Volvo D6 starter battery discharging

[henningbuus]

When trying to start my Cutwater 30CB engine with the parallel switch on, the battery power was insufficient to crank the engine. It would make half turn and stop. I switched the starter battery with the thruster battery, and it started with no problems. The next day I had the same problem, so I switched the batteries again and the engine started with no problems.
To me it looks like the battery that is connected to the engine gets drained over time, and the parallel switch is not connecting all the batteries together. When not in use I always turn the engine and thruster battery switches to off, but the battery connected to the engine is still low after some time. I noticed that the voltmeter showing the engine battery will fluctuate between 11.8 and 12.4 volts every 1-2 seconds when the engine is not running and the engine battery switch off. That indicates that something is turning on and off, and it might be the cause of the battery draining, but what could that be? I wonder if it could be a problem with the charging relay?

 

[knotflying]

Lots of things could be causing a draw and it all depends on how things are wired. a draw every one to two seconds sounds like a lot. Depending on the bilge pump, some of them cycle every once in a while to detect water and are not usually connected to the engine battery. I would trace the engine circuit and see what may be connected to it. You may also want to disconnect the engine battery and see if anything stops working. Are you sure that the ignition is completely off when you leave the boat?

 

[GaylesFaerie]

How old is the starter battery? Is it flooded lead acid?

 

[BB marine]

There seems to be one component that you are not mentioning. The house bank! When you use the parallel switch you are essentially jumping the house bank to the engine battery. When you do this the engine does not have enough battery to turn over. This tells me that the house and engine batteries are not fully charged or being charged. You turn the engine and thruster banks off utilizing the battery switches. The thruster bank charges and or maintains a charge but the engine battery does not. If you have a fully charged engine battery with the battery switch off and the battery discharges it is either a bad battery or a discharging gremlin!!! There is one variable that comes to mind. A bad ACR that is closed linking the house bank to the engine bank. The ACR are wired in between the engine battery and the thruster bank (ACR #1) and the engine battery and the house bank (ACR #2). There is another link cross over switch/parallel switch MUST be in the off position unless utilizing it for a "JUMPER".

You have not indicated if you are on shore power and using the battery charger while not on board. If you are using the battery charger and the battery bank engine and house do not have enough capacity to start the engine you may have a bad battery charger too.

You need to provide more information. From the information you have provided. I would suggest inspecting the ACR for proper function. Confirm it is open when there's no charge and batteries are reading 12.7 or lower. Confirm there is no continuity between the cross over switch when it is in the off position. Confirm that your battery charger is charging all battery banks when it is plugged into shore power or using the generator. This is an easy check with a VOA meter.

My feeling is that the House and engine batteries are somehow connected.

 

[henningbuus]

Thank you for your responses. I forgot to mention the inverter/charger did not work (I am installing a new Kisae 2000 tomorrow) so I could only charge the batteries with the engine alternator and the solar panel. I think I figured out what is causing the engine battery discharge. Apparently, the Propane solenoid is powered by the engine battery, and when we are on a multiple day cruise, we leave the solenoid on all the time. I wish the solenoid panel was located closer to the stove instead of hiding down in the aft berth.