Autostart House Generator




This information is provided as informational only. Your setup and requirements will most likely be different and you most likely will not be able to just copy exactly what I did. Don't be a fool and wire up something illegally as that may kill someone or burn down your house. Follow all electrical code or better yet hire someone who will.

So you are like me and can't afford the latest Generac or Oran whole house generator or just don't think it is worth the money so you went out and purchased a fairly cheap generator like mine the Harbor Freight Predator. These generators are commonly referred to as a chonda (Chinese Honda). They often can take replacement parts directly from Honda depending on how well they were made. You then was smart and purchased a proper generator transfer station. Like me you could not justify $500+ auto transfer and purchased for less than $200 a manual transfer like the one in the picture.

This was a great start. When the power would go out someone would then have to go outside, turn on the gas, enable the choke to full, press the button to start, wait a few seconds, place choke to half choke, go inside and walk in the basement, flip the circuit so those circuits are now on generator power, go back outside and open the choke to full open. Then once the power is back on go back to the basement, flip the circuit back, wait 5 minutes so the generator can cool down, go outside and shutdown the generator, turn off the gas, and close it all back up.

Wouldn't it be nice that there was some way to have something auto detect the line power go out and auto start the generator. Maybe also have the generator auto start on a monthly basis to make sure everything is working as expected.

Hello Arduino. So why are you here because someone else had to have had this idea before right? Well they have but it seems no one is willing to properly document what they used, how they set it up, or really provide any useful information. There are a few out there that also used stuff they had laying around. Yay but not what I want. I wanted something to setup that would work with my requirements and all I had to do is buy and wire up. I don't have an electrical engineer degree and did not want to get that involved in the setup. I wanted to buy stuff and just hook it up.

Here is what I did...

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Requirements

* Have a generator autostart if power loss is detected

* Have an existing electric start generator like a Harbor Freight Predator 8750 known by many as a typical chonda (chinese Honda knockoff)

* Expecting to be able to still manually start the generator along with automatically by tapping into existing generator wiring system, not a complete rewire the generator ignition.

* We have a manual transfer swtich/box that the generator is hooked into. This creates the need for a safe guard in it to require a button to be pushed by a human to indicate someone is home and flipped the switch transfer box to generator power and back.

* Also when power comes back on it will wait 5 minutes after button push before it turns off the generator. The 5 minutes is to provide a cool down session for the generator along with validate the pole power is stable as often we see during power outages a few flickers of power or be back on and then a minute later go right back off.

* Have a LED which when off it indicates the house is on pole power.

* We want to test start the generator once a month and let it run the 30 mintues. This will keep the start battery fully conditioned and fresh fuel flowing through the carb along test the start.

* There is also an enclosure my generator is in so if the temp reaches 90F or higher and generator is running to turn on the vent fan.

* We are using relays and sensors purchased from Amazon. I want to keep things as simple.

Step 2: What to Buy

* Uno/Nano (I have a nano but it is the same as Uno but with a few extra pins)

* 4 relay module

* LC Technologies AC voltage sensor

* Waterproof 20kg servo to control choke

* 12v solonoid valve for gas on/off

* button

* hall sensor 3 wire NO

* 1" LCD SPI display

* DS3231 Real Time Clock

* x2 TMP36 temperature sensors

* green LED to indicate generator is running

* red LED to indicate if safe to stop generator

* yellow LED to indicate gas on

* blue LED to indicate ignition on

* white LED to indicate Starter on

* 2 watertight boxes to house the electronics

IMPORTANT INFO: The 4 way relay I got has NormOpen side be actually HIGH and to enable set to LOW. This way if the board or a wire becomes disconnected then you dont have relays enabled and burning out say your starter. This also saves wear on your relay module since you dont need to energize your relays to open the circuit. So set to HIGH to disengage relay (no power) and LOW to engage relay (with power).

Step 3: The Plan

Don't let the diagrams scare you. It is fairly straight forward. Label everything so you can track what connects to what. I used 50' of 18-5 solid wire normally used for thermostats. I cut it in half as my generator needed 25' of wiring between the inside panel and the generator panel. I combined that with two 16 gauge wires (one red and one brown) to support the power going to the generator box. Then placed that in conduit to protect the wire.

The faint diagram is what I got from Harbor Freight by calling their customer service. This is the wiring for my generator. It may work for you but I do recommend contacting your generators manufacturers customer service for that models wiring diagram.

For the hall sensor I drilled a hole where the plastic fan is for the engine that is between the pull start and the flywheel. I picked up some good plastic epoxy that is good for nearly all materials. That was used to glue the magnet to the plastic fan.

I ran all the wiring on the generator into its electrical box. I also used grommets to protect the wires and give it some weather protection. The boxes are not 100% weather tight to allow for pressure changes and things to breath a bit. All wires go out the bottom while the fronts do have seals to prevent leakage into them. So if the lid of the enclosure is open for some reason and it is raining I don't worry about water.

I made a bracket for the choke servo and used 2 sheetmetal screws to hold it in place. It connects to the choke via a stiff bent wire. That wire has a bend to allow it to go around the gas line. It needed to be stiff enough to not flex but not so large that I could not connect to either the choke or the servo.

The gas line has a metal t that is connected right at bottom of the tank. One side heads to the manual gas valve and the other goes to the electric solenoid. This way auto and manual starts can still happen. Then they come back together at the hose going to the carb with a plastic t.

Step 4: Closing

You will see on my transfer switch I have two little glowing boxes. Those are a little thing I bought on amazon that shows the AC volts and frequency. This allows me to see what voltage and what the frequency is for the power. There are two due to the power is 2 phase so one for each. This helps me identify if there is any possible generator problem like high or low idle or any adjustments needed for it.

I have my generator in a big plastic box normally used for lawn furniture or near a pool. It was the right size for the generator. I extended the exhaust with copper pipe and a metal coupler as a collar to protect the pipe from melting the plastic as it goes through. There is also 2 vents lower (you see the one in the front in the picture) to allow fresh air in and the bathroom fan is the vent out.

Please feel free to provide updates or improvements you made from my setup and documentation.

Be the First to Share


    • Made with Math Contest

      Made with Math Contest
    • Multi-Discipline Contest

      Multi-Discipline Contest
    • Robotics Contest

      Robotics Contest

    6 Discussions


    2 months ago

    I'm getting a lot of error messages in the ino when I attempt to verify in Arduino IDE.


    4 months ago

    Would you be able to send more pictures, i.e. location of 2nd temperature sensor, internal layout of water resistant boxes, etc.


    10 months ago

    Schematic diagram has a low resolution and it is impossible to check the connection and names of components.

    1 reply

    Reply 10 months ago

    The schematic diagram was not one I created but as I said that is what they sent me. I just looked at the diagram on here and that is the quality they gave. I had to zoom in and out a lot trying to make a beat guess of what was what and it worked for me. Maybe reach out to your generator maker and see if they will send you one for your generator and hopefully in higher quality than the one I received.