Directional actuator control circuit

[Tom.G]

The recent posts by @Averagesupernova and @jrmichler are spot on.

I think one of the reasons this thread has gotten so tangled is we here at PF try to follow thru on the original intent of the OP. i.e. we avoid trying to re-engineer everything to our individual ways of thinking.

I contend that generally this is a good approach in that we can teach and lead the OP based on their current understanding.

For instance the particular pushbuttons that the OP specified have the advantage that they indicate the last known position of the load; UP Arrow or DOWN Arrow. Perhaps this is useful, or even vital, in the particular application, we don't know that yet.

Cheers,
Tom

 

[Averagesupernova]

I do have a question about the limit switches. If this is a two wire motor, how do the limit switches tie in? Usually limit switches in a linear actuator have to tie into the main switch because while one limit switch stops the motor in one direction, the motor has to be allowed to travel in the other direction while the first limit switch is open. Pretty sure linear actuators with built in limit switches require more than a pair of wires coming out unless they are using some pretty heavy duty internal diodes to accomplish the reversal. So, what gives?

 

[Rayhaan]

I do have a question about the limit switches. If this is a two wire motor, how do the limit switches tie in? Usually limit switches in a linear actuator have to tie into the main switch because while one limit switch stops the motor in one direction, the motor has to be allowed to travel in the other direction while the first limit switch is open. Pretty sure linear actuators with built in limit switches require more than a pair of wires coming out unless they are using some pretty heavy duty internal diodes to accomplish the reversal. So, what gives?

I really don't know.. I contacted the manufacturer whose told me the motor has 2 leads. The actuator specifies that it has limit switches built in. I agree on the potential simplicity of this entire thing. Thanks for pointing it out. Just want to understand how it could all tie in.. it's more for my own understanding then practical application. I didn't even know what relays were a week ago so this monster thread was great for me to learn. Thanks everyone

 

[Rayhaan]

So in my thread subject and initial post I did mention that I could change my component specs to suit myself. If I instead used a 24vdc actuator which can draw 8a (as opposed to 12vdc 16a max load) would this circuit be any safer? Would short circuit arcs still be a potential problem?

I have no intention of using latching buttons.. I see quite a few comments were made about that. Sorry if I mistakenly mentioned them?

 

[pbuk]

I do have a question about the limit switches. If this is a two wire motor, how do the limit switches tie in? Usually limit switches in a linear actuator have to tie into the main switch because while one limit switch stops the motor in one direction, the motor has to be allowed to travel in the other direction while the first limit switch is open. Pretty sure linear actuators with built in limit switches require more than a pair of wires coming out unless they are using some pretty heavy duty internal diodes to accomplish the reversal. So, what gives?

Linear actuators with built in limit switches have internal diodes; they only carry current for a short period until the switch closes. This is the default configuration provided by most suppliers.

Some applications require external limit switching which is often available as an option; the outputs from the limit switches are generally provided on 2 wires plus a common.

Schematics for linear actuators are available on the internet from many suppliers, it is easy to look these things up rather than guessing.

 

[Rayhaan]

I'll email the manufacturer and tell you guys what's the set up with this one. If the actuator does have an in built surge flyback mechanism due to limit switches with diodes built in would that mean that I don't need to protect the circuit from this anymore?

 

[Averagesupernova]

The diodes in the linear actuator are there for current steering to be able to reverse the motor when one limit switch had been opened. They do nothing for suppression of the flyback pulse.
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I don't really know what you have to protect anyway. If you simply use a rocker switch or pair of individual switches, it's unlikely any damage will occur.

 

[Rayhaan]

Thanks for clearing that up

 

[kinsler33]

I never saw a good description of the actual application. For example, it sounds like it handles a considerable load, and must have some safety features and perhaps a remote control. But I don't recall reading how large it might be. If we're working on the order of 1 meter or more and, say, a 100kg load, the first thing that comes to mind would be a garage-door opener. They've solved most of the problems that were posed here.