Why won't my cold cathodes work?

I just bought a new glass desk and have decided to mount some blue cold cathodes under the frosted glass to give this sort of effect...
cache.gawkerassets.com...
g-cdn.apartmenttherapy.com...

...Anyway I want to convert the cold cathodes kit (made for computer) to run from an AC wall socket. I got an AC-DC transformer that has a molex plug on the end of it then I've plugged this into the molex that runs to the inverter for the lights.

This is the type transformer..
www.ebay.com.au...
And these are the lights...
www.logisyscomputer.com...

Now the transformer works for other stuff like some LED's I had laying around so it can't be faulty, the cold cathodes can't be faulty either because they work when plugged into the computer. The output from the transformer (2.5A) should be able to cope with the (5mA) the lights draw, and they are both 12v.

So why won't it work?

Obviously I don't know how up on electrical stuff you are so, I'll start with basics:

Have you definitely got the polarity (+ & -) the correct way round for the cold cathodes when running from the adapter? The drivers will be polarity sensitive.

Generally speaking the positive lead from adapters is marked with a stripe or line of varying vagueness! I see the PSU you linked has a pre assembled adapter harness, are you actually using that? Just because it's pre made does not mean it's correctly made, as is so often the case these days.

2.5A should be plenty to drive a cold cathode.

did you take the box out of the wiring for the cathodes???
This needs to be in the wiring to create the strike current for the tubes to work... Same as neons...


edited to add that you must wire the box back in and connect the transformer output to the original wiring plug for the tubes..... NOT wire the transformer straight to the tubes, that will never work......

do you have a voltmeter so you can test the output is in the correct range and theres no mucked up connections?

reply to post by supradupradotcom


Yeah I think polarity is correct because they work alright when plugged into the PC, but if I take the molex out of the PC output and plug it into the little psu it won't work. As for the molex plugs, well they only go in one way so I'm assuming they're correct too.

By the adapter harness do you mean the wire thing that converts molex to sata that came with it? If that's the case then no I haven't used it.

Thanks for the reply

Originally posted by Wewillrise77
did you take the box out of the wiring for the cathodes???
This needs to be in the wiring to create the strike current for the tubes to work... Same as neons...


edited to add that you must wire the box back in and connect the transformer output to the original wiring plug for the tubes..... NOT wire the transformer straight to the tubes, that will never work......

edit on 16-7-2012 by Wewillrise77 because: extra

edit on 16-7-2012 by Wewillrise77 because: grammer

You mean the inverter? Yeah its still in there, the lights work just fine when plugged into the molex cord coming from my pc but then when I take the cord straight out, touch nothing else, and then plug it into the little psu they don't work. Yet the little psu works with other stuff.

Originally posted by Maxatoria
do you have a voltmeter so you can test the output is in the correct range and theres no mucked up connections?

Unfortunately no

By the adapter harness do you mean the wire thing that converts molex to sata that came with it? If that's the case then no I haven't used it.

Yep, that's the thing I meant, I assumed you wouldn't be using that.

In an ideal world this should be plug & play but, if the things work on PC but not the PSU & you know the PSU works as it powers other items OK then this only really leaves us with the polarity being off between the CCL's & the PSU.

If you have a volt meter you can check it pretty easily? *EDIT* Just seen you don't have a volt meter - dam!

Trial & error it is then


Just to confirm the cable colours for you..

Black - Ground / Negative / -

Yellow - +12 Volt / positive / +

reply to post by polarwarrior


Maybe the inverter is faulty.

Curiouser and curiouser... So the ac adapter works with other led's but not the CCFL. The CCFL works on the pc but not the ac adapter??? And you haven't cut any wires...

Hmmm, tried wiggling the wires in the Molex connector just in case its not making contact correctly??
Maybe run a molex extension cable off the pc power supply to wire the CCFL's and negate the ac adapter??

Other than testing with a multimeter, I'm stumped...

Originally posted by supradupradotcom

By the adapter harness do you mean the wire thing that converts molex to sata that came with it? If that's the case then no I haven't used it.

Yep, that's the thing I meant, I assumed you wouldn't be using that.

In an ideal world this should be plug & play but, if the things work on PC but not the PSU & you know the PSU works as it powers other items OK then this only really leaves us with the polarity being off between the CCL's & the PSU.

If you have a volt meter you can check it pretty easily? *EDIT* Just seen you don't have a volt meter - dam!

Trial & error it is then

Just to confirm the cable colours for you..

Black - Ground / Negative / -

Yellow - +12 Volt / positive / +

edit on 16/7/2012 by supradupradotcom because: More info added

So should I take apart the plug and swap the wires around and just see if that works

Originally posted by Wewillrise77
Curiouser and curiouser... So the ac adapter works with other led's but not the CCFL. The CCFL works on the pc but not the ac adapter??? And you haven't cut any wires...

Yep

Hmmm, tried wiggling the wires in the Molex connector just in case its not making contact correctly??

Ok I just gave that a shot but its not doing anything, I have tried a couple of cold cathodes to no avail so I must have gotten an ok connection at some point as I've tried it many times now.

Maybe run a molex extension cable off the pc power supply to wire the CCFL's and negate the ac adapter??

Yeah that's the last resort, it would mean the PC would need to be on for the lights to work so I couldn't have the light on just while watching tv or something.

Other than testing with a multimeter, I'm stumped...

Yeah I thought this would be a really simple thing lol.

If the ac adapter powered led's the polarity is not the issue as led's can only be wired one way....

By the way, is it just me or does the ebay pic of the ac adapter wiring shows no conducter for the 12v- on the molex connecter???? Male connecter not female.....

I'd certainly check it all matches up OK, I don't know what your CCL's are terminated in, is that a molex too?

It wouldn't be the first time I'd come across them wired a different way round to how they should be.

The ground return for +12v & +5volt are the same thing so, the PSU uses the same wire for both hence the missing pin.

So I've made sure the pin 1 which is 12v is plugged into the yellow wire 12v. I've swapped them around anyway but still nothing. Here's the pic from the little psu

reply to post by polarwarrior


Now with the missing pin on the PSU it's just occurred to me the ground connection of the CCL's may not be connecting to anything? This needs to be connected to the black cable (pin 3 of PSU)

The CCL plug probably returbns it's ground on pin 2 as it assumes a fully populated socket its being used instead of the 3 pin vershion with only 1 ground as on the PSU.

YES!!!! no 12v- connector.... look at the above pic....
The 12v and 5v rails should have separate negs!!!!

Well, a decent power supply should anyway...

Originally posted by supradupradotcom
I'd certainly check it all matches up OK, I don't know what your CCL's are terminated in, is that a molex too?

It wouldn't be the first time I'd come across them wired a different way round to how they should be.

Yeah, they are molex too. I'm just checking the order of the wires now. Btw I have 3 sets of cold cathodes so they would all have to be the wrong way (or the psu is but then labeled incorrectly and still works on some stuff somehow)

I'm really stumped now.

Ahhh good point, ill swap em now

YES!!!! IT WORKS!!

Thank-you so much guys.