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Old 26-07-2016, 03:09   #1
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SmartGauge -- Real Life Experience

I've been using this device for several months of continuous cruising now.

I am still convinced that amp-counting battery monitors are practically useless (I removed, then finally sold my Victron one). That's not to say that they are not capable of giving any useful information at all, but by the time you keep them in proper calibration and interpret them properly you will have expended a lot more effort to get a lot less precise information, than you can get by other means.

The SmartGauge is widely praised as a superior approach to battery monitoring, and is used by military and commercial operations, has been thoroughly tested by different people including our own MaineSail, all with the results that this device gives a much better picture of the state of your batteries.

This all may be true, HOWEVER -- my experience has been that I am getting practically zero information from the SmartGauge, which I was not getting from simply monitoring system voltage and referring to a simple table taken from the Trojan Batteries site.

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I used system voltage plus the table for several years, and checked the accuracy several times by taking specific gravity measurements.

My method for using system voltage is very simple -- you don't try to do Open Circuit Voltage, after resting the batteries for 12 hours etc., which is the technically correct way to do it. That's because this is completely impractical on a cruising boat which is in actual use. What I do is to read system voltage when there are no big loads on, and no charging has taken place for some time. The idea is that small loads will not pull down the voltage that much, AND any error will understate the battery state of charge, which is a harmless error. I decided that this would work ok because I don't actually need more precision than 10% or so.

Specific gravity tests showed that the method is actually far more accurate than that -- more like 2% or 3%.

I was delighted with this, as it was far simpler than interpreting an amp-counting meter, and required nothing more than a cheap voltmeter (but carefully wired directly to the batts with large cross section cables).

The only problem was that this method cannot tell you how much charging you have accomplished, during a charging run. If you charge for a while on generator and stop before the charger goes into float mode, you just don't know how far you got until some hours later when the surface charge is off the batts.

So I thought the Smart Gauge might be the answer to this. I bought one last year and finally got around to installing it over the winter.

Well, the Smart Gauge is not an answer to this. It does attempt to estimate how far you have gotten during a partial charging run, but it is wildly inaccurate. It settles down and gives you a true reading only -- hah, after several hours, after the surface charge is off the batts.

So in summary -- it's a good device, undoubtedly more useful and far more accurate than amp-counting gauges, but I have not discovered any way in which it is significantly better than simply monitoring system voltage.


Now I am sure that this can be overcome with further development. Voltage rises throughout the absorption bulk phase. This must correspond to state of charge achieved. A really accurate picture could surely be achieved by mapping charging current vs voltage -- no? Then the device could time the absorption phase and estimate the state of charge achieved per minute of absorption charging by "learning". So maybe SmartGauge v2.0 could have a Hall-effect ammeter to measure charging current, and could use this data to calculate state of charge achieved during charging.


Of course it may be that we don't actually need that much information. The main thing we need to know is when to charge. We probably don't need to know that with very great accuracy. But we would not want an error on the wrong side -- where we have an exaggerated idea of the state of charge of the batts, so we charge too late, because we were not informed about how deeply discharged the batts had become.

So for this, actually, simple voltage monitoring fits the bill exactly. The state of charge can be understated if you read the voltage with too much load on, but CANNOT be exaggerated. And it's actually remarkably accurate, about 2% to 3% according to my tests.

I still have my old table from Trojan, on my instrument panel. It's amusing to see that the battery state of charge read from this table, always corresponds EXACTLY to what the SmartGauge is telling me.
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Old 26-07-2016, 03:18   #2
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Re: SmartGauge -- Real Life Experience

Seems the moral of the story is: Stop obsessing about your batteries.
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Old 26-07-2016, 03:27   #3
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Re: SmartGauge -- Real Life Experience

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Seems the moral of the story is: Stop obsessing about your batteries.
Probably right.

The main job is not to wait too long before charging your batteries, so you need to know that. Everything else is much less important.


One piece of really useful information which you get from amp-counting meters, which you don't get from Smart Gauge, is amps of load on. I don't think the cumulative amp/hour measurement is worth much (I think amp/hour counting in both directions is essentially futile), but it really is useful to know what the overall system load is at any given moment.

