0
\$\begingroup\$

Sorry for the dumb question, but I only know enough to get myself in trouble.. I've searched through previous questions and haven't found an answer that dumbs it down enough for me.

I'm trying to activate a 12vDC 12amp linear actuator (https://www.progressiveautomations.com/linear-actuator-ip66#ig_lightbox2[gal]/0/) to travel in/out using 2 solid state relays. (https://www.automationdirect.com/adc/Shopping/Catalog/Relays_-z-_Timers/Solid_State_Relays/Panel_Mount_Relays,_Hockey_Puck_Style,10A_-75A(AD-SSR6_Series)/AD-SSR6M12-DC-200D)

Ultimately an Arduino will control the relays, but for now I'm manually activating them with a 9v transformer for testing purposes. Currently it works fine with 1 relay attached, but when I attach the 2nd it short circuits. I believe the issue is my ground connecting to both leads on the linear actuator, but I'm not certain on how to rewire. Do I need a relay for both positive and negative leads? (4 total)enter image description here

Revised for changeover relay and diodes:enter image description here

\$\endgroup\$
  • 3
    \$\begingroup\$ Uh, no. What you have drawn shows both relays as short circuits directly across the power supply. \$\endgroup\$ – Brian Drummond Jan 4 '18 at 16:47
  • \$\begingroup\$ What does the power supply give you? Does it have +-12V? If not you may need four of those relays. \$\endgroup\$ – Trevor_G Jan 4 '18 at 16:50
  • \$\begingroup\$ Sorry. Yes the power supply is 12vDC. \$\endgroup\$ – Brittio Jan 4 '18 at 16:56
  • \$\begingroup\$ What are you trying to do with the actuator? Is it something like a simple door open/close or are you trying to set it to any arbitrary position and stop? \$\endgroup\$ – Finbarr Jan 4 '18 at 16:56
  • \$\begingroup\$ @Finbarr exactly right. It will be full open or full close. The actuator has a built in limit switch, and I intend to basically go either direction until it stops. \$\endgroup\$ – Brittio Jan 4 '18 at 16:58
2
\$\begingroup\$

With a simple switch type SSR you need to have a bipolar supply to use two of them.

schematic

simulate this circuit – Schematic created using CircuitLab

If you only have a single supply, you can use four of them in a full-bridge.

schematic

simulate this circuit

In both cases care must be taken not to turn on both sides at the same time.

Note: I also showed you how to add diodes to protect the SSRs from the switching spikes that may occur then the switches open. This may already be covered internally to the relays, but extra does not hurt.

You can also drive the actuator with a single, more traditional, mechanical change-over relay.

schematic

simulate this circuit

\$\endgroup\$
  • \$\begingroup\$ I would like to accomplish this in the most space saving manner possible. I assume the mechanical changeover relay would do that. But I'm confused by your diagram. (I'm a total rookie) The relay will connect directly to the actuator, but the diodes are beyond me. I'll try to mock up a drawing to see if my understanding is close. How do you determine the required diode size? \$\endgroup\$ – Brittio Jan 4 '18 at 17:38
  • \$\begingroup\$ Does my revised diagram above seem correct? \$\endgroup\$ – Brittio Jan 4 '18 at 18:02
  • \$\begingroup\$ @Brittio I really cant make the diagrams much clearer and your sketch is pretty meaningless other than the basics. IN the last schematic, both switches move together, to connect the motor one way or the other way to the 12V. It relies on the limit switches in the actuator to actually turn on the motor. The diodes just make the relay last a lot longer. \$\endgroup\$ – Trevor_G Jan 4 '18 at 18:39
  • \$\begingroup\$ Sorry for not being clear. The diodes in your diagram confuse me. I think I've drawn them the way your diagram specifies, but I'm still not sure how to determine the required diode size. The actuator is 12vDC w/ a max of 12amp. Do I look for a diode w/ 12v forward voltage and 12 amp forward current? \$\endgroup\$ – Brittio Jan 4 '18 at 19:15
  • \$\begingroup\$ @Brittio diode needs to withstand 12+ amps for a brief period so needs to have a peak forward surge current more than that. And also need to withstand greater that 12V reverse voltage. 1n4001s might do but may be a little light on the peak I. \$\endgroup\$ – Trevor_G Jan 4 '18 at 19:25
0
\$\begingroup\$

Your "Out" relay will short the power supply when activated.

I assume you need to reverse the polarity to change motor directions. To do that, you will need two relays for each direction, as you need to switch both motor leads.

schematic

simulate this circuit – Schematic created using CircuitLab

If I've drawn that correctly, pressing the "ON" button will connect the positive terminal of the power supply to the top terminal of the motor, and the negative to the bottom.

Pressing the "OUT" button will connect positive to bottom and negative to top.

The double-throw switch I show for the "IN" button will ensure that pressing both buttons will not cause a short across the supply as the "OUT" button will not get power unless the "IN" button is released.

With mechanical relays you could use two DPST or DPDT relays, one replacing RLY1 and RLY2, the other for RLY3 and RLY4, but I haven't seen double-pole solid state relays...

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.