Charging multiple batteries

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Kantara

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After a visit to LIDL a few weeks ago, I now have 3 battery chargers - the Tronic T4X chargers. I have been using them to keep the 3 120AH batteries topped up at home, but I am wondering about whether I can use them on board.

The batteries are kept in 2 banks, 2 batteries for domestic, one for engine start and are connected through a standard 4 postion rotary switch (Off, 1, Both, 2). The boat is kept on a swinging mooring but occasionally I visit marinas where I would like to top up the batteries where power is available. In the past, I have had a single Halfords 2 stage charger and have connected the negative croc to the common negative and have connected the Positive to each battery in turn. This has charged, but very slowly.
Can I connect each charger to a battery and charge them all at once or will I have to disconnect all the terminals?
I would prefer to keep at least one battery providing power to the boat so I can run Navtex, VHF etc.
 
I am sure one of the forum battery experts will give you a definitie on this, but I would imagine that the charging rate is very low from this charger and it would probably be better for you to choose which battery you wanted to attend to and connect just to that one as you have been doing. If your domestics are connected in parallel than that small charge will be shared across both of them.
 
If the batteries are the same technology (lead acid, sealed, gel etc etc) there's no problem with charging them in parallel, i.e. rotary switch in 'both' position. but make sure you turn it back after wards. A better solution is to put in split charge diodes so you can't forget to turn the switch back.

Secondly, I'm not sure exactly how the Lidl chargers work, but there's chargers and there's chargers... Most automotive types won't really achieve 100% charge in your batteries, because they're constant voltage. Best go for something like a Sterling multi-stage charger. I have just fitted one of these:
alternator controllers and possibly is the best £80 I've spent on the boat to date (the box basically controlls the alternator in such a way as to turn it into a much more effective, multi-stage charger) - given you are on a swinging mooring I'd suggest it's a better solution than a mains dependent one. you could of course fit both...
 
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A better solution is to put in split charge diodes so you can't forget to turn the switch back.

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Only if low loss diodes which most aren't. I use a maplins split charge unit made by Kemo :

http://www.maplin.co.uk/Module.aspx?ModuleNo=37767&TabID=1&WorldID=&doy=6m1

But can only work with old fashioned non-maintenance / chip controlled chargers. I tried with an auto-float charger and charger wouldn't have it. Went back to bog standard charger (cheapest best !) and bingo no problem. The unit is designed for max. 8A so is not suited to boost chargers. But it senses battery charge and sends charge to one that needs it and has no drain from one to other.
I have it permanently connected for my shore power charger to batterys. The charger itself is controlled by simple timer in the mains socket on board to prevent over-charging.

There are better, more powerful systems of course and I'm sure someone will be along to say ......... Old Refuelers system is cr*p ... better to have system XXXXXX. But note my system incl. charger is less than 20 quid. Second that despite boost levels of charge - the amps actually when a battery is being topped up charged is very low regardless of charger anyway. It's only when battery is low on charge that a boost charger comes into advantage.
 
If the voltage sensor is place on a battery bank then loss through diodes isn't a problem,as long as they're rated for the current... however a split charge relay like yours has some advantages too! perfectly feasible to get hold of a bigger split charge relay (and more expensive to be fair) that'll handle a boost charger...

given the OP is on a swing mooring and may not often visit a marina, assuming no other charge sources e.g. wind tub, a boost charger/alternator controller will allow much more energy to be harvested in the (relatively brief?) periods of motoring, hence my recommendation of alternator controller. if he had permanent mains available it'd be a different story (but I think I'd still recommend a multi-stage charger)
 
I assume you are talking about still using all three chargers simultaeously.

If you do that you will need to separate all the positive connections. (you can leave the negatives connected) No problem with separating the starter battery as that can be done with the 1,2,off, both switch even if a split charge system does not. BUT can you easily separate the two batteries that form the domestic bank?

Do you have any split charging system, VSR or Diode splitter, that may have some bearing on things (I'd assume that with a 1,2,off, both switch you do not.)

Those Tronic T4X chargers only have a 3.6 amp max output so fine for topping up a nearly fully charged battery or trickle charging but do not expect them to quickly recharge a battery that has been significantly discharged.

If your Halfords charger is an 8 amp one it may be more convenient , but not much faster, to leave the two domestic batteries connected together and use that for that bank and the Tronic for the starter battery.

If you use a lot of power on board you really need to assess how much you do use and determine a size of charger that will replace it in the time you will have available to do it.
 
