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new ballast

Discussion in 'Troubleshooting and Repair' started by tcarterg, Apr 6, 2011.

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  1. tcarterg

    tcarterg

    7
    0
    Apr 6, 2011
    I'm replacing a ballast for an under the counter light and the specs are hard to read i'm pretty sure they are:
    Pri Volt: 120V ~ 50/60hz;
    Sec volt: 12.8v ~> 20khz;
    Input 0.5 amps 60va; Output: 5v amps.

    At first i thought the SL-728 was a good replacement for this but there are only 3lights each pulling 4watts, so i have a min wattage of 12, and the SL-728 has a min of 30.

    I searched around the SL-728 was the closest match I found. I'm about to just go and buy the whole counter light again, but i though i'd see if anyone here knew where to find a replacement ballast?
    Thanks
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,374
    2,769
    Jan 21, 2010
    That's a transformer, not a ballast. (well, maybe it's not a transformer either, but it's certainly NOT a ballast)

    I see no restriction on minimum load, just maximum.

    There are several other models with lower power ratings too.
     
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Why don't you just get the SL-518 then (same place)? It's cheaper, has a 10W minimum load, and is rated at the same power as your original transformer (60W).
     
  4. tcarterg

    tcarterg

    7
    0
    Apr 6, 2011
    Not a ballast you say? I don't know much about electronics, just what i've gathered when i was a kid working with my father. A ballast restricts current and a transformer, well, transfers power/energy, right? That's why i said it was a ballast, more of an educated guess.

    I looked at the SL-518 and it looks good to me. I didn't spot it before because i was looking strictly at ballasts and it didn't come up in the search.

    Thanks again!
     
  5. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Yes, a ballast restricts current by it's impedance which is neccessary to counteract the negative resistance of the gas discharge lamps they're made for.
    If you connected those lamps directly to the mains or to a (normal) transformer they'd blow up as soon as you ignite them.
    A transformer transforms one voltage to another, it does not (normally) restrict current.
    I just searched for "electronic ballast" on that site and the 60W SL-518 came up as the first choice (of 96). The heading (of the 728 too) says transformer.
    They probably include ballast as a search term for those items to make sure customers stumble across/ find them (even if it's incorrect).
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,374
    2,769
    Jan 21, 2010
    Am I blind? I can't see where it mentions a minimum load for these?
     
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    It doesn't - in the spec text section on that site - but it does on the label in the picture of the device itself. Should've been included in the spec's listed though.
    I believe these transformers work pretty much like like CFL ballasts; the lamp current is what feeds back to and determines the base drive for the switching transistors.
    Too little and they won't saturate.
     
  8. tcarterg

    tcarterg

    7
    0
    Apr 6, 2011
    Thanks for the additional information Resqueline. I ordered the SL-518 and expect that they'll work just fine. It does look like they're playing with search terms/keyword for exposure purposes.

    So you said it's not a ballast and possibly not a transformer. Than what is it?
     
  9. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    It is a transformer, albeit an electronic one (that has some restrictions/drawbacks compared to an ordinary iron mains transformer). It puts out high frequency AC.
    A CFL ballast has a built-in inductor after the transforming thing. This sets the lamp current, and makes it a ballast. The electronic halogen lamp transformers lack this.
     
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