UPS mod / hack - hook into car as an inverter - Page 1
Forum section: electronics / projects

author: electron
author_rank: Newbie
timestamp: August 09, 2013, 08:34:19 pm
content: Good morning,Has anyone used an UPS in a car as an inverter for AC power?My thoughts were to wire directly from the 12v battery to the UPS with a fuse inline. I am not looking to plug the UPS into the wall while hooked into the car.Can I leave the original battery from the UPS in circuitRecommended Fuse?Disable buzzer or change to LED indicationThe UPS is a Cyber Power 825AVR, max load 450wattMy project idea anyhow, as I have a long long road trip and would like to run a couple of AC powered devices.

author: Unknown
author_rank: Unknown
timestamp: August 09, 2013, 08:40:04 pm
content: Can't say I ever tried it, but I would expect an off-line UPS, especially a cheap one, to overheat if you run it for longer than the original battery would have lasted.

author: madires
author_rank: Super Contributor
timestamp: August 09, 2013, 08:58:37 pm
content: Quote from: electron on August 09, 2013, 08:34:19 pmIf the UPS is powered by a single internal 12V battery it should work.QuoteI would disconnect the internal battery. The fuse could be a 40A slow blow. And disabling the buzzer is a good idea (maybe with a simple switch).QuoteAs alm already mentioned a small UPS might get quite hot if running for a longer time. If you don't need sinusoidal AC you could also use one of those cheap inverters.

author: electron
author_rank: Newbie
timestamp: August 09, 2013, 09:21:49 pm
content: Thank you for the insight.Would it get hot if running lets say at 25% capacity?example usage would be, 1 string of 50 LED christmas lights, cellphone charger, camera charger.second usage, PC computer to download camera photos, and maybe send an email should there be Wi-Fi. (17minutes normal run time for this setup on original battery)For longer run time, would a fan or two help?I have access to an older style UPS, same watt, just not as efficient, but the cover opens up to the air and I could install a fan much easier.

author: Stonent
author_rank: Super Contributor
timestamp: August 09, 2013, 09:37:41 pm
content: It's an idea but inverters are usually fairly inexpensive.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 09, 2013, 10:48:07 pm
content: Some UPSes won't power on without the mains supply voltage present.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: August 10, 2013, 09:13:04 am
content: Heythe UPS is build like SH**T .1/3 of the power capacity is reqired in order not to harm the transformer . as for the switching fets .. if they run hot .( >80C on the outer body ) take some CPU heatsink and mount hem on it ...at 1/4 of the rated capacity it will run either warm or hot . but I don't think you'll demage it ..Yes I did it ... twice ..one was 1200VA one . it was loaded with 700W load . and after 30 min.... there was smoking transformer ... after opening it up . I saw 400W core ...the secoand time . I was smart ... firstly saw the power of the internal transformer . this time it was bearly 90W .... and on the UPS there was written " 500VA" at PF of 0.7 .... that's 350W . witch is 3X more than the stupid 90W it can hold ... GEEEEEEEEEEEEI used it for only 100W load and it hold for 2Hrs ..

author: Psi
author_rank: Super Contributor
timestamp: August 10, 2013, 09:56:50 am
content: Quote from: alm on August 09, 2013, 08:40:04 pmI can confirm this. I added extra large batteries to my UPS and it started to smell a bit burny after 40min of running on battery. (original batteries only lasted ~10min).It didn't stop working, just yeah, smelled quite hot. I cut some holes and added a few fans and it was fine after that.But yeah, it needed the mod to work continuously.

author: amyk
author_rank: Super Contributor
timestamp: August 10, 2013, 11:08:21 am
content: Quote from: electron on August 09, 2013, 09:21:49 pmExcept for the LEDs those are all low-voltage devices. A direct step-down from the 12V rail on the car will be far more efficient.UPS inverters are built down to a price, so they are not going to be very efficient (and the overheating problems further point to this).