diy projector from the Philippines

[Scubasteve2365]

Originally posted by hertzblaster


Lets clarify it more for the benefit of those who find this discussion interesting..

example using the same ballast
Ist condition : 100 volts x 2 amp = 200va

2nd condition ; 50 volts x 4 amp = 200va

To clarify, The volts is represented as voltage across the lamp not the voltage across the ballast.

Our assumption here is we are running the ballast with correct input voltage in the first condition and low input volatge in the second condition

Another assumption is that we are using a simple reactor electromagnetic ballast ( ballast is connected in series with the lamp)which i believe is most popularly used in our project.

We can tell how much is the voltage drop across the ballast by using a simple multimeter

So the power loss in the ballst is given by
P = voltage drop across the ballast x current

The higher the power loss ( power consumed by the ballast), the hotter the ballast will be.

Ok ... I only know of two types of ballast ..... One an electronic ballast, that is electronically controlled, and the old style coil ballast.

For an electronically controlled ballast, we can not determine what voltage and current is sinking through it .... For example an OP amp that has source voltage of +15 and -15V ..... thats not a 30V drop accross it, but rather the Power supply that the op amp draws from, so therefor with active controlled device its hard to assume the voltage loss across it is the source line voltage minus the output lamp voltage.

the latter type a coil ballast, is nothing more than a transformer really ..... in which case Pin=Pout ..... (with a very minimal power loss in the core)

For example I use a coil ballast in my PJ.

its hooked to 120V...

therefor 400VA = 120V * I .... rework the equation .... the current solves to be 3.33A draw .... this is the current going into the ballast ....

the ballast then uses that current to step UP the voltage.... Voltage increases and current decreases ... but 400VA maintains ...

Ive measured my output voltage to be 275V ...

And my output current from the ballast is calculated as ....

400VA = 275 * I ... where I is 1.45A .....

There is a minimal power loss in the transformer itself, due to the mere physics of it ...

My coil ballast is a multi-tap .. and it has a 240V input as well .... If I used that, the input (primary side of the transformer) would be ...

400VA = 240V * I .... where I solves to be 1.6667A of current. The output side (Secondary of transformer) would be the same .....

In BOTH cases .... the transformer will have similar losses ..... cause you cant really look at current alone, you have to look at power .... The transformer has specific windings .. that equate to a turns ratio .... the turns ratio on the 120V input is .... 275V/120V = a turn ratio of 2.29.

If it were to reduce the input voltage from 120V to 100V .... , then the output voltage would not be 275V, but rather approximately 229V ... and then we would no longer have 400VA.

[hertzblaster]

Back to the school days from me. Ahh! Sweet memories of the 80's.

Here is the link that may help you and others to understand about types of hid electromagnetic ballast that you think about.
http://www.hubbell-ltg.com/products/...t_circuits.pdf

the latter type a coil ballast, is nothing more than a transformer really ..... in which case Pin=Pout ..... (with a very minimal power loss in the core)

In HID ballast application, its what they called " Constant wattage Isolated" type of ballast.

This is what i believe it should be.

Be careful when you say minimal power loss in the core. The hid lamp operates like a short circuit ( negative resistance). Meaning the ballast windings resistance is the one that will limit the current.

Power loss is not minimal.We know that the ballast feels hot. Ballast is consuming power. HID balast is more carefully designed unlike ordinary transformer.

Ordinary transformer is not operated normally under full load unlike the HID ballast and it is not thermally protected.

There is a minimal power loss in the transformer itself, due to the mere physics of it ...

for HID ballast application, power loss is considerable otherwise the ballast won't heat up.

When I designed and diy a transformer, power loss is a big consideration. If I want a certain power delivered to the load at certain voltage and right current, I want a wire that is accurately size otherwise voltage drop is higher in the transformer ( low voltage regulation) delivering high current ( high power loss) that may damage the connected load and overheat the transformer.

I thought about designing and diy my ballast but no time for now, maybe after retirement.

[ace3000_1]

with a very minimal power loss in the core

Alot more loss then an electronic, just take a look at the duty cycles. The materials the ballast is made from also make a diff.

Trev

[hertzblaster]

Alot more loss then an electronic

Yup! its one of the best advantage of electronic over electromagnetic, low heat and low power loss, cheaper power cost.

