Balmar SG-200 Battery Monitor

[witzgall]

When choosing the data to show on the SG200, we purposely omitted AH remaining, or Ah consumed, and similar counters. This was not a blind decision, there is some reasoning behind this. For instance, in our testing, showing AH remaining can be misleading, often quite so.

One of the great things about the SG200 is that it is firmware upgradable. We knew going into this that we would be making changes/additions based on user feedback.
We could add a history item showing AH used (What period, rolling or until reset???) I am sure there will be others.

Concerning the ability to control other items, we do have our sights on this, there are some really cool ideas we are thinking about.

Chris

[Paul L]

Originally Posted by witzgall

When choosing the data to show on the SG200, we purposely omitted AH remaining, or Ah consumed, and similar counters. This was not a blind decision, there is some reasoning behind this. For instance, in our testing, showing AH remaining can be misleading, often quite so.

....

Chris
AH used over a period is really a fundamental need if you want to understand your onboard electrical usage. The examples I have gave above are real needs if you are going to set your system up well and make appropriate adjustments.
You can have the period reset by the user and also do the standard reset of other monitors when you declare the battery at 100%. If your SOC is as good as promised then the AH count will be more accurate than other vendors.

[a64pilot]

My opinion is AH used since last charge cycle end, or reset if that’s too difficult.
I say difficult as I can see how a charge cycle could end more than once a day, depending on what you used to determine “end”.
For example a large cloud could make it so that Solar is in a deficit, and is that an “end”? Most would say not, cause your charging again when the cloud is gone, but depending on how the software was written, it could be.
So you make it so that you have to be in discharge for an hour, but then you lose the first hours consumption?
So I thought have it be consumption since full charge, but not everyone get there every day?
Just knocking things around, maybe that’s not how it works.


However I think it’s important to know how much power do I use on an average day, and for things like I plug in the Engle, what does it cost in AH, etc.?
Helps in planning, and developing a budget.
It’s tough figuring out a monthly money budget, if your not allowed to see how much you spent.

[ontherocks83]

I would argue for an option where the AH counter can be set to user reset only. With the SG200 giving me all of the other info I would need about the battery, I personally wouldn't really care about having it reset at the end of a charge cycle because I would want to control which time periods I was interested in monitoring. i.e. every 24 hours or overnights etc. without having to worry that it is going to reset in the middle of the day because I turned on the engine.

[rgleason]

I would want to control which time periods I was interested in monitoring. i.e. every 24 hours or overnights etc. without having to worry that it is going to reset in the middle of the day because I turned on the engine.

I think this might be a good way to handle it. Depending on the boat's routine, the auto reset could occur at any user selected time and duration, possibly at times of lower charge, or more traditionally, at times when the the batteries are at max charge.


With enough shunts and sensor channels, all loads and charges could be tracked with history. For some simple systems this would involve tracking
Alternator and House Panel loads, and maybe Solar. Thus the amphours used could be determined from the history.

[Antares Sky]

I saw the new sg200 on display at the Annapolis 2018 sailboat show. They are taking preorders.
I was told that the unit checks the batteries impedance and monitors the impedance for change over time and that is used to determine the state of health, how well it is doing as far as ah capacity goes. They also said that the unit will be programable with a specific logarithm based on your battery manufacture type. Will also work with their add on blue tooth doggle to connect with your smart phone or pad. But it’s an extra. I like the Victron 712 with built in Bluetooth.

Glen

[sailinglegend]

Originally Posted by Paul L

AH counting is not inaccurate……

Originally Posted by a64pilot

……an amp is an amp is an amp, regardless of how many batteries or how old they are……

Yes - an amp is an amp is an amp - but - an Ah is not an Ah is not an Ah in a battery monitor!

This may take some explaining.

An Ah is the current (I) multiplied by the Time T (hrs) - but in a battery monitor the amps x the hours is also multiplied by a constant K which applies corrections due to Peukert’s Formula or Battery Efficiency.

So when discharging the Ah = I x T x K where K is a variable constant which is derived from the complicated exponential Peukert formula, which changes continually depending on the discharge current.

So with a 100Ah battery whose design discharge current is 5 amps - 5A x 20hrs = 100Ah - the constant K will be 1 when 5 amps is being withdrawn, so the value of Ah you see on the meter over 1 hour is the actual Ah withdrawn. If the current being withdrawn was 10 amps then K would have a higher value so the Ah shown at 10 amps after 1 hour would be 12Ah, not 10, so the battery has less Ah available.

