You guys may have guessed when we’re not building the Island shack we work on our goat farm in Central Texas. Coming back from our latest trip we found that our automatic gate opener wasn’t working. For you City Slickers, gate openers are a very sticky subject with farmers. There are only two or three companies that make them (at least ones that are readily available) and due to litigation over the years what should be a very simple device has evolved into a computer driven monster. One kid gets stuck in a gate and everyone suffers. So most of them have at least two different ways to prevent that from happening. Unfortunately the gate opener doesn’t know if it’s tall grass or a toddler’s head causing the resistance to movement so this causes endless problems. Also, the companies are very proprietary with their technology, makes it hard to add extra features you may want. For example I would like to be able to have Alexa open and close the gate, but adding that requires buying a $100 add on. So after troubleshooting for half a day I determined the motherboard on the gate opener was dead.
The guys at the Mighty Mule gate opener company were very helpful while troubleshooting. Then they told me a new motherboard was almost $400! A entire new unit at Tractor Supply is only a little more. So being retired I googled it and found a like minded guy who had solved the problem. His name is “SOATMON” (Student of all trades, master of none) and here’s his video. https://www.youtube.com/watch?v=_x0FUXZ8c8c His design worked which is what I was looking for. He used common car relays to do it.
So I went on an amazon shopping spree: These are the control relays you need 4: https://www.amazon.com/gp/product/B07L1L3RJT/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=soatmon-20&creative=9325&linkCode=as2&creativeASIN=B07L1L3RJT&linkId=8ce2f41b6639f807fc096cb1331765fd
These are the Power relays, you need 2: https://www.amazon.com/dp/B017VDI0GY?ref=ppx_yo2ov_dt_b_product_details&th=1
This is the Reversing relay, you need one: https://www.amazon.com/dp/B07F4JLQWN?psc=1&ref=ppx_yo2ov_dt_b_product_details
These are the diodes, you need 4: https://www.amazon.com/dp/B015YSU24G?psc=1&ref=ppx_yo2ov_dt_b_product_details
These are the diode/fuse holders, you need 6: https://www.amazon.com/dp/B07CK784LZ?psc=1&ref=ppx_yo2ov_dt_b_product_details
This is the access keypad, you need one: https://www.amazon.com/dp/B07RHRN1RG?psc=1&ref=ppx_yo2ov_dt_b_product_details
This is the limit switch, you need 2: https://www.amazon.com/dp/B073SP7SXS?psc=1&ref=ppx_yo2ov_dt_b_product_details
Here’s the keyfob remote I used. This one is discontinued but others are available. You need at least 3 channels on whichever one you find: https://www.amazon.com/gp/product/B01CCSG2ZY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
So with all the parts in front of me I started building. And immediately got stumped. I was running off of SOATMON’s diagram: https://drive.google.com/file/d/1Lc0zXopGWAWHGYL93wHNG8q5_vyvdDZ8/view I’m a retired pilot so very familiar with electrical circuits and such. His was confusing to me for some reason so I decided to build my own. I needed to keep the same goals he had but wanted to modify it so I could figure it out. At the time I thought I could save a relay or two but ended up using one more than he did. The main points are that since the actuator motor is wired to both the forward and reverse circuits at the same time you don’t want to have them ever sending power to the motor simultaneously. I also wanted to be able to stop the gate in transit with the remote. And like his design, if the keypad is used to operate the gate mine has to continue fully to the open or closed position before it will stop. Not optimum, but just about the only way to do it.
The main thing I did different than SOATMON was to divide the relay system into low current and high current busses. I have a 10 amp fuse on the low current relays, and a 30 amp fuse on the high current relays. I put a 25 amp fuse right on the battery. So if the motor stalls the first one to go is the one at the battery which is easy to access. I also put on/off switches on each buss. This lets me troubleshoot without activating anything that moves.
Like SOATMON mine is all mechanical switches and relays with no microprocessors except for the keypad and key fob assemblies. And also like his there is no safety device other than the fuses which prevent the gate from closing on an obstacle.
Like SOATMON I tried to recycle the Mighty Mule control box to house my system. I wish I had just bought a much bigger box to put the whole thing in. As it was, I ended up putting the low current part in the original box but then had to put the rest in a water bucket (something UV resistant will work).
