Its the little things that are gonna get me.

I just realized that a device (of all things, a noise maker) that helps me sleep needs 12V @ 500 mA. I _think_ I can get away with less as the device seemed to work fine at 12V @ 300 mA.

What rechargeable battery would provide that for 12 hours?

-- Ralph Shnelvar (ralphs@dos32.com), December 25, 1999

Answers

Depends on how much work you want to do with it, and how much you think you will need it.

If you go some rechargeable battery route, you are not only getting short on time, you probably will run into shortages. You will have to hook up wires, etc. One possible route, if you go with the standard AA's, C's, or D's is to pick up a couple battery trays (you need enough for 10 batteries, since NiCads are 1.2 volts. 10 * 1.2 = 12 volts) at Radio Shack, hook them up in series, then to your device. The mA is the power draw, and whether the device takes 500mA or 300mA isn't really shown by the AC adapter. My guess is that it could take less, but you will see. :) If it does take that, I doubt the device will last the night. Most likely only a couple hours depending on the type of batteries (D's last longer than A's for example).

If you have a uninterruptable power supply (UPS) for your computer, you could use that, and not worry about the wiring. Just plug your wall wart into it. At that small of a power draw, a medium quality UPS should work fine for a few days(assuming that's all you use it for).

-- James Collins (jacollins@thegrid.net), December 25, 1999.

A 12V 4Ah minimum batterie can do this just fine.

Also 2each 6 v latern batteries will do but they are not chargable.

-- RickJohn (rickjohn1@yahoo.com), December 25, 1999.

Just about any automobile battery has enough juice to give you days of continuous use.

-- Gary S. (garys_2k@yahoo.com), December 25, 1999.

"If you have a uninterruptable power supply (UPS) for your computer, you could use that, and not worry about the wiring. Just plug your wall wart into it. At that small of a power draw, a medium quality UPS should work fine for a few days(assuming that's all you use it for)."

I've got gobs of UPS's here. I need them because we regularly lose power here.

As far as I can tell, my largest UPS (APC model 650) will only run for a few hours at no load even when fully charged.

Anyone else have this experience ... or know of a way to make the UPS run for a long time?

I asked APC if it was OK to start one UPS with another UPS and they said "no."

-- Ralph Shnelvar (ralphs@dos32.com), December 26, 1999.

"As far as I can tell, my largest UPS (APC model 650) will only run for a few hours at no load even when fully charged."

In spite of what you may have read in this forum UPS systems do not make good or reliable power systems. We've heard from dozens of folks who have tried this over the years and eventually bought a real inverter/battery system. Now, the bigger commercial type UPS systems can do just fine, they are also very expensive. The "Best" system in the emergency Ops center here is built to provide long run times with ample heatsinking of components and ample cooling. It also contains 16-100ah gell cell batts for 48 volts and 400 ampere-hours. Not cheap.

Many of the smaller UPS systems are meant for limited duration use. The may contain temp sensors in various areas of the system and shutdown when these start getting too hot. This is what my friend discovered with his smaller APC unit...didn't matter that he hooked it to a battery 10X as big as the internal one. His unit still shutdown in the same amount of time so we knew it wasn't battery voltage related. Better to buy a couple golf cart batts and a decent inverter. Your experience may vary though and, well, sometimes you've got to use what you have.

-- Don Kulha (dkulha@vom.com), December 26, 1999.

Hey, Ralph. You might consider either a motorcycle battery or a car battery. You need a battery that can store six amp hours at twelve volts. A car battery will give you as much as 90 amp hours, depending on the battery. In other words, it would "theoretically" run your device for fifteen separate twelve hour nights. I don't know how many amp hours a motorcycle battery has. Again, it would depend on the motorcycle battery.

I used to ride a Honda, years ago. It cost more to buy a new battery for the Honda than it did to buy a car battery. If this is still the cas, get the car battery. Realize that a car battery actually has more than twelve volts (again theoretically, it has 13.2 volts, but this depends on the charge. I suspect your device can tolerat some voltage fluctuation, but if not, you'll have to consider this.

If you don't like the idea of those yucky lead acid batteries, check out the twelve volt nicads which power lots of cordless tools. I don't have data at hand, but my Makita corless drill has a charger that produces 1.5 amps at 9.6 volts. It usually charges the batteries in an hour to an hour and a half, depending on temperature, and ? This is smaller than you'd need, even if it were 12 volts, but check out the 12 volt Makita or another brand. Especially look at the cordless "skill" saws. You may find a big enough 12 volt there, or wire two or more in parallel.

Good luck. Hope you'll keep us posted.

ALK

-- Al K. Lloyd (all@ready.now), December 27, 1999.