Actually, the viscosity (the number indicates viscosity, not weight or
density) is important. The lower the number the better. That's one of
the reasons transformer oil is better for transformers and dummy loads
than drug store mineral oil - it has lower viscosity. The lower the
viscosity the more easily convection currents transfer heat from the
dummy load into the fluid and from the fluid to the can. That means
lower thermal resistance, giving a lower resistor temperature for a
given power dissipation.

73,
Bob AD3K

BOB wrote:
is far motor oil (if you have to use it ) use "nd 30" (or 40 ,20,50 the
weight is not important) the "nd" is non detergent, to not dissolve carbon

i tend to agree try to find an oil closer to what's "right"

bob


--
Robert L. Spooner
Registered Professional Engineer
Associate Research Engineer
Intelligent Control Systems Department

Applied Research Laboratory Phone: (814) 863-4120
The Pennsylvania State University FAX: (814) 863-7841
P. O. Box 30
State College, PA 16804-0030

(Art Unwin KB9MZ) wrote in message om...
(Brian Kelly) wrote in message . com...


"Can motor oil be used " and the correct answer is a
qualified YES

What API spec crankcase oils do you have in mind?

If you want to leave a KILOWATT active overnight then I
would certainly say NO.
I certaily would recommend the Teflon coated cans since
can seams can sometimes 'weep'when thin oils are used.

In the case of a paint can being used for the housing for a dummy load
the outer surface of the can needs to be able to radiate as much power
as possible. A Teflon liner between the oil and inner surface of the
metal can is a thermal insulator and will degrade the ability of the
can and the dummy load to transfer the BTUs in the oil to the air
surrounding the can.

Simply degrease the can thoroughly and resolder the seams. Still won't
get rid of all the oil forever because the relief valves burp and/or
leak here and there.

If viscosity is your main concern then additional
circulation methods will alleviate that in a way far
superior to that using the best known transformer oil
( ARRL shows a method of achieving this)

I once wound a double-layer full length coil of 1/4" copper tubing
which was immersed in the mineral oil and soldered into the lid of a
Cantenna. I ran faucet water thru the coil. The dummy load ran quite
cool under all conditions when we were key-down smoke testing 2kW
output HF amps for an hour at a crack.

If resisters are your main worry
then use a couple of wire resisters with the windings
oriented in opposite fashion since absolute accuracy is
intended for real dummies.
( Note resistors change value
over time even when not in hostile environments.)
Check the values on an old tube/valve reciever for yourself)

Dummy loads are simply places where one can dump RF power without
cluttering up the bands. And I certainly wouldn't get involved with
winding any inductors when non-inductive 50 Ohm deposited-film
resistors are freely available.

As a point of interest, have you considered what creates
the first point of failure,

No, I've never had a dummy load fail.

and why transformers housings
are built so mechanically strong ?

Because they're the stuctural supports and housings for particulaly
heavy AC power machinery often located outdoors and subject to all
sorts of physical abuse. Plus the shells need to be of heavy enough
plate to reliably facilitate leakproof welds. I fail to understand
what this topic has to do with ham radio dummy load mechanicals.

Can you tell me at what
time the 'flash point ' comes into play when considering
it.s use for a dummy load ?

No, but if the flash point ever becomes a concern I'll look up the
temp and take it from there.

These questions go to the very
point that I discussed i.e using industry methods as
pointers BUT with due reference to the different environnments
and duty cycles required with respect to cost and availability.

.. . OK.

Regards
Art

w3rv

Roy Lewallen wrote in message ...
Brian Kelly wrote:

In the case of a paint can being used for the housing for a dummy load
the outer surface of the can needs to be able to radiate as much power
as possible. A Teflon liner between the oil and inner surface of the
metal can is a thermal insulator and will degrade the ability of the
can and the dummy load to transfer the BTUs in the oil to the air
surrounding the can.
. . .

Don't tell my wife that. She's been thinking all along that the food
she's been putting in the Teflon lined frying pan has actually been cooking!

