More Electrical Woes, With a Twist

The twist being that I have solved yet another mystery. Everything is FINE. Perfect even!!!

For days now, I’ve been experiencing gigantic voltage drops in the evening. Tonight, with everything off, I was at about 12.5V. Turn on the fridge and I dropped to 11.9V. Turn on an LED light? Forget it. The voltage drop wasn’t just in the rig, I was experiencing it right at the battery. Something was very, very wrong.

So I haven’t been using any power in the evening except an LED light for just a few minutes at bedtime because I was sure my electrical system or batteries or both were on the verge of going KABOOM.

I didn’t want to put any of this on the blog because I feel that many of you have given me way too many braincells already. I had all the information any outsider could give me. It was time to do the hard work myself and until I either solved this issue or came up with a specific gravity number for my batteries, I was staying mum.

Just before dark this evening, I took some voltage readings. Could my solar array monitor be wrong? It was wildly fluctuating.

I headed outside in the waning light to take a gander at my battery bank. Or, rather, I felt around with my hands. My connections were all tight. I pulled out my flashlight and… wait a minute. Was that corrosion on the positive terminal?

And that was the missing variable, folks. We’ve all been looking at my battery issues as a textbook situation rather than in context. Where I am, context is important. I am by the ocean. I’m seeing rust form on all my exposed metal right now. So it’s obvious in hindsight that some of that salty air would end up on my batteries.

So I recleaned that terminal and then coated all my connections yet again in dielectric gel.

Now, voltage with everything off? 12.55. Fridge on? 12.48. One LED light on? 12.44. Two LED lights on? 12.4. All of the above plus the incandescent stove hood light? 12.38.

The icing on the cake is that my battery (still flashing 0.00V, mind you) is perfectly calibrated. I know I’ll have a full charge by lunch tomorrow and then I can start to plan a strategy for the couple of grey days ahead.

L has the tools and knowledge to remove my motorhome starting battery and test (and repair or replace) the solenoid, so I will try to wrangle him tomorrow afternoon to do that, and early enough to run into town to the auto parts store if we need to.

It’s been a really great day on the beach. Now, there’s a strawberry daiquiri in the freezer with my name on it!

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  • Your voltage readings are finally how they should be for the first time! 🙂

  • For the first time in a while. They were normal until I started to play around with my electrical stuff this summer. 😉

  • Yes, bad contacts will get you every time, no matter how beefy the rest of the wiring might be. And as you reported that the fridge caused a voltage drop of 0.07V (12.55V to 12.48V), while each of the LEDs caused a drop of 0.04V, I deduce that your fridge only uses the 12V to run its control, and not the heating element. The latter would have drawn a much higher current, and caused a much larger drop relative to that of the LEDs. The current draw of 15A as I suggested in an earlier comment was meant for a 3-way fridge running on 12V, not while the fridge runs on propane.

    By the way, I experience this bad contact at the battery posts quite often. A way to quickly check this with a voltmeter is to press the meter probes against the soft lead of the battery posts, so that you can see the voltage right at the battery output, and not after any cruddy clamp or crimp contact.

    One can also check for excessive voltage drop across any contact by measuring the voltage drop across that contact. I have found that even two beefy looking lugs tightened together on a 1/4″ post may still have close to a milli-ohm in resistance. When passing a 100A current that may be drawn by a big inverter, that would cause a loss of 0.001 Ohm times 100A = 0.1V. The power loss due to just that single contact point is 0.1V times 100A = 10 watts.

    In short, electrical contacts have to be checked, and rechecked periodically to make sure that they are tight and corrosion free.


  • All I have to say is that’s it, I am going to find a way to code my blog in such a way that whenever someone comments on electricity, a message will flash in 72 point red letters that a) I set my fridge to propane, not auto b) modern fridges use a little electricity even on propane, and c) my fridge draws 0.5A on propane. It’ll save folks a lot of typing! 😀

  • Rae, we were trying to understand why a 0.5A would cause such a voltage drop even for a 12-gauge wire, assuming that every connection was secure. So, same as Andy Baird might have thought, I was wondering if your fridge was a 3-way, which meant it had a 12V heater that sucked up a lot more juice than the 0.5A control current, and its relay could have stuck, or the control circuit failed in such a way that the heater might have stayed on, while you thought it was supposed to be off in propane mode. And this heater, if stuck on, could have easily drained your battery too.

    When faced with unusual phenomena, people tend to think of extraordinary theories to try to explain it. That’s all.


  • Yes, but at some point, it’s like a cop being fixated on a suspect because one clue leads to him, even if there’s overwhelming evidence he’s not guilty. That’s why I went quiet on this for a bit. My telling folks over and over that the fridge was fine was keeping me from focusing on other possible culprits. In this case, salty air.

    I appreciate all the help I get even if I sometimes sound cranky about it! 😀

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