Adding Limit Switches and Ignition Lockout to My Custom Jack Controller

Nate
3 days ago
7 min read

Updated: 3 days ago

NOTE: I will be adding some additional pictures, once I get them, for clarity.

My modified GAMA motor controller installation worked great, however, I wasn't comfortable with the lack of safety lockout since the jacks would run with the ignition in the off position due to the controller being wired to the chassis battery. The jacks also "ratcheted" loudly at full retraction since the controller had no built in position detection. I thought it would also be nice to have a visual indication of jack position from the driver's seat so that I would know if the jacks are "safed" or not.

Solving the issue of ignition lockout was easy enough. A heavy duty relay on the power line to the jack controller, with the coils wired to ignition power, would easily solve that problem.

I noodled over the ratcheting issue for a while, and eventually I got inspiration from my experience with CNC and 3D printing. Some CNC machines and 3D printers use limit switches to "learn" where the 0 point is for the X ,Y, and Z axes, the controller on these machines can then fairly precisely measure exactly where the tool head is by counting the number of rotations and comparing it to the "Steps per <unit of measurement>" setting stored in it's firmware. I don't really need to measure the travel of the jacks, so I don't need all of that, but a limit switch would be a great way to cut the "Up" signal for a jack, just like taking your finger off the switch. The limit switch would only need to be finely adjusted to cut the signal before the jacks reach full retraction and make the awful sound that I am sure is not great for longevity.

With that problem solved, I considered the visual indicator. Since I was going to use a relay pack to switch the jack signals, powered via ignition power for safety, I figured I could use that same signal to switch LEDs on and off, via other relays. The relay packs I had settled on had both NC and NO contacts, and 4 relays per pack, so I could use one pack to switch two LEDs per jack, red to indicate "down" and green for "up". I also decided I would like to be able to power the whole system down from the control panel, so I would also add a switch that would cut ignition power to the whole system. Coming together great so far, now I had just had to mockup a PoC and make sure it would really work.

I began working on my 3D mockups of the limit switch brackets, as well as the control panel redesign, since I would need mounting holes for the LEDs and power switch. Pictured above is an early version so I could check fitment of all the components. I would also need a large bracket to hold the relay packs, and I figured I would stack them to save space and make wiring a little easier. I also settled on DIN rail terminal blocks to make wiring it all up much simpler.

Final design of the control panel. This time I designed it to print face down so i could print the cover in a material that would not string as badly as PETG.

Another view with DIN mount connectors and relay modules mocked up.

I iterated for a couple of weeks until I got to the final design above, and I decided to finally go ahead and do a full scale test.

Control panel and bracket with nutserts welded in.

Relay modules and DIN rail connectors mounted. This is the input side.

The output side. That's a lot of connections!

LEDs installed and more testing to finalize the wiring scheme and design.

Testing the relays with LEDs using one limit switch for the input signal on all four. Switch closed = jacks up = green light.

So far so good. I was starting to really get excited with how well the design was progressing. Limit switch brackets were next, and I printed up a low infill version and took it out to the RV to test fit.

Version 1 fit perfectly! Slip fit and held on with no screws. That's a first for me as v1 of anything never fits perfectly.

Final version. Had to shorten the mounting leg for the limit switch. Also added an additional mounting hole on each side.

Getting very close, I began ordering the hundreds of feet of cable I would need to wire the limit switches. I also grabbed some stainless mounting hardware for the limit switches. It was about here I realized I had forgotten to order the giant relay to switch the massive battery cable powering the motor controller. Each jack is rated at 20 amps, and they are protected by the GAMA controller which has adjustable internal circuit protection but came set as I needed. The original Atwood system could pull up to 85 amps with all 4 jacks running under load, so I figured a 100 amp continuous duty relay would work well.

With everything pulled together, I set out to pre-wire the control panel, and it's at that point, I realized I would have to reprint the relay module mounting bracket, as I did not leave enough space for the switch wiring. After having done that I set out wiring up the assembly to the point I could then install it in the RV. At the time, I must have been focused, because I have no in progress pics of the wiring.

