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Author Topic: air vs oil dummy load ?  (Read 4308 times)
W8JX
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Posts: 13268




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« Reply #45 on: August 27, 2018, 02:46:53 PM »


It was always fun getting a 6V vehicle started at -20F or so and especially the always gummed up flathead Ford V-8's. When I moved up to MA/NH a 8V tractor battery and adjustable regulator were a big help. Kind of rough on headlights but they were only $.10-to .25 in a junkyard.


A trick I long used with 6 volt tractors was to add a pint or so of kerosene to crankcase in winter. works better than 8v. would add kero to hyd oil too so pump has less drag cranking. In extreme cold I would also use a heated battery blanket or 6v trickle charger to keep battery warm as a warm 6v has more cranking power than a cold 8v below zero as cranking power drops quickly below zero.  I have a cousin how lived in country during blizzard of 78 and his 400 foot drive was drifted 5 feet deep. It was getting down to 15 to 25 below every nite after storm for a few weeks so he would come home, park car by street remove battery and carry it to house and put it on a trickle charger and carry it back out every morning. Old 69 chevy 327 never failed to start that way even when snow blew in under hood at nite.

Also when I lived in Montana during mid 90's even Mobile one does not do flow at 40 below. Block heaters were a must have.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
W8JX
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« Reply #46 on: August 27, 2018, 03:10:59 PM »

I would use straight weight SA rated 10w or 20w20 non detergent oil if you use motor oil


Wow! An oil thread on e-Ham!

I would go for Mobil-1 synthetic myself.  Cheesy

No, you want straight weight non detergent SA oil, you do not want any additives in oil.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KM1H
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Posts: 4722




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« Reply #47 on: August 27, 2018, 04:35:33 PM »

Quote
A trick I long used with 6 volt tractors was to add a pint or so of kerosene to crankcase in winter. works better than 8v. would add kero to hyd oil too so pump has less drag cranking.

I guess you missed the first sentence in my reply. Besides tractors werent high compression (some even had a compression release) or larger displacement such as the V8's.


Looooong before Mobil 1...not Mobile, the cold weather formula was a quart or two of kerosene or diesel added to the non detergent 30W in the crankcase; this was also mentioned in owners manuals.
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W9IQ
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Posts: 2913




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« Reply #48 on: August 28, 2018, 06:21:59 AM »

ratio of water to input power is directly proportional so 1 gallon at 1 kW would also boil in about the same amount of time.

As an empircal data point, there's a graph on my site that shows actual temperature vs 100W input with ~22oz of water which takes into account some degree of convection/conduction to ambient.  Haven't done the calculation but I wonder if that correlates to your 1gal/1kW conclusion.  When we built and tested the 1 gallon ones I'm not sure if it was exactly one gallon, might have been more (whatever the freebie restaurant pickle jars were) and I recall they never boiled after 10 minutes.

Mark,

Now that the tractor forum has run its course (and spare me the discourse since I am in an EROPS tractor nearly every day on the ranch)...

I did the rough calculations in my earlier post to show that a 5 gallon bucket of water will not support 5 kW of heat for anywhere near a full day as the earlier poster had asserted. My numbers said about 23 minutes (not 10 as you stated above) to reach boil but I also stated that this did not account for thermal interfaces and other issues. I also noted that my calculation was based on a fully saturated salt solution. In summary, a first order analysis.

Quick math using US units based on your chart says that your 100 watts was generating 341 BTU/hr. Your container ΔT was 90°F over 30 minutes. 22 fluid ounces of water weighs ~1.4 lbs so it would require 252 BTU/hr to realize that temperature rise. This would indicate that your container is dissipating about 89 BTU/hr or about 26% of the applied power. Neglecting the purported low salt content, your water would reach 212°F in about 50 minutes. This correlates with the dT/dt of the graph showing 1.67°C/minute indicating an 83°C rise to 100°C would take ~50 minutes.

Take note that my earlier example started at a 72°F (22°C) point while your chart shows your measurements starting at 63°F (17°C). Starting at a lower temperature obviously lengthens the time to reach a boil, with all other factors being equal. So if you started your container at 72°F, it would reach a boil in about 47 minutes with 100 watts of applied power.

The thermal dissipation of the container will depend on the material and critically the SA/V (surface area to volume ratio) of the chosen container. This can vary widely so a rigorous analysis requires that the container thermal properties be factored into the calculations.

