Using Smartgauge to adjust current counting meters

[ayates]

On this vessel, I have both a Victron BMV-702/CCGX "standard" battery monitor for the house bank, along with a Merlin/Balmar Smartgauge. If one is to go on the assumption that the Smargauge is more accurate, then I have been puzzling over whether readings from the Smartgauge can used to tweak the Victron configuration (i.e. battery bank size). That is fine tune the battery bank size, without performing an actual 20 hour load test.

Over this past summer, I was able to obtain four sets of simultaneous readings of the Victron and the Smartgauge, three of which were when the batteries were not being charged (key for Smartgauge accuracy). See attached image. In all cases the Smartgauge was reporting a non-trivial lower state-of-charge than the Victron.



Thanks,


Allan.

[billknny]

While it is true that the SmartGauge is not susceptible to the same errors as an amp-hour meter, and that makes it more "accurate" it is also significantly less "precise."

The error bands on the numbers are quite large, and they really can not be used to do the kind of data analysis you are trying to do.

For measuring the SOC the Smartguage published specification is +/-5%. That means if the gauge says 75% it might be 70% or it might be 80%. In fact, you can just throw out that last digit. and round to the nearest 10%. For SOC during charging, the error band is +/-10%.

That number is more than accurate enough to take care of your batteries, but you are asking it to do a task it is not capable of.

[john61ct]

No SoC meter is ever "precise" over time best expectation is better guesstimating.

**If** I was sure SmartGauge was installed properly and a compatible chemistry type, I would use that to guide me in calibrating the coulomb-counting type.

[john61ct]

Go here

https://marinehowto.com

And CTRL-F for

battery monitor

and read closely those three articles

[john61ct]

As soon as your bank is starting to wear, the AH capacity setting needs to be periodically adjusted downward on the AH-counting meters.

That is one factor the SmartGauge can help you estimate if you don't want to do periodic SoH load testing benchmarks.

[a64pilot]

I used it to calibrate my amp counter meter, but was sure to do it soon after the bank had been equalized, and I’m absolutely certain it’s fully, completely charged to 100%.
To get them to stay matched, which they do now too, me inputting that my three yr old 660 AH bank is actually a 600 AH bank.
I know I was being a little conservative, but they track within a couple of percent now.

Way I use the SG, I consider its reading first thing in the morning to be accurate, and during discharge with no charge sources, however during charge, especially under Solar, don’t even bother looking at it, however weirdly as the bank approaches full charge and your dribbling in amps for the last several hours, it seems the SG catches up and it will even say bank is 100% before it actually is.

I only use trailing amps to determine full charge as it’s an AGM bank.
It really does take hours to fully charge a bank after most think it is fully charged, and you need to have a way to hold the charger in absorption, often time just turning it off and back on will work.

When they begin to drift apart, it’s time to equalize, and guess what, after an equalization, they track together again.

[john61ct]

Originally Posted by a64pilot

I only use trailing amps to determine full charge as it’s an AGM bank.

Also the way to go for any other chemistry.

Easiest and no resting period required.