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Thread: Fluorescent lamp ballasts as PS chokes?

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    Supporting Member jmaf's Avatar
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    Fluorescent lamp ballasts as PS chokes?

    So today I came by a big pile of fluorescent lamp ballasts at a junkyard. They're inductive, not electronic, rated at 380 VAC and the guy's selling them for pennies. I think they came off street lighting, they're really rugged and heavy (lots of potting).

    I assume the first problem with using these as DC filter chokes is the iron core as they're probably not air gapped? You guys see anything else that could go wrong?

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    They vary in spec according to the rating of the lamp fixture. Quite a few people have used them both in PSUs and as output-stage plate loads (more so with Hi-fi builds) with varying results. The main issue is space - they're quite large for their rated inductance. Insulation is excellent and they often run hot in their intended application. A guy I know used a large lamp ballast in an SE parafeed amp along with a P-P transformer that had one side of the primary open. That way he got a cheap amp and used scrap parts.

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    Supporting Member jmaf's Avatar
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    Quote Originally Posted by Mick Bailey View Post
    They vary in spec according to the rating of the lamp fixture. Quite a few people have used them both in PSUs and as output-stage plate loads (more so with Hi-fi builds) with varying results. The main issue is space - they're quite large for their rated inductance. Insulation is excellent and they often run hot in their intended application. A guy I know used a large lamp ballast in an SE parafeed amp along with a P-P transformer that had one side of the primary open. That way he got a cheap amp and used scrap parts.
    Thanks for the reply. Interesting idea there. He probably also ran into the core saturation problem using a PP xformer on a SE project?

    I later found a Youtube video where such a ballast is taken apart and unpotted. I haven't ventured there, I guess I'll make it a weekend hobby project to properly test one of these.

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    If they're all the same model, sacrificing one to learn more about them seems like a good idea. Just be careful if they're potted with PCBs (not printed circuit boards!)
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    Quote Originally Posted by jmaf View Post
    Interesting idea there. He probably also ran into the core saturation problem using a PP xformer on a SE project?
    The DC is in the choke. The PP transformer is AC coupled.

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    Exactly. Using the choke as a plate load and a capacitor to AC couple the OT means no DC through the primary. So you can get away with a P-P transformer in an SE build. Or in this case, half a P-P transformer. It neatly sidesteps having a dedicated SE transformer. I never got to hear what it sounded like, though. Making a sound is one thing, sounding good is another.

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