Jump to content

Battery advice needed from Powerforum experts please!


Solo
 Share

Recommended Posts

Battery advice needed from Powerforum experts please!

Issue:

As end users on an upmarket retirement estate, we have multiple inverter systems (up to 30) – all with very similar battery related problems.

The batteries are all Dixon 12V 105ST lead acid, 2 used in series with an Axpert clone 24V 3kw inverter.

During grid outages a typical load of TV, decoder, wifi and a few LED lights is typically 120W or 10A (230V), and the batteries should power this load for more than 8 hours.

What is actually happening is that the batteries will only power the load for typically 1 hour, and then the inverter shuts down at a battery voltage of 21V.  The batteries are all between 12 and 15 months old.

On doing a load test on the discharged batteries, it was found that 1 battery could sustain a load, but the other could not (voltage collapsed from 12V to 6V on applying a load tester)

A similar load test using new Enertec batteries ran for at least 8 hours.

 

Possible solutions:

The supplier has already replaced most of the original Synergi inverters. They had a firmware bug which intermittently disabled battery charging due to incorrectly detecting high mains input voltage.

The supplier may offer to replace out of warranty Dixon batteries at cost price, this is still under negotiation.

However, no battery monitoring or equalization is being considered at this stage.

The vendor supplied a Ctek 24V smart battery charger, which was used on all installations, but it did not rejuvenate the faulty battery, which is possibly sulphated.

No attempt has yet been made to individually rejuvenate the 1 faulty battery that is in use at most installations.

No discussion has taken place regarding alternatives to using entry level lead acid batteries

 

Background:

Inverter application is standby for load shedding etc, on an upmarket retirement estate.

The developer has included the inverter as a standard option on all units, but outsourced the system to a local supplier.

The end users are not the decision makers, the developers and supplier are engaged in negotiations.

Most of the end users are not technology savvy regarding batteries and inverters. They just want a system that works, preferably with a minimum of attention.

 

Link to comment
Share on other sites

29 minutes ago, Solo said:

The batteries are all Dixon 12V 105ST lead acid, 2 used in series with an Axpert clone 24V 3kw inverter.

So this one. The cycle life chart suggests you can expect max 200 cycles if you don't work them hard, and maybe 100 cycles if you do work them hard. At 10A, your capacity is reduced to about 90Ah, so 9 hours is more what you can expect when the battery is new. Depends on temperature as well. This is a UPS battery, and by the looks of it a month of 2008-level load shedding will kill it.

The Enertec you refer to is most likely a "Leisure" battery and will probably do a tiny bit better.

Cheapest advice I can give you now is to double up on the battery so you are closer to a C/20 discharge rate and have a lower DoD.

Link to comment
Share on other sites

Thanks Plonkster!

Are you recommending a 200AH battery and a higher cutoff voltage?

If so, what type of battery (Lead Acid, AGM, Gel) etc and possible vendors?

What about battery monitors and voltage equalisers?

Is there any benefit in trying to rejuvenate the dodgy battery that seems to exist in most installations, by individually charging them. I suspect that the suspect batteries may have sulphated, and could have some more life in them.

Link to comment
Share on other sites

33 minutes ago, Solo said:

Are you recommending a 200AH battery and a higher cutoff voltage?

Yes.

34 minutes ago, Solo said:

If so, what type of battery (Lead Acid, AGM, Gel) etc and possible vendors?

How upmarket is this place? :-P If the money stretches that far, LFP always gives you the lowest cost per kwh, has little maintenance and lasts the longest. Will likely outlive many of the residents. But since this is backup only, my suggestion is a high end AGM, like these. Or some equivalent (Ritar makes some nice ones, I think Trojan also has an AGM line). AGM so that it is no maintenance. These usually have a 700-cycle life of thereabouts.

38 minutes ago, Solo said:

I suspect that the suspect batteries may have sulphated

I've seen many devices (pulse chargers etc) sold on the internet claiming to fix sulfation, but I always get a bit of a scam feeling about them. There is really just one way to test it, give it a good charge, a discharge and a good charge again. If the capacity improves after a good charge, there might be some hope. Otherwise forget it.

I agree though about the batteries probably being damaged. It is also possible that there was a cell imbalance, so adding a battery balancer might be a good idea too.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...