Voltage Meter Issue

[Davidasailor26]

One other caveat using voltages to determine state of charge is that the voltage is also affected by current drain or charging. The voltage is most accurate when checking a rested battery, assuming your voltage chart is calibrated to resting voltages. More details at Under-Load Battery Voltage vs. SoC - Marine How To

 

[Ralph Johnstone]

No can do under load and remember to let it rest at 0% load for 24 hrs. before reading.

@Davidasailor26 , did your "Marine How To" reference mention that ? In too much of a rush to read the whole article.

 

[Davidasailor26]

@Davidasailor26 , did your "Marine How To" reference mention that ? In too much of a rush to read the whole article.

Similar concept, yes. To summarize the article, the load when you’re measuring the voltage has to match the load at which the voltage chart was calibrated. The article’s example was actually a voltage chart calibrated for a 0.05C load, but then using it when there’s no load. That will make you think you’re at a higher SOC than you are, and you could prematurely wear down your batteries by running them below 50% SOC.

 

[Ralph Johnstone]

So, given a nav table and a laptop computer, you could estimate your SOC by plugging in all the variables.

Me ? Too lazy. Installed a Xantrex Link 10 battery monitor. Gives me an idea of where I am on the discharge/recharge cycle.

 

[marchem]

So, given a nav table and a laptop computer, you could estimate your SOC by plugging in all the variables.

Me ? Too lazy. Installed a Xantrex Link 10 battery monitor. Gives me an idea of where I am on the discharge/recharge cycle.

You could do the calculations, but you’d also need to know the specific data for your battery; either from the manufacturer or by measuring it yourself at various loads.

I agree, a battery monitor is a lot easier.

 

[Tin Kicker]

As a licensed aircraft mechanic and engineering investigator who's had or worked on airplanes and boats for most of my life I'm well aware of indicated voltage, rest, capacity, etc. I also have a Victron monitor to go in that just hasn't gotten there since buying the boat earlier this year.

That said, for those who just want to be able to check the battery voltage, which is what the existing switch is for, I shot this photo yesterday while the charger was running to show the digital meter and voltage text. This is the same spot where the big old square meter came out.

The other half likes having "HOUSE" versus "START" so she can remember which is "the big battery."