Help with an electrical problem please.
 

Hi to all. This is my first post on this forum (even though long time lurker) so allow me to introduce myself.

My name is Chris, and I am the owner of a RAM cobra with a serious electrical fault.

This is some background: Have had a problem with a flat battery, so replaced it, as I could not tell how old the original was. Have since driven the car once or twice weekly and the battery has not been holding its charge. Hmmmm out comes the multimeter.

Motor not running Battery showing 12.45v
Motor running Battery showing 12.32v ??

At the alternator with motor running, showing no voltage output???
Now the funny thing is whilst I was checking the alternator and looking for a better ground, the thermo fan kicks in and the Multimeter now reads 13.65v.

So unless I am stationary for long periods or driving like I stole it (which I never do) then I am not getting any charge back to the Battery.

I don't have a lot of electrical knowledge, so my question is, should I be looking for an electrical short circuit somewhere, or perhaps the thermofan relay for a fault.
I should also mention that the thermo fan relay draws its power direct from the alternator, which I thought is unusual.

Whilst driving the car all this time, I have had no problems with warning lights etc, except for this last weekend when my check engine light came on, but by the time I returned home had gone away.I suspect this was from a low battery not being charged.

Any hints as to help narrow the search for the problem down would be greatly appreciated.

Cheers Chris.

Tricky stuff - and welcome Chris. I am not sure which motor or alternator that you have, but this does sound like a problem with the alternator - the rectifier or regulator circuits. I am by no means a specialist, so would suggest that you take it to your local auto-electrician and have it checked out. This may help in the meantime if it is a Ford one.

http://fordfuelinjection.com/?p=63

Merv

Sounds like the exiter circuit for the alternator is playing up.
Is the alternator light illuminating before start up and extinguishing after start up?
If not, that would be where to start looking.

Thanks for your reply Merv and Gav.

Merv my motor is a A9L holden 304 from a group A HDT. It is carbureted and fairly original at this stage.

Gav, prior to ignition I do have the light which extinguishes after ignition, but on my last drive the light came back on while driving. As mentioned earlier I think this is due to a flat battery which was not receiving any charge whilst driving.

What has me stumped is that as soon as the thermo fan kicks in the alternator starts to feed current back to the battery. So my thinking is as the thermo fan relay is connected directly to the alternator, maybe this is the cause for no current flowing untill it receives the signal to open the circuit? My electornics knowledge is limited so I may be way of the mark.

Merv, as you suggested, I plan on going to the auto electrician, but untill then I would like to have a go at tracing the problem. The more I can learn, the better I will feel.

I guess the first thing to try will be to isolate the thermo circuit totally and see if this have any effect, and if it does then look closely to see if it set up corectly.

If this is not the problem, can anyone advise as to how to check the alternator out ?

Sounds like the wiring for the fan is running through a relay that switches the alternator on and off as well as the fans. They have tried to wire the fans directly off the alternator for max power and have inadvertantly switched the alternator output.

In my following reply I am assuming you have had the car for a while and this is a "new" problem?
Also assuming you have not had any recent electrical work (ie fans fitted)

I would suspect you may have 2 issues.
1 : Alternator not charging, it sounds like the exciter circuit is working (light on dash), but the alternator is not being triggered, so I would remove alternator and have it checked and rebuilt (vehicles with 304 engine from memory would have a black unit that bolts onto rear of alternator (internal regulator), any competent sparky should have a test bench and be able to test your alternator.

2 : it would also appear your fans are wired direct to Alternator (or atleast the power supply to relay is), I would go through the fan circuit and make sure it has a relay fitted and that the relay power supply is via a fused supply from battery.

I'm with Mickmate on this one... I'd start there.

I too am with Mickmate. It may be that the wire that should be from the alternator to the battery for charging is open so the fan relay connects it when engaged.
Good Luck!

