UPS(Uninterruptible power supply) Protection Question - Page 1
Forum section: electronics / projects

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 10, 2011, 04:20:43 am
content: I've seen a few threads on here before asking stuff about MOV's(in regards to surge protection) and stuff, so that got me thinking, whats in my UPS, so i opened it up, and i was shock(not literly) the only Mov's are on the the circiut board, and the side thats is "Surge" only, comes straight from the mains(there is a fuse/Circuit Breaker on the "hot" line thats it), so do i really have an "surge" protection on that side? I drew up a schematic in eagle, i'm sure the syblols aren't all correct but it gets the idea accross, i'll also post pics of the actual insides later, i just want to see if my schematic is enough and if it makes sense. here is the schematic for now, there are some notes on the schematic regarding sybols i used and stuff, also i know the transforer isn't shown right on the schematic, as the real one has 6 connections. Also i didn't do a schematic of the PCB, way to much stuff on there, but there is a Pic micro on it, like 5-6 MOV's, a relay, some what i asume are FET's, a small X-former, bunch of caps, reistors, and SMT stuff, 2 "30 amp" blade sype fuses, likes what's in a car:

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 12, 2011, 04:08:18 pm
content: bump.... anyone have any feedback?

author: saturation
author_rank: Super Contributor
timestamp: January 12, 2011, 07:54:57 pm
content: MOVs in a UPS need not be as robustly designed as a dedicated surge protector because the transformer and many high voltage components on the high voltage or primary side of the power supply can take abuse. You normally find 3 MOVs covering L-N, L-G and N-G, at least in 120V style wiring and the usual fuse. For higher joule rating, multiple MOV are sometimes in parallel as a 'selling feature' but for the most part, its poor design, a single properly rated MOV is what's needed per line as a minimum. Other optional components are usually suitable inductors and capacitors which act as line filters but often these, as well as ferrite cores, are on the low voltage or secondary side, to further filter power to the battery.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 12, 2011, 08:48:45 pm
content: Quote from: saturation on January 12, 2011, 07:54:57 pmDid you look at the schematic? cause the mains goes straight to one set of outlets(the surge only) so then do they have any protection? since there are no movs until later on? or does it not matter?

author: saturation
author_rank: Super Contributor
timestamp: January 13, 2011, 12:46:59 pm
content: Yes, but I'm not sure how accurately you transcribed the key components. The image has been lost since the forum upgrade so from my memory, it looks like your MOVs are drawn so they are connected in series with the load, which is incorrect.After the circuit breaker, MOVs connect directly to the mains power lines and ground. That's the simplest way. These MOVs have to be thermal fused for best protection, without it the MOV are a fire hazard when they are activated, so the casing has to metallic; since thermal fused MOVs are only a few cents more than standard MOVs, a cheap design will not have thermal fuses in the circuit.Search on my name in the forum, you'll find a detailed thread and photos of surge protectors and an example of one that blew up.Quote from: mitpatterson on January 12, 2011, 08:48:45 pm

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 13, 2011, 11:51:54 pm
content: Quote from: saturation on January 13, 2011, 12:46:59 pmHere is my schematic image again. and i mean does it mater if the MOV's are after the outlets? or does it need to be before? the what you said about them being in series, i actually didn't put the movs on their as they are on the main circiuit board, those are just some ferrit cores that are in series. I'll see about posting pics of my "disassembly of it" and see if you can make heads or tails of it

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 14, 2011, 12:40:49 am
content: Here is a flickr Photo set showing my teardown of it, i tried to get some close ups of the PCB(it has PIC micro in it, i see a potential for hacking...assuming they didn't lock it down too bad)http://www.flickr.com/photos/56750521@N03/sets/72157625692261659/

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 16, 2011, 03:40:49 pm
content: bump.... does it matter where the MOV's are at?