Additional battery

[cruachan]

currently have 3*110AH batteries with physical space for a fourth. They are lead acid, non sealed, split between engine (one) and domestic (two).
All 3 are identical and 2 years old. Charged by a 70A alternator with sterling regulator or 20A shore powered charger through a split diode.
I intend to move the engine starter battery into the fourth space to give three identical batteries for domestic use and then replace the engine starter battery
- question is - does this need to be a 110A battery - as this seems excessive purely for engine starting (40HP Volvo), I assume it is wise to keep it the same type i.e lead acid and non sealed
any advice?????????????

 

[Anonymous]

Yes, keep the same type throughout, so that the charger is set for the appropriate type. I agree with your choice of flooded lead acid rather than sealed. I have a large generator and solar cells and now have all the batteries parallelled (except for the generator cranking battery) and no separate engine start battery. I do have a battery monitor and keep a close watch on it but in the worst case I could charge the main battery with the generator (80A charger) or gradually with the solar panels (2x180W). The benefit is that I have more usable battery capacity in the house bank but there is a risk if I do not pay attention.

 

[jerryat]

Hi,

No, it doesn't need to be, but I think it better if it is. I have had the same set-up, 3 domestic, 1 engine battery for years and it has the advantage that I can swop the batteries around from time to time so that they all get used in the different regime. It seems to work as my batteries last for many years before needing replacement.

Cheers Jerry

 

[cruachan]

hi jerry, how often do you swap your batteries round???

 

[jerryat]

Hi cruachan!
Three times a year when we're full time cruising, so that all the domestics get a period in the engine starting role. The helps to keep the plates from sulphating too much. While we've been ashore for the refit, we have only changed them once as the engine is not, of course, being used.
Hope this helps

Cheers Jerry

 

[cruachan]

hi jerry
think that makes my mind up then, thanks for that
francis

 

[macd]

Can see the sense of having all batteries the same, as other posts have suggested, but your engine start battery seems bigger than you strictly need. I'm just fitting a new engine (Beta). For their 40-ish hp engine, the handbook recommends a 70-75Ah battery with cold cranking current of 450-540A. As I understand it the latter's the crucial consideration for a starter battery. Something like a Ford Transit diesel battery would be ample for your needs, yet smaller and cheaper than a 110Ah job.

 

[VicMallows]

You're correct that a battery designed specifically for starting engines will be a bit better for that purpose....but it will be very poor and quickly damaged if you use it as a 'domestic' battery. You can either configure your system so you use an 'engine starting' battery for just that only; or simply use so-called 'leisure' batteries for everything (about £40 for 100Ah). (OK you can buy endless exotic variations at a price if you choose).

Vic

 

[Guest]

Personal question ....

I see you say you have a Shore power charger supplying via the spilt diode system .... I tried this and my charger didn't like it ...... in fact I gave up.
I had fitted the split diode block initiallyu to power from alternator - but of course the alternator was machine sensed and V drop was too great.

Interested to know how you did it ... did you increase the voltage out from the charger to compensate for the 0.5 - 0.7 V drop on the split diodes ?

 

[john_morris_uk]

Re: Personal question ....

Many of the better shore-power chargers have several outputs ready fitted for wiring to different battery banks. For instance the Sterling chargers typically have three outputs with the instructions to common them up to charge one bank or at least common up two to the bigger bank if you require two 'outputs'.

I have seen a diode splitter used on an older shore power charger, but there was a voltage sensing connection straight to the battery to ensure that the batteries were still charged at the correct rate.

Diode splitters are more commonly used in connecting an alternator to two banks of batteries whilst also using a 'voltage sensing' wire direct to the battery from the alternator regulator.

 

[Anonymous]

Re: Personal question ....

My charger (Mastervolt) has an internal compensation for 0.6V selectable on a dip switch and it also has voltage feedback - if you use feedback you don't need to have compensation. My Sterling charger had an internal diode splitter and compensated for itself. One word of caution with the Mastervolt approach; the previous owner of my boat had set the system for diode compensation when there were no diodes in the system, and ruined two very expensive 220Ah Sonnenschein batteries /forums/images/graemlins/crazy.gif

 

[Oldhand]

I would have thought that with your name you would have just plugged into the Pump Storage power station of the same name and not worried about batteries?