Working with Battery Monitors and Combiners

[ramblinrod]

Every battery monitor operates based on the assumption of a fixed battery capacity.

As soon as we introduce any form of combiner into the picture, (1/2/Both/OFF switch, diode isolator, ACR, or echo charger) we are now varying the battery bank capacity.

While I don't use a Smart Gauge myself, a friend who is pretty tech savvy, claims it gets extremely confused when the ACR connects the start battery to the house bank.

I personally have only one battery bank that operates all loads (starter, inverter, windlass, refrigeration, and everything else and manually monitor battery voltage), but I often wonder how this affects those with monitors on battery banks that are isolated while loading but combined while charging.

So how are you dealing with the influence of the combiner on the battery monitor?

[john61ct]

First of all distinguish between SmartGauge, and all the others that work off a shunt. The latter are counting coulombs, every flow in and out, you have to tell them the capacity (adjusting down over the years) and if wired properly, they keep their normal level of accuracy such as it is.

SmartGauge figures everything out on its own, and if the ACR is only closed while charging, should be no problem.

Rather than just joining the two banks together if the issue concerns you, a one-way device like a B2B may be a solution, the SmartGauge would see that as any other charge source, should also include Echo Charger or a diode isolator (yuck).

I have designed one-big-bank systems where a Starter/Reserve subset gets isolated from House loads when SoC drops low enough, but that presumes that event is a rare exception.

As long as the "normal situation" prevails most of the time, any SG confusion would correct itself pretty quickly.

[Kenomac]

I use the Smartgauge to give me a very gross approximation of my battery status. Most of the time I find the readings to be off by 10%. Would I buy it again knowing what I know today? No.

I don't think it does anything more than showing voltage.

[barnakiel]

You can place shunts so that each measures only one bank. Two shunts, two monitors. Job done.

Cheers,
b.

[john61ct]

Originally Posted by Kenomac

I use the Smartgauge to give me a very gross approximation of my battery status. Most of the time I find the readings to be off by 10%. Would I buy it again knowing what I know today? No.

I don't think it does anything more than showing voltage.

Put it up on eBay, I could always use more of them.

What method of measuring SoC are you benchmarking it against? It should only be that far off during high-amp charging.

Do you think a shunt-based BM is better for you? Might be if it is reset each Full cycle, but that assumes an accurate charge source, or manually using a hydrometer.

[ramblinrod]

Originally Posted by john61ct

First of all distinguish between SmartGauge, and all the others that work off a shunt. The latter are counting coulombs, every flow in and out, you have to tell them the capacity (adjusting down over the years) and if wired properly, they keep their normal level of accuracy such as it is.

SmartGauge figures everything out on its own, and if the ACR is only closed while charging, should be no problem.

Rather than just joining the two banks together if the issue concerns you, a one-way device like a B2B may be a solution, the SmartGauge would see that as any other charge source, should also include Echo Charger or a diode isolator (yuck).

I have designed one-big-bank systems where a Starter/Reserve subset gets isolated from House loads when SoC drops low enough, but that presumes that event is a rare exception.

As long as the "normal situation" prevails most of the time, any SG confusion would correct itself pretty quickly.

Well my friend declares that the Smart Gauge gets very confused whenever the ACR activates.

And it has to mess up a coloumb counter, as that doesn't know which coloumbs are going into the house bank or starter battery, and the calcs are based on the capacity of the house bank only.

[john61ct]

Originally Posted by ramblinrod

And it has to mess up a coloumb counter, as that doesn't know which coloumbs are going into the house bank or starter battery

Only if it's not wired right.

There should be no connection to the bank's negative post "bypassing" the shunt; every coulomb gets counted.

SmartGauge is still more accurate, assuming it is wired properly and permanently to just the one bank, and you wait a bit for things to settle down once charging stops.

Many boats use both types together.

Is this the same friend who told you the "true deep cycling" batteries aren't really any better, the term doesn't matter just because there isn't an objective industry standard for the term?

Or that relatively inexpensive 12V automotive sized batteries last just as long as 2x 6v?

And that even for large banks (even over a 1000AH) 2V 4V or 6V batteries in series had no advantage over a whole lot of paralleled 12V batteries?

Sorry to be snarky, but maybe don't listen to your friend so much, this is relatively easy to test objectively, just try it yourself.

[noelex 77]

Most conventional battery monitors with a shunt will only measure the current going into one battery. The readings will be accurate for this battery even if the batteries are combined. The shunt is at the battery.

The Smart Gauge works differently and combining the batteries will effect the accuracy of the reading.

[ramblinrod]

Originally Posted by john61ct

Only if it's not wired right.

There should be no connection to the bank's negative post "bypassing" the shunt; every coulomb gets counted.

Referring to the wiring instructions of the XANTREX Link Pro, a popular coulomb counter type battery monitor, consistent with those of other manufacture, we see that when wired properly according to instructions, the current that flows into or out of the "auxiliary" battery does not get accounted for.

http://www.xantrex.com/documents/Acc...-01_rev-C).pdf

It will monitor the current flowing into and out of the main bank, and calculate the corresponding state of charge, of the that bank only.

If other batteries for the starter, windlass, thruster, inverter etc, are not connected to the load side of the shunt, that energy is simply not taken into account.

When the main bank and another bank (not connected to shunt load side) are combined, some current from the charging system flows to the other bank(s) which is not accounted for.

