Understanding my Smartgauge

[Alan de Enfield]

4 hours ago, IanD said:

And the last paragraph is the point -- the SG isn't supposed to be perfect (especially during charging) but that's not its point, it's to tell you what fraction of your battery capacity you've used while discharging, and by all accounts it's pretty good for that

 

How can it tell you what fraction of capacity you have used without knowing what the capacity is ?

 

If it is simply taking the voltage and saying "12.2 volts, therefore you have 50% capacity remaining" I'don't view that as being much help, unless the actual (not original) battery capacity is known.

[bizzard]

It takes a while to learn them but for a few quid a simple digital volt meter wired to your domestic circuit will tell you all of what you want to know.

[Peugeot 106]

2 hours ago, nicknorman said:

it depends on the charging device. If you charge it fast eg with a large alternator (175A alternator as fitted to modern Beta 43 engine), 100% is reached at more or less the right time. If you charge it with eg a 70A alternator, then as you say it will get to 100% well before full charge is reached.

 

Undoubtedly the best solution is a combination of SG and an AH counter such as BMV712. The SG tells you when you need to charge, the BMV tells you when to stop charging (tail current) and the combination tells you the health of the battery if you adjust the battery capacity in the BMV to make the SoC reading of both devices match having discharged significantly.

Mines a 55A alternator charging one 110AH class A leisure battery

[Tony Brooks]

35 minutes ago, Alan de Enfield said:

 

How can it tell you what fraction of capacity you have used without knowing what the capacity is ?

 

If it is simply taking the voltage and saying "12.2 volts, therefore you have 50% capacity remaining" I'don't view that as being much help, unless the actual (not original) battery capacity is known.

 

But is that important for many boaters? What they need to know is if their battery capacity adequate for the load they place on it and the Smartguage will tell you that. When the first thing in the morning state of charge is (say) 30% you know your batteries are getting on for end of life. Even if you are not charging adequately, it still warns you that you need to pay attention to the batteries and/or charging.

 

Like Bizzard, I had 20 years just using an ammeter and voltmeter plus a bit of knowledge with almost no domestic battery problems because I knew when they needed attention or changing.

 

 

[nb Innisfree]

SmartGauge is designed to inform those who can't be arsed to use voltmeters etc and have more important things to do like drinking beer, an easy to use device to able see at a glance what the SoC is and therefore know when to start charging, a clever but simple fit and forget device, though I doubt Gibbo would say it was easy or simple to design 🤣

[nicknorman]

2 hours ago, Alan de Enfield said:

 

How can it tell you what fraction of capacity you have used without knowing what the capacity is ?

 

If it is simply taking the voltage and saying "12.2 volts, therefore you have 50% capacity remaining" I'don't view that as being much help, unless the actual (not original) battery capacity is known.

It only measures voltage, but the way it interprets the voltage is quite clever. For example, is the voltage 12.2 because the battery is at 50% SoC, or is it because the battery is at 80% SoC but you just turned on a heavy load? The SG looks at dV/dt (rate of change of voltage) and so for example if it sees the voltage suddenly dip from 12.5v to 12.2v, it knows that this is due to switching on a big load, and from the magnitude of the dip (0.3v in this case) it can estimate the discharge current in terms of % of the actual capacity. Obviously it is more complicated than that but that is the gist of it.

[nb Innisfree]

I'm guessing the SG compares discharge rate and pattern with known ones from a similar type of battery, it then makes a guess at SoC, after a few charge/discharge cycles it makes increasingly more accurate guesses based on more comparisons. 

 

A simple comparison meter, simple in principle but complex to achieve 🤣

Edited April 28 by nb Innisfree

[Paul C]

Its weird that "Smartgauge Mk2" - the one with the ability to measure current, as well as voltage, and uses a proprietary algorithm to more accurately predict SoC from two inputs instead of one - costs so much. Car manufacturers have been doing battery monitoring for a while now (at least 20 years) and you'd hope some kind of economy of scale would have been passed to boaters by now.

[Grassman]

I don't use the percentage method. I have a Victron 3000 and I tend to just keep an eye on the voltage reading on my phone and ensure it doesn't go below 12.2v, and if it gets close I run the engine. When I get up in the morning I can look at the 'history' and see what it went down to overnight when there's no solar going in. 

 

It's probably not the right or best way, but I'm a thiko with these matters and much of what's been discussed here just goes over my head! 🙂

 

[Tony Brooks]

28 minutes ago, Grassman said:

I don't use the percentage method. I have a Victron 3000 and I tend to just keep an eye on the voltage reading on my phone and ensure it doesn't go below 12.2v, and if it gets close I run the engine. When I get up in the morning I can look at the 'history' and see what it went down to overnight when there's no solar going in. 

 

It's probably not the right or best way, but I'm a thiko with these matters and much of what's been discussed here just goes over my head! 🙂

 

 

That is a perfectly reasonable method, except you are likely to be leaving the bank somewhat discharged for longer, but that goes for anyone who uses the Smartgauge or any other monitor % reading to decide when to start charging.

 

As discussed above, it is not a lot of help in knowing when the batteries are about as fully charges as you can economically get them, but as long as you charge for a good number of hours what you are doing is practical and sensible.

[Tacet]

2 hours ago, Grassman said:

I don't use the percentage method. I have a Victron 3000 and I tend to just keep an eye on the voltage reading on my phone and ensure it doesn't go below 12.2v, and if it gets close I run the engine. When I get up in the morning I can look at the 'history' and see what it went down to overnight when there's no solar going in. 

 

It's probably not the right or best way, but I'm a thiko with these matters and much of what's been discussed here just goes over my head! 🙂

 

My system is simpler.  If it's daylight, it's time to cruise.  The batteries sort themselves

 

[Peugeot 106]

2 minutes ago, Tacet said:

My system is simpler.  If it's daylight, it's time to cruise.  The batteries sort themselves

 

Yes but even you probably stay in the odd place for a couple of days or more and some of us need a simple steer as to when the batteries need charging before they are damaged. I know you can run the engine every day but this may be not very pleasant for fellow moorees . It’s much more considerate if you can wait until when you move off again

[nicknorman]

1 hour ago, Tacet said:

My system is simpler.  If it's daylight, it's time to cruise.  The batteries sort themselves

 

What is wrong with cruising at night? It's great fun!