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Alternator wiring
garyo - 15/5/06 at 07:56 PM

My engine has only been in and running for around 350 miles. Tonight the car battery was dead, and I noticed that last time I started it it also seemed sluggish turning over.

I've connected a meter to the battery, and the voltage is around 11.5 with the engine off, and 11.5 with the engine running.

I'm not sure whether my alternator is knackered, or wired in incorrectly. I bought my donor mondeo as a runner, and it had a flat battery, but I presumed this was because it'd been stood for a while.

The alternator had two wires - one big beefy red one, and one tiny one, which I think was for the instrument cluster. I've connected the beefy one to the starter solinoid - as good as straight to the battery. I've left the smaller one disconnected. Does the smaller one perform some other function, without which the altenator might have burned out, or is this just a simple case of a worn out alternator (the mondeo had 105k miles on it)

Cheers

Gary

gary gsx - 15/5/06 at 08:11 PM

The smaller one is for the ignition light

zzr1100rick - 15/5/06 at 08:15 PM

an alternator needs a feed to start the alternator charging thats what the small terminal does

Peter M - 15/5/06 at 08:33 PM

As previously said the small wire needs to go to the ignition lamp with other side of lamp going to 12volt ignition controlled supply.This wire is used to start the alternator to charging.Without this wire connected via a lamp that is going to 12 volt your alternator will not work.

muzchap - 16/5/06 at 12:01 AM

So to answer your question - nope your alternator is not working

Best of luck fixing it

garyo - 16/5/06 at 05:54 AM

Ah - I thought the lamp wire just lit the lamp - I'll wire it up tonight!

Cheers

Gary

02GF74 - 16/5/06 at 07:47 AM

quote:
Originally posted by garyo
Ah - I thought the lamp wire just lit the lamp - I'll wire it up tonight!

Cheers

Gary


lighting the lampo is a side efrect; it supplies current to the field coils; usaully there is some residual magentism that can self-excite the alternator but you shgouldn't rely on that.

The lamp (and it can be a LED but you stick to a lamp) is wired:

12 V to lamp, other side of lamp is to the alternator.

When alternator is not charging, the voltage at the other side is low so due to the voltage difference current flowas and the lamp lights up.

When the alternator is running, the other side is at 13.5 so minimal voltage = minimal current and lamp goes out. (well it glows so dimly you cannot see it )

garyo - 19/5/06 at 04:00 PM

result - I now have 14.3 volts on the battery with the engine running!

Cheers!

Gary

garyo - 4/7/06 at 02:21 PM

turns out this wasn't as straightforward as I thought :-( A week or so after fixing this problem, I was back to square one - no voltate increase when the engine is running, and the dashboard light always illuminated.

The wiring hadn't changed, so I fitted a replacement alternator. This worked for a short time, but now, once again, nothing.

I think the wiring is somehow burning out the alternators. The dashboard light no longer goes out. I've just borrowed an ammeter from a friend so I'll measure whether there's any output tonight.

Gary

caber - 4/7/06 at 05:21 PM

I would check the earth path all the way from the alternator to the battery. Some alternators have plastic bushes on the pivot and at the adjuster so you may need to add another earth path to the engine block or chassis.

You are probably blowing up the rectifier somehow, it can be quite cheap to get these fixed if you have a good old fashioned auto electrician around, one who knows which end to pick up a soldering iron!

Also worth checking all the wiring for loose or dirty connections including the lamp holder for the ignition light, also check that this is wired the same way as it was in the donor!

Where are you getting your alternators? If they are all ex scrappy they could be already damaged for example if the car was arc welded without the alternator being disconnected!

Good Luck

Caber

garyo - 5/7/06 at 10:43 AM

I trust the alternator bracket - all metallic and clean, but I'll check the earth path.

The lamp wiring is a problem - the car is mid engine'd using a modified FWD escort loom, and I have a mondeo engine sub-loom grafted into that. The mondeo subloom has a 42 way connector, which I've reduced down to 9 or 10 wires by eliminating things like AC clutch, rad fan, and other items that don't exist on the car. I have a niggling feeling it's something on this connector I might have missed.

The first alternator was an unknown from a breaker, and the last one is from eBay, so none were a known quantity really, apart from the fact that they delivered a higher voltage for at least the first 30 or so minutes of running.

Thanks for the suggestions - I'll report back!

Gary

Dusty - 5/7/06 at 09:37 PM

Isnt there an issue with blacktop alternator charging being controlled by the Ford ECU in the original installation. Best to use the usual suspects like suzuki/nissan/rascal or an older ford type if space is not an issue.

[Edited on 5/7/06 by Dusty]

garyo - 6/7/06 at 11:35 AM

I wasn't aware of that. I'm running the standard ECU at the moment, but was planning to fit an MS at some point in the future.

I'll have a search around google... maybe the alternators are fine, and it's just the ECU doesn't have the right information so has told the alternator to stop charging <sound of straws being clutched>

Gary