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Is an electric blanket an inductive load?
I only ask because I'm making up a controller for one. I don't find
the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? |
Is an electric blanket an inductive load?
On 19/07/2020 15:31, Mike McLeod wrote:
I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? I'd say it was mostly resistive.... sure it's 'sort of' a coil - but a big flat one! Can't comment on the suitability of the specific triac - I always like to err on the cautious side and fit an over-rated component in situations like this.... |
Is an electric blanket an inductive load?
On 19/07/2020 15:31, Mike McLeod wrote:
I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? you should be ok. no way is a heating element any more than very very slightly inductive -- It is dangerous to be right in matters on which the established authorities are wrong. Voltaire, The Age of Louis XIV |
Is an electric blanket an inductive load?
The Natural Philosopher has brought this to us :
you should be ok. no way is a heating element any more than very very slightly inductive 0.8amps - I would want something a bit more meaty, at least 10amps. I agree a blanket is a resistive load. Why not take it a stage further, with automatic temperature sensing and control? |
Is an electric blanket an inductive load?
On 19/07/2020 15:31:19, Mike McLeod wrote:
I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Why not use a standard cheap dimmer switch? It'll have a convenient faceplate that will fit standard boxes. Perhaps a couple of cable glands to clamp the in and outgoing cables. It will have the necessary DIAC and a potentiometer with the correctly rated voltage. The blanket will have negligible inductance. I might still use a snubber across the TRIAC if only for mains born spikes. |
Is an electric blanket an inductive load?
Adrian Brentnall wrote:
On 19/07/2020 15:31, Mike McLeod wrote: I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? I'd say it was mostly resistive.... sure it's 'sort of' a coil - but a big flat one! Yes, that's my feeling too, the inductance will be tiny and effectively non-existent at 50Hz. -- Chris Green · |
Is an electric blanket an inductive load?
On Sun, 19 Jul 2020 15:31:19 +0100, Mike McLeod wrote:
I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Mine's 16/31/60W nd the PF is 1; VA and W show no difference. Given the possible ****it! level (fire - bedding - unattended) having a good margin is well worth it. -- Peter. The gods will stay away whilst religions hold sway |
Is an electric blanket an inductive load?
On Sun, 19 Jul 2020 17:13:00 +0100, PeterC
wrote: On Sun, 19 Jul 2020 15:31:19 +0100, Mike McLeod wrote: I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Mine's 16/31/60W nd the PF is 1; VA and W show no difference. Given the possible ****it! level (fire - bedding - unattended) having a good margin is well worth it. It would appear to be already sufficiently de-rated, though. That triac is good for 800mA (and 600V!) and he's only putting a maximum of 350mA through it. Given the load is near enough purely resistive as you say, there should be no problem. Where's the fire going to come from?? |
Is an electric blanket an inductive load?
I assume the blanket is directly mains powered. I've never really liked
mains wires near my body, even if they are switched off. I remember many moons back somebody came up with one that operated at about 30 volts via a psu. Never did know if they caught on though. Brian -- ----- -- This newsgroup posting comes to you directly from... The Sofa of Brian Gaff... Blind user, so no pictures please Note this Signature is meaningless.! "Chris Green" wrote in message ... Adrian Brentnall wrote: On 19/07/2020 15:31, Mike McLeod wrote: I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? I'd say it was mostly resistive.... sure it's 'sort of' a coil - but a big flat one! Yes, that's my feeling too, the inductance will be tiny and effectively non-existent at 50Hz. -- Chris Green |
Is an electric blanket an inductive load?
I was thinking, how are the three adjustments done? Could they merely be
using a triac already in the control box. If so that might be affected by your other triac. Brian -- ----- -- This newsgroup posting comes to you directly from... The Sofa of Brian Gaff... Blind user, so no pictures please Note this Signature is meaningless.! "The Natural Philosopher" wrote in message ... On 19/07/2020 15:31, Mike McLeod wrote: I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? you should be ok. no way is a heating element any more than very very slightly inductive -- "It is dangerous to be right in matters on which the established authorities are wrong." ? Voltaire, The Age of Louis XIV |
Is an electric blanket an inductive load?