- Glenn W9IQ
« Last Edit: August 28, 2018, 06:26:58 AM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9CN
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Posts: 126




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« Reply #49 on: August 28, 2018, 07:13:57 AM »

ratio of water to input power is directly proportional so 1 gallon at 1 kW would also boil in about the same amount of time.

As an empircal data point, there's a graph on my site that shows actual temperature vs 100W input with ~22oz of water which takes into account some degree of convection/conduction to ambient.  Haven't done the calculation but I wonder if that correlates to your 1gal/1kW conclusion.  When we built and tested the 1 gallon ones I'm not sure if it was exactly one gallon, might have been more (whatever the freebie restaurant pickle jars were) and I recall they never boiled after 10 minutes.

Mark,

Now that the tractor forum has run its course (and spare me the discourse since I am in an EROPS tractor nearly every day on the ranch)...

I did the rough calculations in my earlier post to show that a 5 gallon bucket of water will not support 5 kW of heat for anywhere near a full day as the earlier poster had asserted. My numbers said about 23 minutes (not 10 as you stated above) to reach boil but I also stated that this did not account for thermal interfaces and other issues. I also noted that my calculation was based on a fully saturated salt solution. In summary, a first order analysis.

Quick math using US units based on your chart says that your 100 watts was generating 341 BTU/hr. Your container ΔT was 90°F over 30 minutes. 22 fluid ounces of water weighs ~1.4 lbs so it would require 252 BTU/hr to realize that temperature rise. This would indicate that your container is dissipating about 89 BTU/hr or about 26% of the applied power. Neglecting the purported low salt content, your water would reach 212°F in about 50 minutes. This correlates with the dT/dt of the graph showing 1.67°C/minute indicating an 83°C rise to 100°C would take ~50 minutes.

Take note that my earlier example started at a 72°F (22°C) point while your chart shows your measurements starting at 63°F (17°C). Starting at a lower temperature obviously lengthens the time to reach a boil, with all other factors being equal. So if you started your container at 72°F, it would reach a boil in about 47 minutes with 100 watts of applied power.

The thermal dissipation of the container will depend on the material and critically the SA/V (surface area to volume ratio) of the chosen container. This can vary widely so a rigorous analysis requires that the container thermal properties be factored into the calculations.

- Glenn W9IQ

Hi Glen,

Nice Math work here.

You need to calculate the difference in boiling point based upon altitude.  Water boils at a significantly lower temp at higher altitude.

Additionally the lower air density at higher altitudes impacts its ability to transfer heat.  We usually figure 25% reduction at 6,000 foot altitude over sea level.

Can we go back to motor oil now?
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W9IQ
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Posts: 2913




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« Reply #50 on: August 28, 2018, 08:31:04 AM »

Hi Glen,

Nice Math work here.

You need to calculate the difference in boiling point based upon altitude.  Water boils at a significantly lower temp at higher altitude.

Additionally the lower air density at higher altitudes impacts its ability to transfer heat.  We usually figure 25% reduction at 6,000 foot altitude over sea level.

Can we go back to motor oil now?

At 6000 feet, pure water should boil at ~200°F so closer to a 6% reduction. So from the perspective of the salt water dummy load part of this thread, it will have a lower power rating as altitude increases since the boiling point is suppressed accordingly.

But then you need to add a bit back to the boiling point to account for the molal salt solution depending on the type and relative mass of salt. If NaCl is used to make a 0.5 molal solution, then the boiling temperature will be raised by approximately 1°F (0.5°C).  Approximately 5 teaspoons (29.1 grams) of NaCl dissolved in approximately 1 quart (1 kg) of water will make a 0.5 molal solution. It seems that the salt water dummy loads are using a lower molal solution so the effective may be insignificant in the final results.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9IQ
Member

Posts: 2913




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« Reply #51 on: August 28, 2018, 09:41:47 AM »

While all the calculations that I presented should be reasonably accurate, consider that above about 120°F (49°C), water becomes painful to the touch and may cause burns. Notice that with only 100 watts, Mark's chart shows his design reached that point in about 17 minutes (and he kept measuring higher temperatures - presumably under safe circumstances).

Mark's chart also hints at the duty cycle consideration. A 50% duty cycle does not translate to a doubling of usable power or time. The thermal interface is dissipating approximately 26% of the added heat so a 20% on / 80% off duty cycle is more realistic to achieve an appropriate cooling phase.

I bring these points up because no one in the thread even mentioned burns - the focus seemed to be on the boiling point being the tipping point. This is back to Brian's caution about these types of construction projects. It is fun to experiment but if you don't know what you are doing or you haven't considered all of the factors, there is the real possibility of serious injury. I deplore the nanny state mentality but I also don't want to see someone needlessly injured.

