On Sunday, December 23, 2012 9:15:57 AM UTC, A.Lee wrote:

So, an electronic ballast has a rating, as well as, in some cases a lamp
type. OK, thats simple. But then, there are so many lamp types and
wattages, that keeping a stock of ballasts in the van for each type of
lamp would be costly.
Testing a few yesterday, it seems they cannot be reliably inter-changed
between types.
Why wouldn't a 36w linear ballast work with a 28w 2D lamp, and vice
versa?
OK, rating at 8w over rating may be asking too much, but why not run a
28w off a 36w ballast?
And a 2 x 36W works with one lamp lit, the other not working, but
wouldnt work with a single, good, lamp fitted?

A fluorescent tube requires the correct power, or close to it, the right V & i which depend on tube width, length and design features, and also the correct heater power, v and i. Hence ballasts that will by design run more than one tube type are a minority.

A 36w ballast on a 28w lamp would overrun the lamp, reducing life expectancy.

Its certainly possible to do some ballast/tube type swapping. Iron ballasts are easily adapted to run lower power tubes by adding the right capacitor, but the calculation of its value is nontrivial and correct calculation is essential. CFL ballasts often run small fl tubes happily enough. In principle modern electronic ballasts can run lower power tubes with 2 capacitors on the output, but its too far from trivial to be practical.

Perhaps someone should make a ballast with multiple settings.


NT