UPS idle power consumption

Hey everyone! For my home server and PC I have a UPS to protect against power outages. To my utter shock, I recently discovered that it draws around 50 W * idle (meaning with the device turned on, but nothing connected to it), which is also reflected in the unit becoming quite warm to the touch. I found this to be an obscene amount and have since been doing some research.

The UPS I got is a APC Smart-UPS 700VA 230V. I acquired it in used condition from a friend and haven’t changed the battery. I don’t know how old the batteries are, but according to the manual , the device has been manufactured between 1995 and 2000 and the typical battery life is 3 to 6 years. I don’t know whether the batteries have ever been changed, but I suspect not.

Per the website my unit is a line-interactive UPS and the fact that it starts buzzing when I interrupt the power seems to confirm that. However, what I found out on the internet suggests that line-interactive UPSs shouldn’t have such high power draws at idle, which confuses me. Personally, I would blame this on the age of the device and battery. What do you think?

I am not willing to accept this high of a power draw for a device that most of the time just does nothing. I mean I would totally get it with an online UPS, but we’re talking line-interactive here. So I hope someone could share some experiences regarding the idle draw of more modern offline or line-interactive UPSs. Are they as bad? How do offline and line-interactive compare in idle power consumption? Because for a potential new buy I would like to keep the benefits of line-interactive like surge protection and over- and undervoltage compensation.

* that is, assuming my power meter actually measures effective power and not apparent power.

I have never really checked the idle power of a UPS, what are you using to confirm the wattage being used?

It’s a really cheap device that goes between the outlet and whatever you’re powering, the UPS in my case. As stated above, I am not 100% positive it measures effective power [W] and not apparent power [VA].

I can’t comment on the power being consumed at idle, but as far as battery life, I haven’t seen a battery that lasted more than 5 years without significant loss of run time. Usually by that time they have started to swell and lost a lot of capacity. In environments where it matters, we replace the batteries every 3 years.

It’s also good form to write the date on the battery when you replace it. That answers the question “Didn’t I just replace this?” when it fails the self test 3 years later.

Battery life also depends on how and how often it was used. I got 3 years on factory batteries, light usage. The power company went chaos on line quality and due to that, the replacement batteries are dead in under a year, because it had to line condition so much.

Also, the contraption paolo is referring to is typically called a Kill-A-Watt here stateside.

That model shoud have a serial interface that uses a cable to connect to a Windows PC. You can use APC’s Power Chute progran to provide details on battery codition and current draw. Check the manual for the cable part #. Find the cable on ebay if you don’t have one.

I have a model 700 Smart UPS and it runs warm even idle. If the battery is going bad the unit will tell you. Batterys tend to swell when they go bad so a visual inspection may be in order.

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Thanks for the tip! I knew it has the port, but I wasn’t aware you are able to read battery health information from it. I don’t know whether I’ll get an original cable from APC, they seem very expensive. I’ll probably try with a standard RS232 to USB cable first and see if it works.

I’m still looking for some experience from others regarding the idle power draw of their offline or line-interactive UPS though. I am willing to buy new in order to save electricity cost.

The back-ups 350, CS500, and similar small offline UPSes have 3.5W idle consumption, measured with fully charged battery and a calibrated, verified to perform correctly, effective power meter*.
Back-UPS Pro 1500, line interactive, is 6.3W measured with the same meter.
I briefly measured a SmartUPS RT3000 (two-man lift even without batteries), and I believe it would have gone below 50W, but I did not have time to let the batteries charge.

Here is a back-of-envelope tip regarding power dissipation: Consider the outside surface of the UPS as a heat sink, and roughly measure the area of the sides and back. Also add the top, but since the top is not vertical, only add half of that. For the BackUPS 1500, that area comes to about 300000 mm^2. Now, from much experience, I know that a vertical 64000 mm^2 one-sided surface will rise 1K when you dissipate 1W in it. Since the UPS is 4.7 times larger, 6.3W will cause the outside to rise 1.3K. If I average the temperature over the case using my IR thermometer, and subtract the temperature of the carpet it is sitting on, that is about what I get.

Your 700 is smaller, with an outside area of about 100000 mm^2. This means it takes 1.6W per K temperature rise, and with 50W it should be 31K above room temperature. My carpet is currently 27C, so it would be 58C average case temperature, and hotter in places, assuming the fan isn’t going.

*This meter works by sampling tension and current at 50kHz, and then averages the products over a number of periods with first a sliding window and then a low pass filter. The point is that I know exactly how it works, and I can verify it.

As kkp the 50W has to go somewhere - that must be hot to the touch! Or have a very loud hum. If either is not true it would be the power meter misreading.

I got one of those too, my Hopi power meter shows it as using 20-24w idle. The UPS is a bit warm, but nothing alarming.