The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed

On Wed, 21 Jul 2010 22:57:20 -0400 ehsjr wrote
in Message id: :

The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed

"Ribbed - for his pleasure!"

On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr
wrote:

The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed
Nice.

We had some nice variable resistors in the electrical lab at college
longer then my arm I should have stuck a few in my backpack;-)

Actually after that thread I decided what my next project will be.I'm
getting some more brick heat sinks and making an electronic load. I'm
going to be using some to-3pN fets. I figure five of them mounted on a
couple of half bricks with a 38cfm fan should be good for 3-500W.This
would also provide for load step testing.

On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr
wrote:

The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed

Not terribly suited to be a dummy load, it appears to be an inductive
resistor.

PeterD wrote:
On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr
wrote:


The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed


Not terribly suited to be a dummy load, it appears to be an inductive
resistor.


Yup, wirewound. You could make a good dummy load with it for
battery testing/discharging, power supply testing, that sort of
thing, but it's not for RF.

Ed

On Thu, 22 Jul 2010 13:57:03 -0400, ehsjr
wrote:

PeterD wrote:
On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr
wrote:


The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed


Not terribly suited to be a dummy load, it appears to be an inductive
resistor.


Yup, wirewound. You could make a good dummy load with it for
battery testing/discharging, power supply testing, that sort of
thing, but it's not for RF.

Ed

My paralleled carbon 2W resistors soldered between two planes worked
nicely at 144MHz (2 Meter Band, which is where I was interested

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Spice is like a sports car...
Only as good as the person behind the wheel.

"Jim Thompson" wrote in message ...
Yup, wirewound. You could make a good dummy load with it for
battery testing/discharging, power supply testing, that sort of
thing, but it's not for RF.

My paralleled carbon 2W resistors soldered between two planes worked
nicely at 144MHz (2 Meter Band, which is where I was interested

While testing a 1MHz induction heater circuit, I attempted to use a 4 ohm wirewound resistor, Dividohm style.

The divider clamp wrapped around it got hotter than the resistor itself. Apparently, nichrome has a far Q in the MHz range.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

On Thu, 22 Jul 2010 07:15:36 -0400, Hammy wrote:

On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr
wrote:

The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed
Nice.

We had some nice variable resistors in the electrical lab at college
longer then my arm I should have stuck a few in my backpack;-)

Actually after that thread I decided what my next project will be.I'm
getting some more brick heat sinks and making an electronic load. I'm
going to be using some to-3pN fets. I figure five of them mounted on a
couple of half bricks with a 38cfm fan should be good for 3-500W.This
would also provide for load step testing.

Yes, good to have that load step option, one on my todo list as well.

Got some 300W, 5 Ohm resistors special price, but found best value was
some 11W and 17W parts made in India, lots in parallel. I'm not doing
RF, but lots of resistors in parallel at least reduces the inductance.

Grant.

--
MikeK
"ehsjr" wrote in message
...
The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed


That's cool, where did you get those miniature batteries? :-)
MikeK

On Fri, 23 Jul 2010 08:06:53 +1000, Grant wrote:
On Thu, 22 Jul 2010 07:15:36 -0400, Hammy wrote:
On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr

The discussion on SED about a 300 watt resistance prompted me to post
this photo. :-)

We had some nice variable resistors in the electrical lab at college
longer then my arm I should have stuck a few in my backpack;-)

Actually after that thread I decided what my next project will be.I'm
getting some more brick heat sinks and making an electronic load. I'm
going to be using some to-3pN fets. I figure five of them mounted on a
couple of half bricks with a 38cfm fan should be good for 3-500W.This
would also provide for load step testing.

Yes, good to have that load step option, one on my todo list as well.

Got some 300W, 5 Ohm resistors special price, but found best value was
some 11W and 17W parts made in India, lots in parallel. I'm not doing RF,
but lots of resistors in parallel at least reduces the inductance.

Is there a mechanical mounting/wiring scheme where two could cancel each
other's inductance?

Thanks,
Rich

"Rich Grise" wrote in message news
Is there a mechanical mounting/wiring scheme where two could cancel each
other's inductance?

Only if one has "negative inductance".

Presumably, there's no hope of getting all the flux from one going through the other, i.e. making a noninductive resistor. Even if you nested resistors inside each other, you've got leakage from the difference in diameters, so you really can't make it work any better. A proper noninductive resistor is your best bet.

FWIW, you can equalize the terminal impedance by canceling the R+L characteristic with an R+C of the same time constant (i.e., R*C = L/R). But this doesn't share power, it puts HF into the RC and LF into the RL. And you still need a noninductive resistor.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

On Fri, 23 Jul 2010 19:20:40 -0700, Rich Grise wrote:

On Fri, 23 Jul 2010 08:06:53 +1000, Grant wrote:
On Thu, 22 Jul 2010 07:15:36 -0400, Hammy wrote:
On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr

The discussion on SED about a 300 watt resistance prompted me to post
this photo. :-)

We had some nice variable resistors in the electrical lab at college
longer then my arm I should have stuck a few in my backpack;-)

Actually after that thread I decided what my next project will be.I'm
getting some more brick heat sinks and making an electronic load. I'm
going to be using some to-3pN fets. I figure five of them mounted on a
couple of half bricks with a 38cfm fan should be good for 3-500W.This
would also provide for load step testing.

