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I am in the process of building a height-adjusting desk. I am pretty good with computers (I'm a programmer), but I never learned much in the way of electrical engineering.

I recently purchased two Eco-Worthy brand linear actuators. They each have an 18-inch stroke and a 320 lbs. static load bearing capability. They just have two wires, the positive and the negative wires. They are supposed to operated at 12 volts with a 1 amp minimum and 3 amp maximum.

I intend to operate them both at the same time in the same direction. So what I am unsure of is primarily the power source. My understanding is that I would still use a 12 volt power supply to power both at the same time.

But will I need it to have a 3 amp output or more than that? Will the amperage be reduced as it is divided among devices? Am I misunderstanding how this should work?

Also, if I get a momentary rocker switch will I wire both together and then to the switch? Should I get a relay to run this through? Any recommendations on how I hookup the A/C power to it? Since it won't have any plug inputs.

Here is a link to the info about the actuators I purchased. Any help in figuring out the electrical setup is welcome.

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You want to buy a switching power supply with a 12V output capable of at least 6A if you want to be able to operate both struts at the same time under full load. The amount of current drawn will depend on how much force is pushing against each strut. If you only need to operate one strut at once, then a 3A supply will probably do.

You could, in the simplest case, wire them directly in parallel. However, it is unlikely that they will move synchronously unless they are directly bolted together, e.g. if there's one at each end of the desk they may become misaligned and jam or break the desk. If one is under more load, it will move a little slower. So probably you want a separate switch for each strut so that they can be controlled individually.

You will also need some means of reversing the polarity in order to change the direction of travel. The usual means is a DPDT switch or relay; you can google up a schematic pretty easily.

If you buy switches rated for at least 3A (one strut) or 6A (both struts) then those switches can directly control the motor current. More likely is that you might buy smaller/cheaper switches which actuate the coils of large (10A) relays, which are responsible for enabling and reversing the power.

Edit: you might want to look into building your desk so that it has a single central strut to perform the lifting work, supported by stabilising arms/scissors/whatever at each side of the desk. That way, there are no alignment issues and no need to synchronise two struts. If your lifting geometry results in more than 150kg load on the single strut, you could probably put the two right next to each other and they would be mechanically synced and provide up to 300kg of support together.

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  • \$\begingroup\$ Ok, so I can go over the combined amperage just fine then. I do want both to move up and down at the same time (since this is for a desk). I was just going to put one on the left and one on the right. \$\endgroup\$ – Patrick Feb 2 '16 at 7:28
  • \$\begingroup\$ I will read more about the DPDT switches tomorrow. That looks interesting and promising. \$\endgroup\$ – Patrick Feb 2 '16 at 7:34
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Each device must meet specification; if you have 10 of these in parallel then you would need a 12V source capable of providing 3x10 Amps, or 30 Amps.

"Unit can be controlled with a double pole, double throw switch or with the built-in position sensor and optional linear actuator programmable controller."

It looks like you can control it with just a DPDT switch. Regarding the programmable controller inside, good luck getting the specifications to communicate with it as this isn't easy in my experience but you can contact the vendor and they should provide them to you. Some things to think about, are what happens when it gets to the end of its extension?

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  • \$\begingroup\$ The way I see it is if both get to the end of their extensions (they have automatic limiters built-in) then it will essentially synchronize their positions. Full top and full bottom should equally have this effect. \$\endgroup\$ – Patrick Feb 2 '16 at 18:32
  • \$\begingroup\$ Yes, they should resynchronize if you drive both of them to either end of their travel. The only issue is that if you make a number of adjustments without going all the way to the end, they will tend to get out of sync because there will inevitably be a small difference in their speeds. This might be due to differences in their internal friction or because you have something heavier on one side of the desk. It's not a disaster, but something I would find very annoying if I bought a product that behaved this way. \$\endgroup\$ – Entropivore Feb 3 '16 at 8:40
  • \$\begingroup\$ I guess an alternative would be to do something similar to bicycle shock systems. I could have a heavy duty support spring on one side providing a decent amount of lift while putting an actuator on the other side to provide the controlled lift and lowering. But I think it will be ok as is. They are identical. \$\endgroup\$ – Patrick Feb 3 '16 at 17:36
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[Character limit on comments is frustrating, so here's a full Answer.]

@RobertHana, I don't think there's a programmable controller inside. I think the optional controller they're referring to this: http://www.eco-worthy.com/catalog/worthy-single-axis-complete-electronics-tracker-controller-p-323.html As to what happens at the end of travel, they claim it has a built-in limit switch. Not clear exactly how this works given there's only two wires and you presumably reverse the polarity to reverse the direction. They could have a diode arrangement so that when the switch opens at one end of travel the motor stops, but reversing the polarity bypasses the switch and allows it to come off the stop. Dunno...

@WilliamBrodie-Tyrell, my first reaction was the same re the struts getting out of synch. FWIW, the adjustable desks at my office have one motor mounted in the center driving a shaft that runs across the back to the side pillars. This way only one motor is required and the struts are mechanically locked in sync.

The web page says:

Unit can be controlled with a double pole, double throw switch or with the built-in position sensor and optional linear actuator programmable controller.

(Emphasis added.) The odd thing is that I can't see anything in the pictures or the text that suggests the existence of a connection for a position sensor, or a description of how the sensor works. I doubt that it would have any sort of fancy absolute position encoder, but even a single pulse per revolution of the jack screw would be useful.

@pthurmond, is it possible that there are more than two wires in that cable, or is there any evidence of any other electrical connection on the device? I don't know what sort of programming you do, but if you wanted to get into embedded stuff, you could do a nice little project with an Arduino or something like that to look at the output of the position sensor and control the motors accordingly to keep the two in sync. That's assuming there really is some sort of position encoder, that is.

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  • \$\begingroup\$ I see no evidence of further wires or connections for these when I look at them. I am a web developer (mostly PHP and JavaScript). I know a smidgeon of Python. That may be the way to go for a physical controller. But given the two-wire setup I don't think it can be queried for the current position. So I don't think I need to be that complex with this. \$\endgroup\$ – Patrick Feb 2 '16 at 18:36
  • \$\begingroup\$ Also, given it will be attached to the desk won't they be a bit physically synchronized? \$\endgroup\$ – Patrick Feb 2 '16 at 18:36

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