Molex Power Switch

Hi, I was wondering if anyone knows if its possible to get an external switch that would connect to a molex connecter between my psu and optical drives which I could use to turn my cd drives on and off without having to open my case up before playing certain games, something that would mount on an unused floopy disk front pannel would be ideal


Windows would have a fit if you switched on a drive while the OS is loaded. Most likely a complete OS freeze.

I wasn’t planning on switching it off while windows was loaded, I would shut it down then switch it off then boot back up again, it would just save me from having to slide out my computer open it up and disconnect the power lead… I was looking at fan controllers but any that have molex connectors only seem to have 2 wires rather than 4

Yes, there are 2 power leads to the drives, so you need a double-pole switch to switch both hot leads. Radio Shack will have lots of choices, just be sure to get one rated for at least 1/2 amp 12v. Switch the red and yellow leads. Fan controllers use only the one 12v (red) lead.

Thanks but I’m in the UK so does anyone know an alternative to Radio Shack

Switching the power on a drive is not a good idea. If you have two drives on an IDE cable, and you disconnect power to one of the drives, it messes with the termination on the IDE channel, which can make for data corruption, or more likely, poor throughput. It can cause a bunch of trouble, and really mess with the IDE controller. If you’re not going to use either drive on the IDE channel, it will be OK. I suggest getting a double pole single throw switch, and use a covered switch to avoid accidental switching. Either that, or use a key switch, and a relay to control the power to the drives. Not only can switching the power while the puter is running cause it to freeze, it can damage the drives, and the IDE controller! Most of the time, the drives and the mobo will be fine, but sometimes, it can fry stuff. It can cause the machine to fry, I’ve had it happen. Not only that, but the drives weren’t designed to be powered while the machine is running, so the sudden load on the PSU can cause it to shut down’ or the power on the 12v rail to dip, or worse, SPIKE! This is why it can toast stuff, rapid voltage transitions can cause big problems. So, make sure you NEVER hit that switch while the machine is running. Covered safety switches, or a key switch with a relay, or possibly a double pole key switch would be ideal. Allthough, I’ve never seen a key switch that is double pole. Good luck, hope it works. I don’t live in the UK, so I dunno about a source for parts. :slight_smile:

A more sensible approach might be to put the opticals in external enclosures on firewire. Then you can hot-plug, start and stop to your heart’s content.

Thanks for the info Deer Slayer, I have 2 optical drives attached to the ide cable in question so when the switch is turned off nothing will be using the ide channel so there shouldn’t be a problem… my girlfriends dads a electrician so hopefully he can sort me out with a switch, its the yellow and red cables thats need to be attached to the switch isn’t it?

I’ve found a double pole single throw keyswitch here

That’s eaxactly what I had in mind. That would work nicely, the current should be plenty, but it wouldn’t hurt to be a little heavier duty. I think if it can handle 4a @ 125v, it should be able to take 4a @ 12v and 4a @ 5v (assuming 2a max per optical drive, which is the most current I’ve ever seen one eat). You’re correct about the yellow and red wires, you want the yellow (12v) on one pole, and the red (5v) on the other. DON’T get them mixed up on the other side of the switch, or kiss your drives goodbye! Also, DON’T get the 12v, and 5v on the same pole, or it could toast your powersupply, and the rest of your puter! :doh: Definetly get help if you’re not sure about this. :iagree:

it all seems logical enough just wanted to make sure :slight_smile: is there anyway I could attach a small LED to the power supply lead so that it would light up when the connection was made or am I just pushing my luck now :slight_smile: LEDs need a positive and negative don’t they so I’m thinking it probably wouldn’t work. its not really a big deal anyway I’ll know if its on or off if my drives are ejecting

Thanks for your help

You could attach an LED, you’d hook it to the 5v side, where the drives connect. Use a resistor in series with it, or it will burn up. I dunno what resistance you’d need, maybe 200 ohms or so. You could try a few different resistances in series with it, no resistor means the LED will fry. Too much resistance, and it won’t light up, or it will be too dim to see. You’d hook the other leg of the LED to any of the black wires in the PSU, those are the negatives. The case of the puter, and the PSU should also be negative, or ground. So, you may only need one wire, and hook the other to the case. I’m pretty sure the long leg of the LED is positive, which is where you’d put the resistor. They make pre assembled LED indicators designed to go into a pannel. That would be the way to go if you can find it, or maybe a 12v or 5v indicator lamp. You’d just hook it to the appropriate side of the switch, and the case, or black wire. :slight_smile:

LED, series resistor, and if it’s too much to get a ground lead to it (5v-resistor-LED-ground), then put it from the 12v to the 5v on the switch side, calculating the resistor for 7v instead of 5v

The maximum is about 20mA, and I’d recommend a diffused LED for indication, as clears and brights tend to throw a beam, rather than showing up well.

Thanks for the replys adding an LED seems a bit more complicated with having to take into account the resistance… I’ve found an LED that says it can be connected to any voltage between 4V and 30V its at this site

While looking at LEDs I’ve found a few bi colour leds that shine red and green depending on how its connected… would it be possible to wire it up in such away that it shines red when the switch is off and green when the switch is on

it has 3 leads 1 negative and 2 positives depending on which poistive is connected changes the colour, I was thinking if I had the red lead connected before the switch and the green lead after the switch then it would shine red when the switch was off but does anyone know what would happen when both leads are connected? would both red and green shine or what?

How do I calculate the size of resistor to use?

Thanks for your time

That constant current LED is ideal for this application. That will work perfectly, and it comes with the wire lead for you to hook it up. Go ahead and get that, and connect it to the 5v side of the switch. It should work perfectly for you, just to indicate the drives are on. A bi color LED, is going to be a major PITA. The only way I could think of to do it is with an additional relay, and it’s just not worth it. Bi color LEDs still need a resistor, and theyre are two types. One type has 3 leads, and lights up a certain color depending on which is hooked up. If you hook both + leads up, it will light up a funky color, it’s rather fugly. Then you have the two lead type that changes color based upon polarity. You switch the wires on it around, and it will change colors. Those are the more common type, but that one needs a relay to work. The other 3 legged LED could be hooked up using a double pole double throw switch instead of a single throw. Find a DPDT key switch would be a PITA though, and not worth it. Plus you’d still need a resistor. I say just get a simple constant current LED, and be done with it. Good luck, hope that helps. :iagree:

Yeah I thought I was getting abit overboard there :slight_smile: I’ll jsut go with the single colour LED… Thanks for your help

I have a similar idea to this… instead of turning on/off optical drives while the power is off, would it be possible to turn on/off all the LED lights on the front of my computer while the computer is still on? They are powered by a 12v lead. Would there be power drain/spike issues.

Thanks for the help

I can’t see this being a problem though I’m no electrician but I have a LCD TopGun light gun which I’ve rewired so that the 16 leds it uses are powered by the 5v from a molex conector and I can turn it on and off with a switch while the computer is on without any issues

I’m just thinking… I’ve also got a usb hard drive which I power from another molex connector and I have a switch connected to it which I can turn on and off while the pc is going without any problems and it’s bound to be using more power than your leds

that’s all good news…so I would think that the same would be true of a fan on a four pin molex connector with the exception of needing a dual pole switch.

Thanks for all the help

I think you’ll just need SPST (single pole single throw) switch as all you need to do is break the live (red) wire