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Omaga99

Joined 6 July 2008


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Should this article be on wikipedia or not? Please state yes or no with reson bellow. (the original name of it was water resistor. If i were to put it back on it would be liquid resistor. One more thing. Please edit this article if you have info. thanks.)

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Write here (You may delete this sentince after writing something here)


Liquid resistor keep or go. (BETA)

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  • Liquid resistors are used in high voltage ac power equipment. Liquid resistors can absorb lots of heat. The disadvantage is that it can be hard to obtain a precise resistance. The temperature of the solution can change the resistance by a large sum. Because of that, liquid resistors are often in charging systems, dump resistors, High volt power supply, where exact value of ohm’s are not needed. Liquid resistors are also used for soft starter H.V AC motors because liquid resistors block out volage spikes. The earliest recorded use of the water resistor is The variable liquid resistor in 1905. Which is in display at the Bakken library and museum.(Look for it in external reference.) This suggests that the liquid resistor could have been around since 1880’s. However the exact date the liquid resistor has been around will never be known.

Liquid resistors are usually constructed from tubes or containers with flexible insulating material. The reason for the flexible material it so gases (normally steam) will not exert too much pressure and break. The electrodes are usually flat. There are five different liquids that are normally used. (See below)

Liquid resistor solutes

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’’’Copper Sulfate’’’ (CuSO4) Liquid Resistors Copper sulfate (CuSO4) is often used for liquid resistors. A saturated solution of copper sulfate has a resistively of about 90 ohm-cm. When mixed with 1 liter of water, the electrode material should be copper.

Although copper sulfate is one of the most common solutes for liquid resistors, other solutions can also be used depending upon the required resistance. This solution is normally used for low resistance values. When saturated, the resistivity of this solution is ~2 ohm-cm. Stainless steel (SS304) electrodes are used with this solution.

Sodium chloride (NaCl or table salt) solutions can also be used to make low resistance values. The saturated resistivity of this solution is ~5 ohm-cm

Sodium thiosulfate (Na2S2O3) is also used in fabricating liquid resistors. It has only a very small resistance difference from Ammonium chloride, and Copper sulfate.

The use of potassium chloride is relatively new for liquid resistors. Potassium chloride is found in half salt. Half salt when saturated in water has a low resistance. Approximately 1.75 ohms per one teaspoon in a quarter cup of water. The electrode should be aluminum.


Property’s of a liquid resistor

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A liquid resistor always has a solute or impurity in the liquid. (Or it will be an insulator and the resistor will not work) A liquid resistor is always built according to the amount of heat it will need to absorb. The more energy the larger it is. When a liquid resistor heats up its resistance will drop. This is also true for normal resistors. Because its resistance drops a liquid resistor can be built with too much resistance. Then as it heats up It will drop in resistance to the wanted amount. (Liquid resistors tend to heat up fast) When in operation electrolysis will ocure. The prosess will create hydrogen which will exert pressure in an inclosed system.


Water resistor design calculations

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Water resistors will run hot. This is a mathematical formula that is used for calculating the size of a water capacitor. Sample calculation: 10 kJ pulses every minute. Conversions: 1 kJ = 240 calories (approx) Allowed temperature for most liquid resistors. 40-90 degrees Celsius. 1 cm (3/8”) container, 50 cm long. Approximately 35 g. We will assume a specific heat of 1 degree/cal (= 4.184 Joule/K). The delta T for this resistor is 7 degrees C per kilojoules. If you are dissipating 10 kJ per pulse, you are looking at a 70-degree rise, which will probably melt the container. Even if you double the volume, you are still looking at a 30-degree rise. A 200 cm length gives you a 16-degree rise. Try 1.9 cm diameter container. A 50 cm length has 1.6 degree’s Celsius per kilojoules, which is better. Our design 10 kJ pulse now results in a delta T of 16 degrees. How fast will this heat be carried away? The primary limiting thing is the thermal resistance of the container wall, nominally .125 inches (.3175 cm) thick. You need to figure with the mean logarithmic area: Watts = .003 * 350 / .3175 * 16 = 52.5 watts at 16 degrees above ambient. Log mean diameter = (od - id) / ln(od/id) = (2.535-1.9)/ln(2.535/1.9) = 2.2 cm Log mean area = pi * log mean diam * length = 3.14159 * 2.2 * 50 = 350 ( approx) At this rate it will take some 200+ seconds for the water to cool back down from a 10 kJ pulse. Going back to another case, the 1cm I (3/8 nominal) with 1/16” walls, a 200 cm long piece with a 16-degree rise dissipates about 250 watts, for a time constant around a minute.

Health risks

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When in operation will get hot and can boil. Contact with resistor in operation can cause burns and electrocution. The burns may result in scars. Do not ingest resistor fluid. May cause poisoning.


See also

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More reading

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another historic item recorded was the Trautonium amplifier using water resistor in 1930. (see refrence) The resistor was used in the foot pedal. Today company's such as Shanghai Surpass Sun Electric Co, International Electronics, And Kitashiba eletric All sell/manufactuar liquid resistor's mainly for soft starter's for H.V AC motor's For use in industry.


references

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External (references)

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