Double Battery Charging

[California Dreamin]

With a 12 volt charger....you are going to have to disconnect and charge them separately......
Otherwise you will need a 24 volt charger (charging in situe)
This setup has obviously been installed just to power the night heater...

Martin

Oldie, Ghost - I don't really want to disturb the heater (which is working great) or the two batteries which are conveniently located and which, if kept topped up, make for a handy back up to the main leisure battery.

It's a shame I need to disconnect and charge them individually but at least I now know that I do.

Cheers chaps

Ian

I can appreciate that as the heater is working fine you just don't want to change things: however, the reality is swapping the cables on the batteries and adding a small invertor before the heater feed won't be 'disturbing or moving' anything.

But...if you are happy to manually disconnect and re-charge each of these batteries after use that's fine....a pain...but fine.
BUT
Be warned!
Re-charge immediately after use....as the first time you forget to do this, you may well find you end up with two knackered batteries (batteries cannot tolerate being left in a discharged state).

Martin

[isaune]

[/quote]

I can appreciate that as the heater is working fine you just don't want to change things: however, the reality is swapping the cables on the batteries and adding a small invertor before the heater feed won't be 'disturbing or moving' anything.

But...if you are happy to manually disconnect and re-charge each of these batteries after use that's fine....a pain...but fine.
BUT
Be warned!
Re-charge immediately after use....as the first time you forget to do this, you may well find you end up with two knackered batteries (batteries cannot tolerate being left in a discharged state).

Martin[/quote]


Hmmm that's good advice - thanks Martin - which is making me rethink things.

How about this?

I will seldom, if ever, use the diesel heater. If a heater is required (would have to be a VERY cold night) I would use a little fan heater I have if hooked up. The only time I would use the diesel one is if 1) absolutely freezing and 2) not hooked up.

Therefore, I am starting to think it might be worthwhile to take those two perfectly good 85AH heater batteries and connect them in parallel with my leisure battery.

If I'm not mistaken, this will mean:-

1) 3 times the leisure battery capacity when not hooked up
2) all 3 batteries will be charged via the split relay when travelling (albeit I suppose it will take 3 times as long)
3) and all three can be charged at the same time by my 12v intelligent charger (still need to understand where to attach my crocs)
4) and on the (EXTREMELY) rare occasions when I want to bring the diesel heater into use, I will have a 10 minute job of disconnecting and reconnecting

Does that all sound ok to you?

[ghost123uk]

It does, but why not just fit the cheap, small and easy to fit 12 to 24 volt step up device ?

It would take no time at all. is dead easy to do and you then don't ever have to worry about messing about with wiring to use the heater or charging the batteries separately (which is a faff) .

[isaune]

It does, but why not just fit the cheap, small and easy to fit 12 to 24 volt step up device ?

It would take no time at all. is dead easy to do and you then don't ever have to worry about messing about with wiring to use the heater or charging the batteries separately (which is a faff) .

Fair point, Ghost.

I'm just coming round to thinking that I will get more use out of those two batteries if I have them helping out my existing leisure battery than I would if I had them running a diesel heater which may never get used.

Only question remaining is how to charge 3 x 12v batteries in parallel with a single 12v charger? I guess you simply connect to one of the batteries as normal and all three of them get topped up together - is that right?

Ditto with the switch relay to the alternator?

[Oldiebut goodie]

Why not just find out what model of heater it is that you have fitted - it is an Eberspächer is all we have at present, then I can tell you if a small cheap £4 step up converter can be used? There should be a label on the side with the details on. Failing that measure the length,width, height and the diameter of the outlet and I will try to match it against the specifications.
It makes more sense to use them as normal 12v batteries rather than 24v then they can be used for everything.

(You could always charge them by a normal 12v split charge and use a step up on the output to charge them at 26v or so if you are determined to keep them as 24v.)

[The Bishop]

I assume this is the "the backwards ticks" logo ?

[isaune]

Why not just find out what model of heater it is that you have fitted - it is an Eberspächer is all we have at present, then I can tell you if a small cheap £4 step up converter can be used? There should be a label on the side with the details on. Failing that measure the length,width, height and the diameter of the outlet and I will try to match it against the specifications.
It makes more sense to use them as normal 12v batteries rather than 24v then they can be used for everything.

(You could always charge them by a normal 12v split charge and use a step up on the output to charge them at 26v or so if you are determined to keep them as 24v.)

Hi Oldie

As you will know by now, I am not very technical and that is an understatement!!

