Underperforming Balmar alternators

[Celestialsailor]

I'm not sure if it had been asked but how old is the battery bank and what shape are they in?

[Dedzaboy]

Aha! Well despite the fact that this is going to make me look pretty stupid, I'll tell you what the problem was...having stated that my meter was correct and that the batteries were down around 200ah and should therefore be demanding more from the alternator, it would appear that I was wrong! We turned off all power sources (solar and wind), turned the fridge up, left a few lights on and went to bed. In the morning the battery voltage was down to around 12.4V, and on starting one engine the alternator was producing 65A, the highest yet seen. The other engine on it's own produced about the same, although with both running together there was no real difference.
Further, having done a voltage drop test across both the negative and positive sides of each alternator/battery bank, it seems I have a drop of around 1V on the negative side - very bad according to Mr Calder. Cable sizes are fine so must be poor connections somewhere, that's tomorrow's job...
We're hauling the boat in a few days so will have mains power and can therefore fully charge the battery bank and recalibrate the Mastervolt meter.
Many thanks for everybody's help and opinions, and a very Happy New Year to you all!

[Dedzaboy]

Celestial Sailor,

Batteries are 4 x 130ah AGM, 18 months old and in good condition.

[Dedzaboy]

Final comment regarding the Blue Sky charge controller: it doesn't appear to affect the alternator regulator at all - having disconnected the solar input at first, while testing the alternators this morning, I reconnected it and the controller immediately did nothing, i.e. it didn't try and send any power to the batteries presumably because the voltage was too high and it decided it wasn't needed. As soon as the engines are turned off the controller allows solar power again.

[senormechanico]

Find that 1 volt drop and I believe you're golden.

Steve B.

[hellosailor]

"it seems I have a drop of around 1V on the negative side - very bad according to Mr Calder."
Not only "very bad" but totally unacceptable to some of us.[g]

Loose or corroded lug/terminal, or internal corrosion in the cables if they are not tinned. Assuming they are a heavy enough gauge. The drop is JUST in the negative cabling? How long a run of what gauge?

[Dedzaboy]

Yes, obviously unacceptable and it shall be remedied! That was my point. There is a smaller voltage drop on the positive, 0.4V, so I will attempt to remedy that also. The run is around 15ft each way, unsure of the AWG of the cable but it's thicker than my thumb so surely adequate.

[S/V Elusive]

M38A - The wiring will have the gauge imprinted on it ... something like 2/0 .