Alternator/Voltage Regulator issue, Alternator light is on until rpm's increase Options

[PDXMike]

My alternator light stays on after I start the car. It was dim, and it would go off (and stay off) as soon as I got the RPMs up over 1000 or so. I did eventually find a faulty connection between the battery and the Voltage Regulator, which I thought would solve my problem. Instead, I now have a similar condition except that the charge light is on full bright (not just dim, like before) until I blip the rev's up a bit. It will still go off and then stay off for the rest of the time the car is running.

With the car running at about 1000rpm I am getting 14V at the battery. Pulling the VR and shorting D+ to Df results in 16-17V at the battery, so I am assuming my alternator is good.

I thought there was something going on with the VR not applying enough voltage to the field at start-up, so I ordered a replacement. They new Voltage Regulator is an AC/Delco part, not the OEM. I have exactly the same issue with the new Voltage Regulator.

Any ideas?

Thanks!

Mike

[914Sixer]

Do you have a spare relay board to swap out? This will eliminate one item. As always, check and clean all grounding points if not all ready done. Check positive terminal post where all the 3 red harness wires come together for corrosion.

[Spoke]

If the alternator works all the time when running them you should be ok.

The start up thing is rather normal. It's called bootstrapping because the alternator needs itself to generate a voltage at the VR to get started. Mine will do a similar startup if I don't rev the engine when starting.

It could also be that the GEN light is too low wattage.

[904svo]

Try cleaning fuse #9 connections, this fuse supply's power to the alt field to generator power.

[Rand]

I haven't heard of bootstrapping a 914. It is basic electrical circuits, not a computer. My gen light only came on once, and a quick wiggle of the VR fixed it which pointed me to cleaning the terminals. Never happened again. If you only could be so lucky, but point being, if the light light's on, something IS wrong. No way in hell should you write it off as normal. It comes on for a reason which usually indicates a dirty electrical connection. If you start introducing LED lights and such, it gets more tricky because of resistance changes.

[Chi-town]

Usually most alternators won't excite till 700-900rpm

A normal cold start high idle would take care of that but a hot restart may take a blip of the throttle to get it done.

[PDXMike]

I'll check and clean the number 9 fuse, the ground strap, and all the connections at the battery. Other than that, I'll keep an eye on it and check the charge on my battery occasionally. It sounds like it is probably fine as it is. If not, it will eventually get bad enough to offer some more clues to help troubleshoot.

Thanks all!

[SirAndy]

What engine? My /6 does the same thing and i have been told that it is normal ...
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[PDXMike]

'75 with a 1.8.

What engine? My /6 does the same thing and i have been told that it is normal ...
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[mikesmith]

I haven't heard of bootstrapping a 914. It is basic electrical circuits, not a computer.

As others have said, it's quite normal, and the term 'bootstrapping' significantly predates its use in computing.

Alternators require electrical current in the field coil (excitation) before they can generate any current themselves. This current is supplied through the alternator warning light. Once the alternator is spinning fast enough, its internally generated current will take over (self-excite) and none will flow through the warning light (causing it to go out). This is the 'bootstrapping' process.

The current through the warning light is much smaller than the field coil current during normal operation, and it can be affected by many things - the selection of bulb, contact resistance all through the path (fuse, connectors, bulb socket, etc.). This will affect the speed at which the alternator's internally-generated field current takes over (lower bootstrap field current -> less current generation per rpm -> higher rpm required to self-excite). It's also possible for a partial failure of the field coil rectifier to produce these symptoms.

From a practical standpoint, as long as the light comes on before you start (this is critical), and goes (and stays) off in normal operation, you're fine and you probably have better things to worry about.

[Rand]

Yes I know where the term came from long ago. I learn every day. A weak charging cycle is normal? This is when we start to have a problem. Did your car go off the line with a problem? Was it a weak engineering thing? Look at what causes the problems today.

[Spoke]

Yes I know where the term came from long ago. I learn every day. A weak charging cycle is normal? This is when we start to have a problem. Did your car go off the line with a problem? Was it a weak engineering thing? Look at what causes the problems today.

Most likely not an issue coming off the line. As parts wear and time takes its toll along with armature brushes wearing, it could be such that a very low RPM startup could keep the alternator from bootstrapping and getting into regulation.

My 914 with 2056 w/carbs will idle very low (300 RPM) when cold. The alternator gets started but because the battery has just been stressed with starting, I don't get full 14V until I rev the engine to about 1200 RPM or more. The voltmeter will read around 13V until the engine is revved a couple of times then it stays at 14V for all RPM ranges.

[porschetub]

What engine? My /6 does the same thing and i have been told that it is normal ...
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(IMG:style_emoticons/default/agree.gif) same with my rebuilt bosch 911 unit...good to hear.