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Apologies if this has already been covered. I have 3 x 110ah domestic batteries. One has given up but the other two are OK. Do I buy one replacement or a complete new bank. If I replace one can I do this with say a 120ah to work with the remaining 110ah. Pros and cons please?

 

Regards

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Apologies if this has already been covered. I have 3 x 110ah domestic batteries. One has given up but the other two are OK. Do I buy one replacement or a complete new bank. If I replace one can I do this with say a 120ah to work with the remaining 110ah. Pros and cons please?

 

Regards

 

 

Right, I will stick my head up and give you my answer. (Any chance of a smiley in a tin hat!)

 

Good and accepted practise is to replace in whole banks but this is probably derived from professionals needing to protect themselves form comebacks. If one battery in a bank has failed there is every chance will fail very soon - on the other hand it may not.

 

If you connect a battery with a shoring cell to a new battery the new battery will discharge into the faulty one as it tries to recharge the faulty battery. In this way you end up with two very flat batteries. Now if you immediately FULLY recharge the new one there is probably not overmuch harm done but the likelihood is that you will not. Some weeks later you will visit the boat and find a flat bank with the new one nicely sulphated so it has lost a lot of capacity and will never recharge to its original capacity.

 

Now, if you have wet open cell batteries and regularly test them at frequent intervals hopefully you will be able to identify a faulty cell starting to develop so you can remove that battery from the bank before the new one suffers too much harm.

 

It comes down to your ability and willingness to test the batteries at frequent intervals. If you are the just replace the faulty one. If you have doubts replace the bank because if you replace one you may ruin it.

 

I assume this is a 12v boat so all the batteries are connected in parallel to form one big bank. Adding a 120Ah battery to the bank in place of a 110Ah one will just slightly extend the recharging time as the larger capacity suggest. FWIW I ran 2 x 110Ah "Leisure" batteries with an 85Ah "any duty" battery in one bank for about three years with no ill effect.

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Gibbo,

 

I know you have done test that show the volts at dif levels of soc are exactly the same on bats that have lost say 30% of capacity & new ones.

 

Have you also done charge & discharge curves for the old bats to show if it takes the same amount of time & energy to recharge?

 

 

IE will 4 x 100 ah bats that have degraded to 50% take the same amount of time energy to recharge as 2 x 100 ah ones from the same SOC?

 

If so that must be why old forklift banks are good. They might not have the capacity that they started with & they might not be able to take a forklift load but they do work just fine as a domestic bank.

 

There is one particular person I would like to convince that what you say is true as she refuses to accept it (not on this forum) & insists that you can not mix old & new bats.

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If you connect a battery with a shoring cell to a new battery the new battery will discharge into the faulty one as it tries to recharge the faulty battery. In this way you end up with two very flat batteries.

 

True but it rather ignores the OP's statement that

 

One has given up but the other two are OK.
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If you ask me it depends on just how 'ok' the remaining batteries are.

- If the banks 6months old, and ones had an early life failure but you cant find the receipt, go for it, sling an extra one in.

- However if there 8 years old, fairly shot, and the first one has just dropped cell, its probably time time to retire the lot!

 

Two extreme examples but you get the picture, if only as a 'more info required' type post.

 

And ofcause budget may cause or force other options. You could even, just use two of the three!

 

But your right, its a hard call. We're 24v (using 12v batteries) so have to do them i pairs, but when one pair is getting a bit sluggish, they tend all get replaced

 

Daniel

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Gibbo,

 

I know you have done test that show the volts at dif levels of soc are exactly the same on bats that have lost say 30% of capacity & new ones.

 

Have you also done charge & discharge curves for the old bats to show if it takes the same amount of time & energy to recharge?

 

 

IE will 4 x 100 ah bats that have degraded to 50% take the same amount of time energy to recharge as 2 x 100 ah ones from the same SOC?

 

If so that must be why old forklift banks are good. They might not have the capacity that they started with & they might not be able to take a forklift load but they do work just fine as a domestic bank.

 

There is one particular person I would like to convince that what you say is true as she refuses to accept it (not on this forum) & insists that you can not mix old & new bats.

 

50% is the turning point.

 

A 100Ahr battery that has lost 20% capacity due to ageing behaves and reacts exactly the same way as a new 80Ahr battery. It is impossible to tell them apart by electrical tests/measurements. The same thing applies at 70%. At 60% subtle differences start to appear. At 50% it's pretty easy to tell them apart. They start to take longer to recharge, they lose the capacity to provide large currents etc. They are also at the point where they suddenly do odd things like the battery voltage suddenly dropping by (say) 4 volts or so.

