Onan Generator Prime Circuit
Here is a little circuit I came up with a number of years ago to help you with waking up that old "Troll" Onan generator. Read through this then download the instruction sheet at the bottom of the page. Of course if you want to be a "real Man", toss out the verbiage and go to the pictures-- go for it!
The old Onan generator can use any help you can give it to start and run and if, for some reason, it will not start you want to have another option than to stand there and talk to the remote panel, rub it and hope the generator gods will have pitty on you. So, here is your option:
This generator primer circuit is a very simple circuit using only a 5 amp fuse and holder and a momentary push button switch all of which can be had at Radio Shack. It is a fail safe circuit in that if something does happen, the 5 amp fuse will blow making the circuit open and safe.
Here is the theory: Sometimes its necessary to hold the "start button" in for some time when waking up the Onan generator. The problem is 2 fold first, the float bowl of the carb will empty out over time and the electric pump will need to regain its prime , suck fuel from the tank and fill the carb. bowl before the generator will start. The other issue is very simple, if most of the current feeding the generator is going to turn over the starter, the ignition system is starved for juice and cannot give out a good hot spark needed to start up the unit. The electric fuel pump only runs when the ignition is powered up which is when the start button is pushed. If the generator will not start, you can "hot wire" it by jumping power from the positive lead on the battery to the pos. side of the coil. This will energize the electric fuel pump and power up the ignition circuit. If the pump picks up fuel, the spark is good and the starter will spin up, the generator will start. Thats all well & good but how does that help me?
Here you go, the "run" light on the remote panel gets power from the ignition circuit of the generator. It is tied directly to the pos. terminal of the coil. Now, if you send 12 volts back to the coil from the light, the coil will be hot and the fuel pump will pump. Great, pull power from the systems monitor panel next to the remote panel, send it down the power wire for the light to the coil. This will power the fuel pump -- thus you will be pumping fuel to the carb. before you try & crank the unit--- awesome! Now, this will allow you to "prime" the carb. of the generator getting the needed fuel to it before you try and start tthe unit up at the same time you will be feeding the ignition current from another source than the power sucking starter cable. This will give the coil a hotter spark that will greatly aid in the start up on the generator.
How does it work?
Before you swallow deep and try the start button, hold in the prime button say 20-30 sec., this will give the pump time to pick up fuel and throw it at the carb. Now, with the button held in, hit the start button and the generator should wake up right away-- it will have fuel and a hot spark. If you push the prime button but the run light does not come on, check to see if the systems monitor is working, if not you may have a bad fuse in the original 12 volt fuse panel. If it does work, pull the generator remote down and check the 5 a. fuse you installed in the prime circuit.
VERY IMPORTANT WARNING: DO NOT hold in this prime switch and push the "stop" side of the remote generator switch, that will at least blow the 5 amp fuse and at worse could damage the generator PC board. Hey, nothing is perfect or foolproof and this is the situation you must avoid. OK, enough said, you have been warned!
Its just that simple and that helpful. Now,
here is the diagram to follow to install this little gadget for your
own. If you have any problems, feel free to give me a
call. 