# Ultracapacitor to power electromagnet?

1. May 20, 2013

### Pharrahnox

I have been looking for a better way to power my electromagnet than a bunch of AA batteries, and am now thinking of using ultracapacitors.

I have a few questions.

I have been looking on ebay for them, I don't know of better options, and I have seen mostly 2.7V with >1F, up to 1500F. One in particular has grabbed my attention 10X 2.7V 10F ultracapacitors, for < \$25, and they are stated to have: ESR (mΩ, 1KHz, 25℃) : 60

Does that mean that it has 60mΩ of resistance, therefore a maximum current of 2.7/0.06 = 45A?

What are the pros and cons of using capacitors as the power source for an electromagnet?

I think the resistance of my magnet is about 6-7Ω, so 2.7/6.5+0.06 = 0.41A. So I don't think the current would be too much, and I can always add more turns of wire (I have about 2500).

How could I connect the capacitors so that I can get more amperage? I know that connecting them in series adds their voltages, and decreases capacitance, but would that then also increase the resistance, rendering it useless?

Also, since the capacitors are rated at 2.7V, how do I charge them? I don't know of any 2.7V power sources... Also, is it possible to safely charge them off mains power, using a step down transformer?

Are there many dangers of what I am trying to do with these capacitors? If so, I would like to know, so I can prevent any injury or damage to myself or to the electrical circuits involved.

Thanks for any responses. Sorry about all the questions.

2. May 21, 2013

### cjl

You're probably best off sticking with batteries. Ultracapacitors still have much lower energy density than batteries, and you'll only get a couple seconds of use (or less) out of them before they die.

3. May 21, 2013

### Staff: Mentor

You could use batteries to charge them.

Where is the problem with AA batteries? If you need more short-term power, a capacitor in parallel to batteries could be interesting.

4. May 22, 2013

### CWatters

Perhaps use SubC, C or D size NiMh rechargable batteries? They will have greater capacity and higher current capability. Should be able to find chargers easily.

I hesitate to recommend Lithium rechargable for safety reasons. It's just too easy to burn your house down.