How to kill a battery bank, 25 May 2021

 I noted at the end of the last season that my service batteries were not really holding their charge. At night particularly, since the solar panels were not producing any electricity. From Cherbourg, we mainly sailed at night, and every time, after a few hours at night, I was getting an alarm indicating that the voltage of the batteries was getting too low. 

If I ignored the alarm, after another half-an-hour, the whole system would collapse, to the extent that I had even difficulties to start the engine! Not to mention that when starting the engine, I had another alarm for a too high voltage. So what was going on?

In Cherbourg, I was advised by Alubat to contact their partner, Aries-Bateaux. The manager was initially extremely nice and helpful, promising me that during the wintering of the boat in Cherbourg, he would have ample time to take care of this. As no progress was done, I kept contacting him, and he always ensured me that he would take care of it before I come back early May. And he never did! I hope that Alubat will draw the lessons concerning how their partner in Cherbourg is badly treating OVNI owners there!

In Aber-Wrac'h, I consulted a mechanic who would use a voltmeter to check the batteries after they had been charged, and told me that there was no problem with them even though he did not disconnect them from one another. 

But the problem continued to the extent that I had to use my engine during part of the night sailing just to keep the chart plotter functioning. 

My electrician in Sables-d'Olonne checked the batteries using MasterAdjust software. He noted a couple of things:

• I had the equivalent of 90 full cycles in the life of the battery bank, and this is not much. He mentioned that batteries can go up to 900 full cycles before dying of old age. But they can die from other causes...
• The highest voltage that the batteries encountered was indeed over 15 volts, which is neither good for them not for the electronic equipment. This corresponded to the "hypertension" alarm related to the hidden missing black cable.
• The lowest voltage encountered in the life of the battery bank was 7.4 volts, which is extremely low. He indicated that it is usually hardly recoverable for the batteries. 

So, before declaring the batteries dead, he decided to conduct a load test on the service battery bank. We disconnected all sources of power (charger, solar panels, wind mill...). Then we switched on all equipment that we could and reach a consumption of 16 Amp/h. Then we started monitoring on the MasterView the remaining charge and the battery bank voltage. With four service batteries of 90 amps, we had theoretically 360 amps that could be consumed. So roughly, after 10 hours, we should have consumed 160 amps, and the charge should still be 54% (160/360). Note that on the MasterView, the percent charge is only a calculation based on the current consumption, but does not say anything about the real status of the battery. 

It took only half an hour with such consumption to reach a point where the voltage got down just above 11 volts and triggered all alarms. This was a clear indication that the battery service bank is dead! And having noticed the 7.4 volt historical low, it was not a surprise. Yet, if you only sail a few hours during the day with the solar panels on, and connect to 220 volts at night, you can go a long way with that dead service bank. But forget long night cruises using the pilot.

So what could have caused the 7.4 low voltage? Probably the inverter, which is set to on when initializing the MasterVolt network. This way, if you are using any appliance on 220 while not connected to the pier, the inverter will use the battery to provide the required power. I use this often when not on el for charging computer batteries or for getting the perfect Nespresso from the coffee machine on-board. But imagine what may happen in Stockholm during the long cold winter, when you leave on a small electric heater in the boat while you are away, at a time the power at the pier goes off! The electric heater will drain your batteries very rapidly, and this is probably what happened to my service battery bank. 

The inverter can be switched on and off from the MasterView. However, if he MasterVolt system reinitialize, the inverter will get back to on by default. Therefore, the advice of the electrician is to switch the MasterCombi (MasterVolt charger and inverter) to "charger only" by putting the switch on the front of the MasterCombi to the lowest position. Good to know!

As for a load test on the engine battery, he said that the best is to start and stop the engine repeatedly. If you can do it six times, the battery is fine. If you can do it ten times, the battery is great! I did it ten times, so the engine battery is great!

Lessons learned:

• There are good and bad boat service companies and good and bad boat electricians
• The best and easiest way to test batteries is to conduct load tests on service and engine battery banks
• Switch the MasterCombi to "charger only" when not in the boat for some days.