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Post by Simon H on Feb 24, 2018 19:15:30 GMT
Advice please. On a car with a dynamo charging system what is likely to be going wrong when it needs LOTS of revs to get the charging light to go out? (It's a long, long time since I had a car with a dynamo...)
TIA
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Post by lagain on Feb 24, 2018 21:15:24 GMT
It could be the output from the dynamo, or lack of it - bushes ?
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Post by Simon H on Feb 24, 2018 21:50:09 GMT
Thankyou. That's feasible given that the car (and presumably the dynamo) is 47 years old. I suppose things do wear out eventually...
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Post by petervdvelde on Feb 24, 2018 21:53:25 GMT
Best to check what the voltage is when the light goes out. If it is above 12V then the dynamo is charging but not very good. The usual suspect are the voltage regulator and the brushes. The brushes on a dynamo requires more maintenance as the current is higher compared to an alternator. Check the brush length and see if the area on the rotor is clean.
The voltage regulator, especially if it a mechanical one can have issue's. I would think an electronic one either function or is broke and not functioning half. If you dismantle the dynamo, you can also check if the coils on the rotor are partially burned.
A rover has a device connected to the control light and that could also be faulty but i haven't seen this very often. Measuring the voltage gives a lot of info.
Peter
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Post by Simon H on Feb 24, 2018 22:50:55 GMT
The car in question is a 1971 Morris 1800 (landcrab). I would have thought by 1971 BMC would have seen fit to equip all their cars with alternators but this one has a Lucas dynamo. I have now found a detailed diagnostic test procedure for dynamo output and voltage regulator performance. I have bought the car to have something to take to shows whilst my P5B saloon is having some restoration work done. I'm a bit worried that if I start 'doing things' to it I may become attached. I don't need another money pit lol  |
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Post by richardlamsdale on Feb 25, 2018 11:56:22 GMT
Ooh, a landcrab! I used to think they were very odd cars when I was a child, but as I've got older nostalgia has taken-over. I now find myself secretly admiring old British cars like the landcrab and 3-litre, as they seem to encapsulate so much about what was good and bad about the 1960's and 70's in Britain (same as the P5/P5B I guess).
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Post by harvey on Feb 25, 2018 12:42:16 GMT
The car in question is a 1971 Morris 1800 (landcrab). I would have thought by 1971 BMC would have seen fit to equip all their cars with alternators but this one has a Lucas dynamo. Save yourself all the bother of testing and fixing, convert it to an 18ACR alternator. |
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Post by Simon H on Feb 25, 2018 22:04:03 GMT
It's positive earth, just to make things interesting...
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Post by harvey on Feb 25, 2018 22:06:02 GMT
It's positive earth, just to make things interesting... It does, but there are +ve earth alternators, (just not ACR ones AFAIK) and altering the polarity is possible as well. |
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Post by djm16 on Feb 28, 2018 22:54:36 GMT
If the charging issue came on relatively suddenly (over less than 100 miles) then suspect the brushes. If however it has been a bit slower to come on, then it is possible the voltage control contacts in the regulator are either damaged, dirty, or not fully closing.
The easiest test it to jumper a wire between D and F terminals on the regulator without removing any other wires. If when you start the engine and rev it a little your ammeter goes over 30A, then the regulator is the problem.
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Post by Simon H on Mar 1, 2018 17:48:52 GMT
Thanks for the replies. I am awaiting warmer weather before I investigate further. I inherited the problem with the car so I don't know how it developed. What I have found in the few miles I have driven the car is that sometimes it needs loads of revs to get the charging light to go out (and keep it out) and other times the revs can drop to tick over before it comes back on and only needs about 1,000 rpm to get it to go out. I will report back when the snow clears off.
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