Where exactly do you check for polarity at the ballast connections??

Easiest and most reliable way if you're testing many ballasts is to simply set up a fixture with known good lamps, wiring, sockets, etc., with quick connect terminals of some kind for the ballast wires.

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"netvoy" writes:

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First, the polarity. I think what they meant was just wiring it properly, per the instructions or diagram. Each wire of the same color (red, blue, yellow) should be interchangeable. There is no + or - here, it is all AC current. While the voltage output is somewhat high (600v) the current for a

High output lamps are 800mA, standard lamps (in north America anyway), standard T12 lamps are 430mA, T8 lamps are 230mA. At 600V, the output is dangerous, it only takes about 200mA to kill you. As you say, the two reds, blues, or yellows are interchangeable and it's AC so there's no polarity.

Yes, but the 600 V won't be capable of anywhere near 200 mA. Not to say it isn't dangerous, but not quite as instantly deadly.

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Of course, but it's worth mentioning for the novice, wouldn't want them to get the idea that it's completely safe to go touching those wires. I've been bit by the output of a ballast before and it wasn't fun, if I'd been standing on a ladder or something it could have caused quite an injury.

It probably would not be practical in my situation for I have many types of ballast and fluorescent combinations in this 10 story (800+ rooms) building. The type of ballast at any given time will be different. I was hoping they were all designed similarly and to be tested electronically somehow easily. Mind you, if management found out that I was spending time on setting up something that ideally would save on costs around here they likely fire me for wasting time. Yes, they are that limited here.

Allow me a couple of further questions: Voltage output is 600v only at startup correct? What would be a non-self-limiting secondary? The ballast is from the Advance Transformer Co. a 277/60hz/Class P unit. A Mark III Kool Koil High Power Factor Series Ballast specifying at 35w rs lamps 460 Ma Max???!!! I'll definately keep looking for a schematic on the web. Thanks

I'm not sure at this point what you are trying to do. If you have a fixture that doesn't now work but used to and has power to it, and installing new lamps doesn't help, then by process of elimination, the most likely cause is a bad ballast.

If you have a bunch of ballasts sitting in a box that you wan to test, it's still probably easiest to just wire each one up to a dummy fixture and check it under real life conditions.

Else, you could measure voltages or resistances comparing a known good ballast of the same model to the suspect ones.

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Magnetic rapid start ballasts are pretty simple, aside from the power factor correction capacitor on the primary, a ballast is nothing but an inductively leaky transformer with the secondary tapped at each end to provide voltage to heat the cathode filaments in the tubes and a separate tap for the middle set of cathodes (both lamps are wired in series.) They rarely fail and when they do it's usually fairly obvious as they tend to run real hot and scorch the label or drip tar until the internal thermal fuse blows. A quick check I suppose would be to measure the voltage between one of the blue wires and one of the red wires, you should get several hundred volts. Then measure between the two reds, between the two blues, and between the two yellows, each of those pairs should have just a few volts. An even quicker check is to have a set of known good lamps and pop them into each fixture in question.

Basically, I am trying to understand operation and test procedures for the ballast as is without adding anything extra components no bulbs, no end hookups ; I wanted to picture precisely the how it works with the simplest setup (in this case just tie it up to power line and use the multimeter to figure out if it is good. It is apparently a bit more complex than that. My company's philosophy is to ruthlessly minimize expenses --does not matter if it is a savings in the long run

-- yes we know better. So they are unwilling to buy extra anything and it is not a financial priority expense on my part ( actually more like financially unsound for me to invest in any parts due to personal debt ). If i can offer them the knowledge that I can do for them but this is primarily for me; I like to know how things work.

It is unlikely that I will have flourescents, or any other parts to test the ballast no matter how smart of an idea this is; as the budget allowed to us does not even cover half the bulbs we replace in this building per month. We are always short a couple of boxes.

This is basically what I needed to get to. Obviously a complex situation for every ballast is a bit different. And yet up to this point not clear what voltage value for my given chosen test point, mind you, it likely changes value once the flourescent bulb is fully warmed up.

Thank you very much for the info.....

This is very valuable info. I now understand all practical issues with the repair of the unit at hand at least I believe that. In my particular situation we have a misapplication error; the bulb does not match the ballast. It is a two ballast four bulb install; you can bet that we have no replacement parts. One of the ballast has an almost invisible leak and is darkened. Somehow I was expecting at least one to work.

To conclude : 1) Voltage values at ballast check points are probably irrelevant since you have to see the unit in operation to know it is good; the presence of the proper value only tells you that the ballast is likely to be good(ok to save it for further actual use testing). If it is good; it must match the bulb in question.

Only one more doubt : once the bulb is fully warmed up do the voltage values change at the test points?

Tkx for all info....

Yes, the voltage values change as the lamp warms up, as well as from one lamp to another depending on age and manufacturing tolerances. The voltage is not a function of the ballast though, but of the lamp itself, which having a negative resistance curve will settle at whatever voltage it "likes" at the current the ballast is pushing through it. A ballast is a constant-current source whos voltage output will vary depending on the load, unlike the constant-voltage source you get from a wall outlet where the current varies depending on the resistance of the load. The purpose of the ballast is to convert one to the other and due to its very nature it can only be tested accurately while connected to a suitable load.