On Tue, 06 Feb 2018 14:26:54 -0500, Clare Snyder
wrote:

On Tue, 06 Feb 2018 09:57:04 -0800, Larry Jaques
wrote:

On Tue, 06 Feb 2018 01:34:57 -0500, Clare Snyder
wrote:

On 6 Feb 2018 04:18:59 GMT, "DoN. Nichols"
wrote:

On 2018-02-06, Jim Wilkins wrote:
"Larry Jaques" wrote in message
news On Sat, 03 Feb 2018 23:48:24 -0500, Clare Snyder

wrote:


Ah dinna know that. What was the actual resistance, or did you
measure it?

How would you measure a very low resistance? It isn't easy.
-jsw

Put a known current through it -- either with a bench power
supply with a current limit adjustment, or an adjustable voltage across
a known resistance in series with the unknown one. In the second case,
measure the voltage across the known resistance to calculate the
current, and measure the voltage drop between the two ends of the SS
resistor using a low voltage digital multimeter. Divide measured
voltage by the current and you have the resistance. (Or, if you have a
lab multimeter with four-wire resistance measurement (as I do), simply
run two wires to each end of the SS resistor. One pair feeds a known
current from the multimeter, and the other pair measures the voltage
across the SS resistor, eliminating the resistance of the test leads
from the equation. (Known current through one pair, but almost zero
current through the other, for measuring the voltage across the
SS resistance.

Enjoy,
DoN.

I calculated, then cut, and then verified by applying a low voltage
and measuring the current - then checking motor current under load
through the resistor to make sure it was limited to close to the
current I desired.

OK.

And grok the airshocks. I remember guys screaming about the $150 set
of tires that got eaten up every time an exhaust melted a loose air
line to a pair of those.


And remember, for the resistors this was WELL before the days of
"instant information" and the internet.
It involved going to the library and digging up technical texts.

Yeah, technical texts, Library Only (no take-out) reference manuals,
and old magazine copies. Searching the newspapers on microfiche was
another source. And don't forget community college libraries.

I've been both places and prefer the Internet, though the quality is
often hard to find on many things. And with all the copycats, you can
find 10,000 sources for the exact same bad info if you're not careful.


Stainless steel "ribbon resistors" have been used for motor
accelleration and braking applications for years - Powerohm being one
current major supplier.

Stainless steel is also commonly used for the elements of immersion
heaters.

For exposed low temperature use, it was just a slam-dunk to use
stainless ribbon, as it was easily sourced, low cost, and did the job
in commercial applications.

This is the first I've heard of it, as nichrome was the locally
sourced stuff here.


I used copper sheet (ribbons) as battery interconnects as well,
because they were flexible, required no additional terminations, and
were easy to fabricate from readilly available materials. Calculating
the resistance etc from tables allowed me to determine how many
"leaves" of copper to use for the links. I used wel;ding cable from
the batteries to the controller and controller to the motor terminals.

You're not referring to the flat, tinned, braided, copper cables, are
you? (Wow, they still make 'em!) https://is.gd/4wdAMu

--
Stoop and you'll be stepped on;
stand tall and you'll be shot at.
-- Carlos A. Urbizo