How To? Dimmer for 5V Grain of Wheat Bulbs

[XOrionFE]

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?


Thank you

Scott

[ivar hestnes]

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/c380/vrinsk/?action=view&current=MOV00009.flv

Link to manufacturer http://www.oceancontrols.com.au/motor_controller/dc_motor_controllers.htm#KT-5195

:)

[XOrionFE]

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?

[XOrionFE]

Heres another similiar and cheaper....

http://www.lightsosoft.com/servlet/Detail?no=84

[ivar hestnes]

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.

[ivar hestnes]

Heres another similiar and cheaper....

http://www.lightsosoft.com/servlet/Detail?no=84

You can not use that one for sure. Only 3 amperes;)

[XOrionFE]

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.


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!

[ivar hestnes]

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:)

[XOrionFE]

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:)

20 is pretty good. That is 250 lights for the bulbs I will be using and may be enough to get two boards. I havent sat and planned all of the panels yet because I am still awaiting their arrival from Innovative FSP but there are a lot of panels and with grain of wheat bulbs I am figuring around 30 lights on average per panel. I think there are about 20 panels but some will need a lot less than others.

This will be a lot of fun

[Michael Carter]

You can buy a 30 amp rheostat from Mouser. No muss, no fuss, and no guesswork.

[XOrionFE]

You can buy a 30 amp rheostat from Mouser. No muss, no fuss, and no guesswork.

Thank you Michael. I will check that route out as well. I like "no muss no fuss"

[Michael Carter]

Have a look at this one here: http://www.mouser.com/Search/Refine.aspx?Keyword=588-rlsr50e

It's the top one that's in stock. It will handle 120 watts which is what 24 amps converts to at 4 watts per bulb @ 5VDC for 300 of the critters.

The resistance is slightly high though. Your resistance given the above is .20 ohms. The resistance of the rheostat is .5 ohms. It might not make too much of a difference. If so, tweak the voltage on the supply up a quarter to half a volt. You'll have a bit of loss anyway in the wiring.

[jonnydaz53]

Hi guys im no expert but i found this photo of some backlighting looks simple . maybe worth a look .....

Heres the site i got it from ....

http://translate.google.co.uk/translate?hl=en&sl=fr&u=http://www.737ngproject.be/mip.htm&sa=X&oi=translate&resnum=1&ct=result&prev=/search%3Fq%3Dhttp://www.737ngproject.be/mip.htm%26hl%3Den%26rlz%3D1G1GGLQ_ENGB288%26sa%3DG

Regards jonny d

[ivar hestnes]

I measured the current draw for my overhead today, and it draw 13 ampere and the aft overhead draw 2,5 ampere. So I probably dont even need to modify my pwm cards to use this solution.

Good news for me:)

[Photon]

Would something like a 12/24V rotary DC dimmer switch as used on yachts be any good?

http://www.yachtlights.com/item--Rotary-DC-Dimmer--ILVPC


Peter.

[ivar hestnes]

Finished the wiring for my DC motor controller today, and the dimming works just fine:cool:

Need to more testing before I can shout success. But if success, then I will write a detailed tutorial for this setup when time permits. Need to do some more testing over time. And not just a 15 minute run;)

Little video of testing here
http://s31.photobucket.com/albums/c380/vrinsk/?action=view&current=015-1.flv

[XOrionFE]

Finished the wiring for my DC motor controller today, and the dimming works just fine:cool:

Need to more testing before I can shout success. But if success, then I will write a detailed tutorial for this setup when time permits. Need to do some more testing over time. And not just a 15 minute run;)

Little video of testing here
http://s31.photobucket.com/albums/c380/vrinsk/?action=view&current=015-1.flv

Thats great news Ivar. I look forward to it