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  #1   Report Post  
Bill Stock
 
Posts: n/a
Default NiChrome questions

This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is #22
and approximately 1 ohm per foot.

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that low. But
assuming the tables are referring to 120V, that would mean 360 Watts or 15
Amps at 24 Volts? This can't be right?

The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT). I've seen the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature. Although I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps at
24V?

There's obviously something I don't understand here. I would appreciate it
if someone could lead me out of the darkness.



  #2   Report Post  
Paul Kierstead
 
Posts: n/a
Default

Bill Stock wrote:
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.


We do? Maybe this is why my woodturning seems so difficult...

PK

PS: I am not sure about those RC guys either...are they NiChrome experts
for some reason?
  #3   Report Post  
DJ Delorie
 
Posts: n/a
Default


"Bill Stock" writes:
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.


REpository.

I want to build a Hot Wire to bend some Acrylic. The wire in
question is #22 and approximately 1 ohm per foot.


Let's assume you need 3 feet for the sake of the math below

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really
be Watts?


When resistance is fixed per foot, and the manufacturer doesn't know
how many feet you have, they can't use watts. They could use watts
per foot, but that's essentially amps. Constant amps gives a
predictable watts/foot regardless of the length of the wire. For the
same amps (and thus temperature), and twice longer wire uses twice the
watts (and needs twice the voltage).

For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that
low. But assuming the tables are referring to 120V, that would mean
360 Watts or 15 Amps at 24 Volts? This can't be right?


3 amps for a 3 ohm (3 foot) wire is 9 volts (E=IR). You choose the
voltage in order to create the appropriate current.

If you put a 3 ohm wire on a 120VAC outlet, you'll get 40 amps (4800
watts) for a few seconds. If you try this, use a movie camera so we
can all share the excitement ;-)

The second problem is the power supply. Assuming I'm confused about
the Watts and 3 amps at 24 Volts will suffice.


You want a variable voltage power supply rated at, say, twice the
amperage you'll actually need, and high enough volts to generate the
amperage your project will call for. You adjust the voltage to result
in the current needed. Make sure the supply has an ammeter on it, or
use your own.

The average light dimmer will only handle about 500 Watts,


The average light dimmer is a pulse width modulator suitable only for
120VAC circuits.

If you want 3 amps across 3 ohms, with a 120VAC circuit, 3 amps at
120VAC is 360 watts. You'd need a couple lightbulbs in parallel to
get that, or a floodlight. I suppose you could build a box with, say,
3-6 100W bulbs each with their own light switch, to provide variable
current. Each bulb adds ~ 0.8 amps.
  #4   Report Post  
DJ Delorie
 
Posts: n/a
Default


Paul Kierstead writes:
PS: I am not sure about those RC guys either...are they NiChrome
experts for some reason?


RC aircraft wings are often cut with hot wires through foam.
  #5   Report Post  
Leo Lichtman
 
Posts: n/a
Default


"DJ Delorie" wrote: (clip) REpository. (clip)
^^^^^^^^^^^^
SUPpository is funnier.




  #6   Report Post  
Bill Stock
 
Posts: n/a
Default


"DJ Delorie" wrote in message
...

"Bill Stock" writes:
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.


REpository.




I want to build a Hot Wire to bend some Acrylic. The wire in
question is #22 and approximately 1 ohm per foot.


Let's assume you need 3 feet for the sake of the math below

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really
be Watts?


When resistance is fixed per foot, and the manufacturer doesn't know
how many feet you have, they can't use watts. They could use watts
per foot, but that's essentially amps. Constant amps gives a
predictable watts/foot regardless of the length of the wire. For the
same amps (and thus temperature), and twice longer wire uses twice the
watts (and needs twice the voltage).

For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that
low. But assuming the tables are referring to 120V, that would mean
360 Watts or 15 Amps at 24 Volts? This can't be right?


3 amps for a 3 ohm (3 foot) wire is 9 volts (E=IR). You choose the
voltage in order to create the appropriate current.

