battery charging

Submitted: Wednesday, Jul 28, 2010 at 10:25
ThreadID: 80365 Views:2431 Replies:4 FollowUps:14
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Can one charge two batteries of equal size simultaneously?

and/or is best to install isolators and charge separately?
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Reply By: Battery Value Pty Ltd - Wednesday, Jul 28, 2010 at 10:39

Wednesday, Jul 28, 2010 at 10:39
Hello Member,

if the batteries are of the same chemistry, state of charge, and temperature, then you can do this without any ill effects whatsoever.

In case they're not at the same state of charge, the battery with the higher SOC gets slightly over-charged in a three stage charging algorithm.
This effect is more pronounced if the batteries were of different capacity ratings and the smaller battery is the one with the higher SOC at the start of charging.

Love your multitasking liner hehehehe.

Best regards, Peter
AnswerID: 425501

Follow Up By: Member - Bucky - Wednesday, Jul 28, 2010 at 14:33

Wednesday, Jul 28, 2010 at 14:33
Peter
I like that call... one thing I do, is look at matching up battery's all the time...
Just makes sence to me.. even though you can get away without matching,
(for a while anyway)

Cheers
Bucky
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Follow Up By: Member No 1- Wednesday, Jul 28, 2010 at 17:10

Wednesday, Jul 28, 2010 at 17:10
2 batteries are of same make model etc etc

what adoes one do if say a third is not?...does one stick in battery isolators and do it manually?...can it be done automatically?
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Follow Up By: Battery Value Pty Ltd - Wednesday, Jul 28, 2010 at 17:56

Wednesday, Jul 28, 2010 at 17:56
Member,

when mixing batteries, this advice is for you:

In case the charging is done by a (recommended but dear) multistage system, then the boost voltage setting should be adjusted to suit the one battery with the lowest recommended boost voltage.
Similar goes for the float voltage setting, but these don't differ much from battery to battery anyway.

F.e. three batteries: one has a boost recommendation of 14.4V, the next one has 14.7V, and the third one has 14.2V.

Wire them all in parallel, and have the multi stage charging system set to 14.2V boost (and 13.6V float).

Find out which of the three batteries sits in the hottest spot, and attach the temperature sensor to that one.

In case of alternator charging:

the issue of mismatched charging is moot, and all batteries subject to regular substantial depth of discharge will suffer - alleviate this by applying occasional charge top ups manually (again with the lowest boost voltage setting).
Solar is ideal for this because it can supply the higher voltage and low current required for this. Mains powered charger is cool too, but generator is a waste of petrol for this purpose.

Hope this sums it up.

cheers, Peter
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Reply By: CJ - Wednesday, Jul 28, 2010 at 11:50

Wednesday, Jul 28, 2010 at 11:50
YES hok them up in parallel


CJ
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Reply By: jvb1 - Wednesday, Jul 28, 2010 at 12:27

Wednesday, Jul 28, 2010 at 12:27
Hi, don't mean to hijack this thread, but what happens when you install a new battery to an existing one, do you have to make sure they are both fully charged first or am I reading to much into this.

Thanks Jvb1
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Follow Up By: Moose - Wednesday, Jul 28, 2010 at 13:07

Wednesday, Jul 28, 2010 at 13:07
WTH does "what happens when you install a new battery to an existing one" mean?
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Follow Up By: jvb1 - Wednesday, Jul 28, 2010 at 13:20

Wednesday, Jul 28, 2010 at 13:20
Sorry Moose will try to make clearer. The question was asked if you could charge two batteries at once which I was under the impression that you could, but Peter replied "if same chemistry, state of charge, and temperature,....." So my question was do I need to do anything to the existing battery if I was to add a second battery. Hope this makes sense. After seeing a previous thread about a battery dropping a cell I don't want to go there. I'm still new to this stuff and trying to get my head around it all.

Thanks Justin.
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Follow Up By: Battery Value Pty Ltd - Wednesday, Jul 28, 2010 at 14:38

Wednesday, Jul 28, 2010 at 14:38
Justin,

you're under the right impression, yes you can hook 'em up in parallel for charging.

