UPS Battery Backup from Computer?

[Day Dreamer]

I have a CyberPower 1285VA rated at 700 watts that someone gave me. Could I utilize this to charge / power small devices on the road? How much charge time would I get on say just a phone or just a laptop? I have an AC Outlet in the bed of my pickup to charge the UPS while driving.

 

[MrNoodly]

Since you already have it, why not try it out and see what happens?

 

[Day Dreamer]

Good idea. I can try it during my daily routine and see how long it lasts with various devices.

 

[Tom_M]

Usually a UPS will sound an alarm when there is no 120 VAC in. This would get very annoying quickly.

 

[XERTYX]

X2 to what tom said.

HOWEVER.

Most of the UPS units I have disassembled have an SLA battery inside of them. If yours has a removable backplate to replace the battery as most do and you feel comfortable doing so you can look at it and see how many amp hours it is rated for. My first solar bank was built with 4 matching 7Ah 12v SLA batteries pulled from an internet server UPS supply.

It worked a treat once I figured everything out. 28Ah doesnt get you very far so you have to ration your power but it would be great for running LED lights and charging phones etc.

If the UPS unit is very old in my experience it may think the battery is dead and it cant get the battery to a full charge anymore. This doesnt necessarily mean that it is dead though. I dont think most UPS units are built to bulk charge an SLA battery once it's been used. It's more designed to float charge the battery to keep it up and running in the event of a power outage.

 

[Doubleone]

I have a UPS that I modified to power a TV and receiver and it works good for a couple of hours when we can't run a generator (like Walmart-ing).  I have also used it to charge my laptop.  Since the original UPS design was intended for short duration, I slotted the case for ventilation and added a small computer fan to cool the transformer.  Using an infrared pyrometer I verified mine doesn't heat soak or overheat at all.  I hooked the UPS up to the house batteries so it's powered from the big house batteries not the little internal SLA battery.  I didn't want the UPS to backfeed and try to charge the house batteries from the UPS, so my work-around was to still use a small SLA battery inside the case but draw main power from the big batteries through diodes.  It gets almost full forward voltage but nothing feeding back into the house batteries.  I disabled the alarm by unsoldering it from the board; a small led still flashes when I'm on battery.  The UPS is hooked in series with the normal 120v circuit and an unanticipated but very cool benefit is that it keeps continuous power so satellite doesn't reboot when power switches over from shore to battery.  The UPS has a limitation in that it's more sensitive to low battery voltage and it will automatically shut off.  I'm not complaining, it was very cheap to do, and if it ever were a problem I'll just wire in a small pure sine inverter to replace it.

 

[B and C]

I didn't know they made 12V UPS's. Mine are 48V and no way could I tie them into the house batteries.

 

[XERTYX]

I have though of doing something similar. Pretty smart idea on using diodes to prevent the SLA from charging the house batteries.

I have a few questions. 

So the positive terminal and negative terminal are still wired to the SLA battery and also the house batteries?

How exactly did you tie the AC into the AC from the UPS? 

So even if your inverter is off and you have no shore power you still have constant AC power from the UPS?

 

[Doubleone]

- So the positive terminal and negative terminal are still wired to the SLA battery and also the house batteries?

Yes, both power sources are wired to the UPS input.  The SLA is hooked up directly in stock configuration, the diodes go between the cable from the house batteries to that same SLA connector, if that makes sense.  This is so the UPS will alway see 12v. from the SLA until the combined batteries discharge and hit the UPS low voltage cutoff.

- How exactly did you tie the AC into the AC from the UPS?

Same as typical UPS use... UPS plugs into Shore/Generator 120v. and a power strip for the TV/Receiver plugs into a protected circuit on the UPS.

- So even if your inverter is off and you have no shore power you still have constant AC power from the UPS?

I don't have a traditional stand alone inverter; the UPS works as my inverter.  Yes, with no Shore/Generator power the UPS provides 120v. when it's switched on and connected to nominal 12v. power.   I'll typically shut off at the UPS power button when the RV is in storage (after the SLA has time to recharge).  I also have a 75 amp quick connect on the 12v. house power cable that I can disconnect as needed.

