Wednesday, July 3, 2013

A Cheap Simple DIY Electrophoresis Power Supply

As most people trying to run Gel Electrophoresis in their apartment know generating greater than 100V of DC so you can run your gel in a reasonable amount of time can be expensive. Most of these power supplies can run in the >$100 even for ones that are 30 years old. I started messing around with some stuff and came up with a way to build a "power supply" that can output > 100V DC for less than $5.

All our outlets in North America output ~120V AC. Using this for most applications is not plausible because AC is not continuous current. What we usually want for most electronics and gel electrophoresis is DC. People have tried AC with gel electrophoresis and it just screws up the mobility because of the wave constantly changing sign. The beauty of the system here is that is uses AC just rectified. So you still can output >100V.

Full-Wave rectification converts an AC into a oscillating DC. This removes the negative portion of the AC and makes a perfect electrophoresis power supply because we don't care if our DC current oscillates.

What I used :
Small prototyping breadboard
which can be purchased off of eBay for at like 10 for $2
A 200V bridge rectifier. $0.29
Remember 120V is RMS voltage for AC so it can reach up much higher. Go with at least 200V. I choose 1A to keep gel heating down. If you are in Europe you need a much higher rectifier.
A power cord
If you don't have one laying around here is one for $2.25
Banana jack if you need/want them.
Use shrouded banana jacks so you don't shock yourself or burn down your house.

DISCLAIMER: you are going to be working with AC mains voltage. If you don't know how to work with this safely please don't do this.
This is simple. Connect with solder the positive and negative wires/banana jacks to the pins marked + and - on the bridge rectifier diode. Then connect the white and black wires of the power cord to one each of the other pins on the diode(it doesn't matter which ones you connect them to) they should be labeled with a ~. I soldered the green wire off by itself as a "ground"!

Make sure all the components are covered before you plug it in to prevent spectacular shorts and electrocution. I used duct tape for the tests because I am cheap and simple. A good idea for an enclosure would be an old pipette tip box with holes cut in the sides. 

Putting a 250V 250mA or so fuse in the circuit is a good idea to protect yourself.

I also have another connector in between the bridge rectifier and the banana jacks for my home built electrophoresis setup. So ignore the black and green connectors.

That's it.
Plug in your positive(red) plug to the red banana jack and the negative(black) plug to the negative banana jack of your gel box and plug your power supply into the outlet. Plugging and unplugging the jacks is best done while disconnected from AC mains to prevent any accidentally shocks.

The short circuit reading from my multimeter is 108V. Obviously in Europe with 240V AC your voltage is going to be >200V. You can step this down using a voltage divider in the output of your circuit.

Here is the test. I ran a 1% agarose gel in TAE. What I ran is DNA ladder(lane 1) a plasmid(lane 3) and some ~75bp primers(lane 5 hard to see) at 100V for 20 minutes using a Fischer brand power supply from our lab.

~100V for 20 minutes using Fischer Power Supply

I did the same test with my rectified supply.

As you can see the images are almost identical.

And here it after 37 minutes:

Any questions feel free to ask.