Help with battery installation

The numbers that you are listing is the current that the cells are capable of putting out, not what they put out all the time, nor how long they can put out that current.

Those also appear to be the absolute peak numbers for alkaline cells.

What you should be most interested in is the battery capacity. This is generally listed in amp-hours or milli-amp hours. For instance, a two amp-hour battery would be able to put out 0.5 amps for about four hours.

At a guess, a typical AAA dry cell will have a capacity of 250mAh; a collection of them would be able to run your spinner, poorly, for about half an hour. 9V batteries are worse.

If you want to power this from dry cells then you want eight to ten in series (if the thing is a simple motor then you can go over voltage a bit and not harm it). I'd use D cells.

If you want to power this from NiCd or NiMH cells then you want ten in series. The last time I looked (which was years ago) the D cells were just C cells inside a big tube, so you may as well use C cells.

But the best thing to do would probably be to find a cordless tool that advertises itself as being 12 to 14 volts. Some of the contractor tools are marketed as lines that all use a common battery and charger, but have different tools that use the battery. I'd find the cheapest one (probably a flashlight), rip the guts out and use it as a battery adapter. Then I'd buy a few batteries and a charger, and I'd go to town.

She'll be cordless, she won't be constantly buying batteries, and recharging won't be a pain.

--
Tim Wescott 
Control system and signal processing consulting 
www.wescottdesign.com

it depends how poerable you want it to be and, how much you want to spend on batteries, and how often you want to change them.

I'd reccomend AA as a starting point and they last much longer than AAA but cost about the same price.

On the other hand a 12V rechargable tool battery pack might be a better option, especially if you can borrow one to try out.

--
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A big issue here is how long the device needs to run between battery charges (or changes). Batteries are rated in amp-hours. You note that the device normally draws 0.5 A, so you can find the *approximate* running time for each battery type by looking up its A-H rating (sometimes printed on the battery itself, especially for rechargeables). If it's a 1.5V cell, you'll of course need

8 in series, as you note, but the same A-H rating applies. Just divide the A-H rating by 0.5 to get hours.

If it needs long running time but doesn't need to be particularly lightweight, you might consider a 12V sealed lead-acid battery and charger.

Best regards,

Bob Masta DAQARTA v7.21 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusic generator Science with your sound card!

Using a power tool sounds like a good idea. And if the spinner doesn't have variable speed, and if your wife would like it, you might be able to use an electric drill's variable speed circuitry by just disconnecting the wires from the motor and connecting them to the spinner. Be sure the polarity is correct when connecting batteries. Eric

Thank you all for the suggestions. I like the idea of a tool battery. I'm in the hunt for a 2nd charger for one of my 12v power tools. I plan to gut the charger and leave the prongs for battery connection. Wire from the prongs connecting to the required size adapter plug for the spinner. Therefore, the battery will have a holder and I can recharge it with my other charger. Sounds good in my head, I hope it works out that way.

It's already variable speed. I just need the portable power source.

These go on sale for $40 fairly often. Not only will it power her toy, it can jump start a car, or provide emergency lighting.

Well there Ya go. You're all set. Eric