- I didn't know they made 12V UPS's.

The smaller consumer model UPS's intended for home use tend to be 12v. or 24v...  The one I used is an APC ES350 that I got for $5 at a garage sale.  It's 12v. input and about 300 watts continuous output.  Not enough for more than the TV/Receiver.   We'll typically get about 3-4 hours of TV time (while also using house lights, etc.) before we hit low voltage cut off.  The UPS is very sensitive to even a minor low voltage input, but I'm good with 3-4 hours or even longer if we manage power use.

 

[XERTYX]

Oh I see now. I thought your AC was spliced in somehow. You just have the included wall outlet plug plugged into the shore power and your devices plugged into the UPS.

You mentioned diodes. Plural. You use more than one?

I thought youd only need one. SLA+ -|<- House battery +
Sorry that's a crap emoji diode but I think you get my meaning.

So if your house batteries are charged does it not continue to power stuff? Or does the SLA take a long time to recover?

It seems like if the 2 banks were combined youd still be able to run off of the house banks until they were low voltage.

 

[highdesertranger]

sorry, I don't see the advantage for all this work. wouldn't a house battery be much simpler. highdesertranger

 

[XERTYX]

I like having redundancy. My first solar system had multiple redundancies. Even my lighting eventually had it's own separate battery. Also I'm in the market for a few UPS units anyway. Sometimes goodwill has them around here for $3 or less. I've never gotten one that had a completely dead battery. Usually a 7Ah battery inside for $3 and I've had good luck with SLAs. I had a steep learning curve when I first got into solar. I didnt have this resource and I couldnt afford a charge controller at the time. I had to monitor the cells myself and it still took a year for me to kill 1 cell. I foolishly left it on the panels with no controller for 2 days straight. Just one cell.

Even after that abuse it still worked well for lighting. Great batteries IMO. Plus it has a built in inverter. Prob not the most efficient but surely more so than the $10 inverters at Wally world.

I'm on a shoe string budget atm.

 

[highdesertranger]

yeah I use SLA(Sealed Lead Acid) batteries for some of my prospecting gear but all that other stuff, transformers, inverters, diodes, chargers and so on. I just don't get it, I mean how many of those things do you need. highdesertranger

 

[XERTYX]

Yeah. Keeping it simple is usually best.

But no part of you wants a panel of flashing lights, knife switches, and a Jacob's ladder buzzing in the corner?!

 

[Doubleone]

- You mentioned diodes. Plural. You use more than one?
Yes, plural - as in four smaller diodes wired in parallel to increase throughput so I could pull the maximum amperage required by the UPS which was 30 amps.  I used  4x10 amp diodes = 40 amps with a 25% safety margin for 30 amps max draw.  #8 power/ground cable with a 30amp fuse near the house batteries.
 
- I thought youd only need one. SLA+ -|<- House battery +   Sorry that's a crap emoji diode but I think you get my meaning.
If I understand this... Yes, house battery positive passes through the diodes to the SLA positive.
 
- So if your house batteries are charged does it not continue to power stuff?
Yes, it continues to power until house batteries reach the UPS low voltage cutoff, and then the UPS shuts down.
 
- Or does the SLA take a long time to recover?
I used the smallest 12v SLA and it recovers very quick especially because it doesn't go any lower than the house batteries.  Smaller was cheaper and created more room inside the case for ventilation, wiring, and diodes.
 
- It seems like if the 2 banks were combined youd still be able to run off of the house banks until they were low voltage.
Exactly!  It runs for a long time... right up to the low voltage cut off point for the UPS.  Even then, the voltage in the house is enough to power lights, heater fan, and other less 'voltage sensitive needs.
 

 

[XERTYX]

Awesome. Thanks for the info. Yeah that's what I was allaying to with my attempt to make a schematic diode using the keyboard. Pretty smart idea I think.