Back-UPS RS 800 Not charging

[kc8adu]

Re: Back-UPS RS 800 Not charging

just disconnected the anderson powerpole connector to the back of a connext(apc)700.
chirping and replace battery came on.
the battery probably could be totally worn out without tripping the warning.
its an exide d31 agm.

[stj]

Re: Back-UPS RS 800 Not charging

got a datecode stamped on them?
you normally do.

[kc8adu]

Re: Back-UPS RS 800 Not charging

its modded with an external truck battery.
if the date on the battery is what you are after its sometime mid 2013.
no date on the ups.

[vdubbus77]

Re: Back-UPS RS 800 Not charging

There are some terrific pictures in this thread that can be used to help with my situation so I will bump this old thread. I also have a blown f3 fuse, when I removed the fuse I jumped the fuse terminals and my batteries started charging. However, the resistor (r145) right next to it got so hot it melted the solder holding it in place. Any Ideas? Is the resistor No good?

[Agent24]

Re: Back-UPS RS 800 Not charging

A resistor getting hot means it's passing too much current. Probably something downstream from that resistor is shorted - which makes sense considering the fuse blew.

If the resistor wasn't bad already, it likely is now, if it got that hot. You should replace the resistor and you also need to find out where the short is that blew the fuse in the first place.

[vdubbus77]

Re: Back-UPS RS 800 Not charging

It seems one of the mosfets is shorted, Is there anyone that can tell me the value of the r145 resistor? Mine is a tad toasty and from the pictures I am coming up with .78 ohm which is proving difficult to source.

[canadaboy25]

Re: Back-UPS RS 800 Not charging

So I figured I'd post an update in case anyone else happens to have the same problem. Since one person already has, it's probably likely.

After using the UPS as a surge protector for the past 8 years and having my computer turn off after every little power flicker, I figured it was finally time to fix it.

After a quick google search, I was able to find the schematic for this exact UPS complete with proper component designators and values. I don't know if I just previously did not look, or if the schematic has been uploaded since I worked on it last time. I will attach the schematic in case anyone else needs it.

The 5th page of the schematic is conveniently labelled "Battery Charger Circuit". It didn't take long to trace the cause of the blown F3 fuse to a shorted MOSFET Q40. The part number of the MOSFET is 94-2358 which is some discontinued International Rectifier FET with no datasheet available. Since the schematic lists it as a 100V FET and the circuit runs through a 2A fuse, it shouldn't be too critical what replacement is used. I ended up using a 230V 25A FET that I had lying around from a salvaged plasma Y-Sus board. I'm sure this is overkill but it was handy and it had the correct footprint.

After replacing the MOSFET and the fuse, the unit now charges my batteries just fine. I am using two large batteries from a mobility scooter and they seem to be working well.

Hopefully this can help someone else out.