APC 5KVA UPS with NMC 3 giving error; battery charger fault

There's something here that's not making sense.

The two internal modules would be two 8S packs of 12V batteries connected in series, so 192V total.

The external pack is four of these 8S modules connected in a 2+2 arrangement, for a total of 192V again but at twice the Ah.

From a technical perspective, it shouldn't have any effect on the internal charger if a larger capacity battery is connected, it'll just charge slowly and runtime calculations would be incorrect.

A battery cannot demand or pull more power than what is available from the charger, it cannot load it down or stress it out. It'll just take however much is available.

However, it may shorten the lifespan of the battery, not the charger, if a smaller capacity battery is connected to a charger that is configured for a larger capacity battery.

The only way a charger can fail with a higher capacity battery is if there's not enough cooling to keep it running for extended periods of time, but APC would have accounted for that in the design.

A charger may fail beyond repair if the output is shorted, but with lead acid batteries, the opposite happens as they age — they just refuse to take the charge.

In my talks with Vertiv, they say an external battery charger has no effect on the UPS itself, provided it charges at the same voltage as the UPS. In fact, they sell chargers for extended batteries seperately and there's no communications on those things, they're just connected directly to the external battery pack. Some of the UPS they sell can be used with batteries in the hundreds of Ah.

In this case, the fault is more likely to be a component failure due to either poor circulation, debris, or just age — anything with a capacitor will eventually die, and all solder joints will eventually crack.
 
In this case, the fault is more likely to be a component failure due to either poor circulation, debris, or just age — anything with a capacitor will eventually die, and all solder joints will eventually crack.
There could be two reasons: the heatsink had a lot of dust, causing overheating that led to component failure (running 24x7 made this worse). Second, the control card was unaware of the externally connected batteries, which led to some fluctuations and affected some components in the long term.
It could be either or both of these.
but with lead acid batteries, the opposite happens as they age — they just refuse to take the charge.
In this case, when checking the IGBTs, the readings indicated that they were going bad, so I don’t think the batteries are the issue here. Also, the batteries aren’t that old, the replaced one is just a year old and the older ones are 2.5 years old.
APC provides 2 years of warranty on these batteries.
 
Last edited:
The only way a charger can fail with a higher capacity battery is if there's not enough cooling to keep it running for extended periods of time, but APC would have accounted for that in the design.
The charger heatsink is behind the inverter heatsink and the boost converter heatsink and there is only one fan blowing on them. With double battery the charging section has to work for twice the time compared to single battery, it's output current is limited.

Sure APC must have designed it right, but they didn't account for blocked heatsink with dust in our case.

1726453149780.png
 
Back
Top