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I have a spool of Teflon coated copper wire. I am trying to determine
the resistance of a one foot piece, but both of my meters read
differently. How can I get a reliable reading? I am using DVMs.
Thanks in advance.
I have a spool of Teflon coated copper wire. I am trying to determine
the resistance of a one foot piece, but both of my meters read
differently. How can I get a reliable reading? I am using DVMs.
Thanks in advance.
Alternatively, if you know the length of the spool (because it\'s new
and untouched, or at least measurable in some way) measure the whole
spool\'s resistance, and then divide by the length. Hopefully, the far
end of the wire is poking out somewhere!
Hmmmm... If it is sufficiently important to know the precise and accurate resistance of a given (and very short) length of wire, then that method will not work very well. I have never, ever come across a factory-sealed spool of electrical wire that is within even 1% of the nominal length, with the tendency to run a bit long
rather than short. And even shop-cut lengths tend to have a bit added for waste and crimps.
And here is another issue: I keep a pretty good Fluke meter which gives a resolution of +/-0.5% in ohms in ranges above 32 ohms, and +/- 2% at the lowest range. Which may not be good enough in this application.
Again, if it is sufficiently important, then the correct instrumentation and the calibration and set-up of same is critical.
This is what I ended up doing, although I decided to just power theIn article <593b6d9c-02ba-4ec4-b3fd-8a69353caa17n@googlegroups.com>,
peterwieck33@gmail.com says...
Hmmmm... If it is sufficiently important to know the precise and accurate resistance of a given (and very short) length of wire, then that method will not work very well. I have never, ever come across a factory-sealed spool of electrical wire that is within even 1% of the nominal length, with the tendency to run a bit long
rather than short. And even shop-cut lengths tend to have a bit added for waste and crimps.
And here is another issue: I keep a pretty good Fluke meter which gives a resolution of +/-0.5% in ohms in ranges above 32 ohms, and +/- 2% at the lowest range. Which may not be good enough in this application.
Again, if it is sufficiently important, then the correct instrumentation and the calibration and set-up of same is critical.
For most at home the best way for very low resistance is to have an
ampmeter and voltmeter and varitable power supply. Put as much current
as you can through the wire and measure the voltage across it and ohm
law the resistance.
I have a spool of Teflon coated copper wire. I am trying to determine
the resistance of a one foot piece, but both of my meters read
differently. How can I get a reliable reading? I am using DVMs.
Thanks in advance.
That was too much power, at least IMO, for the electric blanket I was
making, so I kept checking current and voltage until a more reasonable
55 W was reached. This meant using 20 feet of the wire and powering at
5 V (11 A).
I\'m under the blanket now and it\'s toasty. Not hot, but warm. I will
The Teflon wire is hot glued to the old blanket. I wasn\'t sure if this
would work as I feared glue melting, but so far so good after some
On Friday, October 30, 2020 at 1:30:43 PM UTC-4, Runner wrote:
That was too much power, at least IMO, for the electric blanket I was
making, so I kept checking current and voltage until a more reasonable
55 W was reached. This meant using 20 feet of the wire and powering at
5 V (11 A).
I\'m under the blanket now and it\'s toasty. Not hot, but warm. I will
The Teflon wire is hot glued to the old blanket. I wasn\'t sure if this
would work as I feared glue melting, but so far so good after some
Dude! I just..........I mean it boggles the mind. You made your own electric blanket with hot glue and duct tape, and you\'re trusting your life to it?
I hope you live alone. I\'m pretty sure you made your own smoke alarms but still.
#darwinawards
On 10/30/20 1:21 PM, Ralph Mowery wrote:
In article <593b6d9c-02ba-4ec4-b3fd-8a69353caa17n@googlegroups.com>,
peterwieck33@gmail.com says...
