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Mike G., Master Electrician
Category: Electrical
Satisfied Customers: 7594
Experience:  Proven Professional 48 years Experience
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I have an electronic lighting fixture that has a 24VAC output

Customer Question

I have an electronic lighting fixture that has a 24VAC output to a halogen lamp running at 250 Watts. I am trying to modify this fixture to use a LED. Im going to power the LED separately but want to still use the dimming information (reduced voltage on 24VAC).
The power supply comes with an analog voltage dimmer. It will accept from 0-12VDC for dimming. So I need to convert from 24VAC to 12VDC..
So my questions are:
1)
Is it true that the "current" is only what the device draws and not constant.. So It would not blow up the LED Dimming input as it has a 0.5A max, but the 24V is capable of delivering up to 10A/250W.
2)
Is there such thing as a variable input/output power supply? Basically the power converters I see online have a fixed output voltage but I need it to vary. Such that 24VAC would convert to 12VDC (The max dimming) and say 12VAC would convert to 5VDC.. Is this possible?
Submitted: 2 years ago.
Category: Electrical
Expert:  AssuredElectrical replied 2 years ago.
Welcome. My name is ***** ***** would be glad to assist.
1)
Is it true that the "current" is only what the device draws and not constant.. So It would not blow up the LED Dimming input as it has a 0.5A max, but the 24V is capable of delivering up to 10A/250W.
Not sure of your meaning on current and not constant?
Current is the amperage being pulled on a circuit
So, anytime the bulb is on it will be drawing current
2)
Is there such thing as a variable input/output power supply?
Need more detail here?
You want something to accept a variable voltage input and output another voltage output?
Basically the power converters I see online have a fixed output voltage but I need it to vary. Such that 24VAC would convert to 12VDC (The max dimming) and say 12VAC would convert to 5VDC.. Is this possible?
Why do you wish to convert the voltage so many times when once will do the job?
You have a fixture now that has a lamp and dimming?
Why not just replace the lamp with an LED that is dimmable?
Need some elaboration on the situation behind exactly what is trying to be accomplished.
Thanks
Customer: replied 2 years ago.
--Not sure of your meaning on current and not constant?
--Current is the amperage being pulled on a circuit
--So, anytime the bulb is on it will be drawing current
I guess my question is if I connect the 24VAC output to a device that has a .05 Max input current, would it blow the receiving device? or would the receiving device just consume what it needs from the 24VAC
--You want something to accept a variable voltage input and output another voltage output?
Yes I want something that can accept between 0-24VAC as input and deliver between 0-12VDC as output (relative to the input and constantly changing input)
--Why do you wish to convert the voltage so many times when once will do the job?
The output 24VAC, which is supposed to be connected to the halogen bulb is powered by a SCR dimmer built into the circuit board of the fixture. Im trying to use this dimming information. The dimming is actually controlled by computer via (DMX) so when set to 10% on the computer, the halogen bulb puts out 10% of its max output. SO I assume it does that by lowering the voltage to the 24VAC bulb.
--You have a fixture now that has a lamp and dimming?
Yes it is a nightclub intelligent lighting fixture from 1992
--Why not just replace the lamp with an LED that is dimmable?
Consumer type LED's are usually rated at 110V input. This is 24V. Also the light output from the halogen is about 6000-7000 lumens. There are no consumer grade LED's that can put out that much light. The closest is the "250 Watt equivelent LED" but its lumens are about 2500.. Also those bulbs tend to be frosted/coated, designed to disperse light in a large area, while I need the light focused onto the prism in the fixture.
I have a lighting fixture here
http://www.myauctionpics.com/High-End-TrackSpot-DMX-Scanner-Light-Fixtures/gallery/634952474380042500/3
It uses a 24VAC bulb here
https://www.divinelighting.com/qt8500-lamp-500-hrs-250-watts-24-volts-qt8500-p-168.html
The whole operation is very inefficient. Most of the light energy is wasted as heat. It was good in the 90's but not so much today.
Schematic for above fixture is here (page 15 has dimming circuit)
https://www.highend.com/pub/products/automated_luminaires/Trackspot/Schematic/Tspotr15.pdf
I found this LED here
http://www.ledquotations.com/three-colors-for-your-selection-high-power-80w-led-chip-integration-45mil.html
I found this matching power supply here (this is the one that accepts 0-12VDC for dimming LED..
http://www.futureelectronics.com/en/Technologies/Product.aspx?ProductID=EUC085S245DVINVENTRONICS9035418&IM=0
Since I have no electronics background, I pieced together the parts myself. The only thing left is the dimming and some way to turn the LED on and OFF by the voltage of the 24VAC rail. Ideally I would love to modify the entire unit to get rid of the 18lb transformer inside it, and possible use the SCR chip itself somehow drive the dimmer on the power supply
Expert:  AssuredElectrical replied 2 years ago.
Ok, thanks.
Looking over the entire scheme, this is a design situation of using different manufacturers parts, a sort of mix and match.
I will have to opt out of the question and put it on the open board for all experts to review and post if they wish.
From experience using many different components associated with LED's, there can easily be many failures of operation.
Manufacturers are most specific with what their equipment works with or does not work with and it becomes very extensive.
May not be on the particular situation you are doing, but I prefer someone with more experience in this type of development to work with you.
Thanks, ***** ***** to respond, the site will notify you when the next expert posts.
Expert:  Mike G. replied 2 years ago.
Hi, I'm Mike and I'll be glad to assist you. Below is a site that can provide you with what you need.
WWW.elementalled.com
Customer: replied 2 years ago.
HEllo that site list a bunch of LED products, none of which do what I need. I already ordered the superior products for the LED and power supply
Expert:  Mike G. replied 2 years ago.
Well it appears you are all set. I'm sure that if you ordered it, it must be what you wanted.
Customer: replied 2 years ago.
No i still need the dimming bit
Customer: replied 2 years ago.
anyone??