I have a halogen torchier lamp that uses the type T bulb. The lamp
will not lite. I've already replaced the lamp but I'd like to make
this a "project." The lamp uses a rheostat type switch and I was
wondering if anyone had any ideas. I was going to use my multi tester
to check to see if juice is getting through. The bulb is new. If no
juice is getting through, should I check the switch next? Anybody know
of any circuitry inside the lamp? I haven't begun to take it apart
yet. Any help will be welcome.
Thanks in advance
What do you mean by "rheostat type switch". Do you mean it's a
continuously variable solid state dimmer?
If so, as previously stated, check continuity from the cord plug prongs
to where the cord splices to the switch/lamp socket.
If it IS a continuously variable solid state dimmer and it's bad,
chances are you'd not easily find an economical replacement. I'd
consider replacing it with a simple on-off switch if you want to keep
that lamp for occassional use.
Dimmers have been known to be burned out when a bulb burns out. The instant
the filament on the bulb burns, there is a spike in voltage (or was that
current) you might see as that last bright flash as it blows out. This
spike can and does damage the SCR (transistor looking 3 pin device in the
dimmer control) if its current rating is borderline (as it may be in cheaper
switches). Better dimmers have a device rated for a much higher inrush
current but it cost a tiny bit more.
You're right, and reverting to my usual pedagogue mode I'll add that the
effect is called a "tungsten arc" and it can create a near short circuit
sized current spike which can easily blow out the small sized triacs
used in solid state lamp dimmers. It happens maybe once in every 5 to 10
I've seen cases where a 75 watt bulb blows with a bright white flash
when you flip the wall switch on, and when you replace the bulb you find
that you have to go and reset the panel breaker for that circuit before
you can light the new bulb.
What happens (As explained to me.) is that when the bulb filament
breaks, if the broken ends don't snap away from each other fast enough,
a small arc between them begins vaporizing the tungsten filament
material, and filling the bulb with a conductive metal vapor through
which current continues to flow. The effect "runs away" and the current
increases as more of the filament end lengths melt away. I've heard that
some "better" brands of lamp bulbs are made with a deliberately thin
section of lead wire inside their bases to act as a fuse to limit the
severity of that current surge.
I used to occasionally blow out the solid state "touch dimmers" in our
bedside lamps when their 150 watt bulbs blew. I did the numbers on it
and installed fuse holders with 3AG 2 amp quick blow fuses under the
lamp bases. I've had to replace a few blown fuses since then when bulbs
burned out, but never again a dimmer.
A triac is essentially two SCR's in parallel. If you remove the switch
assembly and the circuit board attached to it, you'll likely see a 3 legged
device. This is the triac. Triacs control current in either direction, and in
this application, acts like a high power switch. If you can find a part number
on it, I can try and look it up for you.
I've had 3 or 4 crap out like that. I throw away the dimmer, and replace it
with a on-off rotary for about three bucks and ten minutes. (I hate the
buzzing the dimmers make, so only use them on full anyway.) I got the lamps
free, from when I lived in the apartments. At the end of the month (aka
moving day) there were usually 2 or 3 sitting by the dumpsters. Typical ones
these days, the 20 buck specials, are much crappier than the 50 dollar ones
that were common when the style came on the market. The real cheap ones I
left in the dumpster, after stealing the bulb and the little glass
half-round mantle thing for my spares box.
Simple switches (without dimmers) that can be fitted into torchiere
lamps (maybe requireing enlarging a hole) are available at some but not
all hardware stores. Home centers may have these, but I never checked
Radio Shack has a lot of switches but few with adequate ratings (at
least 2.5 amps simultaneously with at least 120 volts AC) and they are
much more likely to require soldering than switches that some hardware
stores have. Also, Radio Shack switches appear to me to be lower in
quality than most that I see in hardware stores - I would only use a
Radio Shack switch on a 300 watt halogen torchiere if it was rated at
least 4 preferably 5 amps 125 VAC.
- Don Klipstein ( firstname.lastname@example.org)
Pretty easy, really- unplug the lamp (duh!), unscrew the nut on the switch,
and then the joint in the middle of the pole to get to the switch, fish it
out, cut the wires on the lamp side of the connectors, connect the new
switch with new wirenuts or insulated crimps, and reassemble. Most places
like Lowes have the switches. It helps to take the old switch along to match
the sizes, especially the switch barrel that sticks through the hole. Don't
forget to buy the wirenuts or crimp connectors, if they are not included in
the bag with the switch. Only tools needed are strippers and maybe slipjoint
pliers to get the nut off the old switch. Note that the pretty plastic trim
knob from the old switch probably won't fit the new one, so all you will
have sticking out is the skinny knurled knob. You may wanna remove the bulb
and glass guard thingie before you start to reduce chances of breakage.
Unless it was really high end stuff just toss the damned thing. I used to
fix them and finally decided they weren't worth the effort. Could be a
component in the dimmer (it's unlikely to be a rheostat, more likely a
triac circuit) or it could be that the socket has given up the ghost.
Either way once it starts giving trouble it's going to be a continued
annoyance until it manages to destroy itself beyond economical repair.
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