But he's talking about when he's connected to shore and wants to charge multiple batterys. The swinging mooring / boost doesn't come into it really based on his question.

As to diodes - I haver split diodes on my boat and I tried to charge through those with a high capacity charger that we use to charge up my truck batterys (actual truck - Mercedes 814). It refused to work - even when we wound up the manually controlled current. It apparently realised there is a voltage drop across the diodes and wouldn't accept it.

A VSR on the other hand such as KDpower etc. can supply would probably do fine.

Most batterys are not drawn down that low before engine started / charging back up again - so small charge splitter like mine does the job. Yes it's designed more for caravans that sit on site, but is efficient for small money.
Kemo say that it can work of a standard alternator, but I think they think in terms of cars where current at charge is low - as batterys are rarely low to create situation of alternator banging out high amps. Boats though are not so lucky and I'm reluctant to connect it to alternator with 8A max.

As I say - at less than 20 quid all in ... I'm happy !!
 
Forgot to add that the split diode bank I have is now disconnected - I have no use for it !! It sits there in the engine bay just taking up space.

If it wasn't so costly to mail out - I'd offer it someone on here or SBC !!
 
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As to diodes - I haver split diodes on my boat and I tried to charge through those with a high capacity charger that we use to charge up my truck batterys (actual truck - Mercedes 814). It refused to work -

Most batterys are not drawn down that low before engine started / charging back up again - so small charge splitter like mine does the job.


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The mains charger probably was looking for a battery voltage, the blocking diodes prevented this, so no charge. We did a similar thing for Sealine, the mains charger would not cut in if it did not have a certain voltage.

The one danger with small vsr to charge engine and service battery from a mains charger, is engine starting. As the service bank is larger, there is a chance of the engine starting via the vsr from the service bank. This cable is normally small for this current, and can lead to fire or welded contacts on the vsr. This is why we always interface our small vsr with the starter motor, drops out relay should starter be used when engaged.

Brian
 
Fair enough, based on his question... I was merely trying to read a little deeper into what was written.

final point on VSR/split diode charging; ideally it's better to measure the charging voltage at the battery, which units like the sterling do; that way it compensates for any losses in the system, due to diodes or undersize cable etc. there are of course issues with this relating to exceeding the rating of said undersize cables. If your charger doesn't have a remote voltage sensor, I agree diodes aren't a good idea and you should go for a VSR or manual switch!
 
No problem and all points are valid ... I was just getting back to his question of charging while shore power available.

As to my small relay from maplins. It has no fear of being in starting circuit as it's fitted separate to the main selector switch. In fact via fuse direct to batterys.
The only way I would be able to get the Split Diode bank to work on my boat would be to cheat the alternator with a diode itself to make the alternator itself up its voltage by 0.7V to compensate for split diode losses ... Garrods excellent book on Boat Electrics illustrates this trick. My alternator does not have facility to battery sense.
 
Back to the original question. You could run into all sorts of difficulties using 2 battery chargers in parallel. So you need to separate the 2 domestic batteries so that you end up with one charger for each battery.
ie take one +ve terminal of one domestic battery then fit 3 chargers to 3 batteries.
You really should have an ampmeter where you can monitor the current into each battery. Man6y chargers will reduce the charge after a while. A 3 stage type hopefully will put more charge in before it reduces.
You don't wan to be sitting around waiting for the batteries to charge when in fact very little is going in.
So the best kind of charger is the older simple crude transformer rectifier type. Here the charge current remains fairly high and is sometimes adjustable because the current flows in pulses 50 times per second the peak voltage being quite high the average voltage determines the average current. The reason these types are not popular is that they must be turned off when the battery is charged manually., You won't have that problem with limited time at the dock.
So get an ampmeter. The clip on type would be best. Get an idea of exactly what your chargers are doing. good luck olewill
 
Thank you all for your replies. What an invaluable forum this is.
This issue seems to split into 2 - overall maintenance of batteries when based on a swinging mooring, and getting as much charge into the batteries as possible when connected to the mains.
I have been skirting around the issue of ALternator controllers, but I think tobble is right - I need to upgrade my alternator. The link supplied pointed to Sterling, bu their proce was nearly double the 85GBP quoted!
As far as the battery chargers are concerned, it looks as though I am going to have to separate them out so I have one charger to one battery. The Tronix ones are multi-stage and do seem to put in a reasonable charge.
As far as diodes are concerned, I think I need to get my head round Nigel Calder's book.
Thanks again
 
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