Hi all,

Firstly I want to check my figures.

Let's start off with my PV system. This has 10kWh of battery. Actually 200Ah at 50V gives the figure of 10kWh (approximately, the figure is rounded for marketing purposes I suppose).

Now my mother has one of these
https://www.maidenelectronics.co.za/new-crystal-intellipower-4-2400va-1440w-long-backup-ups-w-2-x-105ahs

Now, if I'm right 2 * 105aH 12 V batteries gives 210ah, and then 2.3 kWh

If that's right, then she has quite a bit more backup capacity than I had imagined, about 20% of what I have. OK... but current limited. If that 1440W is on the output side then it's about 6A.

Am I right?

There was talk in another thread about fuses. Does this sort of device typically have fuses between the electronics and the battery? I know it shuts down if you overload the output (AC) side.

You cannot really cycle those batteries more than 50% DoD at most. So it's closer to 1.2kWh usable. Most of these systems don't make it to 24 months before you need new batteries.

7 minutes ago, P1000 said:

You cannot really cycle those batteries more than 50% DoD at most. So it's closer to 1.2kWh usable. Most of these systems don't make it to 24 months before you need new batteries.

I'm aware of that. The shop told me that when they first opened they expected (but did not guarantee) +- 5 years battery life. Now, with load shedding, they think 2 years is good going.

But this means that I have really 9kWh useable, and the little box has about 1kWh.

Thanks

10 minutes ago, P1000 said:

You cannot really cycle those batteries more than 50% DoD at most. So it's closer to 1.2kWh usable. Most of these systems don't make it to 24 months before you need new batteries.

PS. Is the 24months because now the batteries get run down further and more often? In this case the inverter is backing up one CFL lamp, a TV and a DSTV decoder, and I don't see that lot drawing 6A.

OTOH today the schedule for outages is 

• 4:00 to 6:30
• 12:00 to 16:30
• 20:00 to 22:30

So a four(ish) hour outage, and then less than 4 hours to charge the batteries before the lights go out again. Goes to show how much stress load shedding imposes.

Also illustrates the power of PV, because with these timings, the batteries would still get some charging during that 4 hour outage and would be in much better shape come 20:00.

13 minutes ago, Bobster. said:

Also illustrates the power of PV, because with these timings, the batteries would still get some charging during that 4 hour outage and would be in much better shape come 20:00.

Depending where you are, not so much in winter after 16:00...  as for the SLA's these usually are specced @10% draw current, so your 12V 210Ah is only really intended for 21A, which would mean 200-odd Wh power production more like 1A on the 220V side... else expect real early battery expiration....

Edited September 23, 20223 yr by Kalahari Meerkat
grammatik...

Yes, those only cut out when the battery is nearly empty, which reduces the life significantly. On the other hand, these batteries also degrade when just sitting there charged fully all the time. It's a very good product from a manufacturer's point of view...

8 minutes ago, Kalahari Meerkat said:

as for the SLA's these usually are specced @10% draw current, so your 12V 210Ah is only really intended for 21A, which would mean 200-odd Wh power production more like 1A on the 220V side... else expect real early battery expiration...

Thanks. Is that for common or garden SLAs? What about deep cycle batteries (which would add R800 to the price of that box)? 

OK, now I wait to be told that there is no actual formal definition of "deep cycle", it's "deep cycle" if the manufacturer says it is.

5 minutes ago, Bobster. said:

deep cycle batteries

for normal SLA's they usually quote a 10% draw, on deep cycle's I think they quote a 20% draw rate, but mostly they don't really last any better... the days of these batteries are over and I would urge anyone that still considers these to stick to Lithium for now, I'm hoping that we'll have options not too long from now, Aluminium/Aluminum Ion and Sodium Ion looking like possible candidates, but not quite yet unfortunately.

Thanks for your replies so far. This has given me some good information.

On 2022/09/23 at 10:11 AM, P1000 said:

You cannot really cycle those batteries more than 50% DoD at most. So it's closer to 1.2kWh usable. Most of these systems don't make it to 24 months before you need new batteries.

And the inevitable happened on the weekend.

First I need to check my figures again. The inverter has a charge current of 20A. So that's 10 to 11 hours to get the pair of 105Ah batteries fully charged. And 20h = 10% an hour.  How am I doing?

So I've been watching my Mum's load shedding schedule. Recently she had a 4 hour outage, followed by another 2 hours scheduled 4 hours later. In reality, with time taken to restore, that unit had about 3.5 hours to recover from a 4 hour outage. So whilst we had stage 6 it was in an impossible position - discharging during a shed and then struggling to get recharged before the next shed. There also doesn't seem to be an easy way of turning the output side off - I am going to check with the company I bought it from.

Then late last week there was theft at two power stations (one Eskom, which feeds the second, which is City Power) which left them without power for at least a day (nobody knows exactly as the load shed was in the wee hours, and it took them a while to figure out the lights hadn't come back on).  At some point the inverter turned off due to low SOC. Yesterday morning the indicator panel on the unit showed it was fully charged, but I suspect those batteries have taken a fatal beating.

Edited October 3, 20223 yr by Bobster.
spelllin