That being said, I've been living without that information for about 4 years by now, and it's not actually a big deal.
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Old 26-07-2016, 04:25   #4
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Re: SmartGauge -- Real Life Experience

I have and still like my battery monitor. Not for the SOC, but for the amps in/out and AH out. This combined the data that my Outback solar controller records I feel tell me the story. I know from years of watching the two that the battery voltage slowly increases as the AH out decreases and that it gets to 0 right about the same time as the voltage gets to 14.6. I have my solar controller absorption set to 14.6 and to hold it for 4 hours (normally run of of light before that).

So for me when I get to the boat normally on Friday night checking the solar controller log tells me the daily AH supplied and how long they were in absorption. If absorption got held an hour or so I feel pretty sure I got fully recharged.
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Old 26-07-2016, 04:37   #5
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Re: SmartGauge -- Real Life Experience

Mine acts a little funny, what it will do is awfully quickly drop to 97% maybe it's 93%, not sure, it seems accurate though on the discharge after several hours, I just don't understand the fast drop.
What it seems to be best for though is that it shows that all three of my charge sources, they all drop into float prematurely.
Recycling them puts them back into absorb and I usually have to do that a couple of times to get to full charge.
But I'd say once you know your batteries, know when they are full by knowing what the draw is on them and when the charge rate drops to the correct level, you don't really need the Smart gauge.



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Old 26-07-2016, 06:58   #6
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Re: SmartGauge -- Real Life Experience

After I saw MaineSail's appraisal about the SmartGauge it has been on my to buy list. But IMHO it should also feature the amps (or whatevertheyrecalledlol) in and out and as it does not, I think I would like to have both the SG and a traditional counter. I like to know how much I've used or charged. Especially as I don't have a huge bank nor a generator.
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Old 26-07-2016, 07:09   #7
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Re: SmartGauge -- Real Life Experience

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After I saw MaineSail's appraisal about the SmartGauge it has been on my to buy list. But IMHO it should also feature the amps (or whatevertheyrecalledlol) in and out and as it does not, I think I would like to have both the SG and a traditional counter. I like to know how much I've used or charged. Especially as I don't have a huge bank nor a generator.
It's a good idea, and I would definitely do this myself except I don't have any way of wiring the shunt for a normal amp counting meter, after rewiring my banks.

I think it would be pretty easy to understand the relationship between amp/hours put into the bank, and change in the state of charge -- won't be linear but should be highly predictable.

I hope that Merlin will come out with a version of the Smart Gauge which will do this.
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Old 26-07-2016, 07:55   #8
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Re: SmartGauge -- Real Life Experience

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I still have my old table from Trojan, on my instrument panel. It's amusing to see that the battery state of charge read from this table, always corresponds EXACTLY to what the SmartGauge is telling me.
I wanted to ask about this Voltage interpretation, do you reckon the SmartGauge is doing nothing more but reading the Voltage and then displaying that as SOC?
I'm not saying you imply that but it would make the SmartGauge a bit less smart.. hehe
Also, I do recall MaineSail wondering how the SG can do its thing.
I suppose I am trying to figure out if the SG really is smart. or not..
Cheers
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Old 26-07-2016, 07:57   #9
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Re: SmartGauge -- Real Life Experience

Dockhead you can find DC current transducers with a hall effect rather then a shunt pickup. I know CR magnetics and NK make them. May not have a large enough window for the wire depending on you battery cable size thou. Might be worth investigating.
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Old 26-07-2016, 08:07   #10
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Re: SmartGauge -- Real Life Experience

Seems like a lot of trouble for dubious gain. You sized your bank for the load and you know what you need to run at any given time. If the bank powers it for an acceptable period of time before an unacceptable voltage drop occurs, your in good shape. If not then it's time for new batteries or a different bank configuration. Batteries should serve you, not you serve them.
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Old 26-07-2016, 08:19   #11
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Re: SmartGauge -- Real Life Experience

Quote:
Originally Posted by ErikFinn View Post
I wanted to ask about this Voltage interpretation, do you reckon the SmartGauge is doing nothing more but reading the Voltage and then displaying that as SOC?
I'm not saying you imply that but it would make the SmartGauge a bit less smart.. hehe
Also, I do recall MaineSail wondering how the SG can do its thing.
I suppose I am trying to figure out if the SG really is smart. or not..
Cheers
SmartGauge is supposed to interpret voltage and supposedly changes in voltage according to some algorithm.

