Alternators, do you need a spare one.

That is a question that was on a french sailing site and I could not refrain posting something I will summarise here as, from past experience I would not leave again for a long cruise (trans-alantic is the perfect exemple) without one and ready to be used.

Here is the reason.

This is the right picture and A1 is bottom right, A2 top left.

During the 2011 ARC crossing there were 2 alternators (A1 and A2) installed on the Volvo D2-55 we have on board. One was for the motor bank and the second one for the house bank. To boot we had 2 100W solar panels, a wind turbine (Aerogen 4 that wasn't not powerfull enough) and ... a power generator (MasterVolt Wisper 2500). What some would call 'belt and braces'. Despite all this redondancy we lost the batteries that discharged too much! But his we learnt only when in Ste Lucia and after 25 days of electrical problems when the solar panels associated to the wind turbine were not enough to keep the batteries up. Hence  during the crossing from France to A Corugna we ran the engine 3 hours a day BUT the batteries didn't charge and we didn't see it before it was too late.

Question: WHY did this happen?
Answer: Because of a full raft of reasons.

The house bank alternator (A2) was not excited by the output of the motor bank one (A1) as the wiring was wrong. As a result it never 'started' and with 800Ah in this bank we never realised it during 18 months of short cruises. There were no monitoring light installed on the two alternator output hence we could not know A2 was not delivering. The A2 alternator was poorly fixed and went a bit loose, hence the belt was not tense enough. It didn't really matter as there was no delivery BUT it could have been the reason if the wiring had been done right. As said before the wind turbine was not powerfull enough The solar panels (100W x 2) didn't deliver enough. I did a previous posting on this topic (click here) and my opinion is that solar panels are "just not enough". On the MasterVolt Wisper 2500, the exhaust temperature probe had a defect and the generator stopped functioning after 5 or 10 minutes. This we sloved by removing the probe and welding the wires so that the monitoring device received an OK signal. There was no risk doing it as it was a "well known bug" as explained by a technician we called on Iridium and the exhaust temperature was OK. Bad luck may be ...

What we did;

We used the switch between A1 and A2 and topped up the house bank using the A1 alternator. After topping it the switch was put back in its initial position to avoid draining the motor bank too. Just imagine the engine not starting because of drained batteries ...

We had the A2 wiring being fixed in A Corugna, where we arrived during a week-end followed by religious days-off, BUT when this was done A2 started becoming hot, some smelly smoke went out and A2 died. Then we changed it and ended up with a 7 days stop-over.

We tweaked the power generator as explained and used it in combination with the engine but almost never at the same time as it didn't help to have them both running.

We closely monitored the batteries' status, every 2 hours, and logged the result in the log-book because the batteries having discharged too much could not keep the charge, forcing us to run engine and power generator twice a day.

We, of course, reduced the electricity consuption to the minimum and did 90% of the crossing using a wind vane (Hydrovane) and not the pilot.

Lessons learnt:

Never trust  marine electricians when they add something on a boat. Ask for a fully documented diagram of what has been done (and pay only when you have the diagram and the test results), THEN check by yourself it works.

Always have 2 alternators with an emergency switch between both in case one dies. Having a spare one is OK but you will have to put it in place, redo the wiring (with some welding in a pounding sea) and so on ... It is much better to have it reday to be used.

Always have some kind of monitoring of the output of the alternators: a control light on each output line is enough.

Check regularly the batteries level and output and log the result in the log-book.

If you plan to buy a wind turbine, take the most powerfull one.

If you use solar panels, don't bet the farm on them. They are fine but it is just an 'addition'.

Always remember that (1) "everything that could go wrong will" (2) as a French President used to say "les emmerdes, ça vole en escadrille", which litteraly translates into "bloody nuisances always fly like fighter squadrons" (3) the 'domino effect' always makes things worse and (4) keep your fingers crossed.