Charging identical batteries

[kingfisher]

I have just bought 2 identical AGM-hybrid type batteries (Varta ULTRA special). My god, at the price those are selling, it would seem VARTA has litteraly found a way to change lead into gold.
Anyway: one will primeraly be used as starting battery, the other is the household one.

Since they are identical, but will have different usages, do I charge them with the switch set to 1+2 or do I still have to charge them individually?

 

[Chris_Robb]

Charge them either 1 2 or both! Are these Gel batteries? if so you can't charge them with such a high voltage - ie up to 14.8 so get the charging voltage right or you will bugger them I believe.
What's wrong with ordinary lead acid, you can mis treat them by over charging - just top up, they accept charge faster, so why pay more? if you can exchange for standard wet batteries - thats what I would do (I think!)

 

[kingfisher]

I used to be happy with cheap led-acid, which I replaced once every two years. But I haven't sailed the boat for three years, because of a stay abroad (which also landed ma some extra cash) and I'm doing a serious upgrade.

And the two most serious incidences that I ran into (one even led to a sécurité bulletin on the whole Westerscheld, don't ask) where both caused by dead batteries. So the whole energy management system gets a review: all lights replaced by LEDs, new batteries, and if the cashflow can handle it: a smart charger.

 

[SvenglishTommy]

Start and charge on the 1+2 setting. A smart charger will not be that beneficial to you, your 2010 probably has a decent 60A battery sensed Valeo alternator on it, and you will not benefit from the high voltage the smart charger will provide as the batteries cannot take it, they will charge just fine as it is.

Rather than having one as start and one as domestic consider alternating their roles to even out the cycling of the batteries, otherwise one will degrade long before the other. The idea is to always have one fully charged battery, not to allocate them dedicated functions.

 

[pvb]

Alternatively...

That high-spec battery is really overkill for starting purposes. You'd be far better off using the 2 Varta Ultra Special batteries in parallel for your domestic supply, and adding an ordinary (cheap & cheerful) starting battery. For minimal expense, you get double the domestic capacity, and your expensive Varta batteries will last much longer because, for a given usage, their depth of discharge will be halved (and it's depth of discharge which speeds the untimely death of batteries). Just a thought.

 

[andy_wilson]

Ohms law will distribute the charge to the batteries exactly in the correct ratio according to the degree of flatness.

I can't exactly agree with Tommys idea of alternating the batteries, I consider it important to have 1 battery that is dedicated to starting the engine as a safety matter, and thus preserved that way in all normal use, one rule for everyone to follow.

Therefore, start on battery 1, switch over to 1 + 2 whilst running, switch to 2 for domestics when stopped.

The only variation to this would be if you have a very depleted domestic battery, the load from the alternator might prevent the engine from increasing the rpm when in gear so you may need to hold off from charging the domestic battery until you have warmed up a bit and got underway.

I too have identical batteries for both duties, though I prefer a slightly more workmanlike truck battery specified for tail lift vehicles, confident that a long period of discharge can be followed by starting a 8- 10 litre truck engine. My twin cylinder 800cc Volvo 2002 isn't much of a problem therefore. 50p per ampere hour is also not much of a problem either when it is time to change them, though the oldest is currently 5 years old and showing no signs of wilting.

In slight agreement with Tommy, as both batteries 'could' start the engine, from time to time I make sure that the domestic battery 'will'. Domestic batteries can appear to work OK under modest discharges, but fail to deliver cranking amps, so the odd check on this is worthwhile I feel.

 

[Danny]

Re: Alternatively...

[ QUOTE ]
That high-spec battery is really overkill for starting purposes. You'd be far better off using the 2 Varta Ultra Special batteries in parallel for your domestic supply, and adding an ordinary (cheap & cheerful) starting battery...

[/ QUOTE ]Agree about these being overkill as engine start batteries. All you need for engine start is lots of CCA/MCA and very little AH. But as far as having the two house batteries permanently in parallel I'd say it's safer to have them switched. If anything serious happened to one battery - maybe a shorted cell, for instance - the other battery would discharge through it and probably end up damaged as well.

