Testing/checking small home UPS

hi guys

I have 3 x small home UPS’s… know the one that takes those 7Amp batteries…
Want to put one in front of the TV/AppleTV/Amp and then the other before my home network bits/switches etc.

I’ve had occurrences of overload on my inverter system than then resets everything and want to give these some extra protection while the system restarts.

But thinking they a bit tired/ need new batteries. want to double check thazIAt they working.
whats the best easiest way to do that. One’s a CPC, other ECM and last ZIAA


Easiest way I can think of, apart from opening them up and measuring each individual battery capacity remaining, is to install them in line and then switch off the mains power.

This way you can see how long they can supply the needed power for that specific device.

If this time is too short, then open them up and simply replace their small lead acid batteries.

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was more thinking of the electronics…

but ye… connecting them making sure they get charged and then disconnecting mains is prob the easiest…


My 2 cents, if the batts need replacement, replace them with lithium cells, like these - if you can find some …

I did that with a 24v APC UPS of mine …

does the charging circuit not need to also change, as it’s expecting seal Lead acid/gel atm.

looks like 2 string of 4 these in series together might be a much better idea,


The BMS should be able to manage that most of the time for you. With LiFePo4 the voltages are very close to what a lead acid would use.
LA are normally charged at around 14.2V which is 3.55V for 4 of these cells.

If you could it would be better to replace the charging circuit but that is much more involved than just slapping on a BMS and cells.

BlueNova sells a drop-in replacement for gate motors, alarms, etc. Under R1000 (although I see Takealot is basically bang on 1k).

Testing a 7Ah battery is usually easy enough. Put some kind of load on it and check the voltage sag. A nice bright halogen lamp from a car (around 20W) makes a good load.

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If I remember correct, these 12V LA/Gel should carry a fully charged capacity of about 13V ?
below that normally implies they cooked.

replacing circuit and batteries… just as much implies new UPS, making then building a new UPS myself. which then implies rather biting bullet, which is not a bad idea either come mont/2 to add a 3rd 2400 Pylontech to the string. probably a much better solution long term to expand the bank to be able to take the Wattage hit when grid drops and we have to much switched on.

Thanks. easily do-able on testing.
Thanks on the blue nova option.

Plonkster what type of sag is acceptable, say on a 7ah alarm battery, which these UPS’s has. ?

Why I figured it, the default charge settings on UPS’es, with the 7ah cells lasting X years, if I can get 2 x X years out of the lithiums, I win, as the price I paid for 2 x 24v BMS’es and 16 cells, was ±R100 more than 4 x 9ah lead-acid.

Also figured, having read a bit on the WWW, the BMS will sort most of the issues, and because a UPS is mostly just sitting there, it does not really matter as much as on a big solar system.

All boils to down Rands and cents, as, in my case, the APC UPS’es tend to last a long time, their lead-acid cells on average 5 years … or less.

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Man, I don’t have exact numbers, it’s a bit of a seat of the pants gut-feeling thing. It’s a 7Ah battery, so a C/5 discharge rate would be around 1.4A. The 20W headlight bulb puts you a bit over that, but it’s close enough I think. The amount of sag you’d accept would be about the same as you’d accept for any other lead acid battery, where basically anything above 11.5V (and holding), but preferably above 12V means it has some life left in it, and if it drops below that you need to replace it.

But often these smaller 7Ah batteries are designed to take a bit more of a punch, because they are used in applications where they have to provide lots of power for only a few minutes. Still, when they die, they tend to sag pretty clearly the moment you put even a modest load on.

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Rather than a wild goose chase doubling up on your UPS rather rectify the overload issue at startup. (And those 7Ah inverter UPS’s are damaging the credibility of the industry :frowning: )

true… thinking

whats the load/wattage 2 x 2400 Pylontech’s can handle. think I might have that set to low, causing the system to trip if grid drops and at the same time I have poo tumble dryer and dish washer on + normal base load of some computers etc.


ye well guess i’m in for problems if inverter has been set to max invert 1750watt and I know base load was higher…
now to figure out whats a better value based on my bank.


Does the system restart automatically? If not what is the startup procedure?

yes it does.

Whats the correct invert setting for 2 x Pylontech 2400’s

pretty sure I had it to low at 1750W anyhow.


interesting :laughing: or disgusting

guess you meant pool

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well my pool is disgusting…