New batteries and charging plans

[irwin37]

Would appreciate advice on my plan to replace my batteries and add a charging device to keep them topped up. The boat is a 1978 Irwin 38 aft cockpit with a Westerbeake 33A.

At this point, I have two very old batteries: an 8D and a Group 31. Planning to replace with HOUSE: two Trojan 105 6v (assuming they're not too tall!) and STARTING: Group 65 | 650cca auto battery. I have a Guest 2515 15amp battery charger and a Guest 2200 "Smart" switch.

I also have an uninstalled Guest BatteryPal N4120 that takes 110v AC and outputs 15 volt 600mA AC. Supposed to be a float charger that will not boil out water. I will have AC at the marina.

Main question is, should I bother with the float charger, or get a solar panel and MPPT charge controller? The solar option would be invaluable for long trips away from ac power, but I'm mainly a weekend cruiser at this point. Not planning to use anything that consumes a lot of amperage. Just LED lights, phone/ipad chargers, and a couple cabin fans if needed.

 

[dlochner]

The usual recommendation for battery charger size is 10% of the Ah capacity of the bank plus some extra for any house loads that might be used while charging, things like lights, refrigeration, stereo, etc. The 2 trojans will have about 250 Ah capacity, so a charger that puts out 30 amps would be sized about right. The Guest 15 amp charger would be undersized.

The 2515 charger is pretty old school. It is a ferro-resonant charger. Modern chargers do a much better job of charging and extending battery life because of their charging profiles. Check MarineHowto.com and/or Musings with MaineSail on this forum. Maine Sail writes extensively and more authoritatively about charging and electrical systems than I do.

 

[irwin37]

Thanks Dave. I appreciate your advice about the 2515. I'll check the sources you recommended.

 

[Maine Sail]

T105's like to be charged at 14.8V and floated at around 13.5V. You'll want a charger that can be set for this plus one that has on-battery temp compensation ..

If going with only two 6V batteries in series for a house bank a back up "deep cycle" as your start or reserve/start is never a bad option. A Group 65 start battery won't do much of anything for you if you need to actually cycle it.

You might also consider the T1275 or J150 which are 150Ah 12V golf car batteries.

Here's some light reading on choosing charger features, what to look for and physically installing a battery charger.

Installing A Marine Battery Charger