Recommend a battery-powered outlet

January 29, 2007 12:28 PM

Recommend a portable battery-driven power outlet, ideally suited to plug a cash register into all day at conventions.

My SO has to go to conventions/trade shows and sell things. Dealing with getting power for these things is generally a hassle, and since only a cash register is needed at the moment, a glorified battery seems like a good approach.

The best balance of cost-to-functionality I've found so far is the Xantrex PowerPack 150 Portable Power Supply. My only hesitation is that this seems to do a lot more than we'd need, and if possible I'd prefer to find something with less features and thus (importantly) less bulk.

posted by Kemayo to technology (7 answers total)

Most of those "portable outlets" are just 12V lead-acid batteries, similar to what's in your car, coupled with an inverter. The weight and bulk are going to be directly proportionate to the amount of energy they can supply.

It's difficult to make a recommendation because you don't say what the make/model of the cash register is, or more importantly, how much power it draws. I can imagine that some registers might be pretty power-hungry, particularly if they have receipt printers or big displays.

If the register plugs into the wall with a "wall wart" (AC to DC transformer) you might be able to rig something up yourself that would power the register, directly from a large battery, without having to go from DC (battery) to AC (inverter) and then back to DC (register's power supply). This would probably be a lot more efficient, and let you get away with a smaller battery for a day's operation.

If I had to guess though, I'm not sure that the power pack you linked to above is going to run a register for a whole day. I think you are going to be looking at fairly substantial units, like car-battery+inverter size or better. I'd get one that's bigger than you need, and put it on a moving dolly or other wheeled carriage so you can truck it around.
posted by Kadin2048 at 12:43 PM on January 29, 2007

What about a portable cash register?

That model gets 12 hours on 4 C batteries.
posted by sanko at 12:57 PM on January 29, 2007

The register is delightfully minimal on its power requirements. It apparently produces a load of only 0.29A. (It's pretty much a glorified calculator, after all.)
posted by Kemayo at 2:11 PM on January 29, 2007

What about a basic PC UPS? You should be able to run an 0.3 amp (36 VA or so) load for a good long time from a fairly cheap UPS, and the reliability and quality of the gear will be better than a car-type portable supply.

Doing some back-of-the-envelope calculations from here, it sounds like a UPS specified at 1000 VA with 5 minutes' runtime at full load would run a 0.3 A device for about 3.5 hours.

If you had a couple of UPSes like that, you could pretty easily last a whole day, especially since you could be charging one at a (potentially faraway) outlet while you use the other. I've seen units with that kind of spec for around $100 on sale, so it shouldn't be too hard to get hold of them. Just make sure you choose ones that can have the alert beep switched off, since UPSes generally make a horrible racket when the power goes out.
posted by pocams at 3:03 PM on January 29, 2007

One problem with UPSes (and inverters in general) is that a lot of them "lose" a lot of energy regardless of the load being drawn.

0.29 amps at what voltage? If that's at 120 volts, that register is drawing almost 35 watts. If you had a Kill-a-Watt, you could see how much current it's actually using.

As cheap as they are these days, a brand new battery powered register and a few sets of rechargable NiMH batteries might be the best way to solve this problem. The nice thing about ones like the unit linked upthread is that if the 4 C batteries turn out not to be enough, you can easily rig up a bigger battery pack and plug it in through the socket for the wall wart with nothing more than a few dollars of supplies from Radio Shack. If it only takes mains voltage, your options are much more limited, and you will be carrying around a lot of bulk.

We used to use the Portawattz that was basically a motorcycle battery and some wiring in a plastic case with an inverter strapped to the front to power our ancient inventory laptops. It was cheaper than buying new batteries for them, they lasted around 6 hours, and you could get them at Sam's Club.

An all DC solution would be far, far better though.
posted by wierdo at 3:54 PM on January 29, 2007

I have seen a lot of craft people at shows with just a car battery and a small inverter. They last all weekend.
posted by MtDewd at 4:56 PM on January 29, 2007

Some places where power is less than reliable use old unpowered cash registers that work by turning a crank. Then again, the ones I've seen are bulky, so I'm not sure how well they'd work for traveling. They might be worth looking into though.
posted by xulu at 1:31 PM on February 5, 2007