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Alternator problem on TVR

"Struggling to work out what's going wrong here. The car ran a small block Chevrolet motor for quite a few years - the alternator was off a Citroen of all things, and the charge light was an LED with a parallel resistor as part of a set of dash lights. Everything was fine - charged fine, always a steady voltage and the charge light worked perfectly.

I've now put in an LS7 and there was no way the old alternator would fit, and hunting about the only 'regular' alternator that was short enough was from a Ford Explorer. First off it seemed to get real hot real quick - this is on a car that's only running a (big) fuel pump, ECU, injectors and data logger/dash. There will be more load if the radiator fans kick in, but even with them off it heats up real quick.

But the bigger problem was the charge light would flash intermittently. I could see voltage spikes on the logs and in an effort to cure I ran another earth direct to the block and rewired the live feed through its own fuse direct from the main power. It didn't cure it, but with nothing else to do really and as it didn't seem to be doing much harm I ignored it. But that alternator packed up in a very short space of time - and it was new, not a recon unit. Regulator knackered apparently, and I got a new replacement unit.

Ran the car again yesterday for the first time after some other engine work with the new alternator, and the same thing - voltage spikes.

So while its mostly at 14.1 volts, every so often it spikes up to 16.5 volts and drops to 12 volts, and at this time the charge light flashes (as before, LED with resistor in parallel). The last thing I want to happen is to break this alternator.

So as an alternative I had a Denso mini-alternator I had always planned to use, so last night I rigged up some brackets.

Different problem now. With ignition on (so power to the alternator Ig feed) and engine off the charge light doesn't illuminate at all (and the alternator is wired properly - I checked many times!), but when the engine is running the light glows dimly, but the logs say its giving a good charge. So the charge light circuitry on the Denso alternator is obviously different to the Ford Explorer (and previous) alternator.

So - 2 choices. Either, any suggestions as to what's causing the voltage spikes in the original alternator and if I can address it I'll use it, or why does the Denso alternator not show a charge light when it's not running, and then shows a dim charge light when its actually charging?"

Any ideas?

Reply to
Dave Baker
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Isn't it obvious? You're using the wrong alternator for the car!

Reply to
The Revd

As a matter of interest, which one?

Reply to
Huge

Pistonheads.

Reply to
Dave Baker

Just a few random musings.

An LED requires a series resistor when run from 12 volts - to limit the current through it. However, some alternators require the warning light to operate correctly - is this why there is a parallel resistor? Also be nice to know the value of that parallel resistor. If it's been worked out of on the basis of the 'lit' current of a bulb, it may not be correct.

Some Fords have the alternator controlled by the engine ECU. Not sure about the Explorer.

First thing I'd do is rig up exactly the same warning light as the car uses for that particular alternator to see if it makes a difference.

Reply to
Dave Plowman (News)

Thanks Dave. I was hoping you'd chip in. I've passed that on.

Reply to
Dave Baker

Sure you haventy got a smart charge alt on there?

Reply to
Tim..

Never having seen one could they be confused? Or have they got special plugs, etc?

Reply to
Dave Plowman (News)

Had one on my Ford S-Type 3.0 and, AFAIK, the only difference is an extra control line running to the alternator. I only looked at the wiring diagrams out of curiosity so I have no idea of the physical side how the connection was made. Waggling this line up and down controlled whether the alternator threw out 16v or 13v.

The same thought as Tim occurred to me when I read about the voltage cocking about - if this line isn't connected to anything it could easily by flapping about, upsetting the gubbins.

Reply to
Scott M

It's a piece of shit, in other words.

Reply to
The Revd

Good point. And better put than I was able to.

Reply to
The Revd

This sounds very possible, along with Dave's suggestion of the warning lamp. It would be worth looking at the diagrams for the car the alternator cam from. As well as the possibility of a smart alternator or engine ECU control, some cars have a charge control unit that may have a part to play.

Reply to
Chris Bartram

Generally, a self contained alternator has two connections only (apart from the ground one)

Large one to battery, and small one to warning light. There may be a third small terminal for a diesel tachometer, which would be unused if not needed.

Some may have two 'battery' terminals to carry the load, which will be 'large' ones.

There are some older or large alternators which have external regulators - but these wouldn't work at all without it.

A Google for the alternator in use should give how the terminals are marked.

Reply to
Dave Plowman (News)

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