Discharged starter battery

[Jen-in-Wellies]

1 hour ago, George and Dragon said:

Only the bilge pump, and judging by the amount of water I pumped out once the engine was running, I need to check that the float switch is working.

That could be significant. If the float switch was working earlier on while you were away and the pump was regularly removing water, then this could have discharged the battery. Once the battery was flat, then the pump might have struggled, leading to the amount of water you had to remove when you got the engine running. Moving the bilge pump on to the house batteries would be better as the current shore line charger will top them up in between pumping sessions.

Jen

[roland elsdon]

We have an advec and the halfords starter battery, distress purchase in 2012  ( based on biggest I could carry) after the batteries walked off while we were away is still fine.

Our abuse has included leaving the boat regularly for up to nine months for 8 years, with a solar panel bridging all batteries.

Probably wont start tomorrow.

[David Mack]

VSR of the type which senses both batteries (some only sense one battery). I have alternator connected to the start battery, solar to the domestic. When the battery connected to the power source is sufficiently charged for the relay to pull in, the other battery also gets charged. Keeps both batteries topped up happily.

[Tony Brooks]

47 minutes ago, David Mack said:

VSR of the type which senses both batteries (some only sense one battery). I have alternator connected to the start battery, solar to the domestic. When the battery connected to the power source is sufficiently charged for the relay to pull in, the other battery also gets charged. Keeps both batteries topped up happily.

 

I know you have not asked but:-

 

Typically, your system is the way far too many lazy boat builders do it and the way shown for  motorhome use but it is not the best for boat use.

 

The start battery will normally be all but fully charged each morning but the domestic battery will be discharged so there is a voltage difference between the engine and domestic bank. When you start up and the relay closes the domestic bank will draw the full alternator output plus even more from the engine battery. This is all passed through the relay contacts/electronics. Long term use like this has been proven to lead to a relatively short life for any type of charge splitting relay and its one reason split charge relays are often considered unreliable by some.

 

Ideally your alternator will be connected to the domestic bank with the relay used to carry the charge for the all but fully charged start battery. This means the relay would carry far, far lower currents that it does at present. It also means that you don't need a dual sensing VSR, not that the price seems to make much difference.

Edited May 11, 2021 by Tony Brooks

[ditchcrawler]

21 minutes ago, Tony Brooks said:

 

 

Ideally your alternator will be connected to the domestic bank with the relay used to carry the charge for the all but fully charged start battery. This means the relay would carry far, far lower currents that it does at present. It also means that you don't need a dual sensing VSR, not that the price seems to make much difference.

They seem to do the same thing with the old split charge relays as well which close when the alternator excites