Best battery monitor system?

[RobbieW]

I didn't make a comparison, i just stated what i fitted and what is showed

I'm not sure exactly how the Victron works out SOC, but you have to program battery capacity and it has an algorithm to tell when the battery is charged. Add to that the ammeter shunt and it's surely simple maths to work out that x capacity - used ah = SOC ?

What Dune16 asked was whether the Smartgauge was still the best option....

SOC isnt exactly related to amps out vs amps in. That doesnt take account of the loss of capacity for a battery over time nor the effect of Peukert. Also amps in from a charger can be fooled by supplying loads as well as battery charging. So you dont really know, without some complex circuitry, how much charge output goes solely to the battery. So far as we know Smartgauge uses a very different technique which has been independently proven.

 

[Richard10002]

I fitted a NASA BM2 in 2012. I added a Smartgauge in 2015 as the SOC of the NASA is very flawed.

I have more confidence in the Smartgauge SOC when discharging, although I'm not so sure between 100% and about 80%, (not that it matters at these levels.

When charging, the Smartguage shows 100% long before the batteries are close to fully charged. Stopping charging based on a Smartgauge reading of 100% will lead to badly sulphated batteries very quickly - How do I know?

I now base my decision that the batteries are full on the NASA showing me a low value for Charging Amps, (around 1% or 2% of actual/calculated battery capacity), and my batteries dont seem to be losing any more capacity for the time being.

So Smartgauge serves a purpose, but it's not as good as is claimed, and can do more harm than good with limited knowledge

 

[PaulRainbow]

What Dune16 asked was whether the Smartgauge was still the best option....

He asked if it was still a good option..........

I doubt that the forum all agreed it was the best option, that would likely be a first

SOC isnt exactly related to amps out vs amps in. That doesnt take account of the loss of capacity for a battery over time nor the effect of Peukert. Also amps in from a charger can be fooled by supplying loads as well as battery charging. So you dont really know, without some complex circuitry, how much charge output goes solely to the battery. So far as we know Smartgauge uses a very different technique which has been independently proven.

The Victron doesn't just measure amps in, it measures net amps, so you do know exactly what goes solely to the battery. I like being able to see volts and amps, probably more than SOC, so the Victron works well for me.

That said, it doesn't work SOC out at all well if one or more batteries have failed. But, being able to see volts and amps shows the failure very well.

 

[prv]

I have more confidence in the Smartgauge SOC when discharging,

I believe the manual agrees with you. The clever SOC measurement technique is aimed at a discharging battery, and it uses a less sophisticated approach when on charge. From memory, I think it warns that SOC will not be fully accurate after charging until it has had a short period to observe the battery at rest or under load.

In my case, the end of charging is determined by when I want to put the sails up, or have finished mooring, rather than what the battery meter says. Fortunately, with my big alternator and Merlin booster, they're generally full at that point anyway.

Pete

 

[Richard10002]

I believe the manual agrees with you. The clever SOC measurement technique is aimed at a discharging battery, and it uses a less sophisticated approach when on charge. From memory, I think it warns that SOC will not be fully accurate after charging until it has had a short period to observe the battery at rest or under load.

Agreed... but it is a long'ish manual, and lots of people dont read them

The fact is that the Smartgauge is "promoted", (not necessarily by the creator and sellers), as a simple fuel gauge by many, so you can imagine lots of people fitting it and treating it as exactly that.

Given the OPs question, I felt it worth saying that it is not all "we" might think, but is useful when you take into account the shortcomings.

When I was first making the choice of the NASA BM2 or the Smartgauge, I chose the NASA because Voltage, Charging/Discharging Amps, and Cumulative Amp hours is more useful to me than SOC. I had a hankering for the Smartgauge, so bought one when i was a bit more flush.

 

[ghostlymoron]

I haven't got any kind of battery state of charge meter (SOC) but many users like the NASA units. I find it difficult to grasp the way the more sophisticated ones work especially as the capacity of the battery decreases with age.
We spoke to the Smartgauge seller at SIBS a couple of years ago who persuaded my pal to buy one.

 

[Playtime]

I reckon those who properly understand DC electrics (volts, amps, ohms, Ah, watts etc.) prefer the Victron/Link/NASA BM approach and rely on net Ah for an estimate of SoC. Those who don't understand electrics just want a battery 'fuel gauge' and buy the Smartguage.

I also reckon the Smartguage predominantly uses simple voltage measurement to determine SoC (as per the table linked to earlier), maybe adjusted with an estimate of battery internal resistance to compensate for internal volts drop when discharging. I don't buy the implied 'cleverness' of "impedance spectroscopy" mentioned earlier.

Just for the record I have a Victron and find it excellent (but never look at SoC!).

 

[knuterikt]

I reckon those who properly understand DC electrics (volts, amps, ohms, Ah, watts etc.) prefer the Victron/Link/NASA BM approach and rely on net Ah for an estimate of SoC. Those who don't understand electrics just want a battery 'fuel gauge' and buy the Smartguage.

