8mm Forum: Difference between bulb voltages.

This is topic Difference between bulb voltages. in forum 8mm Forum at 8mm Forum.

To visit this topic, use this URL:
https://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=001202

Posted by Alan Gouger (Member # 31) on May 23, 2005, 10:13 AM:

Hey guys.

I may mod my Fumeo and add a brighter bulb. It would be real easy to add a 300 watt 120V but there must be a reason our projectors use low voltage verse 120v or 220v lamps.
A few questions come to mind. Do the low Vs run cooler. Would a 120V lamp of the same wattage burn any brighter or should they be the same in theory.
Sorry, I have no expertise in this area.

My thinking is it would real easy to install a 300w 120V and plug it direct into the wall outlet just for testing to see if the increase in light is worth the effort. Just as long as I buy a quartz bulb there would be no modification needed for the mounting of the lamp and no stress on the projectors power supply for this test.

Thanks!!

Posted by Rick Skowronek (Member # 385) on May 23, 2005, 01:12 PM:

As to why the projector manufacturers decided on low voltage/hi-wattage lamps I can only guess that the brighter quartz bulbs of the day could be manufactured cheaper in lower voltage models. The transformers would have to be (and are) made much beefier to handle the step down from 120 VAC line to these voltages and required current/watts so no savings could be had in overall cost.

As to wattage vs. voltage, that I do know and it makes absolutely no difference. Current is the only variable there so a 120 VAC 150 watt lamp would draw roughly 1.25 Amps of current. A 15 VAC 150 watt lamp would draw 10 amps of current from the 15 volt source (hence the beefy transformer in the projector). The light output and heat, as long as bulb design was similar (reflector, shape, filament type and placement), should be pretty close.

Other than that, I leave the fesibility and other considerations up to the considerable talent in the forum.

Rick

Posted by David Pannell (Member # 300) on May 23, 2005, 01:29 PM:

You're absolutely right, Rick.

I've been down a similar road with regard to 120 volt vs. 240 volt lamps for my Elmo E-80 (see much earlier posts).

This particular projector's handbook stated that you could use up to a 750 watt lamp at 120 volts, but only a 500 watt lamp at 240 volts. As there is no lamp transformer in this machine, current could not be, and was not the issue.

NOTE: Although in the UK, our home is wired for both 240 and 120 volts, so I can use either.

To cut a long story short, it turned out that the 120 volt, 750 watt bulb had a much more concentrated filament arrangement, whereas a 750 watt, 240 volt bulb had its filament spread over a much wider area.

A 500 watt, 240 volt lamp had exactly the same filament configuration as the 750 watt, 120 volt lamp.

It then followed that the condenser lens in the projector couldn't pick up and focus all the light from the 750 watt, 240 volt lamp, whereas it could for all the others.

Moral of the story: when trying a different lamp, examine the filament configuration. It must be the same as the OEM for max. brilliance on the screen!

Good luck!

Dave.

Posted by Tim Christian (Member # 48) on May 23, 2005, 04:23 PM:

Lower voltage filaments are smaller than high-voltage filaments. The lower voltage means that filament turns can be closely spaced without risking arc-over, and that there are fewer turns anyway. A more compact filament makes it easier to focus a large proportion of the light onto the film. With 8mm this is a particular problem. As it is, only about 10% of the available light gets to the screen (of the 2% of the power that gets converted into light!).

Posted by Rick Skowronek (Member # 385) on May 23, 2005, 04:42 PM:

Thanks, Tim.

That makes a lot of sense as well. Had to be several reasons why they went that direction and that makes some real sense to keep "the point of light" small and focusable by the lamp reflector to put most of the light on the film gate.

Rick

Posted by David Pannell (Member # 300) on May 23, 2005, 05:19 PM:

Exactly, Tim.

I'm sure we could go on for a long time listing the different reasons and variables on this one.

At least it's good to know we're all talking the same language here.

Dave.

UBB.classic^TM 6.3.1.2