And this works best under the conditions I've stated earlier.

And these conditions are being met easily by leaving them wired in parallel for charging, and discharging.

That way, the batteries will always have equal SOC.

If you only switch them in parallel for charging, but not for discharging, then there is potential for overcharging one battery because the SOCs most likely won't be equal at the moment you switch them in parallel.

Having said this, if they're being 'float charged' by an alternator, then the mismatched SOC can't cause overcharging (but the one battery with the deep discharge will suffer because it's not going to see the required boost charging voltage).

Only in multi stage charging setups, the one battery with the higher SOC (if you allow it to go there by separating them) will get slightly overcharged as described earlier.

cheers, Peter
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Reply By: Maîneÿ . . .- Wednesday, Jul 28, 2010 at 15:18

Wednesday, Jul 28, 2010 at 15:18
Richard,
in answer to your very important question, I believe it's because they only get the headache when horizontal, if you keep them as close to vertical as possible everything will be fine, unlike a solar panel that will work in both horizontal and vertical positions.
Sorry, I could not load the demonstration video, maybe too many pixels ?

Maîneÿ . . .
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Follow Up By: Member - barry F (NSW) - Wednesday, Jul 28, 2010 at 15:37

Wednesday, Jul 28, 2010 at 15:37
Behave! LOL
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Follow Up By: Maîneÿ . . .- Wednesday, Jul 28, 2010 at 16:27

Wednesday, Jul 28, 2010 at 16:27
"Can one charge two batteries of equal size simultaneously" -> yes
"and/or is best to install isolators and charge separately" -> yes

Barry, because I believe solar will charge efficiently, is that really ‘miss-behavior’ LOL

Generators must be horizontal to work efficiently, IMO they also really are a pain
Only Solar works in both horizontal and vertical positions without strain or pain LOL
( no further pain information contemplated )

Maîneÿ . . .
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Follow Up By: Member No 1- Wednesday, Jul 28, 2010 at 17:11

Wednesday, Jul 28, 2010 at 17:11
dont confuse them Mainey

what you talking about!..lol
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Follow Up By: get outmore - Wednesday, Jul 28, 2010 at 18:05

Wednesday, Jul 28, 2010 at 18:05
and only genorators work with no sun
- so whats your point?

and anyway who mentioned genorators?


In partial answer to the question things can turn to crap if charging 2 batteries at the same time if one has died

a dead battery theives all the charge and runs down the good battery

had this happen with a few vehicles running "dumb" solonoids

go to start and even with dual batteries no go despite one battery still being good
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Follow Up By: Maîneÿ . . .- Wednesday, Jul 28, 2010 at 18:11

Wednesday, Jul 28, 2010 at 18:11
I think you have to get out a bit more and smell the roses LOL"

read what was posted then laugh at it :-)
I answered the "very important question" about *headaches* mentioned by the OP "LOL"

Maîneÿ . . .
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Follow Up By: oldtrack123 - Thursday, Jul 29, 2010 at 12:08

Thursday, Jul 29, 2010 at 12:08
Hi Mainey
You surprise me
You do have a sense of humour even if it did go over my head @ first reading .
Now I will have real problems with your posts
Trying to work out if they are tongue in cheek or serious beliefs[ like solar efficiency]


Peter
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Follow Up By: Maîneÿ . . .- Thursday, Jul 29, 2010 at 15:05

Thursday, Jul 29, 2010 at 15:05
Peter,

Yes, I believe I've a SOH, so maybe I should just type slower :-) :-)

Yes, I seriously believe in Solar power, even the Australian Government believes in Solar power now.
Wow, that remark should be deleted, it makes a positive statement into a negative one :-)

As for Solar efficiency, well that would be a whole new subject as there are so many ways of stating the efficiency of Solar systems, none are truly wrong, just some are more correct than others, so lets not go there LOL

Maîneÿ . . .
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Follow Up By: ob - Friday, Jul 30, 2010 at 12:46

Friday, Jul 30, 2010 at 12:46
Mainey, I was with you all the way until "even the Australian Government believes in Solar Power"........the Government whether Liberal or Labour believe most passionately in getting re-elected.........lol
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