PaulRainbow
Well-Known Member
Be some pretty basic electrical systems if you can manage on a single battery.
Domestic Batteries in Parallel
- Thread starter Dave100456
- Start date
Be some pretty basic electrical systems if you can manage on a single battery.
Dave100456
Well-Known Member
Five batteries was only an example as the key question I wanted answering related to balancing batteries.
From the answers so far, I understand the unbalanced load on individual batteries when connected in parallel string is because the resistance of the connecting wires. I'm going to look at resistance values of wires of different diameters -anyone have a good source for this?
Clearly whilst this is not as important when a 5 amp load is applied to the bank it will have a greater effect if an inverter is used with say a 125 amp load.
pvb
Well-Known Member
JohnDL
Well-Known Member
Manufacturers recommendations for connecting batteries in parallel vary somewhat, here are two examples taken for Enersys batteries (Enersys are the worlds largest manufacturer of Industrial Lead Acid batteries, making a premium product)
VLRA (one type, others may vary):
CELLS IN PARALLEL STRINGS
When using constant voltage chargers, ensure that the connections
between the charger and the end of each string within the battery have the
same electrical resistance. Parallel strings must be limited to five strings.
Flooded:
Cells in parallel strings
Vented cells may be connected in parallel to give higher current capability. In the
case of parallel connected strings use batteries of the same capacity, design and
age only with a maximum of 4 parallel strings. The resistance of the cables in
each string must be the same, e.g. same cross-section, same length. Connect the
battery strings in parallel at the end terminals.
FWIW if you take a look at a fork lift truck battery pack (or a submarine or large scale UPS system) you will find everything linked together with cable, bus bars only being used if it more convenient in a particular installation.
It is recommended that the +ve connection should be taken from one battery and the -ve from the other if 2 are in parallel or from the furthest one away if there are more than 2.
So the answer is check out what the manufacturer recommends for a particular battery.
VLRA (one type, others may vary):
CELLS IN PARALLEL STRINGS
When using constant voltage chargers, ensure that the connections
between the charger and the end of each string within the battery have the
same electrical resistance. Parallel strings must be limited to five strings.
Flooded:
Cells in parallel strings
Vented cells may be connected in parallel to give higher current capability. In the
case of parallel connected strings use batteries of the same capacity, design and
age only with a maximum of 4 parallel strings. The resistance of the cables in
each string must be the same, e.g. same cross-section, same length. Connect the
battery strings in parallel at the end terminals.
FWIW if you take a look at a fork lift truck battery pack (or a submarine or large scale UPS system) you will find everything linked together with cable, bus bars only being used if it more convenient in a particular installation.
It is recommended that the +ve connection should be taken from one battery and the -ve from the other if 2 are in parallel or from the furthest one away if there are more than 2.
So the answer is check out what the manufacturer recommends for a particular battery.
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Hoolie
Well-Known Member
You can also do that, possible more conveniently, by varying the lengths of the cables between the batteries.
For instance I have a 3 battery house bank connected as:-
house +ve B1 Length of short cable B2 2x Length of short cable B3
B1 2x Length of short cable B2 Length of short cable B3 house -ve
They are all 50mm2 cables and terminals. All 3 batteries have exactly the same voltage drop between connections. You can also do it with different gauge cables
house +ve B1 Length of 50mm B2 Length of 25mm B3
B1 Length of 25mm B2 Length of 50mm B3 house -ve
But I have two problems with this. It involves buying short lengths of cable and various terminals. And secondly I have an irrational feeling that I shouldn't use thinner cable in my 50mm2 system.
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lw395
Well-Known Member
What are your criteria for the 'best' system?
Reliability? Fault tolerance? Mean lifetime?
How will you use your system?
If high loads like thrusters, microwaves, watermakers are a big part of it, that's a bit different from wanting to run a fridge and some lights for a long time.
Which is better may depend on the exact models of battery in question.
I reckon you might get lower resistance from 5 x 80 than 2 x 200. but even that depends on the physical layout.
2 batteries are easier to treat identically than 5, but the differences should be small.
Depending on how you intend to use it, it might pay to consider splitting into two smaller banks?
Or even changing to 24V?
If you really need 200Ah per day that is a lot of charging.
pvb
Well-Known Member
Why? A large bank works more efficiently.
ffiill
Well-Known Member
I have a three battery set up-two domestic/starter each 110AH and one starter 120AH
I have a row of five of those heavy duty battery switches.
All the three earths are connected to number ones terminal so I can isolate earth
No 2 is starter battery live plus its connected by a bus bar to terminal no.3
The other side of no.3 links through to the domestic lives.
Battery live cables go to one side of the switches and copper connectors link the terminals on the to services side as well as to the number three switch
Basically each battery can be isolated and any number up to all can be fed to start if needed.(or domstic I guess)
A heavy duty lead is also fed from the domestic side to one of those round heavy duty domestic distribution terminals to feed any off battery extras.
My made to measure connectors are lengths of flattened 10 mm copper pipe.
I have a row of five of those heavy duty battery switches.
