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Alternator over-voltage on tick-over

Our narrowboat built in 1999 with a Beta 37.5 HP engine has two alternators - the 40A charging the starter battery and the 80 charging the domestic bank (3 X 110) via an Adverc controller.
Before the start of the cruising season I fitted 3 X 100W solar panels connected via a Victron MPPT controller (the adsorption voltage limited to 14.25V) - mainly so we could leave the boat with the fridge running when away.
This worked fine until the 4 days into our summer cruise when with the engine on tick-over there were two loud bangs. Found cases blown off (gel) batteries. Called out Kings Lock Chandlery as they were nearby - they replaced 3 batteries and checked the charging voltage which was OK but two days later, again on tick-over - the Adverc green lamp started flashing indicating an over-voltage warning. I unplugged the Adverc as recommended when alternator's own regulator should take over (14v) but the meter was still showing 15v. I then disconnected the alternator to prevent further damage and relied on solar panels to run the domestic circuits for the next 5 weeks till we got to Stoke on Trent Boat Builders where we were booked in for re-blacking.
They sent the alternator to a specialist repairer and refitted it. Everything seemed to be OK but I kept monitoring the voltmeter. After 2 days at 14V it started moving between 14.25 and 14.5 V (as Adverc's "what to expect" instructions* predict) but whenever the revs dropped to tick-over the voltage rose to 14.5 and up to 14.8, dropping again as soon as the revs increased. This seems illogical.
I Unplugged the Adverc but still there is still an increase in voltage on tick over
Could the installation of the solar panels have caused the alternator and/or the Adverc controller to fail or was it just coincidence with a 19 year old system? On thinking back the alternator had over the past year been taking increasingly longer to "kick-in".
I have since found that the excitation connection on the domestic alternator is supplied from the starter battery via the "ignition" switch - connecting a lamp between the main output and the excitation terminal limits the voltage rise on tick-over.
Any suggestions or advice, please?

Asked by: JDR Lloyd  | 6.01pm, Saturday 6 April

WW says:

It sounds as though the alternator regulator is being confused somehow; the solar panel fitting should not have affected it and is merely a coincidence.
I am attempting to find some detailed information from Adverc in an attempt to give a more detailed analysis.

Rupert Smedley  | 3.04PM, Sunday 7 April

I have checked the Adverc manual and it looks as though the regulator fitted to the alternator is faulty. The Adverc provides enhanced battery charging by boosting the alternator output when the standard regulator has shut down. It cannot however reduce the output resulting from the standard regulator; which in this case is giving a higher voltage.
The solution is simple; remove the regulator in the alternator (or disconnect it from the field/rotor connection) and just use the Adverc.

Rupert Smedley  | 11.58AM, Tuesday 9 April

Although the alternator was serviced and maybe had a new regulator fitted; it would probably have only had a basic operational check.

Rupert Smedley  | 2.52PM, Tuesday 9 April

Readers say:

Thanks for the advice. The repairer bolted on a new external regulator on with a wire emerging from it and disappearing into the body of the alternator but I suspect just cutting it would be too simple - I'll probably have to remove the alternator to identify the regulator connections and where the additional Adverc connection has been made.

JDR Lloyd  | 4.46PM, Tuesday 9 April

Fitted new alternator - same model (no Adverc connection) - but still getting 15V on tick-over - so what else could be causing the problem?

JDR Lloyd  | 11.09AM, Saturday 20 April

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