I also reckon the Smartguage predominantly uses simple voltage measurement to determine SoC (as per the table linked to earlier), maybe adjusted with an estimate of battery internal resistance to compensate for internal volts drop when discharging. I don't buy the implied 'cleverness' of "impedance spectroscopy" mentioned earlier.

Just for the record I have a Victron and find it excellent (but never look at SoC!).

You must be brilliant! In your own eyes at least.

 

[Playtime]

You must be brilliant!

Thanks. IMHO of course!

 

[Mistroma]

I reckon those who properly understand DC electrics (volts, amps, ohms, Ah, watts etc.) prefer the Victron/Link/NASA BM approach and rely on net Ah for an estimate of SoC. Those who don't understand electrics just want a battery 'fuel gauge' and buy the Smartguage.

I also reckon the Smartguage predominantly uses simple voltage measurement to determine SoC (as per the table linked to earlier), maybe adjusted with an estimate of battery internal resistance to compensate for internal volts drop when discharging. I don't buy the implied 'cleverness' of "impedance spectroscopy" mentioned earlier. Extra information is always useful though to estimate battery capacity as they age. Smartguage just tells you %SOC but not if bank capacity is now 400Ah or 500Ah.

Just for the record I have a Victron and find it excellent (but never look at SoC!).

I can't see how simple voltage measurement would work when the instrument knows nothing of charge going into the battery or amps being discharged. It will work when the battery is not connected and rested for a few hours. How would it determine the rested battery voltage whilst charging via solar or sitting with fridge running?

I find Smartgauge to be pretty accurate most of the time. I have checked batteries at rest many times using temp. corrected SG based on manufacturers data and my own records. Smartgauge has been out a bit a couple of times but usually ties in to 1-2% of reading predicted from SG.

I also have meters showing amps. in & out plus instant and total Wh/Ah Readings for wind and solar. Smartgauge readings in use follow predictable path based on usage and charging. I'm pretty happy with my setup but not 100%. However, coulomb counters have several inherent problems which prevent accurate indication of SOC. Continual resetting helps but isn't always a complete solution.

I remember finding a detailed paper quoting an equation to calculate SOC based of AC measurements. However, I can't find it just now. I do know that papers have been published wrt Impedance measurements at various frequency bands for battery state of health monitoring. The work mentioned did refer to phase differences but I seem to remember the missing paper had a lot more detail.

 

[sailinglegend420]

...I remember finding a detailed paper quoting an equation to calculate SOC based of AC measurements. However, I can't find it just now.....

I found this posting which is interesting!:

How Smartgauge may work

Just thought I'd make a few comments about the idea of measuring state of charge with only voltage measurements and not current.


On their web site, the SmartGauge people say they use "computer modelling" for calculating SOC. I've done a lot of computer modelling (professionally) so here are some observations. Disclaimer: I am a physicist.


Let's assume the SOC is some unknown function of voltage V, current I and time t. Also throw in battery parameters such as capacity and age, maybe even unknown things. We'll call those BP. Let's assume BP is a slowly varying function of time (they age slowly). And battery temperature is a factor too (also slowly varying).


So, SOC(t) = F(V, I, BP, T, t).


F is a gnarly function, most likely you could not write it down. But it exists.


First observation. The current I is likely to be a function of dV/dt (sorry, this is calculus). Q=CV so I = dQ/dt = dV/dt.C. Of course C may be a function of time but let's assume a slowly varying one (so that dC/dt is negligible). In plain speak, this means we have just eliminated the current I and no longer need to measure it. Magic!!


Then:
SOC(t) = F(V, dV/dt, BP, T, t)


Now, any well behaved function of t can be expanded like this:


SOC(t) = F(t) = A + B.V(t) + C.dV(t)/dt + D.d2V(t)/dt2 + etc., where A, B, C, D, etc are constants. This is just math.


In any computer model, aka simulation, that is based on time, you have to convert continuum physics into discrete computer steps. The longer the time steps (intervals) the more error creeps in. That's likely why SmartGauge measures V at a high frequency - they want to measure dV/dt. In fact, it is highly likely that their model also uses d2V/dt2 and higher derivatives. The higher the derivative, the faster they need the V data.


It's then a relatively simple task for a computer to take a time series of V(t), fit it to the equation and obtain the constants A, B, C, ..... Once you know those constants, the problem is solved, you can convert V(t) into SOC(t). Put in plain English, you can accurately calculate the SOC at time t, if you know the *history* of V.


An important point is that you don't even need to understand the physics of batteries to do this - you can do it by brute force using computers. All you have to believe is that batteries obey reasonable laws of physics.p


Give the little chip in the SmartGauge the right algorithm and a starting point, feed it some voltage data, and Bob's your uncle. My guess is it will make measurements, make a prediction for 30 seconds, check the prediction against reality, adjust the parameters, repeat ad nauseum, "learning" as it goes. This is probably how it adapts to battery aging.