How to Choose Between AC and DC Hipot Testing?

Ensuring product safety in manufacturing is paramount, with the Hipot Test serving as a cornerstone method to achieve this goal. While the choice between AC or DC Hipot largely depends on product specifications and industry standards, manufacturers may sometimes need to decide on the methods themselves. At these times, they often encounter challenges due to a lack of clarity regarding the advantages of each method. In this issue, we will explain the differences between AC and DC Hipot testing and their respective advantages, helping you choose the proper testing methods.

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Differences Between AC and DC Hipot Testing

When choosing between AC and DC Hipot testing, several key factors need to be taken into consideration. These factors include the acceptance by safety regulatory agencies, the accuracy of leakage current measurement, the amount of output power, the testing settings, and the testing voltage. In the following, we will introduce the advantages and disadvantages of AC Hipot and DC Hipot in these aspects.

In general, AC Hipot is more widely accepted by safety regulatory agencies compared to DC Hipot. This preference stems from the fact that most products operate on AC power. AC Hipot can test both positive and negative polarities simultaneously, thus simulating the actual usage environment. In contrast, DC Hipot can only perform single polarity tests, which must be considered if the product is used with AC voltage.

When applying AC test voltage, the insulation generates a reactive current different from the leakage current, which is often much larger. This makes it difficult to accurately measure the actual leakage current, complicating fault detection. In contrast, with DC Hipot testing, the initial charging current caused by capacitance gradually diminishes over time. This allows for the precise measurement of the true leakage current of the tested products

The output current required during AC Hipot is typically higher compared to DC Hipot. This is because it needs to supply the necessary current for the stray capacitance of the product being tested. Conversely, DC Hipot has lower output power requirements since the charging current is needed for only a short period.

In AC Hipot testing, because it cannot fully charge stray capacitors, instantaneous surge currents are avoided. This eliminates the need for testing voltage ramp-up settings and discharging the tested product afterward. On the other hand, in DC Hipot testing, voltages start from "zero" and ramp up slowly to prevent excessive charging currents that could trigger an erroneous shutdown of the tester. Additionally, since DC Hipot testing charges the product, discharging is necessary after testing completion to prevent potential electrical hazards.

During AC Hipot, the peak voltage is 1.414 times the displayed RMS (Root Mean Square) value on the voltmeter, which is typically not indicated. Therefore, most safety standards require that if DC Hipot is used, the test voltage must be increased to an equivalent value. The formula for DC Hipot test voltage is: DC Hipot Test Voltage = AC Hipot Test Voltage × 1.414. This ensures that the DC test voltage provides the same level of insulation stress as the AC test voltage.

Advantages of AC and DC Hipot Testing

Let's summarize the advantages of each method in a table:

• AC Hipot testing is more widely accepted by safety regulatory agencies.
• There is no need to set voltage ramp-up or discharge at the beginning and end of the test.

• Leakage current measurement can provide a more accurate reflection of the actual current.
• Testing can be conducted with lower currents.

Choosing the Right Method and Tester for Product Safety

When conducting the Hipot test to ensure product safety, selecting the appropriate testing method&#;whether AC or DC&#;and choosing the right tester from Associated Research's comprehensive solutions are critical. Our Hypot® Series offers versatile options, providing up to 5kVac AC hipot and 6kVdc DC hipot choices, covering a wide spectrum of testing requirements. For specialized ultra-voltage testing applications, our HypotMAX® Series delivers exceptional performance, offering up to 20kVac AC hipot and 20kVdc DC hipot options. Our tester features RAMP-HI and discharge safety mechanisms to prevent false failures during DC Hipot testing and ensure operator safety. If you're interested in delving deeper into Hipot testing knowledge, our dedicated application consulting service is an excellent option. Reach out today to explore the perfect solution for your testing requirements.

Such a test applies a voltage to the DUT that is much higher than normal operating voltage; typically V AC plus twice the normal operating voltage. For a household appliance designed to operate at 120 or 240V AC, the test voltage is usually about to V AC.

A DC hipot test can usually be substituted for an AC hipot test. The best voltage for a DC hipot is normally higher than the AC test voltage by a factor of 1.414. A product that would be tested at V AC would be tested at V DC.

For double-insulated products, the required test voltages may be much higher, such as VAC or even VAC for a 120 VAC power tool. The voltage is applied between the operating circuits and the chassis or ground &#; the parts of a product that a consumer might touch or come in contact with.

Refer to Figure 5 for typical AC hipot test setup. The setup for a DC hipot test would be identical.

The purpose of the test is to make sure consumers do not receive an electrical shock when they use the product. This typically is caused by a breakdown of the electrical insulation. The test also detects possible defects in design and workmanship that cause components and conductors to be too closely spaced. The danger is that air gaps between conductors or circuit components may become clogged with dust, dirt, and other contaminants over time in typical user environments. If the design spacing is inadequate, a shock hazard can occur after a period of use. By subjecting the product to a very high voltage, the hipot test overstresses the product to the point that arcing may occur if the spacing is too close. If the product passes the hipot test, it is very unlikely to cause an electrical shock in normal use.

Withstanding a very high voltage means that a large margin of protection exists for the consumer. Regulatory agencies usually require a stringent hipot test as a product &#;type test&#; before releasing the product for sale to the public and another less demanding test to be used on the production line. As a rule, testing laboratories consider the hipot test to be the most important safeguard for the consumer. They may accept &#;design&#; or &#;type&#; tests for other types of tests, but always require hipot tests for 100% of the units in a production line.

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