01-04-2009, 11:36 AM #1
How To? Dimmer for 5V Grain of Wheat Bulbs
Question for the electronics experts...(You out there Mike?)
I am going to be using 5V grain of wheat bulbs for backlighting per a discussion thread that was seen here a month or so ago.
Can someone provide a simple dimmer circuit diagram that would work well for this application. 5V supply will be from computer power supply and will likely be supplying a few hundred grain of wheat bulbs by the time I'm done. Is this just a matter of throwing in a Pot in line? If so, what size?
01-04-2009, 12:14 PM #2
You cant insert a potmeter directly, because it will probably burn up from the heat generated.
You should use a rheostat capable of the ampere load that the bulbs draw. So you need to measure the total ampere load. A rheostat also generate heat so be careful regarding fire hazard.
What I have purchased is PWM (pulse width modulation) DC-motor controllers for this purpose. They apply the power to the bulbs in a cycle which you adjust with a potmeter. Big benefit with this is that very little heat is generated compared to a rheostat where lots of heat are generated.
I have bought two different modules. KTA-195 and KTA-067. These boards are cheap.
KTA-067 for map-light and KTA-195 for backlighting of panels. I have done a little test already of the map-lights and result is great.
Video of testing http://s31.photobucket.com/albums/c3...t=MOV00009.flv
Link to manufacturer http://www.oceancontrols.com.au/moto...rs.htm#KT-5195
01-04-2009, 12:33 PM #3
The bulbs are 80mA bulbs. So if I estimate approx 300 bulbs that translates to 24 Amps correct?
Would this work for all of them then?
01-04-2009, 12:44 PM #4
01-04-2009, 12:45 PM #5
The theoretical MAX amperage of the KTA-195 is 20 Ampere. Because of the MOSFET`s connected to the board cant handle more. But my brother which is an electronics engineer said that I could install two more MOSFET`s and one more cooling rib in paralel to the existing mosfet to add more ampere capability. Easy to do. Just solder the second mosfet`s on the backside of the board, and make sure they turn the other way than the already installed ones.
But maybe also it is good enough to install a CPU fan to help cooling the Mosfet`s.
I have the boards here, but not have done this testing yet. Will order the needed parts very soon. I also need to measure the ampere load from my IBL panels.
01-04-2009, 12:46 PM #6
01-04-2009, 12:53 PM #7
Ok, I will await your results. Would you please post them once done? This would be very helpful. Thanks for the insight.
If anyone else knows of a similiar solution and one available from a US Supplier please post as well.
Thanks Ivar! Also congrats on your being published!
01-04-2009, 12:59 PM #8
Sure. I will post when testing is done. I would guess in about two weeks, because it take some time before electronic parts is here.
I have done extensive searching for PWM boards that can handle more amperage than 20, and thats not easy to find. But please post someone if you can find
Thanks for the congrats
01-04-2009, 01:05 PM #9
This will be a lot of fun
01-04-2009, 02:00 PM #10
You can buy a 30 amp rheostat from Mouser. No muss, no fuss, and no guesswork.Boeing Skunk Works
Remember...140, 250, and REALLY FAST!
We don't need no stinkin' ETOPS!
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