Hee! Couple weeks ago I got stupid and tried to fry a couple eggs in a
bare aluminum pan. I wound up with one edible egg and one which
alloyed itself with the pan.


Seriously, what you've got is a series of "thermal resistances" in
series. This is a legitimate if simplified way of evaluating temperature
drop, and is widely used in determining chip temperature of transistors
and ICs. From the resistor, you've got the thermal resistance of the
oil, in series with the thermal resistance of the Teflon, then the metal
can, then finally the resistance of the can-to-air transfer, or
"connection". The temperature difference between the resistor and the
air is calculated like the voltage in a circuit, where the circuit's
"current" is the amount of power being transferred. That is, DT = THETA
* P, where DT is the temperature differential, P the power, and THETA
all the thermal resistances in series. In electronics, DT is usually in
degrees C, P in watts, and THETA in degrees C per watt.

Yup. There isn't a steady-state thermal circuit out there which can't
be modeled on the bench with a pile of resistors. Gets hairy when
fluid dyanmics gets into the mix, laminar vs. turbulent flow, etc.
Ditto the electrical network simulation of mechanical vibrations. A
lot of grad school theses were written in the general topic area back
in analog computer days. Mother Nature could care less about the lines
between engineering disciplines.


While the thermal resistance of the Teflon layer is undoubtedly several
orders of magnitude greater than the thermal resistance of the can, I'd
be willing to bet that it's much less than the can-to-air thermal
resistance,

Blow air on the can with a fan. In the limit dunk the can in a bucket
with water running in/out.

and probably (because of its very small thickness) even much
less than the resistor-to-Teflon thermal resistance through the oil
(unless, perhaps, the oil is very rapidly stirred). So, in the big
picture, the Teflon layer doesn't make any difference.

Agreed.

Nobody ever died from an engineering troll.

Roy Lewallen, W7EL

w3rv

On 14 Aug 2003 07:29:40 -0700, (Brian Kelly) wrote:


I spent a day and a half on the phone calling around trying to buy a
lousy two pounds of a specific DuPont Teflon-bearing grease. The
worn-out DuPont tech rep finally wrote an order for a two pound sample
but I had to drive 50 miles to the Dupey warehouse to pick it up.

I imagine it's much easier to simply run a web search today.

73's
Richard Clark, KB7QHC

w3rv

Hi Brian,

That is exactly how I get all my exotic electronics parts, engineering
samples. FREE. Need a 24 bit ADC? How about GHZ GBWP amps?
Precision V-F-V converters? FREE.

Now, if I wanted to buy one they would tell me to take a hike.

As for your last comment about web searching. That is my current
business. I build web robots and if anyone is interested, my current
model that I call GrantBot will search through nearly 2000 pages of
legislation funding of Grants offered and awarded by every department,
agency, institute, consortium, office, bureau, center, program, group,
division, administration, service, ... in the government.

This offer is free to individuals.

I have a generic robot that is workable, but which remains to gain
recent work's improvements. However, it requires that you have some
foreknowledge of potential links (it is a targeted web robot, not a
free roaming one).

That too is free to individuals.

When I say individuals, that means those not using it as a tool of
their paid work. If you are a sole proprietor, I still consider you
an individual.

73's
Richard Clark, KB7QHC

Perhaps that are types and grades of motor oil out there that will work with
certain types of resistors I dont think it very practical to research to
find which are compatible. Perhaps the oil companies already know. You could
make it a project to enquire with them and post the information on this news
group.

"Art Unwin KB9MZ" wrote in message
m...
Russ,
The point I am making is that some comments are repeated
so many times they take a life of their own
Think about it, the resistors of old are a far cry from
the carbon resistors of today which are not as porous,
if it is a worry then coat it with epoxy !
Then there is the "rust" question, the paint cans of today
have a teflon liner ! Even the latest ham data states that
motor oil CAN be used ( no, it will not explode !) but raise
a question of "life", possibly a suggestive comment that you
change the oil every 5000 qso's.
Certainly industry gives a good guide as to what is the best
to use for their circumstances but it doesn't rule out every
thing else for all time, and this includes motor oil of which
there are many types.
Regards
Art

