Smart Battery Monitor?

[BrettB]

I've looked around a bit and haven't come across one yet. Xantrex seems to get me part of the way there, but I am wondering if there are any "smarter" battery monitors available?

Couple of features on my wishlist:

• take into account average power consumption
• take into account average daily power added from solar
• option to view with or without power added
• ability to "tare", to evaluate current/more recent consumption
• rough estimate of remaining power in days+hours, to help with decision to run generator/engine

[boatbod]

Nothing with that specific feature set exists on the market. You could probably write your own though, if you obtained some shunts and a Raspberry Pi and did your own data logging & analysis.

[GILow]

I gave up looking for that kind of functionality and wrote my own as suggested. I used a picaxe chip instead of the raspberry Pi just because I had a couple lying around. Came to about AU$100 in parts and a few nights of stuffing around with the soldering iron. I was lucky that the boat came with a decent battery monitor so the main power bus shunt was already available. Without it there would have been another $50 for the main shunt.


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[smac999]

most give remaining time based on avg comsumption + you solar in.

if you want to know what you solar is doing you'd need a 2nd shunt and meter

and then you just subtract that from net amps shown on meter.

[Delancey]

Smart Gauge Battery Monitoring Unit Photo Gallery by Compass Marine How To at pbase.com

[Dockhead]

You should read up in the archives -- there is a ton of useful information in there.

This is a difficult question, for one important reason -- it is quite difficult to accurately determine the state of charge of lead-acid batteries without taking specific gravity (and even that is not straightforward due to stratification of the electrolyte).

There are different opinions on the best way to do this, but in a couple of words, here is mine:

1. Amp/hour-counting battery monitors (like Victron, Xantrex, etc.) are not practically useful for evaluating state of charge. In fact, they are dangerously misleading, with the large errors which result from this method all in the wrong direction -- misleading you into thinking the battery state of charge is better than it is. They can be made to work better by diligent management and careful interpretation -- but is it worth it? Their main function in my opinion is to give false comfort based on a false impression that you know what's going on with your batteries. The one useful feature of these devices is the ammeter, which is handy to know what is going in or coming out of your batts, but you don't need a $200 gauge for that.

2. SmartGauge doesn't work by counting amp/hours -- it analyzes voltage. It works far better to evaluate state of charge WHEN DISCHARGING WITH NO CHARGING SOURCE ATTACHED.* HOWEVER, you can get the same information from reading voltage from a simple volt meter and interpreting the data yourself. At least if you don't have solar**


So I have a SmartGauge -- and it's handy to just press a button and see the calculated SOC when the bank is being discharged with no charging source attached, and I want to know when I need to start up the generator.

I also have ammeters showing output from my big school bus alternator and input/output to/from my charger/inverter, and a voltmeter attached directly to the batteries with heavy cable (don't forget the fuse). I could live without the SmartGauge.



* We're supposed to evaluate SOC using voltage only when the bank is in "open circuit" condition -- no charging or discharging in the last few hours and no loads or charging sources attached. Obviously not practical at all on a cruising boat being used. What is cool is that if the bank is reasonably large and loads on are reasonably small, the working voltage of the bank will be extremely close to the open circuit voltage and can be used to evaluate SOC. Moreover, any error will be benign -- because loads attached will make the batteries look slightly more discharged than they are. I have tested this against specific gravity and was amazed at how accurate evaluation of SOC this way is. No good if you have any charging source attached, however.


** In another one of these discussions (we've had a few) someone disagreed with me about the uselessness of the SmartGauge compared to a simple volt meter. The claim was that the SmartGauge can take account of solar attached -- IIRC. Whereas your simple volt meter can't. I have no idea whether this is true, or if it is, how it works, but might be worth investigating.

[Tayana42]

Dockhead, I'm always impressed by your comments and not only because of the clearly written style of imparting real information. Your fairness of mind is evident in your inclusion of dissenting opinions.

[sailinglegend]

Originally Posted by Dockhead

You should read up in the archives -- there is a ton of useful information in there......

2. SmartGauge doesn't work by counting amp/hours -- it analyzes voltage. It works far better to evaluate state of charge WHEN DISCHARGING WITH NO CHARGING SOURCE ATTACHED.* HOWEVER, you can get the same information from reading voltage from a simple volt meter and interpreting the data yourself. At least if you don't have solar**......

