SmartGauge -- Real Life Experience

[Timd_chapman]

I've been running a Smart gauge for 5 years now. I think it is pretty accurate but only when discharging, not when charging, to be fair they own up to this in the literature. It's the easiest way to get an instant indication of where you batteries are. Voltage also gives you an indication but there is an additional factor of determining whether there is a heavy charge or discharge distorting the voltage reading. Who knows whether it really 'learns or not! We know that the final 5% of charge takes a lot to achieve and the SmartGauge seems to reflect that; I can regularly get it up to 95% but only a long motor or a number of hours of shore power will get it to 100%. I have a Victron gauge to show me current flow but the SmartGauge is the easiest at a glance meter for battery state of charge, especially when the missus has to decide whether to use the electric kettle or the gas one!
As others have mentioned, no need to stress to much about this.


Sent from my iPad using Cruisers Sailing Forum

[Dockhead]

Originally Posted by Maine Sail

. . .

Voltage is still tough though and you will need to do the homework on your own bank.

Here is an experiment I ran a while ago based on a customers Voltage to SOC chart..

Loaded Battery Voltage vs. SOC

This is very interesting, but I have to disagree with this:

"Voltage can can be used as a predictor of SOC but you really need to know the voltage performance of your battery bank against a known discharge rate and it takes work to figure out and then it will change on you as the batteries age.

This is why generic *OCV to SOC charts rarely help the average boater and often serve to actually help prematurely damage the batteries."

How could using open circuit voltages to decide when to charge, prematurely damage your batteries? Even if you don't know the voltage dip from a given load, if you charge at the point when you would need to charge, if you had an open circuit condition, you cannot make a mistake. The error is all in charging earlier, which is easier on your batteries. So this phrase cannot be true.

I typically start charging when I see 24.5v under light loads, corresponding to open circuit voltage for a bit over 60%. Worst case is 24.1v -- that is my "red line" for charging, no matter what. The real state of charge at 24.5v will be more than 60% since I am measuring voltage with load on (or more than 50%, for the other case).

The difference is very small, within a few percent -- I checked by measuring specific gravity.

And now that I have a SmartGauge -- this method also lines up extremely closely to what the Smart Gauge tells me. In fact, it is mostly dead on, at most the Smart Gauge tells me I have 1% or 2% more charge, than voltage tells me, referring to the open circuit voltage chart.

This works very well on my boat with a relatively large bank of open lead acid batteries -- 420 amp/hours @ 24v. With a load on of only a few amps, there is very little voltage sag, so the state of charge lines up very well with the open circuit voltage chart. But any error, even on boats with smaller banks and bigger loads, will be on the conservative side -- understating the actual state of charge. So you cannot possibly hurt your batteries by using an open circuit voltage chart. There is simply no way for it to overstate your state of charge and lead you to wait too long to charge.

[a64pilot]

My pro charge ultra does a decent job, trips into float at about 93% or so percent SOC, turning it off then back on puts it back into absorption for quite awhile, cycling twice gets me to 100% or very close. Last few percent of course takes awhile, my understanding is there is some sort of algorithm, more to it than just a timer.
My Magnum can be set to stay in absorption until either time, or when a set number of amps is reached, this one will get me to 100% SOC without any games, you just have to know your other loads and calculate them in, and they have to be steady of course, fridge cycle off, and you go into float early, so I still have to watch.
Interestingly my Smart Gauge seems to be spot on with charging, meaning I hit .5% or 3.3 amps right at about the time it says I'm at 100% SOC.
Now admittedly I don't know actual bank capacity, I am going off of rated capacity and I am sure it's not that anymore, but still even if I have lost 10%, that only lowers my full charge acceptance rate from 3.3 amps to 2.97 amps, I can live with that.

One thing that concerns me though is, how good are the lifelines at recombining the gasses back into water? If I'm overcharging a little, will that kill them? Or is it better to overcharge a little that it is to chronically undercharge, even if its only say 10% or so?

[Maine Sail]

Originally Posted by Dockhead

This is very interesting, but I have to disagree with this:

"Voltage can can be used as a predictor of SOC but you really need to know the voltage performance of your battery bank against a known discharge rate and it takes work to figure out and then it will change on you as the batteries age.

