wiring, both positive and negative ( earth ) wiring is in good nick and secured properly.

If you have an amp meter in the car it will only measure power that is actually passing through it, so go and check to see if there isn’t something connected directly to the battery as this may be where you might find you have a drain on the battery.

Cheers and keep us informed.

[Tas_Dean]

A few questions:

What is the brand of battery, and what is the alternator output meant to be?

By the sounds of things I would say that your alternator is incorrectly geared, ie not spinning fast enough. Your battery may be stuffed, due to not being charged properly. You may be able to get it replaced under warranty, depending on the brand of battery. How old is it?

Hope some of this helps,

Cheers, Dean

[Major60]

What is the voltage under idle and load? Sounds a little like a stuffed reg.

[Utemad]

Considering it is a new battery and checked alternator I would go with the above that you are not spinning the alternator fast enough.

My brother has a large aftermarket alternator on a Ford 351 in his Cruiser and it does not charge at idle due to low revs. Have you tried recharging your 'stuffed' batteries using another means such as a 240v charger? If they come up fine then it is your alternator or wiring in the vehicle IMHO.

If your ammeter is showing negative charge which I assume means you are taking out more than you are putting in then I can't see how it is possibly anything other than wiring or the alternator.

When your sparky checked your alternator did you give him the whole car or just the alternator? You should let him test the alternator in the vehicle. I can't see how he couldn't find the problem in minutes if he was given the whole car.

[Busiboy]

A few questions:

What is the brand of battery, and what is the alternator output meant to be?

By the sounds of things I would say that your alternator is incorrectly geared, ie not spinning fast enough. Your battery may be stuffed, due to not being charged properly. You may be able to get it replaced under warranty, depending on the brand of battery. How old is it?

Hope some of this helps,

Cheers, Dean

Thanks for the input guys, I think this is the prob though.

The battery was put on a charger (thought it was due to lack of use) a month ago and was charged up fine.

I will investigate this one though.

Cheers