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Old 1 Week Ago   #1
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Generator light on but battery charging.

So, fancying a drive in the 500 today I go out to my garage and start the car but when reversing out I notice that the generator light is staying on. At this stage I'll admit that I'm no auto electrician, however, I've poked about a bit checking everything looks to be in place, all looks OK, then I connected my multi meter across the battery; engine off 12.54v, engine running at fast idle 13.6v so the dynamo is charging but why is the light staying on?
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Re: Generator light on but battery charging.

Quote Originally Posted by IanEmery View Post
So, fancying a drive in the 500 today I go out to my garage and start the car but when reversing out I notice that the generator light is staying on. At this stage I'll admit that I'm no auto electrician, however, I've poked about a bit checking everything looks to be in place, all looks OK, then I connected my multi meter across the battery; engine off 12.54v, engine running at fast idle 13.6v so the dynamo is charging but why is the light staying on?
Hi Ian you need to check the voltage at the generator indicator light. It should be roughly the same on both terminals on the bulb. One side comes from, the green wire, from the voltage regulator, it's on the same terminal on the VR as the dynamo output, the other wire comes from a constant 12v+, ultimately from the fusebox. Both terminals the same you get no potential difference, so the bulb stays off. If the output from the dynamo drops a bit, like at tickover, you get a slight potential difference hence the generator light glows weakly.

Tony
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Last edited by Vitesse; 1 Week Ago at 22:14.
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Re: Generator light on but battery charging.

I'd consider new brushes in the dynamo....
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Old 1 Week Ago   #4
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Re: Generator light on but battery charging.

Quote Originally Posted by Vitesse View Post
Hi Ian you need to check the voltage at the generator indicator light. It should be roughly the same on both terminals on the bulb. One side comes from, the green wire, from the voltage regulator, it's on the same terminal on the VR as the dynamo output, the other wire comes from a constant 12v+, ultimately from the fusebox. Both terminals the same you get no potential difference, so the bulb stays off. If the output from the dynamo drops a bit, like at tickover, you get a slight potential difference hence the generator light glows weakly.

Tony
Tony, Thanks I'll check this tomorrow.
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Old 1 Week Ago   #5
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Re: Generator light on but battery charging.

Quote Originally Posted by IanEmery View Post
engine running at fast idle 13.6v
Ian, if you read Mattsdad's sticky about dynamo chargng, I think your 13.6V is only just past the point where the cutout connects the output of the dynamo to the IWL. So it sounds like Andrew is pointing you in the right direction; at least there is probably something wrong with the dynamo, maybe even a bad connection or terminal.
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Last edited by fiat500; 1 Week Ago at 23:00.
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Old 1 Week Ago   #6
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Re: Generator light on but battery charging.

Quote Originally Posted by AndrewHarvey View Post
I'd consider new brushes in the dynamo....
Andrew, thanks. Although fine with mechanics I'm not at all electrically minded, and long ago forgotten all that was taught in science lessons, and before I get the spanners out, could you please explain why you think I need new brushes
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Re: Generator light on but battery charging.

Carbon brushes wear to the shape of the dynamo commutator. Springs push them onto said comm. When at end of life - brushes are not getting full contact....so voltage is still there .....current (amps) are not.
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Re: Generator light on but battery charging.

Quote Originally Posted by fiat500 View Post
Ian, if you read Mattsdad's sticky about dynamo chargng, I think your 13.6V is only just past the point where the cutout connects the output of the dynamo to the IWL. So it sounds like Andrew is pointing you in the right direction; at least there is probably something wrong with the dynamo, maybe even a bad connection or terminal.
Peter, thanks. When I took the reading of 13.6v the engine wasn't very much above a fast idle. Are you suggesting that I should run the engine higher to see what the maximum charge output would be? Would this give any other useful info? I wasn't taking continuous readings but I can confirm that the light was still on at higher engine speeds.

Tomorrow, as a first step, I'll run it up a bit faster while keeping an eye on the multimeter, also follow Tony's advice re the IWL plus check all terminals for cleanliness and contact.
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Re: Generator light on but battery charging.

Quote Originally Posted by AndrewHarvey View Post
Carbon brushes wear to the shape of the dynamo commutator. Springs push them onto said comm. When at end of life - brushes are not getting full contact....so voltage is still there .....current (amps) are not.
Andrew, thanks for that explanation, I see the need Now, through the fog of time, I remember rebuilding dynamos with my father broken piece of hacksaw blade carefully cutting the commutator segments, I hope it all comes back when doing it again fifty odd years later!
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Re: Generator light on but battery charging.