This is why generic *OCV to SOC charts rarely help the average boater and often serve to actually help prematurely damage the batteries."

How could using open circuit voltages to decide when to charge, prematurely damage your batteries? Even if you don't know the voltage dip from a given load, if you charge at the point when you would need to charge, if you had an open circuit condition, you cannot make a mistake. The error is all in charging earlier, which is easier on your batteries. So this phrase cannot be true.



The difference is very small, within a few percent -- I checked by measuring specific gravity.

And now that I have a SmartGauge -- this method also lines up extremely closely to what the Smart Gauge tells me. In fact, it is mostly dead on, at most the Smart Gauge tells me I have 1% or 2% more charge, than voltage tells me, referring to the open circuit voltage chart.

This works very well on my boat with a relatively large bank of open lead acid batteries -- 420 amp/hours @ 24v. With a load on of only a few amps, there is very little voltage sag, so the state of charge lines up very well with the open circuit voltage chart. But any error, even on boats with smaller banks and bigger loads, will be on the conservative side -- understating the actual state of charge. So you cannot possibly hurt your batteries by using an open circuit voltage chart. There is simply no way for it to overstate your state of charge and lead you to wait too long to charge.

You don't have a "generic" voltage chart you have the chart for your batteries.. Big difference...


Read the last part of that article, page two, and you'll see how in this application the generic voltage chart was entirely misleading for this customer who was using it as "resting OCV". In reality the chart my customer found was actually much closer to a 20 hour discharge rate while loaded...

I see this with frequent regularity.

FWIW Lifeline does not provide a complete voltage to SOC chart like Trojan does, they just hit a few points along the way such as 100%, 75% & 50% so this customer went to the net and found one, an incorrect one, for his bank...... You also can't open AGM batteries and take an SG measurement to confirm voltage readings....

Originally Posted by Dockhead

I typically start charging when I see 24.5v under light loads, corresponding to open circuit voltage for a bit over 60%. Worst case is 24.1v -- that is my "red line" for charging, no matter what. The real state of charge at 24.5v will be more than 60% since I am measuring voltage with load on (or more than 50%, for the other case).

This is about 12.25V under load and a very good place to start charging, under light loading. The loaded voltage, with an accurate volt meter, under typical light house loading will not be too far off resting.

Even under a 20 hour discharge rate of 5.25A, for a 105Ah rated battery, much higher than the average discharge rate on a cruising boat, the 49.3% SOC threshold for Ah capacity was crossed, under load, at 12.10V.

After the battery rested for 16 hours, at approx 75F, the voltage had rebounded to 12.32V. Based on my customers chart, which he understood as "resting voltage", he would have assumed he was at 70% SOC when in reality he had already removed 50.7% of the Ah capacity. Due to that generic voltage chart, and his misunderstanding of it, he was routinely over discharging his bank based on resting voltage..

As I have said many, many times you CAN use voltage but you really need to figure out what it means for your bank.

[S/V Alchemy]

Originally Posted by Maine Sail

You also can't open AGM batteries and take an SG measurement to confirm voltage readings....

I think AGMs are great for boats sailed off moorings on weekends. I think they are fab if the only place you can put the bank you need is by putting the batteries on their sides in odd corners. But taking an SG measurement manually is so much more factual than an extrapolation from an algorithm in my view. I'm lucky enough to have full access and in a place where the CG of the boat is very close. This influenced my decision to stay with "traditional" liquid batteries.


(By the way, Maine Sail, I followed your instructions on cable length and crimping implicitly.)

[Dockhead]

Originally Posted by Maine Sail

You don't have a "generic" voltage chart you have the chart for your batteries.. Big difference...


Read the last part of that article, page two, and you'll see how in this application the generic voltage chart was entirely misleading for this customer who was using it as "resting OCV". In reality the chart my customer found was actually much closer to a 20 hour discharge rate while loaded...

I see this with frequent regularity.

FWIW Lifeline does not provide a complete voltage to SOC chart like Trojan does, they just hit a few points along the way such as 100%, 75% & 50% so this customer went to the net and found one, an incorrect one, for his bank...... You also can't open AGM batteries and take an SG measurement to confirm voltage readings....



This is about 12.25V under load and a very good place to start charging, under light loading. The loaded voltage, with an accurate volt meter, under typical light house loading will not be too far off resting.

