diy projector from the Philippines

[hertzblaster]

If I had to pick one that would run hotter it would be the 2nd condition No doubt .... but since they are both dissipating the same amount of power then they SHOULd be very close in temperature.

Please enlighten me on this. I maybe be wrong.

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.

The 2nd condition will run much hotter. Power dissipation under this 2 conditions are very much different. (P=I^2 *R) P is power loss in the ballast. The above conditions are using the same ballast so R is constant.

[hertzblaster]

Here is the link for diypj using the 8 inch HAMI lcd.

http://www.allinbox.com/oliwan/oliwan.htm

[Scubasteve2365]

Originally posted by hertzblaster


I had read ( can't rember the site) that newer UL certified electromagnetic ballast is thermally protected. This may somewhat give us a piece of mind when we think about the danger of overheating ballast.

If it has a over heating temperature cut-off similar to that of a car amplifier, it could help ...... but, if still running in too much of an unstable condition it will eventually give up and die .....

When i worked for the stereo shop, we were often told to try and blow stuff up by the manufacturers .... .... Alot of decent amps were thermal protected, but that did nothing when I gave it a 1-ohm load.

[Scubasteve2365]

Originally posted by hertzblaster


Please enlighten me on this. I maybe be wrong.

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.

The 2nd condition will run much hotter. Power dissipation under this 2 conditions are very much different. (P=I^2 *R) P is power loss in the ballast. The above conditions are using the same ballast so R is constant.

It would be too hard to say .... I does change the game when saying that its the voltage across the bulb and not the ballast. Cause in that situation we dont have any clue what power the ballast is dissapating.

and since we dont know what the ballast is made of exactly, we dont exactly know how much current is running through it. Sures its outputting 4amps .... but in both conditions alot more current could be running through it, or not .... we simply dont know.

Also since, the 2nd condition is outputting less voltage, then that must mean that the ballast is dropping more voltage in the second condition than in the first .... which could potentially mean that the current may be doubled by a factor of two, but the voltage reduced by a factor of two and then vice versa..... yeilding, yet the same power dissapation.

[hertzblaster]

and since we dont know what the ballast is made of exactly, we dont exactly know how much current is running through it. Sures its outputting 4amps .... but in both conditions alot more current could be running through it, or not .... we simply dont know.

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.

[hertzblaster]

When i worked for the stereo shop, we were often told to try and blow stuff up by the manufacturers .... .... Alot of decent amps were thermal protected, but that did nothing when I gave it a 1-ohm load.

This maybe a little off topic , but its about heat so its related..

I diy my own subwoofer amplifier and also built the speaker protector for it. Maybe i was just lucky, but i never blow up my power transistor .

In my case, Power transistor is not protected thermally thru the use of heat sensor (like the thermal protection for pc processor) but by monitoring the current delivered to the speaker. SO when the impedance say is 1 ohm, the more current will be delivered to the speaker so that power will be cut-off base on the pre-set. Higher current will heat up the power transistor.

I had also spend some time to study the impedance curve of the speaker when the apllied frequency is varied. I was so surprised that at certain low frequency, the speaker impedance of the speaker can go as low as less than 1 ohm, if left uncontrolled will blow up the amp or the speaker windings because of overcurrent ( overheating). This is where the overcurrent protection ( speaker protector) will come in.

So in our diypj application, a simple overcurrent protection ( like fuse with time delay or a circuit breaker ) may help protect our ballast and our lamp.

[hertzblaster]

If it has a over heating temperature cut-off similar to that of a car amplifier, it could help ...... but, if still running in too much of an unstable condition it will eventually give up and die .....

Its not electronically controlled, the ballast contact is opened by a certain material ( can't recall the material, maybe asphalt but i will check again)) that will expand when heated.

[ace3000_1]

like the thermal protection for pc processor)

A computer proccessor dont have thermal protection at all, its controlled via the motherboard. Not all mothboards have this feature so not all chips that are capable of being thermally shut off (when they reach the overheat threshold), the mobo has to suport it.

If your on about a fried chip, stick it in the freezer for 6 hrs and it will come back to life, atleast thats what used to work on the old k6-2 AMD chips, (i doubt on the new).

Trev

[hertzblaster]

A computer proccessor dont have thermal protection at all, its controlled via the motherboard. Not all mothboards have this feature so not all chips that are capable of being thermally shut off (when they reach the overheat threshold), can be, the mobo has to suport it.

You got it accurately. Its the motherboard that monitors the processor temp not the processor itself. . i guess all new motherboard model has this control..

I didn't know before that you are also into pc building Trev, were you an overclocker (crazy me!) just like me before?

Thanks a lot to you . I can't find time now to do experiments. But because of your so many test and research that you share, it saves me a lot of time and money.

[ace3000_1]

Originally posted by hertzblaster


You got it accurately. Its the motherboard that monitors the processor temp not the processor itself. . i guess all new motherboard model has this control..

I didn't know before that you are also into pc building Trev, were you an overclocker (crazy me!) just like me before?

Thanks a lot to you . I can't find time now to do experiments. But because of your so many test and research that you share, it saves me a lot of time and money.

LOL, yeah i wish there was more of me out there bud to save myself more time and money lol, though everyone at some stage does there bit, and it all helps, including the new guys and their problems.

Ive been into comp building for quite some time bud, since about 1997. I used to overclock but i find these days its not overly needed so i dont realy bother now. I like to modd stuff though, ive got a very compact htpc idea comming up, you wana be good with a soldering iron though.

Trev