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| Author |
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rcurl
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Wiring and Electrical
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Oct 21 06:06 UTC 1996 |
Black is "hot", white is neutral, and green is ground.
These are your guides, if you expect to stay around.
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| 32 responses total. |
rcurl
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response 1 of 32:
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Oct 21 06:09 UTC 1996 |
I'm using a Dimmer Switch at quite low power for a heater. Often if mains
power fails, it stays off on the heater when power returns. Is this a
property of dimmers, or is it faulty? The device would draw ca. 80 watts
at full voltage, and I'm controlling it at closer to 10 watts (the dimmer
is rated 600 watts).
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scott
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response 2 of 32:
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Oct 21 11:06 UTC 1996 |
There does tend to be an effect where you can't just power up into really low
settings. You are using a lamp dimmer for an electric heater? Sounds like
as long as the wattages are reasonable it should be safe.
Anyway, play around with low settings on a lamp some time. You have to go
to a higher setting to get the lamp to light, then you can dim it down. I'm
not really sure where this comes from, though.
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mcpoz
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response 3 of 32:
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Oct 22 22:39 UTC 1996 |
I have noticed that some of these devices have a different setting for "tuning
down" than for "tuning up." Also, some seem to have some initial threshold
setting which may indicate higher resistance until some circuit is achieved.
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rcurl
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response 4 of 32:
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Oct 23 14:51 UTC 1996 |
Yes, those effects are what I am observing. I'm hoping there is some way
around them - a "hack" ? - or maybe a *low* power dimmer that doesn't have
the problem.
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scott
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response 5 of 32:
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Oct 23 16:23 UTC 1996 |
An autotransformer dimmer wouldn't have that problem. However, one of those
would give you a 10 pound lump of iron to mount somewhere...
I think the effects of the SCR (solid state) dimmer are the result of
thresholds where a current can be sustained, but not initiated. SCRs work
by allowing a little leakage that controls things (the technical explanation
requires a lot more words. ;) )
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mcpoz
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response 6 of 32:
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Oct 24 00:29 UTC 1996 |
While we are at it, some of those electronic ("wave chopper") devices buzz,
get alarmingly warm, and disturb nearby radios. Can't be good!
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n8nxf
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response 7 of 32:
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Oct 24 13:58 UTC 1996 |
Most dimers these days do not come on softly. As you turn them up slowly,
from OFF, they suddenly flash ON to about half brightness. You can then
back them off till the filament is only a red grow. Unless your dimmer
is advanced beyond this turn on point, the lamp will not come back on if
power is interrupted for a moment.
The old dimmers, and a very few of the new ones, didn't do this. It seems
to me that dimmers started misbehaving about the same time that triacs
with bilateral triggers built in hit the market. It may also have something
to do with how many quadratures the triac will fire in, but I doubt it.
You may be able to get your current dimmer to work by replacing the
combined triac / diac (bilateral trigger) with discreet units or you
could find a schematic in, say, the ARRL Handbook for a dimmer circuit. If
memory serves, the one in the Handbook was used to convert a fixed speed
drill to a variable speed drill. It should give you nice smooth control
from OFF to full brightness and come back to whatever setting even after
power interuption.
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rcurl
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response 8 of 32:
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Oct 25 16:26 UTC 1996 |
I found only (unclear) descriptions of SRC and TRIAC diodes in the ARRL
handbook. I've done some more studies on a dimmer, and found that the
hysteresis depends upon the load resistance, getting worse as the load
resistance decreases. This makes the effect very pronounced with
incandescent lamps, since when they are cold, their resistance is very
low. I have some data, which I will post after I've done some more
calculations.
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n8nxf
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response 9 of 32:
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Oct 25 20:41 UTC 1996 |
Indeed. No dimmer circuts in the handbook. Just how to use a dimmer
to control soldering iron temp. I have some schematics at home. I'll
try to remember to look for one.
You findings r.e. load are interesting.
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rcurl
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response 10 of 32:
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Oct 25 22:00 UTC 1996 |
I put different loads (resistance R) on a dimmer, and then found the
maximum output voltage at which the unit would not come on again if power
were turned off for several minutes and then turned on again. I will call
this the Cutoff Voltage, Vc. After it did not come on again, I turned the
dial until the unit conducted again and then measured the output voltage.
This I will call the Restart Voltage, Vr.
R Vc Vr Notes
^^^^^^ ^^^^^^ ^^^^^^ ^^^^^^
108 32 40 80w heater with 7w bulb in parallel
155 19 40 80w heater
558 none - 25w soldering iron
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n8nxf
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response 11 of 32:
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Oct 31 17:02 UTC 1996 |
I suspect it has to do with the gain of the triac. If there is not
enough current into the gate of the triac then it won't turn ON.
Triacs do have a minimum gate current rating to get them to turn ON.
The following light dimmer circuit is from an appication note that
came with a 6 Amp Triac I purchased from Radio Shack Several years
ago. It is typical of light dimmer circuits. When the diac and
triac are included in the same package, the resulting device is
called a Quadrac. Gate to Main Terminal 1 voltage drop is about
3 volts while the current to trigger is about 25 ma.
