Resistance in W??

[The little lost angel]

Could anybody please enlighten me why is the resistance value given in
watts instead of ohms?

http://www.brakingresistor.com/metal.htm

Thanks!

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[John Fields]

On Mon, 15 Dec 2003 16:05:22 GMT, a?n?g?e?l@lovergirl.lrigrevol.moc.com
(The little lost angel) wrote:

Could anybody please enlighten me why is the resistance value given in
watts instead of ohms?
---

It isn't. Choose the resistance you need from the resistance _range_
available and the wattage you need from the values available in the
left-most column after you use the derating graph to determine what the
wattage needs to be at the temperature at which the resistor will be
operating.

--
John Fields

 

[The little lost angel]

On Mon, 15 Dec 2003 10:58:20 -0600, John Fields
<jfields@austininstruments.com> wrote:

It isn't. Choose the resistance you need from the resistance _range_
available and the wattage you need from the values available in the
left-most column after you use the derating graph to determine what the
wattage needs to be at the temperature at which the resistor will be
operating.

Sorry I'm slow as usual about getting this.
The only resistance range I see is in the table and it says
Wattage | Resistance Range (W) |
Rating | Standard Type | Non-Inductive Type |

Then the values are like 0.05W - 5KW

Do you mean, I take say "Free Air 100W-150W" which is line 2
At 100C ambient, which is 50% of rated power.

Then resister I would need would be 300W Rating and I can get them
from 0.00067 ohms (0.2W / 300W) to 60 Ohms (18KW /300W)?


--
L.Angel: I'm looking for web design work.
If you need basic to med complexity webpages at affordable rates, email me
Standard HTML, SHTML, MySQL + PHP or ASP, Javascript.
If you really want, FrontPage & DreamWeaver too.
But keep in mind you pay extra bandwidth for their bloated code

 

[DaveC]

On Mon, 15 Dec 2003 8:05:22 -0800, The little lost angel wrote
(in message <3fdddaee.138168045@news.pacific.net.sg&gt:

http://www.brakingresistor.com/metal.htm

All resistors have an ohm value. That's their nature. In some (very few)
applications you don't care about the ohm value of the resistor.

In this case, it seems, these resistors are used to just dump the current
from a motor into a load (any load) resistor so that the motor will stop
turning (hence the "braking" in "braking resistors"). The power is wasted,
turned into heat by the resistor.

The resistance isn't important, just so long as it's a low value. And since
these are all braking resistors, I assume that they're all very low values.

You just need to be sure that the voltage and current you're trying to get
rid of can be handled by the resistor (Power (Watts) = Voltage x Current).

I'm not sure, however, if I had a motor to brake, how I would match one of
these resistors to my motor... maybe measure how much voltage and current the
motor required when running?

Enjoy,
--
DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group

 

[John Larkin]

On Mon, 15 Dec 2003 17:21:44 GMT,
a?n?g?e?l@lovergirl.lrigrevol.moc.com (The little lost angel) wrote:

On Mon, 15 Dec 2003 10:58:20 -0600, John Fields
jfields@austininstruments.com> wrote:

It isn't. Choose the resistance you need from the resistance _range_
available and the wattage you need from the values available in the
left-most column after you use the derating graph to determine what the
wattage needs to be at the temperature at which the resistor will be
operating.

Sorry I'm slow as usual about getting this.
The only resistance range I see is in the table and it says
Wattage | Resistance Range (W) |
Rating | Standard Type | Non-Inductive Type |

Then the values are like 0.05W - 5KW

Do you mean, I take say "Free Air 100W-150W" which is line 2
At 100C ambient, which is 50% of rated power.

Then resister I would need would be 300W Rating and I can get them
from 0.00067 ohms (0.2W / 300W) to 60 Ohms (18KW /300W)?

I've seen a lot of magazines and such use W to indicate ohms. This
must be some sort of Windows-y typographic corruption of the Omega
symbol.

John

 

[The Al Bundy]

"The little lost angel" <a?n?g?e?l@lovergirl.lrigrevol.moc.com> schreef in
bericht news:3fddec74.142653785@news.pacific.net.sg...

On Mon, 15 Dec 2003 10:58:20 -0600, John Fields
jfields@austininstruments.com> wrote:

It isn't. Choose the resistance you need from the resistance _range_
available and the wattage you need from the values available in the
left-most column after you use the derating graph to determine what the
wattage needs to be at the temperature at which the resistor will be
operating.