Hmmmm... If it is sufficiently important to know the precise and accurate resistance of a given (and very short) length of wire, then that method will not work very well. I have never, ever come across a factory-sealed spool of electrical wire that is within even 1% of the nominal length, with the tendency to run a bit long
rather than short. And even shop-cut lengths tend to have a bit added for waste and crimps.
And here is another issue: I keep a pretty good Fluke meter which gives a resolution of +/-0.5% in ohms in ranges above 32 ohms, and +/- 2% at the lowest range. Which may not be good enough in this application.
Again, if it is sufficiently important, then the correct instrumentation and the calibration and set-up of same is critical.
For most at home the best way for very low resistance is to have an
ampmeter and voltmeter and varitable power supply. Put as much current
as you can through the wire and measure the voltage across it and ohm
law the resistance.
This is what I ended up doing, although I decided to just power the
entire 60 foot spool instead of the single one foot piece. I found
that, at 12 V, 7 A was used, so that\'s where I started.
That was too much power, at least IMO, for the electric blanket I was
making, so I kept checking current and voltage until a more reasonable
55 W was reached. This meant using 20 feet of the wire and powering at
5 V (11 A).
I\'m under the blanket now and it\'s toasty. Not hot, but warm. I will
be continuing to check connections for excess heating, but I repurposed
the original Sunbeam connections and those are more than adequate and
saved me a lot of time. The only source of moderate heating outside the
blanket is the power wires to the blanket. Since I used the Sunbeam
wires, their gauge is a bit thin. If it becomes an issue, I will
upgrade to a thicker cable.
I wasn\'t sure if this
would work as I feared glue melting, but so far so good after some
hours.
Originally, I was going to go with the full wire spool and the 84 watt
version, but I wasn\'t sure how I was going to vary the output.
All I
have on hand was a PWM 8 A 12 V lamp dimmer, used for dimming LED
arrays, but it burned out almost instantly.
I wasn\'t surprised of
course, but thought I\'d give it a try.
On 10/30/20 1:21 PM, Ralph Mowery wrote:
In article <593b6d9c-02ba-4ec4-b3fd-8a69353caa17n@googlegroups.com>,
peterwieck33@gmail.com says...
Hmmmm... If it is sufficiently important to know the precise and accurate resistance of a given (and very short) length of wire, then that method will not work very well. I have never, ever come across a factory-sealed spool of electrical wire that is within even 1% of the nominal length, with the tendency to run a bit long
rather than short. And even shop-cut lengths tend to have a bit added for waste and crimps.
And here is another issue: I keep a pretty good Fluke meter which gives a resolution of +/-0.5% in ohms in ranges above 32 ohms, and +/- 2% at the lowest range. Which may not be good enough in this application.
Again, if it is sufficiently important, then the correct instrumentation and the calibration and set-up of same is critical.
For most at home the best way for very low resistance is to have an
ampmeter and voltmeter and varitable power supply. Put as much current
as you can through the wire and measure the voltage across it and ohm
law the resistance.
This is what I ended up doing, although I decided to just power the
entire 60 foot spool instead of the single one foot piece. I found
that, at 12 V, 7 A was used, so that\'s where I started.
That was too much power, at least IMO, for the electric blanket I was
making, so I kept checking current and voltage until a more reasonable
55 W was reached. This meant using 20 feet of the wire and powering at
5 V (11 A).
I\'m under the blanket now and it\'s toasty. Not hot, but warm. I will
be continuing to check connections for excess heating, but I repurposed
the original Sunbeam connections and those are more than adequate and
saved me a lot of time. The only source of moderate heating outside the
blanket is the power wires to the blanket. Since I used the Sunbeam
wires, their gauge is a bit thin. If it becomes an issue, I will
upgrade to a thicker cable.
The Teflon wire is hot glued to the old blanket. I wasn\'t sure if this
would work as I feared glue melting, but so far so good after some
hours. At 84 watts though, it might have been a different story.
