The 'E' Type Forum

Started with poor charging.
Found poor connections on regulator.
Changed regulator and connectors.

Problem now is that when revs go to approx 2000rpm, voltage rises to well over 15 volts, and with a few more revs it can reach 16 volts.

I have turned the voltage screw on the voltage regulator down to minimum, but still high 15 volts.
This voltage is measured at the battery terminals, but it is getting through to the rest of the electrics because the indicators flash much faster.

Is this a faulty voltage regulator? I understand it should react to rising voltages from the alternator by reducing field excitation. Is this what is failing.

What is the in-car voltmeter saying ? Both the current output and the voltage can be affected by the state of the battery, and if it has been in a state of persistent low charge ( as is implied by the earlier lack of charging) it will take a really good period of running to get it back to a normal state . If it is a gel battery, it may not be possible to return it to pristine condition. You really need to give the car a very good run and see what it settles to after say 45 minutes running . If at that stage it drops back to perhaps 14.5 volts, there is no problem at all

Really?
The in car voltmeter reads exactly the same. That's why i put the second digital multimeter on at the same time.

It has indeed been chronically undercharged , so your point seems very valid.

I fear frying the ignition and other electrics if I run it.

Thoughts?

I doubt that you will harm the general electrics by a long run at 15+ volts . Excess heat is generated by large currents rather than slightly high voltages. As far as the Opus ignition is concerned, I would be less confident, but again a consistent excess voltage of about 10% should not cause harm - it is big voltage spikes which tend to damage electronic components . Perhaps someone more expert than me can comment

OK long run duly carried out. No reduction in voltage. Throughout showing about 15.5 volts. After the long run, I couldn't find any hot wiring or battery casing.

So picking up on your comments, I had the battery tested. It shows healthy cranking power and 85% efficiency, and good condition. The discussion concluded with agreement not to worry about the apparently "high " voltage.
We don't think its a gel battery.

However, indicators still flashing at double their normal speed, and drop to normal at tickover, so although we may subsequently conclude that i shouldn't worry about voltage, the the indicators continue to worry!

I guess the voltage stabiliser behind the gauge panel may play a part, but I think it will only smooth the fluctuations, not limit the voltage. I am not even sure the indicators are int the stabiliser circuit....I'm off to check the wiring diagram.

Further comments welcome.

The voltage stabiliser is only there to deal with the fuel and water temperature gauges which are fed at an average 10 volts . The flasher unit should not be connected with it at all. Something else I should perhaps have mentioned is that output voltage via the regulator can be affected by ambient temperature - I cannot now remember the theory of this but will try and look it up

I've been thinking further about this. What alternator have you got ? Does it rely on the external voltage regulator ( usually a 4TR) , or have you got a later alternator which has internal regulation. If it is already internally regulated then using a 4TR as well might lead to all sorts of strange results. However, I am still of the view that for the moment I would not get very worried unless yours is a sealed for life battery ( because you cannot add water) . What I would do is ( assuming that the battery is lead/acid ) keep a close check on the electrolyte levels since this is the surest guide to whether you are doing any harm. If excessive charging is taking place, you will quickly notice a fall in electrolyte levels as the water is boiled off

Incidentally , on the subject of temperature, I have now traced the theory. As battery temperature rises, so its required voltage reduces, and vice versa . Accordingly, the regulator has a thermistor in it to vary the voltage at which the zener diode starts to work , so that as temperature falls , the zener diode ensures that the regulator raises the output voltage to match, thus still providing the differential in voltage necessary to achieve a charge . Thus if you are in a very cold climate, the normal output will be noticeably higher than in temperate or hot zones . You do not state your location, but this may be at least part of the answer . Various articles suggest that the overall difference is between 2.3 and 2.45 volts per cell = 13.8 to 14.7 volts in a 12v battery . There is also some research which shows that an underbonnet temperature mismatch between alternator and battery can result in loss of regulator control

You may find this article illuminating on whether damage is occurring : it shows that the critical factor is whether the battery is fully charged at present

http://www.powerstream.com/SLA.htm

By the way. i'm very appreciative of your input (pun fully intended) on this.

Yes, I think the implication of your last message is correct. We know we're charging well. Something in the control process is amiss.
So having done the basics, we have a charge, we've changed the controller, we've checked the battery, I need to re-trace my steps.

I've just looked at the alternator. There is no metal label on it! My two spare alternators are BUTEC a7/213 (or 8) and a7/1a.
They all look the same.
The one fitted looks the same but with no label......
The voltage controller is SU/ BUTEC.

So which of the three alternators do we know is correct, in relation to the controller. It may well that, as you suggest, the poor connections, masked this underlying problem.

Incidentally, when i followed the workshop manual, it describes the test, whereby, having set the potentiometer to 14 volts at 1000rpm. whilst measuring the voltage at the regulator between field and negative terminals, turning the potentiometer fully clockwise , the voltage should be below 1.5 volts. It wasn't, it hovered between 7v and 8v.

It produced this result with two different regulators. One of which is marked R2/1Z. and the other R2/1. But they both produced the same result in that test.
I'm in Skipton.

Actually looking at the manual, I should fit the A7/1A alternator and the 2R/1 control box. That would at least start from a matched pair.

If the system is over charging the battery will get hot and, as Christopher says, start to boil away electrolyte. The danger is from boiling acid getting sprayed around the engine compartment or, in the worst case scenario, the battery exploding. After a run check the battery temperature. Charging voltage should be 14.3v so I would suggest replacing the regulator and alternator with known good ones because if you ignore it your days out will be ruined by worry!

Christopher , I see the advertisement for the up-graded alternator with built in voltage controller....at cambridge motorsport for example.

If thats the type you mean, mine is certainly not that one.

I found a series of articles by Coolcat Express Corp, they refer to the Lucas model, but the principles appear to be the same.

I wonder what fault, a relay would produce. All faults seem to cause low output. Rather than my high output.

Still thinking it all through.

If your alternator is a fairly recent one, by which I mean post say 1980, then it will almost certainly have internal regulation. It was only the early alternators in Europe e.g. the Lucas AC series, which had separate external regulators . After that Lucas and most other manufacturers incorporated the regulator behind the rear cover of the alternator , and tended to use a plug-in type of connector rather than separate screw on terminals . I think you need to establish exactly what you have got , from what manufacturer , before we can go any further

pcwesthead - Have you been able to resolve your issue with the overcharging? I've got a S3 coupe with exactly the same issue (up to 16 volts). Doesn't do it all the time but often. Alternator has checked out fine and I've ordered a new voltage regulator thinking that's what it must be? Wondering whether I'm missing something??

Update -
just in case someone reads this thread at a later date, my issues have been resolved. Turned out the alternator had a defective stator, which had resulted in the destruction of the diodes. Consequently, I had the stator rewired and the rectifiers rebuilt (new diodes) and reinstalled it in the car. Adjusted the voltage regulator to 14.1v and "Bobs your uncle".
Bonus is the ignition light now goes out once the car is started - first time I've seen that since I bought the car.