Small Space Heater Control.

OK, I scanned a hand sketch of my house current powered, small space 
heater control circuit, that I use for my seismograph.   Wow, that was a 
mouth full,, ha!  Anyway, I use a 100 watt light bulb in one of those 
ceramic sockets, mounted to a hard plastic type box,, could be bakelite 
(spell)??

The original circuit was designed to control up to 25 amps and used both 
halves of the power cycle!  I modified it to reduce parts, and power, 
for better price, so it only controls a half cycle and about 3 amps max, 
which should easily control 150 watts!  In the 11 years or so of 
operation,  I've had to change the light bulb twice!   If I ever come 
across a low watt, screw-in heater (I think they use something like that 
in incubators?) I'll start using one of those!    It would drive 
resistors for heaters, but would take tricky construction to eliminate 
117 volt hazard????

As I understand the circuit, it doesn't chop the wave to control the 
power to the bulb.  It either uses the complete half cycle, or it skips 
the cycle!   In other words, when it needs power, it turns on at or near 
zero volts, thus reducing, or eliminating switching spikes!

My box is set up in two layers.   The seismograph is inside a cardboard 
box!   The NTC (negative temp. coefficient) resistor (thermistor?) is 
inserted into the box through a small hole, with the rest of the heater 
and control set just outside the box.   Over this, I place an insulated 
box.   This way the seismograph is isolated from the thermal currents 
generated by the light bulb.   It is about 3.5 ft from the sensing 
coil.  If there is 60 hz hum, it is being effectively reduced in the 
filter circuit??   Lining the cardboard box with foil would probably 
reduce further, if needed?

There have been a couple of times that the heater changed temp by a 
couple of degrees?   I think it is related to the cheap variable 
resistor that sets the temp, and or the fact that I have it adjusted 
close to the limit of that resistor??   A few other part changes, (to 
put the variable resistor in the middle of its range), or replace it 
with a fixed resistor, (maybe even eliminate it), may make it more 
stable?   I think the original circuit was designed for the human 
comfort range, so I think I'm  probably at the limit, at about 93 
degrees!  The 10k temperature adj. resistor is probably set close to zero?

I got the original circuit out of a circuit design book, but can't 
remember the name,,   in fact, that might be the name???  Anyway I 
scanned it into an  80k jpeg and will be more than happy to share!   The 
engineers in the group are more than welcome to check it for errors, or 
possible improvements, terminology, parts updates, etc.  With minor 
modification, it would probably handle 220 volts AC???  Maybe even lower 
voltages???

  Stephen
  PSN Station # 55    





  
  


Small Space Heater Control.



OK, I scanned a hand sketch of my house current powered, small
space heater control circuit, that I use for my seismograph.=A0=A0 Wow,
that was a mouth full,, ha!=A0 Anyway, I use a 100 watt light bulb in one=

of those ceramic sockets, mounted to a hard plastic type box,, could be
bakelite (spell)??



The original circuit was designed to control up to 25 amps and used
both halves of the power cycle!=A0 I modified it to reduce parts, and
power, for better price, so it only controls a half cycle and about 3
amps max, which should easily control 150 watts!=A0 In the 11 years or so=

of operation,=A0 I've had to change the light bulb twice!=A0=A0 If I ever=

come across a low watt, screw-in heater (I think they use something
like that in incubators?) I'll start using one of those!=A0=A0=A0 It woul=
d
drive resistors for heaters, but would take tricky construction to
eliminate 117 volt hazard???? 



As I understand the circuit, it doesn't chop the wave to control the
power to the bulb.=A0 It either uses the complete half cycle, or it skips=

the cycle!=A0=A0 In other words, when it needs power, it turns on at or
near zero volts, thus reducing, or eliminating switching spikes!



My box is set up in two layers.=A0=A0 The seismograph is inside a cardboa=
rd
box!=A0=A0 The NTC (negative temp. coefficient) resistor (thermistor?) is=

inserted into the box through a small hole, with the rest of the heater
and control set just outside the box.=A0=A0 Over this, I place an insulat=
ed
box.=A0=A0 This way the seismograph is isolated from the thermal currents=

generated by the light bulb.=A0=A0 It is about 3.5 ft from the sensing
coil.=A0 If there is 60 hz hum, it is being effectively reduced in the
filter circuit??=A0=A0 Lining the cardboard box with foil would probably
reduce further, if needed? 



There have been a couple of times that the heater changed temp by a
couple of degrees?=A0=A0 I think it is related to the cheap variable
resistor that sets the temp, and or the fact that I have it adjusted
close to the limit of that resistor??=A0=A0 A few other part changes, (to=

put the variable resistor in the middle of its range), or replace it
with a fixed resistor, (maybe even eliminate it), may make it more
stable?=A0=A0 I think the original circuit was designed for the human
comfort range, so I think I'm=A0 probably at the limit, at about 93
degrees!=A0 The 10k temperature adj. resistor is probably set close to
zero?



I got the original circuit out of a circuit design book, but can't
remember the name,,=A0=A0 in fact, that might be the name???=A0 Anyway I
scanned it into an=A0 80k jpeg and will be more than happy to share!=A0=A0=

The engineers in the group are more than welcome to check it for
errors, or possible improvements, terminology, parts updates, etc.=A0
With minor modification, it would probably handle 220 volts AC???=A0
Maybe even lower voltages???



=A0 Stephen

=A0 PSN Station # 55 =A0 =A0