Hello, My micromaster 440 0.25kw only goes on with a link cable between dc DC/R+ and B+/DC+

When i got it (used item) It did not work, then i noticed the factory fitted link in the quickstart manual so i installed a link cable between these terminals and the unit went on.

Now it is working with my 250w motor and running (hopefully) at 2800rpm. 

Why is this? I have a hard time understanding the DC/R+ and B+/DC+ terminals.

Second question, do i also need to install a braking resistor?

When the first Micromaster MM440 was designed there was a plan to make the DC Link able to have a DC Link choke fitted, the attached drawing shows a link where this could be fitted in seriese with the DC line. this option was dropped for later versions.

A DC link choke is able to reduce the harmonic effect of the input rectifier on the supply, more effective for larger devices than this 250Watt unit.

Loads which posess high referred inertia, a flywheel for example, are difficult to manage when reducing the speed; as the frequency reduces below the speed of the flywheel the motor becomes a generator increasing the Voltage of the DC link beyond acceptable level, causing the inverter drive to trip with Over Voltage, with F0002 displayed. This effect can also be seen when mechanisms are required to ramp down very quickly. A braking resistor if fitted, enables the inverterdrive to dissipate this surplus energy.

If your application is able to ramp down without tripping with F0002 (OverVoltage) then a resistor is not required.

Tractor