[Scubasteve2365]

in a decent transformer, there will be minimal power loss compared to the power on the output .... for example my ballast is 400w .... I have no where near the margin of power lost in the core of the transformer.

The type of load will effect its loss, and you can calculate the Rcore if given the Zcore and vice versa. to determine this loss under different loads.

but with a normal set-up, from a half decent ballast should only lose a fraction of the power compared to the power its outputting.

none the less, regardless if the power loss is minimal, or exceptional in both cases of condition 1 vrs condition 2 similar power will be dissapated in the transformer. A transformer is a linear device, meaning that its output/loss/input are all correlated with a simple linear equation. Likewise Power is correlated with a simple linear equation (I * V) ... therefor when one element rises, the other element falls ... but the same work is done ....

[ace3000_1]

After a 2 second search:

http://www.uppco.com/business/eba_12.asp

A bit about ballast materials:

http://www.fcs.arcelor.com/prd_web/D00_EN.html

Trev

[hertzblaster]

therefor when one element rises, the other element falls ... but the same work is done ....

For the newbies reading this thread , here is the thing to remember

Assuming i have 250 watt Hqi- tsd
Rated voltage : 100v ( voltage across the lamp)
Rated current : 3 amperes

We need to deliver 250w of power to the lamp but can be achieved in different ways.

1. Use a ansi recommended 250w ballast to give 100v running at 3 amperes equivalent to 300va.

2. Use any ballast to give 250w to the lamp, say 60v at 5 amperes is also equivalent to 300va.

I experienced the 2nd case when i wrongfully bought a 250w metal vapor ballast. My iimage is dim in this case. I have to overdrve the this ballast just to get a decent image.

Always look at the rated current and voltage of the lamp so that you will know what ballast to buy.

Ballast are lamp specific . Don't assume that same power rating of the ballast under the 2 conditions will give the same performance.

The 2nd condition will perfrom miserably and can damage your bulb because of high current ( overheating).

If you know how to use a mutlimeter, (Safely!), you can check it now. If we have the same bulb, the voltage across the bulb should be 100v. If its lower, you will have to use a variable voltage regulator to increase the voltage, otherwise the lamp is dim and you will see severe green tint in your projected image.

If its higher than 100v, i guess 10% overvoltage is ok but may not be safe enough.. Expect a very bright image under this condition.

This is true only for electromagnetic ballast.

[hertzblaster]

After a 2 second search:

Great link! I have to spend a lot of time before to get this kind of literaure, and you had done it in 2 secs.

[rastus]

This is an awesome thread.....and very impressive picture quality Hertz!!! ..... straying away from the ballast argument, have you ever tried an xbox through your projector ? (don't know if this has been asked before ) ...... this site ( http://www.xbox-scene.com/ ) may solve your occasional game fix and being able to have a dedicated media player (nearly all codecs and dvd) in most HDTV modes. The best part is being able to dedicate your projector into having a single composite, s-video, component or vga input. It is also capable of digital surround output (dolby digital, optical and/or composite). In particular, please checkout the hardware and XBMC forums. After doing all the DIY mods suggested by that site the only thing I was missing was a DIY projector. Thanks to this site and your thread, hopefully soon I will have that

[hertzblaster]

this site ( http://www.xbox-scene.com/ ) may solve your occasional game fix and being able to have a dedicated media player (nearly all codecs and dvd) in most HDTV modes. The best part is being able to dedicate your projector into having a single composite, s-video, component or vga input. It is also capable of digital surround output (dolby digital, optical and/or composite). In particular, please checkout the hardware and XBMC forums.

This sounds interesting. I1ll take the time to look into this. Thank you for the link. Good luck to your pj project.

BTW, my lcd has just celebrated its first year under severe punishment from me. lol! Its still working flawslessly.

I guess a commercial projector could have not withstand the torture for a year from me. Imagine watching at an average of 3-6 hours a day five days a week.

Turning on, turning off atleast more than twice for every use. And a lot of times experiencing overheating of lcd ( big brown blob at the center) because of carelessness.

I believe its ok now for this lcd to die on me anytime since it has already provided me with lots of fun and goodtime before.