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I have a 220AC universal series wound motor I am trying to connect to a RF Remote Switch using relays and full bridge rectifiers.

I have come up with the following schematic:

enter image description here

The RF Remote Switch takes 220AC through the P-N connection and outputs it through L-N (UP) or L1-N (DOWN) depending on the selected direction on the remote control and it also has a stop button where no output is enabled. The switch seems to be correctly designed and has a small delay when changing from L-N to L1-N or vice versa.

The full bridge rectifiers are KBPC5010 (50A, 500V) and the DPDT relays are LY2NJ or LY2J.

R1 relay is used to control polarity when the L1 output is selected, and the R2 relay is used for dynamic braking through the R resistor.

The problem I encounter is that dynamic breaking seems to work fine when only operating the motor in the UP direction (L-N) and stopping, as the R resistor heats up; but it does not work when operating in the DOWN direction (L1-N). When the motor is receiving voltage through the L1 line and it is stopped, a visible spark comes out of the motor housing.

I think this is because deactivation of the L1 line causes the R1 relay to switch before the R2 relay (R1 activation is caused by L1, while R2 activation comes from the dual bridge assembly) and causes a change in polarity to the input of the motor before the dynamic breaking resistor path can be activated. What would be the correct way to avoid this from happening?

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Your diagnosis is spot-on.

Here's the cure.

enter image description here

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  • \$\begingroup\$ What software are you using for your industrial-grade schematics? They're fairly smart. \$\endgroup\$ – Transistor Jan 23 at 15:47
  • \$\begingroup\$ Thank you, Transistor. I use Microsoft Excel and Paint! \$\endgroup\$ – vu2nan Jan 23 at 15:57
  • \$\begingroup\$ Oooh! That's a terrible workflow! Try Inkscape or some other vector drawing package. You could create a library of symbols and drag stuff around. \$\endgroup\$ – Transistor Jan 23 at 16:06
  • \$\begingroup\$ I agree with you. But I do have a library of symbols and the schematics I've prepared over the years. So a bit of 'cut and paste' and some elbow grease is okay once in a while! \$\endgroup\$ – vu2nan Jan 23 at 16:39
  • \$\begingroup\$ Thank you very much, that is an excellent solution... and it uses only 2 bridge rectifiers! What would be the best position por an emergency stop switch connected to an electrical cord a few meters long? Should it be connected to the input of the wireless relay to avoid driving the whole current through it or would it be better to connect it to the input/output of the rectifier? \$\endgroup\$ – Guillermo Oliver Jan 24 at 18:03
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At a first glance, i do not see any flyback diodes in your circuit. This, for sure, will cause problems. Currents that you did not expect them to be there.

Try to add them, and try again.

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  • \$\begingroup\$ A flyback diode is used to provide a path for the current flowing through an inductor when a circuit is opened e.g. by a switch. In this case the switch connects two closed circuits; when it commutes it does not leave the circuit open, but instead it connects the rotor and stator to a dynamic braking resistor R. I don't think this might be the issue here. \$\endgroup\$ – Guillermo Oliver Jan 21 at 7:37

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