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Warning -- as someone said earlier on s.e.d., there's a law that requires at least one boneheaded obvious math error in any post dependent on arithmetic to make a point. Caveat emptor.
Hi, Pat. By chance, a surplus wiper motor for 2000/2001 Saturns is being sold at All Electronics. It's a 2-speed job, and the blurb says it uses 4 amps for hi-speed at 106 RPM and less than 1 amp for low speed at 41 RPM.
Not a bad deal for 16 bucks. Let's assume lo-speed. 41 RPM = about
1.5 seconds at 0.91 amps. Round it off to 1 amp * 1.5 seconds = 1.5 a-s (amp-seconds, a-s = amp * seconds).Now, even a small car battery is good for 40 a-H (amp-hours), but even for marine and deep discharge batteries, you shouldn't take more than half of that. So lets assume 20 a-H capacity, which means 72,000 a-s capacity. This will give you 48000 shots, and at 6 per hour, you're talking about 333 days of use. Of course, as a practical matter, the battery will self-discharge and go flat well before that, and the above didn't take into account the work that will have to be done by the motor. Short story, though, is you'll probably be OK for a month, maybe two months with this motor, but not 333 days, or forever.
I would lean toward using a marine, R-V or wheelchair-type battery instead of a car battery. Although they're somewhat more expensive, they are made to handle deep discharges better. Also, if you ask around, you can find batteries with better room temperature a-H ratings (battery sellers and manufacturers have this data -- they just don't want to publicize it for some reason). Higher a-H rating is better.
No matter what, stay away from used car batteries, unless you know it's less than a couple of years old and hasn't been in a car with electrical problems. Old car batteries are almost always a disappointment, even for starving artists who have made disillusionment their very sustenance.
Remember -- your 10 minute timer drives a relay, transistor, or SSR to start the motor, and use a cam microswitch to stop it at exactly the same place every time. (These are also available at Allelectronics.com)
By the way, try to get a sealed lead-acid battery, and be sure to clamp or bolt down the battery well. Spilled acid can ruin someone's day (possibly a kid -- be careful). Also, make sure the terminals and any exposed wiring is insulated -- people use (and drop) the darnedest things when setting up and taking down displays. It might be better to get one of those batteries with the built-in carrying handle, and install the battery after the display has been moved.
Good luck Chris