MC4X15A Adapter Board


Earlier I had a BEMF issue with my smaller motor controller, so I have been reading up on other peoples experience and solutions to design my own. What I came up with is 3 changes on the MC4X15A.

  1. Added a 0.33F super capacitor on 3.3V protected by a TVS (on the back) at ca 4V. The supercap will absorb any spike that reaches 3.3V and it will allow the MCU to survive a power dip of several seconds. The later is great as it allow the MCU to monitor and record a Power dip.
  2. Protecting the main PSU with a nasty TVS to avoid that it spikes out of control. This will be set just a few volts higher than the max voltage. This diode is also protecting the surroundings as we have no galvanic issolation on this one. This should also protect against wrong polarity.
  3. I need more capacitors on the PSU, but I have no room for these. I also wanted a battery adapter option. I decided to make room for an adapter board supported by 4 extra M2 screw holes that either can carry extra capacitors or a battery adapter. The example (below) show a 10,000uF/50V capacitor, but notice that this in reality is a vero board so you can add your own design of capacitors.
  4. The connector is a standard 2.54 pitch pin header enabling the adapter board to be engineered on a piece of vero-board. I didn’t want to lock to a specific capacitor at this point so vero-board is fine. This also allows a variety of simpler solutions if I don’t want to use the adapter Board.


I am still not confident that I got everything about BEMF 100% correct, but I will work on that. I might need a combination of capacitors as well as more diodes – not sure. And I need to test this so it will be a few exploding capacitors before I am done :).


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