'Upscaling' UPS Internal Battery

[CommsPlayer]

As an experiment, I recently tested my Mecer 600VA UPS on my Samsung 40" TV, DSTV decoder and one 7W LED lamp (total wattage consumption around 140W). The UPS worked 100%, but only for about 30 minutes, obviously because the UPS battery is only rated at around 12Ah.

The beauty of a UPS is its ability to charge the battery when mains is on, and 'seamlessly' fail over to the inverter when mains fails. So the only downside of a 'cheap' low-wattage UPS is its internal battery's capacity.

Question: can one simply replace the UPS's internal battery with a higher capacity (external larger) battery, say 45Ah or 102Ah, by feeding the battery leads outside of the UPS and connecting them to the larger battery?

AFAIK the only downside of this should be that the UPS is just going to take longer to charge the battery, but surely the UPS' inverter would still receive 12VDC and produce 220VAC, but just for a longer period?

 

[mmacleod]

Question: can one simply replace the UPS's internal battery with a higher capacity (external larger) battery, say 45Ah or 102Ah, by feeding the battery leads outside of the UPS and connecting them to the larger battery?

AFAIK the only downside of this should be that the UPS is just going to take longer to charge the battery, but surely the UPS' inverter would still receive 12VDC and produce 220VAC, but just for a longer period?

Sort of. I've done it before with a slightly bigger battery on my proline UPS.

However there are several potential issues (and the problem is it varies depending on the UPS) which you should keep in mind.

1) The battery charger in a UPS is generally very poor quality and designed for a specific battery size, as it is it kills the battery it is designed for quite fast a larger one it may butcher even faster.
2) Depending on the UPS the way it detects when it is time to cut off the battery can be not very advanced, usually just a hardcoded voltage, sometimes even a hardcoded time limit, so depending on the battery and UPS specs you may see no time increase or only a small time increase instead of the full time increase you were expecting.
3) And this is what worries me the most - The transformer in these things gets quite hot, in the cheaper units they have only been engineered to be able to handle the load specified for probably T+25% (to keep prices down) - so if you run it under heavy load for substantially longer you run the risk of fire.

 

[henry1103]

Question: can one simply replace the UPS's internal battery with a higher capacity (external larger) battery, say 45Ah or 102Ah, by feeding the battery leads outside of the UPS and connecting them to the larger battery?

yes

AFAIK the only downside of this should be that the UPS is just going to take longer to charge the battery, but surely the UPS' inverter would still receive 12VDC and produce 220VAC, but just for a longer period?

yes, as long as the external battery also has the same voltage.

 

[CommsPlayer]

Thank you for the useful responses. I can imagine there are reasons why some UPS's are cheap...

I think I'll go trawl the web for decent charger/inverter circuits or systems.

 

[mmacleod]

Thank you for the useful responses. I can imagine there are reasons why some UPS's are cheap...

The thing is that most of them are designed for e.g. a European/Chinese market, where they have to run for at most a few minutes at a time once or twice a year, they aren't really engineered to be running loads for 2/3 hours at a time on a day to day basis, of course as with all things it depends very much on the actual machine in question etc. though.

 

[CommsPlayer]

The thing is that most of them are designed for e.g. a European/Chinese market, where they have to run for at most a few minutes at a time once or twice a year...

Of course - I lost sight of the fact that those UPS's are actually designed for up-time extension on computers etc. when mains fails, allowing the users to gracefully shut them down, and then sit out the remainder of the load shedding cycle, or hook up a generator. And in SA this now happens more often than in Europe/China etc...