"overvolting" MH bulb

"overvolting" MH bulb

Hi,

I've got an idea of increasing poor brightness of a DIY projector by "overvolting" light bulb. I've built a 15" based projector, equipped with a standard 400W MH bulb. Would it be reasonable to push the power up to about 500W, using two 250W magnetic ballasts, connected in parallel? Does it make sens to wire such ballasts in parallel, will it result in doubling electrical output power? If so, is there a risk, that a 400W bulb will quickly burn out, or even explode instantanously?

Regards
 

Quin

Member
2004-12-08 12:41 pm
England
A 400w MH bulb should be providing you with more than enough lumens for a large screen. Perhaps you should look at possible causes for the dim image - My first check would be making sure the lamp is at the correct distance from the field fresnel, you lose a LOT of brightness if this is too close. Do you use a reflector? Even a basic soup ladel type will give a significant increase in brightness, at the expense of other things but that isn't to be argued over here :D
 

pepe303

Member
2005-04-05 12:12 pm
Poland
Thanks for you replies.

No, 400W bulb does not provide "more than enough" brighntess. Couple of people (including me) have measured total lumen output, and the result is a shame, within a range of 100-200lm. Yes, I use a good reflector (cold mirror), and a condensor lens, and everything is carefully aligned. It is quite sufficient to watch movies (friends make "wow!" when they visit me), but I know the brightness is actually quite poor, which yields poor contrast (as the full contrast range of the LCD is not used). A 400W bulb itself is very bright, but overall efficiency of the whole projector is weak, most of the light is lost. Vast amount i being lost around the bulb (just small percentage is directed to the LCD), than most of this small percentage is converted to heat in dark LCD panel. Then there are cheap, plastic Fresnel lens, couple layers of glass, and cheap projection lens, and in my case one mirror. So you get about 35000lm in, 200lm out, and I see no way to improve that, other, than increasing bulb power. Better optics is either not available, or too expensive. Brigher LCD 15" panels are not available. And the total cost of my projector is already higher than a cheap commercial unit (like new one from cheap brand like Medion, or used ones from more recognized manufacturers)

Regards
 

pepe303

Member
2005-04-05 12:12 pm
Poland
Sorry guys, if anyone of you thinks that you can build a reasonably bright DIY projector with a 400W bulb, he/she is wrong. We are talking about 15" 1024x768 screen, I assume the main purpose of such a huge and ugly box is to get a decent, big screen. In my particular case, big screen means 2.5m-3m wide, that is about 4.7-6.7m2 screen area. Reasonable screen brightness is usually defined as about 100lm/m2, so I would need something like 470-670 lumens. There is absolutely no way to reach even close that, no matter how carefully you build the box, and how much tweaking you do, please, don't try to persuade me, that 100lm or 200lm should do, because there is something visible on the screen. Yes, sure, it's quite watchable (especially for newbies, they usually shout "wow! amazing!" when they see my screen), but it's very far from being a quality picture. I'm aware of that, and I know it's not a matter of tweaking, it's a fundamental issue of such a design.

So I still ask a question: is this a good idea to "overvolt" such MH bulb? If so, how to do it safely, how much extra power would the bulb survive, and still yield acceptable lifetime?

Regards
 

nick[x1]

Member
2004-09-27 11:26 am
Home
No expert on the matter, but I would have thought that "overvolting" the lamp would be a very bad idea.
You really need someone with electrical experience to answer this.
I know what you mean about 400w not being alot, IMO if we had something to go around! the bulb to aim the light at the fresnel, it would result in a brighter image.
But if you want a high quality image, DIY is not really the right route to take, unless you have access to all the correct tools, and are pretty dam good and DIY.

I have got some test shots of my projector with a 400w and its fine for my likeing but I know for a fact they could be alot better with a brighter bulb.

Sorry for the slight thread hijack :smash:
 

pinkmouse

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
It won't work, and the lamp will likely explode, if the ballasts don't burn out first from inductive resonance.

You need to look at a bigger lamp/ballast, smaller arc, and better optics.

Commercial projectors to achieve the screen size/brightness you want are still in the 5k$ plus bracket. You cannot get what you want cheaply I'm afraid...
 
[IMGDEAD]http://www.lumenlab.com/forums/uploads/post-2-1120078354.png[/IMGDEAD]

Hes right when he says he isnt going to make it to 600 lumens .... but what he doesnt know is that the commercial units arent going to either .....

Brightness is an issue, always has been with projection ...... Brightness is an issue for commercial front projectors, and even a rear projection TV is dim compared to a CRT.

I have successfully made two 400W projectors ..... and While it could stand to be brighter, I dont really need it to be ....

The first thing, is that all 400W MH bulbs are not created equal .... what bulb are you using .... The EYE bulb is a great M59 Bulb, with an intial lumens of 39,000 and a mean of 30,000.....

You can get better bulbs with a Venture PS, or a Ushio PS lamp .... both are about the same as the EYE in lumen output (40,000 lumen intial) .... but their center arc is considerably smaller (over 50% smaller) ..... this allows your fresnel to collect more light to send through the LCD .....

You cannot combine ballast power like that ... because they output an AC voltage, it would be impossible to synch the two sources up .....

You could theoritically try a 450W, or a 500W MH magnetic ballast ..... as long as your bulb is probe start, ... you could start by removing the capacitor, to reduce the voltage (the cap for Power Factor correction) .... it will lose effeciency in terms of Lumens/watt .... but a 500W ballast, with the cap removed, it may provide about 420-430W to the bulb ..... You could then try to put the cap back in, and go from there ......

you may get by with a pulse start ballast, but im not sure how the high voltage pulse strike from the ignitor will be higher with a higher wattage ballast

However, Im only speaking in terms of voltages feeding the bulb, I DO NOT KNOW the safe limits the bulb can recieve .... Obviously anything safe at 400W can take a little more because they would have to be designed with a certain tolerance in mind .... its how much more we are in certain of ....

If you have an electronic ballast, then ignore everything I said .... They up the frequency to about 30kHz, and its a square wave response that feeds the bulb ....

Doing any of this isnt going to get a real gain .... I personally would start with making sure I got the best brightest 400W bulb availible with the smallest arc center ... I believe this is the Ushio bulb, Lumenlab no longer sells it because they like the s400DD that has a better color (but reduced lumens at 33000 initial). The ushio that Im referring to comes in an ED28 jacket, 40,000 initial lumens, at a 4K color temp ....
 
Thanks everybody for responding. Now I think I'm not going to tweak with my projector anymore, at least until it really requires some maintenance or repair. I'm afraid of accidentally breaking something (like LCD for example).

Where does this table come from, the one that compares rated vs. actual light output of commercial projectors?

Regards
 
Brainchild posted it on the LL forums ... we had quite a discussion over there, when one member measured his PJ to have like a 175 lumens ..... .... he was trying to compare that to a 2000 lumen rating of a commercial projector, as if it were more than 10 times brighter ...

The measurements came from test site, where they test Projectors and stuff ... it just reflects their ratings versus what you actually see on screen ....