Smartgauge battery monitor - how it works

[jmaja]

Has anyone done any measurements on this? It shows SoC for a lead acid battery based on just two wires going to the battery. Thus it can only measure voltage and possible emit and measure some AC signal. Does it do any of the latter?

Many have tested it's accuracy and found out that it is very good while the battery is not used or is discharged, but not that good during charging (will recover to very good accuracy after charging).

Their homepage doesn't really tell how it works: http://www.smartgauge.co.uk/

E.g. here are some speculations how it might work: http://www.cruisersforum.com/forums/archive/index.php/t-176579.html

[Wilksey]

Sounds like a lot of flannel to throw you off the scent that it probably just is a battery voltage monitor!

[jmaja]

Sounds like a lot of flannel to throw you off the scent that it probably just is a battery voltage monitor!

Could be, but it clearly does something much better that just a simple SoC from voltage based on a look up table. Many users have reported to be very accurate, more accurate than battery monitors based on current measuring.

[amyk]

http://www.richtek.com/en/Design%20Support/Technical%20Document/AN024

Look under "Dynamic Voltage-based Fuel Gauge". If it can be accurate to within a few % for lithium cells which have an extremely flat discharge curve, it will work even better for lead acid. The principle seems to be pretty simple: it guesses whether the cell is under load vs open, and predicts what the discharge curve will look like.

TI and Maxim make similar products too: http://www.ti.com/lit/ds/symlink/bq27621-g1.pdf

https://www.maximintegrated.com/en/design/partners-and-technology/design-technology/modelgauge-battery-fuel-gauge-technology.html

[jmaja]

Could be that as well. I couldn't find any IC's for that. All fuel gauges for lead acid seem to have current and voltage measuring.

[Wilksey]

Maybe it does do current measuring, I've seen some small-ish hall effect CT's from Honeywell that you just pass the wire through.  Do you have one of these units to look at or are you just wondering how it works?

[amyk]

Could be that as well. I couldn't find any IC's for that. All fuel gauges for lead acid seem to have current and voltage measuring.

They made their own which works on the same principle, it's probably just a standard ADC MCU like a PIC that's been programmed with that algorithm.

[jmaja]

Maybe it does do current measuring, I've seen some small-ish hall effect CT's from Honeywell that you just pass the wire through.  Do you have one of these units to look at or are you just wondering how it works?

Can't measure current when you just connect it with two wires straight to the battery. I don't have one. If I had, I would measure with a scope to find out if it emits something or not. It could do some kind of LCR measuring like Electrochemical Impedance Spectroscopy (EIS), which is known method to measure SoC.

[john61ct]

Some very smart people, including EnerSys and others involved in battery system integration for many military clients, have verified the accuracy of Chris Gibson's invention, and expressed amazement and mystification at the fact that it only uses two wires.

If there is a coulomb-counter that comes close (without frequent recalibration) I want to know about it. Note it doesn't work (at all) with LFP, just lead. And Chris has always been very open about accuracy being reduced (but still better than everything else!) while charging.

This thread is a bit funny: http://www.ybw.com/forums/showthread.php?73924-Smartbank-battery-management/page5

In the US, Balmar sells and supports it well.

See also "Maine Sail", Rod @ Compass Marine Services', detailed review, he started out very skeptical too.

"tested against a Vanner Battery Monitor (around £10'000 worth - designed specifically for testing batteries), a Link 10, BEP DCM600 and a Victron BMV. We tested it under various types of load, battery sizes, types etc. After 3-4 cycles (this is needed for the SmartGauge to learn about the battery - and the key to a shuntless design), we found that the SmartGauge was (overall) more accurate than the shunt based meters".


Personally, I think it's got a little neural-net learning that cause it to get **more** accurate over time - you do need to leave it hooked up - clever preprogrammed profiles, dis/charge cycle algorithms to compare its observations against internally and finally (this is key!) I believe it also measures internal cell resistance as that changes over time.

Chris and Merlin are of course playing things close to their chest. Best of luck cracking that nut, other ideas welcome.

And if anyone knows something even close for LFP do Please speak up!

[john61ct]

Bit more detail http://forum.solar-electric.com/discussion/9554/smartgauge-battery-monitor-anyone