AutoElectricians - Charging 24v battery pack with 12v charger

Submitted: Saturday, May 16, 2020 at 13:28
ThreadID: 140026 Views:1357 Replies:6 FollowUps:21
One for the Auto Electricians.

I have a 24v battery starter pack in my vehicle but only have a 12v smart charger.

So when I need to charge the batteries, I disconnect the linking cable between the two 12v batteries and charge each battery individually. Is a bit of a pain.

Someone did mention to me that I didn't have to actually disconnect the batteries and that I could charge each battery from the 12v charger while the other one is still connected. Note this is not connecting the 12v charger across the +ive and negative side of the 24v pack but simply charging each battery with the other connected.

Is this viable or can damage occur.

Thanks
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Reply By: qldcamper - Saturday, May 16, 2020 at 14:30

Saturday, May 16, 2020 at 14:30
If you just connect one 12 volt battery at a time it should be ok.
As long as the charger suits the batteries.
You have given no details of the battery size or type or that of the charger but in theory you can centre trap the batteries and charge individually.
How does it come about that you have or need a 24 volt jump pack and dont have the means to charge them?
AnswerID: 631625

Follow Up By: OzzieCruiser - Saturday, May 16, 2020 at 14:58

Saturday, May 16, 2020 at 14:58
Thanks for the comments - is not a jump pack but as indicated are the starter batteries - vehicle sits for long times so I like to put the batteries on charge at least once a month to keep them topped up - especially in winter.
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Reply By: Allan B (Sunshine Coast) - Saturday, May 16, 2020 at 15:00

Saturday, May 16, 2020 at 15:00
.

Ozzie, charging one at a time whilst still coupled together is quite OK. Just be sure of your polarity when charging each battery. And in order to maintain balance, charge each battery to the same level. This is most easily achieved by charging each fully.



Cheers
Allan

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AnswerID: 631626

Follow Up By: Member - David M (SA) - Saturday, May 16, 2020 at 15:16

Saturday, May 16, 2020 at 15:16
Don't know where the 24v comes in ?. When I give mine a charge every few months I just connect to the crank battery and the solenoid cuts in and charges
both at the same time.
Dave.
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Follow Up By: Allan B (Sunshine Coast) - Saturday, May 16, 2020 at 15:24

Saturday, May 16, 2020 at 15:24
.
David, The "24v" is because Ozzie has a 24v starter derived from a pair of 12v batteries connected in series.
Your setup is two 12v batteries, starter and auxiliary, charged in parallel via the solenoid, but each supplying their own 12v loads.
Cheers
Allan

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Follow Up By: Member - David M (SA) - Saturday, May 16, 2020 at 15:31

Saturday, May 16, 2020 at 15:31
Understand the basics Allan but never heard of anyone with a 24v starter. And the reason for it ? ( other than to be different ) :)
Dave.
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Follow Up By: Allan B (Sunshine Coast) - Saturday, May 16, 2020 at 15:33

Saturday, May 16, 2020 at 15:33
.
Many larger vehicles, trucks and earthmovers have 24v starting systems.
Cheers
Allan

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Follow Up By: OzzieCruiser - Saturday, May 16, 2020 at 15:53

Saturday, May 16, 2020 at 15:53
Thanks Allen - yes is a 24v system and the aux is a 12v system charged via 24v to 12v Dc Dc charger.

Used to have an additional 12v alternator bolted to the engine but have decided it is easier with a Dc Dc charger.
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Follow Up By: Member - David M (SA) - Saturday, May 16, 2020 at 16:05

Saturday, May 16, 2020 at 16:05
Well aware of 24v systems Allan. As the OP had Cruiser in his name and said "vehicle" I assumed he was talking about a light vehicle, as in Toyota. I will endeavour not to jump to conclusions in the future.
Dave
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FollowupID: 907760

Follow Up By: Phil G - Saturday, May 16, 2020 at 22:11

Saturday, May 16, 2020 at 22:11
David, many Landcruisers in the Northern Hemisphere came with 24 Volt systems to aid cold weather starting. That is why 60/80/100 series and Prados usually have a space for a second battery.
The 24V grey imports from Japan can be a pain getting parts.
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FollowupID: 907773

