Repair OVER SPEED Error on Generac 15 kW Generator

Note this is a follow up on the post linked below where we installed an external battery charger on this Generac generator. The Battery Tender we installed has been working well for over 4 years using the same battery that failed twice using the factory charger!

https://fettricks.blogspot.com/2015/06/substitue-battery-charger-for-generac.html

The most recent issue with the generator was a failure to complete its weekly self test. Upon inspection the OVER SPEED error light was on. You could still run the generator in Manual mode and it sounded like it was running normally.

My research indicated that, in addition to a genuine over-speed condition, this error can be caused when the sensor board doesn't have power so the sensor reading is not present, causing an erroneous Over Speed error. So I started looking for reasons that the sensor board might not be getting power. Let the sleuthing begin!

Danger Will Robinson! You should have a qualified generator service technician diagnose any issues with your generator. The voltage levels in the generator and associated switch gear are lethal. Forgetting to disconnect the power or touching the wrong spot at the wrong time can and will kill you. It is too easy to forget that you closed a breaker a few minutes ago. Really, have a technician do the work on your generator.

Safety first, this meant putting the generator in OFF mode and turning off the power to the house. Even then I pretend that every circuit is still live and avoid touching any conductors. Belt AND suspenders type of caution is the only way to go when dealing with electronics that can kill you!

When everything was off, I open up the generator's electrical panel and the transfer switch panel to look for obvious issues like disconnected wires, loose wire terminals and blown fuses. I got luck and found a blown fuse in the top of the transfer switch. There had been thunderstorms in the area shortly before the generator failed it's first weekly test. 

I ordered a pair of fuses, $7 each, and a $15 fuse puller/installer. The fuse were not cheap but I ordered two since there is at least a 50-50 chance that the fuse blew for a reason and the first replacement will blow again as soon as you power the unit back on. If that happens, then back to the diagnostics. I would start with again killing the power and checking the resistance between the fuse terminals and the chassis, looking for a frayed wire shorting against an edge somewhere.

Fuse on Amazon
Fuse Puller on Amazon

The fuses arrived quickly, thank you Amazon, and I repeated the process of turning the generator off and turning off power to the house. I then used the fuse puller to remove the old fuse and install the new one. To be honest, I also wore rubber gloves when working with the fuses. Never bet your life that a power circuit is actually off.

We reconnected the house power, set the exercise time and the generator ran fine. It has now been over a year since the fuse was replaced and the generator has not missed a weekly self-test. It has also automatically started several times during actual power outages. And we still have a spare fuse!

Preview

I am doing some early testing for a battery voltage monitoring system that I put together for this generator. Below is a graph showing the battery voltage during the generator's weekly exercise. Here you can see the battery voltage drop during starting, then the voltage begins to recover while the generator is running and then the battery is topped off by the Battery Tender before dropping back to the standby voltage. I can also configure the system to send me an email or SMS when the voltage drops below a specific voltage (generally this happens during starting so I am notified of start events). My goal is to be able to detect battery deterioration (and indicate that the battery needs to be replaced) before a failure to start occurs. It is also reassuring to see the battery charger topping off the battery following the weekly self test.