Understanding my Smartgauge

[blackrose]

I've had a Smartgauge for many years and never really understood the % SOC display. I realise that when the batteries are being charged from any source that SOC is fairly unreliable as it's based on voltage so will generally read artificially high, but I always thought it would be accurate during battery discharge. However, assuming it says 100% by the time the sun goes down and my panels stop charging but that 100% wasn't really true, would the SG SOC quickly drop down to its real % once I start using the batteries and take the surface charge off the battery plates, or will it still read too high during battery discharge because it started from the wrong high point?

 

Hope that makes sense...

 

Edit: I have a shunt type monitor too by the way so I can use tail current to see when the batteries are fully charged assuming there's a reliable charge source, but that isn't always the case with solar of course as the sun goes behind clouds, etc.

Edited April 27 by blackrose

[Alan de Enfield]

My understanding is that you need to 'tell it' what the real (current) battery capacity is - not the theoretical, so it can work out when the batteries are fully charged.

[blackrose]

Just now, Alan de Enfield said:

My understanding is that you need to 'tell it' what the real (current) battery capacity is - not the theoretical, so it can work out when the batteries are fully charged.

 

Really? That's not my understanding of the Smartgauge. I'm pretty sure it learns the battery capacity by itself after a few cycles below 74% and back to 100%

[nicknorman]

4 minutes ago, Alan de Enfield said:

My understanding is that you need to 'tell it' what the real (current) battery capacity is - not the theoretical, so it can work out when the batteries are fully charged.

Absolutely not.

9 minutes ago, blackrose said:

I've had a Smartgauge for many years and never really understood the % SOC display. I realise that when the batteries are being charged from any source that SOC is fairly unreliable as it's based on voltage so will generally read artificially high, but I always thought it would be accurate during battery discharge. However, assuming it says 100% by the time the sun goes down and my panels stop charging but that 100% wasn't really true, would the SG SOC quickly drop down to its real % once I start using the batteries and take the surface charge off the battery plates, or will it still read too high during battery discharge because it started from the wrong high point?

 

Hope that makes sense...

 

Edit: I have a shunt type monitor too by the way so I can use tail current to see when the batteries are fully charged assuming there's a reliable charge source, but that isn't always the case with solar of course as the sun goes behind clouds, etc.

The Smartgauge works on voltage only. So during discharge, and as you say once the surface charge is off (and the Smartgauge SoC drops a few %) it is quite accurate on the discharging SoC. Unlike other “battery fuel gauges” it doesn’t measure current and thus the battery capacity is irrelevant - it simply gives the SoC as a % of the actual capacity (during discharge). During charge it can either over or under read depending on how powerful the charge source is,

[alan_fincher]

3 minutes ago, Alan de Enfield said:

My understanding is that you need to 'tell it' what the real (current) battery capacity is - not the theoretical, so it can work out when the batteries are fully charged.

 

I may be wrong, but don't think that is correct.

 

It surely gives its estimate of state of charge based on voltage.

If your battery bank is 50% degraded it will still come up with a state of charge - say 80%  Replace it with a new battery bank, and it may also give an 80% state of charge.  The difference is that the latter may represent 80% of 220Ah, whereas the former represents 80% of only 110Ah - i.e. what your batteries have degraded to.

I'm sticking my neck out here, so wouldn't be surprised to hear I am wrong!  If I am, I'm keen to see the corrected version!

9 minutes ago, blackrose said:

 

Really? That's not my understanding of the Smartgauge. I'm pretty sure it learns the battery capacity by itself after a few cycles below 74% and back to 100%

Correct.

[jonesthenuke]

3 minutes ago, Alan de Enfield said:

My understanding is that you need to 'tell it' what the real (current) battery capacity is - not the theoretical, so it can work out when the batteries are fully charged.

With a Smartguage, the gauge indicates what is left in the battery as a percentage. The gauge neither knows nor indicates the capacity (total Ah) of the battery.  The gauge works out the state of the battery solely from monitoring the battery terminal voltage over time.

 

I find that when charging has finished and the battery starts to be "used", the gauge stays at 100% for some time and only then starts to drop.

 

Regarding the OP, if the gauge has indicated 100% for some time during charging, then the battery holds as much as it can and I would expect to behave as I have indicated above.

 

Note if your battery bank is old/degraded/sulphated the capacity (the useable Ah) will be far far less than when the batteries were new. The gauge will still go to 100% when the battery has absorbed as much charge as it can, but will drop more quickly under discharge as the capacity of the bank is reduced.

[Alan de Enfield]

1 minute ago, alan_fincher said:

 

I may be wrong, but don't think that is correct.

 

It surely gives its estimate of state of charge based on voltage.