Follow Up By: qldcamper - Sunday, May 17, 2020 at 08:03

Sunday, May 17, 2020 at 08:03
The 24 volt landcruisers i have seen run a series parallel solenoid so runs a 12 v system but uses a 24 v starter. The solenoid just reconfigures the batteries to series on start and supplies the starter only with 24 and everything else with 12.
The same as many euro trucks used to be.
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Follow Up By: Member - David M (SA) - Sunday, May 17, 2020 at 08:57

Sunday, May 17, 2020 at 08:57
Allan. Seems like the Military prefer 24 volt to. Found that on Google. "A wonderful source of information"
Dave.
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FollowupID: 907779

Follow Up By: Phil G - Sunday, May 17, 2020 at 09:09

Sunday, May 17, 2020 at 09:09
qldcamper - The BJ42 and HJ61 with 24V were 24V everything and called NATO spec. The HDJ81 I'm not sure but may have been as you describe?
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FollowupID: 907780

Follow Up By: qldcamper - Sunday, May 17, 2020 at 09:20

Sunday, May 17, 2020 at 09:20
The ones i worked on were private imports. Have never seen a full 24v model, not saying they dont exist, just never worked on one.
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FollowupID: 907781

Reply By: RMD - Saturday, May 16, 2020 at 16:07

Saturday, May 16, 2020 at 16:07
OzzieCruiser
I understand/know some earlier Cruisers had 24v systems. So did some Nissan vehicles. As Allan has mentioned, simply attaching the clips to each battery in turn Pos Pos and Neg Neg of each battery, you can charge them with no worries. In fact, if you had two chargers one can be attached to one battery and the others clips to the next battery and both can charge simultaneously as the battery chargers are only seeing one battery each anyway. Used to do that when I was a 3rd yr apprentice and had to run the auto elec section for quite a while by myself. Time was of the essence quite often, so being able to charge both, with two chargers, worked out well for me.
If in possession of two identical same make simple ( not smart) chargers, which each can charge a battery, Linking one Pos and One Negative clip together effectively makes a 24v battery charger with the other Pos and Neg clips. Alternatively, if in possession of a solar panel which has an OC voltage of a little above 24v, it too can be used directly for a period of time to charge the 24v starters. Monitored of course. Just a few options, don't know exactly what gear you have. I often have to improvise to achieve an aim.
AnswerID: 631627

Follow Up By: OzzieCruiser - Saturday, May 16, 2020 at 17:11

Saturday, May 16, 2020 at 17:11
Thanks for those tips - only have the one charger so I will stay with that - as I indicated is only for when the vehicle is laid up so urgency is not an issue for me.

Yes I have some solar panels but have them wired in parallel so max voltage is around 17v not enough for the 24v system. In the future I might consider rewiring so I have the option of in series (34v) or parallel (17v) - my Mppt regulator can handle both.

However your advice and the advice provided by Allen solves my current issue.

Thanks
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FollowupID: 907765

Reply By: Peter_n_Margaret - Saturday, May 16, 2020 at 17:17

Saturday, May 16, 2020 at 17:17
Alternatively, get a couple of 12V x 5W solar panels from fleabay in series and set and forget.
EDIT - actually, 2 or 3W would be enough.
Cheers,
Peter
OKA196 motorhome
AnswerID: 631632

Reply By: Zippo - Sunday, May 17, 2020 at 10:44

Sunday, May 17, 2020 at 10:44
Apart from all the other advice, the ONLY risk I see is in the unlikely event that the chargers' output side is earthed i.e. not fully floating. Straightforward to determine with a multimeter.

Unlikely, but not impossible. Where TWO similar/identical chargers are used to hit up the battery pair, there would be some fireworks!
AnswerID: 631641

Follow Up By: RMD - Sunday, May 17, 2020 at 13:27

Sunday, May 17, 2020 at 13:27
Two of same chargers linked together in series acts as one 24v charger. Not sure about hitting something up, whatever that is.
I used to use two like that to run a foam hot wire cutter too. They simply supplied a level of DC at the output.
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FollowupID: 907788

Follow Up By: Zippo - Sunday, May 17, 2020 at 14:27

Sunday, May 17, 2020 at 14:27
Yes RMD, "Two of same chargers linked together in series acts as one 24v charger."

