# Using PV cells to energize an air core coil

1. Apr 7, 2009

### Robin07

I'm using PV cells to energize an air core coil. Is there a method in which I can determine the maximum length of 32 gauge magnetic wire to use, so that I don't use too few windings and burn the coil out or too many windings limiting its' potential. I'll be using 2 PV cells that are each rated at .180ma, 1/2v and hooking them up in series to maximize the amperage. So if I understand this correctly, hooking these up in series will give me .260ma at 1/2v. How do I use Ohms' law, V=IR to figure this out?

Thanks

2. Apr 7, 2009

### Bob S

If your purpose is to store energy in a coil, then you want to load the inside of the coil up with magnetic material to maximize the energy density. For a given number of amp-turns per meter from your pv cell, you can increase the energy stored by several 1000.

Basicaly, you want to increase the inductance L (henrys) of the coil

where the energy stored is E = (1/2) L I2

so for a given number of amps, the stored energy is larger when L is larger. You also want to use copper wire to minimize the resistive losses.

The big problem with storing the pv output in a coil is that as soon as you disconnect the coil from the pv cell and interrupt the current, the stored energy is lost.

Last edited: Apr 7, 2009
3. Apr 8, 2009

### Robin07

Thanks Bob S, but no I'm not attempting to store energy in the coil, I'm trying to create a maximum electromotive force. The coil itself is a closed loop that houses the two PV cells. The coil and PV essembly are mounted on a center horizontal pivot. When the cell collects and sends current through the coil, the coil will realize an expanding magnetic field(flux). The resulting field will reflect off of a permanet magnet that is located under the essembly, causing the coil to spin. I realize that the coil will need to switch on and off, hence the cells are mounted facing only one direction, this will ensure that the cells will only be activated when they are facing the light source. I hope my explination makes sense. Increasing the inductance as you mentioned previous, will that increase the emf(electromotive force)? Thanks again Bob S.

4. Apr 8, 2009

### mheslep

In series you'll have 1VDC at 0.18ma, so you want R=5.6kohms. Look up the resistance per unit length for AWG 32 wire to get your 6kohms, that will be quite a bit, more than you want Im sure, so add a resistor. You also say you want to use the coil as an electro magnet. Note that as you move some other metal object towards or away from the coil you change the inductance of the coil and simultaneously induce a voltage in the coil when the object moves away/towards, i.e., you introduce another effective voltage source into your circuit.

5. Apr 9, 2009

### Robin07

Thanks Guys, I stand corrected here. If I want to increase my amps I will need to hook them up in parrallel, which will give me 1/2v at .360ma. I looked up the resistance per unit lenght for AWG 32 copper wire and for my application it calculates out to be 35.75 feet, thanks mheslep. And yes if I introduce a metal object into the mix this will change the inductance of the coil. In this case, a permanent magnet which, I hope, will induce an equal and opposite force, futher assisting in the spinning of the coil. Well it's all experimental.

Thanks for your input thus far and any other comments that follow. I'll post my results if any one is interested. Thanks again.

6. Apr 10, 2009

### mheslep

?? Do you actually mean milli-amps as you say? 0.00036A? AWG 35 is 329ohms per 1000ft. In parallel you want a 1388 ohm, ~1.5kohm load to draw rated current, or ~4000ft of AWG 35 copper wire. Use a resistor instead. In series, the same .36ma will flow through your coil.

7. Apr 10, 2009

### Robin07

My appologies for the confusion, I am very much a novice at this. This is the information I recieved from the PV cell supplier.

2 cells in series 1v@180ma
in para 1/2 volt @ 360ma

I would like to use the above specs to make the most efficient coil possible.