If your battery bank is 50% degraded it will still come up with a state of charge - say 80%  Replace it with a new battery bank, and it may also give an 80% state of charge.  The difference is that the latter may represent 80% of 220Ah, whereas the former represents 80% of only 110Ah - i.e. what your batteries have degraded to.

I'm sticking my neck out here, so wouldn't be surprised to hear I am wrong!  If I am, I'm keen to see the corrected version!

 

Maybe that's where I am getting confused.

 

You could have a 110Ah battery that is sulphated and only has 6Ah capacity but it can still be fully charged at 12.9v and show 100%

You can have a brand new 1000Ah battery bank that shows 12.9v and show 100%.

 

Voltage alone gives no idea about battery capacity.

[nicknorman]

Just now, Alan de Enfield said:

 

Voltage alone gives no idea about battery capacity.

Correct. But capacity is not particularly interesting, what is interesting is when the batteries are so discharged that they should be recharged, and the SG is good at telling you this.

[alan_fincher]

1 minute ago, Alan de Enfield said:

 

Maybe that's where I am getting confused.

 

You could have a 110Ah battery that is sulphated and only has 6Ah capacity but it can still be fully charged at 12.9v and show 100%

You can have a brand new 1000Ah battery bank that shows 12.9v and show 100%.

 

Voltage alone gives no idea about battery capacity.

 

Agreed.

 

If you have a Smartgauge it is important to understand what its stated capabilities are, and not to assume it will do more than those.

It is marketed as providing a fairly accurate estimate of state of charge, (as a percentage), irrespective of original size of bank and of any subsequent loss of capacity.

It does not pretend it can ascertain the current usable capacity of the bank once sulphated to some degree.

[Alan de Enfield]

Just now, nicknorman said:

Correct. But capacity is not particularly interesting, what is interesting is when the batteries are so discharged that they should be recharged, and the SG is good at telling you this.

 

Ok I now understand what the smartgauge can do, but for me I can easily measure a battery and ascetain its SoC, what I need to know is does it have enough capoacity for what I want.

[Bod]

^{My  Take on how to read a Smart Gauge.}

^{Battery takes a long time to run down-- takes a long time to charge = all good.}

^{Battery takes a short time to run down-- takes a long time to charge = heavy drain on battery.  (using to much power)}

^{Battery takes a short time to run down -- takes a short time to charge = battery has reduced capacity. (battery at end of life, needs replacing)}

^{Smart Gauges tell it as it is, you may not like what they say, but are almost unknown to be wrong.}

^{It won't tell you if, only 1 battery in a bank is duff, only that the bank has a problem.}

 

Bod

[blackrose]

39 minutes ago, nicknorman said:

 

The Smartgauge works on voltage only. So during discharge, and as you say once the surface charge is off (and the Smartgauge SoC drops a few %) it is quite accurate on the discharging SoC. Unlike other “battery fuel gauges” it doesn’t measure current and thus the battery capacity is irrelevant - it simply gives the SoC as a % of the actual capacity (during discharge). During charge it can either over or under read depending on how powerful the charge source is,

 

Ok thanks, understood.

 

6 minutes ago, Bod said:

Smart Gauges tell it as it is, you may not like what they say, but are almost unknown to be wrong.

 

I don't think that's correct. Please read my original post about how they are generally wrong during charge cycles.

Edited April 27 by blackrose

[Bod]

6 minutes ago, blackrose said:

 

 

 

I don't think that's correct. Please read my original post about how they are generally wrong during charge cycles.

Smart Gauges tell it as it is, you may not like what they say, but are almost unknown to be wrong.

This refers to the speed of change to the figures, how fast the battery depleats.

The instructions do refer to the charging accuracy being variable, it's the battery losing capacity that is often not understood, the expection is that an old poorly maintained battery will have the same capacity as a new one. 

 

Bod

[MtB]

3 hours ago, Bod said:

Smart Gauges tell it as it is, you may not like what they say, but are almost unknown to be wrong.

 

Cobblers.

 

Even the manual tells you that during charging the display cannot be relied upon to be accurate.

 

 

[Bod]

5 hours ago, MtB said:

 

Cobblers.

 

Even the manual tells you that during charging the display cannot be relied upon to be accurate.

 

 

Read what I wrote.

I and the forum are aware of your "problems" with Smartgauge, and accept that your opinion towards them may be coloured.

 

Bod

[nicknorman]

10 hours ago, Alan de Enfield said:

 

Ok I now understand what the smartgauge can do, but for me I can easily measure a battery and ascetain its SoC, what I need to know is does it have enough capoacity for what I want.

