Water Cooled Power Resistor Gets Rusty

[Glen Walpert]

Soooo..
I'm going to coat the terminals and stick with water.
(as per Phil post).
But.. The tap contact on the tube power resistor is ferrous and I
can't coat that..

You could coat the tap contact and the entire length of the exposed
resistance wire the tap slides on with silicone grease without
increasing contact resistance or losing adjustability. The silicone
grease sold in auto stores as dielectric grease is best as it has no
additives and therefore the lowest water absorption of any silicone
grease, but pretty much any grease should do the job for short term
testing.

At a paltry 100 watts your reason for not using an air cooled load
must be a parts on hand issue. I have used air cooled loads up to
1250 kW, and they make them much bigger than that.

 

[D from BC]

You could coat the tap contact and the entire length of the exposed
resistance wire the tap slides on with silicone grease without
increasing contact resistance or losing adjustability. The silicone
grease sold in auto stores as dielectric grease is best as it has no
additives and therefore the lowest water absorption of any silicone
grease, but pretty much any grease should do the job for short term
testing.

At a paltry 100 watts your reason for not using an air cooled load
must be a parts on hand issue. I have used air cooled loads up to
1250 kW, and they make them much bigger than that.

Yeah..I've been thinking of grease too. It's a good solution.

Point taken about the Pdisp. qualified for air cooling.
I created a chemistry pita instead of just going back to the surplus
store to dig out a 100W power resistor rated for air.
The one I'm forcing to use with liquid cooling I suspect is an
underrated 50Watts. (No markings.) 0.8"d x 7"L

One the other hand, I find liquid cooling resistors appealing:
* No super hot item on the bench. ( Bad enough I have wires
accidentally land on my soldering pen.)
* A cool down from 100C takes less time to handle the resistor to make
a R adjustment.
* Then there's the camp fire effect.. Oooooo Ahhhhh... . Watching
that steaming resistor has an achievement effect.
Ok...that's a bit goofy but it's a "like what you do" thing.


D from BC

 

[Jim Thompson]

Yeah..I've been thinking of grease too. It's a good solution.

Point taken about the Pdisp. qualified for air cooling.
I created a chemistry pita instead of just going back to the surplus
store to dig out a 100W power resistor rated for air.
The one I'm forcing to use with liquid cooling I suspect is an
underrated 50Watts. (No markings.) 0.8"d x 7"L

One the other hand, I find liquid cooling resistors appealing:
* No super hot item on the bench. ( Bad enough I have wires
accidentally land on my soldering pen.)
* A cool down from 100C takes less time to handle the resistor to make
a R adjustment.
* Then there's the camp fire effect.. Oooooo Ahhhhh... . Watching
that steaming resistor has an achievement effect.
Ok...that's a bit goofy but it's a "like what you do" thing.


D from BC

I'm surprised that no one has suggested an active load... no sliding
contacts.

...Jim Thompson

 

[Gary Tait]

But.. The tap contact on the tube power resistor is ferrous and I
can't coat that..
It'll rust but not erode due to electrolysis (the other terminals are
coated.)

Is it a variable tap, or one or more fixed taps? if the latter, bring them
out to external terminals, and seal the contact on the resistor.

 

[D from BC]

I'm surprised that no one has suggested an active load... no sliding
contacts.

...Jim Thompson

Thinking...
Active load...uhhh.. I can use a power current sink...almost the same
thing I think..
A power fet sprinkled with other components on an aluminum heat.
Perhaps dunk the whole thing in water and use silicone spray to stop
the electrolysis.
....or fan cool.
I'd have to put time into making sure I have a predictable
temperature stability.
The current stability is allowed to be say.. +/- 0.2Amps.
It'll be new for me to design a stable power current sink that can
boil water.
Fun project.. but I think using a power resistor instead has less
implementation time for my app.

D from BC

 

[Rich Grise]

It's the liquid breathing rats stuff!
http://en.wikipedia.org/wiki/Fluorinert

It's going to be exxxxpennnsive....