On Sun, 19 Jul 2020 18:23:54 +0100, "Brian Gaff \(Sofa\)"
wrote: Well I think an inductive load would be a motor, cos it has a coil. Most blankets are not coiled! That's exactly what I'm querying, though. The element snakes around the blanket layers alright, you can see that plainly enough, but what is not visible without cutting it open is if it - the element - formed from *coiled* resistance wire? |
Is an electric blanket an inductive load?
Brian Gaff (Sofa) wrote on 19/07/2020 :
I was thinking, how are the three adjustments done? Could they merely be using a triac already in the control box. If so that might be affected by your other triac. They usually use a simple parallel series arrangement. I have one which works like that, but includes a timeout system. |
Is an electric blanket an inductive load?
"Brian Gaff (Sofa)" wrote in message ... I assume the blanket is directly mains powered. I've never really liked mains wires near my body, even if they are switched off. I remember many moons back somebody came up with one that operated at about 30 volts via a psu. Never did know if they caught on though. There are some heated jackets and pants done like that now. Used by motorbike riders and other outdoor workers. "Chris Green" wrote in message ... Adrian Brentnall wrote: On 19/07/2020 15:31, Mike McLeod wrote: I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? I'd say it was mostly resistive.... sure it's 'sort of' a coil - but a big flat one! Yes, that's my feeling too, the inductance will be tiny and effectively non-existent at 50Hz. -- Chris Green |
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Is an electric blanket an inductive load?
In article , Mike McLeod
writes I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. This means that the initial current at switch-on will be higher than the normal operating current. For a filament lamp where the operating temperature is in the order of 2000degrees Celsius, the cold resistance is about a tenth of the resistance at operating temperature. In the case of an electric blanket the operating temperature of the element is much less than that of a lamp filament so this effect will be less significant; still a good idea to use a generous rating for the triac. ) -- Chris Holford |
Is an electric blanket an inductive load?
On Sun, 19 Jul 2020 18:47:51 +0100, Harry Bloomfield, Esq.
wrote: Brian Gaff (Sofa) wrote on 19/07/2020 : I was thinking, how are the three adjustments done? Could they merely be using a triac already in the control box. If so that might be affected by your other triac. They usually use a simple parallel series arrangement. I have one which works like that, but includes a timeout system. Indeed. By using 3 different elements within the one blanket, they have eliminated the necessity for any form of temperature control at all. It's all done by just a simple switch; nice 'n' cheap! |
Is an electric blanket an inductive load?
Harry Bloomfield, Esq. wrote:
The Natural Philosopher has brought this to us : you should be ok. no way is a heating element any more than very very slightly inductive 0.8amps - I would want something a bit more meaty, at least 10amps. I agree a blanket is a resistive load. Why not take it a stage further, with automatic temperature sensing and control? From memory, an electric blanket is typically 70W on high - about 0.3A @ 240V. Stick a smart plug on it and control it with Alexa (or Google Home etc). Ideal if you are out for the evening and returning late, just turn the blanket on remotely. -- https://www.unitedway.org/our-impact...an-trafficking |
Is an electric blanket an inductive load?
On Sun, 19 Jul 2020 21:58:31 +0100, Chris Holford
wrote: Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. This means that the initial current at switch-on will be higher than the normal operating current. Yup, I was aware of that and measured the current draw under warmed-up running conditions. |
Is an electric blanket an inductive load?
Cursitor Doom wrote:
On Sun, 19 Jul 2020 18:47:51 +0100, Harry Bloomfield, Esq. wrote: Brian Gaff (Sofa) wrote on 19/07/2020 : I was thinking, how are the three adjustments done? Could they merely be using a triac already in the control box. If so that might be affected by your other triac. They usually use a simple parallel series arrangement. I have one which works like that, but includes a timeout system. Indeed. By using 3 different elements within the one blanket, they have eliminated the necessity for any form of temperature control at all. It's all done by just a simple switch; nice 'n' cheap! Before disposing of an old electric blanket, I looked inside the controller. As you say, it was a simple switch to select the elements. It didnt have any obvious overheat detection in the controller. There could have been a simple thermal switch buried in the blanket. Weve had several over the years, all the same brand from memory. Weve varied between single temp/setting ones and variable ones - the latter have always ( from memory) had cables between the blanket and controller suggesting multiple elements. -- https://www.unitedway.org/our-impact...an-trafficking |
Is an electric blanket an inductive load?
