Brushless Motor Circuit Protection SOLVED

I need a component or device that can protect a DC Brushless Motor from excessive on/off power cycling. My Product is a Battery Powered Sprayer which uses a Normally Closed Pressure Switch to shut it off when the Spray Handle is released (shut off). It comes back on when the Pressure is relieved by Squeezing (opening) the Spray Handle. The Pump Speed needs to be adjusted to match, or be less than, the output needed for the Spray Tip. If the Output flow is restricted to much, the Pressure Switch and thus the Pump Motor will oscillate (turn off and on) rapidly which eventually destroys the Pressure Switch and or the Motor Electronics. I would estimate it cycles on and off 30 to 50 times per second.

by mkurimski
June 18, 2019

What technology are you using?-- relays or electronics such as an Arduino sequencer or hard wired electronics. It's not hard to design a fix for this cycling but I would like to stay within your present design. As I see it while the handle is squeezed the pump runs but stops on overpressure which lowers the pressure so the pump restarts and so on and on as long as the handle is squeezed

by Foxx
June 18, 2019

Hard Wired. No Electronics outside the Brushless Pump Housing. You are correct on the basic operation.

by mkurimski
June 18, 2019

2 Answers

Answer by Foxx

Take a look at This shows a relay circuit to get the action you need. It requires 2 relays, coil voltage whatever you are using. One relay needs at least 1 normally closed contact and the other needs 1 normally closed and 1 normally open contact. The general idea is that you can squeeze the handle to run the pump but on overpressure the OPR relay picks up, seals around the pressure switch relay contact and stops the pump. The pressure will then fall but the OPR relay will not drop out until you release the handle. The auxiliary pressure switch relay is only to reverse the sense of the pressure switch contact and if the existing pressure switch has a normally open contact available it can be used in place of the relay. Hope this is some help

ACCEPTED +1 vote
by Foxx
June 19, 2019

Answer by mkurimski

The link on the previous answer takes me to a screen used to build circuits. It is blank. I understood your answer to indicate it would take me to a sample circuit with 2 relays.

+1 vote
by mkurimski
June 19, 2019

Sorry about that. It's worked for me in the past. If you could give me an email address I'll send it to you as an attachment. And in the meantime try panning around the workspace and enlarging it. I'll see what I can learn to get it to work.

by Foxx
June 20, 2019

I've redrawn the circuit using the circuitlab symbols, etc for the components and made it public and it's saved under URL Perhaps this will work. The circuitlab is a wonderful program normally but for relay circuits it's a disaster so I've added an image to give you something comprehensible. Let me know if this works and if not give me an email address.

by Foxx
June 20, 2019

This is not how my Sprayer works. Please send me an email to and I will send you a wiring diagram.

by mkurimski
June 20, 2019

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