Why is the motor not turning off and delaying? T4071207

Hi @DigiKey_Internal,

Anyone have any suggestion as to why the motor has a delay and the switch doesn’t instantaneously turn the motor completely on and off?

Sensor - 59630-1-T-03-A (DK # F7185-ND)
Relay - 1432793-1 (DK # PB1773-ND)

Schematic:

motor

Video:

Have them measure the voltage on the relay coil when activation occurs. It could be the high inrush to the relay coil is pulling down the power supply voltage of 12V momentarily. Might need a charge cap to take
the sudden inrush current needs of the relay coil.

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There could be several reasons why it is still experiencing a bit of power leakage and delay. If the magnet is too close to the reed switch it could be attempting to close the switch but not all the way, second thing is what is the required voltage for the relays to turn on and off? If it is in that in-between region, they may see the motor still getting power.

As for delay, that is a curious behavior. Is the motor just taking DC voltage? It seems like it is. Is there a control module underneath the rotor (what is that block part)? From what I know, some DC motors aren’t instantaneous, but it certainly shouldn’t take that long (so there may be continuity problems in the rest of the circuit).

It would be great to see the connections a bit clearer.
A few questions:

  1. what is the black object with red and black wires going to it?
  2. the resistor is not in the Scheme-it drawing. Is anything else missing?
  3. It looks like all of terminals of the relay have connections to them in the video but not in the Scheme-it drawing. The video moves past it rather quickly and the wires kind of run together from that angle.
  4. if he could add a volt meter on the motor/pump connection to show what it is getting, that would help.

I think there’s a pretty good chance it is wired incorrectly. This relay has a diode wired in parallel with the coil. If one wired it backwards (putting the output of the reed switch to contact 85 rather than 86), it would likely behave as yours does.

When the reed switch is not activated, the motor operates normally (connected to the normally closed contact 87a) seeing 12V. However, when the reed switch is closed, current would bypass the coil and flow through the diode, nearly shorting out the power supply. The relay would not switch, but the voltage passed to the motor would drop down to the forward voltage drop of the diode, less than 2V probably. Eventually, I would expect that the diode would burn out, as well as the reed switch from the high current passing through both the reed switch and the diode.

Here’s where current would flow if the polarity were reversed on the coil, applying the + voltage to contact 85 rather than 86:
image

The relay would not switch, but the power supply would be shorted to just a diode drop above ground. This would cause the motor to slow, but not necessarily stop.

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