On 19/07/2020 21:58:31, Chris Holford wrote:
In article , Mike McLeod writes I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. Nichrome is a sufficiently cheap material there is no need to worry about cold resistance. In fact having a wire with a high temperature coefficient would cause hot spots. This means that the initial current at switch-on will be higher than the normal operating current. For reasons above there will be no switch on surge. For a filament lamp where the operating temperature is in the order of 2000degrees Celsius, the cold resistance is about a tenth of the resistance at operating temperature. We are talking about something completely different and using a Tungsten filament with a resistance temperature coefficient far removed from Nichrome. In the case of an electric blanket the operating temperature of the element is much less than that of a lamp filament so this effect will be less significant; still a good idea to use a generous rating for the triac. An 80W blanket is 0.3A and will take the same at switch on. The OP is proposed a 0.8/0.9A TRIAC. That should be sufficient margin. Personally I might go a little higher as more rugged ones don't cost the earth. |
Is an electric blanket an inductive load?
On Sunday, 19 July 2020 23:17:07 UTC+1, Mike McLeod wrote:
On Sun, 19 Jul 2020 21:58:31 +0100, Chris Holford wrote: Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. This means that the initial current at switch-on will be higher than the normal operating current. Yup, I was aware of that and measured the current draw under warmed-up running conditions. what you need to know is cold resistance. NT |
Is an electric blanket an inductive load?
On Sunday, 19 July 2020 23:56:53 UTC+1, Fredxx wrote:
On 19/07/2020 21:58:31, Chris Holford wrote: In article , Mike McLeod writes I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. Nichrome is a sufficiently cheap material there is no need to worry about cold resistance. In fact having a wire with a high temperature coefficient would cause hot spots. This means that the initial current at switch-on will be higher than the normal operating current. For reasons above there will be no switch on surge. For a filament lamp where the operating temperature is in the order of 2000degrees Celsius, the cold resistance is about a tenth of the resistance at operating temperature. We are talking about something completely different and using a Tungsten filament with a resistance temperature coefficient far removed from Nichrome. In the case of an electric blanket the operating temperature of the element is much less than that of a lamp filament so this effect will be less significant; still a good idea to use a generous rating for the triac. An 80W blanket is 0.3A and will take the same at switch on. The OP is proposed a 0.8/0.9A TRIAC. That should be sufficient margin. Personally I might go a little higher as more rugged ones don't cost the earth. 0.3A blankets take 0.45A peak. A 0.8A triac should be fine. The elements may be wound, but their inductance is still tiny. NT |
Is an electric blanket an inductive load?
On 19/07/2020 17:45, Cursitor Doom wrote:
On Sun, 19 Jul 2020 17:13:00 +0100, PeterC wrote: On Sun, 19 Jul 2020 15:31:19 +0100, Mike McLeod wrote: I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Mine's 16/31/60W nd the PF is 1; VA and W show no difference. Given the possible ****it! level (fire - bedding - unattended) having a good margin is well worth it. It would appear to be already sufficiently de-rated, though. That triac is good for 800mA (and 600V!) and he's only putting a maximum of 350mA through it. Given the load is near enough purely resistive as you say, there should be no problem. Where's the fire going to come from?? Is the 350mA an average over the temperature range of the blanket. Could the current be higher than 350mA at some point during the heating cycle? -- mailto : news {at} admac {dot} myzen {dot} co {dot} uk |
Is an electric blanket an inductive load?
wrote:
On Sunday, 19 July 2020 23:17:07 UTC+1, Mike McLeod wrote: On Sun, 19 Jul 2020 21:58:31 +0100, Chris Holford wrote: Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. This means that the initial current at switch-on will be higher than the normal operating current. Yup, I was aware of that and measured the current draw under warmed-up running conditions. what you need to know is cold resistance. NT Plug it into a Kill-o-Watt meter and watch the power consumption from cold and see if it changes. The Kill-o-Watt meter also has power factor, and the PF should be 0.99 (indicating little in the way of inductance). 1.00 would be purely resistive. https://www.amazon.co.uk/YOUTHINK-El.../dp/B071NZ53WR Power(W) === Mine has Watts and VA instead Energy (kWh) Voltage Amps Hertz Power Factor === Old PC ATX about 0.65 (capacitive), light bulb 0.99 [ideal] Minimum and Maximum power These meters use sigma-delta converters operating at 500KHz to 1MHz or so, and are capable of TrueRMS readout. (The same tech as whole-house digital power meters.) Even for the idle current of an ATX power supply (which is a severely distorted waveform), the meter gives the right answer. That's why I like the instrument for various purposes, as I can trust it to "do the sums correctly". I have other instruments that claim to do this and that, which are off by miles when doing such measurements. The only problem with the meter concept, is they use a shunt resistor for current measurement. And if you spend your day "measuring electric kettles", in the past this made the shunt hot enough the solder inside melts. A few of the meters have failed when used for high power characterization. It's a pretty nice instrument to add to a collection. And mainly, because it actually works, and the thing makes measurements for you. You may have to search around to find just the right one, as some of them have "junk functions" that are worthless. And you also need the right "hole" on the front, for your typical cords and plugs. There's no sense buying one for the wrong country. Paul |
Is an electric blanket an inductive load?