Russ wrote in message
. ..
On 10 Aug 2003 08:19:18 -0700, (Art Unwin KB9MZ)
wrote:

Well it would seem that the 'don't use motor oil' comment
which has been passed on by mouth to mouth over the decades
doesn't seem to stand up to scruteny.
Yes, the question is raised so many times over the years
and the same old stories pop up, but without any
substantiation such that it just appears to be gossip.
One statement mentions attack on resisters, where's the proof,
If it is true then it surely can be easily overcome.
Hopefully this time, one of the many posters over the
years on this subject will make observations that are
relevant to the present day instead of waiting for a book.
Art


Well Art, the detergents in modern motor oils are specifically
formulated to dissolve carbon deposits and sludge (largely made up of
carbon) and keep in in suspension. I'm pretty sure that the resistor
in my Cantenna is carbon. Transformer oil is formulated to have a
high dieletric strength. Mineral oil is relatively pure, lightweight
petrolatum (like liquid Vaseline(r)) and has a pretty high dieletric
strength just because of low impurities. Motor oil? I don't know.
ATF? I don't know about that either. What I do know is that the
designers of my dummy load specify either transformer oil or mineral
oil. That's good enough for me. I'll mosey on down to the
transformer shop of the local electric utility and buy the folks there
a round of coffee in the morning or over to the veterinary supply and
buy a gallon of mineral oil U. S. P. I think it's safer that way. We
hams are in interestingly cheap lot. We'll spend thousands on a new
rig that could break down tomorrow and then pour a gallon of
"whatever" into the dummy load instead of spending twenty bucks for
mineral oil or fifty bucks for MFJs transformer oil. This in a unit
that with ordinary care will last a lifetime. Sheesh!

Russ








"Keyboard In The Wilderness" wrote in message
news:4q8Za.31351$ff.14186@fed1read01...
From the Google Group Search Engine: For what it is worth

The Handbook (at least my 1990 edition) has some information on this
subject.
In the Station Accessories chapter there are plans to build a couple
of
Cantenna type dummy loads. They mention an oil sold by Texaco (if I
remember
correctly) for turbine lubrication that is, according to the author,
the
same
oil as is used in transformers. They quote the exact product
designation.
Apparently, it's sold in minimum 5 gallon quantities and I think it's
about
$5 per gallon. If anyone's interested, let me know and I'll look up
the
information and pass it along. It's supposed to be PCB-free, also.

The article also cautions against using motor oil for various
reasons, among
which is that it attacks the resistor (actually, I think it's the
additives
that cause the problem).




"Art Unwin KB9MZ" wrote in message
m...
"Keyboard In The Wilderness" wrote in message
news:fjUYa.31252$ff.5358@fed1read01...
Jav -- asked many times before -- for the answers go to Groups
Google.com
http://groups.google.com/

I don,t fully understand why motor oil should not be used
in a dummy load! I need to make one so I can calibrate
one of my instruments. I intend to use one of the uptodate
gallon paint cans that has a PTFE liner and solder the lid on.
Since we now have the means to use low wattage signals for
tuning up purposes there is obviously no reason to store it
in the shack . So what really is the problem with using
available oil instead of emulating the aproach of industrial
transformers or regurgitating old thoughts ?
Art








Search for Oil For Cantenna or Oil For Dummy Load

Mineral Oil works well for me.


"Javier Henderson" wrote in message
...
I got a Heathkit Cantenna recently, sans oil.

Where do I find transformer oil? The few industrial suppliers
in my
area (Monterey, CA) want to sell me drums of the stuff. I only
need
a gallon...

Is motor oil OK to use?

73,
-jav w6vms

On Fri, 15 Aug 2003 06:31:04 GMT, "Jimmy"
wrote:

Perhaps that are types and grades of motor oil out there that will work with
certain types of resistors I dont think it very practical to research to
find which are compatible. Perhaps the oil companies already know. You could
make it a project to enquire with them and post the information on this news
group.


