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Looking for R114 in small quantities

Charles on Thu July 24, 2003 10:27 PM User is offline

I have a Tektronix P6015 40 KV scope probe that is liquid-insulated with a few ounces of R114 (1,2-dichlorotetrafluoroethane) aka CFC-114 or Halon 242. Like any refrigerant, the R114 has gradually leaked past the seals since it was made over 30 years ago, and it needs a refill. Since, just like R12, manufacture and importation has been banned, it is hard to find. The smallest tank I have been able to locate is a 30 lb. cylinder. I don't know if 114 ever came in small cans. Does anyone know where I can get a pound or so? Or know of an acceptable substitute with high dielectric properties (I have read that perfluorocarbons like furan may work)?
thanks
Charles

NickD on Fri July 25, 2003 12:12 AM User is offline

Ebay P6015 Probe

auction closes in 26 hours, looks like a can of refrigerant is in the case, ha, wonder if that is empty.

Gosh, finding the electrical characteristics of refrigerants sounds difficult.

Charles on Fri July 25, 2003 9:17 PM User is offline

Unfortunately, the cans are invariably empty due to slow leakage once opened.
I have found that Aldrich Chemicals has it, for $65 per 100 grams or $217 for 900 grams! Ouch. Guess I may be buying 30# cylinder (unless it's $600 like R-12!)

Mitch on Fri July 25, 2003 9:39 PM User is offline

The US Navy uses R114 in their older 200 ton York AC water chillers. A couple of hundred pounds at a time. The newer ones use 134a. I believe that the evaporating pressure of 114 at 40F is about 0 psi; therefore, the 114 units cannot be converted to 134a. I heard that they are converting the 114s to something like R236fg. Maybe you can retrofit your probe too!

I'll bet that there is a lot of that stuff sitting around somewhere. I called one of my contacts, and he said he would poke around and see what turns up. Don't hold your breath though.

NickD on Fri July 25, 2003 9:41 PM User is offline

I did some searching on the net and couldn't find any cans of R-114, nor any dielectric constants, ha, I thought most refrigerants were conductive, so I learn something new everyday. Wonder how the engineer that designed that probe came up with that, my HP HV probe is resistive so I don't have to fool around with gases. Hardly use it anymore and was curious what you use yours for.

Mitch on Fri July 25, 2003 9:53 PM User is offline

It's HFC-236fa , Hexaflouropropane. It replaces Halon 1211 also.

They are using it as a fire extinguishing agent in diesel generator enclosures also.

You can find it on the net, but a quick look found only 120 kg containers.

Edited: Sat July 26, 2003 at 10:43 AM by Mitch

NickD on Sat July 26, 2003 10:36 AM User is offline

I am not really familiar with the P6015 probe, but I wonder if my thinking is backwards on the function of the gas. Perhaps rather than it acting as an insulating dielectric, they are using it to form a resistive conductive element. Probes of this type normally incorporate "real" high voltage resistors in the order of several hundred megaohms. Frequency compensation is always a pain with the probes due the required high impedance and just guessing that the Tek probe is using the enclosure for the capacitance and perhaps the gas as the resistive element.

When I was doing lots of ignition work, I found it more effective to measure the spark current rather than just the spark voltage that was a lot easier and safer to measure and with a low impedance shunt, also far more accurate.

Ha, over the last several years I cleared out a lot of old stuff, just wasn't worth the effort anymore, maybe I should have tried to sell it on ebay, " I don't know what this is, don't know what it does, have no means of testing it, can't answer any questions so don't brother, but it looks good and complicated, therefore this item is being sold, as is, with no returns nor questions."

Charles on Sat July 26, 2003 8:38 PM User is offline

No, it's definitely for electrical insulation and heat dissipation. The center of the probe has a long 1000 megohm resistor which provides the appropriate attenuation. But it's not so long that 40kv might not arc across it. Also the resistor has to dissipate (40^2)/(1000) = 1.6 watts at max voltage. This won't burn it up but high-value resistors generally have very large temperature coefficients so the accuracy will change as it's being used, unless the heat is carried away by the liquid CFC-114.

I thought about using hexafluoropropane since it is the retrofit substance - but it has a much higher pressure which the Lexan body of the probe probably is not designed to withstand. Also I'm not sure it wouldn't attack the resistor or probe body...

NickD on Sun July 27, 2003 9:14 AM User is offline

I would think that dielectric gas would only be necessary at the high end of the scale, if you are measuring CRT voltages, they would be much lower, but you don't need a scope probe for that. Typically, waveforms are low duty cycle so power dissipation is not a problem, arc over may be a problem, but only at the much higher voltages. Ha, can't tell you are many 25KV shocks I got already, but don't even pay attention to those anymore. Lately I have been working with this 2 volt stuff with problems of a different nature.

