# Coil to give 3 volts

I need 2.5 volts from a coil when a 10mm magnet is passed over.
What awg of copper wire and how many turns do I need for an air core coil.
This is to charge a super capacitor.

iceng2 years ago

Voltage = Number-of-turns x Change-of-Flux / Unit-of-time

So if you know the number of turns and the flux density of your magnet all you need to control how fast you plan to pass the magnet over ( through) the coil of wire.

The kind of wire (Aluminum, Copper, Gold, Iron, Silver) and diameter is never going to impact your current needs with the limited flux of the small 10mm magnet.

I suspect the capacitor charge will take some time ..... especially if your hand is the source of motion !

petercd2 years ago

Most of the online calc's are for inductance calc's, there's nothing much to tell you how many turns for a desired voltage.

A general rule is that the ID of the windings should be the same as the OD of the magnet and that the coil height should be the same as the thickness of the magnet.

You don't say whether the magnet is 10mm square or 10mm thick, but for that scenario the coil ID and thickness would be 10mm, width would depend on getting your desired voltage, so as Steve says keep winding until you get 2.5V.

Wind about 5 layers (about 150 turns) then scratch off some insulation to check the voltage, if it isnt enough, keep winding.

To boost coil performance you can add a core in the form of copper coated brazing rods. These would be as many 10mm long pieces as can be stacked in the core center, or better still a black magnetic sand and epoxy resin mix.

I would use a fairly thin wire (0.32mm dia) which would limit the current carrying ability but also keep the overall size smaller.

rickharris2 years ago
steveastrouk2 years ago

Unfortunately there is no practical way to calculate it. The GAUGE of the wire makes no difference to the voltage, only the rate of change of the flux through the coil and the number of turns does. Wind a bunch of turns in thin wire and see what happens.