You can’t easily measure a battery and ascertain its SoC. You can measure it using a hydrometer - a faff. You can measure the resting voltage by turning all loads off and waiting an hour or two - a faff. SG seamlessly measures the SoC without any user intervention.

 

You ask if your battery has enough capacity for what you want. Assuming a fairly regular usage pattern as per most boaters, you have enough capacity if the SG is reading over 50% at the next time you start to charge.

 

But if you want to know whether you can run the new inverter you just bought to operate the new electric kettle, toaster, coffee machine and air fryer, no it doesn’t tell you that.

Edited April 28 by nicknorman

[Peugeot 106]

In my experience if you drop to say 70% charge and then run the engine to charge the battery it Will not be fully charged when it reads 100%. If you then take it off charge and carry on using the battery the  SOC will drop quicker than you expect. The engine needs to run for quite a while after it reads 100% to fully charge so this agrees with it not being very accurate during charging.

i find it reassuring as it gives a good indication as to when the battery needs recharging so i can sleep easy. I just look at the extra running at 100% to be topping up and am aware that it seems to reach 100% before it should

[MtB]

3 hours ago, Bod said:

Read what I wrote.

I and the forum are aware of your "problems" with Smartgauge, and accept that your opinion towards them may be coloured.

 

Bod

 

 

I quoted the cobblers you wrote. Read my post.

 

 

 

 

You said "but are almost unknown to be wrong", which itself is wrong and therefor cobblers.

 

The SG manual itself tells us the display is likely to be wrong during charging, which happens regularly.

 

 

[jonesthenuke]

1 hour ago, Peugeot 106 said:

In my experience if you drop to say 70% charge and then run the engine to charge the battery it Will not be fully charged when it reads 100%. If you then take it off charge and carry on using the battery the  SOC will drop quicker than you expect. The engine needs to run for quite a while after it reads 100% to fully charge so this agrees with it not being very accurate during charging.

I would also suggest there is a delay in the reading starting to rise after starting to recharge batteries, nothing seems to happen for the first 30 minutes or so, even though a lot of current is going in.

 

Once these behaviours are known, the meter is a useful pice of kit as it's the discharge monitoring that is most useful in my opinion. PS also, they are very easy to set up in comparison to most battery monitors.

[IanD]

52 minutes ago, jonesthenuke said:

I would also suggest there is a delay in the reading starting to rise after starting to recharge batteries, nothing seems to happen for the first 30 minutes or so, even though a lot of current is going in.

 

Once these behaviours are known, the meter is a useful pice of kit as it's the discharge monitoring that is most useful in my opinion. PS also, they are very easy to set up in comparison to most battery monitors.

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 -- at least, for LA batteries. It won't tell you that your battery capacity has degraded over time because it doesn't monitor current, but that should be obvious as discharge times get shorter and shorter.

 

If you want something better (current, battery health/capacity) there are more complicated (and considerably more expensive) battery monitors on the market (e.g Balmar, Victron) which also measure current (and need a shunt installing), but for most people (not @MtB obviously...) just concerned about remaining capacity the Smartgauge is "good enough".

[Bod]

1 hour ago, MtB said:

 

 

I quoted the cobblers you wrote. Read my post.

 

 

 

 

You said "but are almost unknown to be wrong", which itself is wrong and therefor cobblers.

 

The SG manual itself tells us the display is likely to be wrong during charging, which happens regularly.

 

 

They are almost unknown to be wrong in displaying the percentage of available battery capacity.

At least you agree that the the readings during charging may be incorrect, as per the SG manual.

 

Bod

[blackrose]

43 minutes ago, Bod said:

They are almost unknown to be wrong in displaying the percentage of available battery capacity during discharge cycles.

 

 

I think my caveat in bold is where your first sentence needs clarification and why some here are disagreeing with you. But you're actually both saying the same thing.

Edited April 28 by blackrose

[Tony Brooks]

9 minutes ago, blackrose said:

 

I think my caveat in bold is where your first sentence needs clarification and why some here are disagreeing with you. But you're actually both saying the same thing.

 

I agree, the topic got pretty silly in my view once that was pointed out - especially as it is in the manual.

[nicknorman]

6 hours ago, Peugeot 106 said:

In my experience if you drop to say 70% charge and then run the engine to charge the battery it Will not be fully charged when it reads 100%. 

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.

[blackrose]

2 minutes ago, nicknorman said:

Undoubtedly the best solution is a combination of SG and an AH counter

 

Yes that's what I've got. SG and a BEP shunt-type battery monitor. Tells me all I need to know. 

 

I've had them both for about 16 or 17 years. I remember when I ordered the SG from Gibbo he was surprised because he knew I already had the BEP monitor, but it seemed obvious to me at the time that having both would be beneficial.