Using UPS + Car Battery

[soytusandwich]

Is it possible?
can i wire a small sized UPS directly to the car battery and make it function as a DC-AC converter for a long period?

something like

 

[Bomo]

I suppose you could, but I was always under the impression that car batteries don't offer a whole lot of output for prolonged times. They're more for short but high voltage bursts (like starting a car) and then long but rather low voltage output for things like a car radio and what not.

I could be completely wrong though.

 

[Christopher]

If you do, you'd want a "deep cycle" battery, not a "starter" battery used in most vehicles. See http://en.wikipedia.org/wiki/Deep_cycle_battery for more details.

I think the best way to do something like this would be to forgo the UPS, and get a decent inverter. Then wire the inverter directly to the battery. Most UPS systems are designed to pass main power (AC) directly through, and only switch to battery power in the event of main power failure. They usually have a large capacitor to hold the load during the switchover. The UPS will also have a charging circuit to recharge its battery when main power returns. That is a lot of extra bits that would be unnecessary in a situation like that.

 

[Red Squirrel]

I asked something similar a while back here: http://www.hardforum.com/showthread.php?t=1578667

Basically you'll want a deep cycle battery. Amp hour rating is what you are after, cold cranking amps, not really.

Keep in mind they produce produce hydrogen, and need water added to them. I ended up chickening out and going with some sealed batteries I got from a local electrical distributing (and it was cheaper then the APC replacement ones). I eventually want to do this, but I want to build a battery room, and vent it outside.

These also look very interesting: http://www.xantrex.com/power-products/inverter-chargers/overview.aspx

Could probably do a portion of the house with one, for lighting and what not.

 

[drescherjm]

Is it possible?
can i wire a small sized UPS directly to the car battery and make it function as a DC-AC converter for a long period?

something like

I would not bother with a UPS like that for this type of modification.

Get an APC SmartUPS 1500. These are 55lb and go for less than $200 refurbished with new batteries on ebay. This will come with 2 12V 18AH batteries and some models will come directly with the ability to add 4 more 18AH batteries via an expansion port. A 2 pack of batteries will cost about $70 at batteryspec.

http://www.batteryspec.com/cgi-bin/cart.cgi?action=link&product=182

Extended run batteries are around $85

http://www.batteryspec.com/cgi-bin/cart.cgi?action=link&product=681

There are also 4 packs.

 

[mmmmmdonuts]

Is it possible?
can i wire a small sized UPS directly to the car battery and make it function as a DC-AC converter for a long period?

something like

Using a small UPS for extended periods of time on a battery (hours) can burn out the circuitry because they are designed to be on battery maybe a half hour at most. You need a robust UPS if you want extended periods of time like the one drescherjm listed.

 

[drescherjm]

Agreed. I would expect that UPS to in the best case scenario to just burn out or in the worst case to catch fire when used with batteries that have enough power to deliver hours of runtime. The charging circuitry will in no way be able to handle the current and these are not designed to run for long periods of time.

My APC SmartUPS 1400 has a fan that kicks in when the system is on UPS to keep the inverter and main transformer running cool when it is on batteries or even when it gets warm charging.

 

[drescherjm]

BTW, What kind of load is this for? A laptop?