Helius

Hi Alistair, I would not mix charged batteries with uncharged or low charged in a bank of batteries. But if you do not have another choice then it is better than leaving the batteries without a charge. Please remember to increase your charge current if you do. You should also not run the inverter on the batteries only, until the bank is fully charged. The Optimate-6 looks fine. Edit: If you choose to add the other batteries then yes use Mike's diagram for the connections.

That is why I asked if DB9 is completely off-grid. This setup cannot work otherwise. 3 phase gives 380 Volt between phases and 220 Volt from phase to neutral. That is why the inverter can be connected in this way as long as there is no 3 phase equipment connected and no 3 phase grid connection. With this setup you will still get 220 Volt from phase to neutral but your phase to phase voltage will now be 0 Volt. If Jaco_n wants to still feed his inverter with the grid, he can disconnect 2 phases and just feed his inverter with one phase and neutral, and with DB9's setup feed the house. The problem will then be that the 3 phases from the grid will be unbalanced as you will only draw current on one phase. This should be fine up to 5Kw. The best is to get an open Delta transformer to convert 3 phase to single phase if you still want to be connected to the grid or get three small inverters.

Hi Alistair. Pitty the Axpert does not have a 25 amp charge current setting. It will affect your charge times as follows 100% discharged will now take 15 hours and 50% will now take 7.5 hours. On solar only you can discharge 33% if you want it charged back in one day of 5 hours sunshine. Reading the Axpert Manual, option 29's default setting is 21.0 volts which gives 1.75 Volts per cell. This value is when the battery is considered 100% discharged. I guess this is when the inverter will switch off. It does not seem that you can set a DoD of 50% or less. But as I said I do not have experience with the Axpert. Maybe somebody else can comment.

DB9 Are you still connected to 3 phase Grid with this setup or are you completely off-grid?

On more expensive inverters you will see sense wires running to the battery pack specifically to compensate for the voltage that was selected on the inverter and the actual voltage at the battery pack. Also there is temperature sensors placed at the battery pack to compensate the charging voltage according the current temperature.

Hi Alistair. I would increase float to 2.3 Volts i.e. 27.6 Volts. Better yet. Increase the float voltage until the value measured with your multimeter over the battery with the lowest voltage (Battery D) is 2.28 Volts i.e. 13.68 Volts. Please make sure that the voltage on Battery C stays within the Float range and do not exceed 2.31 volts i.e. 13.86 Volts. Bulk charge will be fine seeing that you can not change it any further. Yes give Battery D more time. Please set your charge current to be no more than 25 amps. For one bank of two batteries in series the max charge current is 25 amps. If later you add another bank of batteries to double your 100 amp/hour to 200 amp/hour you can set it to 50 amps. Unfortunately I do not know the setting of the Axpert will first have to look at the user manual. Any three stage charger that can charge SLA will do and that fits your pocket.

Hi Alistair, Out of your measurement you can see that there is a problem. The average voltages range from 2.25 to 2.22 Volt per cell. Normally for SLA at 20 Degrees C Float is 2.26 - 2.31 and Bulk is 2.43 - 2.53. The only Stride datasheet that I could get is for a N100MF Battery. The Float on the datasheet is 2.30 Volt and max charge current is 0.25C which is 25 Amps. Unfortunately the data sheet does not give a Bulk charge voltage. It seems that the Axpert is giving the voltage that you selected. Does the Axpert indicate that it is Float charging? (4 bars on in the battery symbol with charging legend). What is the charge current? I would adjust the settings to 2.30 Volt for Float and 2.45 volt for Bulk. Lets look at Charging Time. Reading the datasheet it shows that if the battery is 100% discharged it will take 12 hours to fully recharge at 25 Amps. If it is 50% discharged it will take 6 hours to fully recharge. For your 24 Volt 200 Amp/Hour pack it translates to 100% discharged it will take 12 hours to fully recharge at 50 Amps and at 50% discharge it will take 6 hours. To calculate other charge times use this formula - Divide the amount of amp/hours discharged by the charge current and multiply the result of hours by a factor of 3 to compensate for the declining output current from the charger. Also use this formula to calculate the charge time if you want to reduce the charge current. To charge your battery pack with Solar only you can see that you can only discharge 41% if you want to charge it back in one day at max current. Please also get the batteries that is measuring 12 Volts on charge as soon as possible. They can still be saved if the sulphation was not to severe. Never leave batteries without charge if they are below 12.6 volt out of circuit. (OCV) Open Circuit Voltage. If however the do not come back after 48 hours of charging, you can trash them. Hope this helps.

Hi Alistair. Gel has more advantages than flooded but more expensive to buy. Also charging voltage is more critical. Gel will give better service life which makes it cheaper in the end. Other than that it is still a lead acid battery.

Some nice to read stuff. https://www.cdtechno.com/pdf/ref/41_2128_0212.pdf

Thanks Alistair.

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.

Hi Dope. I would recommend NARADA REX-C 12volt 200a/h. They will be more pricey than you are willing to spend but they have good specifications. http://philsolar.ph/wp-content/uploads/2014/05/REXC-Series-Lead-Carbon-Battery.pdf

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.

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

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.