So the battery monitor can display what goes in and out of the house bank (as designed) but does not represent what total boat energy is produced or consumed, as some may expect.

If those additional banks are connected to the load side of the shunt, and connected via a combiner (e.g. ACR) for charging, it throws all the calcs off, as the battery capacity is variable.

To accurately monitor the SOC of charge of all batteries in the boat, a separate coulomb counter type monitor is required for each bank that is isolated under load, and connected via any form of combiner during charge.

The Balmar Smart Gauge gets all confused when batteries are combined in all cases, because the voltage sensed changes with every make or break, and it has no way of knowing what is going on. It also gets confused between load, charge, and load and charge simultaneously.

There are pros and cons to every device design, configuration, and implementation. The purpose of this thread is to help promote awareness and discuss possible solutions for accurate battery monitoring when combiners are used.

[ramblinrod]

Originally Posted by barnakiel

You can place shunts so that each measures only one bank. Two shunts, two monitors. Job done.

Cheers,
b.

Correct. (For coulomb counter type monitors.) One monitor per isolated bank to be monitored.

For a boat with many isolated banks, (e.g. split house bank, starter, windlass, thruster, inverter) it could take a lot of monitors to get accurate SOC data for all batteries, and for total Amps in/out one has to manually sum the data from each monitor.

This is why I have elected to go with a single bank for everything.

The voltage displayed by a simple digital meter with two decimal place resolution, (after loading / charging is taken out of the equation) is a pretty good indication of battery state of charge.

[ramblinrod]

Originally Posted by john61ct

Is this the same friend who told you the "true deep cycling" batteries aren't really any better, the term doesn't matter just because there isn't an objective industry standard for the term?

Or that relatively inexpensive 12V automotive sized batteries last just as long as 2x 6v?

And that even for large banks (even over a 1000AH) 2V 4V or 6V batteries in series had no advantage over a whole lot of paralleled 12V batteries?

Sorry to be snarky, but maybe don't listen to your friend so much, this is relatively easy to test objectively, just try it yourself.

Your statements above do not accurately represent my position in any way, on totally unrelated matters.

Lets focus on this subject.

[skipmac]

I don't see any problem with monitoring battery SoC (within the limitations of the monitor).

Set up one large house bank (or two if you like that stay combined except for repair or dealing with a bad battery in one bank) and monitor that bank. With a counter all amps in/out go to that bank.

Have a separate starting battery charged via an automatic combiner and monitor voltage only on that bank.

Smartguage, don't have one so can't comment on how it will react if wire the same way but based on other discussions I would guess it wouldn't be too confused about a start battery paralleled in just for charging.

[ramblinrod]

Originally Posted by skipmac

I don't see any problem with monitoring battery SoC (within the limitations of the monitor).

Set up one large house bank (or two if you like that stay combined except for repair or dealing with a bad battery in one bank) and monitor that bank. With a counter all amps in/out go to that bank.

Have a separate starting battery charged via an automatic combiner and monitor voltage only on that bank.

Smartguage, don't have one so can't comment on how it will react if wire the same way but based on other discussions I would guess it wouldn't be too confused about a start battery paralleled in just for charging.

I agree with most of this.

Normally one wishes to monitor batteries to know what the current state of charge is, and to keep an eye on the health of the bank.

My single bank for "everything" is actually split in two but always combined. (The isolation switch is just for testing / servicing.)

Monitoring this (even by just voltage) lets me know the SOC and health of my batteries.

For a system consisting of a start battery and single house bank, a standard coloumb counter that monitors the house bank and just the voltage of the start battery is often adequate, as the start battery usually only expends / consumes are few A-hrs per day.

But when one adds isolated banks via combiners that can consume some real A-hrs and charge capacity (like inverters, windlasses, thrusters, refrigeration) a single coulomb counting monitor won't really cut it, and a Smart Gauge won't have a clue what is going on when the various banks switch in and out.

[john61ct]

Originally Posted by ramblinrod

It will monitor the current flowing into and out of the main bank, and calculate the corresponding state of charge, of the that bank only.

If other batteries for the starter, windlass, thruster, inverter etc, are not connected to the load side of the shunt, that energy is simply not taken into account.

When the main bank and another bank (not connected to shunt load side) are combined, some current from the charging system flows to the other bank(s) which is not accounted for.

So the battery monitor can display what goes in and out of the house bank (as designed) but does not represent what total boat energy is produced or consumed, as some may expect.

I never heard of anyone expecting a "total boat energy" monitor.

AFAIC only the House bank needs detailed tracking, but I think anyone with a clue knows if you want to shunt-monitor any additional banks each needs their own.

I stand by my previous comments and qualifications about SmartGauge, and that it is the most accurate SoC BM for lead, including in this context.

[ramblinrod]

Originally Posted by john61ct

I never heard of anyone expecting a "total boat energy" monitor.

AFAIC only the House bank needs detailed tracking, but I think anyone with a clue knows if you want to shunt-monitor any additional banks each needs their own.

I stand by my previous comments and qualifications about SmartGauge, and that it is the most accurate SoC BM for lead, including in this context.

I concur that a Smart Gauge may be a useful tool on a system consisting of only one battery bank. As soon as one addes a combiner, it gets fooled, as does any battery monitor, hence the purpose of this thread.

In my estimation, about 10% of boaters who have a battery monitor they did not personally install, understand that it will be fooled by a combiner (that they also may not have a clue even exists).