Maha 8-cell charger + battery backup = hot cells

[ProofTech]

Recently, I've noticed that when my Maha C801D charger is plugged in to my small APC uninterruptible power supply and charging a bunch of Eneloop AAs from the same flashlight, some of the cells will finish at a decent temperature, but the other cells will finish 10-20 minutes later and at a much higher temperature (too hot to hold for 10 seconds). BTW, the UPS is not running on its own battery while this is happening. When the charger is not plugged in to a UPS, all of the cells will finish at about the same time and none will be hot. Has anyone else experienced this same phenomena?

ProofTech

 

[Mr Happy]

I believe I have seen a similar report here recently.

Do you have any other load on the UPS at the time? It is possible that the UPS output waveform may not be very good unless it has close to the expected load on it. A battery charger will be a very light load, relatively speaking. Some electronic devices can be sensitive to the shape of the input waveform and may not perform well if it is not close to the expected sine wave.

 

[ProofTech]

Usually there is no other load on this UPS. When there is, it's just one or two other battery chargers. I was under the impression that cheap UPS units simply feed the incoming house current to their protected outlets until the house voltage gets too low. Is this incorrect? Are the protected outlets powered by the units square-wave power inverter at all times?

 

[Mr Happy]

I think it depends on the particular model of UPS. Some may act in standby mode and pass the incoming supply to the outlets unless incoming power fails, and some may operate the inverter all the time. Almost invariably however a UPS attempts to provide some kind of power conditioning and output protection.

I figure yours must be doing something to the output to explain the difference you observe between running with and without the inverter, unless it is only coincidence and the differences happened by chance.

Sometimes when batteries finish charging late and get hot it is due to a missed charge termination, and this may have nothing at all to do with the power supply.

 

[zipplet]

Thanks for starting this topic ProofTech. I planned to do the same with my BC-900. I think I will try this and let you know if there are any problems.

I can confirm the cheaper APC units work by passing line current untouched when it is present, with some noise filtering and surge protection only. I'm using one right now. Also, I think any respectable charger would not be affected even when the UPS kicks in with a modified sine wave because the power supply should have enough smoothing to provide a clean source of power to the charger.

But then, who knows? Time to test.