I have a couple of UPS'es connected to computer equipment. The UPS on my laptop and screen started switching off immediately when there is a power dip. I removed the battery and installed a new one. However, when I tested it by switching off the supply to the inverter it still dropped out. I measured the output voltage and it drops to 160V which is obviously way too low. It did not even have any load attached to it.

I then tested another UPS, this one drops to 170V, only a DSL router attached to it. WTF?

So then I tested the 3rd UPS, this one drops to 207V, load is a 27" iMac and a Macbook. So that seems reasonable. However, this UPS is attached to a 100Ah deep cycle 12V battery (I modified it a bit when it's battery died).

All 3 UPS'es are APC units, I thought they are some of the better quality available.

Question is now, is this normal? Anyone else on here checked the output voltage on their UPS when AC is switched off? Will the low voltages damage the equipment? I know a lot of electronic equipment is spec'ed as 110/220 V but I assume it is not any voltage in between, rather two discrete voltages?

Will appreciate your comments and knowledge.

Cobus

So is the output voltage of the UPS dipping? So if connected to normal AC power from the inverter then the power is fine. But when die power is gone it will dip or does it dip when you connect ot to the inverter?

What happens if you unplug the ups ac side from the inverter? Does the volts climb back to 220v?

This sounds fishy. I use UPS'es all the time, on Eskom and solar, and I never have this problem.

The dip in voltage occurs when the input (grid) to the UPS is switched off. I am basically simulating a power failure.

This is not related to the inverter, the grid voltage is very stable at around 235-240V. It is a problem that the UPS output drops when a power failure occurs.

I ordered a new UPS, should arrive soon, I'll also test that and give feedback here. 

Has anyone else tested the output from their UPS? How do you know that the output voltage is OK? The equipment remains switched on? In my case, on two of the three UPS'es the equipment remain on, the only sign of power failure was the regular beeping of the UPS. However the voltage is way lower than I expected.

If the batts are ok, then I think the UPS'es are faulty. 

The test is: Pull the power cord out, assuming the UPS can still operate with power cord plugged out (cold start) or switch off the plug. Equipment MUST still work perfectly. 

In my opinion, the newer APC models are not of the same quality as those of a few years ago. I think there where too many cheaper ones so they made a plan.

Cobus, couple of questions:

Q1) Is the UPS a modified sine wave output or a pure sine wave?

Q2) Are you measuring the output voltage with a true RMS meter or an average responding meter? 

Q3) Is it line interactive or a double conversion on-line UPS?

 

12 hours ago, Carl said:

Q2) Are you measuring the output voltage with a true RMS meter or an average responding meter? 

Yes! I completely forgot about that, and I am so glad you brought this up. Watch this and forever consider yourself educated (unless you forget, like me) :-)

 

18 hours ago, Carl said:

Cobus, couple of questions:

Q1) Is the UPS a modified sine wave output or a pure sine wave?

Q2) Are you measuring the output voltage with a true RMS meter or an average responding meter? 

Q3) Is it line interactive or a double conversion on-line UPS?

 

Q1: Probably modified sine wave. Regular 300 - 800W APC UPS'es

Q2: This is probably the cause, it is a regular cheapy multi meter so it does not measure RMS. Will get one of those.

Q3: No idea what this means.

 

Thanks for the video plonkster, I think this is my problem. New UPS arrived, it tests 170V. So this is probably normal. According the video computer and screen equipment does not really care about the MSW output. I suppose it is OK then.

C

43 minutes ago, cvzyl said:

According the video computer and screen equipment does not really care about the MSW output. I suppose it is OK then.

Correct. Only time it is an issue is with some TV's and motors / compressors.

Computers are 100% fine to run on a modified sine wave.

You UPS'es are definitely not  double conversion on-line UPS'es. Those UPS'es are quite expensive.