 

But ex professional use batteries usually have lots of good life left in them because they tend to replace them at 80% SoH

 

By the way, to OP. If you have one battery knackered and the others are OK there is a very high chance the bank isn't wired up properly.

 

Are the main power leads connected at one end? Is that the end where the duff battery is?

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Hi

 

Can some one explain why a knackered battery voltage on charge goes up.

My knackered batterys have about 14.0v when the alternators are putting out 14.4V - ie hardly any difference.

I have been told this is a sure sign that they are knackered.

 

Alex

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Hi

 

Can some one explain why a knackered battery voltage on charge goes up.

My knackered batterys have about 14.0v when the alternators are putting out 14.4V - ie hardly any difference.

I have been told this is a sure sign that they are knackered.

 

Alex

 

You're just measuring the voltage of the charge source (in this case the alternator) minus voltage drop through the (too small) cables. It's got nothing to do with the condition of the batteries.

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True but it rather ignores the OP's statement that

 

 

Why only do partial quotes so they are out of context?

 

I did not ignore the OPs statement, what I did was to try to explain things to him so he could form an opinion on which of the likely following posts would be correct and which would not - spell chucker and old age excepted.

 

It is this sort of thing that get forums etc. a bad name.

 

When I started the post there were no replies but several came in whilst I was tying, hence why I thought an explanation would be in order.

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[snip]

 

By the way, to OP. If you have one battery knackered and the others are OK there is a very high chance the bank isn't wired up properly.

 

Are the main power leads connected at one end? Is that the end where the duff battery is?

 

Slightly off topic, but I'm about to connect my Smart Gauge to a bank of 3 parallel batteries. The load is connected to "diagonally opposing" terminals, so should the SG be similarly connected, or is it OK to connect directly to an individual battery -- as far as I can see it is not mentioned in the installation guide.

 

Weeble

Edited by weeble
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Slightly off topic, but I'm about to connect my Smart Gauge to a bank of 3 parallel batteries. The load is connected to "diagonally opposing" terminals, so should the SG be similarly connected, Yesor is it OK to connect directly to an individual battery -- as far as I can see it is not mentioned in the installation guide.

 

Weeble

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Slightly off topic, but I'm about to connect my Smart Gauge to a bank of 3 parallel batteries. The load is connected to "diagonally opposing" terminals, so should the SG be similarly connected, or is it OK to connect directly to an individual battery -- as far as I can see it is not mentioned in the installation guide.

 

Weeble

 

I think diagonal is probably best but to be honest I doubt it makes much difference. Why not try it both ways and see if you get different readings - I'd be interested in the results.

Edited by blackrose
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It should be connected to the main take off points. As should everything else. Without exception.

 

There should only ever be two connection points to a battery bank. One for positive and one for negative. Anything else is wrong. Always.

 

From....

 

http://www.smartgauge.co.uk/batt_con.html

 

"Finally, if your battery bank has various take off points on different batteries, change it now! It is extremely bad practice. Not only does it mess up the battery balancing, it also makes trouble shooting very much more complicated and looks awful. "

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Apologies if this has already been covered. I have 3 x 110ah domestic batteries. One has given up but the other two are OK. Do I buy one replacement or a complete new bank. If I replace one can I do this with say a 120ah to work with the remaining 110ah. Pros and cons please?

 

Regards

 

It'll work to some degree. Checking the SG (if non sealed batteries) from time to time will tell exactly how well it's working or not.

 

If they're about the same across the bank when charged or discharged I can't see any problem.

 

cheers,

Pete.

Edited by smileypete
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50% is the turning point.

 

A 100Ahr battery that has lost 20% capacity due to ageing behaves and reacts exactly the same way as a new 80Ahr battery. It is impossible to tell them apart by electrical tests/measurements. The same thing applies at 70%. At 60% subtle differences start to appear. At 50% it's pretty easy to tell them apart. They start to take longer to recharge, they lose the capacity to provide large currents etc. They are also at the point where they suddenly do odd things like the battery voltage suddenly dropping by (say) 4 volts or so.

 

But ex professional use batteries usually have lots of good life left in them because they tend to replace them at 80% SoH

 

By the way, to OP. If you have one battery knackered and the others are OK there is a very high chance the bank isn't wired up properly.

