The charging system needs to be professionally tested. All "AC generators" develop three phase output which is very stable and efficient. They all use at least six "diodes" that convert that to DC voltage that can be stored in a battery. The symptom you're describing, the battery running down over a few days to a few weeks, is the common symptom when one of those six diodes has failed. When that happens, all you'll be able to get under a "full-load output current" test is very close to one third of what the generator is capable of. For your model, the standard generator is a 105-amp unit. If a diode has failed, the most it will be able to develop is 35 amps. That's not enough to run the entire electrical system and keep the battery charged. The battery has to make up the difference as it slowly runs down. To put some perspective to this, two low-beam headlights draw ten amps, not counting all the other running and tail lights. The electric fuel pump draws over five amps, and a heater fan can draw ten amps. That doesn't leave enough to run all of the computers and the rest of the electrical system, and recharge the battery after starting the engine.
Replacing the battery is not a solution. The cause of the problem must be addressed. For most models, it is not practical to replace a defective diode. They can be really difficult to remove, and they usually come as a block of three or of six. You're much better off with a professionally-rebuilt generator with a warranty.
You can start the testing yourself with an inexpensive digital voltmeter. If you aren't familiar with them, start by looking at this article:
https://www.2carpros.com/articles/how-to-use-a-voltmeter
The meter shown here has expensive features you don't need. You can find a nice one for $7.00 from Harbor Freight Tools. Also look at Walmart or any hardware store. I can help if you need it to set it up.
Measure the battery's voltage while the engine is running. It must be between 13.75 and 14.75 volts. It usually will be when there's a defective diode in the generator. Correct voltage only means it's okay to continue with the rest of the tests, but those require a professional load tester. You'll need to visit a shop for that.
Besides rechecking that charging voltage test, they will measure "full-load output current", (which should come close to 105 amps), and "ripple" voltage. My drawings below show what ripple voltage looks like. The top waveform shows all three phases of output current. Ripple voltage is 0.5 volts, shown in red. The battery is the main component that smooths that out, and here it is very easy to do.
When one phase is missing due to the bad diode, ripple voltage will look like the red line in the lower drawing. Here it's 5.2 volts. There are a few testers that can make paper printouts. Those actually measure ripple voltage as a voltage. The majority of testers do not provide the actual voltage. Instead, they show it as "low" or "high" depending how many of a group of lights are flashing or lit up. When ripple voltage is high, output current is going to be one third of expected. Those two tests take just a few seconds to perform, and point to the failed diode.
By the way, "diodes" are one-way valves for electrical current flow.
If you have these tests done, I'd be interested in knowing what they find. Some shops print the numbers right on the invoice. If they don't, they will have been written on the back of the repair order. Just ask to see them, then write them down.
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Saturday, January 6th, 2024 AT 8:02 PM
