How to tell if a ballast works?

[Coderabit2]

I have a magnetic ballast that I am wanting to sell, but I'm pretty sure the bulb burned out and not the ballast. Is there anyway to check without getting a bulb?

[Tom Fay]

Check the output with a volt meter.

[renisel]

I don't think that simply checking it with a voltmeter would be sufficient. It could be delivering current, but not doing it in the manner necessary to start the bulbs. I think the only sure-fire way to check is to put in a bulb that you know works. Maybe you can find somebody who is going to be changing their bulbs soon and will give you their worn but still operational bulbs.

[Tom Fay]

A balast takes 115 VAC and ramps it up to 600 VAC (typical fluorescent balast). An electronic balast does this with transistors, a magnetic balast does this with a transformer. The typical transformer failure is a broken coil winding, when this happens the outout is zero. So if he gets 600 VAC on the output the balast is good.

[PaulErik]

What type of ballast is it? The testing method will be different for different ballasts.

Depending on the ballast you can use a volt meter / multi meter to measure the voltage. With some metal halide ballasts the output is pulsed and can reach 6000 volts. Most meters are not compatible with this type of output and will fry your meter.

The only metal halide ballasts that do not generate a high voltage starting pulse are standard (probe start) magnetic ballasts. HQI, pulse start and electronic ballasts have a high voltage starting pulse.

With magnetic fluorescent ballasts you can measure output voltage. The Open Circuit Voltage (OCV) is usually listed on the ballast label. Depending on the type (pre heat, rapid start, instant start) the OCV will vary but can be as high as 1000V (with some instant start ballasts). Make sure the meter is rated properly.

[Coderabit2]

This is the ballast http://www.hellolights.com/index.asp...PROD&ProdID=68

When I hooked up the Multimeter it read 285VAC does that sound right?

[PaulErik]

That voltage is correct for a probe start 175-watt ANSI M57 metal halide ballast. You may also want to check the capacitor and see if it is within specs. The capacitor has a label showing the correct value.