SCR dimmer control for portable electric heater??
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From: KR on 22 Mar 2010 05:04 On Mar 22, 2:56 am, m...(a)privacy.net wrote: > mike <spam...(a)go.com> wrote: > >How much improvement are you expecting? > > The goal was to keep internal thermostat contacts from > wearing out.....IF and only if I could get a heavy duty > enough unit at low cost that is > > Plus it seems to me it would help give more even heat? They wont wear out in a hurry. I would also be wary of removing the existing thermostat from the circuit, as in most cases, it not only regulates the temperature to the point you set, but also has a second function of "over temperature" emergency cutoff, that will kill power if the temperature exceeds a certain limit. (usually can only be reset by pressing a button once this trips). While you may think this isn't needed, if it is bypassed and the unit were to overheat, it could start a fire or even rupture from the pressure of the overheated internal oil (if an oil filled heater) , spraying very hot oil everywhere. A light dimmer type setup, if it fails, will typically result in the internal TRIAC short circuiting, which will leave the heater on full power, constantly, resulting in a risk of overheating. AS a light dimmer also has no "thermostat" to measure the heat coming from the unit, you would have to constantly adjust it as the temperature changes, whereas a thermostat will try to maintain a temperature at a certain level, regardless of the existing room temperature. (ie: if the room is a couple of degrees colder than last night, a thermostat will simply leave the power on for longer time if needed until the desired temp is reached, then shutoff. A light dimmer will still only leave the power on at a % of full, and will not give it any extra to compensate for this. This means you will have to keep adjusting it on a "trial and error" basis to set the right temp as room temperatures change with weather.
From: GregS on 22 Mar 2010 17:04 In article <rk3dq5h1oj5ma64jh080ndgrlemk4rao7e(a)4ax.com>, mm <NOPSAMmm2005(a)bigfoot.com> wrote: >On Sun, 21 Mar 2010 14:23:49 -0400, "Michael A. Terrell" ><mike.terrell(a)earthlink.net> wrote: > >> >>William Sommerwerck wrote: >>> >>> >> I rather like the idea of wiring two heaters in series. This >>> >> will reduce the total output to half of what it was, but it will >>> >> be better spread around the room, which might be a net >>> >> improvement. >>> >>> > Why not use 4 heaters in series? Or maybe even 8 or 12 or 16? How about warming the whole floor. >>> How about four in series-parallel? That would be the same heat output as >>> one, but you'd (probably) need to cycle them on less often for the same >>> degree of comfort. >>> >>> Regardless, I've never understood why radiators and heating fixtures are >>> place right next to the windows. Much less of a problem with efficient windows. >> >> If they are placed along inner walls the room temperature is uneven. >>Since heat escapes through walls, windows & doors you need to replace >>it. Then, the center of the house will stay warm from convection >>currents and the lower heat loss through a ceiling or roof. > The upward current warms that ordinary cool downward draft. Drafts affect overall rooms comfortability. I installed, or rather insulated my front door, and the room is much better. >He makes a good point however. By placing them near the window, the >hottest part of the room is near the window and the most heat loss >occurs, compared to placing it somewhere else. > >Maybe having the room temperature even is something some people would >sacrifice to save money, and that pesky old environment and balance of >payments. And that way the people who like it warm could sit on one >side of the room and the ones who are hot all the time could sit on >the other.
From: mike on 22 Mar 2010 17:54 me(a)privacy.net wrote: > mike <spamme0(a)go.com> wrote: > >> The whole idea of the radiator >> is to have some thermal mass and keep heat even. > > > there is no thermal mass in this heater.....it is > mica-thermic You probably shoulda been more accurate with your initial "radiator" description. Garbage in >>> garbage out...
From: Robert Macy on 23 Mar 2010 10:38 On Mar 20, 8:17 pm, isw <i...(a)witzend.com> wrote: > In article <ho40m3$t3...(a)news.eternal-september.org>, > "William Sommerwerck" <grizzledgee...(a)comcast.net> wrote: > > > >> Does anyone know of an SCR control hefty enough > > >> to handle this kind of resistive heating load?? > > > > Or (maybe) better yet, how about some kind of PWM > > > control? > > > SCR dimmers use PWM. > > > I rather like the idea of wiring two heaters in series. This will reduce the > > total output to half of what it was, but it will be better spread around the > > room, which might be a net improvement. > > It will reduce the current to (approximately) half, which will reduce > the heat output (power) to one-quarter that of a single unit. Power is > I^2*R. > > Isaac well said, now include the thermal coefficient for the filament...
From: GregS on 23 Mar 2010 12:25
In article <isw-99FC9A.20175320032010@[216.168.3.50]>, isw <isw(a)witzend.com> wrote: >In article <ho40m3$t33$1(a)news.eternal-september.org>, > "William Sommerwerck" <grizzledgeezer(a)comcast.net> wrote: > >> >> Does anyone know of an SCR control hefty enough >> >> to handle this kind of resistive heating load?? >> >> > Or (maybe) better yet, how about some kind of PWM >> > control? >> >> SCR dimmers use PWM. >> >> I rather like the idea of wiring two heaters in series. This will reduce the >> total output to half of what it was, but it will be better spread around the >> room, which might be a net improvement. > >It will reduce the current to (approximately) half, which will reduce >the heat output (power) to one-quarter that of a single unit. Power is >I^2*R. > You forgot to multiply twice the resistance. It will be 1/2 the watts total. Each unit will be 1/4. greg |