Originally, I was going to go with the full wire spool and the 84 watt
version, but I wasn\'t sure how I was going to vary the output. All I
have on hand was a PWM 8 A 12 V lamp dimmer, used for dimming LED
arrays, but it burned out almost instantly. I wasn\'t surprised of
course, but thought I\'d give it a try. Any ideas as to how to vary the
power welcome.
Re: varying power.
Since the resistance of copper goes up with temperature (R is ~ temperature)
controlling the voltage might be best. (no thermal runaway)
Are you using AC or DC power.
DC will be trickier (\'cause that power has to go somewhere) and some
PWM scheme might be the way to go. Or buy a variable DC supply...
you can use it for electroplating when not staying warm. :^)
In general I\'m wondering why not try a heating pad and a nice down
comforter?
George H.
On Fri, 30 Oct 2020 13:30:37 -0400, Runner <run...@aolnospam.com
wrote:
On 10/30/20 1:21 PM, Ralph Mowery wrote:
In article <593b6d9c-02ba-4ec4...@googlegroups.com>,
peterw...@gmail.com says...
Hmmmm... If it is sufficiently important to know the precise and accurate resistance of a given (and very short) length of wire, then that method will not work very well. I have never, ever come across a factory-sealed spool of electrical wire that is within even 1% of the nominal length, with the tendency to run a bit long
rather than short. And even shop-cut lengths tend to have a bit added for waste and crimps.
And here is another issue: I keep a pretty good Fluke meter which gives a resolution of +/-0.5% in ohms in ranges above 32 ohms, and +/- 2% at the lowest range. Which may not be good enough in this application.
Again, if it is sufficiently important, then the correct instrumentation and the calibration and set-up of same is critical.
For most at home the best way for very low resistance is to have an
ampmeter and voltmeter and varitable power supply. Put as much current
as you can through the wire and measure the voltage across it and ohm
law the resistance.
This is what I ended up doing, although I decided to just power the
entire 60 foot spool instead of the single one foot piece. I found
that, at 12 V, 7 A was used, so that\'s where I started.
You did that through a 1 ft length of wire?
P = E * I = 12v * 7A = 84 watts
In a 1 ft length of wire, that should have gotten the wire red hot
(depending on wire gauge and contract resistance).
That was too much power, at least IMO, for the electric blanket I was
making, so I kept checking current and voltage until a more reasonable
55 W was reached. This meant using 20 feet of the wire and powering at
5 V (11 A).
I have a small complaint. If you expect usable answers, it\'s really
helpful if you would describe:
1. What problem are you trying to solve?
2. What do you have to work with?
3. What have you done so far and what went wrong?
My initial reply assumed that you were doing some kind of measurement.
I replied accordingly with the instruments required. My answer would
have been very different if you had supplied the details and numbers.
I\'m under the blanket now and it\'s toasty. Not hot, but warm. I will
be continuing to check connections for excess heating, but I repurposed
the original Sunbeam connections and those are more than adequate and
saved me a lot of time. The only source of moderate heating outside the
blanket is the power wires to the blanket. Since I used the Sunbeam
wires, their gauge is a bit thin. If it becomes an issue, I will
upgrade to a thicker cable.
Hint: Real electric blankets use nichrome or some form of resistance
heating wire. See list at step 6.
\"DIY Heating Pad - (small Electrical Blanket)\"
https://www.instructables.com/DIY-Heating-pad-small-electrical-blanket/
Any clues as to the source and tupe of \"teflon insulated wire\" you\'re
using? If its copper wire, be advised that soft copper wire work
hardens fairly easily. Just bend it a few times and it will break.
The Teflon wire is hot glued to the old blanket.
The wire is not made of teflon. It\'s probably copper, nichrome, or
something similar. The insulation is Teflon.
Make sure you\'re using high temp (195C gun) glue. Low temp (130C gun)
will work, but methinks high temp is a better choice.
I wasn\'t sure if this
would work as I feared glue melting, but so far so good after some
hours.
The standard high temp hot melt glue melts at about 200C. That\'s
quite a bit warmer than the 25C to 55C range of a typical electric
blanket.
