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# Power Supply For Science Fair Project

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#### sturner333

##### New Member
My son is doing an experiment with a simple electro-magnet. It requires a battery, but it looses voltage quickly. I wanted to use a power supply I found, but the current is too high. Can someone help a non-electrical person with this problem. Either how to modify the power supply circuit, or a different idea for a power supply for the project.
Thanks

put a resistor is series on the output to set the current you want

but still why do you think the PSU will deliver too much current?. A PSU normally has a maximum volts and maximum amps - if it is a good one you can change the output volts and output amp limit.

if it is a fix output voltage then use the resistor. NOTE power rating

It's hard to comment on the battery or power supply without knowing more. I am guessing that the electromagnet is home-made with a limited number of windings. If you know the wire size and the number of feet you used let us know that - we can estimate the DC resistance of the wire/magnet. If we know that we know how much current it will draw at given voltages.

You'll want to limit the current based on several things:
A. The wire size (we can help).
B. The power supply voltage (battery or PSU)
C. The power supply current (battery or PSU)

A resistor is one way to limit the current. An incandescant light bulb is another - it's essentially a resistor that also gives you a visual indication of the voltage drop. If you wanted to just experiment - find a low wattage or small bulb that matches (doesn't have to be exact) the battery voltage then put it in series with the magnet coil and see what happens. You already know that the coil can tolerate the current delivered by the battery (based on what you posted). You may find that the light glows brightly - that indicates that most of the voltage drop is taken across the bulb - however there may be sufficient current to demonstrate the electromagnet. To increase the current put bulbs in parallel with each other - then those paralleled bulbs go in series with the magnet.

You might also use the "bulb" idea with the PSU.

In all cases, be careful as the coil can get quite hot. Take care to see that the PSU doesn't have exposed high voltage.

Good luck, have fun.

I would suggest you increase the number of wire-turns of eletromagnet. It will automatically reduce current as resistance is increased and it will also increase battery life. The magnet formed will be a powerful one.
If possible, you can use 12V relay coil for this purpose. If forms a powerful electro-magnet.

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