 

[pvb]

Re: Alternatively...

[ QUOTE ]
But as far as having the two house batteries permanently in parallel I'd say it's safer to have them switched. If anything serious happened to one battery - maybe a shorted cell, for instance - the other battery would discharge through it and probably end up damaged as well.


[/ QUOTE ]So you'd rule out having domestic battery capacity larger than a single battery then? Thousands of boats have 2, 3, 4 or more batteries permanently paralleled as the domestic bank without problems (I have 6). There's too much emphasis in this forum on "bad things that might happen once in a lifetime if you're unlucky" rather than getting on with the business of making the boat practical and enjoyable to use.

 

[roly_voya]

Re: Alternatively...

I would weigh in on the side of using both the Vatas for house bank and getting an engine start battery, much better use of capacity but I would also say get rid of the 1,2 both switch and replace it with a diode splitter. If the Alt is engine sense that gets over the voltage loss, if not fit a seperate charge controller. The most common cause of flat batteries is not poor batteries but the crew forgetting to set the 1,2 both switch and discharging the stat batt as well as the house one!

 

[pvb]

Nearly...

[ QUOTE ]
If the Alt is engine sense that gets over the voltage loss, if not fit a seperate charge controller.

[/ QUOTE ]I guess you meant to say "battery-sensed", which would overcome a voltage drop in the diodes. Fully agree with you on the 1-2-Both switch, these are dreadful things which have no place in a boat in the 21st century. But I'd probably favour a VSR rather than a diode splitter.

 

[Chris_Robb]

Just completed my first w/e on the new Stirling altenator reg. - absolutley brilliant. The charge used to trickle in at between 10 (at start) to 3 within minutes. Now it starts at 40 and reduces to about 15 -20 continusuoly until it goes into float.

Hurray, I can use the fridge again!

 

[boguing]

Re: Nearly...

Slight drift here, but I bought a splitter for £20 at Maplin. Fitted it to the car, alternator to splitter, outputs to the two batteries. 10Amp fuse in supply to splitter keeps blowing when the engine runs. Any ideas? Did try fully charging both batts with mains charger, in case it was asking too much of the splitter to charge what were pretty low batts 11.5 and 10. Still blew the fuse. Has it destroyed the regulator on the alternator, or is just a duff splitter?

 

[Guest]

Re: Nearly...

[ QUOTE ]
Slight drift here, but I bought a splitter for £20 at Maplin. Fitted it to the car, alternator to splitter, outputs to the two batteries. 10Amp fuse in supply to splitter keeps blowing when the engine runs. Any ideas? Did try fully charging both batts with mains charger, in case it was asking too much of the splitter to charge what were pretty low batts 11.5 and 10. Still blew the fuse. Has it destroyed the regulator on the alternator, or is just a duff splitter?

[/ QUOTE ]

The maplins splitter I have I would never fit between car alternator and batts ... as far as I know - it's only designed to go between charger and batts. A car alternator can pump out 40A or more after starting ... for short period.

 

[boguing]

Re: Nearly...

The instruction sheet that came with it specifically mentions car use - with regard to not needing a regulator as there's one in the alternator. But, it does state the need for a 10A fuse upstream, which certainly implies that it's not up to the job if the alternator is going to whack out 40A. That's why I tried it on fully charged batteries - in the hope that the alternator might not send too much out.

I'm taking it back this afternoon, but don't know if a replacement will be any better.

 

[boguing]

Re: Nearly...

Exchanged at Maplin as planned. Also arranged to borrow a clamp ammeter to find out what I'm dealing with.

Any boffins out there know whether the following might be practical?

S'pose that these £9 (not £19 as I thought) jobbies handle 10A constant, 20A peak - as alluded to in the data sheet.

And subject to testing I find that the alternator/regulator is exceeding 20A.

Put another in parallel seems like a good idea, so it can't be. The sensing would get horribly confused. But - if I put a third battery into the system, and had splitter 1 charging A and B, with splitter 2 charging B and C? Would that fool them enough?

ps Pretty certain that the regulator is not fried. Batteries are now both at 12.76 after 50 miles driving, lights off. Would have expected them to have boiled by now - wouldn't I?

