Umair Gaines
Electric choke coils are an important component of engines, particularly older ones, and they can be tested in various ways. One common method is to check the choke's response time by opening the throttle when the engine is cold and observing whether the upper butterfly valve snaps closed. If it doesn't, the choke may need adjustment or replacement. Another test involves examining the power supply to the choke assembly with a meter or test light, ensuring voltage is present when the key is on, and adjusting the choke body cover to control the rate at which the choke opens. Choke coils can also be tested for current and voltage using devices like ohm meters, inductance meters, and meggers, which can help identify voltage leaks and calculate safe working voltages. It's important to note that choke coils may not function optimally in extremely cold weather, and adjustments may be necessary to suit individual vehicles.
| Characteristics | Values |
|---|---|
| Voltage | 12V |
| Current | 0.250mA cold, 0.500mA warm |
| Resistance | 28 ohms |
| Inductance | Easy to test with an inductance meter |
| Temperature | Check temps |
| Breakdown voltage | Use a megger to assess |
| Safe working voltage | 400V |
| Voltage rating | Test with a variable DC power supply |
| Fuse rating | Compute for 95% of the fuse rating |
| Voltage leak | If the fuse pops, there is a voltage leak |
| Core saturation | Inductance will drop |
| Power supply | Place a DC current source in series |
| Choke canister | Move the throttle arm to pull off 'High Idle' |
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What You'll Learn
Check the choke coil's voltage and current
Checking the voltage and current of an electric choke coil requires some testing equipment and a careful approach. Here is a step-by-step guide:
Firstly, it is important to understand the role of choke coils in a circuit. Choke coils, or simply "chokes", are inductors designed to block higher-frequency alternating currents (AC) while allowing direct current (DC) and lower-frequency ACs to pass through. They are commonly used in applications where voltage ripple needs to be minimised or eliminated.
To test the choke coil, begin by inspecting the circuit when the car is cold. Remove the air cleaner assembly from the engine and slightly open the throttle. Observe the upper butterfly valve for the choke. If it does not snap closed, the choke is either misadjusted or faulty. Proceed to the next step to confirm power delivery to the choke.
Now, turn the car to the run position but do not start it. Use a meter or a test light to check for power in the wire connected to the choke assembly, typically a green wire. If there is no power, investigate the cause. If power is present, proceed to the next step.
With the wire connected, observe the upper choke plate. It should gradually open and be fully opened within a couple of minutes. If it fails to open, the choke is likely broken or misadjusted. If it opens too quickly or slowly, adjust the choke body cover, where the green wire connects, to achieve the desired rate of opening.
To directly measure the voltage and current, use a digital multimeter (DMM) to measure the drop in AC and DC volts. From these measurements, you can compute the choke's reactance and solve for inductance. Increase the DC current and measure the reactance again; it should decrease. This process helps determine the choke's minimum inductance for power supply design.
Additionally, you can use a device called a megger to test the choke coil. A megger applies a high voltage to the device and measures any leakage to the ground, allowing you to assess the breakdown voltage and calculate a safe working voltage.
When performing these tests, exercise caution and ensure you have the appropriate equipment and knowledge. Voltage and current measurements can provide valuable insights into the condition and functionality of your choke coil.
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Test for a voltage leak
To test an electric choke coil for a voltage leak, you can use a variable DC power supply (0 to 500 volts) and run the choke up the ladder to determine its voltage rating. Compute for 95% of the fuse rating and use that voltage to test across a known load. If the fuse blows, it indicates a voltage leak causing a short. The highest voltage that does not blow the fuse is the choke's voltage rating.
Alternatively, a device called a megger can be used to test for voltage leaks. This device applies a high voltage to the device and measures any leakage to the ground, allowing for a safe assessment of the breakdown voltage.
It is important to note that voltage on a choke is the point at which the insulation fails, and testing beyond this point will damage the choke. Therefore, it is crucial to estimate the voltage rating and avoid going too high.
When testing for voltage leaks, it is also important to consider other factors that may impact the results, such as the sensitivity of the meter or ohmmeter used, the presence of solid-state devices, and environmental factors like air humidity.
Additionally, when testing an electric choke, it is essential to perform a comprehensive inspection of the choke's functionality. This includes checking the choke's adjustment and power supply. For example, when the car is cold, you can open the throttle slightly and observe if the upper butterfly valve for the choke snaps closed. If it doesn't, the choke is either misadjusted or broken.