The process was to first, wire up the panel switches, as in v1 of the control panel, with the "up" leg of each switch left loose so that it would complete through the NO side of one of the relay modules, and the down leg wired as before. I installed the LEDs but left the wires loose for now. Next, I glued on the bracket that holds the stacked relay modules, and wired the LEDs, with the red LED + to the NC and green LED + to NO contacts of the output of the lower relay module. I connected the GND of the output side of the lower relay to a common power block and grounded the relays to common ground. Then I wired the "up" lines for each jack to the NO and GND outputs of the top relay pack. I also wired up the input side of the relay modules to the common power and ground DIN rail connectors and wired in the power switch so that it cut the power to the common power DIN rail connector.

Left side of fully wired control panel showing the common power and ground DIN rail connectors.

With all of the pre-wiring done, I moved on to the installation. Not shown is installing the limit switches, but that was pretty straight forward. I installed the switches and brackets with the jacks up, and adjusted them so that each switch just barely "clicked", then tightened them down. I ran a 2-conductor cable to each jack, and connected them to the NC and GND terminals of the limit switches. On the other end of the cable, I routed to the front of the RV and used the existing hole for the control cables to the GAMA. I had to remove the existing control cable and open the hole up using a step drill, which meant using another, larger grommet. I also rewired the existing control cable, using a terminal block to terminate it where it comes into the dash from the controller, then making another cable to connect to the control panel. Next, I ran some 2-conductor cable to the electric bay where the controller lives for the main power relay, fed by the common power and ground at the control panel. I then connected the panel to ignition power using more 2-conductor cable. Wiring it in this way adds a measure of safety, since with the ignition off, the system is completely deenergized.

Right side showing the common limit switch power block (red) and the common LED power block (yellow)

I then installed the main power relay, attaching it to the existing adapter plate for the motor controller, and using a short piece of 4 AWG cable to match the factory wire gauge. I hooked up the relay power from the control panel to complete the final connection, then tested everything out. I should have gone immediately to buy a lottery ticket, because it all worked perfectly the first time!

Business end of power relay. Rated for continuous duty @12V 100A.

Barely fit existing board, but it did! Keeps it nice and tidy.

Another tight fit, but it's not going anywhere.

This is a simplified schematic of the wiring for one jack. It is logically correct and includes wiring for the core components. Not shown are common connectors, or all of the wiring for the switch pack.

The wiring was lot of work, and if I had to do it again, I might change a couple of things. For starters, I would probably make some wiring sub assemblies to reduce or avoid using the DIN rail connectors. They were fast, and they look cool in a picture, but I should have built up some wire harnesses with solder and heat shrink. This would be more "correct" I suppose, but I wanted some flexibility, in case I needed to rewire anything. I would also try to eliminate one of the relay modules by getting my LED signals from a different source, but using the relay module was a quick, easy way to achieve this.

Completed install. Looks pretty clean, almost factory.

Overall, I am very satisfied with the final product. It accomplished everything I wanted, I can now use my jacks without worrying about putting extra wear and tear on them, and I now have an overall safer and more functional system. For version 3, I might try my hand at some programming, as these relay modules are intended for integration with SBCs and having auto-leveling capability again would be pretty sick!

I hope I've inspired or helped you in some way, and if you have any questions, drop me a line in the comments. Happy to answer any questions.

Parts List (Sizes and lengths may vary based on your model of RV)

My Custom Jack Controller v1

1 x Control Panel Faceplate and Bracket

2 x 4 Channel 12V Relay Module

1 x 12mm Latching LED Push Button Switch

4 x 12V 3mm Pre Wired LED with Holder, Green

4 x 12V 3mm Pre Wired LED with Holder, Red

4 x Panel Mount Roller Plunger Micro Action Switch

4 x Limit Switch Mounting Bracket

1 x 250A 12V Continuous Duty Relay

4 AWG Battery Cable