- Glenn W9IQ

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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
K6BRN
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Posts: 1219




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« Reply #52 on: August 28, 2018, 10:12:39 AM »

Focus. Glenn, focus.  Life is not about boiling water with RF, unless you're in the microwave oven business.

Carl:  Kerosene in tbe crankcase?  Really?  All I had to use in --10F weather to start the junkers I had available to drive was a few shots of 180 proof vodka down the carburator throat.  Never failed.  Sometimez caused a backfire through the carb, but when the flames died down, the carb bad warmed up and the engine turned right over.  Booze is surprisingly handy.

Never had an oil problem until the temp hit about -30 F,  which was rare.
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KC4ZGP
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Posts: 1961




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« Reply #53 on: August 28, 2018, 10:15:42 AM »


Vodka...throat...I like that.

Kraus
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W9IQ
Member

Posts: 2913




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« Reply #54 on: August 28, 2018, 12:24:40 PM »

The engineering constructs that I used for water base cooling can be applied to oil based coolants in a metal container. With oil, you need to add the flash point to the calculations and be careful to consider any vaporous effects from a noxious or carcinogenic perspective.

Most "motor oils" are problematic simply because the formulation is not published so the effect of the additives is not known. Mineral, vegetable and transformer oils are generally more fully documented. In some cases, such as transformer oils, an MSDS sheet may yield additional beneficial information.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KM1H
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Posts: 4722




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« Reply #55 on: August 28, 2018, 02:18:16 PM »


Carl:  Kerosene in tbe crankcase?  Really?  All I had to use in --10F weather to start the junkers I had available to drive was a few shots of 180 proof vodka down the carburator throat.  Never failed.  Sometimez caused a backfire through the carb, but when the flames died down, the carb bad warmed up and the engine turned right over.  Booze is surprisingly handy.

Never had an oil problem until the temp hit about -30 F,  which was rare.

Well, it was/is in my 37 Buick Roadmaster owners manual and vodka might not have gone over well with some owners Roll Eyes I still have that car but it is only a warm weather long distance cruising toy. Fuel economy is horrible from that 320 cubes OHV straight 8....it aint light either.

BTW, single weight detergent and multi viscosity oils werent readily available until the mid 50's. Multi viscosity oils (only 10W30 at first), were initially pricey and took the horsepower/engine displacement wars of the 60's to gain wide acceptance when 20W50 arrived. I ran Kendall 50W Racing Oil in my 64 GTO and parked it for the winter.

Carl
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W8JX
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Posts: 13268




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« Reply #56 on: August 28, 2018, 02:49:31 PM »


I guess you missed the first sentence in my reply. Besides tractors werent high compression (some even had a compression release) or larger displacement such as the V8's.


Guess you missed it completely. The 235 cu or so flat head V8 is SMALLER and lighter that 260 to 321 cu tractor motors I was starting dah.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
W8JX
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Posts: 13268




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« Reply #57 on: August 28, 2018, 02:55:47 PM »

I ran Kendall 50W Racing Oil in my 64 GTO and parked it for the winter.

50w oil is what you used in a worn engine that used oil or had low oil pressure, not one is prime condition as it actually cost you HP. Make for a good brag factor though. Only engines that actually need 50w are air cooled motors whose oil temperatures can be a lot higher and super charged drag racers with no cooling systems and life expectancies of mere minutes.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WE6C
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Posts: 105




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« Reply #58 on: August 28, 2018, 04:58:54 PM »

I never tried to make an RF dummy load from salt water but I did try to make a dummy load for a power supply project I was working on. I wanted to put a 25 amp load on a power supply and tried salt water. I did not want to use a perfectly good radio until I was sure I had all the bugs worked out.

I quit before I got it "dialed in" after a friend warned me of salt water vapors possibly being dangerous. Does anyone know about that?

Bob
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KM1H
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« Reply #59 on: August 28, 2018, 05:35:37 PM »

Quote
50w oil is what you used in a worn engine that used oil or had low oil pressure, not one is prime condition as it actually cost you HP. Make for a good brag factor though. Only engines that actually need 50w are air cooled motors whose oil temperatures can be a lot higher and super charged drag racers with no cooling systems and life expectancies of mere minutes.

Gee whiz, that engine, built for me by professionals, campaigned for a local Pontiac dealer, a consistent drag strip winner and a lot of street driving was still in top shape when I sold it at 24K miles. Im glad I didnt go to some farmer for help.
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