Power switch

Hey everyone, I wasn't quite sure where to post this, but since it involves TEK's and extra power supplies, I guess here is a good place.

I am making a water chiller, that uses 2 110 watt pelts, and 2 really crappy 300 watt power supplies to power them.

To turn the power supplies on I want to build a bit of a switch that I can put on one of the molex connectors from my main PSU. I will connect this switch to the power wires from the cooler psu's (green and ground).

The idea is, you put voltage into the switch (ie turn on the main psu) and the resistance between the ground and power wire from the cooler psu's goes to zero, turning them on.

I could do this easily enough with a small sylinoid, but would prefer to keep things purly electronic. I don't really remember enough about working a transistor to make this switch, but I don't think it would be complicated at all.

Does anyone know how to make ths switch, or where I can find some decent information on how to? Thanks.

here is someting i saw at circuit city....i dont know if it will do the job u want it to do....never tried it yet....Link

Thanks for the reply.

I did a quick bit of review on transistors, and a little expermenting on some I had. Turns out it is even easier than I thought.

I found that if I put 5V into the Base, the resistace between the collector and emitter droped to about 5 ohms, which I think is low enough to turn on the coolers PSU's. Not sure though, will have to test that too....

I'm sure I could mod that tester to turn on the power supplies, but I'm looking for an easier (ie. cheaper, ie. free) way to do it.

hmm... well.... this is really turning out to be me talking to myself late at night... oh well...

I got the thing working, so for anyone who wants to make a simple switch to turn on secondary power supplies whenever your main one is on here is how:

Get a transistor from something, mine is a "2N 4124 M 322", idunoo exactly what that implies, but the transistor itself is about 4mm tall.... so something in this range should work for you.

Connect 5V from a molex connector to the Base of the transistor (the middle terminal)

Connect the ground of both power supplies to the collector of the transistor (look at a transistor diagram online to see what this is)

Connect the green power wire from the secondary PSU to the emitter of the transistor (look online again)

Now when you turn on your computer, the switch will turn on the secondary PUS as well, and when you turn of your computer, both PSU's will turn of.

I know this may seem obvious to those of you who have an electrical background, but it should help out those who don't.

This seems pretty easy, but I have never messed with electronics/PSUs.

Do you have links/diagrams, especailly for the transistor?

Ehheem !!!

Hello people!

You should NOT put 5V DIRECTLY on a transistors base !!!

The base of a ordinary bipolar NPN or PNP transistor only uses (or consumes) about 0.7V. Putting 5V and unlimited current will kill it.

So, use a series resistor of 500 or 1K ohm to properly feed the base of the transistor.

So: Powersource -> resistor -> base of transistor

Some transistors have a built in series resistor, but those are few and rare compared to other transistors.

Yea, good call on that one..... I was doing a little reading on the specs of the transistor I was using, It was from an electrical engineering lab I was doing a while ago. It is one of those ones with the built in resistor, I guess so everyone in the lab doesn't kill a bunch of them. It goes into saturation mode at 5V base, but yea, 0.7V is what the transistor actually sees.