Hi, I know this subject has been discussed quite a few times already, but my situation is a bit of a catch 22.

I have an Axpert 2kw inverter with 2 x 105ah deep cycle lead acid batteries and 2 x 330w solar panels.

The main objective for the system is basically to be a backup/ups for lights.

The total load is about 150w, so quite low.

I would like to make use of solar as much as possible, but I don't want to discharge the batteries too low as I would like to get as long a service life out of the batteries as possible.

At the moment I have set solar and battery power as first priority with the voltage where the system switches back to utility at 25v (24v system).

The problem I have is that when the load is connected at night it cycles between 25v and 27v almost every 20min so I basically only use solar for the 1st cycle and for the rest of the time utility is charging the battery back to 27v (float) and during the day solar only keep the batteries on float.

I think my settings need some adjustment.

Here are my current settings:

SETTING	DESCR	SET TO
01	LOAD POWER SOURCE PRIO	SBU
02	MAX CHARGE UTLITY + SOLAR	40A
03	AC INPUT RANGE	APL
05	BATTERY TYPE	USER
06	AUTO RESTART ON OVERLOAD	LTE
07	AUTO RESTART OVER TEMP	LTE
09	OUTPUT FREQ	50
11	UTILITY CHARGE CURRENT	20A
12	SWITCH BACK TO GRID	25V
13	SWITCH BACK TO BATTERY	27V FULL
16	CHARGE SOURCE PRIORITY	CSO
18	ALARM CONTROL	BON
19	AUTO RETURN MAIN SCREEN	TEP (STAY)
20	BACKLIGHT	LON (ON)
22	BEEP WHILE PRIMARY SOURCE OFF	AON (ON)
23	OVERLOAD BYPASS	BYE (ENABLED)
25	RECORD FAULT	FEN
26	BULK CHARGE VOLTAGE	28.1V
27	FOLAT VOLTAGE	27V
29	LOW VOLTAGE DISCONNECT	24.4V
30	BATTERY EQUALISATION	EDS (DISABLED)
31	EQUALISATION VOLTAGE	28.8V
33	EQUALISATION TIME	60MIN
34	EQUALISATION TIMEOUT	120MIN
35	EQUALISATION INTERVAL	30
36	START EQUALISATION IF ENABLED	ADS

This may not work for you, but I've set 16 (Charge Source Priority) to OSO, basically only solar can charge the batteries.

Hi, I thought about that, but that may cause the batteries to be discharged too low, which may shorten battery life, because it will then basically draw power from the batteries until it reaches the low voltage disconnect setting if I understand it correctly.

If it stops at the "back to grid" setting (12) it should work perfectly, I think I will try and check what happens, thanks.

3 hours ago, Adri76 said:

02 | MAX CHARGE UTLITY + SOLAR | 40A

I would set this to 20 A. With a maximum utility charging current of 20 A (500 W) and 660 W of solar, you could send 1000 W (40 A) into your battery. It is 105 Ah (when in series, the voltages add, but the Ah capacities do not), so that's 0.38C (max should really be 0.15C). You might also increase your panels one day.

What I do with my 5 kVA model is I set the maximum utility charge current to 2 A. But that's not available for you, only 20 A and 30 A I believe. So as @viceroy says, use setting 16 at OSO. When in line (bypass) mode, the battery will indeed drain at (I'm guessing) 20 W or so (0.4 A), which will indeed drain it from ~50% SOC to 20% SOC in some 79 hours (3.3 days) if there is zero solar input. Unlikely, but if you have a lot of rainy days in a row, just change the OSO back to CSO until you get better solar weather. You might want to increase the voltage in setting 13 (back to battery) so that it doesn't cycle so quickly.

I think I misunderstood the 40a setting as the manual says solar + utility, did not think that it would use both at the same time.

If I set the back to battery higher than the float, would it ever reach that voltage, as the battery basically never go above float?

I think maybe I must set my low voltage disconnect to 50% soc.

 

 

I've changed the settings to OSO, but now I get a low battery warning when the voltage go below the back to grid voltage and it does not switch to bypass.

Will it go back to utility if it reaches the low voltage disconnect voltage?

 

 

 

8 hours ago, Adri76 said:

If I set the back to battery higher than the float, would it ever reach that voltage, as the battery basically never go above float?

Yes, it will. With normal settings (parameter 02 is ≤ 5 times parameter 11), the utility charger doesn't suffer from the premature float bug (assuming no brown-outs of AC-in). So it will utility charge to the bulk/absorb setting. With many models, you can set the back to battery voltage setting (setting 13) to FUL, meaning the charge has to be complete before the inverter switches back to battery mode.

7 hours ago, Adri76 said:

I've changed the settings to OSO, but now I get a low battery warning when the voltage go below the back to grid voltage and it does not switch to bypass.

