Version 1.6 - May 28, 2012
11
6. Warnings
The following warnings should be heeded when using the MegaMoto to avoid failure of the
device:
1. Bench type power supplies do not tolerate regenerative current i.e. current flowing
back into the power supply. Often their voltage will increase until the extra power is
dissipated. If the MegaMoto is operated at 24V with a power supply of this type it is
possible to exceed the maximum rating of the device and destroy the power chips.
When using a bench supply it is recommended that you operate at a lower voltage
Adding a battery in parallel with the output of the bench supply will provide a buffer
which can absorb the extra energy and avoid this type of failure.
2. Sensible driving of the load will increase the life of both the electronics and the motor.
Do not repeatedly switch instantly from full forward to full reverse. If possible reduce
the applied load voltage gradually by reducing the PWM duty cycle over the period of a
few milliseconds. This allows the inductive energy in the circuit to dissipate without the
inductive voltage “kick” that often occurs on abrupt interruption of the load current.
When using a bench supply even switching from full speed to full stop may cause an
inductive kick that can damage the device if the operating voltage is close to the upper
limit.
3. Monitor the device temperatures. The power chips will protect themselves against
overloads but repeated operation until the over temperature or current protection
circuits are activated will shorten the life of the device. Add a fan to speed the cooling
and increase current capacity. During development and testing the devices should not
exceed 100C (painful to the touch) or they may exceed the operating temperature
limits during extended use.
4. Attempting regeneration while the battery is fully charged may lead to larger than
expected voltage rise at the battery possibly exceeding the maximum for the
MegaMoto. Many batteries have significantly increased impedance when fully
charged. This can cause a large voltage spike when attempting to flow current into the
fully charged battery. Once the battery has discharged some its impedance to reverse
current should be much lower and regeneration can safely be used.