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Battery help needed


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Hi everyone,


I am clueless when it comes to the finer details of setting up a stand-by system and need an experts guideline.


Basically I have purchased a 3kw UPS unit ( see attached file , my model is the AV5K ) , and need to know what kind of batteries

to buy for this kind of unit. The supplier advised me to purchase 12v180ah for a 4 hour backup , but the price of 180ah batteries are out of my budget.

So the second choice was 12v100ah . I found a supplier selling me 12v105ah TASMAYA batteries at R1400 per battery. I ordered 8 batteries for a start.


I don't think im going to power a lot of things in the beginning , just my LED lighting and TV systems. I worked out total power where LED lighting is 700w and my TV + Decoder is in the region of 400w , giving a total of 1100w/ph . Now I would like to power my fridges , is this possible ? I don't know how many watts per hour my fridges use. How do I work this out ?


LAst but not least, I don't know who to use to set up this system ! ! Im based in Centurion. Any recommendations ?


Any advice will be highly appreciated.


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Well, normally you would only use a UPS for short time periods, basically long enough to ride through a power dip or give you enough time to start your genney in a power failure.

Mostly the UPS will also provide over and under voltage protection.


So you looking at around 200Ah of backup time. (2 x 48V100Ah strings)

Of this you should not use more than 50% capacity to save on battries, so 100Ah usable.

So at 1200W constant load, you should be good for at least 4 hours.


Adding a fridge in there can be done, but not reccomended.

The compressors use very high current to start and how long they run is difficult to work out.

Your fridge should be good for 12 hours without power.


Personally I would use the ups only for my critical equipment, like computers, decoders and TV's and a couple of lights.

The rest can be powerd via a genny if required.


P.S. You have 700W of LED lights!!! That is over a hundred downlighters :blink:


Only electrical contractor I have used in JHB have been Henstra. They should be able to help you out with wiring and CoC.

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Thanks for your reply Wetkit.


Yes im only backing up critical stuff right now. I've got two 3kw UPS systems so will install the second one powering the fridges etc. I will most likely run a solar system with those ones.


I have a big 500 sq/m house , so 100 downlights is emergency. the rest I don't need to power up :)


Any advice on batteries brands to use ?

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Current Automation   Head Office (Johannesburg) Phone +27 (0)10 591-1713 Fax +27 (0)11 462-4310 Alternative numbers 011 462-4253 / 011 462-0448 / 011 462-2452
011 462-1031 / 011 462-1620 / 011 462 2600
011 462 0390 / 011 462 2310 Delivery address 16 Staal Street
Kya Sand
South Africa Postal address PO Box 2051, 


I hope admin don't mind me posting this

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The single biggest killer for UPS battries is tempreature. If the temp goes high, the life goes down rapidly.

UPS battries is normally not rated for deep discharge, but rather longer life at full charge.


Solar battries for solar systems is rather more geared for cyclic operation.


Anayway, it all depend on your budget. Those TASMAYA battries should be great and last a long time.


Make sure you check the date stamp on the battries, so that they did not give you old stock.

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  • 3 weeks later...
  • 3 weeks later...

Regarding what a fridge/freezer uses: I recently swapped my aging cheapies for new models. My fridge is a Bosch A++ unit, which uses less than 1kwh per day (sure, it was around 8k to buy, but payback will be <5years).


My freezer is an even beter bang for buck proposition: It's a 210 liter Defy "eco" unit. A rated. Cost R1999. Payback should be around 2 years.


Both units have 90W motors. Starting torque is still around 5 times that, so 450W spike, but that depends on what your UPS/inverter can handle. My little Victron Multiplus can do 3kw surges, so I'm more than fine.


Now the old ones had 250w compressors and they ran pretty much 12 out of the 24 hours, so around 3kwh per day per fridge/freezer, and starting torques of over 1kw.


(Can't start an Air Conditioner though, AC needs 5KW spike to start, for that I need to go to inverter AC units).

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  • 3 weeks later...
  • 4 weeks later...

I'm going to post pictures soon :)


Last week the council was doing a repair on some Transformer since 2pm. when I saw my UPS system at 12am (after 10 hours) , it was only 50% drained.

If I have a look at what was being powered ...

1. Sony 46" LED + DSTV being used from the morning till 11pm ( 5 kids so TV stays on )

2. Took note that my Freezer had power all that time.

3. Was shocked to see my domestics fridge/freezer and TV had power ( took it off the UPS yesterday )

4. My bedroom 46" LED TV + DSTV + Laptop

5. Lighting everywhere when needed.


So all in all, I am very happy with the performance of my backup system.


I need to know one thing though , I have 2 battery banks currently . 4 in series 2 parallel. If I add another bank of batteries , does it matter what kinf of batteries they are ? My intention is to link 4 x 12v100ah GEL batteries . These GEL ones are far superior the normal 12v100ah batteries  fitted. I do know that putting different batteries in Series could be an issue.



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Putting diffrent types of battries in parallel is not recomended, but can be done.

I would really not like to mix normal acid and gel battries, for the simple reason that each type have diffrent settings for charging and float voltages.

No problem for the short term, but not sure of the long term effects.


Just not sure why, as you said you ran 10 hours on your existing battries and they were only down to 50%. That is pretty decent!!

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  • 2 months later...

How is the setup going? Any pics yet?

I am super new at this solar inverter battery thing and have a few odds that I am throwing together to get backup power going.

Takes a crazy amount of research and work at home to get a system up and running hey.

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Attached is a brief shot of the setup. I also realised that my current batteries are not Lead Acid but Lead Calcium. So I conned into buying them.

So it worked out well that my UPS supplier is delivering to me (hopefully this week)  8 x 12v100ah DC Gel batteries at R2200 each. Attached is the Life characteristics chart of the battery. Looks good to me, but  opinions are always welcome.



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