Batteries

[BHH]

I have 4 x 100ah Gel bateries connected in series to produce 48v supply to my Growatt spf5000es 5kw inverter, I know everyone says gel batteries won’t last, but I have just started using them running my fridge and a light, charge does not last more than 45 mins, I would have thought 100ah could provide enough charge to run a ceiling fan a light and fridge for 2 hours, welcome any comments

[zsde]

In theory you have 4800Wh stored energy.
Lead Acid batteries are best not drained below 50%, i.e. you have 2400Wh available for use if you wish to prolong the battery life.
Thus if you are certain it's only for 2 hours, that would give you 1200W per hour to use. 
Add up the wattage of the devices/implements you intend to run and see if that total is equal to or less than that.

[MeepMoop]

6 minutes ago, zsde said:

In theory you have 4800Wh stored energy.
Lead Acid batteries are best not drained below 50%, i.e. you have 2400Wh available for use if you wish to prolong the battery life.
Thus if you are certain it's only for 2 hours, that would give you 1200W per hour to use. 
Add up the wattage of the devices/implements you intend to run and see if that total is equal to or less than that.

Also consider that the inverter uses 80w or so as self consumption.

[BHH]

Ok so I added the fridge @ 400 watts + two lights Led down lights @ 12 watts and a ceiling fan of 100 watts plus the inverter usage at say 100 watts so added together should give 612 watts per hour, if I have 1200 watts available it should last just under 2 hours

[Dylboy]

The cut off voltage of the inverter may be set to high perhaps ? So it's cutting off at only maybe 80% capacity left.

[Scorp007]

2 hours ago, Dylboy said:

The cut off voltage of the inverter may be set to high perhaps ? So it's cutting off at only maybe 80% capacity left.

Or the batteries cannot provide the needed 1040Wh to get to 2hrs. Unless each battery is tested for capacity - not just 10sec test as a lot of dealers use you are hunting in the dark without a spot light to find the possible reason 

[zsde]

4 hours ago, BHH said:

charge does not last more than 45 mins,

What are your settings on your Inverter?

[BHH]

Inverter cuts of at 42 v

in the book it refers to battery equalisation does anyone think that may help? 

[MeepMoop]

15 hours ago, BHH said:

Inverter cuts of at 42 v

in the book it refers to battery equalisation does anyone think that may help? 

That's a big "maybe". With pure lead acids, If it's done often enough, like once every 90 days, while the batteries are still generally healthy it can extend their life and reduce capacity loss. 

Not sure if it works for Gel batteries though.

See thread here:

 

Edited March 18, 2023 by MeepMoop
Added link

[RocketBoy]

How old are the batteries?

Before I switched out to lithium I went through a LOT of AGM batteries.

What I found is that the realistic cycle life before they are close to useless is around 300-500 cycles.

If I avoided depleting the batteries past 60% then I could get close to 500 cycles. If I went below 50% even a few times then it dropped to around 300 cycles.

Take loadshedding where it happens 3 times in a day... that is 3 cycles for a day. At that rate you could be looking at 4 months before you start getting 45 mins of run time out of the batteries.

If you are at the point where you know they are only lasting 45 mins then I would say the damage is already done to those batteries because you have hit cutoff to find that out. This assumes that your inverter isnt set to a high cutoff voltage with that being the cause.

[jacksdad]

There are a number of reasons why this may be happening, overcharging, undercharging, discharging too deeply, charging too fast, excessive temperature, etc. 

One of the primary reasons for premature LA battery failure currently is simply because of the present load shedding schedule. Lead acid (GEL and AGM are categorised as lead acid) need 6-8 hours to charge correctly. If your batteries do not get fully charged before the next load shed kicks in the are going to start the next period not fully charged and deplete further and lower than the previous period. With load shedding, this cycle will just continue and eventually damage your battery. 

So as in the examples above, with a fully charged battery bank you have 1200Wh available. But say your bank only charges to 90% before the next load shedding starts, you now only have 1080Wh to safely use... and so it goes. A few weeks of stage 4, 5, and 6 of load shedding and your batteries are in trouble, they are never getting a full charge and they starting to drop below the theoretical 50% DoD. As little as 1 or 2 deep discharges can easily do permanent damage to your batteries.

That's the beauty of lithium's, aside from the deeper discharge they can handle without damage, they can also be recharged a lot faster. A decent 12V 100Ahr lithium can accept a charge of up to 50A so a battery discharged to 80% DoD can be recharge to 100% within a couple of hours.