Looking for APC BE750G UPS circuit diagrams - Page 1
Forum section: electronics / projects

author: quanttrom
author_rank: Regular Contributor
timestamp: August 18, 2013, 12:40:50 am
content: So I bought the APC BE750G UPS and unfortunately slightly after the warranty expired it bit the dust. It powers up for a second but it immediately shuts down after that.I took it apart and I've been trying to find what failed but this would be a hell of a lot easier if I had the schematics for it.Do you know where I would be able to find them?So far I have been going over the traces, starting from the battery and working towards the outputs. The UPS starts up, the MOSFETs are driven correctly for a second, and then it stops. Not sure why it stops driving the MOSFETs. My knowledge of UPS' is limited so I am learning as I go along as well.

author: JoeO
author_rank: Frequent Contributor
timestamp: August 18, 2013, 01:59:04 am
content: In order to get started, watch the EEVBLOG #504 about UPS Supplies.

author: quanttrom
author_rank: Regular Contributor
timestamp: August 18, 2013, 03:57:47 am
content: Quote from: JoeO on August 18, 2013, 01:59:04 amYeah I had a look at that. Thanks !

author: JoeO
author_rank: Frequent Contributor
timestamp: August 18, 2013, 01:56:56 pm
content: Look for a schematic on the web using Google.Search the web for any hits regarding the model UPS you have.Search for other topics here that include discussions of UPSs.

author: quanttrom
author_rank: Regular Contributor
timestamp: August 18, 2013, 02:55:32 pm
content: Quote from: JoeO on August 18, 2013, 01:56:56 pmI've already done that and did not come up with anything....

author: JoeO
author_rank: Frequent Contributor
timestamp: August 18, 2013, 03:50:01 pm
content: Well next time please put all the steps you did into the first post.It will save other people from wasting their time.From what I have read, the warranty is 3 years. Sounds like the battery/ies are dead.

author: SeanB
author_rank: Super Contributor
timestamp: August 18, 2013, 04:10:12 pm
content: 3 years is about right for dead batteries. Disconnect them and check voltage. For a 12V SLA if it is under 11V it is dead, not recoverable and only good for recycling. If above 11V then apply a load of around 50W ( car headlamp, 12V downlighter or other 12V halogen lamp of around 20-60W) and measure the voltage across the battery terminals. If under 11V charge it from an external charger for 2 hours and try again. If it is under 11V after 5 seconds of applying load then replace the battery.Most UPS faults are this. If the battery is left in for a long time with shorted cells it will burn out the internal charger as well, or burn out the inverter MOSFETS.

author: quanttrom
author_rank: Regular Contributor
timestamp: August 18, 2013, 06:37:06 pm
content: sorry JoeO.The battery appears fine. I've load tested it as well. I am fairly certain the issue is with UPS electronics itself rather than the battery. I will test it further just to verify that it is indeed fine.PS. Also the UPS does not report anything wrong with the battery. If I can trust the signals it is giving me it reports an overload condition on the output. Regardless if it's powered from the battery or the mains.I was mainly hoping to get the schematics and go from there.