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Assess the choke coil's safe working voltage
To assess the choke coil's safe working voltage, it is important to understand the role of choke coils in electrical circuits and the factors that can affect their performance.
Choke coils, also known as inductors, are used to oppose applied voltages and smooth out voltage waveforms. They are typically made of a coil of copper wire wound on a laminated iron core with negligible resistance. When an AC voltage is applied, a self-induced electromagnetic force (emf) is created in the coil due to self-inductance, which opposes the applied voltage. This property of inductors makes them useful as power supply filter elements, as they can reduce voltage drop and improve voltage regulation.
The safe working voltage of a choke coil is the maximum safe voltage that can be applied between the coil and its frame, which is usually grounded. It is important to operate within this safe voltage range to prevent damage to the choke coil and the circuit it is connected to.
To determine the safe working voltage, it is necessary to test the choke coil's voltage rating. This can be done by using a variable DC power supply and gradually increasing the voltage until the choke coil's breakdown voltage is reached. The breakdown voltage is the point at which the insulation of the choke coil fails, and it is important to stay well below this level during normal operation.
Additionally, the climate and design of the choke coil can impact its performance and safe working voltage. For example, in extremely cold weather, the choke coil may require additional warming mechanisms to function optimally.
By understanding the voltage requirements, testing the voltage rating, and considering environmental and design factors, one can effectively assess the safe working voltage of a choke coil and ensure its proper functioning within an electrical circuit.
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Check the bi-metal flat coil spring
To check the bi-metal flat coil spring in an electric choke coil, you can perform the following tests:
Firstly, take off the choke cover and disconnect the wire. Run hot water over the cover and observe if the spring expands. Then, run cold water over it and check if it retracts. This test utilises the bi-metal spring's property of unwinding when heated and winding back when cooled due to the differing thermal expansion values of its two bonded metal alloys.
Another test involves holding a lit match close to the spring, observing its reaction to the heat. This test can also be performed by using the heat from a flame.
Additionally, for choke covers with a bi-metal switch, place the cover in a freezer for an hour. Then, connect a jumper wire from the positive battery terminal, through a test light, and to the choke cover's electric wire connector. Finally, ground the choke cover case to the negative battery terminal.
It is important to note that the bi-metal flat coil spring is located under the black plastic cap on the choke mechanism, with one end anchored to the cap and the other attached to the choke shaft. This spring plays a crucial role in controlling the opening and closing of the choke by rotating the cap.
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Observe the choke canister and carb linkage
When testing an electric choke coil, it is important to observe the choke canister and carb linkage. This will help you identify any issues with the choke coil and determine if it needs adjustment or repair.
Firstly, understand that the choke is designed to be 'ON' when it cools down. This is its ''Fail Safe' or 'At Rest' position. When you start the engine, an electrical current is sent through the bi-metal 'Flat Coil Spring', heating it up and causing it to straighten out, which pulls the choke 'OFF'.
Now, when you ''Hot Wire' the choke circuit, pay attention to the linkage between the choke canister and the carb. If this linkage does not move, it indicates that either there is no power reaching the choke or the coil spring is damaged. If the linkage moves, you need to adjust the throttle arm to allow the choke/linkage to pull off the 'High Idle'.
The ''High Idle' should remain on with the choke until you 'Blip' the throttle and free the linkage. With the hot wire still in place, you should be able to move the throttle linkage slightly, observing the choke blade move completely 'OFF' over a few minutes, depending on the choke canister setup. A properly functioning system will pull the blade completely off within 5 minutes. If it fails to do so, the choke requires adjustment or is faulty.
Choke canisters rarely fail catastrophically; instead, they tend to deteriorate gradually over time. This can result in a rich fuel mixture, leading to poor fuel mileage and a sluggish engine response.
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Frequently asked questions
First, check if the upper butterfly valve for the choke snaps shut when the car is cold and the throttle is slightly open. If it doesn't, your choke is either broken or incorrectly adjusted. If it does, turn the car to the run position and check if there is power going through the green wire connected to the choke assembly. If there is no power, the choke is likely broken.
With the car in the run position, observe the upper choke plate. It should slowly open up and be fully opened within a couple of minutes. If it is not opening, the choke is either broken or needs to be adjusted. If it opens too fast or too slow, adjust the choke body cover accordingly.
The electric choke should be hooked to a keyed 12-volt power source, with a good ground. Verify that there is no voltage when the key is in the off position.
