115 volt to 82volt???

[Newpaltzwonder]

Howdy,

I have a few ENX lamps and I want to wire one up in a projector..I have the mounts, but I don't have the transformer to power them. I'm looking for a cheap and easy substitute/

Any ideas on how to knock 115v down to 82v?...so I can run the lamps rated for 82v @ 360w.

Thanks,
Newpaltzwonder


I'm also looking for cdmt lamps and ballast, they are impossible to find a place to order from.

[diylabs]

I had an overhead projector that used those lamps. It didn't use a transformer though. Instead, it ran a transistor in series with the lamp to eat up the other volts and turn 'em into heat instead. I think I still have the transistor lying around here somewhere ( I disected that OHP long ago). If you email me a little reminder, I'll look for it and post the part number so that you and others can finally use 84v lamps on a 120v line voltage.

As for the lamps and ballasts, I've got ballasts, but I'm not sure what the lamp voltage is for the particular metal halide. Check out www.diylabs.org/projector/ if you're interested. I'll help you however I can.

[uvodee]

Originally posted by diylabs
I had an overhead projector that used those lamps. It didn't use a transformer though. Instead, it ran a transistor in series with the lamp to eat up the other volts and turn 'em into heat instead.

The ones you find in the dukane and infocus OHP are aluminum housed resisistors with a high wattage probably 50 or so.......

they are indeed used in a schematic to reduce some of the current however, the FXL's are still getting a bit more than 82 volts. That is why a) they blow fast unfortunately, b) they have an extreme white output those ohp's have an extra switch to bypass a circuit so that even more volts get in the lamp, resulting in an even higher output..I sugested the whole idea, last year it was, to develop a circuit for home made projectors based on the fxl 82 volts which are readily available at less than $7 a piece. but there was no one that reacted. Me personally, I think this whould be the way to go for a compact enclosure.



J-P

[diylabs]

I agree that the FXL's are physically a nice little package, but I think that if you are to get a good color out of them, than you will have to have the lamp blow often. What you would need, in my opinion, is a line conditioner (not the same as a surge protector) to eliminate spikes. I know that Monster makes a home theater surge supressor that conditions the line voltage, but I don't know if this idea would even give you much increase in lamp life. I'd hate for someone to buy a $200 line conditioner only to find that they got an extra 30 seconds of life from their lamp!

I do think that using a dimmer knob would greatly help. Some top of the line halogen projectors use a soft-on technique to dim the lamp into its max output instead of just turning it all the way on. The reason is that using a switch will give the lamp a very short jolt of electricity to the order of 10KV, which theoretically weakens the filiment. I suggest getting a cheap dimmer from Home Depot and wiring your FXL or any other halogen lamp directly to it. The only problem being that you'd need to take extra care not to turn it up to high because it would be really easy to give it too much juice. That wouldn't be dangerous at all, but would burn up your lamp like a single-use flashlamp ... sadly I've done that before with a brand new FXL-5 lamp and it was my last replacement (no store was open that late for a replacement, so I had to cut the movie short ... that sucked).

[uvodee]

what I am going to do?

I am going to try the dimmer idea... I have some of them still laying around in the garage .

I think that would really do the trick, I have enough fxl's to run a small store


will let you know if it worked this week.


J-P

[tesla500]

Dropping 115V to 82V is very simple. Just insert a diode of appropriate voltage and current in series with the lamp. Here's proof that this will work:

82V @ 360W = 4.39A

Therefore, lamp resistance is 18.68 Ohms

115V directly connected across this lamp would draw

(115)^2/18.68 = 708W

Since the diode cuts off all negative going halves of the sine wave, the power to the lamp with the diode connected in series is

708/2 = 354W

Very close to 360W. The AC line is usually slightly higher than 115V, so the lamp will run at full power.

This setup avoids the losses of a resistor or transformer, and is extremely cheap to set up. You'll need a diode rated at least 200V and 5A.


David

[ace3000_1]

I suggest getting a cheap dimmer from Home Depot and wiring your FXL or any other halogen lamp directly to it.

Just a word of caution, most light dimmers are only rated at 50 - 100w, if you run a ( for example)400w halogen on these it will result in a fire or personal injury as the current being drawn is too high above the designed operating current.

Trev

[diylabs]

About Dimmers:
Almost all of the dimmers I could find, including both the older knob style and the newer digital pressure sensative kind, are good for 500w-600w. Trev was probably thinking of the older style dimmer switches that used a variable resistor to convert energy into heat, but any dimmer made in the past decade will be fine up to 500w. Check the back of the switch for a power rating if you're not sure.

About turning 115v into 82v:
Tesla is right that it is actually a diode and not a transistor or resistor. I just found the part in my garage. The part number is GP104 and has a diode schematic icon under that number. Definitely mount this against a piece of metal to help remove heat - that's how this baby works to reduce the voltage.

[uvodee]

that we solved a 2 year period of try and error findings by thinking about the 110 to 82 volt ....

I went to get a dimmer from a floodlight (rated at 1000 watts) cost me $8.00 and the lamp is as brighter as the result out of the ohp Dukane 410 !!!!!!!!!!!! ???????????...........

considering the size, i just need to have some cooling, and I have plenty of fans to work with and the enclosre can be reduced by, let's say....... 600 pct!

this is like the egg of Columbus!
.


J-P

[diylabs]

I'm confused. Are you saying that you're getting a better image using a standard floodlamp? Sorry - I just didn't comprehend.