Question on Ballasts

[cperez]

Patrick,

This is very interesting news.

Realizing that the amount of UV output can vary, I wonder if it would be a close enough approximation to reality to perform the following calculations:

1) Old system total watts is 162 = 6 * 27 watts, while your new system is 240 watt = 12 * 20 watts

2) Percent increase in available UV in your new system based on total watts = 48 percent (calculated as x - 1 = 240watts/162watts - 1)

3) Your old system increases the total print time by 40 percent over your new system (calculated as 14mins/10mins * 100)

4) Your old spiral system produces a watt to exposure minute ratio of 11.57 to 1. Your new tube system produces a watt to exposure minute ratio of 24 to 1. Thus showing (if I did everything correctly) the efficiency of the spiral bulbs in this application.

What this seems to mean is that your old system is more efficient than your new system. I wonder... hold on... there's something that I need to consider... I'll figure out what that is after the holidays/holandaise... [burp]

It seems that by adding 40 percent more light to the old spiral bulb box (adding approx 60 watts by installing 2 more 27 watt spiral BLBs) you might be able to achieve a similar print time to your new tube-type system.

It would be very interesting to observe the all up costs of UV output by adding up the ballast and bulb costs and comparing that number against the total cost of the spiral BLBs. Maybe something that calculates the cost per watt?

It seems that watt for watt the two systems are nearly equal. Sandy King may have pointed this out in the past. I'll have to go back and look. Though if my calculations are correct, the spiral BLBs are better at outputting UV than your new tubes.

Amazing what information and numbers will do to a person.

I just wanted to thank everyone for their support. I just finished my lightbox and am really pleased with the results. I used 12 20-watt tubes , spaced 1 3/4 inches apart and 3 inches above the paper. Using the electronic ballasts mentioned above, I am getting a time of 4 minutes for 90% black on step 4 on my step wedge.
Thanks again and Happy Thanksgiving

 

[Patrick Kolb]

Hi Chris,

Watt for watt, the light box using spiral lights is about half the cost of the one using tubes, of course you have to factor in "do-overs", my wife only grants me very limited access to power tools.

The 24 inch tubes is a very big box compared to the spirals, and I was wondering if the density of the lights has some impact on the times. I think Sandy has mentioned that. I finally went with electronic ballasts that had a ballast factor of .92, does anyone know how this compares to the spiral lights? Maybe this could account for some of the difference in times.

Chris, with the long weekend, you are welcome to come over and see the box and bring some coated paper and we can give it a try.

Patrick

 

[nworth]

The "ballast factor" noted in the original post looks like a power factor specification to me. Power factor is a measure of how efficiently the lamp and ballast use AC electrical power. Possible values run from 0 to 100 percent (i. e. 0 to 1), the higher the better. The ballast with the 61 rating is probably a simple inductive ballast (iron cored coil). These are usually the cheapest. They work fine, although you pay for somewhat more electricity when using them. Some ballasts add a capacitor to bring the phase of the current and voltage in the lamp closer together and thereby to use power more efficiently. These have higher power factors. The one rated 85 is probably one of these. True electronic ballasts usually have high power factors, but some are made poorly and have short lives. Some ballasts that are marked as "elecrtronic" are really just cheap coil ballasts.