>---LOAD----,--100uH---,------------------------,
(LAMP) | | |
| 100K MT2
| POT (Triac)
120 vac LINE | |--15K--,--DIAC-----GATE
0.1uF | | MT1
| 0.1uF 0.1uF |
| | | |
>____________|__________|_______|________________|
The 100uH choke is to keep triac switching noise out of the line.
The capacitors should be rated to be across a 120vac line.
The triac has three terminals: MT1, MT2 and the gate. Gate current
flows between the gate and MT1. Load current forlws between MT2 and
MT1. Gate current polarity is + or - , same goes for the diac. The
diac (bilateral trigger, gate trigger diode, etc.) conducts when the
current across its terminals exceeds ~20v.
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rcurl
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response 12 of 32:
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Oct 31 17:08 UTC 1996 |
One more data point, to confuse the issue: with a 150w lamp as the load,
with R = 7 ohms (cold), Vc = 18 and Vr = 39. I think I am going to abandon
this line of research as it doesn't seem to have a future. It did,
however, raise another issue - what voltage does my Micronta (RS) 22-185
digital VOM read on the nonsinusoidal output of the dimmer? I would guess
that it reads the mean (absolute) and then multiplies that by 1.11 to
report rms for a sine wave. It could calculate the true rms, though. The
manual does not say.
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n8nxf
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response 13 of 32:
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Nov 2 15:59 UTC 1996 |
Who knows is the more accurate answer I would guess. I'd use a true RMS
meter. (Got one at the Chelsea swap for $0.75. Another $25 to get a new
display. Nice Fluke 8060A will measure freq. too.) It would be interesting
to look at it with a scope too.
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rcurl
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response 14 of 32:
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Jun 1 05:20 UTC 1997 |
Still not able to control that 80W resistive load at low power with a
dimmer - I've started it and dialed it down to 12V (less than Vc for
that load), and even left undisturbed it cuts off after a while. I am now
considering trying working it through a 120VAC->25VAC transformer. I am,
however, a little leery about putting a transformer on a dimmer. Phases
are shifted, and if one side of the triac goes, I've got DC! What do you
think?
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scott
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response 15 of 32:
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Jun 1 12:24 UTC 1997 |
The output of a triac is pretty messy... The transformer may have to dissipate
some of the higher partials as heat?
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scott
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response 16 of 32:
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Jun 1 12:25 UTC 1997 |
What kind of cable would I use to run a buried line out to a lamppost?
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mcpoz
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response 17 of 32:
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Jun 1 13:50 UTC 1997 |
There is a grade of cable certified for underground burial (at a specified
depth). I think it is "SE" grade, but any electrical supply house would know
what it is.
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n8nxf
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response 18 of 32:
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Jun 2 14:48 UTC 1997 |
Rane, perhaps you should call some of the electrical shops around town and
see if one of them can't set you up with a decent dimmer that doesn't have
the threshold problem your seeing. Madison Electric, etc. I know they
exist, though they will cost a little more.
On another note: I got a copy of _Wiring Simplified_ a couple of weeks
ago. Pretty good book for the money. I was, however, disapointed that
they didn't cover underground service enterances and meter connections.
Nor did it cover how to handle wiring in metal studs and under metal
floor trusses. Oh well, what can one expect for $7. It would help scott
with his question though.
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scott
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response 19 of 32:
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Aug 13 17:23 UTC 1997 |
I need to replace my fusebox. I've currently got a 60amp service (not the
original service, it looks like) and a little 5 circuit box. I'm happy with
60 amps, since all the major appliances get their heat from gas. I do need
more circuits, though. Any recommendations for an electrician to do the
transplant? I'd do it myself, if it weren't for the sticky problem of how
to turn off the power out at the pole, etc.
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mcpoz
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response 20 of 32:
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Aug 13 23:00 UTC 1997 |
Can't you pull your meter and thus break the circuit outside your house? If
not, I believe Edison will do so if you call them. In any case, I'd pull it
myself and call them right away and tell them what I did and they will come
back out and seal it.
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n8nxf
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response 21 of 32:
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Aug 14 11:43 UTC 1997 |
Yep, that's what you do. Call your provider before you do it just to be sure
it's not something they need to do. I'd pull your old box and put in a new
one. I even have a book that shows one way to do it. Looks pretty simple.
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scott
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response 22 of 32:
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Aug 14 12:13 UTC 1997 |
Hey, can I borrow that book?
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n8nxf
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response 23 of 32:
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Aug 15 11:18 UTC 1997 |
Sure. It's only a few pages out of book on general home repair and
maintenance.
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blh
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response 24 of 32:
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Sep 13 00:36 UTC 1997 |
Years ago when I did replace a service at Six Lakes (remnember doing the
wiring on the annex scott?), I ws able to take it off, and connect it back
up with no problem.
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