Battery Monitor Reviews Wanted

[secrabtree]

Also, I wish to thank all of you that have posted replies to my question and other pertinent information. It is very obvious that there is quite a body of knowledge out there, and quite a few others that have interests similar to mine. And, it is also obvious to me that very valid opinions vary between knowledgeable people, that their opinions agree just about as much as anchor opinions agree when a bunch of cruisers get together.

[goboatingnow]

Originally Posted by secrabtree

From my reading of the SmartGuage info it appears that the definition of state of charge is the ratio between the amount of charge (energy?) in the battery compared with the amount of charge (energy?) that the battery could hold. This is an interesting number to me, but only out of curiosity. What I would like to know is the amount of energy that the battery holds and that is a completely different number than the ratio between what exists and what is possible. I haven't yet found any instrument that can instantaneously tell that. Battery voltage while at rest gives a fair indication, but that isn't perfect. The "percent of charge" reading of an Amp hour counter may not be an accurate reading of the percentage of charge, but it seems just as accurate of an indication of the amount of energy still available as a true "state of charge" meter like the SmartGuage. A new 100Ahr battery has a certain amount of available energy. At an SOC of 75% it has about 50%, realistically, of the original available energy. But as it gets older and, let's say, realistically has the capacity of a 50Ahr battery at a 100% SOC it will only have the same available energy as a new 100Ahr battery at 75% SOC. So SOC is a meaningless number unless one knows what the available amount of energy is when the SOC = 100%. And if one knows that then an Amp-hour counter will be perfectly fine.

In my case I would mainly use the Amps function (not on the SmartGuage) to help determin when to run the watermaker and/or refrigerator, the largest consumers of electricity on my boat. Negative charge and I must turn off one or both. The "Amp Hours Remaining" function I use only as an indication of when I must be careful and miserly about cabin lights and other discretionary uses of power. I have 210Ahr of battery capacity so I never want to use more than 105Ahr, and, to play safe, I try to keep it under 75Ahr. And, realistically, with my 6 solar panels I rarely get that low.
Now you know my reasoning behind my selection of an Ahr counter rather than a SmartGuage.
I have selected the TriMetric45 mainly on the recommendation of the Morningstar technition and not hearing anything bad about it. (Although Morningstar makde my TriStar 45 controller, and the similarity of the TriStar and TriMetric names, Morningstar does not make the TriMetric, Bogart Engineering does.
I guess my question has been answered about as well as it ever will be.

This isnt correct, Smartgauge provides you with a fuel gauge, just like almost all battery monitors do. In that respect you use it just like to would use the situation you described above. Since Smartgauge isnt a columb counter, it obviously cant report the consumption of loads

dave

[colemj]

All of my computers tell me SOC, time remaining to charge, time remaining in battery under different load conditions and total capacity of battery along with %capacity from new - even as the battery ages.

And it all seems VERY accurate and never needing resetting, no matter the load on the computer or condition of the battery.

How is this being done? Or is it more a matter of the different battery chemistry allowing simpler monitoring systems?

Mark

[Paul Elliott]

Originally Posted by goboatingnow

There is a documented, understandable relationship between battery voltage and SOC, even in dynamic situations, ie , where the discharge rate changes and there is a switching between discharge and recharge cycles.

The terminal voltage is an indication of discharge current, its just that deriving SOC from that isnt straightforward.

SmartGauge from what I can see, uses an iterative approach, building discharge maps to refine the underlying algorithm

dave

I just don't see where this approach (as I think I understand it) can tell the difference between (say) a lightly-loaded battery at 50% SOC vs a heavily-loaded battery at 80% SOC. (these numbers pulled out of the air for discussion purposes). With steady current drain there is no way to tell the difference by just measuring the terminal voltage.

I suppose if the device were seeing voltage variations, and knew the nominal battery capacity, it might be able to reach some conclusions. But without knowing the magnitude of the current transients that were causing these voltage variations I still think any conclusions would be fairly inaccurate.

Of course we haven't even touched on the effects of ambient and battery temperature in all this.

For my AGM bank I have a Link 2000R monitor/controller. It's way out of calibration, and even in the slip with no house load (except for the monitor), and with my solar panels giving it a trickle charge, the monitor shows the fully-charged bank slowly losing Ah over the course of days and weeks. I end up checking the battery voltage and resetting it from time to time. The monitor is still useful for keeping track of voltage and current, and the Ah display is good for short-term trends, but when at sea I essentially ignore it and monitor the voltage and current, noting the numbers in my logbook.

By the way, once every two years or so I do a 24-hour (or 48-hour) load test on my batteries. I turn on lights, electronics, and other stuff that will present a relatively steady load, and monitor the battery voltage and current during the test. My lightly-used AGM bank is 12 years old and is still holding up well.

[Paul Elliott]

Originally Posted by colemj

All of my computers tell me SOC, time remaining to charge, time remaining in battery under different load conditions and total capacity of battery along with %capacity from new - even as the battery ages.

And it all seems VERY accurate and never needing resetting, no matter the load on the computer or condition of the battery.

How is this being done? Or is it more a matter of the different battery chemistry allowing simpler monitoring systems?

Mark

It's the battery chemistry. Lithium, and certain other types, show much less voltage variation under load, and so a simple voltage measurement is a good indicator. However, I've had computers with marginal batteries (old or abused) where the SOC indication was pure fiction.

[Therapy]

Originally Posted by Paul Elliott

For my AGM bank I have a Link 2000R monitor/controller. It's way out of calibration, and even in the slip with no house load (except for the monitor), and with my solar panels giving it a trickle charge, the monitor shows the fully-charged bank slowly losing Ah over the course of days and weeks. I end up checking the battery voltage and resetting it from time to time. The monitor is still useful for keeping track of voltage and current, and the Ah display is good for short-term trends, but when at sea I essentially ignore it and monitor the voltage and current, noting the numbers in my logbook.

.

That was what happened to mine. You explained it better.

Which means to me that something is not set correctly.

And like MainSail said about you gotta know more than the monitor......

Loved those AGMs though.

[Maine Sail]

Originally Posted by colemj

All of my computers tell me SOC, time remaining to charge, time remaining in battery under different load conditions and total capacity of battery along with %capacity from new - even as the battery ages.

And it all seems VERY accurate and never needing resetting, no matter the load on the computer or condition of the battery.

How is this being done? Or is it more a matter of the different battery chemistry allowing simpler monitoring systems?

Mark

My MacBook Pro has been telling me I am at 0% for the last 20 minutes and it is still going......

No where is that darn wall wort.....