I posted earlier about how I got a 120/277 autotransformer to power my 35 watt Beta 5. It was rated at 50 VA, and after a few minutes smelled like it was burning and was too hot to touch. I measured it on my Kill A Watt and found it was pulling 80 watts, and 140 VA!

I tried a different lamp on an 120/60 autotransformer ballast. Same result: 80 watts with 60% power factor.

I understand that kind of power factor, but 80 watts? How can this be?

The ballast losses and losses in the small transformer. A 50VA unit would be made for efficiency of about 80..90%, so 5..10W losses when loaded by the rated 50VA. By loading it by 100VA, it means the transformer losses would quadruple, so easily become in the 20..40W range. Just within the transformer.

If you properly compensate the power factor on the 277V side (if I calculated well, it would be something around 4.5uF rated at 330VAC of permanent loading), the loading and losses in the transformer will drop back to it's rated range.

Thanks. Is that the same issue on my 120/240 volt autotransformer type ballast. The ballast has two leads for a capacitor, but does not specify what value is needed. I measured a power factor of .6 and about 140 VA, same as my European choke type ballast setup.

Thanks. Is that the same issue on my 120/240 volt autotransformer type ballast. The ballast has two leads for a capacitor, but does not specify what value is needed. I measured a power factor of .6 and about 140 VA, same as my European choke type ballast setup.

Power factor 0.6 and 140VA means the capacitor has to provide 140*sqrt(1-0.6^2)=112VAr of reactive power. With the multitap ballast it is most efficient to use the highest voltage tap for the capacitor where the capacitors are still available, so the 240V one in your case. That means about 5.1uF (or 5uF if that would be more readily available), rated for at least 270VAC/60Hz of permanent loading.


But with the 120/277V transformer and PFC capacitor be aware, when the lamp would not strike, the transformer becomes again heavily overloaded, this time by the capacitor current. So better use some thermal cut out contact to protect the transformer...

I have the same issue with my 18w SOX setup. Lamp runs just fine but ballast pulls like 34w and gets untouchably hot fast!  Some members believe there is a fault in it

I have the same issue with my 18w SOX setup. Lamp runs just fine but ballast pulls like 34w and gets untouchably hot fast!  Some members believe there is a fault in it

I measured my 18 watt, and also got 33 watts input.

Is there any reason why they have so much loss  ?  They are supposed to be a very efficient light source.

Perhaps i'll have to transplant my lamp and gear into another fixture (before going into service) that allows better heat dissipation or the addition of heat sinks on the ballast itself

55 watt LPS = 78 input watts, .8 power factor