pls remind me! Link two service batteries = double amp hrs??

[carrswood]

Hi
I forget the facts so easily, but if I was to link my two 110ah Trojan batteries to form one large service bank would I get double the amps? Could someone remind me and is it worth doing if I was to fit a seperate cranking battery?

(to summurise id like more amps available)

 

[pvb]

Hi
I forget the facts so easily, but if I was to link my two 110ah Trojan batteries to form one large service bank would I get double the amps? Could someone remind me and is it worth doing if I was to fit a seperate cranking battery?

(to summurise id like more amps available)

Yes, and yes.

 

[VicS]

two 110Ah batteries in parallel double the Ah to 220 Ah. Volts stay the same

(Two in series double the volts ... same Ah)

Yes if you want more domestic battery capacity link the existing two in parallel and fit a separate starter battery.

 

[mdonnelly]

This is of interest to me! Want to do the same. Have a splitting diode with output to each battery. If I add a second domestic battery do I need a splitting diode with 3 outputs or can one charge 2 batteries?

 

[VicS]

This is of interest to me! Want to do the same. Have a splitting diode with output to each battery. If I add a second domestic battery do I need a splitting diode with 3 outputs or can one charge 2 batteries?

If you link two batteries in parallel as a permanent bank one output from the splitter can charge the two together. The other output charges the other (starter ?) battery.

 

[carrswood]

Thanks Vics. Couple of questions:

1) Without starting a full debate on diodes, regulators, splitters etc etc can I
asume I can still use my simple (but happy with) 1,2,Both battery isolator?

2) I have a 115ah alternator but cruise from a swing mooring. The volvo D1-20 doesn't seem to struggle to get to full charge but will the new setup pose a problem - i suspect not as its a great alternator

3) for my 20hp Volvo whats the smallest ah cranking battery I could go for. Reason - the 3rd battery needs to be compact - I believe ODESSEY do some?

 

[VicS]

1) Without starting a full debate on diodes, regulators, splitters etc etc can I asume I can still use my simple (but happy with) 1,2,Both battery isolator?

Yes you can. Presumably you have taken the alternator output away from the switch to go directly to the splitter common terminal and the splitter outputs going directly to the batteries.

However it's the time really to separate the engine circuits from the domestic circuits and do away with the 1,2 both off switch in favour of separate isolators and an emergency linking switch.

Keeping the 1,2,both off switch leaves you sort of trapped between the old manual change over system and dedicated starter and domestic batteries with simultaneous charging via the diodes

2) I have a 115ah alternator but cruise from a swing mooring. The volvo D1-20 doesn't seem to struggle to get to full charge but will the new setup pose a problem - i suspect not as its a great alternator

Your trouble may be the volts drop across the diodes. About 0.7 volt. You really need the alternator to be "battery sensing" so that it compensates for that. A 115amp alternator is quite large. It should be more than adequate if there is nothing wrong with it esp if converted to battery sensing unless you have all a lvat amount electrical equipment with a huge demand.

3) for my 20hp Volvo whats the smallest ah cranking battery I could go for. Reason - the 3rd battery needs to be compact - I believe ODESSEY do some?

Its cold cranking amps that really count not Amp hour capacity. You need very little out of a battery in terms of Ah but you need a big current .. lots of amps.
However its usually Ah that is specified.
Your owners manual recommends a 70 Ah battery Look at the cca figures for some typical 70Ah batteries ( quick look at the one in my car .. its 540 )

So if you now choose a compact battery choose one with the same CCA as the normal battery. Although I'd guess 540 CCA is far more than you actually need.

Red flash is another popular brand of compact batteries.

Dont mix different types of battery, eg gel with others, or at least ensure thay are suitable to be charged alongside each other.

Have also to say we have run into some misunderstandings about some of the figures quoted on battery suppliers websites. See the posts towards the end of this thread. http://www.ybw.com/forums/showthread.php?t=268581

 

[William_H]

Thanks Vics. Couple of questions:

1) Without starting a full debate on diodes, regulators, splitters etc etc can I
asume I can still use my simple (but happy with) 1,2,Both battery isolator?

2) I have a 115ah alternator but cruise from a swing mooring. The volvo D1-20 doesn't seem to struggle to get to full charge but will the new setup pose a problem - i suspect not as its a great alternator

3) for my 20hp Volvo whats the smallest ah cranking battery I could go for. Reason - the 3rd battery needs to be compact - I believe ODESSEY do some?

Yes 2 batteries in parallel will be just like one larger battery. The 1,2,both switch will be then "off, engine battery, house battery or both. You could however fit another 1,2,both switch to the 2 house batteries. You would normally operate in both position but it would mean you could isolate one battery if you thought one was dieing. You can do the same thing of course if you suspect problems by removing connectors to one battery. Eventually one will die and this may degrade the performance of the other. So if you have any doubts about house battery performance try each individually.

The 115A rating of the alternator is probably never used or achieved. In practice the difficulty is not in generating the 14volts for charging and supplying it at 115 amps but rather in getting the batteries to accept any large charging current. The current the battery accepts will diminish with charge level so a battery might start accepting (being charged at) 30 amps but after 1 minute this goes down to 20 amps and after 5 minutes is down to 10 amps and continues to diminish. So to get anything like a full 100% charge takes a long time. With 2 batteries the charge current will be double (the same to each) except that they will not be so far discharged so probably less.

Sorry not familiar with what batteries you have available however generally car batteries are made for cranking current and are cheapest due to high volume sales. good luck olewill

 

[VicS]

How about something like this.

It retains the 1,2,both off switch, using it to select which battery to use for engine starting and to act as the starter battery isolator.

It connects all the domestics to the domestic bank via a new isolator.

 

[pteron]

Make sure that the two batteries are at more or less the same voltage when you connect them else you could get some rather large equalising currents flowing.

 

[ditchcrawler]

I linked up my two 113ah batteries and put in a Red Flash 1100 to start my Volvo 28hp engine.Merlin said the R.F 1000 would be fine but I opted for the bigger battery as at the time it was not much more.The R.F 900 might do you.They are not cheap but well priced on www.tayna.co.uk You do need to limit your charging to 14.4v for the AGM starter batteries and I did this with my Sterling Alternator Manager.

 

[tarik]

Battery prices

Can I extend the thread a little. I want to connect the batteries in the way the OP has raised, but I'm going to have to bite the bullet and get a new battery ( might get two if the price is right).

Any suggestions as to price and supplier???


Many thanks


David

 

[VicS]

Can I extend the thread a little. I want to connect the batteries in the way the OP has raised, but I'm going to have to bite the bullet and get a new battery ( might get two if the price is right).

Any suggestions as to price and supplier???


Many thanks


David

http://www.batterymegastore.co.uk/ just to get you started

Tayna already mentioned.