Alternator overcharging at 18.5 volts

Talk about the E-Type Series 3

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SESH
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#1 Alternator overcharging at 18.5 volts

Post by SESH » Sun Aug 30, 2020 12:31 pm

My series 3 alternator is overcharging the battery at 18.5 volts. The battery is warm and the battery is hissing with vapour, so not using it. I have ordered a new voltage regulator. The alternator was overhauled and reconditioned about 1000 miles ago. Are there any other things that can cause this.
Thanks
Mike
1973 Series 3 OTS Signal Red

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MarekH
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#2 Re: Alternator overcharging at 18.5 volts

Post by MarekH » Sun Aug 30, 2020 2:48 pm

If you look at one of my previous posts, the operation of the regulator is explained.

Basically, the field coil current is too high on average. Instead of switching on and off continuously, it is staying on continuously. Either it is sensing that the battery voltage is too low or the the big transistor is continuously conducting.

Trace through why either of those two conditions is true and you have your answer as to why it is overcharging.

kind regards
Marek

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#3 Re: Alternator overcharging at 18.5 volts

Post by SESH » Sun Aug 30, 2020 4:51 pm

Thanks Marek,
To the electrical novice, will the replacement of the voltage regulator cure the problem or could something else be going on?
Mike
1973 Series 3 OTS Signal Red

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#4 Re: Alternator overcharging at 18.5 volts

Post by MarekH » Sun Aug 30, 2020 6:12 pm

Dear Mike,

You should at least attempt to isolate where the problem is before spending money first.

The last time someone came on to this forum with the same problem, it turned out that the electrical connector was corroded and broken, so it under reported the battery voltage back to the regulator, so buying a new regulator would not have solved the problem.

Use the wiring diagram and a long spare wire and an ohm meter to determine via loopback tests whether the harness and its connectors are sound first. Without the right input, a correctly working regulator doesn't give the right output. You may simply find that the 12v battery connection to the regulator is poor.

kind regards
Marek

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SESH
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#5 Re: Alternator overcharging at 18.5 volts

Post by SESH » Sun Aug 30, 2020 6:54 pm

Thanks Marek,
Appreciate your advice, as always.
Kind regards
Mike
1973 Series 3 OTS Signal Red

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