Lotus Elan and Lotus Elan Plus 2 Forums

If it's getting that hot in 10 min's, check that the pulleys & belt are all compatible. I had much the same symptoms on another car a few years back, only just, or not keeping up with battery drain & alternator getting too hot to touch in just a few min's. It turned out to be the belt was fractionally too narrow for the pulleys & was bottoming out on the alternator pulley & slipping when there was any electrical load. I couldn't detect any slippage, the belt looked fine, & I couldn't believe it would make the alternator so hot, but after changing the alternator/battery etc made no difference, I fitted a slightly wider section belt that nipped in the 'V' of the pulley well before it could bottom out & problem solved, plenty of electricity & a nice cool alternator. The belt cost about ?5, I had spent over ?100 on a new alternator, battery & cables !

Regards, Tim

A point that may be worth mentioning with regard some clone Lucas alternators and could be a reason of low output.
Clone alternators shown in adverts with a BLACK pulley fitted have a different type of pulley drive, conventional drive is via a straight shaft, keyway and nut.
Clone with black pulley uses a taper with NO keyway, two problems if you have one 1. Changing pulley size. but this is why I mention it, as supplied not necessarily a FULLY Tightened nut. So a quick check to ensure the nut is fully tightened and no slippage takes place under electrical load.
FWIW
Ron.

Andy

Looks to me that your voltage regulator is failing I've had this in the past

If you are removing it for checking and testing here is some info on ACR,s

Parts are cheap on the net make sure you know the model and the connections you have as you will see from the info there are variations
I have tried to upload a Zip file on the ACR,s but is to large, If you want it send me private message and your email address


Good luck

andyhay wrote:I think it does get hot by itself. It was hotter than the engine after running for 10 minutes. I will try and investigate the regulator and charging loops. I think I'm getting out of my depth doing this. Should I just take it to an auto electrician?

Thanks again for all help everyone.

Regards

Andy

around here if your go to an reputable automotive electrics shop they'll test your alternator free of charge (they have a setup which brings the adequate testing voltage and an adjustable pulley to make it charge) : that'd be a fully functional check.

What you can test rather simply with a meter is wether a diode has gone bad (typically would conduct in both directions, hence the alternator dissipating the corresponding current rather than sending it to the battery). You should also check if there is a short (i.e. 0 Ohm) to the body of the alternator : what can happen from vibrations is a varnished wire from one of the windings getting loose and the varnish getting worn out and making a short.

Then just replacing the regulator and/or the diodes is easy, just take your time, make sure you look carefully how the insulating washers are located when you take them off ... and test with your meter when putting it back together.

It's not really the voltage that you want to check, it is the Current that is flowing from the alternator to the battery shortly after startup.

It should be around the rated output of the alternator in Amps.

As the battery recharges the power lost during startup, the current flowing into the battery will diminish to the one or two amps needed to keep the battery fully charged.

This action is done by the controller in the alternator which arranges to reduce the output voltage of the alternator.This action is caused by the reduction in the voltage difference of the output of the alternator and the rising voltage of the battery.

So there may be nothing wrong with your alternator & battery at all.


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This is why an ammeter is a better diagnostic tool that a voltmeter for alternator problems.

If your battery is running down when you have full lights and fan on, it is probably not because of a FAULT in the alternator, merely that you need one with greater output.

billwill wrote:It's not really the voltage that you want to check, it is the Current that is flowing from the alternator to the battery shortly after startup.

It should be around the rated output of the alternator in Amps.

As the battery recharges the power lost during startup, the current flowing into the battery will diminish to the one or two amps needed to keep the battery fully charged.

This action is done by the controller in the alternator which arranges to reduce the output voltage of the alternator.

.

Bill,

Don't want to seem picky, but that isn't how it works. An alternator is a constant voltage source - as long as it is spinning fast enough and you don't draw too much current, the internal regulator will do its best to keep the alternator output somewhere around the 13.8V level.

The reason a battery draws less current as it charges is its internal cell voltage rises as the battery charge state increases. A 'flat' battery might have an open circuit voltage of 12V, a fully charged battery will float at around 13.6V. It is the difference between the alternator output voltage and the battery internal cell voltage which controls the amount of current flowing into a battery.

As the battery charges, the internal cell voltage increases, the difference between this and the alternator output voltage decreases and the charge current goes down.

OOOps, yes you are right, so I have re-edited the message above to avoid leaving a false impression, only one sentence was wrong really so it now reads.:

This action is done by the controller in the alternator which arranges to reduce the output voltage of the alternator.This action is caused by the reduction in the voltage difference of the output of the alternator and the rising voltage of the battery.

We don't seem to have a strike-out font on this forum, so I've made the error sentence tiny.

Which brings us back to the original question which can be summarised as:

An old alternator and a brand new one both seem to generate only 13 volts instead of 13.8 volts in the OP's car.

One common factor here is the voltmeter! Have you checked that it is reading correctly?

And I still think it is more important to check the current flow to and from the battery with an ammeter rather than fuss about the voltages.

Yes. Have checked with another volt meter. Same results. I will try and check some of the suggestions tomorrow.

Thanks for all the help.

A quick update on the alternator charge issue. I haven't had a moment to do much investigation but was out for a drive and popped the bonnet to check the oil. I noticed a white wire to the starter solenoid was loose. I pushed it on and kept driving. When I got home I checked the alternator charge and it was up at 14v! So I think nmaudit's post may have been on the money. Does this sound like the likely cause. Also noticed the alternator wasn't hot.

Had a great drive as well.

Thanks for all your help.

andyhay wrote:A quick update on the alternator charge issue. I haven't had a moment to do much investigation but was out for a drive and popped the bonnet to check the oil. I noticed a white wire to the starter solenoid was loose. I pushed it on and kept driving. When I got home I checked the alternator charge and it was up at 14v! So I think nmaudit's post may have been on the money. Does this sound like the likely cause. Also noticed the alternator wasn't hot.

Had a great drive as well.

Thanks for all your help.

That doesn't make much sense, I regret, unless the white wire was somehow shorting to Earth.

Normally there is only one thin wire to the solenoid and it is only activated by the start-position of the ignition switch. If the car starts that one is OK.

If you have a 'ballasted' ignition coil, then the solenoid would have an extra output terminal to connect direct to the coil instead of the normal route through the ballast resistor. (this bypass wire might well be white). Its terminal on the solenoid is merely another output contact and is only live while the solenoid is activated.

So as far as I can deduce that was not the cause of your original problem, and indeed it seems that there really was no problem anyway, your alternator seems to be working as designed; it was merely that you didn't drive long enough on your earlier tests.

I'll take a photo of the wire in question. Maybe it's not the solenoid - I'm the first to admit my knowledge of such things is lacking. I had taken the car on many long drives previously.

It was the white wire in this photo (not my car - photo from google search)

Check the conection of the brown wire at the solenoid. A loose connection can cause a high resistant connection which will result in heat.