If you put a 3 ohm wire on a 120VAC outlet, you'll get 40 amps (4800
watts) for a few seconds. If you try this, use a movie camera so we
can all share the excitement ;-)


No plans to try this any time soon.

The second problem is the power supply. Assuming I'm confused about
the Watts and 3 amps at 24 Volts will suffice.


You want a variable voltage power supply rated at, say, twice the
amperage you'll actually need, and high enough volts to generate the
amperage your project will call for. You adjust the voltage to result
in the current needed. Make sure the supply has an ammeter on it, or
use your own.


Yep. Priced the Variacs. I tried using the dual variable power supply
(3A/37V) that I built 20 years ago. I smoked the PS before the wire got hot.
Fortunately I only fried the output caps and not the transformer. (I love
the smell of burning Tantalum in the morning.)

The average light dimmer will only handle about 500 Watts,


The average light dimmer is a pulse width modulator suitable only for
120VAC circuits.

If you want 3 amps across 3 ohms, with a 120VAC circuit, 3 amps at
120VAC is 360 watts. You'd need a couple lightbulbs in parallel to
get that, or a floodlight. I suppose you could build a box with, say,
3-6 100W bulbs each with their own light switch, to provide variable
current. Each bulb adds ~ 0.8 amps.


Thanks. This may be the easiest solution.



  #7   Report Post  
Mike
 
Posts: n/a
Default

Bill Stock wrote:
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is #22
and approximately 1 ohm per foot.

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that low. But
assuming the tables are referring to 120V, that would mean 360 Watts or 15
Amps at 24 Volts? This can't be right?


Watts ? No. The required wattage for 3Amps (400F) depends on the length of
the wire. Fir example 1 foot (1 ohm) would need 3 V to drive 3A through the
wire - Watts = I^2 * R or Watts = E * I Wattage needed would 9 Watts at
3V to give you 400F for 1 Foot.

For longer pieces of wire work the math:
Given: Current (I) 3A
Length of wi Whatever you need
Resistance: 1 ohm/foot

Voltage (or Electromotive force E)
R = 1 (ohm /foot) * Length needed (in feet)
E = I * R

Power = E * I





The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT).


If you're using 2' of wire with 1 ohm/foot then you're getting you've got 12A
with a 24V transformer, and drawing 288 watts, and the 500w lamp dimmer should
be ok. You'd need to bring the voltage down to 6V for 3A with a power of 9W.

These currents are on the secondary side of the transformer - the primary
(120V side) the currents would be approximately 1/6 as much.


I've seen the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature. Although I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps at
24V?

There's obviously something I don't understand here. I would appreciate it
if someone could lead me out of the darkness.



  #8   Report Post  
DJ Delorie
 
Posts: n/a
Default


"Bill Stock" writes:
Thanks. This may be the easiest solution.


It's also the most dangerous, because you have exposed metal with
120VAC on it. If ANYTHING happens, you get electrocuted. DO NOT USE
WITHOUT A GROUND FAULT INTERRUPTER. And rubber gloves. And make out
your will first. And have someone nearby ready to pull the plug. I'm
not kidding.

Better yet, just don't do it.
  #9   Report Post  
Paul Kierstead
 
Posts: n/a
Default

DJ Delorie wrote:
Paul Kierstead writes:

PS: I am not sure about those RC guys either...are they NiChrome
experts for some reason?



RC aircraft wings are often cut with hot wires through foam.


Ahhh...I am just old enough that I only know of tissue covered balsa
wood planes; didn't know ppl were fabricating their own foam ones, but
of course it makes perfect sense.

Also old enough to have used djgcc a fair bit; many many thanks for
rescuing me from the perils of the crap commercial compliers of the day
(not that things are so much better today).

PK
  #10   Report Post  
DJ Delorie
 
Posts: n/a
Default


Paul Kierstead writes:
Ahhh...I am just old enough that I only know of tissue covered balsa
wood planes; didn't know ppl were fabricating their own foam ones, but
of course it makes perfect sense.


