Login Join Maker Pro

# Improvised power resistor

T

#### Thomas Carlan

Jan 1, 1970
0
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

Thomas Carlan

C

#### Charles

Jan 1, 1970
0
Thomas Carlan said:
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

You can wind nichrome wire around a ceramic core.

D

#### D from BC

Jan 1, 1970
0
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

Thomas Carlan

I'm curious if anyone will mention how a power mosfet can be turned
into an active resistor..
D from BC

B

#### Bob

Jan 1, 1970
0
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?
This would be more appropriate in sci.electronics.basics

Depends what resistance you want and how much inductance
and temperature drift you can tolerate.

100meters of thin insulated wired on a drum typically has a resistance
of
a few tens of ohms but has signfiicant inductance. You can usually get
access to both ends of a wire on a drum to connect drums in series or
parallel.

The lead from a graphite pencil is a few ohms end to end.

R

#### RST Engineering $$jw$$

Jan 1, 1970
0
Depending on the value, salt water in a ceramic mug. Power capacity is
strictly a function of how hot you will let the water get and the thermal
transfer characteristics of the ceramic.

Jim

J

#### Jan Panteltje

Jan 1, 1970
0
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

Thomas Carlan

Sure 20-50W lightbulb.

(So now 'what resistance', also note a lightbulb when cold has a 10 times lower
resistance then when warm).

Or you can wind your own resistors using special wire with a low temp coefficient.

J

#### John

Jan 1, 1970
0
I'm curious if anyone will mention how a power mosfet can be turned
Probably the best way is to do a web search for "electronic load".
Lots of info and schematics out there.

-- remove SPAMMENOT for e-mail responses --

R

#### Robert

Jan 1, 1970
0
Thomas Carlan said:
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

Thomas Carlan

I heard of one guy who took one of those hollow tubular resistors and ran
Surgical Tubing down the center of it then circulated water through the
tubing and back to a large reservoir kept cold.

Don't know how well it'd work.

Robert

S

#### Spehro Pefhany

Jan 1, 1970
0
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

Thomas Carlan

Any kind of metal will work as a (generally low-value) resistor. Steel
strapping, for example, but the resistance won't be very constant with
temperature.

Best regards,
Spehro Pefhany

M

#### MooseFET

Jan 1, 1970
0
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

A long length of hookup wire.
A light bulb.
A couple of wires in a bucket of water.

R

#### RST Engineering $$jw$$

Jan 1, 1970
0
MooseFET said:
A long length of hookup wire.
A light bulb.
A couple of wires in a bucket of water.
^
salt or hard

Jim

R

#### Robert Baer

Jan 1, 1970
0
Thomas said:
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

Thomas Carlan
Metal ribbon.

W

#### Winfield

Jan 1, 1970
0
John said:
Probably the best way is to do a web search for
"electronic load". Lots of info and schematics out
there.

It's useful to put some of the story here on s.e.d.
First, we'll make the MOSFET's current follow Ohm's
law for a resistor, I = V/R, using a current-sense
resistor Rs, and a resistive divider, R1/(R1 + R2).

--+--------------+- V
| |
R2 |
| __ ||-'
+-----|+ \__||-,
| ,--|-_/ |
| |___________|
R1 |
| Rs
| |
--+--------------+---

If we select Rs so that R = Rs (1 + R2/R1), and also
R1>>Rs, we'll have made a nice active power resistor.
It's necessary to add an RC to the opamp output, to
prevent oscillation, as we've written about here many
times before, but that's the basic idea. If the R1 R2
voltage divider ratio involves a multiplying DAC, it's
easy to create a digitally-programmable power resistor.

M

#### MooseFET

Jan 1, 1970
0
^
salt or hard

It doesn't matter much so long as it isn't super pure.

J

#### John Popelish

Jan 1, 1970
0
Thomas said:
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

Yes.

Stainless steel safety tie wire works well, if you don't
need very high resistance values. Supporting the wire so it
can heat air or water without shorting is more trouble than
just making resistance.
e.g.
http://www.stainless-rebar.com/american.htm

What range of resistance are you needing, and energy at what
frequency do you need it to absorb?

D

#### D from BC

Jan 1, 1970
0
I heard of one guy who took one of those hollow tubular resistors and ran
Surgical Tubing down the center of it then circulated water through the
tubing and back to a large reservoir kept cold.

Don't know how well it'd work.

Robert

I've been using a 50W tubular resistor as a test load recently..
I got it dissipating 100Watts..so I keep it in a bucket of water...
D from BC

D

#### D from BC

Jan 1, 1970
0
It's useful to put some of the story here on s.e.d.
First, we'll make the MOSFET's current follow Ohm's
law for a resistor, I = V/R, using a current-sense
resistor Rs, and a resistive divider, R1/(R1 + R2).

--+--------------+- V
| |
R2 |
| __ ||-'
+-----|+ \__||-,
| ,--|-_/ |
| |___________|
R1 |
| Rs
| |
--+--------------+---

If we select Rs so that R = Rs (1 + R2/R1), and also
R1>>Rs, we'll have made a nice active power resistor.
It's necessary to add an RC to the opamp output, to
prevent oscillation, as we've written about here many
times before, but that's the basic idea. If the R1 R2
voltage divider ratio involves a multiplying DAC, it's
easy to create a digitally-programmable power resistor.

Cool! Looks like a great way to dodge buying power resistors.
D from BC

D

#### D from BC

Jan 1, 1970
0
I know it is possible to make an improvised capacitor by using layers
of mylar sheet (or glass) and metal foil.

Is there any equivalent solution for a power resistor in the 20-50W
range?

Thomas Carlan

I liked all the suggests posted..wires, ribbons, ionic liquid, bulbs
...etc..
But I gotta add one obvious wacky suggestion. (IFAIK..not posted
yet..)
Using lots and lots and lots of 1/4W resistors together!!!

D from BC

R

#### Robert

Jan 1, 1970
0
D from BC said:
I've been using a 50W tubular resistor as a test load recently..
I got it dissipating 100Watts..so I keep it in a bucket of water...
D from BC

How do you insulate the electrical connections from the Water?

Robert

D

#### D from BC

Jan 1, 1970
0
How do you insulate the electrical connections from the Water?

Robert

Pure water is a poor conductor. All my connections to the power
resistor are bare..
I put it in a plastic bucket.
The only thing bad that happened was a little rust and there's steam.
D from BC

Replies
14
Views
3K
Replies
4
Views
2K
Replies
9
Views
1K
N
Replies
1
Views
1K