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On Wednesday, February 27, 2013 1:24:33 AM UTC, Arfa Daily wrote:
wrote in message
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On Tuesday, February 26, 2013 11:47:54 AM UTC, Arfa Daily wrote:


There are various step down switcher topologies, I don't see how we
could
know which is in use there. I guess you don't have the space to slot in
a
complete halogen lamp ballast.

I guess there are a couple of 'flavours', but from what I've seen, most
seem
to be chip-less self-oscillators that have no primary side smoothing on
the
raw DC, and just a transformer at the secondary side. This one certainly
falls into that category. And it *is* effectively a complete halogen lamp
ballast - allbeit an open frame one. The answer to whether there's space
to
slot in a 'packaged' off the shelf ballast is yes, but there are a couple
of
reservations. Firstly, I would have to re-instate the hold-off relay
that's
on the existing board, as an external component. But the potential killer
for doing this, is that the lamp is 24 volt and 150 watts. Most of the
'electronic transformers' readily available, are for 12 v halogens. There
doesn't seem to be many with a 24 v output, and especially at 6 amps ...
This is actually a 'personal' project rather than a paying customer job,
so
it's not really important how long it takes to get to the bottom of it.
Now
that I've discovered that it does run just fine with a reduced input
voltage, it shouldn't be too difficult to get to the cause. Says he,
confidently ... ! d:-)
Arfa

12v 6A = 72w, a pair of those would surely be quick, cheap & easy.


NT


Well, I've fixed the bloody thing now, and I have to say that it had me
fooled. The problem turned out to be a knackered lamp socket. Looking closer
at the specs, it's actually 250 watts not 150 as I first thought, so even
with the forced air cooling it has, the lamp house runs pretty damned hot,
and the lamp socket with it. Basically, the ballast is not a very good
design. It doesn't run at all with no load on it, and as the lampholder was
effectively open circuit, it indeed didn't run, which was the first way that
it fooled me. The second way was that not only does it not run with no load,
it only runs properly with the full designed load. So when I had it out on
the bench, and just had a couple of 50 watt 12 v halogen lamps in series as
a test load, it ran, but only until the mains input voltage got to 160 v on
my variac. Once it went past that, the switching activity progressively
died, until it stopped altogether again.

I had a replacement ceramic holder to hand, as I fix a fair few of these
lighting fixtures, so I grafted it in, and reconnected the lamp wiring to
the ballast. This time, it kicked up and ran the lamp at full intensity
without issue, so that's one to remember if I come across another of this
particular fixture type.

Arfa