It depends on the plane. WHen I was doing it, foam cores and carbon
fiber spars were used for gliders and covered spar-n-rib was used for
powered and/or high performance planes.

Also old enough to have used djgcc a fair bit; many many thanks for
rescuing me from the perils of the crap commercial compliers of the
day (not that things are so much better today).


Well, djgpp is much better today :-)


  #11   Report Post  
Lobby Dosser
 
Posts: n/a
Default

"Leo Lichtman" wrote:


"DJ Delorie" wrote: (clip) REpository. (clip)
^^^^^^^^^^^^
SUPpository is funnier.




A nichrome suppository is funny??
  #12   Report Post  
George
 
Posts: n/a
Default

Think about it. Cut and cauterize....

"Lobby Dosser" wrote in message
news:sOmwd.7661$E_6.2438@trnddc04...
"Leo Lichtman" wrote:


"DJ Delorie" wrote: (clip) REpository. (clip)
^^^^^^^^^^^^
SUPpository is funnier.




A nichrome suppository is funny??



  #13   Report Post  
Lobby Dosser
 
Posts: n/a
Default

"George" george@least wrote:

Think about it. Cut and cauterize....


High Pucker Factor!


"Lobby Dosser" wrote in message
news:sOmwd.7661$E_6.2438@trnddc04...
"Leo Lichtman" wrote:


"DJ Delorie" wrote: (clip) REpository. (clip)
^^^^^^^^^^^^
SUPpository is funnier.




A nichrome suppository is funny??





  #14   Report Post  
mac davis
 
Posts: n/a
Default

On Thu, 16 Dec 2004 11:19:13 -0500, "Bill Stock"
wrote:

rec.crafts.woodturning
is a knowledge base for NiChrome??

I must have NiCHrome filtered out.. never seen it mentioned here..


This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is #22
and approximately 1 ohm per foot.

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that low. But
assuming the tables are referring to 120V, that would mean 360 Watts or 15
Amps at 24 Volts? This can't be right?

The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT). I've seen the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature. Although I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps at
24V?

There's obviously something I don't understand here. I would appreciate it
if someone could lead me out of the darkness.



  #15   Report Post  
Ken Moon
 
Posts: n/a
Default

Bill,
See comments interspersed:
"Bill Stock" wrote in message
...
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is
#22
and approximately 1 ohm per foot.
==============================

Is that at room temperature or at 400 degrees?
Nichrome, as all metals, change resistance as temperature rises. Therefore,
you'll have higher currents (Amps) at lower temps, so your supply needs to
have adequate reserve to heat the wire. As it reaches the higher temps, the
current will self limit according to voltage available.
================================
Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that low.
But
assuming the tables are referring to 120V, that would mean 360 Watts or 15
Amps at 24 Volts? This can't be right?

================================
The normal Ohms law rules won't work here since the resistance is variable
as well as the Voltage. (Ohm's law is valid, just not as you'd normally
think of it in linear terms).
================================
The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT). I've seen
the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature. Although
I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps at
24V?

There's obviously something I don't understand here. I would appreciate it
if someone could lead me out of the darkness.

===================================
If you could find an old filament transformer like used in old tube type
radios, etc., it would probably get you into the desired range, but you'd
need to find out more about the cold to hot characteristics of the Nichrome.




  #16   Report Post  
Bill Stock
 
Posts: n/a
Default


"Ken Moon" wrote in message
nk.net...
Bill,
See comments interspersed:
"Bill Stock" wrote in message
...
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is
#22
and approximately 1 ohm per foot.
==============================

Is that at room temperature or at 400 degrees?


25C.

Nichrome, as all metals, change resistance as temperature rises.

Therefore,
you'll have higher currents (Amps) at lower temps, so your supply needs to
have adequate reserve to heat the wire. As it reaches the higher temps,

the
current will self limit according to voltage available.
================================
Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the

400F
that I require. The tables I've seen don't actually show temps that low.
But
assuming the tables are referring to 120V, that would mean 360 Watts or

15
Amps at 24 Volts? This can't be right?

================================
The normal Ohms law rules won't work here since the resistance is variable
as well as the Voltage. (Ohm's law is valid, just not as you'd normally
think of it in linear terms).
================================
The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT). I've seen
the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature.

