Author Topic: Type 3 (Fastback) Generator voltage question  (Read 221 times)

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Offline kinggeorge13

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Type 3 (Fastback) Generator voltage question
« on: August 24, 2017, 08:29:39 PM »
1967 Fastback with original 1600 engine, dual carbs, 30amp 12v generator, original Bosch regulator.   Our red warning dashlight came on and does not go out until we shut off engine.    Took a voltmeter first to battery to see how things look.   Engine off the battery is over 12.5 volts.  Start engine, idling and drops to around 12.2 volts (hmmmm) and rev engine to ensure generator is generating and voltage at battery drops to almost exactly 12 volts.   So it's not charging at all and the battery is basically supplying all the voltage for running the car, spark plugs, etc.   Check the input to the regulator from the generator and at fairly high revs it's producing no more than 6 - 8 volts on my digital voltmeter and the output of the regulator (B+) is basically less than a volt or two.   There is a procedure in the Bentley on how to disconnect the generator from the regulator (only for a few short test seconds cuz apparently this test can burn out windings if you keep it going) to test the output from the generator and it showed 6 - 8 volts at around 1000 - 1300 rpm and if we really revved the engine (3000rpm) it got around 10 volts on our digital voltmeter but the manual said you should get more than 30 volts with no regulator at high rpms.   I'm wildly assuming that my digital voltmeter is reading the output of this kind of generator accurately and I don't need to find an old-style voltmeter with a needle that sweeps across the scale to read these voltages.   

Time to find a new generator?
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Offline kinggeorge13

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Re: Type 3 (Fastback) Generator voltage question
« Reply #1 on: August 25, 2017, 06:41:32 AM »
Oh yeah and we did a kinda dumb thing without measuring total current but we added a couple of small fog lights with H3 bulbs which would draw some considerable extra current (55W each at a total current draw of around 4 x 2 = 8 amps).   With the generator only rated at 30 amps I'm sure we were pushing the limit total.   Everything worked and drove for a couple days/nights with all lights on but it seems like a bit much of coincidence that suddenly we then started suddenly having this problem.   
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Offline BUSDADDY

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Re: Type 3 (Fastback) Generator voltage question
« Reply #2 on: August 25, 2017, 07:38:46 AM »
Did you inspect the brushes?, if there is no brush sticking up higher than the holders they are worn out. While you are in there look closely at the end of the commutator where it meets the windings of the armature, any fresh shiny solder visible? If the regulator F'd up or the Df wire shorted out it may have melted and thrown the solder from an overload.
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Offline kinggeorge13

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Re: Type 3 (Fastback) Generator voltage question
« Reply #3 on: August 25, 2017, 09:07:30 AM »
I did inspect the brushes and they are up above the holders by a little over 1/4" and I ordered a new set last night just to see if I would be lucky but I don't have a lot of faith that will be the answer but worth a shot.   I don't see any obvious problems at the end of the commutator but I would say I have to wonder a little at how good the connections are from the braided wire that comes off the brushes to where they are screwed in as there is visible green corrosion there.   

Another thing I should have mentioned and just thought about there was one night (1st night with the new 55w foglights) when we turned off the engine and the red dash indicator came on and stayed on even with the key out.   I restarted the engine, turned it off again and the light went out and I thought that was both curious and possibly not good but it never reoccurred so I pushed it to the back of my mind.  Now I see in the Bentley that is caused likely by the points/contacts in the regulator being stuck/welded shut by too much (or too long) arcing and don't open properly when the engine shut off.   So that just feeds my feeling that I've had too much current (or too much current for my aging electronics) with my additional lights and I've likely damaged the contacts inside the regulator so I've gone ahead and ordered one of those as the one in there looks very original and I'm sure I've done at least some life-shortening damage to it's contacts even if it ends up not being the culprit of this no recharge problem. 

-George
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Offline BUSDADDY

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Re: Type 3 (Fastback) Generator voltage question
« Reply #4 on: August 25, 2017, 09:42:00 AM »
Yes that sounds like stuck contacts in the reg, but if grounding Df didn't get you 30+ volts there may be issues in the generator as well. Fingers crossed for you the regulator does the trick, if not there's deeper tests and potential repairs that can be done, but do the easy stuff first.
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