Even under a 20 hour discharge rate of 5.25A, for a 105Ah rated battery, much higher than the average discharge rate on a cruising boat, the 49.3% SOC threshold for Ah capacity was crossed, under load, at 12.10V.

After the battery rested for 16 hours, at approx 75F, the voltage had rebounded to 12.32V. Based on my customers chart, which he understood as "resting voltage", he would have assumed he was at 70% SOC when in reality he had already removed 50.7% of the Ah capacity. Due to that generic voltage chart, and his misunderstanding of it, he was routinely over discharging his bank based on resting voltage..

As I have said many, many times you CAN use voltage but you really need to figure out what it means for your bank.

OK, now I think it's clear -- you had a client reading not an OC voltage chart, but some kind of LOADED voltage chart, and figuring his SOC from that. Wow, that's crazy. I can sure imagine how fast he killed his batts doing that. I didn't get that from your article, but now that you describe it like this, it makes sense.


What you say about the voltage of a lightly loaded bank being very close to OC voltage corresponds to my experience.

So I will say again my thesis --

* You don't need to be an electrical engineer, to use voltage to know when to charge.

* All you need is the open circuit voltage chart for your batteries, and an accurate voltmeter wired directly to your batteries with reasonably thick cables.

* If you assume that the voltage you see when the bank is lightly loaded (all heavy loads off, and no heavy loads nor any charging done recently) is the same as OC voltage, and read the chart, you will get a very accurate picture of your state of charge. Any error (the deviation will be bigger, the smaller the bank, and the bigger the loads) will be harmless, as any error will slightly understate, rather than overstate, your state of charge.

* Even if you have bigger loads on, so you know the deviation between observed system voltage and open circuit voltage is bigger, the system voltage cannot mislead you, into thinking you don't need to charge, if you really do. The system voltage read against the open circuit voltage chart gives you the worst case scenario, for your state of charge.

[a64pilot]

I don't think I have ever discharged my bank below 75%, unless your in a circumstance where you can't charge for whatever reason, why take it below what it gets to overnight?
The less you discharge a bank before charging it back up, increases its life rather dramatically, why pull it down to 50%?
https://voyagesofagape.files.wordpre...lifecycles.jpg

50% discharge gets me 1000 cycles, 25% discharge 2000 cycles

[Dockhead]

Originally Posted by a64pilot

I don't think I have ever discharged my bank below 75%, unless your in a circumstance where you can't charge for whatever reason, why take it below what it gets to overnight?
The less you discharge a bank before charging it back up, increases its life rather dramatically, why pull it down to 50%?
https://voyagesofagape.files.wordpre...lifecycles.jpg

It depends on your needs, and circumstances.

You don't want to run the generator too often -- that's inefficient, wears it out, and uses extra fuel. Your generator wants long hard runs from a bank discharged as deeply as possible.

Also -- charging from 70% or 75% is very inefficient, because your practical top range is 85% or 90%, so you might be working with only 20% or even 10% of the total capacity of the bank, if you charge at 70% or 75%. 50% to 90% is 40% of the total bank capacity.

Your batteries want the opposite -- not to be pulled down too far.

So there is a tension here.

At anchor, I charge at 60%, or 65%, or any time I need to use a lot of AC power (running a load of clothes for example, or using the electric oven).

Underway, however, it can be difficult to do any charging, if you are on a long upwind passage with a lot of heeling. Neither your main engine nor your generator likes to run on a heel.

So on a long passage like this, I might let them go right down to 50%, because I will need to shorten sail or heave-to to do it, which loses miles. If you don't do it too often, it's not that harmful. 50% is a fairly normal discharge for batteries which are even semi-deep discharge types.

We use a lot of power sailing because of the pilot, hourly tea kettles, etc. In light winds I just run the main engine for a while every few hours, but going upwind in stronger conditions you can't do that.

[chris95040]

Does anyone's product just measure the current locally (right at the battery) and send that data to your actual user interface in some digital (or just amplified) format?

It seems a big problem in the current-counting method is all the noise in that very, very weak signal you get by taking voltage across a shunt and measuring it at the other end of a run of wire.

If you just had a bunch of little shunts-with-an-ADC that you'd stick inline with each battery in your bank and wire digitally to your user interface, you'd probably get better, more actionable data.

