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Alternator charging at excessive voltage

Ian on Leo

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We have a Beta 43 engine with twin alternators. The domestic 150A alternator charges four domestic AGM batteries which are now just over 2 years old. The boat and the alternator are nearly 9 years old. Normally the domestic alternator charges at a voltage ranging from 13.8 to 14.5 volts. On a recent trip it was charging at 14.8 to 15.2 volts. The batteries were not hot after several hours at this charging rate. I have no way of measuring the current at which it was charging.


Should I be worried about this and what might be the reason?


We have no separate regulator between the alternator and the batteries. We do have a solar panel (100W) charging the same four batteries through a regulator. The solar installation is also about 2 years old.


Any ideas?

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Suggest you fix this quick


"Charging voltages over 14.7 volts can prematurely dry the battery by boiling out electrolyte, and increase risk of a battery hydrogen gas explosion."




Looks like the alternator has a faulty voltage regulator.

Edited by Tiggs
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Certainly the Iskra 175 amp alternator has a peak charge voltage of 14.6 volts.


I understood from the Beta engineer that attended our 150 amp alternator that they were troublesome. We had 3 in 2 years under warranty and then they said we were being upgraded to the new larger one.

Edited by pearley
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A new regulator shouldn't cost much. The last I got for an Iskra alternator cost me about £15 from a motor electrics specialist I use in Loughborough. He fitted it and tested the unit as well, at no extra cost!

I was getting a failed unit repaired as a spare, having got a new one from Beta so didn't want to spend a lot on it.

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You could fit an advanced external regulator or even an alternator to battery charger.



On the first option the duff regulator would probably over rule the external one, you normally leave the internal one in circuit and the highest one controls the alternator, on the second would it be happy having a higher voltage coming into it.?

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Many thanks for all the suggestions. I've taken the alternator off the boat and will take it in for testing when I have time. Fortunately we don't do a lot of cruising in the winter so I've plenty of time to get it sorted before next Spring. It is reassuring to hear thata new regulator won't be too expensive.


Thanks again.

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