Battery bank drops drastically to 12.4 volts!!!

[cmutwiwa]

Hi,
I'm experiencing a drastic drop in voltage when the sun sets from 13.7v (float) to 12.4v with less than 200 watts load (lights & tv set)
My setup is a simple 12v system (will upgrade to 24v, waiting for 24v inverter). Setup is as follows:
2 x 265w poly panels connected in series
30 amps epever MPPT charge controller
2 x 200ah 12v inva tubular FLA batteries connected in parallel
500w, 12v victron pure sine inverter

The batteries are always in float by 12noon, they remain in float until the sun sets, the voltage drops to 12.4volts immediately the lights come on (10 x 9 watts LED)

Is this drop in voltage normal with such a setup or is there something wrong with it?

I'm not an expert in solar, this is just a DIY setup so any advice to improve my system will be highly appreciated.

[Ampster]

What is the resting voltage of your batteries with no load? By resting, I mean no Float, no load.

[Paul Land]

Check your Battery Over-Voltage set point on charger you could have set to low

[SunEagle]

Also how old are the batteries or how many cycles have they go through and about what dept of discharge?

[cmutwiwa]

Thanks guys for the reply.
I havent been able to check the resting voltage since I've read that to know the resting voltage batteries should be fully charged then left for 24hrs without load, thats has not been possible since am yet to buy a generator and am relying 100% on this system.

Some of the controller battery settings are as follows:
Overvoltage disconnect - 16.0v
Charge limit - 15.0v
Equalize charge - 14.8v
Boost charge - 14.6v
Float charge - 13.8v
Equalize time - 120min
Boost time - 120min

The batteries manufacture date is labeled as Feb 2019 for one and the other May 2019 , I bought one of them in May 2019 and the other in Aug 2019 then installed them at the same time. The batteries discharge to 12.3v every day since they were installed.

Edit : cable size 10.0mm square

[Mike90250]

When you mean "drastic drop", it may just be the Charging Source (solar 14V) goes away and batteries drifting down to their "resting " voltage.
Like this effect i see on my 48V system. At 6pm (18:00 hrs) the last of the sun goes, and the voltage crashes. (my NiFe bank does not use FLA voltages, just look at the trend)
The effect will vary with bank size and loads. Try recording voltages and charging amps in the morning, if it charges right up in 30 minutes that's a sad indicator of sulfation.

Also, attached below , is a battery voltage table, 12.4 ain't that bad

battery-state-of-charge LeadAcid.jpg


Aug29th_leak.jpg

[cmutwiwa]

Thanks Mike, yes it could be batteries drifting down to resting voltage, I was just worried since I've seen other voltage charts showing 12.4v as 50% SOC but if the chart you've posted here is accurate then I think I shouldnt worry that much since the lowest I've seen the battery bank drop is 12.2v that is in the morning before the sun hits the panels.

The charging amps when sun hits the panels is 20amps, sometimes droping sometimes going up especially when there is some load...its 10:15am here, the sun has been hitting the panels since 8:30am and the controller shows 14.0v, 20amps, is this bad?

[cmutwiwa]

This is the status shown by CC at ard 4pm...I'm uploading more images showing controller settings just incase there are values I'm supposed to change for better performance.

[cmutwiwa]

CC battery settings are as shown in the images...

[cmutwiwa]

Batteries type and connection

[Mike90250]

I'm off grid and pay for each cellular Mb of data, no pics for me. 20A at 10am seems light, if you are taking them down to 12.2v I'd increase absorb time half an hour, and see what the AM voltage is. You have to log and chart this stuff daily, to get things dialed in. Do you have temperature compensation on your batteries? That's really needed in cold weather when batteries need higher voltage for proper charging . Do you have a manual or something with specs for battery care and EQ instructions? You may need to charge with generator in early am, let solar do the absorb at 10am, and EQ at 1pm, before you loose sun. Not enough sun, start the generator early. EQ can't start till batteries are fully absorbed.

[cmutwiwa]

Thanks Mike and sorry abt the pics...
I will try and increase the absorb time and see what happens... However, I live in Kenya and at this time of year the sun is in plenty, I know abt the sun hours and I can say that am getting the maximum 5-6hrs. Yes I have the temp compensation attached to the CC.
I have a manual but unfortunately it doesnt mention EQ, only boost and Float

[littleharbor]

Those look like very tiny battery cables. Are you running an inverter off these batteries?

[cmutwiwa]

Hi Littleharbor,
The cables are 10.0 mm square or 8 AWG
Yes I'm running a 12v 500 watts victron pure sine inverter, cable length from battery to inverter 4ft...should I use a bigger cable?

[littleharbor]

What does your inverter manual recommend?