Hi all, looking for some help to solve an ignition warning light/alternator problem on my Felicia. Driving to the shops recently I could hear a whining, consistent with engine revs increasing/decreasing. On parking I checked the belt, OK., but I noticed that the ignition warning light stayed on (dimly) even when switched off. Luckily the car restarted and I could drive home.

I've since removed the alternator and replaced the voltage regulator/brushes assembly, as one of the brushes was much more worn than the other. However, the problem still remains, even with the new brushes etc. in that the warning light stays on and increases in brightness with engine revs. However the warning light no longer comes on when the ignition is switched off, so hopefully I don't need to worry about flattening the battery when the car is not being used.

My next thought is perhaps the diode assembly is faulty, but before I go ahead and order a new assembly, I'm wondering if perhaps it would be wiser to simply buy a replacement alternator?

Anyone have any suggestions/ideas?

Thanks!

Increasing battery light as engine revs increase is a tell tale sign of BAD RECTIFYING DIODES

Buy a new alternator or refurbish the existing one if you're on a tight budget.

On 08/07/2021 at 11:39, Sympol said:

My next thought is perhaps the diode assembly is faulty, but before I go ahead and order a new assembly, I'm wondering if perhaps it would be wiser to simply buy a replacement alternator?

 

 

Check with a multimeter the V that comes from the alternator and buy a pair of diodes, this way is far simplest and cheaper

if that won't work then you can visit an electrician to check the rectifier the reel and the spiral if can refurbished.

 

Keep in mind that if you buy a new BOSCH alternator the regulator of your old one WILL NOT fit on it so i case that in the future you will need a new one you have to go to a BOSCH parts store.

On BOSCH the regulator is not easily visible and accessible as in the stock one !

Yes, if the rectifying diodes are on their way out, the alternator will be trying to charge the battery with AC.....which it doesn't generally like.  Get a multimetre, put it into AC mode, one point to ground, the other to the positive and see what the AC voltage is....if you have varying AC voltage, you definately need new rectifying diodes or a new / changed alternator.

There are usually 2 sets of diodes in an alternator. A big hefty set of six that rectify the output that charges the battery and supplies the vehicles electrical requirement. The second set of three or six are small diodes that supply the voltage regulator and power the field coils. When one of these go open circuit, the voltage regulator loses its ability to regulate at the correct voltage. The light on the dash is connected between the output of both sets, so a dimly shining light indicates an open circuit diode somewhere. If you measure the battery voltage with the engine revving, and the voltage is too high its one of the small set that's gone, if its too low then its one of the big set. If its one of the small set, then voltages can reached 18 or more volts which is extremely dangerous both for your cars electrics and the batterywill get super hot and boil over, (which I've seen happen) and boiling sulphuric acid will make a mess of your car, believe me. Under no circumstance touch it if you see any acid!

 

The small set of diodes may be hand wired internally and be difficult to access.

 

https://www.pinterest.co.uk/pin/391672498829116541/

 

If I were you I'd just source a replacement alternator, unless you have the right tools and skills to strip and fully refurbish your alternator. And its probably cheaper.

Edited 12 July, 20214 yr by xman

Thanks for the responses. I've checked around and rather than buy a used alternator from a wreckers yard, or a set of replacement diodes, I've opted for a new alternator, as the price differential is not that great. And now I've got a spare voltage regulator if I ever need one. The new alternator is on the way to my local (20km distant) collection point, so it looks like a decent cycle trip in the next few days to collect it - I don't want to use the car in its current condition and risk any further damage to the electrics....

Thanks again for the responses

2 hours ago, Sympol said:

 And now I've got a spare voltage regulator if I ever need one.

 

The new alternator is the same with the old one?

8 hours ago, Sympol said:

current condition and risk any further damage to the electrics....

correct decision

On 13/07/2021 at 11:14, D.FYLAKTOS said:

 

The new alternator is the same with the old one?

Yes, it's from the same supplier, so a direct replacement, thanks.
Installed the new alternator this morning and everything back to normal. Thanks all for comments/suggestions