Low AC voltage on UPS with battery power. - Page 1
Forum section: electronics / general

author: romantronixlab
author_rank: Regular Contributor
timestamp: December 05, 2013, 08:42:43 pm
content: Hi mates,I have an issue with my tripplite Smart1000LCD this under battery power the battery protected outlets have only 85v instead of at least 110v but when under mains power it does provide 120v. Dont know if it is a false reading on my cheap multimeter(dont think is it TRMS, i really want my 87 to arrive) or there is something in the sinewave of the inverter.A schematic would be helpful but tripplite don't want to provide me one to diagnose their little inefficient device and google around does not provide one either.If some does have by chance the schematic.

author: SeanB
author_rank: Super Contributor
timestamp: December 05, 2013, 09:03:26 pm
content: Simple test is to plug in a real incandescent table lamp of about 40W and see if it is a lot dimmer. Most likely is the meter underreading the somewhat square output waveform.

author: romantronixlab
author_rank: Regular Contributor
timestamp: December 05, 2013, 10:01:29 pm
content: Quote from: SeanB on December 05, 2013, 09:03:26 pmMost of the bulbs at the lab and around the house are either CCFL or LED's but Ill see if I can find one and make the test.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 06, 2013, 03:31:37 am
content: A friend of mine actually did that to explain why you shouldn't buy cheap multimeters (or at least if you do, don't trust them too much).http://www.refrigeration-engineer.com/forums/showthread.php?8200-Why-you-should-not-buy-a-cheap-multimeter

author: trackman44
author_rank: Regular Contributor
timestamp: December 06, 2013, 04:15:25 am
content: Cheap multimeters don't do true RMS AC(current or voltage), the reading is averaged. So if 85V is the average, then your getting about 170V positive peak x 0.707=120V RMS. Your UPS is outputting the correct voltage.Will

author: romantronixlab
author_rank: Regular Contributor
timestamp: December 24, 2013, 11:39:58 pm
content: Did not know that formula good to learn it, Im waiting for my Fluke 87V to arrive, Still waiting.

author: Dawn
author_rank: Regular Contributor
timestamp: December 25, 2013, 01:14:47 am
content: I ran into this problem supporting UPS's that had dead batteries that were used to support home medical equipment such as CPAP/APAP and Oxygen concentrators. Many of the computer units don't generate a sinsusoial wave form at the RMS rated voltage. You can't get service docs from most of these companies, but you can comapre the output of working units both with a scope and an RMS voltmeter. Often they don't meet idealiszed specs, but do keep the usually computer working but other equipment might have problems with the output. Most of these copanies are rather specific that they are used to back up computers and not other equipment. My strategy was to design AGM battery banked backed up inverters to support these devices as the computer type backup units are less then ideal for backing up other then computer related switching supplies. They do work for their intended target, but not for everything that expects a pure wave form.

author: gxti
author_rank: Frequent Contributor
timestamp: December 25, 2013, 01:22:05 am
content: These days it is easy to get a sine-wave UPS, they are usually marketed as "PFC compatible" because active PFC power supplies do not like the garbage that square wave or "modified sine wave" (ha ha) inverters put out. They don't cost much more, I like the CyberPower brand ones.