Selecting MOV Transient Voltage Suppressors
Tech Tip
Description
CKE, Inc. features two radial loaded MOV product lines:
- Standard Series
- High Energy Series
Our Standard Series will continue to offer the optimum value in quality and economy.
The High Energy Series offers a premium quality in a higher density package, allowing a reduction to the next lower mm size from standard MOV ratings. This can be allowed because the current and energy ratings have increases of up to 50% over the standard series MOVs.
CKE, Inc. identifies its Z-MOV product line by using various characters and actual electrical specifications that are incorporated into the part number. CKE uses a "Z" prefix as its identity for all Z-MOV products and an "H" suffix to identify the High Energy Series parts. All parts 7 mm and larger with a voltage rating of 130 V and up have the RMS voltage ratings in their part number. All 5 mm parts and those with voltages lower than 130 RMS are identified by the mm size and the peak nominal clamping volts at the 1 milliamp level.
CKE, Inc. uses the latest in manufacturing technology in the production of our varistors. Both the Standard Series and High Energy Series MOV parts conform to UL1414, UL1449 and CSA class 2221 01. All of CKE'’ line voltage parts are UL recognized and listed on File E90510 (M).
Parameter Definitions
| Maximum Applied Voltage | Maximum AC RMS value of a sine wave or maximum DC value "filtered." |
| Varistor Voltage | Voltage between terminals when 1 mA of DC current is applied (0.1 mA for 5 mm parts). |
| Energy | Maximum energy of two 2 ms pulses at 1 minute interval which cause > 10% change in varistor voltage. |
| Maximum Clamping (VI) | Peak voltage value for peak current applied with 8ms rise time, 20 ms decay to 50% value of the current. |
Maximum Power Dissipation Ratings
| Package | Dissipation |
| 5 mm | 0.1 Watt |
| 7 mm | 0.25 Watt |
| 10 mm | 0.4 Watt |
| 14 mm | 0.6 Watt |
| 20 mm | 1 Watt |
Selection Procedure
MOVs are transient voltage clipping devices and cannot regulate the line voltage. Therefore, there are important steps to follow in selecting the correct MOV:
- The open circuit or surge voltage must not exceed the maximum applied continuous voltage.
- The energy rating of the varistor, in joules, must not be exceeded. The transient energy rating may be calculated by W = ½ LI 2, where "L" is the inductance of the component or the system inductance responsible for the transient. "I" would be the current flowing in the inductance during the interruption.
- The peak current interrupted will determine the clamping voltage. Review the VI characteristics to determine if the MOV selected will clamp at the maximum peak voltage required. A larger MOV will provide a lower clamping voltage.
NOTE: Higher voltage MOV selection is acceptable as long as the maximum clamping voltage meets your requirements. Higher energy ratings are also acceptable provided the physical space is available. Under no circumstances is a lower voltage rating MOV to be used.
Article condensed from CKE, Inc. Metal Oxide Varistors
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