 

[Guest]

Re: Nearly...

[ QUOTE ]
Exchanged at Maplin as planned. Also arranged to borrow a clamp ammeter to find out what I'm dealing with.

Any boffins out there know whether the following might be practical?

S'pose that these £9 (not £19 as I thought) jobbies handle 10A constant, 20A peak - as alluded to in the data sheet.

And subject to testing I find that the alternator/regulator is exceeding 20A.

Put another in parallel seems like a good idea, so it can't be. The sensing would get horribly confused. But - if I put a third battery into the system, and had splitter 1 charging A and B, with splitter 2 charging B and C? Would that fool them enough?

ps Pretty certain that the regulator is not fried. Batteries are now both at 12.76 after 50 miles driving, lights off. Would have expected them to have boiled by now - wouldn't I?

[/ QUOTE ]

Interesting as mine is not that rated ... mine if I remember rightly is ... 8A cont. only and max 20A for 5 secs ...... nowhere near enough to survive a car alternator no matter what state batterys in.

Yes it does say car batterys but I think that it means OFF car not on. It is really designed - the sheet says it and also on Maplins web-site - for Caravans / Boats etc. to split charge to twin battery systems. I knowq it does have a section about car generators - but IMHO this is optimistic given the Ampage design of the module. I've had mine wired in to my boat for over a year now and it's worked beautifully ... charging from a standard cheapo car charger ... (non-auto-float - as they don't work with this item ....).

 

[boguing]

Re: Nearly...

Take your point Nigel. You can read it either way!

What do you think of my doubling up plan?

 

[Guest]

Re: Nearly...

[ QUOTE ]
Take your point Nigel. You can read it either way!

What do you think of my doubling up plan?

[/ QUOTE ]

Honest reply ? Not in my opinion a good idea ... if one fails you are back very quickly in the sh*** They also run hot when pushed ...

I'm happy to relegate mine to off-car charging ..... basically on boat. At 7 quid as I paid ... and now 8.99 - a very good buy ! Its a pity that the charge regulator they do is too limited in ampage - as the two together would be an excellent package if the reg. could handle the amps.

An engtine alternator can handle two batts in parellel easily ... so why need a splitter ?

 

[boguing]

Re: Nearly...

The device I want to use in the car is rated at 12V max. Over that and it locks down.

So the peak voltage that it would see from the alternator in a single or dual batteries in parallel is no good.

Hence the separate battery need. What I have done is to make up a switching system (relays etc) that isolates the second battery for engine start, then reconnects it when the engine is running and the alternator voltage is stable. Then I have a second battery charging at some voltage (over 12). The clever bit was taking a soldering iron to the top of battery two, exposing the link between cells five and six, made a connection to it, which now can be no higher than 12V.

I suppose I could modify it so that it does charge in parallel, just that the splitter was so cheap it seemed like such a good idea.

The third battery is actually ten NiMh 2.4 Amp AA cells in series - used during switching supply and as a power supply when battery two gets too low. These were what I was going to use in the dual splitter plan.

 

[Guest]

Re: Nearly...

[ QUOTE ]
The device I want to use in the car is rated at 12V max. Over that and it locks down.

So the peak voltage that it would see from the alternator in a single or dual batteries in parallel is no good.

Hence the separate battery need. What I have done is to make up a switching system (relays etc) that isolates the second battery for engine start, then reconnects it when the engine is running and the alternator voltage is stable. Then I have a second battery charging at some voltage (over 12). The clever bit was taking a soldering iron to the top of battery two, exposing the link between cells five and six, made a connection to it, which now can be no higher than 12V.

I suppose I could modify it so that it does charge in parallel, just that the splitter was so cheap it seemed like such a good idea.

The third battery is actually ten NiMh 2.4 Amp AA cells in series - used during switching supply and as a power supply when battery two gets too low. These were what I was going to use in the dual splitter plan.

[/ QUOTE ]

Interesting ... but seems to me as a layman ... to be way outside what the item was intended for ...