:-)

It would make as much sense to fill the can with mud, add one
electrode, and feed it against the shell. Some may no doubt find
their life's mission in then determining what grade of oil (to replace
the water) would improve this option.

It would certainly offer more caloric mass than a resistor, is freely
available, and all would quite agree - conductive and lossy.

[How many errors can you find in this proposal? Submit answers on the
back of a $20 bill and post to:]

73's
Richard Clark, KB7QHC

Man, a simple question I asked, and it's still being debated!

I'll reserve my next question, "Can I store a battery on a bare
concrete floor", for another slow day.

73,

-jav w6vms

Richard Clark wrote in message . ..
On 14 Aug 2003 07:29:40 -0700, (Brian Kelly) wrote:


I spent a day and a half on the phone calling around trying to buy a
lousy two pounds of a specific DuPont Teflon-bearing grease. The
worn-out DuPont tech rep finally wrote an order for a two pound sample
but I had to drive 50 miles to the Dupey warehouse to pick it up.

I imagine it's much easier to simply run a web search today.

73's
Richard Clark, KB7QHC

w3rv

Hi Brian,

That is exactly how I get all my exotic electronics parts, engineering
samples. FREE. Need a 24 bit ADC? How about GHZ GBWP amps?
Precision V-F-V converters? FREE.

There are people who have that skill down to an art form.
Unfortunately I've never been able to well in that field.

Now, if I wanted to buy one they would tell me to take a hike.

Right. Getting you off their phones is worth much more to them than
the widget and/or the paperwork are worth . .

As for your last comment about web searching. That is my current
business. I build web robots and if anyone is interested, my current
model that I call GrantBot will search through nearly 2000 pages of
legislation funding of Grants offered and awarded by every department,
agency, institute, consortium, office, bureau, center, program, group,
division, administration, service, ... in the government.

This offer is free to individuals.

I have a generic robot that is workable, but which remains to gain
recent work's improvements. However, it requires that you have some
foreknowledge of potential links (it is a targeted web robot, not a
free roaming one).

That too is free to individuals.

When I say individuals, that means those not using it as a tool of
their paid work. If you are a sole proprietor, I still consider you
an individual.

I'm just a sole these days, not a sole proprietor. For now anyway. I
freelance in the industrial machine design biz but ran out of work in
March and decided to coast with my feet up on the handlebars for a few
months and do some radio, etc. Which is much easier when yer finally
positioned to plunder the Social Security fund like I am now. Thanks
for the offer Richard but I'm unloading tools rather than acquiring
new ones.

73's
Richard Clark, KB7QHC

w3rv

On Fri, 15 Aug 2003 06:31:04 GMT, "Jimmy"
wrote:

Perhaps that are types and grades of motor oil out there that will work with
certain types of resistors I dont think it very practical to research to
find which are compatible. Perhaps the oil companies already know. You could
make it a project to enquire with them and post the information on this news
group.


Yeah, or hey! You could just use transformer oil. Art is being
pedantic and difficult.

Russ

"Art Unwin KB9MZ" wrote in message
om...
Russ,
The point I am making is that some comments are repeated
so many times they take a life of their own
Think about it, the resistors of old are a far cry from
the carbon resistors of today which are not as porous,
if it is a worry then coat it with epoxy !
Then there is the "rust" question, the paint cans of today
have a teflon liner ! Even the latest ham data states that
motor oil CAN be used ( no, it will not explode !) but raise
a question of "life", possibly a suggestive comment that you
change the oil every 5000 qso's.
Certainly industry gives a good guide as to what is the best
to use for their circumstances but it doesn't rule out every
thing else for all time, and this includes motor oil of which
there are many types.
Regards
Art

Russ wrote in message
...
On 10 Aug 2003 08:19:18 -0700, (Art Unwin KB9MZ)
wrote:

