Generator Starter Battery Charger Problems
My wife's parents have a 15kW Generac generator, model 0046753, that has a problem keeping the starting battery charged. After charging the battery the weekly auto-start would work for a month or two and then fail to start. The unit has been serviced and tested and the battery replaced without resolving the issue. I wanted to see if I could figure out how to fix the problem.
A quick Google search reveals that battery charger issues seem to be common with Generac generators (not to pick on Generac, this may be a common issue). I found a system schematic in the owner's manual and began studying the battery charger wiring.
Generac Generator page
Generac Owner's Manual
It appears there are two configurations, both using a dedicated battery charging module. One configuration receives power via a pair of contactors that selects power from either a transformer when utility power is available or a dedicated BATTERY CHARGE WINDING when the generator is running. The other configuration has the battery charger labeled (UTILITY) which appears to indicate that the charger runs only from utility power and not while the generator is running
Why would the generator not run the battery charger from the generator's output rather than adding a separate winding and a set of contactors? I found several posts that mention that the Generac battery charger does not charge while the generator is running, so utility only charging appears to be common.
Replacement battery charger modules are available at prices starting round $120. Below is a link and photo of a charger module similar to the one in generator I was working on.
Replacement Generac battery charger module
It is not my intent to cast stones at another engineer's design, but the module looks a little kludgy with the mix of internal and external parts, most encapsulated but several not. I do understand that the orange overcurrent protection devices must be able to expand to function properly.
Given the number of complaints I found online about Generac battery charging, I was reluctant to recommend another service call to replace the OEM charger module.
I suspect the core issue is that designing battery chargers is not Generac's primary focus so the battery charger was not seen as a high engineering priority. Perhaps a battery charger designed by people who are in the business of designing and selling battery chargers might be more reliable in keeping the generator starter battery topped off and ready to go.
Charger Options.
I wanted a charger with a few specific features:
- designed to be left connected to the battery
- waterproof for outdoor mounting
- can be powered by the generator
- good brand reputation
There are several chargers on the market designed for continuous charging of the battery during storage but the list narrows quickly once you focus on chargers that are designed for outdoor mounting. I ended up selecting the Battery Tender 800.
Battery Tender 800, $40 at Amazon
This unit is epoxy encapsulated with an IP67 rating (which means the unit is dust tight and can tolerate submersion in water to 1 meter). It is also highly rated on Amazon (most complaints were that warranty replacement requires $10 for processing and you pay shipping).
The ability to operate on 240 VAC was a plus simply because it let me use convenient screw terminals for power attachment in the generator. Using a 120 VAC powered unit would require a large ring terminal to fit the larger Neutral terminal. The Battery Tender 800 has two mounting holes and comes with mounting screws (not used here but handy if you want to mount it in a convenient spot near your motorcycle, boat, lawnmower, et cetera). And at this price you can replace it 3 times before reaching the price of the OEM charger module.
Battery Tender 800 Owner's Manual
Danger, Will Robinson!
There are so many dangerous parts to a generator that it is hard to know where to start with warnings. You can get burned, mangled or just plain dead. You should not work on your generator unless you are confident you know what you are doing. Bet your life on it confident. Even then, it's not a good idea. Have a generator service technician install the battery charger for you. If you are so foolish as to proceed, here is what I did.
Note that while I am an electrical engineer, I have little relevant experience with 240 VAC and generators and you should not think for a minute that I know what I am doing. I know that there must be a more elegant way to accomplish the task at hand. My overriding goal was not efficiency but rather not killing myself or blowing up something.
First I went through the house shutting down sensitive electronics like the PC and TV's since I was going to turn off the power. Then I went to the generator and turned off the generator's breaker. Then I used the transfer switch to disconnect the utility power (the generator and house were now without power). Then I removed the top panel from the generator electronics board and removed the front panel of the generator to provide access to the battery bay.
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240 VAC is available on terminals N1 and N1 near the bottom center of the photo. Note notch in top left of photo where I will route the power cable. The large terminal with the cable wrapped in white appears to be the NEUTRAL terminal. |
Then I checked the battery voltage with my multi-meter and install the battery charger on the battery using the ring terminals. I placed the charger on top of the battery positioned so I could see the status LED.
The 240 VAC input was available on screw terminals labeled N1 and N2. Next I cut the 120 VAC plug from the cord and crimped terminals on the wires. I could have used 120 VAC by connecting one terminal to N1 or N2 and the other to the NEUTRAL terminal (it looks like a large ring terminal would be needed). I could also have wired a short extension cord for 120 VAC and not removed the plug from the charger in case I needed to have it replaced under warranty. I will try that approach if I have to replace this charger.
Then I ran the power input lead to the back of the battery bay and through a vent at the left rear of bay. This brought the cable into the rightmost side of the engine bay where it can be routed up and into the back left corner of the electronics bay. There is a notch that allowed the electronics bay cover to be replaced without conflicting with the wire. Here is a blurry photo (how did I not see how blurry this was when I was taking the pictures).
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I ran the charger cable to the back of the battery bay and through a small vent to the engine compartment and then up through a notch in the sheet metal to reach the electronics control area. It's the lamp cord looking cable just beneath the hinge. |
I wanted to connect the battery charger power lead to terminals N1 and N2. First I carefully used my multi-meter and verified that there is no voltage on the terminals. Next I pretended the terminals still had lethal voltage levels and carefully placed one terminal at a time on the screw terminals (this meant two spade terminals on the terminal so I went slowly and made sure everything looked clean).
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Charger terminals installed on N1 and N2. |
Once the terminals were snug, I reversed the process, putting the cover back over the electronics bay (I kept the breaker off for the moment) and used the transfer switch to restore power to the house. Now I turned on the breaker on the generator and checked the status LED on the charger. The LED indicated the battery was being charged (yellow) but could have been green if the battery was already fully charged. I measured the battery voltage and verified that the voltage was increasing (if the LED indicates the battery is charging). Then I used the manual switch to start the generator.
The generator started without a problem. Finally I turned off the generator, placed the red safety cover back over the battery positive terminal and replaced the front panel on the generator. The charger has been working well for 6 months.
As of March, 2017, the generator battery charger has been working well for almost two years.
Update 1
The manufacturer has updated the design of the selected charger (for higher efficiency and 4-stage charging) and the input voltage range was reduced to 100 - 130 VAC. The new model has a red LED to indicate charging status and has a red and green battery icon to the left of the LED. The new models retain their awesome IP67 rating. Always verify the voltage range marked on the charger!
The reduced operating voltage range means you must simply have your electrician or generator service technician connect one terminal of the charger's power cable to EITHER N1 or N2 and the other to the large NEUTRAL terminal (bolt with the cable wrapped in white tape).
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New design with red LED and 100-130 VAC input voltage. |
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Older design with a yellow LED and yellow and green battery icon to the left of the LED and 100-240 VAC input voltage. |
Update 2
Following a thunderstorm, the generator failed the first weekly exercise with an OVER SPEED error on the control panel. The post below describes how I diagnosed and corrected the issue.