Although
I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps

at
24V?

There's obviously something I don't understand here. I would appreciate

it
if someone could lead me out of the darkness.

===================================
If you could find an old filament transformer like used in old tube type
radios, etc., it would probably get you into the desired range, but you'd
need to find out more about the cold to hot characteristics of the

Nichrome.


The adjustment factor is only 1.037 for the temp I want.



  #17   Report Post  
Bill Stock
 
Posts: n/a
Default


"mac davis" wrote in message
...
On Thu, 16 Dec 2004 11:19:13 -0500, "Bill Stock"
wrote:

rec.crafts.woodturning
is a knowledge base for NiChrome??

I must have NiCHrome filtered out.. never seen it mentioned here..


Probably not as frequently as the RC group. I believe you guys use it to
make "hot pens" to sign your work.


This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is

#22
and approximately 1 ohm per foot.

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that low.

But
assuming the tables are referring to 120V, that would mean 360 Watts or

15
Amps at 24 Volts? This can't be right?

The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT). I've seen

the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature. Although

I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps

at
24V?

There's obviously something I don't understand here. I would appreciate

it
if someone could lead me out of the darkness.





  #18   Report Post  
Bill Stock
 
Posts: n/a
Default


"Mike" wrote in message
nk.net...
Bill Stock wrote:
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is

#22
and approximately 1 ohm per foot.

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the

400F
that I require. The tables I've seen don't actually show temps that low.

But
assuming the tables are referring to 120V, that would mean 360 Watts or

15
Amps at 24 Volts? This can't be right?


Watts ? No. The required wattage for 3Amps (400F) depends on the length

of
the wire. Fir example 1 foot (1 ohm) would need 3 V to drive 3A through

the
wire - Watts = I^2 * R or Watts = E * I Wattage needed would 9

Watts at
3V to give you 400F for 1 Foot.


Thanks Mike, I get the V=I*R. Although it's been a good number of years
(decades) since my basic electronics course. It just surprises me that the
amperage specified per foot, would not be for a given voltage. For example:
I tried to test my wire using a variable power supply (3A/35V) a built a
number of years ago. But the wire never did start to glow before the PS
smoked itself. Everything past the regulators got fried. The regulators have
thermal protection and there is a fuse on the mains side, so I guess the
parts (diodes/caps) were underrated. It should not be a big deal to fix
these components. But I'm surprised I did not get some colour out of the
wire at 3A/35V.

Thanks.

For longer pieces of wire work the math:
Given: Current (I) 3A
Length of wi Whatever you need
Resistance: 1 ohm/foot

Voltage (or Electromotive force E)
R = 1 (ohm /foot) * Length needed (in feet)
E = I * R

Power = E * I





The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT).


If you're using 2' of wire with 1 ohm/foot then you're getting you've got

12A
with a 24V transformer, and drawing 288 watts, and the 500w lamp dimmer

should
be ok. You'd need to bring the voltage down to 6V for 3A with a power of

9W.

These currents are on the secondary side of the transformer - the primary
(120V side) the currents would be approximately 1/6 as much.


I've seen the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature.

Although I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps

at
24V?

There's obviously something I don't understand here. I would appreciate

it
if someone could lead me out of the darkness.





  #19   Report Post  
william_b_noble
 
Posts: n/a
Default

why the heck do you want to use a nicrome wire for this purpose? How sharp
a bend do you need? is a 1/2 inch radius OK - if yes, use coper pipe with a
halogen bulb inside. Or take apart a toaster or something and use that
heating element.
If you use either a lamp or a 115V element, you can put a lamp dimmer in
series and control the power with the dimmer. measure temp with a
thermometer and adjust as requred.


