Battery advice please

C

ChrisKaye

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www.photobox.co.uk
Been slowly gathering bits needed for my next project on the boat, nice big long batt boxes now arrived.

I am planning to double up the domestic battery bank to give us longer batt life without having to run the generator.

Currently I have 2 x 110Ah batteries supplying the domestic side and also the bow thruster (but they only give me about 4hours of power when I'm not on shore power and I dont like running genny for long periods, I know it dont sound long but everyone ends up on our boat and the kids watch DVD's with all the bl@@dy lights on so we end up with everything running) so I thought an easy upgrade would be to double them up with another pair of 110Ah giving me a total of 440Ah and maybe 8hours. Now my question is will I have to replace the existing battery cables or is it just a simple job of just getting some more cables made up same size to parallel them up
 
The current flowing from your battery bank will under normal conditions be determined by the characteristics (resistance) of the loads connected to it. More loads, less total resistance hence higher current flows.

Assuming the existing cabling is correctly sized and fitted with fuses/breakers to protect the existing circuits you may be OK, it depends on the size of the main cable/fuse.

It is possible by increasing battery capacity that, should a short occur in the main cable between the battery bank and main fuse, excessive overheating will occur due to excessive fault current flowing.

This may cheaply be resolved by a short link of heavier cable to a main fuse close to the new battery bank, sized to match existing main fuse size that protected existing circuits.

Others may have different opinions/solutions but without and data on main cable size I would probably recommend a short heavy cable and new fuse/breaker!
 
Hi Chris

I would recommend you isolate them with a switch.

ie

either charge and use set 1

or

charge and use set 2

I know it adds a bit of extra hassle but 4 x bats is too many to join together.

Any one weak battery with hog all the charge so the 3 good ones will remain empty.

At least if you split them one bank will be full and the other 3/4 full.

cheers
Pete
 
No. I'd say parallel wire them directly to your existing batteries, (using cables the same size as the cables from your current batteries to the main DC distribution solenoids box), and do no more. If the new batteries are right beside the old ones, that means just some short wires, battery post to battery post (you'll need 4 if you are 12v, 3 if you're 24v)

You haven't installed any more appliances, so your current draw with new set up will be no different from what it was before. You therefore do not need to upgrade the cables that run from the battery bank to the main DC distribution solenoids box, or anything downstream of that
 
Each to their own, but I wouldn't do that. I'd want all 4 charged by the altenrators and shore power, not be faffing with switches to charge these ones, then those ones, oh no I mean those ones, etc.

As for the statement "4 is too many to join together" that is simply not correct. I have 4 joined together, ex factory. I can show you installations on bigger boats with loads joined together. A battery istelf is 6 cells joined together in series inside the box, so 4 connected together is 24, for starters (in a mix of parallel and series, of course)
 
Well done JFM, that is exactly what I wanted to hear, it does seem to be the simplest solution and as you mention there are no additional electrical items installed so current draw will be the same as previously, it will just last longer. Brillo and beer owed
 
Hi KevB, you're not back on that again are you ?? /forums/images/graemlins/laugh.gif

There's one for sale at Grange Int'l at the mo with CATS and then we can both have one
 
"It is possible by increasing battery capacity that, should a short occur in the main cable between the battery bank and main fuse, excessive overheating will occur due to excessive fault current flowing"

But hang on
1. such a short is very rare, and all systems are designed to make the chances of it happening near zero. If it happens, for sure excessive current will flow, could start a fire, even in OP's present set up. Adding a couple of extra batteries isn't going to change it from safe to unsafe. The only way to deal with such shorts is to make sure they never happen.
2. Anyway, the extra batteries on the bank will not increase the current flowing through the short. The current could run for longer, but it'll be the same amps
3. Really, no-one sizes cables so they can handle a short across the terminals of a battery like these. The boat would need several tonnes of copper to do that!
 
I am not arguing, just adding to my reasons or as my retired ex business partner would say

now you understand I am not criticising but /forums/images/graemlins/wink.gif

In this case I thought Chris was going to add two new batteries to 2 existing ones.

I guess at least one of his existing ones will not be 'as new'

chargers will send current to 4 batteries
the weakest battery will take the charge leaving the good batteries without any charge.

I accept a switch is a pain, but great when at anchor and you loose power, just switch the battery bank and you know you have the same time again.

And agree even more hassle to switch banks while on passage or after a day on shore power.

I am just concerned that 2 extra batteries added to an existing bank may not actually add any usable extra power if any one battery is getting weak.
 
Chris,

I don't know the answer but will you need one of those split diode thingies so both alternators are charging all the batteries rather than one doing all the domestics and the other doing the lonely starter battery?

I had one fitted cause the alternator which did all the work went awol a couple of times and a split diode thingie was required (so I was told)
 
Bit more to add.

Current setup is 3 batt banks with on/off switches:-

2 x recent 110Ah batts for domestic /bowthruster /windlass
2 x old 110Ah batts for stbd engine
2 x old 110Ah batts for port engine

Plan to get 6 new 110Ah batts
4 x new for new domestic setup (so all new & linked together)
2 x new for port engine
2 x recent (ex domestic) now for stbd engine

I already have one of them (split charge diodes) thingy's KevB
 
[ QUOTE ]


Plan to get 6 new 110Ah batts
4 x new for new domestic setup (so all new & linked together)
2 x new for port engine
2 x recent (ex domestic) now for stbd engine



[/ QUOTE ]

in that case my posts above are irrelevant and should be ignored, sorry jfm.
 
Dont apologise - you were just saying how you'd do it and I was just saying how I'd do it! Both answers valid!

Chris, as a matter of interest, which batteries does your shorepower batt charger charge in that set up? Is it a 2-outlet charger, which does the domestics and one engine, or what? Or does it send all the charge into the diode thing and charge domestics plus one engine? And is there a link switch to start engines if flat battery? If so, what does it link to what, and which batteries power the coil in the link switch relay?

Oops sorry lots of questions. I'm used to just 2 battery banks, one for doms+ an engine, and another for t'other engine

Halcyon will maybe chip in later and shed more light
 
Hi John, I'll try to explain as best I can although might be wrong
3 banks of batteries (not sure if banks is correct terminolgy but 3 seperate boxes with batts in. each have 2 x 110Ah batts in.
I assume that shorepower (Newmar charger ) charges all 3 x sets of batts.

Also another box for Generator batt I assume is charged directly off geny, wonder if thats charged from shore power too ?

3x big Key-switches for Port/Stbd/Domestic and smaller one for Genny

There is battery crossover for eng starting (although I've never used it)
Also batt crossover for Genny starting (again never used)

Dont know if batt charger is 2outlet and dont know much about the diode thingy either sorry, better on mechs than electrics (electrics make my head go spinny)
 
Hi just a thought,i think you can get batteries up to 135a/h in the same dimensions as the 110s,which will also increase your reserve capacity,regards m m 1.
 
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