SCR dimmer control for portable electric heater??
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From: Robert Macy on 23 Mar 2010 13:14 On Mar 20, 5:07 pm, m...(a)privacy.net wrote: > I have one of those 1500 watt radiator style portable > electric heaters. Love it > > However, rather than the built in thermostat turning > the unit OFF?ON every 15 min's or so, I was thinking > it would be more efficient to use an SCR dimmer control > to vary the amt or power it gets? > > Does anyone know of an SCR control hefty enough to > handle this kind of resistive heating load?? 2nd attempt to post this reply! use a saturable core reactor, which is a variable inductor controlled by a DC current through a secondary winding. Used to be made by Northlake near Chicago. The inductor, with 0 DC current has maximum inductance and 'starves' the resistive load down to 5 to 10%, then at maximum DC current the inductor is saturated and almost all the power makes it to the load. The transfer/control is monotonic, but very weird. L vs Idc The DC control winding is wound in a 'fgirue eight' pattern so that one adds, one subtracts with no net to the other winding, but due to the high number of turns, saturates the core locally. Saturating locally interrupts the magnetic field lines and is like opening up a large air gap in the core, thus the inductance drops to nil. I prefer radiant heaters, too. You can point them at yourself and sit very comfortably like in front of a fireplace. Used to have hot air blast heating but that made the room's air excessively hot in order to be comfortable when sitting. Then when you get up and move around you swelter. Whereas with radiant heat, the air can stay cool so when you move around, you're still comfortable. But those contact closures!!! very irritating if you went to sleep, they get very loud. The variable inductor is great for controlling resistive loads especially in the 1kW to 10kW ranges. ...you can actually make your own if you want.
From: Jeffrey D Angus on 23 Mar 2010 17:37 me(a)privacy.net wrote: > Robert Macy <macy(a)california.com> wrote: > >> The variable inductor is great for controlling resistive loads >> especially in the 1kW to 10kW ranges. ...you can actually make your >> own if you want. > > > Is this called a "Variac"? Not really, a variac is just a variable auto-transformer. giving you a 0-100% range of output vs input voltage, and has a defined curent limit based on physical size. The variable inductor, is more of a magnetic amplifier type of device and relies on the core of the inductor saturating to vary the series imedpance with the load. Jeff -- �Egotism is the anesthetic that dulls the pain of stupidity.� Frank Leahy, Head coach, Notre Dame 1941-1954 http://www.stay-connect.com
From: Robert Macy on 23 Mar 2010 18:04 On Mar 23, 2:30 pm, m...(a)privacy.net wrote: > Robert Macy <m...(a)california.com> wrote: > >The variable inductor is great for controlling resistive loads > >especially in the 1kW to 10kW ranges. ...you can actually make your > >own if you want. > > Is this called a "Variac"? No, a variac is a tapped inductor with a wiper to make contacts along the inductor's turns to provide a variable output voltage.. The input voltage is applied to fixed points across the variac's fixed core inductance. Then, by varying the tap for the output, the output voltage can be adjusted. The ones I've seen usually are rated for 100VA to 500VA, sometimes 1kVA, look like a torroid with bare turns exposed on the top edge. They have a mechanically operated wiper [much like a rheostat, or potentiometer] that by rotating taps into the inductor's windings. By turning the knob the wiper goes from slightly above input voltage down to zero volts. But, most of the ones I've seen have their last turns near zero darkened, or worse, burnt, because the higher currents the lower voltage often supplies, and for some reason the concept of maximum current for a wire size just never comes to mind. People seem to think that 500VA should be able to supply at least 100Watts at 5 volts, NOT! I've seen several types of saturable core reactors. From memory, the multi kW controllers from Northlake [again, from memory costs $150- $250] looked like 3 phase transformers. The center core had the main inductor winding on it and the two legs had the cross wound DC control windings on them. Essentially, the two windings were wired to subtract two large signals to get zero volts, but that never happens very well and there are a lot of energetic signals appearing across the DC control windings. The idea is that the DC windings were a huge number of turns, so 100mAdc would saturate the legs, and, voila! no inductance anymore. The smaller types, varied a bit. some were cheerio sized with a hole drilled through the side. I've made some in the lab using metglas ribbon cores that I simply punched a hole through from outside to inside to make a place to wind the figure eight. You can make one from a high quality high voltage isolation transformer, low loss type. Do you have any lying around and feel like drilling it?
From: petrus bitbyter on 23 Mar 2010 20:01 "Robert Macy" <macy(a)california.com> schreef in bericht news:39086479-0a6b-4906-ab22-e8a499725026(a)x12g2000yqx.googlegroups.com... On Mar 20, 5:07 pm, m...(a)privacy.net wrote: > I have one of those 1500 watt radiator style portable > electric heaters. Love it > > However, rather than the built in thermostat turning > the unit OFF?ON every 15 min's or so, I was thinking > it would be more efficient to use an SCR dimmer control > to vary the amt or power it gets? > > Does anyone know of an SCR control hefty enough to > handle this kind of resistive heating load?? |2nd attempt to post this reply! | |use a saturable core reactor, which is a variable inductor controlled |by a DC current through a secondary winding. Used to be made by |Northlake near Chicago. | |The inductor, with 0 DC current has maximum inductance and 'starves' |the resistive load down to 5 to 10%, then at maximum DC current the |inductor is saturated and almost all the power makes it to the load. |The transfer/control is monotonic, but very weird. L vs Idc | |The DC control winding is wound in a 'fgirue eight' pattern so that |one adds, one subtracts with no net to the other winding, but due to |the high number of turns, saturates the core locally. Saturating |locally interrupts the magnetic field lines and is like opening up a |large air gap in the core, thus the inductance drops to nil. | |I prefer radiant heaters, too. You can point them at yourself and sit |very comfortably like in front of a fireplace. Used to have hot air |blast heating but that made the room's air excessively hot in order to |be comfortable when sitting. Then when you get up and move around you |swelter. Whereas with radiant heat, the air can stay cool so when you |move around, you're still comfortable. But those contact closures!!! |very irritating if you went to sleep, they get very loud. | |The variable inductor is great for controlling resistive loads |especially in the 1kW to 10kW ranges. ...you can actually make your |own if you want. | | Interesting solution though to me it looks like an overkill in space, weight and cost. Modern electronics might not be that interesting but are very effective. petrus bitbyter
From: William Sommerwerck on 23 Mar 2010 20:47
> Wheee! This "Phil Allison" ride is a great thrill, eh? > I see they finally fixed it so that it works reliably now. > Any response gets a torrent of abuse ... No, any response he doesn't agree with. He can be quite courteous, if you don't say something he finds insufferably stupid. |