Did you read the part where all of the test rats died? It's probably
excellent for heat transfer, but I wouldn't recommend using it for
deep-diving until they solve that pesky "died of lung trauma" problem. ;-)

And, well, "The Abyss" was pretty stupid overall anyway.

Cheers!
Rich

 

[Paul Hovnanian P.E.]

[snip]

The device under test is safe to overload..so if I get a liquid short
out..it's ok...

If it can tolerate the lower cold filament resistance, use a light bulb
(or several with switches to vary the load).

 

[Rich Grise]

.

Yeah..I've been thinking of grease too. It's a good solution.

Point taken about the Pdisp. qualified for air cooling.
I created a chemistry pita instead of just going back to the surplus
store to dig out a 100W power resistor rated for air.
The one I'm forcing to use with liquid cooling I suspect is an
underrated 50Watts. (No markings.) 0.8"d x 7"L

That's a 100 watt resistor already:
http://www.alliedelec.com/Images/Pr...HMITE/Ohmite_Actives-and-Passives_2960672.pdf

What you need to do is watch your current when you adjust the tap -- the
100W rating is for the whole resistor. (IOW, if you've got it tapped at 50%,
you could only dissipate 50W in air, etc.)

Good Luck!
Rich

 

[Tam/WB2TT]

"Tam/WB2TT"



** Realise that is because you CANNOT use water for a radio frequency
dummy load.

The OP is not restricted to using a bad and highly DANGEROUS heat
absorber like oil.




........ Phil

The commercial units I referred to are all used at RF. The one I have will
take a KW for short periods at 50 MHz. Like you say, probably overkill for
DC or power line frequency. For those, I would use a bank of resistors with
a fan blowing air across them, or just bigger resistors. I think the OP said
100W, which doesn't seem like a big deal at low frequencies.

Tam

 

[Tim Williams]

Ah, but they're refining it more now. In fact, it's used standard these
days for some cases, drowning for instance. Displaces the water while
carrying O2.

Tim

 

[D from BC]

Did you read the part where all of the test rats died? It's probably
excellent for heat transfer, but I wouldn't recommend using it for
deep-diving until they solve that pesky "died of lung trauma" problem. ;-)

And, well, "The Abyss" was pretty stupid overall anyway.

Cheers!
Rich

I liked The Abyss..
I think my favorite scene was when some guy uses his wedding band to
hold open a pressure door.
http://en.wikipedia.org/wiki/Wedding_ring
(Damn..wiki is useful..)
Wedding bands come in titanium, tungsten carbide and stainless steel.

D from BC

 

[D from BC]

[snip]

The device under test is safe to overload..so if I get a liquid short
out..it's ok...

If it can tolerate the lower cold filament resistance, use a light bulb
(or several with switches to vary the load).

My laziness to get a bunch of sockets.. exceeds my hate of soldering
wires to household light bulbs.


D from BC

 

[David DiGiacomo]

I know you like to do things the hard way, but think about buying a
Clarostat 240-C power decade box on eBay. If you are patient, you should
be able to get one for under $50. It saves a huge amount of time.

 

[Michael A. Terrell]

"Tam/WB2TT"

** Realise that is because you CANNOT use water for a radio frequency dummy
load.

The OP is not restricted to using a bad and highly DANGEROUS heat
absorber like oil.

........ Phil

Your ignorance and ego know now bounds. There is nothing dangerous
in using the right oil to cool electronics. Pole pigs are full of it,
and I have NEVER hear of anyone overheating a properly filled cantenna.
They have been around for at least 40 years. If they were dangerous,
they would have been pulled from the market.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

How about peanut oil? About 50% higher dielectric constant than
mineral oil, better temperature characteristics, IIRC, and available
at any grocery store. But any oil is going to be vasty inferior to
water in heat capacity (like 1/2 or 1/3 as good). Maybe just add a bit
of radiator antifreeze to the water (it contains corrosion
inhibitors).

A can of water pump lubricant has more inhibitors, and costs less.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

It's a heat transfer medium *and* a salad topping.