[conachair]

Originally Posted by a64pilot

I don't think I have ever discharged my bank below 75%, unless your in a circumstance where you can't charge for whatever reason, why take it below what it gets to overnight?
The less you discharge a bank before charging it back up, increases its life rather dramatically, why pull it down to 50%?
https://voyagesofagape.files.wordpre...lifecycles.jpg

50% discharge gets me 1000 cycles, 25% discharge 2000 cycles

Worth adding the importance of getting them back to full charge as often as possible as well. How many cruising boats actually manage to get back to fully 100% regularly I wonder, probably not that many.

[Dockhead]

Originally Posted by conachair

Worth adding the importance of getting them back to full charge as often as possible as well. How many cruising boats actually manage to get back to fully 100% regularly I wonder, probably not that many.

Well, probably ALL solar boats do, regularly. Solar power and lead-acid batts go together like cookies and cream.

Generator boats I've been on, usually go into a marina for a night or two a week, for water, and for doing a thorough 100% charge of their batts.

I used to keep a 1kW Honda suitcase generator specifically for the purpose of giving my batts a long finishing charge once in a while, when on my mid-river mooring.

I guess once a week ought to be enough; it's a recommendation I read somewhere.

[Sandero]

The amp hr stuff... "bank account" is just a waste of time... "navel gazing"????

You need a sensitive accurate volt meter.... digital... which should show amps in and amps out...that is being used... When you turn on a charging source you see how many amps it supplies... a load source...how many amps it consumes...

Your battery state is revealed by their voltage at rest...with no charging sources or loads on. Easy peasy.

NB... older batteries lose capacity... they drain faster and charge faster but don't accept lots of amps... These are signs of old/used up batteries ready for replacement

You won't be or shouldn't be running your batts down. You should having charging on (wind, solar, shore, alternator etc...) as you use them. You need to do an energy audit budget and have a protocol to keep your batts up. This may include fuel!

If you are not out in the middle of the ocean... and coastal... this is all a tempest in a teapot really.

[chris95040]

Originally Posted by Sandero

You need a sensitive accurate volt meter.... digital... which should show amps in and amps out...t

A voltmeter doesn't measure amps, it measures volts.

And measuring amps is presently done in a very inaccurate manner, at least in the hardware I've seen.

Originally Posted by Sandero

Your battery state is revealed by their voltage at rest...with no charging sources or loads on. Easy peasy.

Unless you happen to be using them. I'm generally not all that interested in my batteries' state of charge when I'm not using them.

[S/V Alchemy]

Originally Posted by a64pilot

I don't think I have ever discharged my bank below 75%, unless your in a circumstance where you can't charge for whatever reason, why take it below what it gets to overnight?
The less you discharge a bank before charging it back up, increases its life rather dramatically, why pull it down to 50%?
https://voyagesofagape.files.wordpre...lifecycles.jpg

50% discharge gets me 1000 cycles, 25% discharge 2000 cycles

That is precisely why I have a big bank. Well, that and the weight stiffens the boat. It's not because I need that many Ah, but because I wish to keep the range of USABLE amp-hours in that 75%-100% band because I want to get 2000-3000 cycles out of them, which means "greater than one five-year circ". Care and feeding and proper monitoring are all part of that. My metric was "five cloudy, windless days at anchor without running the engine, and icecubes on Day 5". I don't actually have a lot of draws and the switch to LEDs all over the place are making the boat less amp-hungry. But I really believe (and the battery literature backs this up) that avoiding 50% discharges gives you many, many more cycles before your batteries are used up.

[conachair]

Originally Posted by Dockhead

Well, probably ALL solar boats do, regularly..

Maybe with big solar arrays and a good regulator set up by someone who knows, but most I would very much doubt they get to full on a daily basis. It takes a long long time to get to full charge, add a fridge and other bits stealing power along the way, a few clouds and you might be getting up in the 90 plus % bracket, but all the way?? Doubt it very much. Add to that regulators set to a low absorption time and voltage.

Mainesail, you know more than most about these things - care to comment?

And as the threads drifting around a little already..... ... is it better to set your absorption voltage high and time long to have a better chance of regularly getting a full charge in but risk a little damage that way or risk damage from not getting a really good charge on a regular basis?