Advice on charging a battery bank with ctek mxs 25

Submitted: Friday, Jan 23, 2015 at 22:52
ThreadID: 110856 Views:3207 Replies:2 FollowUps:13
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Hi Folks
This is my first post so I hope its not a stupid question.
I have 5 yuasa uxf100-12 AGM batteries(100amp hour)The specs for these batts say 10A normal charge and 20A max charge so the issue is that my charger is putting in 25 amps 5 more than recommended.My intention is to run these batteries in parallel making one 12v 500amp battery.The reason I bought this charger was that it was certified for AGM batteries and able to maintain upto 500amp hours in float maintanence,(pity I hadn't read batt specs before purchasing charger) so here is the question. If I am charging one of these batteries ie 100 amp hours with a 20amp max charge rate this is obviously 5 amps over but if it is wired in parallel with four of the other batteries and the charger was linked pos at one end of bank and neg at other end of bank would this somehow lower the amperage per battery bringing me back into safe parameters again.
Thanks in advance ,,Kirko
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Reply By: Allan B (Member, SunCoast) - Friday, Jan 23, 2015 at 23:20

Friday, Jan 23, 2015 at 23:20
Hi Kirko,

If the batteries are connected in parallel and the charger is connected to that combined battery bank then the charge current will be shared by the batteries. The current passing to each individual battery will be approximately equal but dependant on the battery condition, temperature, age and similar factors.
Therefore, your 25 Amps (maximum) charger will supply a maximum of about 5 Amps per battery.
Cheers
Allan

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Reply By: kirko - Friday, Jan 23, 2015 at 23:27

Friday, Jan 23, 2015 at 23:27
Thanks Allan,
I had my fingers crossed whilst waiting for the answer,,
Happy travels,,
Kirko
AnswerID: 544794

Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 23, 2015 at 23:39

Friday, Jan 23, 2015 at 23:39
Maybe I should have commented also about the charger's ability to restore charge to your 500ah battery bank.

If the bank was depleted to say 50% SOC (state of charge) then it will take your 25A charger about 12-14 hours to recharge the bank to 100% SOC. ( It is not a simple linear function of 250ah/25Amps )
Cheers
Allan

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Follow Up By: kirko - Saturday, Jan 24, 2015 at 00:03

Saturday, Jan 24, 2015 at 00:03
Thanks again,

Yeah I did read something to that affect in the chargers specs.

My biggest concern was battery damage due to putting in more amps than the battery was designed to receive.This aside I am happy for lengthy charge times if it means happy batterys.

Am considering splitting batterys for charging to one 200 amp hour and one 300 amp hour bank , charging these individually to 80% then linking all parallel back to 500amp hour to leave on maintanence charge .My thoughts being this would keep charging closest to being inside the 10-20amp charge range specified per battery .please let me know your thoughts.
Thanks again Kirk
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Jan 24, 2015 at 00:12

Saturday, Jan 24, 2015 at 00:12
Yes you could do that. It is a bit of mucking about and probably of no real benefit, but if it suits you then OK.
In fact total charge time may be a little less that way. You could even take each group up to 100% SOC before re-linking if you wished.
Cheers
Allan

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Follow Up By: Member - John and Val - Saturday, Jan 24, 2015 at 07:42

Saturday, Jan 24, 2015 at 07:42
Kirk,

As Allan says, the charging rate (ie amps) is not constant, and tends to drop off with time since your charger also limits the voltage applied to the battery. It is this voltage that controls the amps flowing to the battery. Once the maximum acceptable voltage is reached, the charging current will start to decline. So.... If you set out to charge a single battery with your 25 amp charger, it would probably see more than 20 amps for only a few minutes. For that reason I wouldn't be too reluctant to charge a single battery.

There is another factor worth bearing in mind. When you connect batteries in parallel as you intend, it's best if they are all very much the same - similar age, history, use, etc. For this reason, I'd be inclined to leave them permanently connected in parallel so they all get identical treatment when charging and discharging.

Cheers

John

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Follow Up By: Racey - Saturday, Jan 24, 2015 at 10:19

Saturday, Jan 24, 2015 at 10:19
I agree what the others have said. With 5 batteries in parallel, it is advisable to have your load and charger positive and negative connections taken from opposite ends of the bank. E.G. the positives connected to the positive on B1 and the negatives to the negative on B5. This spread the load and charging current more evenly between each battery.