At 84 watts though, it might have been a different story.
Queen size electric blankets typically draw about 60 watts or 100
watts for a twin size.
Originally, I was going to go with the full wire spool and the 84 watt
version, but I wasn\'t sure how I was going to vary the output.
A light dimmer should work. If you try to use a linear regulator,
you\'ll end up dissipating quite a bit of heat in the regulator. The
switching regulator in the light dimmer is far more efficient.
All I
have on hand was a PWM 8 A 12 V lamp dimmer, used for dimming LED
arrays, but it burned out almost instantly.
It should have worked. However, when the wire is cold, the resistance
is rather low and the inrush current is rather high. When it gets
warm, the resistance increases, and the operating current is reduces.
My guess(tm) is that the initial inrush current exeeded the 8A rating.
I wasn\'t surprised of
course, but thought I\'d give it a try.
Learn by Destroying(tm). Ok, what have you learned?
Any ideas as to how to vary the power welcome.
Nope. I can\'t do much without detailed specs on the wire.
- 25C resistance/ft
- 60C resistance/ft
- Type of wire used.
- Length of wire used.
- Estimated blanket insulation value.
- Thermostat system used.
- Power source. 12V, 117VAC, or variable power supply?
- Over-temperature protection (thermal fuse)?
A Google search might help:
https://www.google.com/search?q=electric+blanket+controller
The commercial controllers usually have the power control and
temperature regulating devices included. If one of the controllers
from your failed blankets is still available, it might be worth
testing and trying. Or, roll your own:
https://www.qsl.net/ve3lny/blanketcontroller.html
Note that the design is for a 117VAC blanket, not 12V.
Be careful and have a fire extinguisher handy.
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
JOn Saturday, October 31, 2020 at 12:17:38 AM UTC-4, Jeff Liebermann wrote:
On Fri, 30 Oct 2020 13:30:37 -0400, Runner <run...@aolnospam.com
wrote:
On 10/30/20 1:21 PM, Ralph Mowery wrote:
In article <593b6d9c-02ba-4ec4...@googlegroups.com>,
peterw...@gmail.com says...
Hmmmm... If it is sufficiently important to know the precise and accurate resistance of a given (and very short) length of wire, then that method will not work very well. I have never, ever come across a factory-sealed spool of electrical wire that is within even 1% of the nominal length, with the tendency to run a bit long
rather than short. And even shop-cut lengths tend to have a bit added for waste and crimps.
And here is another issue: I keep a pretty good Fluke meter which gives a resolution of +/-0.5% in ohms in ranges above 32 ohms, and +/- 2% at the lowest range. Which may not be good enough in this application.
Again, if it is sufficiently important, then the correct instrumentation and the calibration and set-up of same is critical.
For most at home the best way for very low resistance is to have an
ampmeter and voltmeter and varitable power supply. Put as much current
as you can through the wire and measure the voltage across it and ohm
law the resistance.
This is what I ended up doing, although I decided to just power the
entire 60 foot spool instead of the single one foot piece. I found
that, at 12 V, 7 A was used, so that\'s where I started.
You did that through a 1 ft length of wire?
P = E * I = 12v * 7A = 84 watts
In a 1 ft length of wire, that should have gotten the wire red hot
(depending on wire gauge and contract resistance).
That was too much power, at least IMO, for the electric blanket I was
making, so I kept checking current and voltage until a more reasonable
55 W was reached. This meant using 20 feet of the wire and powering at
5 V (11 A).
I have a small complaint. If you expect usable answers, it\'s really
helpful if you would describe:
1. What problem are you trying to solve?
2. What do you have to work with?
3. What have you done so far and what went wrong?
My initial reply assumed that you were doing some kind of measurement.
I replied accordingly with the instruments required. My answer would
have been very different if you had supplied the details and numbers.