"Bill Stock" wrote in message
...
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is

#22
and approximately 1 ohm per foot.

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that low.

But
assuming the tables are referring to 120V, that would mean 360 Watts or 15
Amps at 24 Volts? This can't be right?

The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT). I've seen

the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature. Although

I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps at
24V?

There's obviously something I don't understand here. I would appreciate it
if someone could lead me out of the darkness.





  #20   Report Post  
Bill
 
Posts: n/a
Default


There are 3413 BTU's per kilowatt. A BTU will heat one pound of water,
one degree F. A BTU will raise the temp of one cubic foot of air about
one degree F.

Bill in WNC mountains



  #21   Report Post  
mac davis
 
Posts: n/a
Default

On Thu, 16 Dec 2004 18:30:32 -0800, "william_b_noble"
wrote:

or a heat gun...
you can bend plexi almost double with a good heat gun and patience...
wouldn't your light sabre be more effective??

(posted only to the REC to hopefully slow down this dumb ass cross
posting)


why the heck do you want to use a nicrome wire for this purpose? How sharp
a bend do you need? is a 1/2 inch radius OK - if yes, use coper pipe with a
halogen bulb inside. Or take apart a toaster or something and use that
heating element.
If you use either a lamp or a 115V element, you can put a lamp dimmer in
series and control the power with the dimmer. measure temp with a
thermometer and adjust as requred.


"Bill Stock" wrote in message
...
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is

#22
and approximately 1 ohm per foot.

Most of the temperature tables I've seen for NiChrome wire show the
relationship between Amps and Temperature. But shouldn't this really be
Watts? For example the tables show that I need about 3 Amps for the 400F
that I require. The tables I've seen don't actually show temps that low.

But
assuming the tables are referring to 120V, that would mean 360 Watts or 15
Amps at 24 Volts? This can't be right?

The second problem is the power supply. Assuming I'm confused about the
Watts and 3 amps at 24 Volts will suffice. The average light dimmer will
only handle about 500 Watts, but if I short out (2 Ohms) the transformer
secondary I will fry the dimmer and/or transformer (DAMHIKT). I've seen

the
light bulb in series trick, but even a 200 Watt bulb on the Transformer
secondary would not give me enough Amps to reach my temperature. Although

I
suppose a 200 Watt bulb on the Transformer primary would give me 8 Amps at
24V?

There's obviously something I don't understand here. I would appreciate it
if someone could lead me out of the darkness.





  #22   Report Post  
Dan Bollinger
 
Posts: n/a
Default

I want to build a Hot Wire to bend some Acrylic. The wire in question is
#22
and approximately 1 ohm per foot.



Tons if info at this website: http://www.infraredheaters.com/



  #23   Report Post  
Mike
 
Posts: n/a
Default

Bill Stock wrote:

Thanks Mike, I get the V=I*R. Although it's been a good number of years
(decades) since my basic electronics course. It just surprises me that the
amperage specified per foot, would not be for a given voltage. For example:
I tried to test my wire using a variable power supply (3A/35V) a built a
number of years ago. But the wire never did start to glow before the PS
smoked itself. Everything past the regulators got fried. The regulators have
thermal protection and there is a fuse on the mains side, so I guess the
parts (diodes/caps) were underrated. It should not be a big deal to fix
these components. But I'm surprised I did not get some colour out of the
wire at 3A/35V.


400F is pretty dark, as an example - look in your oven set to 450F - it
doesn't glow (visible) red. 35V would have tried to drive lots more than 3A
through the wire - more like 12 if I remember your numbers (in the bit bucket
now) that would fry a 3A supply.

mike



  #24   Report Post  
Mike
 
Posts: n/a
Default

Bill Stock wrote:

Thanks Mike, I get the V=I*R. Although it's been a good number of years
(decades) since my basic electronics course. It just surprises me that the
amperage specified per foot, would not be for a given voltage. For example:
I tried to test my wire using a variable power supply (3A/35V) a built a
number of years ago. But the wire never did start to glow before the PS
smoked itself. Everything past the regulators got fried. The regulators have
thermal protection and there is a fuse on the mains side, so I guess the
parts (diodes/caps) were underrated. It should not be a big deal to fix
these components. But I'm surprised I did not get some colour out of the
wire at 3A/35V.


