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Old 17-01-2014, 01:55   #1
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24v Batteries.. Series or Parallel First?

I have 2 banks (4 each) of 12v batteries that are connected in Series to make a 24v System

I originally wired as in “Series FIRST then Parallel” …where each pair was in put in Series (4 Purple) as in First Drawing

In my rewiring project I was advised by an electrical engineer that I will get better charging properties if I connect “Parallel FIRST then Series” with just the (one Purple series) to connect the 2 banks of 4.

Simply means changing a few lengths and new terminals but/
Does this make sense to the electrical gurus out there?


Would appreciate a 2nd opinion as my original "Series First" used slightly less cable, which I thought was more efficient.

I charge with Victron 24V charges
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Old 17-01-2014, 08:08   #2
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Re: 24v Batteries.. Series or Parallel First?

Well, if no-one is answering.....

There is no difference.
Batteries require good connections with the right sized cables. Thats whats important.

To optimise charging properties, its more important is that your Victron charger is properly configured to charge at the exact specs given by the battery manufacturer.

What's the absorbtion voltage currently set to and what type/make of batteries are they?
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Old 17-01-2014, 08:37   #3
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Re: 24v Batteries.. Series or Parallel First?

Can only tell that my bank was wired (originally, by yard) like on Your drawing 2 (Parallel then Series). When upgrading the bank I retained the original scheme, not giving it a thought. However I can not imagine the reason for Your first configuration to be less effective, but I'm by no mean electrical guru

Best regards

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Old 17-01-2014, 09:13   #4
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Re: 24v Batteries.. Series or Parallel First?

I agree with the advise you received. Parallel then series will give you considerably longer battery life, probably more than twice.

The biggest killer of batteries in series is mis-matching. If one of a pair of batteries in series discharges before the other the remaining 11 cells will force current through the discharged cell and rapidly destroy it since that is the only path through the battery(ies).

By putting them in parallel first you have averaged out any mis-matching over 4 batteries so the other 3 will help keep the voltage up on the one that discharged first and prevent polarity reversal on a discharged cell. You have 3 alternate paths for current to flow without forcing it through the first discharged cell.
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Old 17-01-2014, 10:40   #5
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Re: 24v Batteries.. Series or Parallel First?

Quote:
Originally Posted by Fuss View Post
.....There is no difference.
Batteries require good connections with the right sized cables. Thats whats important.
Well, if no-one is answering.....

There is a difference. Wiring all 6 volts in parallel first keeps them all balanced at the same voltage.

The positive and negative cables should be at each end dof the bank - not as shown.
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Old 17-01-2014, 12:37   #6
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Re: 24v Batteries.. Series or Parallel First?

Attaching battery banks end-to-end works fine for small banks, but results in poor service as the battery banks get larger. With four batteries per bank I would be tempted to get more complicated. Take a look at method four here SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank
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Old 17-01-2014, 12:47   #7
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Re: 24v Batteries.. Series or Parallel First?

Cheers Stumble. I just stumbled across this thread (see what i did there? Har har har!) and i'm certainly glad that i did. Simple and effective!
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Old 17-01-2014, 16:47   #8
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Re: 24v Batteries.. Series or Parallel First?

Quote:
Originally Posted by sailinglegend View Post

The positive and negative cables should be at each end dof the bank - not as shown.
Correct...I did not draw properly as I was focusing on the Series issue
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Old 17-01-2014, 17:00   #9
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Re: 24v Batteries.. Series or Parallel First?

I think the general rule is:
Parallel to capacity
then Series to voltage

Chris
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Old 17-01-2014, 18:05   #10
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Re: 24v Batteries.. Series or Parallel First?

Thanks Andina Marie for your simple explanation.
The guy who advised me to do Parallel First, said this was from recent studies of LiFe-Po Battery banks and he said the study went into benefits of Peukert’s formula issues???.

Also thanks for the link Greg…. The calculations between Method 2 and 4 is very informative and the comment from author that he would not bother unless bank was more than 8 or expensive has me still sitting on the fence between method 2 and 4 .

