BATTERIES

[dmarler]

Two ordinary car-type 60amp/hr batteries wired in series, used conventionally: Batt 1 - engine start; Both - engine running, charging; Batt 2 - engine off, sailing or moored, for instruments, lights, etc.
Batt 2 dies of old age and is replaced by a 70amp/hr battery.
Are there any adverse effects? On Both will Batt 2 always be undercharged or conversely will it take all the charge going? Or no difference? Can any one advise?

 

[ccscott49]

Shouldnt be a problem, but you normally change batteries together, just dont leave them on both unless charging, as long as it's isolated it should be fine. I would swop them over, use the new battery for engine start and use the old one for domestics. When it dies, do the same again. IMHO

 

[cliff]

I hope you do not know the difference between series and parallel wiring coz if you have wired them in series you now have a 24v system.

Assuming you do not know the difference and have in fact wired them in parallel........

As to your question it will not make any noticeable difference to your charging - both will charge to the same level / voltage when switch set to both. The leisure battery will normally take most of the available amps as it is normally the one that is "flat".

The difference on 10Ah capacity is nothing you need concern yourself over otherwise how would you account for say a 75Ah start battery connected to a 330Ah leisure bank (soon to be 660Ah) via an off-1-both-2 switch.

State of charge depends on type and capacity of charger - an ordinary alternator will not charge the batteries either fully or efficiently.
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"Artificial intelligence is no match for natural stupidity"

 

[john_morris_uk]

Do you really mean 'series'. Connecting two 12v batteries in series would produce 24 volts.

Assuming that is a typo error, or error in terms, I am not convinced about putting your new battery as the engine start. The 'domestic' battery is the one that gets the most abuse (in battery terms) and it might be better to put the new battery in this position.

A further potential problem is that 70 amp/hrs is not a lot of amp hours for a domestic battery.

Bearing in mind that one shouldn't allow a battery to be discharged below 50% capacity too often (if ever) and the fact that you will probably never get it to 100% charge unless you are plugged into a mains charger for a day or two, you are only left with 30 or 4 amp/hours of usable energy.

A couple of lights on for a few hours and you've used the lot. Of course, the lights won't go out for another few hours, but if you flatten the battery completely many times, you will destroy it...

 

[Guest]

Not in Serial surely ?unless batteries are 6V ...

The real matter is internal resistance and voltage level of the batterys in charging as I understand it ... therefore charging both together should be ok ..

I have an 80a/hr start + an old 110a/hr domestic .... never worry about both / 1 / 2 etc. Have a routine I stick to and thats it ....

 

[duncan]

if Bat 1 is in any way 'on it' s way out' then it may hog the charge without holding it causing Bat 2 to suffer a lack of charge.
put another way the relationship between the relative size of the 2 batteries isn't relevant to whether they will, given time and available charge get to the best your charging system can deliver; their condition is.
having done a similar thing I simply give each 'dedicated time' from the charge from time to time rather than leaving both 'on' with the engine running.

 

[ccscott49]

Thats why I said, use the new one for engine, (best one for reliabilty) as the old one will be getting old!!! So use it up first, then replace, I understand what I mean, maybe not explaining proper like!

 

[Westy]

Aren't cranking (engine start) and leisure (domestic) batteries different types anyway?

 

[Joe_Cole]

Yes they are, but the original poster said that both batteries in his installation are car batteries.

In any event I don't think that Leisure batteries are very different from car/cranking batteries. They are certainly not deep cycle batteries, even though many peeps describe them as such. FWIW It would be better to describe a leisure battery as a shallow cycle battery.

 

[William_H]

I advocate occasionally testing the services battery in engine start service provided that an occasional start won't damage a deep cycle battery.
One of the reasons for having 2 batteries is to give you an alternative start battery should the engine start battery fail. (which ultimately it will) so it would be no good to have the engine battery fail obly to find the services battery has not been able to start the engine for a long time due to old age.
Hopefully the 2 batteries together will get you out of trouble but I reckon it is worth occasionally testing each battery alone. regards ollewill

 

[Guest]

Re: BATTERIES - why have 2 ?

My reason for having 2 batterys is purely to ensure that I have a start capability .... it is not to have an either / or situation as my domestic is well past its start engine days ... maybe after a full charge and not left standing it may start my engine but I wouldn't count on it ... But it gives me reasonable domestic service as I do not have power hungry items to warrant replacement yet.

As to charging .......... I will charge my start battery from engine alternator for a reasonable period after start ... then swap to domestic battery charging for remaining engine run .. till just before stopping engine ... giving the start battery a boost before shutting down. That is my regime and it has stood me in good stead for some years. I rarely BOTH my batterys as I know my Domestic is in bad health.

I'm starting to think a trip to breakers yard is called for .... replace the domestic and possibly give myself chance to start of Domestic ... or even add it to the bank !!

My suggestion regardless of set-ups basically is sensible approach to charge regime from engine or other charge source is most important matter - not actually where thne charge is from .... my Halfords charger and engine standard alternator have served me well for years and I expect them to continue so.

/forums/images/graemlins/grin.gif

 

[Graham_Wright]

Why not fit two alternators? They are relatively cheap and it probable that the belting problems can be overcome. Apart from anything else, you now have the possibility of surviving an alternator failure. Saves all this trouble with diodes and relays.

 

[dmarler]

Thanks, every one, for the reassurance. And thank you for pointing out my error as regards series v. parallel. Which rather answers the question about my trying to wire up a second alternator! Anyway, no room. Both batteries are car-type, so could swap uses, but I think I'd go along with the view that the services battery gets the most hammering so could do with the larger capacity. Batt 1 is in any case less than a twelve month old.

 

[cliff]

[ QUOTE ]
In any event I don't think that Leisure batteries are very different from car/cranking batteries. They are certainly not deep cycle batteries, even though many peeps describe them as such. FWIW It would be better to describe a leisure battery as a shallow cycle battery.

[/ QUOTE ]Well said young man!
A very appropriate description of leisure batteries.
IMHO the only deep cycle batteries are traction batteries, the so called leisure batteries are nothing like deep cycle. I fitted traction batteries on my boat and the difference between them and the original leisure batteries was immense.
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"Artificial intelligence is no match for natural stupidity"