By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
This question was asked by Matthew E. on our Facebook group RV Advice.
“I need some help deciding if my power inverter is dying. Twice now, while plugged into power, when I try to use a 12v device like the slideouts or leveling jacks the lights dim and fluctuate. It happened the first time when I was closing it up and the last time right after I plugged it in and was setting up. The last time it only lasted a few minutes and then never had a problem the rest of the weekend. Can I test the power inverter? It’s a 2012 Keystone Avalanche 5th wheel. Had it for about 5 years or so. My thought was the battery being bad but I don’t see why that would matter while being hooked to power. Any advice?” —Matthew E.
This is really a 2-step diagnostic procedure.
Step 1: You have to make sure your batteries are healthy, so you should go to a battery shop or even an auto parts store to use something called a Carbon Pile Tester to put a large load on your batteries (hundreds of amperes of current) for 30 seconds or so to determine if they are still healthy. This is done after the batteries are fully charged with an external charger. If the batteries pass, then move to step 2.
Step 2: You need to measure the voltage of the batteries while they’re hooked up to your converter/charger and it’s plugged into shore power. When powered externally, you should measure something around 14.5 volts across the 12-volt batteries if your charging is working properly.
And when you unplug from shore power, you then read the actual state of battery charge per a standard chart like this one:
Once you know all of that, it’s pretty easy to see if your batteries are still good, if the charger is working, and if your batteries are being fully charged. It’s also possible that you have corrosion on a connector between the batteries and the slide or jack motors. Have you been reading my series on short circuit troubleshooting procedures? That will have a lot of information on how to do this sort of testing.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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