Battery Bank considerations/advice : 38 ft yacht

[sailaboutvic]

There many more people who's posted here with better knowledge on batteries then me .
But here a thought , we have just 200W of solar which we plain to increase to 400W this year .
We been in a marina since the first week in Dec and although we on shore power , it's only being used for our electric heater .
Everything else is powered by batteries which are being charged by solar only , our fridge isn't working while we been here ,
but we still been useing the same amount Amps as we do on anchor , ( lights , inverter , radio , vhf )
if any thing more as we useing the light for longer periods, our uses as been around 19A over night our battieries have been on float most day by 10.30 so in reality if you add on what a fridge would use over night , there no problem getting the batteries back up to Float over the summer months while sitting around at anchor .
Ofcause once on the move and useing all the other stuff we now all seen to have on board it becomes a different story .

 

[Pasarell]

I am no expert, and have not traveled farther South than the Spanish Rias, but wonder whether increasing your solar capacity is more important than increasing battery capacity - so that during the day you are generating sufficient power to both run the fridge AND get the batteries nearer to full capacity to run the fridge through the hours of darkness without over discharging? Perhaps you could try that first before adding a battery of a different age to the others in the bank?

200w would struggle to keep our 345ah batteries topped up on greyer days, when we deploy our extra 107w roving panels which can be pointed at the sun to supplement our 240w (fixed) panels

I've found 200W is plenty for me the majority of the time. It's a rare day from March - November when my batteries have not been on float charge for a significant time. The panels are 2 x 100W mounted on an arch and both can be rotated 45 degrees fore and aft which makes a big difference. I do have a Honda 2KW generator but have only used it in anger once, November 2017.
Summer is when I consume most power with the fridge but it's also the longest daylight time. If the boat is sitting E - W to some extent I can make a big difference to output from the panels by angling them to the setting sun and then, before bed, angling them to rising sun to maximise output
Battery bank has dropped to about 60% a couple of times (based on voltage and amps in/out, not SOC% on the BM1) but never more than that. Typically in the summer months they operate between 70 - 100%

 

[Pasarell]

There many more people who's posted here with better knowledge on batteries then me .
But here a thought , we have just 200W of solar which we plain to increase to 400W this year .

Where are you going to put the extra 200W Vic? I have 2x 100W on the arch which I can rotate 45 degrees fore and aft which seems to work well. I would like to add another 200W as you are but the only place I can come up with, without them being in the way, is on frames which hang from the lifelines and rotate up to horizontal. Your deck layout is very similar to mine so very interested to steal your ideas if you don't mind!

 

[sailaboutvic]

Where are you going to put the extra 200W Vic? I have 2x 100W on the arch which I can rotate 45 degrees fore and aft which seems to work well. I would like to add another 200W as you are but the only place I can come up with, without them being in the way, is on frames which hang from the lifelines and rotate up to horizontal. Your deck layout is very similar to mine so very interested to steal your ideas if you don't mind!

For many year on my other boat and now on this one I had two 100w panels on the pushpit on arms see photo , you have to be careful if your moored to a wall or pontoon no one comes along side and catch them but so far we never had the problem , my next two will be going onto davit I having made in Tunisia , I will be able to pivot them too .

 

[Mistroma]

400W should sort you out over the summer, probably 150-160Ah most days in May-August. Not running the fridge will be a big saving just now and I doubt you'd manage on solar if it was on over Dec./Jan.

We had a very efficient fridge during a lot of late/early season sailing in Scotland. It was a coolbox in the cockpit.

I ran some figures for Tunisia with 200W panels sitting flat, not being tilted. Not too bad, just double them to get figures for your 400W setup. Output doesn't fall too quickly out of season in Tunisia, I think Dec./Jan. was about 15Ah/Day in the Rias and 5Ah/Day in Scotland.

These are estimated daily average Ah during each month for your existing kit.

Month	Ah/Day
Jan	31
Feb	40
Mar	57
Apr	64
May	74
Jun	81
Jul	82
Aug	72
Sep	56
Oct	45
Nov	33
Dec	27

 

[sailaboutvic]

400W should sort you out over the summer, probably 150-160Ah most days in May-August. Not running the fridge will be a big saving just now and I doubt you'd manage on solar if it was on over Dec./Jan.

We had a very efficient fridge during a lot of late/early season sailing in Scotland. It was a coolbox in the cockpit.

I ran some figures for Tunisia with 200W panels sitting flat, not being tilted. Not too bad, just double them to get figures for your 400W setup. Output doesn't fall too quickly out of season in Tunisia, I think Dec./Jan. was about 15Ah/Day in the Rias and 5Ah/Day in Scotland.

These are estimated daily average Ah during each month for your existing kit.

Month	Ah/Day
Jan	31
Feb	40
Mar	57
Apr	64
May	74
Jun	81
Jul	82
Aug	72
Sep	56
Oct	45
Nov	33
Dec	27

Lucky where we are mike , we parked just right for the sun and keeping them tilted max us out .
We not taken much on board because we useing very little over night but the times I was running my batteries down to do some test was getting 700/723 w

 

[Mistroma]

Lucky you can do that in winter. Tilting makes much less difference in summer but huge impact in winter.

At 32 deg. tilt instead of lying flat:
Dec. output jumps from 27 to 44 Ah/day
Nov. & Jan. up from 32 to approx. 51Ah/day

 

[KellysEye]

House batteries should be deep cycle we had two Trojans wired in series, start batteries should be Cold Cranking batteries,