PicoScope EV Testing and the Milli Ohm Motor Tester

Steve Smith introduces the MT03A Milli-Ohm and Electric Motor Tester. This remarkable tool allows you to measure extremely low resistances and test motors. Steve takes us through concepts and testing a motor from a Toyota Hybrid Vehicle.

A multimeter is useful above 1 ohm. The milli-ohm meter works for resistances below 1 ohm.

Having found the problem, Steve also performs an insulation test using the Pico Insulation Tester - enjoy the fireworks!

Running Time 26min 46sec

Toyota Hybrid Motor Testing Continued

A new YouTube Video. Steve performs a quick balance test on the Toyota Hybrid Motor. He then tests the resistance of a bus-bar and shows the effect of loosening a connecting bolt, even slightly.

I * R = V. At 100A an increase of 10 milli-ohms produces a 1V drop. Think of the effect at 800A, a reasonable starter motor current. The voltage drop would be 8V, enough to prevent most vehicles from starting! Also consider the power that would be dissipated. V * I = P, 1V * 800A = 800W, enough to produce lots of heat at the connection.

PicoScope EV Diagnostics - Renault Zoe Type 2 charging error

Type 2 Charger Pin-out

Is it a car or charger fault? Steve Smith investigates a charging error on a Renault Zoe. The Charger-vehicle proximity line resistance (Type 2) Guided Test is consulted. Again, various techniques are discussed, including using a resistance lead, a differential probe, safety considerations and how to manually test and engage the lock pin.

Steve also found and discusses a charger anomaly in that it emitted a PWM signal even though it was not connected to the vehicle.


CP means Control Pilot which provides bidirectional communications between the electric vehicle and the charging system. This checks the maximum amount of current that the EV is able to take at any one time.
PP means Proximity Pilot which tells the charging equipment what type of cable is connected to the socket. Different cable thicknesses can carry different amounts of electrical current.

When to use the 2-Pole Voltage Detector

Steve Smith discusses common errors when using a multimeter. You could inadvertently mis-configure your multimeter and think the system is safe.

Steve shows us why the Two-pole Voltage detector is such a handy tool to make absolutely sure that you have safe conditions when you work on high-voltage systems.

DC Charging fault on a BMW i3

Steve Smith discusses how Power Line Communication (PLC) 'rides' on top of the PWM signal. He then discusses the Electric Vehicle Charge Controller (called LIM by BMW). This wasn't the problem, however.

Connections to the vehicle:

Steve then analyses the PicoScope traces and describes the progression of the charge cycle. It seems that the contactor contact resistance was too high, but how does one measure it? Steve starts with the resistance lead and finds that the negative contactor remains open circuit when energised. He then measures the contact resistance of the positive contactor with the Milli-ohm and Motor Tester. Testing proved that both contactors have failed, although in different ways.

Steve then discusses the value of verifying your fix with your PicoScope.