Need Help With A Cold Cathode Setup...

[squeakytoy]

Hi folks, I am trying to get a couple of night lights on my tanks, and I picked up two sets of 2 each 12" tubes. I have one set rigged to an ac adaptor putting out 5v at 2 amps. I can get the tubes to light, but the light only goes about a third to half up each tube. The results were the same with only one tube plugged into the inverter. Any suggestions?

I realize that they usually take off the 12v line in a PC case, but everything I have read says that the full 12 makes them unusably bright.

 

[Mikaila31]

12v makes them too bright for some people. I've got 2 12" tubes on my 55gal and I run them at 12v. I do know the fish will not sleep with them on, but IMO that does not matter unless you plan on keeping them on all night. So it's really up to you what voltage to run them at. At 5v they are not going to light competely, like you found out. Here is a good article on them. Scroll down the page to power supply and there is a chart on voltage that should help. I would suggest buying a unversial adapter that way you can pick the voltage you want to run with.

I have a similar problem in my car. I installed 4 of these myself, in all the foot wells. For the front I had to add addtional wire between the inverter and the tubes. For some reason it makes them dimmer . They are still running off the 12vs from the car, the only difference is distance between the inverter and the bulbs. I haven't been able to figure out why this makes them dimmer.

 

[Scotty001]

i run cold cathodes on all my tanks, all have 2x 12" tubes connected to a multi voltage adapeter purchased from either wilkinsons or comet, theyre only cheap ones but do the job, i only set them to 5v (the tubes are not fully lit, for that your looking at 9v+ but if your wanting to use the cold cathodes all night long as moonlight this is not an option as is too bright for the fish.)

placing the cold cathodes in the right place on the tank hood is crucial where i have mine they illuminate all the tank, the 5v setting i find is not too bright that the fish cant get a good nights sleep too.

dependant on the size of the ank you can adjust the spacing of the cathodes and the volts till you ge it suited to your set up.

Scott

 

[squeakytoy]

Oh mama!! just dug out an old 12v, and well....


12v = freakin lightsaber

sooooo, gonna have to get a little creative on this one. I have four tubes, and really will only need 2 of them, so I will try a few things and let you guys know how they turn out. I want to keep the 12v as it lights the entire tube giving a better spread of light. But I will have to figure out how to tone it down a bit.

 

[Scotty001]

Oh mama!! just dug out an old 12v, and well....


12v = freakin lightsaber

sooooo, gonna have to get a little creative on this one. I have four tubes, and really will only need 2 of them, so I will try a few things and let you guys know how they turn out. I want to keep the 12v as it lights the entire tube giving a better spread of light. But I will have to figure out how to tone it down a bit.

you cnt "tone it down" with cold cahodes and keep a full spread of light, if you reduce the voltage which is the only means of making the cathode less bright, then the cathode will only part light, its the way they are designed.

 

[Mikaila31]

Oh mama!! just dug out an old 12v, and well....

12v = freakin lightsaber

Thats what I always call them ! Wonderful creations they are! You can hook them up to a 9v battery and duel .

 

[smegforbrains]

They are still running off the 12vs from the car, the only difference is distance between the inverter and the bulbs. I haven't been able to figure out why this makes them dimmer.

A longer cable increases the resistance, therefore you have less current through the cathode.


A similar principle to the Voltage Drop law

 

[Mikaila31]

They are still running off the 12vs from the car, the only difference is distance between the inverter and the bulbs. I haven't been able to figure out why this makes them dimmer.

A longer cable increases the resistance, therefore you have less current through the cathode.


A similar principle to the Voltage Drop law

Many thanks! I figured there was a simple answer as to why that happens. I really don't know much about wiring and electrics in general. I found it easy to wire the cathodes for the fish tank. I approached my car thinking it would be the same way. I guess it technically was I just had a lot more wires which all looked the same, which I didn't bother to label . Also I got a lot more sparks from my car and went through a whole packet of fuses...... But in the end it worked.

 

[Rooster]

Theres no "magic" to all this.... cold cathodes work with high voltage, imagine a spark - the higher the voltage, the larger the spark right ?
Well, its the same here - 12VDC is converted into a LOT higher voltage by the little circuit board that feed the tube - this jumps the gap between the tube ends and produces light (in a round about sort of way !)

To jump a gap in air needs massive voltage, but inside the tube is a gas that conduct electricity at a much lower voltage than air, so we dont have a "spark" as such, just a load of pulses of light (these are to fast for the eye to see) as the gas conducts.

 

[squeakytoy]

Theres no "magic" to all this.... cold cathodes work with high voltage, imagine a spark - the higher the voltage, the larger the spark right ?
Well, its the same here - 12VDC is converted into a LOT higher voltage by the little circuit board that feed the tube - this jumps the gap between the tube ends and produces light (in a round about sort of way !)

To jump a gap in air needs massive voltage, but inside the tube is a gas that conduct electricity at a much lower voltage than air, so we dont have a "spark" as such, just a load of pulses of light (these are to fast for the eye to see) as the gas conducts.

I just would have expected a dimmer spark, not a partially completed one... it seems illogical to me for it to only "fire" part of the way across the gap.