Back UPS 1500 RS doesn't seem to work with Antec supplies?

[Anonymous user]

I just bought a second 1500VA Back-UPS because I thought I had too many PC's on the first one. The first one is a couple years old, the second one two days old. Neither will prevent a new 64-bit AMD CPU PC with a 550-watt Antec supply from rebooting when I remove power from the UPS. Both work with other PC's, including combinations that exceed this nominal rating.

A had two PC's plugged into the first one (an RS) for two years working fine without any problem - it held them both up just fine through frequent power glitches. When I upgraded one of the PC's to a 64-bit motherboard and an Antec 550 watt supply and I started having trouble - every time the power would glitch (frequent up here in the mountains) the new PC would reboot, while the other one would stay up.

My first thought was that the two together were somehow exceeding the power capacity of the UPS. So I bought the second one. But it doesn't work any better, even when all it has on it is a 550 watt nominal PC. Now I am thinking that it is just the new PC which doesn't get along with either of these UPS's.

According to the LCD display, the actual load of the PC+LCD display is about 78 watts. I even tried disconnecting everything but the PC itself (no display, no ethernet, no sound, nothing for ground loops), but it still reboots when I unplug the UPS. Yet, if I put the other 350 watt PC on the UPS it holds it up just fine through an unplugged power test.

Has anyone experienced anything similar to this? I doubt there is anything wrong with the UPS's - it would be too coincidental for both to be bad. They are not even exactly the same model (one is the tall 1500 RS model beige, the newer one is the squat LCD black).

Any help would be appreciated.

--Jeff

[ginbot86_apc]

Step-approximated sine wave? I didn't get that... Is it a step wave or sine wave?

[Anonymous user]

I have an Antec Earthwatts 500 PS and a dual core AMD processor and I am having the exact same problems. UPS works great on other things, but not my PC. Is there a fix for this, or did I buy a useless UPS?

[TheNotoriousKMP_apc]

Hi Jeff,

Thanks for the detail, that makes the discovery process a lot easier.


Have you contacted Antec and see if the Power Supply is sensitive to modified sine wave input? The UPS outputs a step-approximated sine wave while on battery (as opposed to a pure sine wave which is normal AC output), which could very well explain the rebooting of the new machine.

[voidstar_apc · Accepted solution]

See this:

http://img338.imageshack.us/img338/3759/waveformln6.gif

Historically, power supplies weren't particularly sensitive to the shape of the waveform and step-approximated sine waves worked great. The power supplies would just grab power near the peak of the waveform. Because these supplies didn't take power across the entire line cycle, they would distort the AC line. As more and more power supplies are attached to the line, this becomes a problem.

So regulators stepped in and require power supplies to avoid distorting the line, but this also means that newer power supplies can be sensitive to the shape of the incoming AC waveform.