On Board Battery Charger

[chopper515]

I'm installing a dual battery system with the blue sea add a battery switch and ACR. I have a starting battery and 120AH group 31 deep cycle and I'm looking for an on board charger. I wired the ACR on the boat side of the switch so I can get a dual bank charger and charge separately while the switch is off. I've read that you should have an amp rating equal to 10% of the AH rating of the battery which puts me around 10-12 amps. My question is if I'm not worried about speed, is 4 amps per bank acceptable? Is this 10% guideline for the health of the battery, or just in order to get the battery charged overnight? If I need the 10amps I might just get a single bank 10 amp since my starting battery will only be used for starting and the alternater will keep it topped off. Here is the dual bank charger I'm looking at:

https://www.amazon.com/dp/B00CBTRMZ4...GQNYNANU&psc=1

[chpthril]

Its not really about the quickness to reach a full charge. Think about for how long that 4A charger is going to be running at its full capacity, called bulk rate mode, in order to recharge a dead 120 Ah battery. Small charger with small output has small heat sink mass for heat dissipation. It will not only take long, but it will run at its peak output for much longer than larger charger. This means more heat for longer time. Larger charger absorbs more heat but will also spend less time in bulk mode. This all equals charger longevity.

[chopper515]

Thanks for the insight Mike. I think I'll probably go with a single bank 10 amp and assume my starter battery won't need help from regular charging.

[Bryan]

May not be the most efficient way, and mike will know best... but I just grabbed 3 of these guys from Walmart and wired one on each of my batteries... plug them into a 3way splitter on the end of an extension cord and they've worked great for me for 2 summers now.. they charge me up fully overnight just fine.. would one unit make for a cleaner install? No doubt, but these were available when I was looking for a fix and they haven't stopped yet so I haven't messed with them

http://www.zbattery.com/SEM-1562A-CA...EVzhoCvXLw_wcB

[chpthril]

Schumacher 12 Volt and 6 Volt 1.5 Amp Hour Battery Charger, SEM-1562A-CA

Unique automatic battery charger maintains both 6 and 12 volt batteries keeping them at full charge using float-mode monitoring. Perfect for charging small batteries. Great for maintaining small and large batteries kept in storage -

First thing id look for, is it ignition protected as per the ABYC or similar? If not, you'd likely not want to mount this and use this in the engine bay/bilge area of a boat. Waterproof/Sealed is the next up. Even mounted in a safer location in the boat, the humid conditions can take their tole on the internal components, resulting in a failure which could result in a fire while in use.

A 1.5A, a unit like this does not have the capacity to recharge a deeply discharged battery any larger than a garden tractor or side x side battery. Will it top off a shallow depleted battery? likely. Will it maintain a charged battery? it says it has a float mode, so maybe.

Not saying those are bad units, just offering some things to consider when looking for an on-board marine charger. Especially one that might be required to recharge a large house bank after 6-8 hrs at the sandbar.

[BlackoutATX]

Mike is right on the money as usual. When I expanded my battery system last summer, I went through this same thing. Mainly because I already had a pro mariner system. Ended replacing the pro mariner with 1 NOCO 4 bank 40AMP for the house batteries and 1 NOCO 1 bank 10AMP for the starter. In the end, batteries are expensive. Might as well spend the little extra cash to make sure they're maintained correctly.

That beings said, I love the NOCO chargers. Top notch all the way. I went ahead and added their port plug too. This way all the wiring can be tucked away.