I\'m under the blanket now and it\'s toasty. Not hot, but warm. I will
be continuing to check connections for excess heating, but I repurposed
the original Sunbeam connections and those are more than adequate and
saved me a lot of time. The only source of moderate heating outside the
blanket is the power wires to the blanket. Since I used the Sunbeam
wires, their gauge is a bit thin. If it becomes an issue, I will
upgrade to a thicker cable.
Hint: Real electric blankets use nichrome or some form of resistance
heating wire. See list at step 6.
\"DIY Heating Pad - (small Electrical Blanket)\"
https://www.instructables.com/DIY-Heating-pad-small-electrical-blanket/
Any clues as to the source and tupe of \"teflon insulated wire\" you\'re
using? If its copper wire, be advised that soft copper wire work
hardens fairly easily. Just bend it a few times and it will break.
The Teflon wire is hot glued to the old blanket.
The wire is not made of teflon. It\'s probably copper, nichrome, or
something similar. The insulation is Teflon.
Make sure you\'re using high temp (195C gun) glue. Low temp (130C gun)
will work, but methinks high temp is a better choice.
I wasn\'t sure if this
would work as I feared glue melting, but so far so good after some
hours.
The standard high temp hot melt glue melts at about 200C. That\'s
quite a bit warmer than the 25C to 55C range of a typical electric
blanket.
At 84 watts though, it might have been a different story.
Queen size electric blankets typically draw about 60 watts or 100
watts for a twin size.
Originally, I was going to go with the full wire spool and the 84 watt
version, but I wasn\'t sure how I was going to vary the output.
A light dimmer should work. If you try to use a linear regulator,
you\'ll end up dissipating quite a bit of heat in the regulator. The
switching regulator in the light dimmer is far more efficient.
All I
have on hand was a PWM 8 A 12 V lamp dimmer, used for dimming LED
arrays, but it burned out almost instantly.
It should have worked. However, when the wire is cold, the resistance
is rather low and the inrush current is rather high. When it gets
warm, the resistance increases, and the operating current is reduces.
My guess(tm) is that the initial inrush current exeeded the 8A rating.
I wasn\'t surprised of
course, but thought I\'d give it a try.
Learn by Destroying(tm). Ok, what have you learned?
Any ideas as to how to vary the power welcome.
Nope. I can\'t do much without detailed specs on the wire.
- 25C resistance/ft
- 60C resistance/ft
- Type of wire used.
- Length of wire used.
- Estimated blanket insulation value.
- Thermostat system used.
- Power source. 12V, 117VAC, or variable power supply?
- Over-temperature protection (thermal fuse)?
A Google search might help:
https://www.google.com/search?q=electric+blanket+controller
The commercial controllers usually have the power control and
temperature regulating devices included. If one of the controllers
from your failed blankets is still available, it might be worth
testing and trying. Or, roll your own:
https://www.qsl.net/ve3lny/blanketcontroller.html
Note that the design is for a 117VAC blanket, not 12V.
Be careful and have a fire extinguisher handy.
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Just to add a bit of information to this guidance, joining nichrome wire to nichrome or copper can be a bit of a challenge if you are not aware of the metallurgy issues. It does not solder with lead free rosin core solder. Connections to nichrome wire are often done with a crimp style connector. This may not be a workable solution for an electric blanket, depending on the area where the splice is applied.
Nichrome can be soldered but you need a acid type flux and the degree of success is somewhat dependent on the type of nichrome (A: has no iron and behaves like stainless steel, B: contains some iron and can be more easily soldered).
I\'ve had good luck joining both types using Ruby fluid flux and in one case using flux for soldering copper pipe, e.g. plumbing flux. Some people have had good luck with 60/40 acid core flux but I have not tried it. My guess is that it would work better on C type nichrome.
I also have used a small tack welder but its not a common household or shop tool.
If you look on the web am sure you will find lots of alternatives.
J
whoops - typo - I have used 60/40 acid core with some success...(sorry, wrong sentence when doing 3 things at once...)
