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Hydrometer battery status


alistair
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I have 4 x 12v 100ah stride batteries connected in series and parallel for 24v. 2 of the batteries are 2 months old, the other two a month old.

They are connected to an Axpert 3kv/2400w inverter being charged via solar/AC mains.

I noticed today that the battery connected to the inverter positive cable shows replace on the hydrometer.

I am not sure why all of a sudden 1/4 batteries is faulty.

Could it just be a dud or other reason - overcharging?

Appreciate any advice on this.

Thanks

Alistair

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Thanks Mike. They are connected as per diagram except that they are 100ah as mentioned.

Could it be that the Axpert settings are causing an overcharge situation.

bulk charging setting - option 26 = 28.2v

floating charging setting - option 27 = 27v

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Batteries in series will not double the current. Batteries in parallel will. Therefore each series string will be limited to 30 amps. The two series strings in parallel will therefore be limited to 60 amps. Thus 720 watts.

 

EDIT: 720 watts per string which will be 1440 watts for two strings in parallel.

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Thanks Helius, Clint. However still not sure what this means in terms of what i have experienced with 1/4 batteries showing they need to be replaced as virtually brand new.

Checked bulk and float settings on battery and close to Axpert defaults posted above.

Bulk charge = 14.7v = 28.4v

Float charge = 13.65v = 27.3v

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you should also connect your batteries across the bank pos one side and the neg from the back neg - draw across the bank rather than from the front - they will always discharge more equally ....that is what i always do.

 

post-13-0-31275600-1435640413_thumb.jpg

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Alistair,

 

What is important about a battery bank is that each battery is balanced. Each battery must have the same potential across it when charging and must be discharged with the same current draw.

 

That is why it is important to have all the batteries at the same (SOC) State Of Charge before they are connected in a battery bank. Maybe that particular battery that failed was at a lower SOC when you connected it in your bank. This battery could be at a different SOC because it is from a different batch or manufacturing problem. Did you charge all the batteries individually before you connected them together? The best thing to do is what is called bottom balancing. Have a look at https://en.wikipedia.org/wiki/Battery_balancing This article makes as if it is important more for lithium batteries but it is important for lead acid as well.

 

Also it is important to use the same wire thickness and length for connecting the batteries in the pack. You do not want one battery to get more voltage and current than the others. Remember that wire has a resistance. Even a centimetre longer at the current draw can be half a volt difference. Every thing must stay in balance.

 

Best is to use a multimeter and measure the voltage over each battery in the pack when they are charging and discharging and see if they are all the same within a couple of millivolts. If not then you have a configuration problem with your wiring connecting the batteries or the batteries have internal differences that you will have to live with.

 

That is why it is important to balance the batteries before you connect them in a battery pack. It is a lot of work yes but your pack will last longer. 

 

From: http://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing

 

"With use and time all battery cells become mismatched, and this also applies to lead acid. Cells that develop high self-discharge will lead to imbalance and subsequent failure. Manufacturers of golf cars, aerial work platforms, floor scrubbers and other battery-powered vehicles recommend an equalizing charge of 3

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When you buy batteries they could be from different batches and the batches could differ in manufacturing dates. This will give you different SOC on the batteries due to internal resistances discharging the batteries while they are awaiting installation. 

 

It is therefore good practice to get the batteries as close as possible to the same SOC before you connect them into a battery pack. After they are connected in a pack it is not needed to individually adjust there SOC as you can then do an equalising charge to level things out. Just remember you would not like to do this regularly as an equalise is in fact an overcharge which does shorten your battery life.

 

Hopefully this shows also that you should not mix batteries bought at different times or mixing different makes/ types of batteries.

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Got home today to find another 2/4 batteries showing "replace" so now a total of 3/4.

Disconnected all 4 and each still give 12v on voltmeter.

Gave the 3 a shake and can hear electrolyte. 1 of them came back to life (green on hydrometer) and have now connected only remaining 2 x 12v in series to 24v inverter.

Any ideas what could cause this kind of outright failure or is it faulty hydrometer if still getting 12v reading?

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Some sealed battery designs can happily withstand a full discharge such as the Lead Crystal, Optima Yellow-top and Narada Rex-C.

 

When charging sealed batteries the gases are allowed to recombine and reform as water so no need to top up the electrolyte. It is important not to charge too fast as the gasses will build up too quickly and this can lead to permanent battery damage.

 

Any chance the batteries were left uncharged for a period of time as this could lead to sulphation and premature cell failure.

 

You mention that all your batteries still measure 12 Volts on your multimeter but as the range between a fully charged and fully discharged battery is only about 1.2 volts it is important to note the voltage to at least one decimal place.

 

Also may be worth checking the date that the batteries were manufactured. Normally stamped onto the battery.  Are the batteries still under warranty?

 

What are your settings on the Axpert for the Max charging current (Option 2) Battery Type (Option 5) and Max Utility Charging Current (Option 11) 

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Thanks Carl.

I bought original 2 batteries end April and then a further two in June.

Was initially using two in parallel before adding the additional two in series/parallel a week and a half ago.

On Saturday i changed the Axpert settings to run my backed up circuits from solar/battery first with a fairly small load with max around 800w for short intervals.

It was after doing this for a day that i noticed the first battery showing replace.

at this point i stopped charging all batteries for two days due to concern around this only to find 3/4 batteries yesterday with this issue.

After one came back to life i ran two batteries last night but this morning back to situation where 1/2 shows replace.

i havent checked the dates yet but per dates above were purchased recently albeit different suppliers.

setting 2/11 i reduced initially from 30a to 20a but back to 30a.

setting 5 was originally changes to flooded but had changed after this issue to user defined to change settings 26/27 to battery specifics for float 13.65v (

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Hi Alistair, it sounds like your batteries have been undercharged and this could be due to the settings on your Inverter.

 

I am not an expert on the axpert but it could be that you have inhibited the Utility from charging the batteries.

 

If your PV solar was not enough then your batteries would slowly die and show symptons similar to  the ones you are experiencing. 

 

Would suggest that you charge up all your batteries as soon as possible by setting up your Axpert with the Output Source Priority as Utility First (01) and Set your Charger Source Priority as Utility First (16)

 

Also what setting have you got you power saving mode (04) on?

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You can try reducing your charging current. I found with my flooded batteries that if the charging current was too high, the battery voltage came up very quickly, then the charger thought they were charged, and stopped charging until the current dropped down again. Consequenty they weren't charging properly. I have 4x150Ah in series and they charge nicely at 20A, but not well at all at higher amperages.

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Hi Alistair.

 

If they are sealed batteries, how are you using a hydrometer on them?

 

It is also sounding more like an under charge problem to me. Can you confirm that it is the older batteries giving the problems.

 

Also make the changes Carl has suggested to the Axpert and then measure with a multimeter the voltage over each battery while they are charging and report it here if you can. Please measure as Carl said to at least 2 decimal points.  

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Thanks Carl.

Prior to running only on pv the settings were as you describe. I reverted back to these last night for 2/4 "good" batteries where hydrometer still showed green. However this morning after a full night of utility charge 1/2 shows "replace". Question is whether it is faulty hydrometer (unlikely if impacting 3/4 batteries) or actual battery failure. Is it safe to continue trying to charge up all 4 if 3/4 show "replace" or are you saying this could potentially reverse the 3/4 and could get them back to "green".

Setting 4 is on default not enabled.

Deepbass9, thanks i will reduce to 20a.

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