Smartguage *and* smartshunt

[GHA]

Well that was interesting. If a little embarrassing.
Couple nights ago heading to bed glanced at battery voltage. Boat's in a boatyard and power goes off at 10pm. WOW!! That's too low, something not right..
"Check battery water" is on sundays weekly repeating check list on todoist, but not been warm & absorption voltage set quite low (T105 batteries) so I've been bit lax pretty crap and not done it for a while.
First though, check the water. Down near the plates. Oooops!!!!
Topped up and voltage jumped back up a bit when fridge turned off. Might have got away with that....

Yesterday first thing checked the smartguage - 80% , smartshunt - 94%. Something still not right so changed profile to 14.8v & switched off & on mains charger a few time to force it into absorption again til current going in graph was fairly flat then blasted them in equalize at 15.5v for an hour.

This morning graph shows back to how it used to look, 12.64v with 0.85A going out. Smartgauge says 93%, smartshunt says 93.5% .

Phew, might have got away with that one, they're not even a year old yet!

Smartguage was from a sale or demo for hundred quid & I thought it was worth a go the see if comparing "real" state of charge to the smartshunt state of charge could say anything useful about the health of the batts.
Looks like it was worth a punt! Could be well worth considering on a cruising boat.
Smartguages were tested by Rod Collins/compass marine , like many he was skeptical about how a little box with just 2 wires could be produce useful results but was just the opposite after testing.
Balmar Smartgauge Battery Monitoring Unit - Marine How To

SmartGauge Electronics - SmartGauge battery monitor

Good article, also show just what a big deal capacity testing lead acid batteries really is.
Limitations though, smartguage will tell you how full the battery bucket is but not how big, Smartshunt & similar will measure how much power went in/out and how full the bank is but only after you tell it the capacity. Which you don't know.
Both together seem a very useful match
Shame windows laptop gave up , not so easy to get screenshots now on a crappy linux notebook..

Equalizing charge, bubble that electrolyte! Interestingly they didn't heat up much.

Wow - something wrong! Top graph is current in/out.

When the previous elderly t105's were on their last legs the voltage got very volatile like that.

Gold dust in the data!!!!

 

[Gumpy]

I've been using a Smartgauge since they were first developed and have owned 4 or 5 over that period.
Never bothered with counting Ah as its just to much faff keeping the meter accurate. I do have an ammeter mainly to measure tail current so I can see when to stop charging when using the engine.
Smartgauge has one failing and that is when charging the % is only a guesstimate . This means that you cant rely on it to tell you when the batteries are fully charged, hence my need to measure tail current. Also if you have a decent solar array, mine is 500watts, it can be up to 10% out when the solar is working, something to bear in mind. I tend to rely on it only at night just to save any miscalculations.

 

[GHA]

Yep, though don't mind a smartshunt so long the batts are getting back to 100% regularly.
Biggest downside of a normal battery monitor isn't that it can drift though, it's that it can tell you nothing about the capacity of the bank. Just count out and count back in again.
Combining the two to give some info about the actual battery capacity is a game changer for cruising boats which can spend years at a time only ever anchoring.

Test data would be interesting to see how accurate you could get. That ain't gonna happen though. Major undertaking.

Boats batteries usually have 3 states >
Brand new
Lights came on so ignore
Flippin heck it's dead...
??

 

[roaringgirl]

If a smartgauge only has 2 wires, it must be measuring voltage. I don't know what value it is adding that you wouldn't get by keeping an eye on voltage as well as smartshunt info.

The times when batt voltage and shunt info have disagreed the batteries have needed my attention.

 

[GHA]

If a smartgauge only has 2 wires, it must be measuring voltage. I don't know what value it is adding that you wouldn't get by keeping an eye on voltage as well as smartshunt info.

The times when batt voltage and shunt info have disagreed the batteries have needed my attention.

Check the marine how to link. From just 2 wires it will accurately display the state of charge of a lead acid battery. How it does this is a secret but it does.
If you tell a smartshunt your batteries are 200ah and overnight from fully charged it says they are, say, 80% full, if the smartguage says they are 50% then your batteries don't have a capacity of 200ah any more.
Extremely useful.

 

[roaringgirl]

Check the marine how to link. From just 2 wires it will accurately display the state of charge of a lead acid battery. How it does this is a secret but it does.
If you tell a smartshunt your batteries are 200ah and overnight from fully charged it says they are, say, 80% full, if the smartguage says they are 50% then your batteries don't have a capacity of 200ah any more.
Extremely useful.

If a smartshunt says your AGM batteries are at 80% but the overnight lowest voltage is 12.2v then you have the same information.

 

[GHA]

If a smartshunt says your AGM batteries are at 80% but the overnight lowest voltage is 12.2v then you have the same information.

Unfortunately not. You might have *some* information bt you won't know much about about what it is telling you.
Any state of charge derived from voltage will likely be very inaccurate. Temperature(makes big difference, warm batteries have a bigger capacity than cold batteries) , make/chemistry of battery, age of battery - all makes a difference. Plus you need to let the batteries rest for a good few hours with no load for the voltage to stabilize.
12.2v might tell you something, but not much and you won't actually know what it is telling you.
A smartguage only tells you one thing, an accurate indication of state of charge of that battery, then and there.
Rod Collins extensive testing backs this up.

 

[GHA]

Try factoring in Peukerts coefficent first thing before coffee if you really want your head to explode

 

[roaringgirl]

Unfortunately not. You might have *some* information bt you won't know much about about what it is telling you.
Any state of charge derived from voltage will likely be very inaccurate. Temperature(makes big difference, warm batteries have a bigger capacity than cold batteries) , make/chemistry of battery, age of battery - all makes a difference. Plus you need to let the batteries rest for a good few hours with no load for the voltage to stabilize.
12.2v might tell you something, but not much and you won't actually know what it is telling you.
A smartguage only tells you one thing, an accurate indication of state of charge of that battery, then and there.
Rod Collins extensive testing backs this up.

See here for an explanation of how the smartgauge uses voltage alone to determine charge state: Balmar Smartgauge Battery Monitoring Unit - Marine How To

 

[GHA]

See here for an explanation of how the smartgauge uses voltage alone to determine charge state: Balmar Smartgauge Battery Monitoring Unit - Marine How To

Not sure what your point is ?
Any of us looking just at voltage will not be able to tell all that much about a battery, a smartguage seems alone by being capable of calculating accurate state of charge.

 

[roaringgirl]

Yes, temp makes a difference, and yes load makes a difference, but if you are suspicious about your shunt telling porkies, switching off charge sources and loads for a couple of minutes and checking the voltage against a voltage chart for your battery type will tell you whether your shunt is right or not. If that's the only thing you're using a smartgauge for, it doesn't seem worth it!