 

Are the main power leads connected at one end? Is that the end where the duff battery is?

 

 

Gibbo, the wiring was set up as charge in one end and service out the other. The service end is where the US battery is. I changed the wiring as in your Smartgauge info site to get a better balance as advised. Battery still US!

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50% is the turning point.

 

A 100Ahr battery that has lost 20% capacity due to ageing behaves and reacts exactly the same way as a new 80Ahr battery. It is impossible to tell them apart by electrical tests/measurements. The same thing applies at 70%. At 60% subtle differences start to appear. At 50% it's pretty easy to tell them apart. They start to take longer to recharge, they lose the capacity to provide large currents etc. They are also at the point where they suddenly do odd things like the battery voltage suddenly dropping by (say) 4 volts or so.

 

Gibbo

 

We have 8x120ah AGMs wired for 24v (480ah) which after a 2 hour charge drops to about 8 amps and then after a couple of hours running tv and fridge etc it levels out at roughly 24.6v. 22 hours later when at roughly 23.7 we recharge for 2 hours again and once a week do an 8 absorption which reaches 28.9v and drops to about 2 or 3 amps. Though the voltages are low they stay stable and we have no probs with with them dropping suddenly, in fact apart from lower than normal voltages the batteries behave themselves giving us 65ah @24v per 24hrs. We have a Smartgauge fitted but with those voltage readings it would appear batts are below 50% and therefore SG will not be accurate. What capacity do you think we have left, above or below 50%?

 

Cheers

 

Chris

Edited by nb Innisfree
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Gibbo, the wiring was set up as charge in one end and service out the other. The service end is where the US battery is. I changed the wiring as in your Smartgauge info site to get a better balance as advised. Battery still US!

 

Changing the wiring will not bring a un-serviceable battery back to life.

 

As Gibbo said the one at the service end has been doing all the work.

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Changing the wiring will not bring a un-serviceable battery back to life.

 

As Gibbo said the one at the service end has been doing all the work.

 

Yes I picked that up from Gibbo's site and posts. Need to replace the US battery (worn out due to wrong wiring?) at the service end. Seems from helpful comment by members I will be OK to replace just one battery. Thanks all for responses.

 

Alex

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It should be connected to the main take off points. As should everything else. Without exception.

 

There should only ever be two connection points to a battery bank. One for positive and one for negative. Anything else is wrong. Always.

 

From....

 

http://www.smartgauge.co.uk/batt_con.html

 

"Finally, if your battery bank has various take off points on different batteries, change it now! It is extremely bad practice. Not only does it mess up the battery balancing, it also makes trouble shooting very much more complicated and looks awful. "

Had a good day today. 3x110Ah batteries fitted and connected as advised, Smartgauge connected, turned it all on and lo and behold it does what it says on the tin :lol:

The new batts were fully charged but had been standing for a couple weeks so I left the SG at its default 75%, ran the engine and the indication rose to 100% in about 2.5 hrs. I know that it take a few charge/discharge cycles to get properly into sync, but first impressions are very good indeed.

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Gibbo

 

We have 8x120ah AGMs wired for 24v (480ah) which after a 2 hour charge drops to about 8 amps and then after a couple of hours running tv and fridge etc it levels out at roughly 24.6v. 22 hours later when at roughly 23.7 we recharge for 2 hours again and once a week do an 8 absorption which reaches 28.9v and drops to about 2 or 3 amps. Though the voltages are low they stay stable and we have no probs with with them dropping suddenly, in fact apart from lower than normal voltages the batteries behave themselves giving us 65ah @24v per 24hrs. We have a Smartgauge fitted but with those voltage readings it would appear batts are below 50% and therefore SG will not be accurate. What capacity do you think we have left, above or below 50%?

 

Cheers

 

Chris

 

On your 2 hour charge what does the charge current start off at?

 

I might be able to hazzard a guess with that info.

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On your 2 hour charge what does the charge current start off at?

 

I might be able to hazzard a guess with that info.

 

Sorry to be late answering, been off line for a while.

 

Our 100 amp alt starts charging at 100+ amps for several mins before commencing a gradual drop. Used to be like this with batts new but took longer to reach absorption stage after which everything behaved as it does now. (which would be expected as batt capacity is now smaller) Someone mentioned in an older post that their AGMs seemed to operate at a lower voltage than flooded lead acids which seems to be the case with ours but I think I recall you saying AGMs should be same which seems logical. Just seems a bit odd.

 

Cheers

 

Chris

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