Ha, I just phased out an old FAA vacuum tube clunker, makes me feel bad that someday I will be phased out too, but I can carry the new solid state version with one hand where it took a crane to move that old cast iron monster. I have a friend that loves playing with Tesla coils, a bunch of guys to that, not sure how they get their kicks out of that, they sure generate a lot of EMI. Suggested to my friend he get his pilots license and take a spin in a thunderstorm, difficult to duplicate that kind of energy on the ground.

Charles on Mon July 28, 2003 7:50 PM User is offline

After talking to Deane Kidd (a former Tektronix engineer who retired after 40+ years and now sells parts for the old stuff) he says they tried filling the barrel with silicone potting compounds to eliminate the inevitable slow leakage, but they still would often be returned for repair after breakdown at or near 40 kv with a carbon-track burned right through the silicone.

I may have to experiment with substitutes. Advanced Specialty Gases was kind enough to quote me 500g (1.1 lb) of CFC-114 for $729, plus $39 for the cylinder. Yes, you read that right, not a 30 lb cylinder but 1.1 lb for over seven hundred dollars! I think they've been sniffing their own products, myself. And I thought Aldrich wanted a lot at $217 for 900g...

NickD on Mon July 28, 2003 8:33 PM User is offline

Are you actually making measurements even close to 40KV? Ha, I have to use my probe to measure a puny 2.5KV, I don't have anything else that goes that high.

It seems to me if you draw a deep vacuum on that probe to get out all the moisture it should be good to around 30KV.

Ha, a lot of this older stuff is getting full of headaches trying to find replacement parts, not even ten year old 30 cent chips are on the black market now for $250.00. HV silver mica capacitors are worth their weight in gold, unless you are trying to sell some.

Charles on Thu August 07, 2003 3:32 PM User is offline

Quote
Are you actually making measurements even close to 40KV?
Not so far, but I want to be prepared Highest so far has been the +8350 in one of my other scopes. I was thinking of using it to measure the HV for my video game monitors (25kv), maybe playing with some Tesla coil or flyback HV supplies.

Quote
It seems to me if you draw a deep vacuum on that probe to get out all the moisture it should be good to around 30KV.
Sure thing - except how do you keep the outside humid air from slowly leaking in? And how do you know what the breakdown voltage is until it arcs over and destroys the divider resistor... tell you what, come on over and YOU hold the probe in your hand and we'll see

Quote
Ha, a lot of this older stuff is getting full of headaches trying to find replacement parts, not even ten year old 30 cent chips are on the black market now for $250.00. HV silver mica capacitors are worth their weight in gold, unless you are trying to sell some.
Ain't it the truth. Anything prized by audiophools, or used in electric guitar amps, is incredibly expensive. Have you checked the prices for 12AU7 tubes lately? 20 years ago you couldn't give them away...

I got a quote from refrigerant-supply.com on the CFC-114. 30 lb minimum at $70 per lb, yes, $2100 for a cylinder. If I bought 120 lb it's only $40 per lb So I spent $65 on the cute little 100g tank from Aldrich... and of course for that price I could have bought a probe that doesn't require fluorocarbons!

-Charles

NickD on Thu August 07, 2003 5:57 PM User is offline

Hmmm, I must have dozen 12AU7 NOS tubes in my junk box, should look into selling those, I won't mind holding the probe, got my share of 40KV and 25KV shocks from designing ignition systems and aquadag voltages, hasn't killed me yet.

Unless you are really working on an old VT tube type TV set with that HV rectifier, gee I can't remember that most common tube anymore, all the new flybacks have the HV diodes embedded so can't measure the 15,734 Hz frequency anyway, any much cheaper HV probe, plenty on ebay for ten or less bucks would do the job as this is strictly DC, even at that the DC measurement of the aquadag voltage was the most accepted method back then, some of the better sets used a gas tube HV regulator as well.

The ring voltage reflected in the primary circuit is identical to the secondary, but much safer to play with, and we used a spark gap for the secondary testing. Tesla coils have way too much voltage for your probe, the rule of thumb is 60KV per inch of spark gap so shoot for a 36" gap to impress your friends.

Just trying to say that probe isn't worth the effort, heck pull a vacuum on it right before you use it.

Anonymous on Tue October 14, 2003 3:21 AM User is offline

We have the possibility.

Please visit our website: www.leempeng.com.sg

NickD on Wed October 15, 2003 8:44 AM User is offline

What is you US price for recycled R-12? And do you have a US distributor?

pribyl on Fri December 12, 2003 7:02 AM User is offline

I found that a 30 lb cylinder is available for $500, including shipping, from www.trsssales.com.

Given that the probe needs about 1/2 ounce at most (you don't actually fill it up), this would take care of 1000 refills. Probably more than I need in a lifetime, unless the seals are truly bad. But then it would be way too expensive to use the probe. Also socially irresponsible.

At any rate, can tell me any more about the aldrich chemical connection? Thanks

NickD on Fri December 12, 2003 7:44 AM User is offline

Ha, dump that Tek probe and get an HP.

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