Quote Originally Posted by fiat500 View Post
Ian, if you read Mattsdad's sticky about dynamo chargng, I think your 13.6V is only just past the point where the cutout connects the output of the dynamo to the IWL. So it sounds like Andrew is pointing you in the right direction; at least there is probably something wrong with the dynamo, maybe even a bad connection or terminal.
The output relay in the VR operates at 12.6v + or - 0.2v. To me what Ian is seeing at battery sounds ok and suggests the dynamo is fine. the fact the voltage at the battery rises when rev's increase suggests that as well.

The generator light is reliant on voltage and potential difference across it. It has absolutely no interest in the current output of the dynamo, in reference to another later post from Andrew.
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Old 1 Week Ago   #11
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Re: Generator light on but battery charging.

Quote Originally Posted by Vitesse View Post
The output relay in the VR operates at 12.6v + or - 0.2v. To me what Ian is seeing at battery sounds ok and suggests the dynamo is fine. the fact the voltage at the battery rises when rev's increase suggests that as well.

The generator light is reliant on voltage and potential difference across it. It has absolutely no interest in the current output of the dynamo, in reference to another later post from Andrew.
Thanks again Tony. So, following your earlier posting, what do I need to do if there is a difference in the voltage readings across the generator bulb connections?

I've just had the fuse box out and cleaned all connections thoroughly due to chasing some strange front light problems which needed sorting for the MOT and turned out to be bad earths, so I'm confident there are no problems there.
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Old 1 Week Ago   #12
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Re: Generator light on but battery charging.

Depends Ian which side is lacking the 12v +? If it is the green wire that goes back to the voltage regulator terminal 51, that is the shared output terminal that has the dynamo output. So worth checking the voltage there to earth but I would imagine that is ok. If it is ok at terminal 51 but not at the end of the wire at the generator light, physically follow the wire back through the loom as best you can. There are some bullet connectors where the rear of the loom comes from the back of the car into the bonnet area, just behind the fuse box, make sure it is getting a good connection there. Then it runs to another set of bullet connectors behind the speedo. Again check for a good connection there.

The other terminal for the generator light is supplied voltage via a generic connection that supplies 12v's for the oil pressure light and the fuel warning light if they both work ok then the you will have 12v's to one side of the generator light as well. It's a light blue wire that plugs into a socket on the rear of the speedo, pull it out and check for voltage there to earth. Ultimately that light blue wire goes back to the fuse box terminal marked 15/54 so measure it there as well if nothing at the speedo.

It's the one of the two light blue wires in the picture below that feed the speedo 12v's for the oil pressure light, generator light and fuel warning light. It's possible the other two aren't working and you don't realise it yet especially if you have had problems at the fuse box? The other light blue wire goes to the ignition switch for the lights.

I have checked the wiring diagrams for the difference between the D and the F and it says the wires are the same colours on both, so hopefully you should be able to sort it.

Tony
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Old 1 Week Ago   #13
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Re: Generator light on but battery charging.

Quote Originally Posted by IanEmery View Post
Are you suggesting that I should run the engine higher to see what the maximum charge output would be?
Yes I am Ian...for the effort it takes I would just want to check you're actually getting your full 14.something volts. I had the situation a while ago where I had the opposite and it was was up at nearly 16V.

It sounds like Tony has this matter in hand but I recommend that if you haven't, that you download the "Mattsdad" sticky as it logically sequences all that might be wrong including the downright obvious and the most technically challenging possibilities. "Good for Mattsdad (and Tony)" I say.
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Re: Generator light on but battery charging.

Quote Originally Posted by Vitesse View Post
Depends Ian which side is lacking the 12v +?
I hope you've told Ian if you're charging for all this illumination Tony. Just a warning to him that otherwise he may see red at the upset your invoice generates.

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Old 6 Days Ago   #15
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Re: Generator light on but battery charging.

Thanks again everyone for all the help.

Now, 1st thing I did today was I checked the battery voltage reading again; resting voltage = 12.54v BUT raising up to about 15.8v at high engine revs! Aha I thinks, never mind the generator lamp for a minute, is there a problem with the voltage regulator (please remember here, I know nothing (as Manuel says!)) so I cleaned all the terminals on that, even exchanged the VR from my '64 car but I've still got the same problems!

Unfortunately other business stopped play for today at that stage.

I'll be reading Peter's postings regarding his high voltage problems later tonight as I think that needs sorting ASAP but the car now has too wait as we are away until next Monday. When we're back I'll get onto checking the wiring as Tony suggested.
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