Smartgauge doesn't just analyse voltage, it does other things with the two wires - but they won't tell us exactly what. The instructions say that you must use 14 gauge wires direct to the battery - which are much bigger than needed just to measure voltage!!!

The designer Chris Gibson has "suggested" - search other threads - that by adding short circuits pulses and high frequency Electrochemical Impedance Spectroscopy he can give a very accurate SOC measurement - even when charging - 10% at all times. When discharging it is probable accurate to 1%. These figures are far better than any shunt based Battery Monitors.

Not many people can't or even want to interpret the voltage readings to estimate a state of charge. These voltage readings change anyway as the battery ages, which is why Smartgauge works so well as it takes 1100 voltage readings a second and is always learning about your batteries and modifying its algorithms.

[boatbod]

If I had to guess, I'd be inclined to think the SmartGauge might be attempting something similar to a modern transconductance battery tester. e.g. Midtronics

[Dockhead]

Originally Posted by Tayana42

Dockhead, I'm always impressed by your comments and not only because of the clearly written style of imparting real information. Your fairness of mind is evident in your inclusion of dissenting opinions.

Very kind, really, thank you.

[Dockhead]

Originally Posted by sailinglegend

Smartgauge doesn't just analyse voltage, it does other things with the two wires - but they won't tell us exactly what. The instructions say that you must use 14 gauge wires direct to the battery - which are much bigger than needed just to measure voltage!!!

The designer Chris Gibson has "suggested" - search other threads - that by adding short circuits pulses and high frequency Electrochemical Impedance Spectroscopy he can give a very accurate SOC measurement - even when charging - 10% at all times. When discharging it is probable accurate to 1%. These figures are far better than any shunt based Battery Monitors.

Well, let's separate marketing hype, speculation, and known facts.

We have heard the hints that SmartGauge uses Impedence Spectrography, but the manufacturers have not revealed how or what. They are inviting us to believe. Perhaps this or some other secret technique allows the SmartGauge to evaluate SOC of the battery bank when a small charging source is attached like solar. Someone has said that SmartGauge works with solar attached, so maybe there is something to it. I can't say because I don't have solar and haven't tested SmartGauge this way.

One thing I can absolutely say, however, based on about a year of using a SmartGauge every day -- is that SmartGauge has practically no idea about the state of charge during charging using a normal battery charger or alternator. It picks a state of charge number seemingly at random and stays at that sometimes for hours before it figures out where you are. No way is that within 10%.

Heavy wiring is needed to ensure accurate voltage readings. I actually used 10 gauge wiring for my SmartGauge; and also for my volt meters. 0.1 volt voltage drop is no problem for a consumer; but it is a big problem for a volt meter.

Originally Posted by sailinglegend

Not many people can't or even want to interpret the voltage readings to estimate a state of charge. These voltage readings change anyway as the battery ages, which is why Smartgauge works so well as it takes 1100 voltage readings a second and is always learning about your batteries and modifying its algorithms.

Voltage vs. SOC don't change during the life of a battery -- but capacity does.

The fact that SmartGauge "takes 1100 voltage readings a second and is always learning" blah blah blah may or not be meaningful at all. It sounds good, but since the maker does not reveal how the device works, we can only have faith (or not) that it's doing something super duper.


But I do agree with you that many people don't want to be bothered by looking at a table, and want to have an instant readout with the results. For this SmartGauge is perfect for this, and worlds better than amp counting meters. I have done a lot of testing against SG readings, and both SmartGauge and voltage readings with light loads attached (but in both cases, no charging for long enough for surface charge to be off) give SOC readings within 1%. What we really care about is knowing WHEN TO CHARGE, and for this both SmartGauge and voltage readings work perfectly.

[conachair]

Originally Posted by Dockhead

Heavy wiring is needed to ensure accurate voltage readings. I actually used 10 gauge wiring for my SmartGauge; and also for my volt meters. 0.1 volt voltage drop is no problem for a consumer; but it is a big problem for a volt meter.

Little Fred Rift but,
Afraid you're off the track a bit there...
The smartgauge might do some wierd stuff but voltmeters shouldn't need heavy wire to get accurate readings unless you have the world's worst voltmeter( and I'm sure that's not the case ) . The input impedance should be many Megohms, next to no current being drawn so any voltage drop even on long runs of very skinny wire is insignificant and likely way below the capability of the meter to even register.