400F is pretty dark, as an example - look in your oven set to 450F - it
doesn't glow (visible) red. 35V would have tried to drive lots more than 3A
through the wire - more like 12 if I remember your numbers (in the bit bucket
now) that would fry a 3A supply.

mike



  #25   Report Post  
Mike
 
Posts: n/a
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Bill Stock wrote:

Thanks Mike, I get the V=I*R. Although it's been a good number of years
(decades) since my basic electronics course. It just surprises me that the
amperage specified per foot, would not be for a given voltage. For example:
I tried to test my wire using a variable power supply (3A/35V) a built a
number of years ago. But the wire never did start to glow before the PS
smoked itself. Everything past the regulators got fried. The regulators have
thermal protection and there is a fuse on the mains side, so I guess the
parts (diodes/caps) were underrated. It should not be a big deal to fix
these components. But I'm surprised I did not get some colour out of the
wire at 3A/35V.


400F is pretty dark, as an example - look in your oven set to 450F - it
doesn't glow (visible) red. 35V would have tried to drive lots more than 3A
through the wire - more like 12 if I remember your numbers (in the bit bucket
now) that would fry a 3A supply.

mike





  #26   Report Post  
Bill Stock
 
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"Mike" wrote in message
...
Bill Stock wrote:

Thanks Mike, I get the V=I*R. Although it's been a good number of years
(decades) since my basic electronics course. It just surprises me that

the
amperage specified per foot, would not be for a given voltage. For

example:
I tried to test my wire using a variable power supply (3A/35V) a built a
number of years ago. But the wire never did start to glow before the PS
smoked itself. Everything past the regulators got fried. The regulators

have
thermal protection and there is a fuse on the mains side, so I guess the
parts (diodes/caps) were underrated. It should not be a big deal to fix
these components. But I'm surprised I did not get some colour out of the
wire at 3A/35V.


400F is pretty dark, as an example - look in your oven set to 450F - it
doesn't glow (visible) red. 35V would have tried to drive lots more than

3A
through the wire - more like 12 if I remember your numbers (in the bit

bucket
now) that would fry a 3A supply.

mike


Thanks Mike.

I think I solved the mystery yesterday. I picked up a cheap switching PSU at
the surplus store to continue my experimenting. But I still wasn't getting
much heating. So I decided to check the resistance of my test wire and it
was 3+ x what I expected. It turns out that the vendor shipped me the wrong
wire, 3.5 ohms/ft, not the 1 ohm/ft I ordered. They're shipping the correct
wire, so this should solve my problem.



  #27   Report Post  
Bill Stock
 
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"Dan Bollinger" wrote in message
news:brIwd.516931$wV.403584@attbi_s54...
I want to build a Hot Wire to bend some Acrylic. The wire in question is

#22
and approximately 1 ohm per foot.



Tons if info at this website: http://www.infraredheaters.com/



Thanks, good site.



  #28   Report Post  
Ken Grunke
 
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Bill Stock wrote:
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is #22
and approximately 1 ohm per foot.


I did a lot of acrylic bending years ago making picture keyframes and
the like. I used a coiled nichrome wire inside a heatproof channel,
lined with asbestos paper (!) connected to full house current. It was
about 18" long, and the element, which was about an inch below the
channel's 1/2" opening, glowed a dark red. Turning a piece over once, it
took about 15 seconds to get the acrylic up to bending temp. and it
worked really well.

I would use a coiled element sized to give a much higher temp than 400
degrees at 115v, and with a lamp dimmer (no stepdown transformer). If
your element is only at 400 degrees, you could be waiting forever to
reach bending temp.