And if the discharge current is about 2 amps then the Ah withdrawn would be 1.6 amps not 2 amps - the battery actual has more capacity than the original 100Ah.

So yes everything is working fine and you really are seeing the right Ah displayed - but only at 77F - yes temperature affects this reading, but the battery monitor does not compensate for this - error number 1.

Error number 2 is assuming that the battery monitor has been programmed with the correct Peukert value - the normal default setting is 1.25 for FLA batteries. But AGMs should be set at 1.12, and Lithium almost 1, and because this is an exponential function small changes can make a huge difference.

Error number 3 is when the batteries age and the Peukert values goes higher, maybe to 1.32, but this cannot be measured only guessed. Most users would not programme this change.

Error number 4 is the self-discharge which can be up to about 10% per month which the shunt cannot detect. This can introduce large errors in the Ah count.

That is just the discharge side - so next consider the errors in Ah counting during the charge cycle.

Error 1
An accurate charging Ah count is mainly affected by the “efficiency” of the battery at accepting charge. Wet cells may be only 75% efficient whereas AGMs may be 98%. These figures are given as an overall efficiency, but they change with the state of charge. At 50% SoC the battery efficiency maybe nearly 95% but at 85% SoC the battery efficiency maybe less than 50%.

If a bank is always only discharged to 80% before re-charging then the Ah count you are seeing will be very wrong. I’ve just tested this myself on my new Lifeline AGMs and they were taking about 30Ah overnight but we were putting 60 Ah back in to get to fully charged. I changed the Battery Efficiency to 60% and it counted about 30Ah until it showed fully charged - on both the Smartgauge and the BEP Battery Monitor.

Error 2
There is an effect similar to Peukert's during charging where the Ah returned can also depend on the actual charging current. Chris Gibson who designed Smartgauge says there are 3 separate effects that are impossible to calculate because of the way charging causes the chemicals reactions to take place.

A. The resistance of the battery due to the interface between the plates and the electrolyte.
B. The resistance of the electrolyte itself and......
C. The bulk resistance of the electrolyte due to the bubbles being produced within it .

These effects can be dramatic on the Ah count.

Balmar did say that in their testing, “showing Ah remaining can be misleading, often quite so.“

So this is just the Ah counting error - there is also the problem of the automatic re-set to 100% and the problems of errors caused by initial installations - or subsequent installation errors.

[ayates]

I run the original SmartGauge along with a Victron BMV-702/CCGX. One of the limitations, from my perspective, is the lack of logging capability. The SG-200, with the upcoming NEMA gateway, will solve that issue (with a NEMA logger). It will be very interesting to plot the two state-of-charge curves against each other.





Allan.

[Paul L]

Sailinglegend
None of the errors you listed apply to the examples I gave of using an AH counter. All your errors apply to trying to determine the actual battery state.
How much energy did I use overnight? Simple answer with an AH counter.
How much energy do I burn when sailing offshore, under sail, with my autopilot and chartplotter running during a day? Simple answer with an AH counter.

AH counters with the typical shunt setups are accurate.

[john61ct]

Yes, and a $50 counter will give you all that, including diagnosing specific loads or the contribution of your different sources.

None of which has that much to do with monitoring my bank IMO.

[Paul L]

Originally Posted by john61ct

Yes, and a $50 counter will give you all that, including diagnosing specific loads or the contribution of your different sources.

None of which has that much to do with monitoring my bank IMO.

Primarily because you don't cruise or live on a boat.

There is no reason to add another monitor and another shunt, when one we'll designed one will work fine.

[tanglewood]

This may be heresy, but here goes. For the first 8 years I ran an off grid system I obsessed over SOC and gauges.

Then I realized only two things matter; when the battery is fully charged, and when I need to start the generator.

For the next 10 years I dumped the SOC meter and set a simple gen start when voltage lingers below a certain level for more than a certain time. It works great.

I then extended the approach to our boat. All that really matters is whether I need to start the generator, and I do that totally based on voltage. It’s simple, and very effective.

[ontherocks83]

Originally Posted by Paul L

Primarily because you don't cruise or live on a boat.

[rgleason]

"Upcoming Nmea Gateway???" What do you mean, I don't see anything like that in the specs. I agree plotting the two state of charge curves against each other would be interesting.

The SG-200, with the upcoming NEMA gateway, will solve that issue (with a NEMA logger). It will be very interesting to plot the two state-of-charge curves against each other.

[john61ct]

Post #90, Panbo puff piece