Hi there, some help/advice needed please?

 

I have:

• Fullcircle Solar Inverter 3Kw, same as Axpert I assume
• Victron BMV-702 BMS
• Victron Battery Balancer
• 4 x 400 Watt Solar Panels 
• Currently 2 x Inkwenkwezi GEL-VRLA 100Ah Batteries, in Series for 24V
  • Had 2 x Omnipower AGM/Gel 180Ah Batteries, see issues below

My Issue:

First battery in the bank died, when there is load (~400-600Watts) the first battery would very quickly go down to 8-10Volts, causing the overall to go down to 21V then the inverter switches off, second battery fine. I then replaced these batteries with the Inkwenkwezi ones (Didn't have a lot of money). The Omnipowers lasted about a year before they started doing this, now the Inkwenkwezi batteries are doing the same after a month, first battery very quickly drops to 8-10 volts then shuts down.

What am I doing wrong? Why would the first battery in the bank always die? I can share all my settings but there is so much I would first like to heard what should be checked, then we can go from there,

VERY simple drawing included as setup,

Thanks in advance!

Dion

 

 

Edited February 6, 20223 yr by dionvdberg
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I think the problem is that you are overloading your batteries.  The max charge or discharge should be kept under 0.15 x AH rating which is 100AH x 0.15 = 15 amps. 15 amps x 24 volt = 360 watt. So any charging or discharging over 360 watt can cause permanent damage to your batteries. Did you reduce the charging rate when you put in smaller batteries? 

Thanks,

I do limit the charge to 15 amps yes, but the draw is average 400-600watt. But that draw is on 220v?

Dion

Thanks, I understand Ohm Law, but what I'm saying is I'm pulling 600W at 220v, so 2.72 Amps from the battery, wich is fine?

 

Or am I completely wrong?

 

Thanks!

Dion

Ok, I understand the explanation thanks!

 

So.... I'm on 24V, if according to De0n19 ("should be kept under 0.15 x AH rating which is 100AH x 0.15 = 15 amps. 15 amps x 24 volt = 360 watt") I can draw only 360 watt, I need 4 x 100Ah batteries, 2 serial and 2 parrallel, that would give me 24v at 200Ah and 720Watt (30Amps)?

Have I been over drawing my batteries the whole time? I would think 2 x 12v 100Ah AGM batteries can easily do 400-600Watt

 

Thanks

Dion

1 hour ago, dionvdberg said:

Have I been over drawing my batteries the whole time? I would think 2 x 12v 100Ah AGM batteries can easily do 400-600Watt

Not really, the battery will tell you what its maximum current is.  But for 100Ah "AGM" it will almost certainly be more than 600w continuous.

But there are multiple factors with lead acid batteries

• Your depth of drain determines the number of cycles you will get.  For these cheap batteries any depth of drain > 50% will kill them very quickly
• The amount of usable power you get from your battery drops if you drain more current. So in other words, by draining 600w continuous, you may end up draining it more than you think.

That all said, sounds like you are getting a dead cell, what does your wiring look like? (pic).

• What thickness is the various wires?
• How did you crimp them?
• What is your charge voltage?
• What voltage do your cells hit during discharge?

Edited February 8, 20223 yr by Gnome

A pic of the wiring is difficult, all inside a cabinet, will try,

• What thickness is the various wires? - 35 mm2
• How did you crimp them? - Bought them pre-crimped
• What is your charge voltage? - See below
• What voltage do your cells hit during discharge? - Steady around 25v then drop quickly because of first battery going to like 8V

29 minutes ago, dionvdberg said:

I assume these are the settings being set on the Axpert?

So 14.25v bulk (per battery) and 13.8v float (per battery).  Your float voltage is a bit higher than it was for my AGMs.  They were specified at a maximum float of 13.6v and my bulk on my AGMs were 14.6v if I recall.  That doesn't mean your values are wrong, but I assume you got these values from the manufacturer (of the battery) based on your temperature range? (lower temps = higher voltages)

I've had dead cells before by apply too high a voltage to a battery.  This is especially a problem if the cells weren't matched in terms of charge.  Like I had batteries that weren't completely matched and one of the batteries would charge up more rapidly and then because they are in series it would hit a 15+v very quickly and it killed one of the cells.

Does your "BMS/Balancer" provide you with per battery voltages? (And those look ok when you look at the data logs?)

EDIT: I think I should also just point out, that battery is dead.  You'll need to replace them... Again.  So this exercise is more about figuring out what is wrong than trying to fix it.  That ship has sailed, sadly

Edited February 8, 20223 yr by Gnome

The bms shows seperate voltages yes, and charging is fine, discharge the one battery drips very fast. 
 

Yeah i know the baterry is gone, what i’m trying to figure out is why it happens, this is the reason I bought the new baterries, the old omipower batteries had the same issue after a year, one battery started failing. 
 

Don’t want to replace to have it happen again. 
 

edit: Can a bad connection somewhere cause this?

Edited February 8, 20223 yr by dionvdberg

Bump please?

On 2022/02/08 at 2:52 PM, dionvdberg said:

edit: Can a bad connection somewhere cause this?

No, the batteries are in series, and thus have the same current.

The inverter cannot choose to do this. If your balancer works, this only happens because of the quality of the batteries. The only solution is to get better quality batteries.

Thanks,

 

I would have thought the Omnipower batteries was good, but the same hapenned to them? Allthough they laster about a year,

 

Maybe time to get Lithiums? Any recommendations?

On 2022/02/06 at 8:21 PM, dionvdberg said:

Thanks,

I do limit the charge to 15 amps yes, but the draw is average 400-600watt. But that draw is on 220v?

Dion

Ah is normally determined over 20 hours, unless otherwise specified.
See http://support.rollsbattery.com/en/support/solutions/articles/216766-what-is-amp-hour-capacity-

Lead Acid batteries suffer from "Peukert Effect".
See https://battlebornbatteries.com/peukert-effect/

You have 2 x 100Ah 12V AGM batteries, so 200Ah / 20h = 10A.
When quoting Ah, it's important to include Volts so you can calculate Watts (Energy)

As other have stated, to prevent damage, don't discharge completely.

Edited February 11, 20223 yr by system32