EVT100 Electric vehicle tester

Any warning conditions while using the EVT100 will appear on the display with an error code. Screen instructions will guide you through the troubleshooting process.  

If the instrument does not behave as normal and the warning messages do not disappear, the instrument has a fault and needs to be repaired.

Full details can be found in the instrument’s user guide, or by contacting our technical support lines. Below are the main warning messages and their meanings:

• Test failure - Lost connection

The EVT100 will notify you if the connection is lost during the test. You can re-establish the connection and then restart the test after a few seconds by pressing the test button or by reconnecting to a test piece.

• Failed export

The EVT100 will notify you if the export fails. This may be because the receiving USB device is faulty, disconnected, full, or fails in some other way.

The EVT100 will return to its previous screen.

• Fuse Failure

No measurements can be carried out if a fuse fails. A message will appear each time you try to run a test.  

Close the message by pressing the tick/check button and refer to the user guide.  

NOTE: A fuse failure warning could indicate a very low insulation resistance. Check the lead connection and try again.

• Battery Low

The battery is too low to perform a test. Please charge the batteries or replace them to continue using the instrument safely.

• Charging Fault

This is a generic charging fault warning screen.  

Turn the instrument off and disconnect the charger. Then reconnect and try again.

• Battery not chargeable

The battery settings are not correct to allow battery charging.

Check that the correct battery type is in the instrument.  

Check that the battery settings are for NiHM.  

In either case, refer to the user guide for more information.

• Battery Charging Warning

Only NiHM battery cells are rechargeable. Do not attempt to recharge alkaline or lithium cells since that is a high-potential fire hazard.

If charging the EVT100 while the instrument is turned off, an animated battery will display across the screen to show charging is taking place. Once the battery is fully charged the screen will display a solid green battery.

• Code 1000 or higher  

Follow the instructions on the screen, which will suggest rebooting the instrument. If the problem persists, contact Megger.

• The screen displays a “Voltage Detected” warning during a test.  

Even if you don’t expect it, a voltage can be present or can develop during a test. The instrument will inhibit a test when the voltage detected exceeds dangerous limits, and will stop the test. This voltage threshold can be set as a lockout voltage.  

The lockout voltage is active on all test modes. It is hard-coded to activate at 20 V. The only exception is the insulation resistance tests, where the lockout voltage can be set as 20 V, 30 V, 50 V, or 75 V.  

A low-resistance measurement is typically a measurement below 1 Ohm. At this level, it is important to use test instruments that will minimise errors introduced by the test lead resistance and contact resistance between the probe and the material under test.

At this level, standing voltages across the item being measured can cause thermal electromotive forces (EMF) at junctions between different metals. These can cause errors that need to be identified.

Testing conditions at the time of tests can also provide essential information. Maintain records of the temperature, humidity, altitude, and any electrical interference recorded by the instrument to allow space for further corrections in the test results.

There are different approaches to expected values on a test, with international standards suggesting best practice and expected values.

The low-resistance test is vital when detecting changes in electrical bonding and mechanical equipotential structures. That is particularly true in electric vehicles and its system components exposed to heavy vibrations, environmental conditions, and corrosive environments.  

A good insulation resistance value means a relatively high resistance to current flow, as well as the ability to maintain a high resistance.

Insulation resistance is highly temperature dependent, and thus the results should be corrected to a standard temperature, usually 40º C.  While temperature effects will be covered later, a good rule of thumb is that for every 10º C increase in temperature the current doubles and the resistance halves. The key to making the test valuable is consistent timekeeping, effective record keeping, and constant trending of results.

Minimum acceptance values for insulation testing and test voltages are recommended by car manufacturers and international standards bodies like IEE and ANSI. 

The resistance and insulation resistance tests of a component can vary with its temperature. To use the instrument with the temperature compensation function enabled, a temperature measurement must establish the temperature of the unit under test.

The thermocouple supplied with the EVT100 is set as default for type “T”, and can also be configured for “J” and “K” types.

The temperature compensation is set to “OFF” by default, and is available in a selection of test range sub-modes:

• Insulation resistance
• IR tests
• Three-phase Insulation and low resistance test
• Timed test
• DLRO (Low Resistance Ohmmeter)
• Uni-directional
• Bi-directional 

Diagnostic insulation tests electrically stimulate the insulation and measure the response. We can draw some conclusions about the condition of the insulation depending on that response. 

Diagnostic insulation testing covers a very wide range of techniques:

• Spot reading test (IR)  
  This is the simplest of all insulation tests and the one most associated with lower voltage insulation testers. The test voltage is applied for a short, specific period of time. 
   

• Polarisation Index test (PI)  
  This requires only two readings followed by a simple division.

  IEEE standard 43-2000 (Recommended Practice for Testing Insulation Resistance for Rotating Machines) defines PI as the ratio of insulation resistance at 10 minutes divided by insulation resistance at 1 minute.  

  The thermal mass of the equipment being tested is usually so great that the overall cooling that takes place during the 10 minutes of the test is negligible.

  In general, a low ratio indicates little change and hence poor insulation, while a high ratio indicates the opposite.  

  PI results >1.5 are regarded as acceptable by IEC60085:-01:1984 for thermal class rating A, and PI results >2.0 for thermal class ratings B, F and H.

• Dielectric Absorption Ratio (DAR)  

  This measures resistance over time expressed as a ratio of resistance at time t2 divided by resistance at time t1.

  The assumption is that insulation temperature does not vary widely over the duration of the test so the resulting DAR and/or PI values are temperature independent.  

  This test is defined as the ratio of insulation resistance at 1 minute divided by insulation resistance at 30 seconds.

  In general, a low ratio indicates little change and hence poor insulation, while a high ratio indicates the opposite.  

• Timed insulation resistance test T(s)

  A timed test will automatically terminate an insulation test after a preset time. The default timer is set to 1 minute and is adjustable in the settings function. This is a useful feature that saves you from watching the display for the full duration of the test, and the possibility of missing the 1-minute reading.