Just not at the same time! ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[D from BC]

On Sat, 22 Sep 2007 14:50:31 -0400, "Michael A. Terrell"

[snip]

A can of water pump lubricant has more inhibitors, and costs less.

"Zerex Water Pump Lubricant and Protector The Zerex Water Pump
Lubricant and Protector is a patented 5,702,631 cooling system
additive formulation designed to protect all cooling system metals
from corrosion. It also helps protect nonmetallic parts in the cooling
system, like gaskets, hoses and seals. The Zerex Protector prevents
the accumulation of cooling system deposits and helps lubricate the
water pump. The Zerex Protector is recommended to boost any engine
coolants protection and for those who want to recharge the coolant
corrosion protection but do not want to change the fluid. It can be
used in stored vehicles like collector cars, classics, hot rods and
specialty vehicles, for applications where enhanced corrosion
protection is a concern."

"Gunk
Anti Rust With Water Pump Lube
- Mixes with all ethylene glycol based anti-freeze/coolants.
- Prevents evaporation, formation of rust and corrosion.
- Keeps entire cooling system clean and running efficiently.
- Lubricates and protects all aluminum and/or metal parts, hoses and
seals"

This is a proposed solution if I don't want to coat the metals that
are rusting on the power resistor in the bucket of water.
After reading (the above), I think there's a chance that electrolysis
erosion at 100VDC may happen on the resistor terminals.
Funky trade secret stuff is in those lubricants.
Free ions or not, I dunno....

Gunk Msds is:
Naphthenic petroleum distillate
Triethanolamine
Zerex MSDS is: Unavailable!
Ah...so what.. I'm not a chemist.

10 hours of research or just buy it and try it in an hour.
Risky..Nah..

I still like the ideas of coating the terminals and greasing the tap
for 'in the bucket' tap water cooling.

D from BC

 

[ChairmanOfTheBored]

It's the liquid breathing rats stuff!
http://en.wikipedia.org/wiki/Fluorinert

It's going to be exxxxpennnsive....
D from BC

Wrong.

That media was, and is a PERFLUOROCARBON fluid. Highly oxygenated, it
can and IS used in human medical procedures.

The stuff I pointed out is specifically made for electronic industry
use.

Both for infants born without fully developed lungs, and for elderly
folk that have damaged their lungs to an extreme point.

The stuff is real.

http://www.google.com/search?hl=en&q=liquivent&btnG=Google+Search

So is fake blood, made by the same pharma co.

http://www.allp.com/

They took a dump though.

 

[ChairmanOfTheBored]

Did you read the part where all of the test rats died?

You're a goddamned idiot.

It's probably
excellent for heat transfer, but I wouldn't recommend using it for
deep-diving until they solve that pesky "died of lung trauma" problem. ;-)

As usual, you don't know what the **** you are jacking off at the mouth
about... again.

And, well, "The Abyss" was pretty stupid overall anyway.

No, actually, YOU are pretty fucking stupid anyway... any way one
looks at it, you are a fucking uninformed, over-aged dweeb.

Cheers!
Rich

Yes, YOU!

 

[ChairmanOfTheBored]

I have a big O wirewound resistor I keep cool in a container of water.

[100 ohm adjustable, 100W range]

The terminals and tap are rusting.

You can use several solutions: exchange the water for a nonionizing
fluid
(mineral oil with high flashpoint is cheap, transformer oils and
fluorinert
are also available), or just lower the water's corrosivity (add rust
inhibitor
from the auto parts store to deionized water), or use resistors that
are water-safe.

Every electric water heater, from tea kettles to home hotwater tanks,
has such an immersible resistor. Some have several. One here in my
junkbox
is rated at 4500W at 240VAC - so it's 12.8 ohms. Eight of those,
and you can pick resistances from 1.5 to 100 ohms with no rust.

Neat...
I can picture myself filling a shopping cart full of used water
heaters at the local thrift store..

D from BC

Or buy 8 of those free standing, liquid filled radiant room heaters.
The heat sink (and radiator elements) are built right in!

They're EMI/RFI shielded too! (the element is inside a can).