UPS not charging batteries - Page 1
Forum section: electronics / projects

author: Intel
author_rank: Newbie
timestamp: January 21, 2014, 01:40:21 pm
content: Hello,Firstly, I would like to say that I really like EEVBlog videos on youtube, they are great. That's how I came up to this forumNow the problemBackground:I have an APC RS 800 UPS which was working great for many years and just a few months ago batteries died. So I bought new ones and after a day they are dead too. I quickly connected them to a charger and luckily still got ~90% of capacity. Next thing I did was connect them to ups via current meter and what I found out is that UPS is not charging in standby mode. It's draining ~150mA from them, probably for control circuits. Other than that UPS is fully functional.Pics:PCB is much bigger but the rest is inverter stuff and relays.2 Leads on the bottom connect to a 50Hz transformer which gives 40VAC. Then they go to two mosfets above.All 3 mosfets have sources connected together. From the top mosfet drain (tab) it goes through one diode into the big capacitor and then through another diode into yellow choke and finally into the 24V battery+ (marked with red lines).The chip on the left is LM324 quad opamp which probably controls mosfets.All 3 mosfets are PHB27NQ10T:http://pdf.datasheetcatalog.com/datasheet/philips/PHB_PHD_PHP27NQ10T_1.pdfI measured the voltage on the top mosfet relative to battery ground and it gave -13V. It should be >24V ?Then I checked all diodes and they seem to be ok. And this is where my knowledge ends.Has anyone repaired a similar UPS? Or maybe someone could point me where the problem could be?Thank you

author: Zucca
author_rank: Unknown
timestamp: January 21, 2014, 02:39:49 pm
content: Hi Intel, I'm sorry in advance I can't help you too much.Do you have a electronic DC load to simulate different batteries charging situations?The measurement you take are with or without batteries attached?I would looking for where exactely the 150mA are going.Z

author: Wytnucls
author_rank: Super Contributor
timestamp: January 21, 2014, 03:24:51 pm
content: I'm not sure if this fix applies to yours, but I got my RS500 UPS working again following this procedure:http://www.heime.org/post/17

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 21, 2014, 03:31:41 pm
content: Wire in an external charger circuit.

author: Intel
author_rank: Newbie
timestamp: January 21, 2014, 05:52:31 pm
content: I found out that battery+ is connected directly to rectifier and ground is regulated. There was also a strange looking fuse that was blown and there was a reason. Charger actually works but gives 37V (I was measuring wrong that's why I got -13v) with load. I don't think I will be able to sort it outI tried taking it to local electronics repair shop but they seems to be fixing only 90s TVs...Quote from: zucca on January 21, 2014, 02:39:49 pmUPS doesn't even turn on without batteries because all control circuitry is running from batteries while they are being charged. That's where those 150mA come from.Quote from: Wytnucls on January 21, 2014, 03:24:51 pmI've seen it but unfortunately circuits are way different.Quote from: NiHaoMike on January 21, 2014, 03:31:41 pmI had this idea but UPS has very little space inside and another transformer wouldn't fit. Maybe I could find a very small smps

author: Sylwerdragon
author_rank: Newbie
timestamp: January 20, 2017, 05:16:53 pm
content: Hi friend. I have same problem with same UPS. Did anybody find solution to it ?