Ken Grunke
La Farge, WI US


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Bill Stock
 
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"Ken Grunke" wrote in message
...
Bill Stock wrote:
This is somewhat OT, but you appear to be the biggest suppository of
knowledge when it comes to NiChrome.

I want to build a Hot Wire to bend some Acrylic. The wire in question is

#22
and approximately 1 ohm per foot.


I did a lot of acrylic bending years ago making picture keyframes and
the like. I used a coiled nichrome wire inside a heatproof channel,
lined with asbestos paper (!) connected to full house current.


Thanks Ken. Did you make your own coils of buy then ready made? Do you
remember the gauge/resistance? Did you use an insulator on the coil or let
it hang free in the channel?

How did you construct your channel? I was thinking of MDF base, reflective
aluminum, masonite (channel sides), covered with some heat resistant
material, perhap fiberglass.

It was
about 18" long, and the element, which was about an inch below the
channel's 1/2" opening, glowed a dark red. Turning a piece over once, it
took about 15 seconds to get the acrylic up to bending temp. and it
worked really well.

I would use a coiled element sized to give a much higher temp than 400
degrees at 115v, and with a lamp dimmer (no stepdown transformer). If
your element is only at 400 degrees, you could be waiting forever to
reach bending temp.


Thanks again Ken, useful info.


Ken Grunke
La Farge, WI US


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  #30   Report Post  
Ken Grunke
 
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Bill Stock wrote:


I did a lot of acrylic bending years ago making picture keyframes and
the like. I used a coiled nichrome wire inside a heatproof channel,
lined with asbestos paper (!) connected to full house current.



Thanks Ken. Did you make your own coils of buy then ready made? Do you
remember the gauge/resistance? Did you use an insulator on the coil or let
it hang free in the channel?

How did you construct your channel? I was thinking of MDF base, reflective
aluminum, masonite (channel sides), covered with some heat resistant
material, perhap fiberglass.


It was
about 18" long, and the element, which was about an inch below the
channel's 1/2" opening, glowed a dark red. Turning a piece over once, it
took about 15 seconds to get the acrylic up to bending temp. and it
worked really well.

I would use a coiled element sized to give a much higher temp than 400
degrees at 115v, and with a lamp dimmer (no stepdown transformer). If
your element is only at 400 degrees, you could be waiting forever to
reach bending temp.



Thanks again Ken, useful info.


Bill, the way I made my bender jig I wouldn't recommend doing it the
same way to you, it was pretty cobbled up and not very safe.

I would use a ready-made coiled element or take one out of a milkhouse
heater whose element might be broken, but at least half of it's length
usable. The dimmer will take care of having a shorter length (I
think--see disclaimer below).

Make a U-shape from steel sheet (NOT aluminum) and get some ceramic
insulators from an appliance store to hold the element in the channel. I
think the old Maytag dryers used ceramic thimbles that the element
threaded through, that might be just the thing.

A quartz heater element would be even better, it's self-supporting so
you don't have to worry about shorting a coiled element to the sheet metal.

Won't go too much further into the design, except to recommend that the
channel be a seperate piece from the top surface where you lay the
acrylic--you only want heat to come out of the slot.
I would not use any flamable material, but fabricate the whole thing
from sheet metal probably pop-riveted together, with an enclosed box at
one end to hold the dimmer and protect the connections from fingers (and
vis versa!)
I am NOT an electrical engineer, so I don't wanna tell you how to wire
it and get blamed for your demise--just be safe and find the correct way
to do it! If for some reason the dimmer is not appropriate, you could
use a limiter control from an electric stove, one of the burner controls
which cycles the heater on and off in short periods.
Think I'd better stop here before I *really* get into trouble from those
who ARE electrical engineers!

Ken Grunke


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Dan Bollinger
 
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I would not use any flamable material, but fabricate the whole thing
from sheet metal


Good thinking, I wouldn't use flammable materials like lacquer thinner or
gasoline to build the thing either. Come to think of it, I wouldn't use any
combustible materials like wood, either.

Get your ceramic grommets at: http://www.infraredheaters.com/

Dan


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