A confusing part was figuring out how the relays work. Once I figured that out I ended up doing this for the control circuit. This is a general diagram of how it works, not where the wires actually go. I’ll put detailed diagrams of how to wire relays later:
The way the 2 control relays are wired prevents them from passing power to the high current relays if they are activated at the same time. In this case, both relays will be “activated” but due to the way they are wired they will not activate the high current relays. That’s where the “cross power” arrows between the control relays comes in. The stop relay kills all power to both control relays. The keypad power relay is necessary if you end up with a positive ground (vs standard US negative ground) keypad from our Chinese friends like I did. When you push the open or close buttons on your key fob, the appropriate relay will activate. The diode prevents the activation signal (which is short) from “leaking” out and keeps the relay on long enough for the relay coil to be powered by the stop relay input. Otherwise you would have to hold the key fob button down through the entire gate transit. The relay will remain on till the gate hits the limit switch on the diode circuit and opens it. At that point all power is killed to the control relays. Since the keypad input is not “open or closed” but only one signal it goes to both relays at the same time. However, if the gate is fully open or closed the appropriate limit switch is closed which enables that relay to power up while the other one is disabled by the open limit switch and does not activate. If the gate is between open and closed then both control relays activate but no movement occurs due to the “cross power” way the relays are wired. One bad thing is that though the gate doesn’t move both relays are stuck “on” and to reset you have to use the key fob to move the gate to fully open or closed before it will run normally again. Also, while the gate is stuck those relays are on and draining power from the battery so eventually it will flatten the battery if not fixed.
The high current buss is a lot easier to wire. Instead of buying the $30 fwd/reverse relay you can also make one with 2 SPDT Bosch relays and some diodes but by the time I got to this point I pushed the easy button and bought a ready made one. This one is a very well made unit with epoxy potting. Directions weren’t really clear but it has 3 studs on each side. One side of three (all 1/4 inch studs) studs is where you connect the ground and the two motor leads. On the other side 2 studs are smaller and one larger. The larger one is +12v from the bus, the other 2 take the +12v output from your power relays. Check the polarity when bench testing to make sure motor is running the correct way. You may have to swap the leads to get it right.
This is how to wire the control and stop relays. I need to mention it’s a lot easier to wire all this stuff if you have a nice busbar to attach the power and ground wires to. I had a small one was frequently cursing it. There are probably 10-15 different connections to this busbar when you are done. The control relays are wired so that even though both relays may be “active” at the same time the power will not reach the high current relays. Another mention is that the biggest possible problem is that a limit switch may stick closed which will result in the motor grinding away until a fuse blows. You could put an additional limit switch in series with the single one I have to prevent that. If it becomes a problem later I will put one in myself. Also, remember the limit switches should be wired so that they are open when pushed against, the limit switch I used can be wired either way so check how yours works.
I ended up spending $30 on a keypad system that wouldn’t work for this application until I found the one that does work. One important feature is the ability to change the duration of the “signal” the unit puts out. As the gate moves off the limit switch in reaction to the keypad signal the limit switch that was open will close after a second or two. If the keypad is still putting out the “signal” at that time the other control relay will activate and the gate will stop moving and become stuck between the limit switches. So the signal needs to be long enough to activate the control relay and for the stop relay to start providing its power, but not long enough to still be on when the limit switch closes as the gate moves. In my case .2 seconds was not long enough to activate the relay. 1 second worked fine, 2 seconds was too long. Depending on how you physically set up your limit switches and brackets you may find that the limit switch closes too quickly to even operate the relays. In my case my gate opens fine, but will not close until I physically hold the appropriate limit switch long enough for the gate to start moving closed. I’m working on a cam system that should fix this, another way would be to use springs. I would suggest if possible to put the “closed” limit switch on the other side of the gate. This involves digging and running cable across the driveway, but is more reliable than mounting both switches on the hinge side post of the like I did.
The keypad system I used was a positive ground. If you put positive voltage across any of the relay contacts on this unit the entire unit would shut down. It works fine when on the negative side of the circuit. I needed +12v for the signal and my entire system is a negative ground so I ended up using another relay to provide the signal. If you have a unit that is negative ground you can skip that relay. If you use the same keypad I used suggest you get a battery or DC power supply to run it inside the comfort of your house while you program it. A lot easier than standing in the hot sun typing in a bunch of numbers. Check out my Amazon review of the unit for helpful tips that will save you the 2 hours I spent learning how to program it.
I haven’t added Alexa to the mix yet but shouldn’t be hard. If you have wifi available then any of the Alexa enabled switches on Amazon could be used to run it provided that you can change the signal duration. You would need to have a camera covering the gate like I do to make sure the gate ends up in the position you desire.
Hopefully this thing will be almost maintenance free. If you fuse it properly then maybe occasionally you will have to change a sticky relay which shouldn’t be hard since they plug into sockets.
Finally, remember this design has no safety features at all. Use it at your own risk. I’m comfortable using it on our farm since usually we will be the ones operating it. If you need one that multiple people will be using then I would suggest going back to the Mighty Mule control board.