I'm sure that's what it does, but it mostly seems to just track system voltage.

It does a dreadful job with partial charges. For example, I'm sitting here at my nav table right now, having stopped a partial generator run more than four hours ago. I've had the inverter on and have been using quite a bit of gear, have made coffee, etc., but the SmartGauge has been reading 66% without change for the whole time.

I think that it's waiting to be convinced that the surface charge is off, and probably its algorithm is telling it that it won't consider the system voltage until that falls to about 24.6 volts, which corresponds to where the SmartGauge thinks we got with the partial generator run. Bleh. The problem with that is that the SmartGauge cannot determine the results of a partial charge.

System voltage is now 24.9 and I'm smarter than the SmartGauge it seems -- I know that the surface charge is off, so I know that right now I have just under 80%.

Again to put all that into perspective -- several people have said -- don't serve your batteries, or don't obsess about them, etc. They are right -- we don't need extremely precise information, mostly we just need to know when to charge. So the Smart Gauge is doing a great job at that -- it is now understating the SOC because it's still not sure about how far we charged last time, and it will pick up tracking SOC when we get down to where it thought we were, which means we will definitely find out when we need to charge, even if we don't know very well where we are now.
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Old 26-07-2016, 08:21   #12
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Re: SmartGauge -- Real Life Experience

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Dockhead you can find DC current transducers with a hall effect rather then a shunt pickup. I know CR magnetics and NK make them. May not have a large enough window for the wire depending on you battery cable size thou. Might be worth investigating.
The problem is not installing the shunts (although that is a minor PITA). The problem is I don't have a single cable through which all the DC power passes, and can't create one without creating a long detour which would be harmful to system performance.

What I really need is an ammeter, or even better a counting ammeter, which can AGGREGATE the data from two different shunts or hall effect sensors.

I have never been able to find such a device. If someone has any hints, I would be very interested.
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Old 26-07-2016, 08:39   #13
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Re: SmartGauge -- Real Life Experience

I looked at the Smart Gauge but finally decided to fit a NASA battery monitor - principally because it enables me to check at any time the draw of various items of equipment on the boat.

It also provides an (admittedly rough) indication of state of charge, which together with system voltage tells me all I need to know.

What the Smart Gauge doesn't do is tell you when something is drawing more amps than it should (e.g. water-cooled fridge pump filter clogged), which is more important IMHO than knowing exactly where you stand between 100 per cent and 60 per cent state of charge.

Anyway, chacun à son goût as we used to say before Geoffrey Chaucer came along.

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Old 26-07-2016, 08:58   #14
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Re: SmartGauge -- Real Life Experience

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I looked at the Smart Gauge but finally decided to fit a NASA battery monitor - principally because it enables me to check at any time the draw of various items of equipment on the boat.

It also provides an (admittedly rough) indication of state of charge, which together with system voltage tells me all I need to know.

What the Smart Gauge doesn't do is tell you when something is drawing more amps than it should (e.g. water-cooled fridge pump filter clogged), which is more important IMHO than knowing exactly where you stand between 100 per cent and 60 per cent state of charge.

Anyway, chacun à son goût as we used to say before Geoffrey Chaucer came along.

GORDON KNIGHT

Knowing what I know now --

I think this is maybe the optimum approach.

I'm not getting more information from the Smart Gauge than I can get from watching voltage.

I might really prefer to have my old Victron meter -- if I could wire it (which I can't).

THEN, I would absolutely ignore the useless state of charge display --- I would measure state of charge by watching system voltage. But I would pay attention to the amps and amp/hours measured by the Victron, for exactly the reasons you state.
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Old 26-07-2016, 08:58   #15
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Re: SmartGauge -- Real Life Experience

One issue with it just interpreting voltage to a SOC is it doesn't know battery chemistry, and that does change the voltage / SOC doesn't it?

At least I don't remember telling it battery chemistry, just remember hooking up three wires and that was it.
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