I thought it should switch to line (bypass) mode but just not charge the battery from utility. The warning should happen (from memory) at 1.0 V (for 24 V models) above the low DC cutoff voltage setting (setting 29).

7 hours ago, Adri76 said:

Will it go back to utility if it reaches the low voltage disconnect voltage?

If it hasn't switched at the back to utility voltage, then I don't think so.

It did go back to utility eventually, but I'm not sure at what voltage.

When I checked it was in bypass mode and battery voltage at 25v, but that voltage was after the battery was resting for a few hours.

For now I think these settings will work for me, I will fine tune it a bit, but thanks Coulomb and Viceroy for the help.

Good morning,

 

I have been scanning the feedbacks for advice on my charge rate for my system, but I am still not sure what the correct setting is for charging my system.

I am using a Mecer 5KVA inverter. 48V 

I have 4 backs of batteries 230AH

How do I calculate what the max charge must be for the banks.

I know it must be 10% x 230 = 23amps for a battery on it's own.

In a bank I believe it should be the same, but what about 4 banks?

Does it split the amps by 4 when charging?

is it 4 x 23 = 92Amp?

May you have a great day.

4 hours ago, Ernie Green said:

How do I calculate what the max charge must be for the banks.

I know it must be 10% x 230 = 23amps for a battery on it's own.

In a bank I believe it should be the same, but what about 4 banks?

It depends on what you mean by 4 banks. Usually, you need 4 battery modules in series for 48 V. If that's what you've got, you have a 48 V 230 Ah battery (assuming each 12 V module is 230 Ah). When people say "4 banks", they usually mean 4 strings of 4 battery modules, or 16 battery modules total. In that case, you'd have a 48 V 920 Ah battery.

So if you have just the 4 battery modules, then you're stuck with 23 A max, so you should use the 20 A setting. Some say you can go up to 15% of Ah capacity; in that case you could go to 34.5 A, and the next lowest setting is probably 30 A. Ideally, you'd get the correct figure (10% or 15% or some other figure) from the manufacturer's datasheet, or sometimes it's written on the battery modules.

Coulomb,

Thanks for the feedback.

one bank(string) = 4 x 230AH deep cycle batteries in series, this give me in total 16 modules

so if I understand your feedback correct then I must not go more then 30Amp setting 

Thanks for the feedback.

 

Ernie

If you have 16 battery modules, each 230 Ah, then the maximum current setting needs to be 90 A.

I've had some problems with my inverter and have bought a new one. (Axpert type 3000va)

My batteries have been standing disconnected for about 3 weeks at +-25.4V (24v bank so almost 100%)

Last night I connected the new inverter to the batteries an it went to 27v float within a few minutes.

I disconnected the utility power to drain the batteries a bit to get it to start a charge cycle with a load of 120w.

The batteries reached the 24v low voltage disconnect within 5min.

I reconnected the utility power and it did start a charge cycle which lasted probably 2hrs.

Could the batteries have been damaged by being disconnected for about 3 weeks? Surely it should last much longer than a few minutes and charge for much longer if drawn to 24v.

The batteries are about 2 months old. 

13 hours ago, Adri76 said:

Could the batteries have been damaged by being disconnected for about 3 weeks?

It seems very unlikely.

The battery is acting like it's very high internal resistance. That could be a ruined battery, but it could also be a bad connection to the battery / fuses etc. Try checking for voltage drops, and/or simply inspect every battery clamp and crimp.

Thanks I will do that.

I should probably also measure the voltage under load at the battery as well as the connections to the inverter.

Checked everything and the voltage at the batteries is the same as at the inverter under load. My max draw is about 150w and usual draw is about 80w. I know it is a difficult question, but with a 24v lead acid bank of 105ah, what would a good lvd point be to use max solar and keep the amount of cycles I can get out of the batteries as high as possible

7 hours ago, Adri76 said:

Checked everything and the voltage at the batteries is the same as at the inverter under load.

Yes, but is that voltage well under 24.0 V just before it gives up?

7 hours ago, Adri76 said:

My max draw is about 150w and usual draw is about 80w.

That's a very light load. So you should see little voltage sag under load, perhaps 0.1 - 0.2 V. Are you seeing more sag than that when the load comes on, or more rise than that when the load goes off?

Quote

I know it is a difficult question, but with a 24v lead acid bank of 105ah, what would a good lvd point be to use max solar and keep the amount of cycles I can get out of the batteries as high as possible

According to this page:

https://marinehowto.com/under-load-battery-voltage-vs-soc/

50% "under load" (but they don't say what the load is) is around 12.11 V per 12 V module, and 80% SOC is around 12.50 V. So something between 24.2 and 25.0 V, depending on how much you want to trade battery life versus usable time in a load shed. I'm a little surprised that your 24 V model allows 24.4 V in the load DC cutoff setting (setting 29). Does it go as high as 25.0 V?