Sorry I'm slow as usual about getting this.
The only resistance range I see is in the table and it says
Wattage | Resistance Range (W) |
Rating | Standard Type | Non-Inductive Type |

Then the values are like 0.05W - 5KW

Do you mean, I take say "Free Air 100W-150W" which is line 2
At 100C ambient, which is 50% of rated power.

Then resister I would need would be 300W Rating and I can get them
from 0.00067 ohms (0.2W / 300W) to 60 Ohms (18KW /300W)?

In IE 6.0.28 I see the Ohm sign instead of the 'W'. Maybe incorrect/missing
Font settings?

Al

 

[Costas Vlachos]

"John Larkin" <jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote in
message news:mm1stvc7h0frrcr4kqvq4ojsvpqrq01f56@4ax.com...

I've seen a lot of magazines and such use W to indicate ohms. This
must be some sort of Windows-y typographic corruption of the Omega
symbol.

John

Correct. The Greek uppercase Omega in the Symbol font is in the same place
as W in standard fonts. The reason is probably because the lowercase Omega
looks like w.

Costas

 

[DarkMatter]

On Mon, 15 Dec 2003 16:05:22 GMT,
a?n?g?e?l@lovergirl.lrigrevol.moc.com (The little lost angel) Gave us:

Could anybody please enlighten me why is the resistance value given in
watts instead of ohms?

http://www.brakingresistor.com/metal.htm

Thanks!

Perhaps because such resistors re always the same value in Ohms, and
the only requisite for a user to select one by is dissipation ability.

 

[DarkMatter]

On Mon, 15 Dec 2003 10:58:20 -0600, John Fields
<jfields@austininstruments.com> Gave us:

On Mon, 15 Dec 2003 16:05:22 GMT, a?n?g?e?l@lovergirl.lrigrevol.moc.com
(The little lost angel) wrote:

Could anybody please enlighten me why is the resistance value given in
watts instead of ohms?
---
It isn't. Choose the resistance you need from the resistance _range_
available and the wattage you need from the values available in the
left-most column after you use the derating graph to determine what the
wattage needs to be at the temperature at which the resistor will be
operating.

Look again. Under "resistance range" Wattages are given, not a
range of available resistance values.

I presume that all of that class of resistor for that purpose are
all the same value, and wattage is the only criteria a field service
person or designer need consider for applications that involve
"braking resistors". Probably some very low value, like an Ohm or
such. They rely on back EMF to achieve a "braking" action from what
would otherwise be a motor. Dead short the armature of a motor that
is spinning with an energized field, and one will get a back emf that
will fight the spindle speed. Braking action.

 

[DarkMatter]

On Mon, 15 Dec 2003 11:11:00 -0800, John Larkin
<jjlarkin@highSNIPlandTHIStechPLEASEnology.com> Gave us:

I've seen a lot of magazines and such use W to indicate ohms. This
must be some sort of Windows-y typographic corruption of the Omega
symbol.

In the "Symbol" font, the "value" for the OHM symbol is a capital W.
I have an app that distills pdfs this way, such that I had to
actually create a bit map of the symbol to include it.

I would think that Adobe could distill a pdf, and catch it. It is
on my list of things to look into.

 

[John Fields]

On Mon, 15 Dec 2003 17:21:44 GMT, a?n?g?e?l@lovergirl.lrigrevol.moc.com
(The little lost angel) wrote:

On Mon, 15 Dec 2003 10:58:20 -0600, John Fields
jfields@austininstruments.com> wrote:

It isn't. Choose the resistance you need from the resistance _range_
available and the wattage you need from the values available in the
left-most column after you use the derating graph to determine what the
wattage needs to be at the temperature at which the resistor will be
operating.

Sorry I'm slow as usual about getting this.
The only resistance range I see is in the table and it says
Wattage | Resistance Range (W) |
Rating | Standard Type | Non-Inductive Type |

Then the values are like 0.05W - 5KW

Do you mean, I take say "Free Air 100W-150W" which is line 2
At 100C ambient, which is 50% of rated power.

Then resister I would need would be 300W Rating and I can get them
from 0.00067 ohms (0.2W / 300W) to 60 Ohms (18KW /300W)?

Kind of.

Looking at the table, the wattage rating is the column on the left and
indicates that they make resistors in this series with ratings from 60
to 1000 watts. Next to that is a column labelled "Resistance Range
(omega)" which is divided into two columns, one labelled "Standard Type"
and one labelled "Non-Inductive type".

Looking at the first row, there will be an entry in the left-hand
column which reads "60", an entry in the center column which reads
"0.05 omega - 5K omega", and an entry in the third column which reads
"0.1 omega - 2.5k omega", with 'omega' meaning ohms.

