Hi All,

I am new to the whole backup power / solar setup.

Lately, I've been having issues with a Rentech 3kva (2400w) Axpert inverter.

My initial installation was 2x JPC Lead carbon batteries in series (100ah ea) with the inverter.  I was able to run 3x monitors, 2x laptops, TV, DSTV and PS4 for roughly 4-6hrs.  That stopped a few months ago. 

I am barely reaching 2hrs right now.  I replaced my batteries with 2x 105ah Royal Gel deep cycle batteries but the issue is the same.  My overall peak load is usually in the region of 94-111w.  On about 96w, I cant get through 2hr loadshedding.  If I run 1x laptop, fibre router and 2x monitors I am get through 2hrs but with load battery warning within the first 1hr15m.  It will stay steady on 22.4v.

Now the inverter has been tested and they confirmed that all is in good standing with it and that the issue is the new batteries that I bought.

I am planning on getting a lithium 100ah 24v battery but I am afraid of spending the money if its not going to solve my issue.  The inverter testing was, amongst other things, tested on a lithium battery with 420w load and it seemed to work great.

 

Any words of wisdom that might aid my decision?

Thanks

As with other recent threads, it’s highly likely your existing Lead acid batteries Are kaput. The default cutoff for the inverter is likely 12v or lower, and running the batteries down to that level just a few times kills them

I recently purchased what was meant to be a slighty used Delkor Royal 105AH battery - apparently used for 2 months to power a router only.

However when I connected it to my 720W Mecer inverter with my usual load, straight away it jumped from 100% to 75% and only lasted 45 minutes - if I compare this to my Enertec 105AH battery which I have had for over a year it lasts about the same as the Enertec with the same load and the Enertec does not jump straight to 75% when grid power is lost.

 

If you purchased your Delkor batteries brand new and sealed, maybe there is a bad batch?

I assume you had the issue of the batteries not last from the beginning? As soon as they were installed and it did not degrade over a short period of time?

Hi @PsyCLown

I had issues with them since the beginning.  Although they were tested and confirmed in 100% working order.  If I have the bare minimum running, they last 4hrs with a low battery warning ... I already wasted R6k buying the Royals.  I just dont want to waste another R15k on a Lifep04 battery.  Looking at the SVOLT 2.7kwh battery

@madness_za My current cutoff is set to 21.1v (set by Rentech when they tested my inverter).

2 minutes ago, KobusM said:

Hi @PsyCLown

I had issues with them since the beginning.  Although they were tested and confirmed in 100% working order.  If I have the bare minimum running, they last 4hrs with a low battery warning ... I already wasted R6k buying the Royals.  I just dont want to waste another R15k on a Lifep04 battery.  Looking at the SVOLT 2.7kwh battery

@madness_za My current cutoff is set to 21.1v (set by Rentech when they tested my inverter).

Yeah, that does not make sense to me.

Either your load is much higher than you think or the Royal batteries are not 100%.

With a load of 110W and 2x 105AH batteries, you should easily reach 4 hours and still have capacity left (taking into consideration not to discharge below 50% because its Lead Acid).

 

I think going for a lithium battery would be a good idea. I picked up an Svolt 51.2v battery yesterday, have not yet got the comms between the inverter but in lead acid mode so far it is working well but its literally brand new. Cells are not balanced but I will give it a bit of time for the balancer to try balance the cells.

I have reached out to Svolt for assistance with the comms between my Luxpower and the battery.

You’re running 2 x 12v batteries? That works out to 10ish V per battery which is definitely too low

15 minutes ago, madness_za said:

You’re running 2 x 12v batteries? That works out to 10ish V per battery which is definitely too low

It is, although OP has been experiencing the issue from the very beginning with the batteries not last.

So I do not think the issue has been caused by the low cut off voltage.

 

I found this online, a quick chart showing the voltage and SOC. With lead acid one does not want to go lower than 50% DoD.

On 2023/09/07 at 11:17 AM, KobusM said:

My current cutoff is set to 21.1v (set by Rentech when they tested my inverter).

As others have mentioned, that is way too low, you shouldn't go below 24V. Lead acid banks are usually designed to only use 20-30% of their capacity if they are to last for years which is totally possible 

Another thing is to make sure the batteries are charging properly, a lot of these inverters will charge to bulk voltage and switch straight to float without any absorbtion time. Make sure your inverter holds the bulk voltage until the amps drop right down before it goes to float or you will be undercharging the batteries which is worse than overcharging.

I had similar 2 new batteries for my trolley and 8 months of usage the batteries packed up. 

Here is one of the best lead acid battery. A bit pricey but i got a 230ah 12v in 2014 and it still working at my parents'. Was doing about 30% usage each cycle.

https://www.bushpower.co.za/product/discover-ev27a-dry-cell-100ah-deep-cycle-battery

I suggest you invest in Lithium battery if you can

Thank you everyone for the great info.

I've decided to go with a new Conderenergy 3kva Inverter, SVOLT 24v Lithium, 2x 425w solar panels. 

I dont think the lead acids are worth keeping around.  At this point they are slightly better than paper weights