"John Keiser" wrote in message
news:aPidnUviOuk2XMPUnZ2dnUVZ_v3inZ2d@hawaiiantel. net...
I notice that some - but not all -electronic ballasts specifically mention
"1 or 2" bulb operation.
Since I have 2 single bulbs fixtures that will need new ballasts and I
happened to have on hand 2 "2 bulb" electronic ballasts of more than
sufficient wattage, any electrical reason why I could not make use of
these?
Thanks for any comments or wiring suggestions.


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AFAIK, this 'problem' was originally one that was associated with
non-electronic ballasts i.e. ones that were a pure line frequency
transformer. To have the voltage at the output anything like the specified
value, the load had to be known, and it was always recommended that if a
bulb failed, it should be replaced ASAP, as the output voltage would
increase with the reduced load, over-volting the remaining bulb(s). It's
also important of course, not to overload such a device with too many bulbs,
hence the wattage rating on it.

It's a little different with the electronic ballasts in that they are
fundamentally a switch mode power supply, so in theory, you would expect
them to give a reasonably stable output whatever the load, up to some
specified maximum amount, where you would start to overload it. However, all
the ones that I've seen, this side of the pond at least, only nod in the
direction of a 'proper' switcher. The output is a high frequency square
wave, modulated at line frequency, due to the fact that that there are no
primary or secondary-side filter caps. There is also no kind of regulation
applied to the design. So, the short answer to your question is that I think
the only way that you will see if the ballasts that you have are suitable
for continuous driving of a reduced load, is to stick a 'scope across the
output, then load it with first one bulb, and then two, and see if there is
any significant change to the output waveform, or brightness of the first
bulb, when the second one is connected.

Arfa