batterybank for weekend cruising

[arjand]

Hello!

A 'simple' question... what is the best battery bank design for weekend cruising? Situation : Boat on a mooring, solar panels, 20 weekends a yr. Fridge is currently engine cooled but hope to put in a 12V as well, electric head etc. Will not run an invertor. Lights will be LED.

Currently the boat in in a slip with 2 automotive batts of 100Ah (one house, one start). NO monitoring system in place. 50 Amp balmar alternator, no external regulator.

Money and time are of the essence and again, this will be summer weekends only with maybe a wk max.

Can I keep a two batt design (one start, one house?) (this way I do not need to install exta cabels/switches and what have you). What Ah should I consider? (50 and 150?).

I will install a combiner and likaly an external multistage reg for tge alternator and I would like to put AGM batts in place.

Is there a cheap and simple batt monitor system?

Any tips/tricks very much appreciated!!

Ari

[Privilege]

Your set-up seems sound although you won't be able to run your fridge when you're away from the boat on such a small bank. I'd get a voltage sensitive relay (VSR). It's a combiner that will keep the batteries separate until you have an incoming charge. Easy to set up. Also, a basic xantrax link 10 will show you all your battery levels and stats.

Your starting battery needs to be rated for cold cranking amps (CCA's) not ah. CCA's is how much your engine needs to crank. A deep cycle battery may be fine as long as it has sufficient cranking amps.

[4arch]

I wouldn't run the fridge for more than a single overnight on the hook with that small of a house bank. If you have room, consider 2 or 4 6V GC2 golf cart batteries for a 225 or 450 AH house bank. AGM for a weekend cruiser is not worth it, IMO, unless you have difficult installation circumstances necessitating it. I'm also not sure the multistage regulator is worth it unless your solar is not up to snuff to keep up with refrigeration usage. It might be better to put the money toward more solar. The Victron BMV602 is a perennial favorite battery monitor. The Balmar Smartgauge is apparently more user friendly but I believe is not AGM compatible.

[donradcliffe]

It would help if you could tell us how big the solar panels are.

[Colin A]

For the cheap part golf cart batteries a better bet then AGM. It also depends how big your fridge is and what it draws. If you have a really small fridge it may work on one battery. I helped a guy with a small camper and an Engel fridge (like a cooler) he drew 24-30 AH a day (minimal opening and closing the fridge 75 degree days) For him a group 31 battery and an 80W solar panel worked well for weekends. but it really varies.

[john61ct]

4x 6V GCs

48 hours away from shore **if**

small efficient compressor fridge, contents frozen or at least chilled before loading

is the only heavy load

Then no solar really needed, or at least no need to rely on it, will extend bank lifetime though.

Duracell flooded from Sam's or Batteries+ the best value, or Trojan T-105s a bit better, RE variant much better but pricier.

Make sure good shore charger custom set to mfg specs.

[a64pilot]

For weekends only, with the occasional but rare week trip, you can get by with a couple of golf cart batteries, IF you forget the fridge, by an Engel or similar and only run it while your on the boat, or leave the fridge they way it is now.
The essential part is to leave the boat during the week with nothing on but an anchor light, to run a fridge 24/7 will take a lot of Solar and a big bank

He is on a mooring, no shorepower.

[john61ct]

Then at least a small inverter genny +100w solar required.

Unless at least 200w solar, more like 400+ for suboptimal conditions if solar-only.

Key Q is how long between shore charging and pre-chilling or freezing contents.

Otherwise may be better off using block ice and big Teti or Pelican cooler.

[guyrj33]

2 or 4 flooded lead acid golf cart batteries are the way to go.
Multi stage voltage regulator will help get the most out of your alternator.
leave the refrigeration connected to the engine.

[jkindredpdx]

I'd replace the car batteries with deep cycle marine batteries like Trojan SCS150s. They should be about the same size and require minimal changes to the rest of your setup.

It sounds like you have an AB switch. Later you could have two batteries for the house bank and one for starting. One or two solar panels with a proper controller and isolator will keep the batteries topped off.

[john61ct]

Originally Posted by jkindredpdx

Trojan SCS150s.

Decent batts, but like most 12V format, ated at half the duty cycles of the 6V GC ones.

And more expensive than those posted above.

[jkindredpdx]

Originally Posted by john61ct

Decent batts, but like most 12V format, ated at half the duty cycles of the 6V GC ones.

And more expensive than those posted above.

Agree, but wouldn't GCs require new, more sensitive, alternator and battery charging/monitoring equipment?

[john61ct]

No, of course we're talking flooded, and all flooded batts are very robust, have a pretty wide range of acceptable charge profiles, mostly similar across product lines and even manufacturers.

AGM and especially GEL are the more finicky chemistries.

Plus those are lots more expensive if quality, and harder to make last a long time.

with LFP the most fussy, super expensive, definitely want to treat right.

My recommendation is when putting in relatively permanent "infrastructure", pay a bit more so as you use up (consumable) banks, you can later switch to other chemistries without having to rewire, replace chargers etc.

Anyone with an expensive bank, no matter the type, should IMO have good monitoring to keep track of what's going on, make adjustments before damage is done.

[Pizzazz]

If money is a concern: two golf cart batteries, $200. A simple, 100 amp/voltage meter from Amazon, $20. Nothing else. You do not need to be running the fridge between weekends, most food will go bad after a week anyway.

When you add a 12V compressor for the fridge, keep the engine setup as well. The fridge will use 30-50 amps per day, so you're need at least 300W of solar power. Not worth it for a weekend cruiser.

[Emouchet]

This is my setup for exactly the same needs:

3x group27 (27TMX) Trojan batteries deep cycle wet lead acid, all in parallel (could not get a larger battery because of space).
1x group24 startup battery for the engine into a separate circuit.
60 Amps alternator.
2x 50W solar with PWM controller.
Bluesea SI-ACR automatic charging relay.

Solar charge the house bank first.

We can run the fridge over the weekend for 2 days without getting the batteries getting too low. (12.3v at the end of the weekend). The fridge draw about 4.5 amps/hours, and runs about 30% of the time.

The rest is all LED, instruments and a few hours on the auto pilot.

On sunny days, we get enough with solar so that battery voltage does not go below 12.5v.

On cloudy days, I usually runs the engine 1 hour, monitoring output currents from the alt. When batteries are low, output current is typically 50 amps for the 45 minutes, then slowly decreasing. When it decrease to about 30 amps, I know the batteries are almost at 80% charge, and stop the engine at that level. Solar will finish the job.

I try to run the engine in the morning, so that if solar is delivering amps, the baterries are already at 80%, so the low amps output of the solar is still beneficial, and batteries this way doe snot stay below 80% for too long.

Typically, when back on friday night to the boat, batteries are full. Solar has done a great job over the week. When motoring to exit the mooring field, I check the alt output current that is usually around 15-17 amps, so the batteries are just in absorption mode, each taking about 5 amps.

The engine cranking battery is the first being charged by the alternator. Then the SI-ACR close to charge the house bank.

My setup was to isolate completely the engine battery so that this one is never use for house. This way, it is always charged, can start the engine that will take care of charging the house bank if needed.