Adapter size?

[Anonymous]

Hey all,

I have two Sharkoon CCFLs hooked up to the inverter that came with the
package. Instead of putting that in my computer I want to use it with an
external power adapter. It works great, only the adapter does develop quite
a bit of heat. After 20 minutes it's hot..

The adapter is rated 12V, 400mAmp, 4,8VA

The inverter's info is:

CCFL Voltage: 200~1000V (?!)
CCFL Current/Inverter Output: 5mA
Power: 2,85 / 0,3W
Input voltage of inverter: 12V (DC)

I thought those cold cathode things don't use a lot of juice, I never
learned to do the math..

Can anyone tell me if 400mAmp is too small? If it is, what do I need, a
thousand?


Thanks, Erik

 

[CFoley1064]

Subject: Adapter size?
From: "Anonymous" ask.me@for.it
Date: 4/25/2004 2:20 PM Central Standard Time
Message-id: <408c0fc8_1@news.arcor-ip.de

Hey all,

I have two Sharkoon CCFLs hooked up to the inverter that came with the
package. Instead of putting that in my computer I want to use it with an
external power adapter. It works great, only the adapter does develop quite
a bit of heat. After 20 minutes it's hot..

The adapter is rated 12V, 400mAmp, 4,8VA

The inverter's info is:

CCFL Voltage: 200~1000V (?!)
CCFL Current/Inverter Output: 5mA
Power: 2,85 / 0,3W
Input voltage of inverter: 12V (DC)

I thought those cold cathode things don't use a lot of juice, I never
learned to do the math..

Can anyone tell me if 400mAmp is too small? If it is, what do I need, a
thousand?


Thanks, Erik

Hi, Eric. From the way you describe your problem, it sounds like you're headed
in the right direction. A 12VDC adapter with a higher current rating will
probably do the job. 1000mA sounds good.

Good luck
Chris

 

[Soeren]

Hi Eric,

I have two Sharkoon CCFLs hooked up to the inverter that came with
the package. Instead of putting that in my computer I want to use it
with an external power adapter. It works great, only the adapter does
develop quite a bit of heat. After 20 minutes it's hot..

The adapter is rated 12V, 400mAmp, 4,8VA

The inverter's info is:

CCFL Voltage: 200~1000V (?!)
CCFL Current/Inverter Output: 5mA
Power: 2,85 / 0,3W
Input voltage of inverter: 12V (DC)

I thought those cold cathode things don't use a lot of juice, I never
learned to do the math..

200V @ 5mA (200 * 0.005) is 1VA
1000V @ 5mA is of course 5 times this - 5VA

The voltage will start high and then drop once the CCFL tube strikes,
but I cannot tell you how much it will drop.

The inverter is not 100% effective, perhaps it is only 70% to 80% (or
even lower). This means that you will have to divide the numbers with
the effiency rating.
It will then need an input power rating of eg.:
1VA/0.7 = 1.4 VA
to
5VA/0.7 = 7.1VA

So your adapter of 4.8VA might bee too small.

But, how many degrees are "hot" in your case ?


--
Regards,
Soeren

* If it puzzles you dear... Reverse engineer *