The first entry in the center column corresponds to the first entry in
the "Wattage Rating" column and indicates that if you need a standard
(not non-inductive) 60 watt resistor you can get them with resistances
anywhere between 0.05 ohm and 5000 ohms. The first entry in the third
column indicates that they can supply non-inductive 60 watt resistors
with resistances anywhere between 0.1 ohm and 2500 ohms. The rest of
the table follows suit, and serves to show what resistances in standard
and non-inductively wound resistors they can supply at the wattage
ratings they offer.

Their "% of Rated Power" VS "Ambient Temperature" graph is pretty
straightforward and indicates the derating that must be done with the
resistors either on a proper heat sink or in free air at different
ambient temperatures. Let's say for instance that you do your
calculations and find that your resistor will need to dissipate 100W in
free air at an ambient temp of 25°C. Since the second plot down
corresponds to 100W ~ 150W, draw a line vertically starting at 1/4 of
the way from zero to 100°C until it hits the second line and then
continue the line you're drawing horizontally from that point until it
hits the 0 to 100% line. It'll fall somewhere a little bit higher than
70%, so if you use 70% you'll be safe. Now, since you need for the
resistor to dissipate 100 watts and the graph shows that the resistor
needs to be derated to 70% of its rating to dissipate 100W at 25°C, that
means you have to start out with about a 143 watt resistor, so 150 watts
would be a good choice. Now go back and look at the range of
resistances available with a 150W rating and you'll find that they have
from 0.1ohm to 12000 ohms available, so it's probably likely they'll
have what you need. OK?

--
John Fields

 

[DarkMatter]

On Mon, 15 Dec 2003 20:16:42 -0600, John Fields
<jfields@austininstruments.com> Gave us:

Kind of.

Looking at the table, the wattage rating is the column on the left and
indicates that they make resistors in this series with ratings from 60
to 1000 watts. Next to that is a column labelled "Resistance Range
(omega)" which is divided into two columns, one labelled "Standard Type"
and one labelled "Non-Inductive type".

Looking at the first row, there will be an entry in the left-hand
column which reads "60", an entry in the center column which reads
"0.05 omega - 5K omega", and an entry in the third column which reads
"0.1 omega - 2.5k omega", with 'omega' meaning ohms.

Yes, except that that is not how it appears. To most, the "omega"
you refer to appears as a capital W. Easily confused for the vendor
supplying wattage ranges.

However... it is all clear to me now.

 

[DarkMatter]

On Mon, 15 Dec 2003 20:16:42 -0600, John Fields
<jfields@austininstruments.com> Gave us:

so it's probably likely they'll
have what you need. OK?

You must have a LOT of free time to have actually sat there, typing
away, at several huge paragraphs of re-iterated information.

Quite informative. Not the post... the free time, and the fact
that you felt Usenet was worth that much of it. Life must be boring
for you.

 

[John Fields]

On Mon, 15 Dec 2003 17:49:38 -0800, DarkMatter
<DarkMatter@thebarattheendoftheuniverse.org> wrote:

On Mon, 15 Dec 2003 10:58:20 -0600, John Fields
jfields@austininstruments.com> Gave us:

On Mon, 15 Dec 2003 16:05:22 GMT, a?n?g?e?l@lovergirl.lrigrevol.moc.com
(The little lost angel) wrote:

Could anybody please enlighten me why is the resistance value given in
watts instead of ohms?
---
It isn't. Choose the resistance you need from the resistance _range_
available and the wattage you need from the values available in the
left-most column after you use the derating graph to determine what the
wattage needs to be at the temperature at which the resistor will be
operating.


Look again. Under "resistance range" Wattages are given, not a
range of available resistance values.

---
I don't know what _you're_ looking at, but I clearly see omegas. That
is, the greek symbol used to indicate resistance.
---

I presume that all of that class of resistor for that purpose are
all the same value, and wattage is the only criteria a field service
person or designer need consider for applications that involve
"braking resistors".

---
'Criterion' is the singular, _and_ you presume incorrectly. Just
inspecting the first entry, even the most casual observer would find
0.05 watts to be ridiculously low for a braking resistor.
---

Probably some very low value, like an Ohm or
such. They rely on back EMF to achieve a "braking" action from what
would otherwise be a motor. Dead short the armature of a motor that
is spinning with an energized field, and one will get a back emf that
will fight the spindle speed. Braking action.

---
Yes, but a range of resistances is available and necessary so that the
motor can come to a more or less graceful halt.