But if you bothered to READ, in the case where the outputs are EARTHED - i.e. connected to the AC supply earth - there WILL be fireworks.
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FollowupID: 907790

Follow Up By: RMD - Sunday, May 17, 2020 at 15:06

Sunday, May 17, 2020 at 15:06
Zippo
You mentioned the "earthed" output, I DID bother to read it but dismissed the issue, all the battery chargers I have ever had have two 240v ac pins, One Active and One Neutral. The charging section can't be connected to an "earth" which is not there. Very early ones may have had the transformer laminations connected to a 240v "earth" pin but not the secondary windings. What exactly is the problem?
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FollowupID: 907793

Follow Up By: Zippo - Sunday, May 17, 2020 at 20:12

Sunday, May 17, 2020 at 20:12
You dismissed the whole point.

The problem is very obvious, if you haven't worked it out (as the resident expert on everything) then I won't waste my time explaining it any further.
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FollowupID: 907802

Follow Up By: OzzieCruiser - Sunday, May 17, 2020 at 21:56

Sunday, May 17, 2020 at 21:56
Hey guys - mute point as I only have one 12v charger not two. If I was to buy another charger I would just buy a 24v charger but is not needed for my needs.

Cheers

Garry
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FollowupID: 907805

Reply By: qldcamper - Monday, May 18, 2020 at 08:21

Monday, May 18, 2020 at 08:21
Good morning Ozzie,
Just as a matter of interest, what sort of vehicle is it ?
There were all sorts of creative systems installed in converted busses before switch mode tech was developed specifically for automotive applications, some successful, some not.
What size are the batteries and charger?
There are some basic rules of thumb to follow that you may already be aware of.
No need for me to go into them unless you ask, pretty sure someone else will jump in now the matter has been raised with lots of technical words and theories, just give him time to google it to become an expert on the matter lol.
AnswerID: 631649

Follow Up By: OzzieCruiser - Monday, May 18, 2020 at 12:25

Monday, May 18, 2020 at 12:25
Its a V8 Land Rover - standard charging system - 24v alternator charging 2x12v standard starter batteries - most car systems are 24v.

Like other 4wd vehicles I have installed a deep cycle 12v aux battery that is charged via a 24v to 12v Dc Dc charger.

This all works fine, it was just that I have been disconnecting the two 12v batteries in the 24v pac to charge them with my 12v charger - question has been answered.

Thanks to everyone who provided input.

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FollowupID: 907815

Follow Up By: RMD - Monday, May 18, 2020 at 14:57

Monday, May 18, 2020 at 14:57
QLD
Seeing you have often accused me of using Google, AND demanded to know and I, provide my qualifications to you before you will believe anything, I presume you are again having another go at me.
You seem unable to be corrected. Often you have been wrong or misleading or inaccurate, sometimes quite sound. A couple of others also seem to be grumpy people who can't entertain another point of view and also seem to have grog on board, seeing it is mentioned frequently, and the brain is somewhat affected as a result.
NO, I do not google for information, maybe 4 times this year so far regarding RC systems, so the claim I do could not be further from the truth. A cheap shot there by you. Everyone has experience in something, some more than others it seems. I relate what I definitely know, not "definately"as you say. If the forum Moderators want erroneous and misleading info for genuine people asking genuine questions there are too many who do that and no one seems troubled by it. I try to provide options for those who don't know. Your expertise seems to be fairly limited.
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FollowupID: 907820

Follow Up By: ModSquad - Monday, May 18, 2020 at 16:38

Monday, May 18, 2020 at 16:38
qldcamper and RMD, guys please tone down the sniping and baiting act here and across the forum. This is an "around the fire" kind of forum and not the place for digging in trenches and lobbing artillery at each other as it detracts from the forum experience for everyone and actually inhibits people from asking questions that may provoke another barrage of artillery fire. Just don't do it.

Any more of such behaviour will earn you both some time in the sin-bin with a temporary ban which I am sure that neither of you want. Nor us.

The Squad


Moderation is just rules

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