Thanks Alistair.

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

Thanks Helius. Very detailed indeed.

Would a change to gel batteries do away with some of these "challenges" making installation less problematic.

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. 

Hi Helius. Readings below as you requested. Hope this helps shed some light on my issue.

I have yesterday disconnected the 4 batteries from their original series/parallel setup and only have 2 x 12v connected in series to the inverter.

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 Helius.

Thanks for the comprehensive feedback.

Battery is n100mf.

On the battery itself it shows follows:

Float charge 13.65 (slightly less than datasheet 13.8 i assume [2.3x6]

Bulk charge 14.7 (same as your suggestion [2.45x6]

Current axpert settings:

Float charge is 27.3 (should i increase to suggested 27.4 but could differ to datasheet and battery values?)

Bulk charge is 29.0 as max axpert setting (assume 29.4 is ideal based on 14.7 x 2, is this an issue?)

I do currently see 4 solid bars with axpert battery reading toggling between 26.9-27.0v

Concern is battery D still shows "replace" after 41 hours of charging although actual battery reading is showing 13.35-13.38v while connected. So not sure if trashed or not while battery C is still "green". Should i give it more time and expect battery D to return to "green" on battery hydrometer?

Can you recommend a cost effective battery charger please which is readily available.

For charge duration, axpert is currently set to 30a with only other option 20a. Should i leave as 30a?

Also to set DOD, would this be option 29 on axpert currently on default setting of 31.0v

thanks again!

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.

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. 

Thanks Helius.

Will set to 20a as only 20a and 30a as available options.

Appreciate any advice you can offer later on Axpert DOD settings.

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.

Thanks Helius.

Battery D is coming back to life. Should i reintroduce the other two as 2nd 24v bank and charge via inverter and connect up as Mike had posted earlier on as i currently do not have a separate charger?

Or should i rather charge separately before reintroducing.

Can get hold of following charger

http://optimate-battery-charger.co.za/shop/optimate-6/

if this up to spec

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. 

Thanks Helius, have increased charge to max 30a.

I managed to recover all 3 batteries so all "green".

Was using the monitoring software and noticed when charging via utility/pv it shows battery capacity as 100% but when i swop to battery only it shows battery capacity as about 60% and declines quite quickly.

Could this be that axpert believes batteries fully charged but in fact not the case? Saw earlier post about this suggesting dropping the bulk charging setting?

Appreciate any advice on this.

I managed to recover all 3 batteries so all "green".

Was using the monitoring software and noticed when charging via utility/pv it shows battery capacity as 100% but when i swop to battery only it shows battery capacity as about 60% and declines quite quickly.

Could this be that axpert believes batteries fully charged but in fact not the case? Saw earlier post about this suggesting dropping the bulk charging setting?

Appreciate any advice on this.

I am beginning to think this is a "problem" (?) on the Axpert inverters as well, since I'm seeing the same thing. The inverter sees my 48V bank as full @ 54V, but as soon as I switch off the mains power it drops to 51V! Though I've been thinking it might be the batteries, you're now the third person so far to say you have seen the same phenomena. 

If I may comment here. The same thing happens to my bank on the infini, but I think it is normal and I'll explain why. Referring to one 12V battery, you charge it to approximately 13.8V (55.2V for 4 batteries), but a fully charged battery sits at approximately 12.7V (Open circuit voltage) (50.8V for 4 batteries) - but keep in mind that this is open circuit voltage - no load on the battery.

 

If your charger/inverter thus charges the batteries and keep them in float charge mode when they are full, you will read approximately 55V (depending on specific batteries used) and to the inverter that is 100% charged.  As soon as the mains fail and the inverter starts to draw power from the batteries, the battery voltages will drop, depending on the load, to say about 50V (12.5/12.6V per 12V battery).  Although the batteries are still fully charged at that moment, the voltage dropped from 55V to 50V and the inverter displays 60% charged, although they are actually say 95% charged.

 

I'm not sure what happens on other inverters, if they maybe take 50/51V and above as 100% charged, but on the Axpert and infini inverters that is definitely not the case.

 

The battery charge indicator on the Axpert and infini inverters are therefor not accurate at all and I think one should rather set the display to show "battery voltage" instead of "charge %" and keep an eye on the battery voltage instead.

What superdiy said. While charging the voltage is higher, only when you remove the charger (and the load) will you be able to read the state of charge from the battery voltage.

 

I get that problem if I am using my inverter/charger to charge batteries by generator while the solar charger is also connected. The solar charger is applying 55+V which the inverter reads as fully charged, so doesn't charge further. So I must either switch the solar charger off or only use the generator before dawn and after dusk (which is when it is required, so no problem there) 

What superdiy said. While charging the voltage is higher, only when you remove the charger (and the load) will you be able to read the state of charge from the battery voltage.

 

Without any load, when the battery is disconnected from the charger it will only show approximately 12.6V (open circuit voltage) after a certain period of time e.g. a few days - the battery will not read 12.6V immediately after it is disconnected from the charger with no load connected.

Thanks guys. For now i have resorted to charging my batteries individually using a separate charger and will then reintroduce them with same SOC and see what happens when disconnecting inverter from the mains.