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Has anyone else configured a Hickory system with 400V Sigma7 drives of 5.5kW or greater? For example, SGD7S-210D or SGD7S-260D?

If so, you may have encountered an unexpected "A.042" alarm at startup, even after initializing drive parameters to defaults.

In a departure from 200V Sigma7 drives and from any SigmaV drives, the larger 400V Sigma7 drives require an external braking resistor network for dynamic braking during emergency stops.

Note that this is entirely separate from the regenerative resistor connected to terminals B1 and B2.

The dynamic braking resistors are connected across the motor power leads, and switched with an external contactor. See section 5.3.3 in the product manual:
https://www.yaskawa.com/downloads/searc ... PS80000180

Guidance for selecting the braking resistors is minimal. Resistance values are clear enough (section 5.3.2 in the manual) but for power dissipation, the only advice is to calculate absorbed energy per emergency stop, and expected number of emergency stop events in the lifetime of the machine, and then "confirm these specifications with the manufacturer of the Resistor."

If you have been through the resistor selection process and wired a braking circuit as described in the Yaskawa product manual, I would be interested in hearing what resistors you selected, and on what basis.

Hello Marc,

I have not done the configuration with this size of Sigma7 drive but I do have some thoughts to offer towards resistor selection.

It seems to be implying that pulse rated resistors are required for this. Of course, I cannot find a pulse rated chassis mount power resistor datasheet that actually provides a chart or ratings for energy. That is probably why Yaskawa says to contact the manufacturer.

I've worked through it for a sample system using a SGD7S-210D, SGM7G-55D, and inertia ratio of 150% but am stuck on the power requirement of the resistor. The missing piece of the puzzle for me is the time required to reach a stop. They give a formula for the angle traveled before it stops but I have to go back to some basic physics to figure out the time there.

I made a lot of progress on this but have not gotten to any hands on testing yet. The main difficulty is finding a suitable NC contactor. The Mitsubishi part suggested by Yaskawa is not the easiest to get but is still available.



Resistor selection is much easier. I took the coasting distance and initial speed to approximate the time for the motor to stop with a linear deceleration. This time gives the total power dissipated in the resistors, which is then used to select the resistor's power rating.

I reached out to Ohmite and from what they told me, my resistor selection method should be correct. Get the power it dissipates and verify that the duration and magnitude of the pulse are within the short term overload ratings.

For instance, the Ohmite 280 series resistors are rated for 10x overload for 5 seconds. The application I am working on dissipates 2300W per resistor over about 1 second. A 500W model from this series should handle 5000W for 5 seconds. I also considered the Bourns BR/BRT series but the Ohmite 280 series is available to higher power ratings. Other manufacturers products and other series from those two may also be suitable.

Thank you for researching this subject.

There appear to be a couple alternate options, besides providing an external dynamic braking circuit.

1) If it is a relatively low-speed, high-friction machine with no gravity effects (i.e. vertical axes are counterbalanced), then you can set Pn001.0 to a value of 2, so that the axis is allowed to free coast to a stop.

2) If the free coast distance is excessive (high-inertia, low-friction, or unbalanced axis) then -- if you install a SGDV-OSA01A safety module in the drive -- it is reportedly possible to program the drive to do a "category 1 stop" in the cases it would otherwise need to free coast or dynamic brake. In the category 1 stop, it actively decelerates the motor under servo control (using the regenerative resistor when needed) until stopped, and only then removes motor power.

I have a couple of the SGDV-OSA01A safety modules on hand, but have not yet had time to install and configure one to see how that works. On the first project where this issue came up, I found that the free coast distance from rapid speed was less than 1/2", which is tolerable in the application.

Thank you for those alternatives! I should look into those safety modules and add a calculation for the free coast distance for a direct comparison.


I'll send you the resistor calculator spreadsheet I made after verifying it works with the actual hardware. At the motor rated max speed, this axis is estimated to coast about 13 inches with 100 N*m of braking torque from the dynamic brake circuit.