Dynamic brake

[millman52]

I am using a small 12V linear actuator on a project I am working on. The actuator has quite a bit more drift than I want after releasing a momentary switch controlling the actuator.

The actuator needs to run in forward & reverse.

Does anyone have a diagram for a dynamic brake for this type of use? The actuator draws 3.4A Full load @ 12V DC

[gar]

071105-1700 EST USA

Is your actuator a brush type permanent magnet DC motor?

If so, then use a relay to switch power to the motor and when the relay is de-energized short the motor leads together.

You can do this with a SPDT relay switching one line to the motor. This is the broad concept. To do this the moving contact is connected to the motor wire. The fixed contact that is made when the relay is energized, normally open contact, goes to the power source. The other fixed contact goes to the other motor lead.

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[millman52]

The motor is Perm magnet brush type.

I'll have to sit down & draw it out to get my hillbilly mind wrapped around it. But off hand it I can see what you suggest working for 1 direction only. But when I think of it with reverse added. It seems to me there would be a short circuit.

Again I haven't drawn a diagram to paper. I may very well be wrong.

[Al_The_Man]

If you are using a two relays or contactors for reversing the relay that Gar suggests goes between the reverser and the motor, the motor is disconnected from the reverser when braked.
The advantage on this method is that it is active after the power is removed and reduces back-feeding etc.
Try shorting the motor terminals together and turn the actuator or motor shaft if possible, you will see the effect.
Al.

[gar]

071105-2041 EST USA

millman52:

For changing direction you use a DPDT relay (double pole double throw). In one state this makes the polarity + - to the motor, and the other - +. I think I would put the reversing relay closest to the motor, and the on-off and braking relay before the reversing relay. You might also make the on-off relay a DPDT and switch both sides of the power from your DC source.

I do not put pictures or drawings on may posts because they have to be somewhere other than at this site. Therefore, they are not very permanent. A few I want for my purposes I put on my web site which is reasonably permanent. Sometimes some are useful here.

Try to draw the circuits I have described. The reversing relay wiring is an assignment for you to figure out on your own. The reversing relay is only a two state device so you can not use it to stop the motor.

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[Al_The_Man]

If you are using relays to reverse the actuator, you can also wire it using just two 3 pole relays, each would have two normally open to reverse the direction and a NC contact on each wired in series with each other connected across the armature will give you the dynamic braking.
Al.