Cheers
Jon
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Jan 24, 2015 at 11:04

Saturday, Jan 24, 2015 at 11:04
Hi Jon,

If you have used appropriate sized cabling between the batteries, the scheme you referred to will make less than 'half an iota' difference to the current distribution. It was a scheme dreamed up by someone who wished to say... "Look, aren't I clever?"

The cable impedances are lower than the relative battery impedances...... or at least they should be. Connect the external connections wherever convenient. But if it makes you feel good, do it diagonally!
Cheers
Allan

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Follow Up By: kirko - Sunday, Jan 25, 2015 at 19:44

Sunday, Jan 25, 2015 at 19:44
Hey Allan,,

The cable I am using is 2B&s 32mmsq,255 amp. Its the same cable that runs from your car battery to starter motor. Should do the job I hope,,sure wasn't cheap.

Thanks again for all your help.
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Follow Up By: Member - Wide ranger - Monday, Jan 26, 2015 at 21:27

Monday, Jan 26, 2015 at 21:27
Kirko
If you have to do cabling like that again use welding cable ,
I found it to be at least half the price and higher quality and double insulated . Use heat shrink sleeving to colour code the cables , this gets around it being one colour only . 16 , 25 , 35 and 50 sq mm
are common sizes .

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Follow Up By: kirko - Wednesday, Jan 28, 2015 at 18:55

Wednesday, Jan 28, 2015 at 18:55
Hi Folks ,,
so I finally goy my mxs 25 charger.Hooked 2*100amp hour batteries in parallel, connected em up to the charger and they charged fine.Next I charged a car battery , no probs.Next was to connect up my remaining 2 *100 amp hour batteries in parallel and top them up.connected them to the charger and got a flashing light in the desulphation soft start stage.If any one is familiar with ctek chargers is this normal for the light to flash in this stage,.I ask this because the car battery I charged was at 10.2v and it skipped this stage.The 2 * 100 amp hour batteries I am trying to charge read 12.52v in parallel and as single batteries one was 12.78v and the other 12.40. I tried charging these batteries individually and also got a flashing light in the desulphation stage with each.
any clues ? is this normal ? thanks in advance Kirko
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Follow Up By: Bushranger1 - Wednesday, Jan 28, 2015 at 20:49

Wednesday, Jan 28, 2015 at 20:49
Kirko,
Not had any experience with your specific charger but my understanding that a sulphated battery will have a higher resistance (ohms) if it is sulphated.
So I would think the Ctek would detect this condition so would automatically run the desulphation program. I have had batteries that have shown reasonable voltage but high resistance meaning they were suffering from sulphation.
Hope this helps.
Cheers
Stu
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Follow Up By: kirko - Wednesday, Jan 28, 2015 at 21:23

Wednesday, Jan 28, 2015 at 21:23
Thanks Stu.
Mate I ended up connecting the 1st of my 2 remaining uncharged batteries to the other 2 charged ones in parallel making a 12v 300 amp hour battery and the charger ran fine putting them all the way through to float charge.I have now added another battery bringing the total up to 400 amp hours and the charger is running fine ,, fingers crossed. Think I might get a kick up the bum from Allan B though ,, LOL,, Kirko
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Follow Up By: Allan B (Member, SunCoast) - Thursday, Jan 29, 2015 at 18:58

Thursday, Jan 29, 2015 at 18:58
Kirko, I dont't understand why i would "kick you" but let me say this.........
From many years of experience, I would say "If it works, then it works". Don't fret about the theory.
Cheers
Allan

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Follow Up By: kirko - Friday, Jan 30, 2015 at 20:51

Friday, Jan 30, 2015 at 20:51
Ha Ha ,, just a figure of speech Allan,,
Didn't want to do anything silly considering all your goood advice.
Had a slightly bad feeling in my bones and later found out it can be damaging to their longevity when a battery that is not fully charged is added in parallel to a bank of batteries that is fully charged.the ctek FAQ mentions the risk of current surges between batteries. wish these type of things were mentioned in the manual.Although the batterys charged well and are sitting at 12.86 volts after close to 48 hours of settling time after charging.
Thanks again gents for all your help and have a tops weekend
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