Here's another angle...not sure of the alternator design but...The brushes could be on the way out. Only just touching the slip rings... then when the fans come on they create a large current draw and the tiny arcing gets bigger. If you can remove the brush holder have a look at the slip rings. If they look burned up. there's your problem.

RAM Rare in Aus
 

Hi Chris, I see you have a RAM. There are only 3 of these that I know of in Aus, yours, Dean Fava from S.A with a big block, and there was an incomplete one squirreled away in a shed in Queanbeyan NSW.

With the 304 fitted, I am assuming yours was built here. Did you build it or were you involved in importing it?

In the late 80's? early 90's there was a controlled race series using RAM's in UK and Europe. I think it was even endorsed by Shelby.

Thanks for your input everyone. Mickmate, PDUB and Infletcher, you think like me. However I had a good look at the wiring last night, and the fused relay is attached to the alternator but in parallel not in series so this blows the relay theory to bits.

So I think Boxhead and/or Rob might be right. I will let you know how it goes after i've been to the sparky.

David you are right, the RAM is rare. I bought it already built about 12 months ago from the third owner.
It is a 1992 first registered model and verry original. By that, I mean the previous owners have not spent a lot on maintenance, so I plan on slowly going through a renewal process. It was assembled here in Sydney originaly, then registered in QLD for a few years, before comming back to NSW for a few more years before I acquired it.

You are also spot on about the race pedigree of the RAM and the Shelby endorsement. It sits on a spaceframe built by Adrian Raynard of racing fame, and is renowned in the UK for its strength. They are still raced in the UK even though they have not been produced for many years.

I really like the shape and poise of this car, but being a largish bloke, the huge tunnel and cramped seating has got me thinking about some more changes that I originally had not planned for. It all adds up to fun in the end.

Cheers Chris.

Hi Chris,

If you've not resolved this yet I would try the voltage test and then turn on other heavy use items such as headlights & wipers together etc to see if this triggers the same response (ie a lift in voltage). If so it has to be the regulator to my mind.

-Andy

I will give that a go Andy. Never thought to try increasing the load. Thanks.

Rip it out and off to the auto sparky for you Pills.
You could dick around for days looking for something that they will diagnose and fix in minutes.
I would think you have done just about all you can do.

I feel your pain tracing down electrical gremlins, I have had to do that several times myself. My symptoms were similar to yours and mine turned out to be my alternator.

One of the best things I have done to my car was when I put in my battery cut off switch,. Lead line from battery ground goes directly to my swithch and then to a combo ground (engine and frame). Every time I exit my car after turning off my key I turn my battery switch off---eliminating any drain on the battery.

Clois

Pills,

Have you checked your earths? Is it possible that the when the fan switches on the alternator is earthing through the fan circuit? Is the alternator earthed properly? I may be totally wrong, but it was just a thought.

Liam

Engine paint could prevent alt earthing to block. Also make sure there is an earth strap from block to chassis/battery

I think the Alternator earths through the mounting bracket on the engine (from memory). So as you say David, that earth strap from the block to chassis is probably the culpret. Could just be a bit of corrosion that has formed under the connection.

On an older car/motor it is always a good idea to get the alt checked by the autoelectrician. New brushes, new bearing/s and check the rectifier and regulator. That way u know that all is fine and it not expensive.

Haven't had much time over the last couple of days to check things out, but I did try starting her up and turning on lights, heater etc as suggested by Andyl, to see if the increased load would replicate the thermo fan effect, but this made no difference. The "earth" suggestion has been crossing my mind as well as I get a big variation in voltage reading when grounding the multimeter to the chassis or the motor. The weather should be better tommorow, hopefully I can have a good look and try a few of your suggestions. Again, thanks for all your input guys. This forum is trully great.
By the way, the alternator appears to be fairly new or reconditioned at least, considering the age of the rest of the mechanicals. My hunch is either its a badly wired relay or the alternator has developed a fault. The earth through the bracket should be good, if not, I would think it would appear as an intermittent light on/off situation.