[ inverter trouble shouting ]

[texane]

Hi,

I recently got a defective apc back ups es 550 inverter,
and try to bring it back to life.

The problem: I can start the inverter, voltages seems ok
to me. But, it completely stops when I connect a load. I
am trying with a simple 25W desktop light.

I thought the issue cam from the inverter internal battery,
an acid lead 12V 7.5AH. Thus, I tried with a 60W lab power
supply, but the problem remains.

I checked the inverter DC output without a battery, it is
13.7V.

I checked the AC output with a multimeter, it is around
165V (I live in France, 220v AC). With an oscillo, I saw
that it is a modified sine wave based inverter, so the
measured voltage seems ok.

Do you have any idea what to check? Any troubleshouting
advice is more than welcome!

Thanks for your help,

Fabien.

[texane]

I forgot to mention that I checked the PCB and it looks
alright to me. I replaced some caps that looks a bit
suspicious, but it did not change anything. Here some
photos:
http://sd-38205.dedibox.fr:8484/~texane/tmp/apc_back_ups_es_550/pic/

[SeanB]

Use a good battery and try again. Most commonly the battery fails as open circuit. the UPS draws a very large current from the battery, even when driving a very small load.

[texane]

Actually, I did some tests with a very small load, an old mobile phone
and a 220v ac to 5v dc transfo. The inverter DC alim prints 1.6A at 12V,
but the inverter does not turn off. If I use my laptop, the alim goes up to
5A / 12V and the inverter turns off. Thus, I underestimated the power
consumed by the inverter, and my problem is now to find a more powerful
alim or a more efficient inverter.

Thanks for helping,

Fabien.