I need a small, cheap 277vac to 12vdc LED driver

[jgeesen]

I need to find an inexpensive way to run some 12vdc LED work lighting on 480v 3ph equipment. Problem is - all the small transformers/drivers take from 80ish to 240ish vac. I am only looking for about 1w. My idea is for the lights to come on with the machine - wired into one of the 3ph legs.
Is it kosher to just throw a resistor inline to the driver to knock the voltage down withing the range of the driver? Any drawbacks with doing it this way? What resistor would I need? Any better ideas to make this happen under $10/machine? I'll probably use SMD 5050 or 3528 strip lights for the LEDs. I need to get rid of some "shadowy" areas on ,mostly, old presses. Most of the machines do not have any other transformers for control voltage on them, so tapping off one of those is not an option.
Thanx for any and all help with this project.
John

[Robert Reed]

At 12v, 1 watt of LED power would require 80 ma. Dropping off 255 vac through a resistor would result in a wattage dissipation of 20 watts and a resistor rated at 30 watts minimum for safety. A better way would be to use a small value series capacitor followed by some rectifiers accompanied by a moderate value 'lytic and a zener at 12 volts. Better yet, why not go with just a small 240v/15 v tranny wired phase to phase. Tamura 1.6 VA series will run about $4 then just add standard raw power supply components. As to the series capacitor solution, there have been several postings in the last year that discuss this method. You could probably locate these by scrolling back thru them.

[jgeesen]

I meant to place the resistor between 277v and the LED driver (85-240vac input, 12vdc output).

[sofaspud]

Check out the modules from Bias Power. They have some LED driver types that are rated up to 308VAC.
I learned of these via obtaining a couple 14VDC 2W models from All Electronics. These seem so much more sane than transformerless
power supplies. They are only about 1" square and 0.5" high.

[jgeesen]

That link showed ac out - I think I need dc.

[sofaspud]

Uhhh... maybe you should look again.
Especially since "led-drivers" is part of the url!?!?!!!!

It's all I can do to avoid hitting CapsLock....

[rshayes]

You probably want a control transformer for safety reasons. Otherwise, all of the wiring will have to be insulated for the full line voltage and meet the other requirements for conductors carrying line voltage.

The most likely control voltage would be 24 VAC and the LEDs can probably be hooked in series and operated with a bridge rectifier with a current limiting resistor.

[dyarker]

http://www.biaspower.com/wp-content/upl ... 182011.pdf

???? AC out???

I think you were looking a low AC input row on this page:
http://www.biaspower.com/led-drivers/

High AC input models on next row. 4W model number link gives page at top.

Cheers,

[MrAl]

Hello there,

The usual method is to use a series capacitor and then a set of rectifiers or a bridge rectifier after that. This creates a voltage drop and at the same time does not require the extreme loss of power that a single dropping resistor would have to consume. The thing here though is that the voltage is so high. So high that you would have to use a high voltage rated capacitor, very high rated. The current is relatively high too, like four times the usual amount, so you'd need a decent value for the capacitor too, like 2uf. That means at the very least probably a 2uf cap rated at 630vac. I havent priced these in a long time, but that's probably not too cheap either. The best way is as already mentioned by rshayes, a transformer. Might not be the cheapest, but it's a good idea.

[jgeesen]

I just got 2 of these for $10.
http://cgi.ebay.com/ws/eBayISAPI.dll...L:COSI:US:1123
These are what I had in mind to power the LEDs and be fed off one leg of the 3ph 460v 60Hz power already at the machine. I thought it might be best to scrub off a few volts to get within range of the transformer. If 265v is close enough to 277v for input, I doubt a mild overdrive on the LEDs would harm them.
I assume I will need to know the exact LED load to size a resistor. The led strip lights can be cut along their length in 3 LED increments.

[jgeesen]

This project may not be as simple as I was expecting. I am out of my depth with designing a circuit to pull this off. I may just wire the driver up and see what happens. I just need to figure out how many LEDs to keep in the strip lights.

[gerty]

Do you have an old 480v to 24v transformer?
Wire it to the 277, it should give you about 14v out.

[haklesup]

Besides the loss of power 468Vx80mA=37W buut on the negative cycle you will reverse bias that poor diode to the full 480V and blow it to heck.

If you don't want all the bulk of a transformer or a bunch of big bipolar electrolytic caps then you might take a look at this LED driver from this company

http://www.clare.com/home/pdfs.nsf/0/71 ... HV9910.pdf Less than $1

Says it will run off 450VDC so all you may need is a bridge rectifier and a handfull of discrete parts.

and a 550V version
http://search.digikey.com/scripts/DkSea ... =CLA330-ND

less than $2

[jgeesen]

I would love to find that driver in a package I could use. Probably still out of my league figuring out how to incorporate it myself.

[Robert Reed]

Scratch