Battery charger question

[Martin Cole]

I recently installed an AC shorepower battery charger. It is a 10-amp three-stage charger that I intend to leave connected during the week while the boat is at the dock, in order to keep the two house batteries topped off and fully charged. The boat already has a small solar panel that provides "some" charge to keep battery 1 topped off but it doesn't really have enough charge to replenish the battery between sailing trips.My question is whether I need to install a cut-off switch on the solar panel, so that during the week it is not feeding its charge also to the batteries? I'm fairly certain that the AC charger won't cook the batteries, but will the addition of the small amount of charge from the solar panel interfere with this protection? I would like to keep the solar panel installed for what help it provides when I'm anchored out for several days.One other "complication" that may affect the answer is that I also have a dedicated starting battery. I installed a Xantrex (Heart) Echo-charger that is supposed to divert some of the charging source to top off the starter battery. This will be the only charging source for the starter battery because I did not connect it to the alternator. All the literature from the Echo-charger states that it won't interfere with normal charging of the main house batteries.I have read Don Casey's electrical book (among other info sources) and studied the manuals from all the devices. But I would appreciate any advice as to whether I have over-complicated my system or have done anything that will damage electrical components or done anything that might lead to electrical fires while I'm away from the boat.Thanks,Martin Coles/v ARES

 

[Rich Stidger]

Think twice

If all you want to do is to keep your batteries topped off, I would put a timer on the charger to run 2-4 hours/day. That way an overcharge condition should not occur.IMO, the solar charger will not have any effect on the battery charging system you have because it's capacity is so low, and any current contributed by the solar panel will raise the battery voltage and the charger will reduce it's output accordingly.If you don't have refrigeration or some other DC load that you want to run all week, I wouldn't leave the boat connected to shore power at all when not there. The danger of constant connection to shore power is primarily that of electrolis damage to your underwater metals. IMO this is a serious risk and not worth taking just to keep batteries charged. Upon arriving at your boat, connect the shore power and charge overnight before leaving to bring your batteries up to snuff.Why don't you have the engine alternator connected? The alternator is normally the only source needed to keep the starter battery fully charged. If your starter battery loses charge significently between uses, you have a more serious problem to correct and charging the starter battery will only mask the problem.Rich

 

[Martin Cole]

Thanks, Rich

Thanks for the reply. I will take your advice about avoiding electrolosis problems by not keeping the boat plugged in all week, especially since the solar panel will be contributing a small charge all week.The main reason I didn't want to add the new third battery to the alternator circuit is because I was told that I would have to change out the alternator for one that had a higher capacity, and all my reading about possibly having to redo the alternator supports made it sound like too much work.As for plugging in when I get to the boat, the charger instructions said that all load to the batteries should be turned off while it's charging and that would involve not running any of the lights or CD player while charging. Is it really that critical that you don't draw any load from the battery while it's being charged?Thanks again for your reply,Martin

 

[Eli Melnick]

The little charger that could

Hi Martin:Your charger is rated at 10 amps. If you run DC loads like a (loud) radio and lights, you'll be "consuming" some of that charger output leaving less amps to charge the batteries. Additional loads like refrigeration may eat up the whole 10 amps or even more, meaning that your batteries will be discharging even though you're hooked up to shore power and the battery charger is functioning.