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# AA Battery Emulating Transformer? Answered

One of my many hobbies is collecting tabletop water fountains. I have about 6 fountains, two independently powered and 4 that run on 2 AA batteries. Since I have these fountains on all the time, as you can imagine they are costly to power. One day I finally got sick of putting new batteries in these things and rewired their battery wires in a parallel circuit for running on DC power from a wall. Now the only thing I need is a power supply. Now, motors aren't too picky about voltage. They'll operate on different voltages but if it isn't just right the motor will be too loud or too weak to pump the water correctly. This rules out and transformers I have in my bin. Upon measuring the current from the 4 fountains, I found that it uses about 440mA. I have kept my eyes open for a good power supply but have not yet seen one. I've also toyed around with the idea of using the closest one I have (Nokia 3.7v 500~?mA) and applying a voltage regulator on it, but I don't want to buy one yet as I am still a novice at some of the mechanics of most electrical components. Would that be an effective plan? If not, any other ideas? My fountains haven't turned on in a few weeks and there are starting to urge for the sweet trickle of water down their dry, dusty flumes.

## Discussions

Have you checked inside the 'independently' powered units and see if they have the 3v you need? fwiw, brand new AA cells are often 1.8volts, then 2 in series will be 3.6 volts, so the Nokia should work OK without any regulation. To play it safe, get a 1N4001 diode and put that between the + of the charger and + of the motor, with the stripe side towards the motor. That will drop about .6 volts to give you 3.1v.

Yeah, problem is that one of the fountains runs straight off of 120v AC and the other has a transformer that outputs 12VAC.

Hmmm... so you have 4 pump motors that take 3v each, which adds up to 12volts! So if they are all the same size motors - ie running in the 100mA range, you can rectify the 12vac and run the 4 motors connected in series!

But then I wouldn't be able to power the AC motor? (Which is the coolest, coincidently. :P)

It's not an either-or situation. You can leave the 12v motor connected, just attach 2 new wires to the transformer and hook that to a simple rectifier-capacitor cicuit to power your other 4 pumps. Check if there is a power rating on the 12v tranny : if it's 250ma, you should be fine.

I understood that part, but wouldn't the rectifier make the electrical current DC, rendering the AC motor useless? Or would placing the rectifier after the AC motor in series solve that?

The diodes will basically make it into 2 separate circuit. The ac part will stay the same.

It makes sense. So whats the purpose of the capacitor?

With just the the diodes you'll get half-wave AC, but still AC. The capacitor smooths it out into DC, like what you get out of a battery.