My Own Batteries are 8 x 260Ah Fullriver 12v AGM’s

Unfortunately Greg's Link did not address in Method 4, best way of doing 2 banks of 4 x 12v’s in Parallel/Series for a 24v House Bank.

I sketched using Method 4 concept for Par/Series …
Does anyone see a mistake or improvement on this?

I numbered the batteries to make suggestions easier.
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Old 17-01-2014, 18:41   #11
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Re: 24v Batteries.. Series or Parallel First?

I would not parallel then series connect lead acid batteries.

I would series each pair to make 24 volts, then parallel each pair using #3 on the smart gauge site.

This comes from 2 recent experiences, the last one was 10 L-16 Trojan 6 volts, that were 5 parallel each and series connected at what would be your #4 & #8 batteries. Battery #8 was the first to die from warped plates, then battery #4. This bank was less then 8 months old, and deep cycled(50% SOC) less then 20 times.

The other bank was 20 X L-16 Trojans in a 5 each parallel, then series to make 24 volt, then each bank of 10 bats parallel connected. They died at 9 months, with the exact same symptoms 4 batteries cooked and the rest under charged.

Both banks could not keep water in the 2 bats that made the series connection. Each of these suffered from warped plates, the rest were hard sulphated. Trojan did not warrant any of the bats, because of the misconfiguration.

Not one singe Lead Acid Battery Manufacture I know, recommends first parallel then series. As a matter of fact they each show series pairs then parallel, each pair.

Lloyd



Quote:
Originally Posted by Pelagic View Post
Thanks Andina Marie for your simple explanation.
The guy who advised me to do Parallel First, said this was from recent studies of LiFe-Po Battery banks and he said the study went into benefits of Peukert’s formula issues???.

Also thanks for the link Greg…. The calculations between Method 2 and 4 is very informative and the comment from author that he would not bother unless bank was more than 8 or expensive has me still sitting on the fence between method 2 and 4 .

My Own Batteries are 8 x 260Ah Fullriver 12v AGM’s

Unfortunately Greg's Link did not address in Method 4, best way of doing 2 banks of 4 x 12v’s in Parallel/Series for a 24v House Bank.

I sketched using Method 4 concept for Par/Series …
Does anyone see a mistake or improvement on this?

I numbered the batteries to make suggestions easier.
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Old 17-01-2014, 19:23   #12
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Re: 24v Batteries.. Series or Parallel First?

Wow Lloyd what a nightmare for you.
Would you have the same concerns for AGM batteries?

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Old 17-01-2014, 19:38   #13
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Re: 24v Batteries.. Series or Parallel First?

It wasn't my nightmare, it was the 2 different boat owners nightmare coupled with big money spent 2 X's to do the job right.

I would not parallel first then series to make any lead acid bank, whether FLA, SLA, or Gell, without the manufactures written consent.

I have been installing lead acid bat banks exceeding 30 years.

It was with in a 2 year period, that I came to a boat installed by someone else, that I found my-self confronting parallel first then series.

Lloyd





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Wow Lloyd what a nightmare for you.
Would you have the same concerns for AGM batteries?

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Old 17-01-2014, 19:46   #14
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Interesting.

Thanks for the feedback. My boat is wired series then parallel with 4 - 6v to make 24v then parallel two strings for capacity.

Has been working well for over 20 years. With new high amperage chargers, large inverters, and upgraded wiring I was wondering which way with all of the lithium folks going the other way.

I will keep it the way it is!
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Old 17-01-2014, 20:52   #15
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Re: 24v Batteries.. Series or Parallel First?

Thanks Flying Cloud…What a wealth of real life knowledge CF offers, versus theoretical opinions.

So, back to Series First!... and decision to use either Method 2 or Method 3 depending on installation configuration issues

Understand that Method 3 is best and important to keep all branch cables the same length even if it means having longer than needed cables.

However if I can do with significantly less cable in Method 2, is it a better trade-off to accept the slight imbalance of this?

I am also wondering if the Series First connections between each pair would make that Method 2 inequality even less??
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