DC motor drive controller for shunt type motor

Thread Starter


Joined Feb 1, 2016
I'm working on a project which is to run a 8f Bridgeport mill feed controller to run with a Minarik motor drive controller and a set of relays. I am basically copying a set up that I found online. https://www.atechfabrication.com/information/Bridgeport_Feed_Controller.htm I followed the wiring diagram on the web page and when I attempted to run it it wouldn't work. Eventually I found out the it blew the fuse I had in place for the input L1 voltage. I swapped out the fuse thinking I may have accidentally shorted out the wires while moving things around and the second fuse blew. At this point I knew I had an issue I just was not sure if the problem was at the board or the motor and relays that I had set up. I unplugged everything from the board, changed the fuse and only connected input power, it still blew the fuse. At this point I suspect an issue with the board. I had purchased the board used from ebay. I was hoping to get some feedback and ideas on how to verify if the board is any good or confirm if in fact it is shorted. Any trouble shooting tips would be greatly appreciated.



Joined Jan 8, 2017
I suggest that you start by testing the the diodes (4 surface mount diodes.) in the bridge rectifier for the field winding for shorts. (Using the diode test range on your DMM.) Also check that the MOV on the output of this bridge has not gone short circuit. The thyristor bridge that supplies the armature will consist of two diodes and two thyristors (SCRs) These will be the TO220 package devices at the edge of the board. The SCRs look to be the end devices and the diodes the 3 middle devices. I have not traced out where the third diode is in the schematic. Check these diodes for short circuits and check the SCRs for anode to cathode shorts. (The gate pin will be the one with the thin track going to it to save you looking up the datasheet on them to find the pinout.) There are also two large MOVs in that area. (MOV501 and MOV502) Check that they have not gone short circuit.



Joined Jul 18, 2013
The bridge usually also has a same diode connected reverse biased across the bridge itself, IOW 3 Diodes and two SCR's.
They are very similar to the KB versions.
Digikey sell Littlefuse equivalent replacements if needed.
Test the board without motor first.


Joined Jan 8, 2017
Hi Max,
I've just traced out a bit more of the schematic and you are correct about the location of the third diode. Also R501 is the current sense resistor. It is similar to the speed controller on my Seig X3 mill.

santimari, Also check that you are not feeding the board with 240 volts with the voltage selection switch set to the 120 volt position. (This switch just seems to select the tap on the transformer primary winding.)

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