I've seen several people using ballasts to power other light sources, for example using a 70 watt Metal Halide ballast with the igniter removed to power a 100 watt Mercury vapor, or a 39 watt magnetic Metal Halide to power a 40/50 watt Mercury vapor.

Do you know of other ballast / light combo's that work ? I was thinking of making a list and posting it up here so people can see what works, as some ballasts are getting hard to source..

The arc voltage is a function of the lamp. The current is then function of the ballast, that depends on the ballast itself, the arc voltage it sees across the lamp, and the line voltage

If your lamp is the same arc voltage as the intended lamp for this ballast, it will get the same current and about same power

If your lamp is not, this depends on the ballast :

 - With CWA the ballast is a current source. The lamp arc voltage does not have much effect on the current, and the lamp power is related mostly to the lamp arc voltage

 - With chokes the ballast is an inductive impedance. Higher lamp arc voltge will lower the current, lower arc voltage will make it higher. The lamp power is still related more to the voltage than to the current

 - HX can be seen as step up transformer + choke combined in one device, so they behave about same as a choke



Some calculations :

Lamp power factor is about 0.85 for most HID and FL lamps. This is caused by the voltage waveform, which is approximately squarewave

Lamp rated power = Lamp apparent power * 0.85

Lamp apparent power = Arc voltage * Arc current



In a choke (applies also to HX), the voltage drops are :

 - The lamp = Arc voltage

 - The ballast inductance = Arc current * Reactance = Arc current * 2 * pi * Frequency * Inductance

 - The ballast wire resistance = Arc current * Resistance

The voltage drop on the inductance is at 90 deg phase shift to the other two. The overall voltage is whats supplied from the line with a choke, or the OCV with HX :

Supply voltage = sqrt ( ( Arc voltage + Wire resistance voltage drop )^2 + Inductance voltage drop^2 )

By solving this equation for the current, you get close estimate of what the current will be



Most ballasts dont have the wire resistance and the inductance rated on them. But you can measure the resistance and estimate the inductance from the rated current with the rated lamp if you know the lamp's arc voltage

With a choke, you can also measure the current when it is connected across the line without a lamp, and put that into the equation (omitting the lamp arc voltage) to find the inductance - though most chokes are getting closer to saturation in this mode and the inductance you'll find is somewhat lower than what it really is when working normally



Some example :

http://www.lighting-gallery.net/index.php?topic=4137

The 1.15 in the calculations is 1/lamp power factor, ie. 1.15 = approximately 1/0.85



If the current is okay for the lamp, it will work - if the current is off it will be underpowered or overpowered respectively. Most lamps do handle little under or overpowering

With ballasts, they may be overloaded by some lamps :

 - CWA is overloaded by too high voltage lamp (more power input)

 - Chokes and HXs are overloaded by too low voltage lamp (higher current)

They might be able to stand little overloading but most of them are borderline on thermal design, so avoid it



Some lamp combinations from 230V hemisphere -

40W Mercury on 18W PL + 26W PL ballasts in parallel (fairly close)

70W HPS on 80W Mercury (lamp underpowered, ballast overloaded - not good but they appear to still handle it)

80W Mercury on 2 36W T8 ballasts in parallel (fairly close)

125W Mercury on 3 36W T8 ballasts in parallel (fairly close)

125W Mercury on 70W HPS/MH (somewhat underpowered)

125W Mercury on 100W HPS/MH (almost spot on, little overpowered)

400w Mercury on 400W MH (it actually is the same ballast, just not always rated for Mercury anymore)

One time I tried a M59 MH 400W lamp on my 1Kw MH ballast tapped to 208V with 120V fed into that-Did work!Guess you can do that in an emergency.Was my only ballast "Mr Wizard" experiment.

I connected some double ended low pressure sodium lamps namely SLI/HO 200W on to a VHO F96 215W RS ballast. It did match the voltage fairly close and the OCV is high enough to ignite the tube instantly without ignitor or starter.