However, if I understand you right, this is what you are saying:-

1) these two batteries are currently connected in series to provide 24 volts to my heater
2) it is likely that I could make a small and cheap adjustment (step up converter) which would allow them to be connected in parallel and thus power the heater with only 12 volts
3) I could even attach the third battery (my leisure battery) in parallel to the other two
4) this would mean I have 3 times the leisure battery capacity I currently do
5) and these 3 batteries would be charged via the existing split charge relay that charges the leisure battery (albeit it would take 3 times as long)
6) and simply connecting my 12 volt smart charger to ONE of the three batteries will ensure all three are charged and kept topped up

If all that is correct, OIdie, then I agree it does sound like the perfect solution.

And, yes, that is the logo Bishop!!

[ghost123uk]

I am not OBG, but the answer to all your points is = Yes

Note though that when connecting 3 batteries in parallel it is considered good practice to ensure that all 3 are the same Ah rating and in similar condition, ie if one of them is in poor condition, it can prevent the other two from working properly.

A word of extreme caution. If you are in ANY doubt whatsoever about how to wire batteries in parallel, please do not guess. Ask here or even better get someone who (definitely) knows to show you. Exploding batteries is summat you NEVER want to see or be near.

[isaune]

I am not OBG, but the answer to all your points is = Yes

Note though that when connecting 3 batteries in parallel it is considered good practice to ensure that all 3 are the same Ah rating and in similar condition, ie if one of them is in poor condition, it can prevent the other two from working properly.

A word of extreme caution. If you are in ANY doubt whatsoever about how to wire batteries in parallel, please do not guess. Ask here or even better get someone who (definitely) knows to show you. Exploding batteries is summat you NEVER want to see or be near.

Thanks Ghost - good news about my 5 points.

Fortunately the 3 batteries are all 85ah and all in good nick so that should be ok.

I must admit I was assuming it was simply a case of joining positive to positive to positive and negative to negative to negative with the battery nearest the heater to connect to that and the existing leisure battery to be connected (as now) to the split charge relay?

But from your warning, I am guessing it is not that simple???

[The Bishop]

Do you really need 85 +85 +85 Ah = 255 Ah of battery? That seems an awful lot.

1) Most people survive with one. It will be recharging when you drive and it's not the end of the world if it does go flat.
2) I would have thought the space could be better utilised
3) When 1 of the batteries start to fail you won't know about it until it brings down all three.

[isaune]

Do you really need 85 +85 +85 Ah = 255 Ah of battery? That seems an awful lot.

1) Most people survive with one. It will be recharging when you drive and it's not the end of the world if it does go flat.
2) I would have thought the space could be better utilised
3) When 1 of the batteries start to fail you won't know about it until it brings down all three.

Fair point Bishop.

The thing is, the three batteries are already there (2 for the heater and 1 as a leisure battery) and I just thought this seemed like a worthwhile improvement.

As things stand, the two "heater" batteries will be seldom if ever used and will require regular disconnecting (because they are in serial) and topping up to keep in good condition.

The way proposed will at least mean it's easy to keep all 3 topped up and give them all a decent "workout" every now and then when camping without hook up.

[CJH]

Another point to remember is that you should ensure that the three batteries are fully charged individually before linking them together, as otherwise there is the potential for high current to flow between them until they equalise, and there's the risk that an 'intelligent' charger will get confused about the state of charge of the combined battery bank.

Use fat cable too, beyond what you might think is necessary for the current that will be flowing in the circuit, since you want to avoid voltage loss so that all the batteries will charge and discharge at as close to the same rate as possible.

[Oldiebut goodie]

There is a very good piece on connecting more than 2 batteries together here: (ensuring balanced output etc)

http://www.smartgauge.co.uk/batt_con.html

Methods 3 and 4.

[California Dreamin]

There is a very good piece on connecting more than 2 batteries together here: (ensuring balanced output etc)

http://www.smartgauge.co.uk/batt_con.html

Methods 3 and 4.

Good piece but just like his own comment about being skeptical I can see more that one obvious flaw ...the main one being the rate of draw and recharge.
100 amps honestly....whilst I reckon the average draw wouldn't be much over 5 amps...15 with a tele and laptop on the go.
And if the bank of batteries are sat next to each other connected with a continuous 'buzz bar' arrangement, linking the pos/neg terminals I really can't see where the difference would be feeding off either end.

Good info if the batteries are located in difference places with longer connecting runs..

Martin

[Oldiebut goodie]

I think that Smartgauge has developed from being mainly a marine concern where large battery banks and current draw is the rule rather than the exception so their advice is usually biased to marine usage rather than our puny systems.