loading

Convert DC Light bar to AC


I'm trying to help out a friend. He's an animation student and he frequently has to use a light box while he's sketching. For those unfamiliar, he draws on a paper, and then puts another paper on top and traces it again, but with a slight change from the first. This process continues over and over until the animation is complete. In order to be able to trace, he's got a piece of white plexi (with a 90° bend in it) as his "table". He then places an off the shelf Energizer "Under Cabinet Light" under the plexi.

This light has a fluorescent bulb and is powered by 8 AA batteries. Simple calculations means it's running on a 12V battery pack. Since he's often doing homework for 6 hours straight, the 8AA batteries become costly and the light dims over time. He was asking if I could hack the light to take AC power instead.

I have an old wallward ac adapter that has these specs:
Input: 120VAC 60Hz 30W
Output: 12V @ 1.2A.

I also took pictures of the circuit board I found inside the light. While I can't distinguish exactly what's on the board, I can pick out a capacitor, a transformer and some sort of regulator. I should've  got a quick schematic... from the looks my google searching, it's a simple fluorescent lamp circuit.

Would it be as simple as stripping the ends of the AC adapter and soldering it to the positive and negative contacts on the light bar's circuit board? The adapter itself takes AC and makes it DC so it should work right?

Another thing he is thinking of is having me swap out the tube for LED's. I'll just need an LED driver and I can use the same power supply I found in my junk box... it's just a question if the high powered LEDs would be bright enough. Surely if the tube is bright enough on fresh AA batteries, 3 high powered white LEDs would be brighter right? Also he's on a budget, so the AC/DC hack would essentially free for him!


Picture of Convert DC Light bar to AC
bar.JPG
sort by: active | newest | oldest
mrsayao (author) 6 years ago
Does anyone know what those components are? I managed to burn something out. Finding it a little hard to pinpoint the short when I take readings with the multimeter...
Yes, should be as simple as soldering on the wires. That PSU looks about right.

Steve
mrsayao (author)  steveastrouk6 years ago
When I measured the output of the psu, it read about 16.5V... the casing says 12V but is it that normal that it'd read slightly higher?
Its completely normal. As soon as you load it, it will drop significantly.

Stee
Yeah, that's open circuit voltage, it drops under load.
NachoMahma6 years ago
> Would it be as simple as stripping the ends of the AC adapter and soldering it to the positive and negative contacts on the light bar's circuit board?
.  Yep. See if you can find something on the light that tells how many amps or watts the unit pulls (not just the wattage of the lamp) and size your wall wart accordingly.

> The adapter itself takes AC and makes it DC so it should work right?
.  A lot of wall warts convert AC to DC, but not all of them do. Check the label to be sure.
mrsayao (author)  NachoMahma6 years ago
Theres no indication of the current draw on the unit, but if I put a multimeter in series to gather the mA readings, where would I put it? The wires going to the tube? Or coming from it? These tubes have two prongs at the end but they don't seem polarized since the metal contacts touch both prongs.

I think I just screwed myself because I bought a multimeter... and it says in the instructions "do not connect this meter to current test circuit, there is no fuse protection in this meter" GrRR!!
. Measure the current through the battery pack (going to + and - on the PCB). Measure during startup and that should give you max current flow.
mrsayao (author)  NachoMahma6 years ago
so with the pack disconnected, measure from + of the pack to the + of the board, and then the same with the - terminals? In series right? I just returned the multimeter I bought and I'm headed out to pick up a new one right now. Thanks for your help!
.  Connect battery - directly to PCB - (or use a wire)
PCB+  -meter+  +battery-  -PCB
.