Yes, good to have that load step option, one on my todo list as well.

Got some 300W, 5 Ohm resistors special price, but found best value was
some 11W and 17W parts made in India, lots in parallel. I'm not doing RF,
but lots of resistors in parallel at least reduces the inductance.

Is there a mechanical mounting/wiring scheme where two could cancel each
other's inductance?

No, but putting them in parallel at least reduces inductance, rather
than build a series string of resistors.

If measuring current for a switching regulator feedback, one might use
an RC to smother the switching peak.

Grant.

On Fri, 23 Jul 2010 22:56:48 -0500, "Tim Williams" wrote:

"Rich Grise" wrote in message news
Is there a mechanical mounting/wiring scheme where two could cancel each
other's inductance?

Only if one has "negative inductance".

Is that what a capacitor does / is / has?

Presumably, there's no hope of getting all the flux from one going through the other, i.e. making a noninductive resistor. Even if you nested resistors inside each other, you've got leakage from the difference in diameters, so you really can't make it work any better. A proper noninductive resistor is your best bet.

If you really need it, I'm working with batteries, nice slow
chemical processes

FWIW, you can equalize the terminal impedance by canceling the R+L characteristic with an R+C of the same time constant (i.e., R*C = L/R). But this doesn't share power, it puts HF into the RC and LF into the RL. And you still need a noninductive resistor.

Grant.

Tim

On Fri, 23 Jul 2010 19:20:40 -0700, Rich Grise
wrote:



Is there a mechanical mounting/wiring scheme where two could cancel each
other's inductance?

Thanks,
Rich

You could try twisted pair with all interconnects and dedicated
returns with single point grounding. I dont know how effective it
would be in this case but it would be worth a try.


Some examples

http://www.physics.utah.edu/~kieda/ott.pdf

Considering it's just a dummy load I dont think its much of a big deal
unless you plan on testing supplies at HF PULSE steps near the SRF.Not
likely for SMPS load step testing BW of most is in kHz not MHz.


Worst you are likely to see is an inductive transient at the current
pulse leading edge which may get into the feedback path just RC
filter the feedback to the opamp to filter out the inductive leading
edge transient.

"Grant" wrote in message ...
Only if one has "negative inductance".

Is that what a capacitor does / is / has?

No, the reactance is capacitive, but the equation isn't the same:

X_c = 1 / (jwC)
X_L = jwL

Negative inductance would have capacitive reactance (-j direction), but the magnitude would increase with frequency, the opposite of a capacitor. You could make some interesting filters with one of those, just as you can make interesting circuits with negative resistance.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Jim Thompson wrote:
On Thu, 22 Jul 2010 13:57:03 -0400, ehsjr
wrote:


PeterD wrote:

On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr
wrote:



The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed


Not terribly suited to be a dummy load, it appears to be an inductive
resistor.


Yup, wirewound. You could make a good dummy load with it for
battery testing/discharging, power supply testing, that sort of
thing, but it's not for RF.

Ed


My paralleled carbon 2W resistors soldered between two planes worked
nicely at 144MHz (2 Meter Band, which is where I was interested

...Jim Thompson

Air cooled, or did you put the assembly in oil?
I seem to remember that you operated EME - is that correct?

Ed

On Sun, 25 Jul 2010 17:41:29 -0400, ehsjr
wrote:

Jim Thompson wrote:
On Thu, 22 Jul 2010 13:57:03 -0400, ehsjr
wrote:


PeterD wrote:

On Wed, 21 Jul 2010 22:57:20 -0400, ehsjr
wrote:



The discussion on SED about a 300 watt resistance prompted me
to post this photo. :-)

Ed


Not terribly suited to be a dummy load, it appears to be an inductive
resistor.


Yup, wirewound. You could make a good dummy load with it for
battery testing/discharging, power supply testing, that sort of
thing, but it's not for RF.

Ed


My paralleled carbon 2W resistors soldered between two planes worked
nicely at 144MHz (2 Meter Band, which is where I was interested

...Jim Thompson

Air cooled, or did you put the assembly in oil?

Muffin fan on the end.

I seem to remember that you operated EME - is that correct?

Ed

EME? Earth-moon-earth? No.

FM voice, Phoenix-to-Tucson line-of-sight, LA via a repeater system...
starting point: South Mountain.

I don't remember (†) all the details now, but I used a pumped-varactor
tripler. Remember, this was early '60's, getting to 144MHz was not a
easy event with readily available semiconductors.

I drilled a hole in the center of the roof of my '61' Renault Dauphine
and installed a thru-panel BNC. Rubber cap normally. 5/8 Vertical
gamma-match (‡) antenna when operating ;-)

(†) I got out of ham radio (I was K7ZAE) after that... I wasn't in it
for the talking, just seeing what I could make work.

(‡) What I remember it called, but I can't find anything but dipoles
in recent ARRL handbooks.

At home I had 4CX...something or other tubes, driving a V-beam
(definitely illegal ERP :-)

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Spice is like a sports car...
Only as good as the person behind the wheel.