[Dockhead]

Originally Posted by conachair

Little Fred Rift but,
Afraid you're off the track a bit there...
The smartgauge might do some wierd stuff but voltmeters shouldn't need heavy wire to get accurate readings unless you have the world's worst voltmeter( and I'm sure that's not the case ) . The input impedance should be many Megohms, next to no current being drawn so any voltage drop even on long runs of very skinny wire is insignificant and likely way below the capability of the meter to even register.

That sounds pretty convincing, actually.

However, for whatever reason, or possibly incorrectly, I HAVE read somewhere that for accurate voltage measurements over long cable runs, you need heavier cabling.

[sailinglegend]

Originally Posted by Dockhead

Well, let's separate marketing hype, speculation, and known facts......

I have been giving you facts direct from the owner of the Smartgauge brand who I know very well - Jason Hortop MD of Merlin Equipment.

Originally Posted by Dockhead

......SmartGauge has practically no idea about the state of charge during charging using a normal battery charger or alternator. It picks a state of charge number seemingly at random and stays at that sometimes for hours before it figures out where you are. No way is that within 10%.....

The I suspect that your Smartgauge is not installed correctly - it must be directly to the battery terminals, positive on one end of the bank and negative on the other end the bank, and the negative must not be on the load side of any battery monitor shunt if you have that as well - like I do.

Originally Posted by Dockhead

Heavy wiring is needed to ensure accurate voltage readings.

This is incorrect - as pointed out by another poster - but Smartgauge does more than just read voltage which is why you do need a heavier gauge wire. Please read the Smartgauge manual.[/QUOTE]

Originally Posted by Dockhead

Voltage vs. SOC don't change during the life of a battery.....

This is also incorrect see this link:

Battery State of Charge Determination

One quote from here on Voltage Vs SOC tables:

Estimation Accuracy of SOC Estimates Based on Look Up Tables

"Manufacturer's claims of SOC accuracy of better than 5% are typical but this seems hard to justify considering the factors outlined here and errors may diverge even more as the cells grow older."

Also see the Lifeline AGM manual :

Under SOC % Vs OCV Tables page 28:

"The voltages are approximate and give an indication of a battery at rest. As the battery ages these voltage measurements will be lower."

One final fact - The M1 Abrahams tank has just had major upgrades to its battery monitoring equipment by Merlin (US) based on the Smartgauge technology, which is now 10 years old.

[Dockhead]

Originally Posted by sailinglegend

I have been giving you facts direct from the owner of the Smartgauge brand who I know very well - Jason Hortop MD of Merlin Equipment.


The I suspect that your Smartgauge is not installed correctly - it must be directly to the battery terminals, positive on one end of the bank and negative on the other end the bank, and the negative must not be on the load side of any battery monitor shunt if you have that as well - like I do.


This is incorrect - as pointed out by another poster - but Smartgauge does more than just read voltage which is why you do need a heavier gauge wire. Please read the Smartgauge manual.

This is also incorrect see this link:

Battery State of Charge Determination

One quote from here on Voltage Vs SOC tables:

Estimation Accuracy of SOC Estimates Based on Look Up Tables

"Manufacturer's claims of SOC accuracy of better than 5% are typical but this seems hard to justify considering the factors outlined here and errors may diverge even more as the cells grow older."

Also see the Lifeline AGM manual :

Under SOC % Vs OCV Tables page 28:

"The voltages are approximate and give an indication of a battery at rest. As the battery ages these voltage measurements will be lower."

One final fact - The M1 Abrahams tank has just had major upgrades to its battery monitoring equipment by Merlin (US) based on the Smartgauge technology, which is now 10 years old.[/QUOTE]

The facts are very few and the hype is very much. Why doesn't the maker explain how the thing is supposed to work, rather than inviting us to speculate, and blindly believe, just on the basis that fat wires are used, so there JUST MUST be some sophisticated process going on?

Why don't you invite the inventor to come on here and explain exactly how the device works, and to answer questions about what it can and cannot do, and how best to use it? Many makers of marine equipment do so on here, and it can be a great way to reach the customer base. Can also be very interesting and educational for us.

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