FAQs - Coil & Current

Why is my Clark Cooper valve drawing a higher current than what is listed in the catalog/product page?

Some AC solenoids are rated in watts, but actually have VA (volt*amp) rating that are much higher. VA is a measure of the “apparent power” of an electrical circuit, which is equal to the product of root-mean-square (RMS) voltage and RMS current. It is the value to be used for sizing wires and fuses. For example, a VA rating of 47 using 120V AC would have a current draw of 0.38 amps.

The “real power” is watts in the power that performs work or generates heat. It is the rate at which energy is consumed.

In DC circuits, the real power is equal to the watts listed,the product of voltage, and amperage.

Why does the solenoid on my valve get hot when it is being used?

Temperature rise is expected when the solenoid is energized. Class “H” insulation, for example, has an allowable temperature of 320°F. Beyond that, thermal degradation of wire insulation will begin to occur.
Always use care when handling an energized coil.

Why did the coil on my valve burn out?

The ratings for our valves are based on the “holding” power rating which describes the power consumption after a solenoid has been energized. When an AC solenoid is first energized, there is an “in-rush” of current that is much higher than the normal “holding” current. If an internal component is “stuck” for any reason, this in-rush current will continue longer and can burn out the coil. This is one reason that Clark Cooper recommends using filters in all valves that could be exposed to any kind of particulate.

Other causes of burn out could be the application of improper voltage and exceeding the duty cycle for AC valves. Higher cycling frequency means more in-rushes and will not allow adequate heat dissipation.

Why is there a limit for cycling an AC coil and no limit on DC coils?

An AC coil is limited to a certain number of cycles per unit time due to the heat generating in-rush current. We are essentially limiting the number of in-rushes per unit time. The DC coils do not have this in-rush, so they then can have high cycle frequency.

Is there a minimum ambient temperature for coils?

There is no minimum ambient temperature for coils. Heat is what actually damages them. The customer, however, should be aware that more current is actually drawn at very lower temperatures due to lower wire resistance.

The recommended maximum ambient is 150° F for 10 watt and 77° F for 22 watt coils. This assumes a very hot fluid in the valve and cycle frequency. Higher ambient are allowed where the fluid temperature is lower.

The internal temperature of the coil must not exceed values as shown in the chart below.

Coils are rated by insulation classes that correspond to a maximum allowable coil temperature. The maximum allowable coil temperature is the temperature to which the coil can be exposed without experiencing thermal degradation of the magnet wire insulation. These classes and corresponding maximum temperature levels are:

Class Nominal Class Temperature Permissable Temp. by Change of Resistance Method (UL) Temp. Rise Above 25° C (77° F) Ambient Temp.
A 105° C (221° F) 110° C (230° F) 85° C (153° F)
B 130° C (266° F) 120° C (248° F) 95° C (171° F)
F 155° C (311° F) 140° C (284° F) 115° C (207° F)
H 180° C (356° F) 160° C (320° F) 135° C (243° F)

Coils meeting Classes F and H are sometimes referred to as "High Temperature Coils."