Harry Bloomfield, Esq. Wrote in
message: The Natural Philosopher has brought this to us : you should be ok. no way is a heating element any more than very very slightly inductive 0.8amps - I would want something a bit more meaty, at least 10amps. That's 2.3kW, you would indeed become meat. -- %Profound_observation% ----Android NewsGroup Reader---- http://usenet.sinaapp.com/ |
Is an electric blanket an inductive load?
On Sun, 19 Jul 2020 17:45:57 +0100, Cursitor Doom wrote:
On Sun, 19 Jul 2020 17:13:00 +0100, PeterC wrote: On Sun, 19 Jul 2020 15:31:19 +0100, Mike McLeod wrote: I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Mine's 16/31/60W nd the PF is 1; VA and W show no difference. Given the possible ****it! level (fire - bedding - unattended) having a good margin is well worth it. It would appear to be already sufficiently de-rated, though. That triac is good for 800mA (and 600V!) and he's only putting a maximum of 350mA through it. Given the load is near enough purely resistive as you say, there should be no problem. Where's the fire going to come from?? Electronic components - magic smoke and pretty lights seem quite common. -- Peter. The gods will stay away whilst religions hold sway |
Is an electric blanket an inductive load?
Chris Holford wrote:
In article , Mike McLeod writes I only ask because I'm making up a controller for one. I don't find the 3 heat settings provide enough choice so I'll be controlling a small triac via a PWM chip. Although the max current draw of this appliance is only 350mA, the triac (a Z0607) is pretty puny and I don't want it operating at too close to its max ratings obviously. I'm using a snubber to be on the safe side WRT to back EMF anyway. Here's the datasheet for the triac: https://www.st.com/resource/en/datasheet/z00607.pdf Will that do it or is something more meaty required? Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. Not by much, it's nothing like an incadescent lamp. Normal resistance wire will only change by a percent or so even when it's very hot indeed. -- Chris Green · |
Is an electric blanket an inductive load?
|
Is an electric blanket an inductive load?
Brian Reay wrote :
Weve had several over the years, all the same brand from memory. Weve varied between single temp/setting ones and variable ones - the latter have always ( from memory) had cables between the blanket and controller suggesting multiple elements. Our blanket is a machine washable one and between blacket and switch is a multi-pin plug and socket. That suggests multi-elements. |
Is an electric blanket an inductive load?
"Harry Bloomfield"; "Esq." wrote in message ... Brian Reay wrote : Weve had several over the years, all the same brand from memory. Weve varied between single temp/setting ones and variable ones - the latter have always ( from memory) had cables between the blanket and controller suggesting multiple elements. Our blanket is a machine washable one and between blacket and switch is a multi-pin plug and socket. That suggests multi-elements. Mine are washable too, but only have two pin sockets. |
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Is an electric blanket an inductive load?
On 19/07/2020 18:27, Brian Gaff (Sofa) wrote:
I assume the blanket is directly mains powered. I've never really liked mains wires near my body, even if they are switched off. I remember many moons back somebody came up with one that operated at about 30 volts via a psu. Never did know if they caught on though. Brian They did for a while. Most famous brand was Windak. I still have a couple of their transformers in the garage. Blankets long worn out. https://www.ebay.co.uk/itm/1948-WIND...-/150987416465 It used a three setting isolating transformer. Later models used a continuously variable isolating variac transformer from 0 to 30vac. Cheap mains based ones had a nasty habit of electrocuting bed wetters back in the 1950's and 60's if the insulation had worn or cracked. An electric blanket is essentially a pure constant resistive load - it doesn't get anything like warm enough for the resistance to change much. FWIW I find the modern two elements in parallel, in series, and in series with a diode electric blankets perfectly adequate. It hardly ever gets used on any other setting than the lowest unless it is *very* cold. -- Regards, Martin Brown |
Is an electric blanket an inductive load?