All the three earths are connected to number ones terminal so I can isolate earth
No 2 is starter battery live plus its connected by a bus bar to terminal no.3
The other side of no.3 links through to the domestic lives.
Battery live cables go to one side of the switches and copper connectors link the terminals on the to services side as well as to the number three switch
Basically each battery can be isolated and any number up to all can be fed to start if needed.(or domstic I guess)
A heavy duty lead is also fed from the domestic side to one of those round heavy duty domestic distribution terminals to feed any off battery extras.
My made to measure connectors are lengths of flattened 10 mm copper pipe.
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lw395
Well-Known Member
And then fails as a single unit.
It might be worth looking at failure modes and so forth over the whole lifecycle of the batteries.
This seems to be a big bank, where maybe the advantages of it being a single bank are wearing thin.
One duff cell will bring the whole system down.
If you don't treat each battery in a bank identically, they will fail prematurely.
If you do treat them identically, they will tend to fail together.
Plus if you have two banks for different loads, what constitutes acceptable performance might be significantly different.
Hoolie
Well-Known Member
According to my calculation, based on 0.7mm wall thickness, that gives you a 22mm2 connection. Less than half the 50mm2 cables on my installation and probably less than your "heavy duty lead".
pvb
Well-Known Member
That's a rather pessimistic view. In 40+ years of boating, I've only experienced one cell failure, in an 8 year old battery which was part of a 6-battery bank.
A single large bank has many advantages - it accepts charge more readily, it experiences less depth-of-discharge for a given load, the currents in each battery are lower.
pvb
Well-Known Member
Agree with that.
skipmac
Well-Known Member
I quite agree. This issue came up a few months ago on another forum and an electrical engineer who also designs and manufactures marine electrical equipment, mostly used in battery charging and related. She said the concern with wiring batteries in a multi-battery bank to give all batteries the same charge path, resistance, cable lengths, etc is completely unnecessary in a real work setting. Yes in theory it looks good but when you actually calculate the differences in charging current, cumulative resistance of cables and connections, and all the issues claimed to be a problem the numbers show that the charging problem is less than negligible. I ran the calculations myself and had to agree with her conclusions, even though I had already wired my battery bank to comply with the other theory.
Note that this applies to a typical marine battery setup and usage. If one has frequent needs for very high current from and/or deep discharge of the battery bank then it starts making sense to wire for equal charge/discharge paths.
halcyon
Well-Known Member
skipmac
Well-Known Member
Beat me to it. I was going to recommend the same. I also have 6 X 6V GC2 size golf cart batteries. Based on extensive research I concluded:
1. Standard FLA batteries are the most forgiving, abuse tolerant batteries technology and certainly on the vast majority of boats battery charging is not set up to be optimal for battery health.
2. Very few if any, 12 V batteries are truly deep cycle. To get a real deep cycle battery which means heavier, thicker lead plates, more clearance between plates, more clearance in the bottom of the case where salts accumulate and can short the plates and other factors that make a true, deep cycle battery you are best served with 6V golf cart batteries.
3. 6V golf cart batteries give by far the most usable capacity and battery life for the dollar. One possible exception might be new technology like LiFEPO batteries but these require a huge upfront investment in cost, charging system upgrades and a very steep learning curve to use them without killing them.
skipmac
Well-Known Member
Quite right. No intention to correct or demean your post. I started mine earlier but had to leave for a bit and did not see your post when I sent mine.
It does however prove that we are both very smart and erudite boaters.
skipmac
Well-Known Member
Similar experience in my 40 years boating re bad cells. Also I use my batteries as one large bank for the reasons stated.
Also, if there is a bad battery or cell in my bank, it's just a matter of a couple minutes to remove a cable or two to isolate the one bad battery.
halcyon
Well-Known Member
Quite right. No intention to correct or demean your post. I started mine earlier but had to leave for a bit and did not see your post when I sent mine.
It does however prove that we are both very smart and erudite boaters.
Not meant that way, just that I agreed with you, I've spent the last 45 years working on battery charging, today to much is controlled by the marketing people.
Brian
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skipmac
Well-Known Member
:encouragement:
lw395
Well-Known Member
Was it skipperstu who had an awkward battery failure experience earlier this year?
That could have been a serious nuisance had he just started the ARC or been in an obscure corner of nowhere.
If you want to design your system to be more resilient and avoid that kind of trouble, it's worth considering different configurations.
There can be other benefits too. We once added an extra sub-bank just to run the fridge. Doing it this way meant:
+ We didn't have to buy all new batteries
+ The fridge could not run down the main house bank
+ we could minimise wiring by having the fridge bank nearer the fridge.
+ we could fuse the two banks separately
+ when the older batteries began to lose performance, it was easy to diagnose.
+ no single point of failure exists which could leave the boat with no house power.
+ it avoided the issue of not really having space to have all the batteries together anyway.
+ no worries about the different banks being at different temperatures and not sharing charge.
- limited capacity to run the fridge for days on end. We bought some ice with the savings.
Depending on what your electrical needs are, it might be worth considering, but fair enough, it's not for everyone.