A few weeks ago, I asked, “Does voltage matter?” I was not satisfied with the answer that I got.
As a reminder, voltage can be compared to pressure. You can have all the battery capacity (amps) in the universe, if you have no pressure (voltage) to get that capacity to your electrical devices, you won’t have power. The amount of voltage your electrical system has depends on the state of charge of your batteries and the size of your wiring as it relates to your load. Small load through big wires means less resistance and more pressure, big load through small wires means more resistance and less pressure.
Voltage is a very poor indicator of the state of charge of batteries. This is because it fluctuates wildly depending on the load on the system. But because voltage is almost useless to determine the state of charge of batteries does not mean it is a meaningless number. Voltage can tell you some useful things about the state of health of your entire electrical system. I therefore disagree with folks who claim that voltmeters just about useless.
Again, voltage is akin to pressure. You only have so much pressure and that has to feed your entire electrical system. If you put too big of a load through wires that are too small (like a a torrent of water trying to pass through a garden hose), you will get a lot of resistance and reduced pressure. This reduced pressure is called voltage drop.
For most applications, a voltage drop of up to 2% is acceptable. For lower wattage items, like lights, up to 4% may be okay. This is where the voltmeter comes in handy. Turn on a typical load one evening, say the inverter, TV, and a light or two. Check the voltage at the batteries and check it again inside. If you’re reading 12.5 at the batteries and 12.3V inside, you’re doing okay. But if you’re reading 11.8V inside and your lights are flickering, you have a problem.
The causes of big voltage drops can be minor, like loose and/or dirty terminals or low water levels. Such corrections can be made easily. The causes can also be major, like undersized wiring for the load. The temporary solution there is to reduce the load and the permanent solution is to run bigger wiring (with a smaller gauge number) for that application.
Regardless of the reason for the voltage drops, keeping an eye on them is a good way to monitor the state of health of your electrical system. I have hit the road in the morning with 12.5V showing and stopped for lunch at to 10.5V, with my fridge having turned off. Did I leave a load on? Nope, a terminal connection got loose during travel over a bumpy road. If I only relied on my battery monitor, I wouldn’t have known there was a problem until my freezer contents started to soften.
I struggled with low voltage at the start of my boondocking experiment on the beach. Not being satisfied with answers that focused on the health of my batteries and their state of charge, I ignored anyone who told me voltage readings were a red herring and not relevant. I knew voltage was a clue and I was right. I wound up having loose and dirty terminals as well as undersized wiring for my application. I’ve resolved all those matters (although the latter one needs a more permanent solution).
Now, I have the satisfaction of starting my evening with 12.5V on the voltmeter and never seeing that number go below 12.3 even with the fridge and a couple of lights running while my computer is charging. I haven’t seen a light flicker in recent memory and I can turn on my inverter to print or use the vacuum cleaner in the evening. If I had believed that voltage doesn’t matter, I would be a much unhappier boondocker this morning. Heck, I probably wouldn’t even be a boondocker anymore.
Tomorrow, I will have been here a month, a full 31 days, and I don’t anticipate having any trouble making it to the end of the first week of March, another two weeks or so.
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