On Monday, 20 July 2020 09:03:05 UTC+1, Chris Green wrote:
tabbypurr wrote: On Sunday, 19 July 2020 23:17:07 UTC+1, Mike McLeod wrote: On Sun, 19 Jul 2020 21:58:31 +0100, Chris Holford wrote: Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. This means that the initial current at switch-on will be higher than the normal operating current. Yup, I was aware of that and measured the current draw under warmed-up running conditions. what you need to know is cold resistance. As I've said above the cold resistance will be very close to the hot resistance, it's not being heated up to thousands of degrees like an incandescent bulb. Anyway the element will be made of resistance wire which will have a very small change of resistance with temperature. Yup. But from the triac's POV, cold R is what matters. Apply 330v to that R to work out the peak i the triac sees - it will not be 0.35A for a 0.35A blanket. NT |
Is an electric blanket an inductive load?
On 20/07/2020 09:04, Harry Bloomfield wrote:
Brian Reay wrote : Weve had several over the years, all the same brand from memory. Weve varied between single temp/setting ones and variable ones - the latter have always ( from memory) had cables between the blanket and controller suggesting multiple elements. Our blanket is a machine washable one and between blacket and switch is a multi-pin plug and socket. That suggests multi-elements. That's how they control the power, 1, 2 or 3 elements in parallel. -- In todays liberal progressive conflict-free education system, everyone gets full Marx. |
Is an electric blanket an inductive load?
|
Is an electric blanket an inductive load?
On 19/07/2020 23:52, Brian Reay wrote:
Cursitor Doom wrote: On Sun, 19 Jul 2020 18:47:51 +0100, Harry Bloomfield, Esq. wrote: Brian Gaff (Sofa) wrote on 19/07/2020 : I was thinking, how are the three adjustments done? Could they merely be using a triac already in the control box. If so that might be affected by your other triac. They usually use a simple parallel series arrangement. I have one which works like that, but includes a timeout system. Indeed. By using 3 different elements within the one blanket, they have eliminated the necessity for any form of temperature control at all. It's all done by just a simple switch; nice 'n' cheap! Before disposing of an old electric blanket, I looked inside the controller. As you say, it was a simple switch to select the elements. It didnt have any obvious overheat detection in the controller. There could have been a simple thermal switch buried in the blanket. There is a fuseable link inside the little controller which blows if the thing starts to draw unexpectedly high current or after about 5 years whichever occurs sooner. They die much quicker if you use them on maximum a lot the internal switch contacts are very cheap and cheerful. The resistive load tends to fail open circuit eventually. Weve had several over the years, all the same brand from memory. Weve varied between single temp/setting ones and variable ones - the latter have always ( from memory) had cables between the blanket and controller suggesting multiple elements. It is usually a single cable with 3 to 5 way multicore cable with a flat connector on the blanket. Some do have temperature feedback. -- Regards, Martin Brown |
Is an electric blanket an inductive load?
On Tuesday, 21 July 2020 16:08:56 UTC+1, Martin Brown wrote:
On 19/07/2020 23:52, Brian Reay wrote: Before disposing of an old electric blanket, I looked inside the controller. As you say, it was a simple switch to select the elements. It didnt have any obvious overheat detection in the controller.. There could have been a simple thermal switch buried in the blanket. There is a fuseable link inside the little controller which blows if the thing starts to draw unexpectedly high current or after about 5 years whichever occurs sooner. They die much quicker if you use them on maximum a lot the internal switch contacts are very cheap and cheerful. The resistive load tends to fail open circuit eventually. My 1950s one had none of that. I'm sure it'd have been safer if it had failed! NT |
Is an electric blanket an inductive load?
On Tue, 21 Jul 2020 16:08:51 +0100, Martin Brown
wrote: There is a fuseable link inside the little controller which blows if the thing starts to draw unexpectedly high current or after about 5 years whichever occurs sooner. Not a fuseable link - a thermal fuse. Different principle altogether: https://www.ebay.co.uk/itm/Thermal-T...AOSwAVRde~U F |
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