Well it would seem that the 'don't use motor oil' comment
which has been passed on by mouth to mouth over the decades
doesn't seem to stand up to scruteny.
Yes, the question is raised so many times over the years
and the same old stories pop up, but without any
substantiation such that it just appears to be gossip.
One statement mentions attack on resisters, where's the proof,
If it is true then it surely can be easily overcome.
Hopefully this time, one of the many posters over the
years on this subject will make observations that are
relevant to the present day instead of waiting for a book.
Art


Well Art, the detergents in modern motor oils are specifically
formulated to dissolve carbon deposits and sludge (largely made up of
carbon) and keep in in suspension. I'm pretty sure that the resistor
in my Cantenna is carbon. Transformer oil is formulated to have a
high dieletric strength. Mineral oil is relatively pure, lightweight
petrolatum (like liquid Vaseline(r)) and has a pretty high dieletric
strength just because of low impurities. Motor oil? I don't know.
ATF? I don't know about that either. What I do know is that the
designers of my dummy load specify either transformer oil or mineral
oil. That's good enough for me. I'll mosey on down to the
transformer shop of the local electric utility and buy the folks there
a round of coffee in the morning or over to the veterinary supply and
buy a gallon of mineral oil U. S. P. I think it's safer that way. We
hams are in interestingly cheap lot. We'll spend thousands on a new
rig that could break down tomorrow and then pour a gallon of
"whatever" into the dummy load instead of spending twenty bucks for
mineral oil or fifty bucks for MFJs transformer oil. This in a unit
that with ordinary care will last a lifetime. Sheesh!

Russ








"Keyboard In The Wilderness" wrote in message
news:4q8Za.31351$ff.14186@fed1read01...
From the Google Group Search Engine: For what it is worth

The Handbook (at least my 1990 edition) has some information on this
subject.
In the Station Accessories chapter there are plans to build a couple
of
Cantenna type dummy loads. They mention an oil sold by Texaco (if I
remember
correctly) for turbine lubrication that is, according to the author,
the
same
oil as is used in transformers. They quote the exact product
designation.
Apparently, it's sold in minimum 5 gallon quantities and I think it's
about
$5 per gallon. If anyone's interested, let me know and I'll look up
the
information and pass it along. It's supposed to be PCB-free, also.

The article also cautions against using motor oil for various
reasons, among
which is that it attacks the resistor (actually, I think it's the
additives
that cause the problem).




"Art Unwin KB9MZ" wrote in message
m...
"Keyboard In The Wilderness" wrote in message
news:fjUYa.31252$ff.5358@fed1read01...
Jav -- asked many times before -- for the answers go to Groups
Google.com
http://groups.google.com/

I don,t fully understand why motor oil should not be used
in a dummy load! I need to make one so I can calibrate
one of my instruments. I intend to use one of the uptodate
gallon paint cans that has a PTFE liner and solder the lid on.
Since we now have the means to use low wattage signals for
tuning up purposes there is obviously no reason to store it
in the shack . So what really is the problem with using
available oil instead of emulating the aproach of industrial
transformers or regurgitating old thoughts ?
Art








Search for Oil For Cantenna or Oil For Dummy Load

Mineral Oil works well for me.


"Javier Henderson" wrote in message
...
I got a Heathkit Cantenna recently, sans oil.

Where do I find transformer oil? The few industrial suppliers
in my
area (Monterey, CA) want to sell me drums of the stuff. I only
need
a gallon...

Is motor oil OK to use?

73,
-jav w6vms

On 15 Aug 2003 10:08:30 -0700, Javier Henderson wrote:
Man, a simple question I asked, and it's still being debated!

Yup, every time.

I'll reserve my next question, "Can I store a battery on a bare
concrete floor", for another slow day.

Will that be before or after asking about which editor to write
web/text/??? documents?

sdb

--
| Sylvan Butler | Not speaking for Hewlett-Packard | sbutler-boi.hp.com |
| Watch out for my e-mail address. Thank UCE. change ^ to @ |
It may be better to live under robber barons than under omnipotent moral
busybodies. The robber baron's cruelty may sometimes sleep, his
cupidity may at some point be satiated; but those who torment us for our
own good will torment us without end, for they do so with the approval
of their consciences. -- C. S. Lewis