On 11/12/20 9:27 AM, ggherold@gmail.com wrote:
Re: varying power.
Since the resistance of copper goes up with temperature (R is ~ temperature)
controlling the voltage might be best. (no thermal runaway)
Are you using AC or DC power.
12 VDC.
AC might be easier, get a transformer
(maybe filament transformer?) and drive it from a variac.
I had originally considered this, but variacs in general are not
isolated from the AC line and I felt I would have needed an additional
isolation transformer, something I don\'t currently have and they seem to
be quite costly.
DC will be trickier (\'cause that power has to go somewhere) and some
PWM scheme might be the way to go. Or buy a variable DC supply...
you can use it for electroplating when not staying warm. :^)
I am currently using the PWM controller with the DC lines to the
blanket. So far so good. I have been monitoring temperature of the
blanket wiring. It does get up to 180 F, but I am using a timer to
cycle the system on and off so that the blanket is not running
continuously. I\'m not sure how much I will have to vary the duty cycle
yet as the house hasn\'t reached its wintertime lows, but the hope is for
a 33% time on and the rest off. Just have to wait and see. I\'m
currently using a mechanical timer, but I may switch out to a
programmable one I have here.
In general I\'m wondering why not try a heating pad and a nice down
comforter?
I did this several years ago. No heating pad, but two stacked down duck
filled comforters. I still have this set up on the bed in the other
room. Took a long time to heat up, but once warm I couldn\'t cool down
so ended up having to turn a box fan on at full blast at 3 AM in a 47 F
bedroom! I suppose I could set the fan up on a timer to do this
automatically, never thought of that.
George H.
I don\'t recommend electric blankets. For a multitude
of reasons.
On 11/13/20 12:57 PM, legg wrote:
I don\'t recommend electric blankets. For a multitude
of reasons.
I just bought a new one.
I turn it one 20-30 minutes before I go to bed.
I turn it off when I go to bed.
But when I go to bed, the bed is nice and warm.
Beats the shit out of laying there swearing for 15-20
minutes waiting for the bed to finally get warm.
On Fri, 13 Nov 2020 12:18:15 -0500, Runner <runners@aolnospam.com
wrote:
On 11/12/20 9:27 AM, ggherold@gmail.com wrote:
Re: varying power.
Since the resistance of copper goes up with temperature (R is ~ temperature)
controlling the voltage might be best. (no thermal runaway)
Are you using AC or DC power.
12 VDC.
AC might be easier, get a transformer
(maybe filament transformer?) and drive it from a variac.
I had originally considered this, but variacs in general are not
isolated from the AC line and I felt I would have needed an additional
isolation transformer, something I don\'t currently have and they seem to
be quite costly.
DC will be trickier (\'cause that power has to go somewhere) and some
PWM scheme might be the way to go. Or buy a variable DC supply...
you can use it for electroplating when not staying warm. :^)
I am currently using the PWM controller with the DC lines to the
blanket. So far so good. I have been monitoring temperature of the
blanket wiring. It does get up to 180 F, but I am using a timer to
cycle the system on and off so that the blanket is not running
continuously. I\'m not sure how much I will have to vary the duty cycle
yet as the house hasn\'t reached its wintertime lows, but the hope is for
a 33% time on and the rest off. Just have to wait and see. I\'m
currently using a mechanical timer, but I may switch out to a
programmable one I have here.
In general I\'m wondering why not try a heating pad and a nice down
comforter?
I did this several years ago. No heating pad, but two stacked down duck
filled comforters. I still have this set up on the bed in the other
room. Took a long time to heat up, but once warm I couldn\'t cool down
so ended up having to turn a box fan on at full blast at 3 AM in a 47 F
bedroom! I suppose I could set the fan up on a timer to do this
automatically, never thought of that.
George H.
Why not use a proper thermostat?
I don\'t recommend electric blankets. For a multitude
of reasons.
Add or subtract blankets, as required.
RL