--
John Fields

 

[John Fields]

On Mon, 15 Dec 2003 18:23:42 -0800, DarkMatter
<DarkMatter@thebarattheendoftheuniverse.org> wrote:

On Mon, 15 Dec 2003 20:16:42 -0600, John Fields
jfields@austininstruments.com> Gave us:

so it's probably likely they'll
have what you need. OK?

You must have a LOT of free time to have actually sat there, typing
away, at several huge paragraphs of re-iterated information.

Quite informative. Not the post... the free time, and the fact
that you felt Usenet was worth that much of it. Life must be boring
for you.

---
Not at all. On the contrary, it delights me to be able to give someone
knowledge that they didn't have before. I don't suppose you've ever
seen the lights go on in someone's eyes when loose ends that they had in
their mind suddenly get connected, because if you had you certainly
wouldn't say making that happen was a waste of time.

--
John Fields

 

[John Fields]

On Mon, 15 Dec 2003 18:21:03 -0800, DarkMatter
<DarkMatter@thebarattheendoftheuniverse.org> wrote:

On Mon, 15 Dec 2003 20:16:42 -0600, John Fields
jfields@austininstruments.com> Gave us:

Kind of.

Looking at the table, the wattage rating is the column on the left and
indicates that they make resistors in this series with ratings from 60
to 1000 watts. Next to that is a column labelled "Resistance Range
(omega)" which is divided into two columns, one labelled "Standard Type"
and one labelled "Non-Inductive type".

Looking at the first row, there will be an entry in the left-hand
column which reads "60", an entry in the center column which reads
"0.05 omega - 5K omega", and an entry in the third column which reads
"0.1 omega - 2.5k omega", with 'omega' meaning ohms.

Yes, except that that is not how it appears. To most, the "omega"
you refer to appears as a capital W. Easily confused for the vendor
supplying wattage ranges.

However... it is all clear to me now.

---
You're welcome.

--
John Fields

 

[The little lost angel]

On Mon, 15 Dec 2003 20:16:42 -0600, John Fields
<jfields@austininstruments.com> wrote:

to 1000 watts. Next to that is a column labelled "Resistance Range
(omega)" which is divided into two columns, one labelled "Standard Type"

Ah, so it's my browser/font that was throwing me off totally.
Thanks for the clarification and I appreciate the detailed explanation
on how to read/use those charts.

--
L.Angel: I'm looking for web design work.
If you need basic to med complexity webpages at affordable rates, email me
Standard HTML, SHTML, MySQL + PHP or ASP, Javascript.
If you really want, FrontPage & DreamWeaver too.
But keep in mind you pay extra bandwidth for their bloated code

 

[DarkMatter]

On Mon, 15 Dec 2003 20:45:46 -0600, John Fields
<jfields@austininstruments.com> Gave us:

--
I don't know what _you're_ looking at, but I clearly see omegas. That
is, the greek symbol used to indicate resistance.

It is obvious, however, that you are clearly ignoring the fact that
the orig poster, and many others see the W symbol.

 

[DarkMatter]

On Mon, 15 Dec 2003 20:45:46 -0600, John Fields
<jfields@austininstruments.com> Gave us:

Yes, but a range of resistances is available and necessary so that the
motor can come to a more or less graceful halt.

Not really. Banks of resistors can be set on a conductor rail, and
hooked up in sequence, in parallel, according to the braking load
desired. A giant rheostat.

Most trolley brakes I've seen (Siemens) are a sliding rheostat
"looking" arm on the operator's control console. Were there banks of
a given value resistor hooked up, they would each dissipate the same
heat as each was brought into use during braking, and the brake
operator only engages as many of the resistors as are needed to effect
the smooth stop curve needed to keep that last second jolt out of the
picture for the passengers.

 

[DarkMatter]

On Mon, 15 Dec 2003 21:14:01 -0600, John Fields
<jfields@austininstruments.com> Gave us:

Not at all. On the contrary, it delights me to be able to give someone
knowledge that they didn't have before. I don't suppose you've ever
seen the lights go on in someone's eyes when loose ends that they had in
their mind suddenly get connected, because if you had you certainly
wouldn't say making that happen was a waste of time.

What I actually said was that you redundantly repeated what was
already on the site, and STILL didn't "fix" the "problem".

The answer was:

"The capital W is shown that way, because your browser did not
catch the use of the other font utilized in the document. The capitol
W in the SYMBOL font is the upper case Omega symbol, widely used in
the electronics industry, as it stands for a basic electronic unit of
measure.

Replace the "resistance range" "W"s with the term Ohms, and all
should be clarified, or save and edit the page, and attempt to point
to the font usage yourself.

Much shorter. Still it was a very good job, and fine effort, as
that is all any of us should need.