For motor animations, see Educypedia.
A BLDC motor controller works a bit like a buck converter. Therefore, the motor current can be higher than the controllers input current.
For measuring the motor power, you can consider the motor and the controller as one unit. So, the motor power is simply Ubattery x Ibattery. The motor current itself is of no importance. Therefore, a motor controller can measure simply the input current by a single shunt.
I use a cheap ($15) and small 6-FET motor controller from China which is described here.
In the EU, for a pedelec, motor assistance above 6kmh shall be provided only when the cyclist pedals forward. Therefore a pedelec requires a PAS (pedal assist sensor) to detect weather the rider pedals.
To meet the regulations, the motor controller must behave as follows:
Most pedelecs don’t have a throttle. The motor assistance starts automatically when starting pedalling. The motor power can depend on the pedal speed or pedal force. The disadvantage is that even at low speeds there is pedal assistance, which is not needed. It uses unnecessarily a lots of battery power. Assistance is just needed at hills or at wind.
At pedelecs, a throttle is allowed, it must be disabled automatically when not pedalling. At my e-bike, the pedal assistance is controlled by a three position switch. The cyclist can select maximal, medium or no assistance.
Many Chinese motor controllers can be used without pedalling, which is not allowed for pedelecs. Here we need additional electronics that adds the extra functionality to meet the EPAC standard. I developed a pedelec legalisation device which can be built into the motor controller.
There is a category of RC speed controllers which are called "high voltage". Some of them can be powered with batteries of 12 Lithium cells in series. Under certain conditions, these can also be used for e-bikes. The advantage is that they are lightweight and powerful.
The Amass XT90S is an anti-spark connector with built-in discharge resistor.
Connecting the battery pack to the motor controller creates sparks at the battery connector because of the sudden charging of the motor controller input capacitors. The in-rush current can be greater than 100A. An anti-spark circuit is used to prevent pitting of the connector contacts. But it also prevent other components from power-up stress, such as the input capacitors.
A simple solution is to charge the capacitors inside the motor controller through a resistor of for instance 15Ω before the connectors will be plugged. The capacitor is charged in a split second and the charging current is limited, so the connector contacts will not be damaged. The anti spark resister can be mounted through a separate pre-charge cable or integrated into the connector, see here:
I use an anti spark circuit from this source. Just simply insert the connector, no sparks will occur. There is no need for a separate pre-charge cable or connector modification. The anti spark circuit can be built into the battery pack or into the motor controller.
The simple anti spark circuit requires no PCB:
Anderson Powerpole connectors are used to connect the battery to the motor controller:
The inrush current is limited to a safe value because the gate voltage rises slowly by the capacitor.
Building the anti spark circuit into the battery pack is only possible when the battery pack has a power switch. Note that in this case we need an additional battery charge input connector. The circuit can’t be used to prevent sparks from the battery charger connector. For this purpose another anti spark circuit has been developed, see here.
Note that the contact resistance of an ordinary toggle switch can be much larger than the MOSFET on-state resistance. With the anti spark circuit built into the battery pack we can eliminate the power switch in the motor current path, see here:
The motor current flows through the power MOSFET PSMN2R0-60PS from NXP Semiconductors which has a on-state resistance of about 2mΩ. At 10A the power loss is just 0.2W, the MOSFET remains almost cold. However it is possible to prevent the power loss completely when we mount the anti spark circuit just in series with the capacitor(s) inside the motor controller.
This solution requires a rigorous modification of the motor controller PCB if it contains more than one capacitor that must be switched trough the anti spark circuit.
Manufacturers would do well to standard build in an anti-spark circuit into their motor controllers. Then an external anti spark circuit is no longer necessary. If a motor controller contains a microprocessor, an anti spark circuit is easy to achieve, see here:
For currents above 10A use MOSFETs parallel to reduce the loss. MOSFETS TO220 with low RDS(on):
|RDS(on) [mΩ]||VDSmax [V]|
The values above are for a Vgs (V gate-source) of 10V. RDS(on) can be reduced by increasing Vgs from 10V to 20V. To be sure to stay under the limit of 20V we use a Vgs of 15V.