Some tips on a variable electromagnet controller?

[shellfritsch]

variable electromagnet

Hello,

I am building an array of 4 electromagnets & my goal is to have control over intensity & polarity for each one, independently.
I can power the magnets at either 18v dc (5.6A draw) or 24v dc (7.5A draw). I would prefer to work at 24V because that gives me a significantly stronger magnet. My trouble lies in finding a transformer that can do 24V dc at 7.5A
I found this transformer:
www.mpja.com/productview.asp?product=7846+TR
- but I read on a forum that it can only handle 5 amps at 24v... is this correct?
I was thinking that instead I could get two 24v transformers that do 4 amps & wire those together- would that give me 8 amps @ 24V or 48 volts @ 4A? My electronics knowledge is limited so any help with this is greatly appreciated.
Regarding variable strength- I was thinking of running a wall dimmer switch from the AC to each transformer (or set of transformers). Would this work?
I haven't figured out how to quickly reverse polarity.. if there was a way to do it gradually that would be great, but I'm fine with just flipping a switch or pushing a button or something.
Any ideas? What is the best way to wire this up?
Thanks again!

 

[IanP]

electromagnet controller

This would be a perfect job for H-Bridge and PWM (pulse-width-modulation) ..
See example at:


If you don't want to go that far then transformers+rectifiers should work well too ..

If you have two identical transformers you can connect their windings any way you like: in series or in parallel ..
To increase output current connect two secondary windings in parallel but I would use small power resistors, such as 0.1Ω/5W, or even less than that, per each output to balance currents drawn from both windings ..

Regards,
IanP

BTW .. Make sure windings are connected in the right phase .. note phasing dots on secondary connection points 5 & 7 .. see picture below

 

[shellfritsch]

variable controller electronic electromagnets

Thanks for the tips... I think the H-Bridge and PWM method might be a little advanced for me.

Could I just use some rectifiers in place of the transformers? They are much cheaper
what are the best ones to use? do you think i could just put a wall dimmer in between that and the ac main? i'm trying to find the cheapest, simplest solution.

thanks again!