water cooling low watt resistors to increase watt allowance - Page 1
Forum section: electronics / beginners

author: Capernicus
author_rank: Frequent Contributor
timestamp: January 21, 2022, 10:23:11 pm
content: If I put a 1/4 watt resistor in a water vessel, how much does it increase the watt allowance of the resistor?If you were putting together a car amplifier set up, and u needed some 200watt resistors, this would be heaps cheaper than forking out the $50 per resistor you need to do it normally ->https://au.rs-online.com/web/p/chassis-mount-resistors/1742546?cm_mmc=AU-PLA-DS3A-_-google-_-PLA_AU_EN_Passive_Components_Whoop-_-(AU:Whoop!)+Chassis+Mount+Resistors-_-1742546&matchtype=&aud-828197004210:pla-341658484038&gclid=CjwKCAiA0KmPBhBqEiwAJqKK40anqpEp8HEz7fry6CdEkgH0m6iMOQ6eCftZgchT1pItd5bNazh5fBoCCioQAvD_BwE&gclsrc=aw.ds

author: Manul
author_rank: Super Contributor
timestamp: January 21, 2022, 10:50:32 pm
content: Better use mineral oil, not water. It will increase power dissipation, but I can't say by how much. Up to 10 times is my guess. Best is to try. Car amplifier does not need 200 watt resistors. Almost nothing these days needs, only very specific applications.

author: Zero999
author_rank: Super Contributor
timestamp: January 21, 2022, 10:54:06 pm
content: The problem is insulating the leads to prevent corrosion.When I was a teenager, I had some fun making a heater to boil water in a mug, using a glass coated 10W resistor, run at a couple of hundred watts.

author: TimFox
author_rank: Super Contributor
timestamp: January 21, 2022, 10:54:21 pm
content: Example: Start with the actual specification of the resistor: maximum power at specified case temperature. Not all "1/4-W" resistors have the same specification.Then perform the calculation of heat conduction to either flowing water or through oil to a very large heat sink.After that, remember that the heat sink will, of course, heat up so you need to calculate the temperature that the heat sink achieves given the heat flow into it.These questions are quantitative, and hand-waving will not go very far.

author: Capernicus
author_rank: Frequent Contributor
timestamp: January 21, 2022, 10:55:27 pm
content: Quote from: Zero999 on January 21, 2022, 10:54:06 pmThats a cool experiment! thankyou!!

author: Benta
author_rank: Super Contributor
timestamp: January 21, 2022, 10:57:27 pm
content: Why would you want 200 W resistors in a car amplifier?I thought the idea was to dissipate the power in the loudspeakers.

author: Capernicus
author_rank: Frequent Contributor
timestamp: January 21, 2022, 10:57:47 pm
content: Quote from: TimFox on January 21, 2022, 10:54:21 pmIf your hopeless at maths, I guess u can experiment instead, and ull get the truth the same.So the problem is the water boils. (even tho you get something useful out of it.) So maybe if you add a condenser to it as an enclosed system - and maybe the water will pump itself?

author: Capernicus
author_rank: Frequent Contributor
timestamp: January 21, 2022, 10:58:52 pm
content: Quote from: Benta on January 21, 2022, 10:57:27 pmYeh I might be wrong there, I just sillyly thought because they look cool, they might be an aesthetic bonus next to your amp, I dont actually know if you actually use them for that.

author: TimFox
author_rank: Super Contributor
timestamp: January 22, 2022, 12:20:13 am
content: Quote from: Capernicus on January 21, 2022, 10:57:47 pmHigh-power RF vacuum tubes have successfully used "vapor-phase cooling", since the maximum plate (anode) temperature is high enough to boil water. Seehttps://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1966/05/page18/index.html.Eimac made such tubes with boilers included. If you properly run the water and steam connections to a condenser (not a capacitor) to allow proper feed of the condensate back to the boiler by gravity, no pump is needed and the overall operation can be less noisy (acoustic) than forced-air cooling.However, be sure to check that your resistor can tolerate that high a temperature.

author: tooki
author_rank: Super Contributor
timestamp: January 22, 2022, 01:37:24 pm
content: Quote from: Capernicus on January 21, 2022, 10:57:47 pmThen you don’t understand the role of the math. Experimenting is very instructive, but it lacks the predictive power of calculations. So they serve different purposes.What they aren’t is substitutes for each other: math only lets you calculate for the factors you know and model into your equations, so the simplified models often used only get us close to how real-world circuits and components behave. Experimentation, on the other hand, gives you glimpses into real-world behavior, but often doesn’t explain why something is the way it is.As always, your lack of structured electronics training — and above all, your belief that experimentation is an adequate (or superior!) substitute for it — is something you need to rectify.

author: Zero999
author_rank: Super Contributor
timestamp: January 22, 2022, 01:51:25 pm
content: Water vapour phase cooling has its limits. If the power per area is too high, the water surrounding the resistor will vaporise, which will allow the temperature to rise above boiling point.

author: mawyatt
author_rank: Super Contributor
timestamp: January 22, 2022, 02:01:52 pm
content: Quote from: TimFox on January 22, 2022, 12:20:13 amA few decades ago we were briefed on a new RF Power Amplifier by Harris that used a alumina hybrid that had a closed loop vapor-phase cooling system integrated in the substrate. Completely self contained closed loop cooling system with no pumps or power required.They also had some nifty heat-pipes used to route the heat flow with a demo where you would take a ~150mm long thin pipe and holding one end in your hand while dipping the other end into a cup of boiling water. Almost instantly the holding end got uncomfortably hot, amazing thermal velocity thru the heat pipe!!Very neat stuff indeedBest,

author: CaptDon
author_rank: Super Contributor
timestamp: January 22, 2022, 08:38:03 pm
content: The ceramic 225 watt resistors are no where near $50 each. Get some ceramic hollow body 50 watters and put them in mineral oil or Automatic Transmission Fluid. I know you want to use these as dummy loads. What planet were the other answers about how you were going to use them from?? I have an elaborate lash-up of 4 ohm 100 watters in oil. They can be patched as 2,4,8 or 16 ohm loads. They are wirewound ceramic hollow tube style resistors. I can easily test CBA-1000 Monoblock Carver amplifiers at 1000 watts at 4 ohms all day. My resistors are sitting in about 4 gallons of A.T.F. in a steel pail with fins soldered to the outside and a window fan blowing across it. No need for the fan unless I intend to do some long term 500+ watt stereo testing or 1kw monoblock. At one time my oil was Inerteen 50% PCB but I sold that of to some hams with Heathkit 1 gallon 'CanTennas'. Good for up to 1kw short term.

author: Benta
author_rank: Super Contributor
timestamp: January 22, 2022, 08:51:40 pm
content: Before people continue presenting scientific papers here, I suggest you look at reply #7.