Simplest battery monitor and shunt? Advice for non-expert

Skibane wrote:

pianotuna wrote:

Skibane wrote:

pianotuna wrote:

Skibane wrote:

pianotuna wrote:
Hi,

If you are NOT using Li batteries the very best meter may be the smartgauge. It actually tracks the "real" capacity. It checks the voltage several thousand times per minute.

http://www.smartgauge.co.uk/

I don't look at my meter several thousand times per minute.

Why would my meter need to make several thousand battery voltage measurements every minute?

Read about how it works at this link: https://marinehowto.com/smartgauge-battery-monitoring-unit/

There isn't anything on that page which explains why it needs to measure battery voltage several thousand times a minute.

The word "minute" doesn't even appear on that page.

It checks 1500 per second. When I was in school a second was part of a minute. But perhaps they don't teach that anymore.

Why does that matter?

Why does my battery meter need to check its voltage 1500 times per second?

How is this a meaningful feature, and not just techno-babble?

Skibane, that's why it needs no shunt. If you want more information ask them, not me. Merry Christmas.

Well, I am learning a lot and have (as usual) learned myself into a corner. I was leaning toward an Amp/hour counter, like the Victron. (Am I right about that -- is that the main advantage of the Victron over the voltage-based monitors? I certainly want to know how many amp/hours I've got in the tank!)

But then I went to the Smartgauge site and started to plow my way through the article Don referenced above. And I came to this significant passage:

"The problem with traditional Ah or Coulomb counters is keeping them accurate. As batteries age their capacity changes, the charge efficiency changes as does the Peukert’s constant. A battery is an ever moving target, so the 100Ah battery you bought three years ago may now only be a 75Ah battery."

I'm going to ignore Prof. Peukert -- I only use one battery at a time. (I know, I know -- I am leaving money on the table by not using the batteries in parallel -- but I just like the rock-solid safety of using one and holding another as a spare, just in case.)

But the big problem is that I really don't know, and won't know, the true amp/hour capacity of my dumb lead-acid deep cycle battery. When it's brand-new, it's rated at 110 a/h, which means I can draw it down to about half of that without getting a pain in my anode (or whatever it is that happens when you over-discharge an old-school FLA battery).

But as the article points out, FLAs degrade over time, even when we baby them by never going below 12.1 volts (or 50% state of charge).

So that is now my question -- for those of you who are fans of Victron-type monitors, how do you deal with the problem of AHDS ("Amp/hour dwindle syndrome")?

That article goes on to say, by the way, that you can determine if your capacity is dwindling by conducting a 20 hour load test. The author says that no one really does that, in the real world.

My guess is that if you have lithium batteries, you don't have to worry about this phenomenon.

Bottom line -- if actual battery capacity is a moving target, then an amp/hour counter may provide a misleading over-estimate of the remaining juice. And if I have to indulge in guesswork, I can just whip out my cheap old-school multi-meter, measure the voltage, interpolate state of charge, and call it done!

Thanks again for all of the expert input - I know that this is a surprisingly touchy subject, and reasonable minds can differ about all of this. Battery care is both a science and an art!

pianotuna wrote:
Skibane, that's why it needs no shunt.

Measuring the battery voltage 1500 times per second doesn't explain why it needs no shunt.

What we're seeing here is two unrelated facts - and then an inexplicable claim that one of them is why the other exists.

Fact: The capitol of South Dakota is Pierre.
Fact: Some pizzas contain anchovies.
Claim: Pierre is the capitol of South Dakota because some pizzas contain anchovies.

“So that is now my question -- for those of you who are fans of Victron-type monitors, how do you deal with the problem of AHDS ("Amp/hour dwindle syndrome")?”

You’re being distracted by a clever marketing tactic which glosses over the weakness inherent with the Smartgauge voltage-tap only meter design (what’s their fairy dust??) …You’ll find no more accurate a meter than a shunt based meter, and since you have FWC batteries, a budget meter should easily do the job (an even more sophisticated meter req’d for LFP), this with zero problems tracking SOC - and if you’re of the persuasion that the batts capacity decline will result in a perceptible inaccuracy over a time, then just simply re-program to a slightly lower capacity in a few years…But after about 14 yrs of measuring my former FLA SOC’s with a shunt based Xantrex LinkLite meter I have some difficulty relating to your perceived concern…However, I might well agree if we were talking about something like the Mars Rover :)

3 tons

As long as you don't plan on running your battery down to 0% SOC, which it sounds like you aren't planning on, then it is not really that critical to know your capacity down to the Ah. Assuming you have a 100Ah nominal battery, if you plan on regularly pulling 50Ah out, then you are running it down to 50% SOC if it is new, or 38% SOC of charge if your capacity is degraded to 80Ah. Either is totally fine.

If you are really concerned about capacity, pull 50Ah out, disconnect the battery and let it sit for a few hours, then look at the voltage on your monitor, that will give you a fairly good idea what your actual capacity is.

While I did bring it up, I would highly recommend NOT getting the Smartguage. While it may give very accurate SOC for a lead acid battery it will be useless when you upgrade to LiFePO4 or what ever the next great battery technology is. Secondly, shunt based monitors provide more than just the SOC. Particularly with solar, knowing the current can be really helpful - you can adjust your panels to maximize the power harvest (super easy with bluetooth). Finally it is by far the most expensive, the original smartgauge or the newer SG200 is around $300 once you add in bluetooth.

If you are concerned about Peukert, the Victron monitors will account for this in their calculations.

profdant139 wrote:
Well, I am learning a lot and have (as usual) learned myself into a corner. I was leaning toward an Amp/hour counter, like the Victron. (Am I right about that -- is that the main advantage of the Victron over the voltage-based monitors? I certainly want to know how many amp/hours I've got in the tank!)

But then I went to the Smartgauge site and started to plow my way through the article Don referenced above. And I came to this significant passage:

"The problem with traditional Ah or Coulomb counters is keeping them accurate. As batteries age their capacity changes, the charge efficiency changes as does the Peukert’s constant. A battery is an ever moving target, so the 100Ah battery you bought three years ago may now only be a 75Ah battery."

I'm going to ignore Prof. Peukert -- I only use one battery at a time. (I know, I know -- I am leaving money on the table by not using the batteries in parallel -- but I just like the rock-solid safety of using one and holding another as a spare, just in case.)

But the big problem is that I really don't know, and won't know, the true amp/hour capacity of my dumb lead-acid deep cycle battery. When it's brand-new, it's rated at 110 a/h, which means I can draw it down to about half of that without getting a pain in my anode (or whatever it is that happens when you over-discharge an old-school FLA battery).

But as the article points out, FLAs degrade over time, even when we baby them by never going below 12.1 volts (or 50% state of charge).

So that is now my question -- for those of you who are fans of Victron-type monitors, how do you deal with the problem of AHDS ("Amp/hour dwindle syndrome")?

That article goes on to say, by the way, that you can determine if your capacity is dwindling by conducting a 20 hour load test. The author says that no one really does that, in the real world.

My guess is that if you have lithium batteries, you don't have to worry about this phenomenon.

Bottom line -- if actual battery capacity is a moving target, then an amp/hour counter may provide a misleading over-estimate of the remaining juice. And if I have to indulge in guesswork, I can just whip out my cheap old-school multi-meter, measure the voltage, interpolate state of charge, and call it done!

Thanks again for all of the expert input - I know that this is a surprisingly touchy subject, and reasonable minds can differ about all of this. Battery care is both a science and an art!

“ The author says that no one really does that, in the real world…”

I agree with Smartguage’s parsing on the head of a pin - why??…because for the most part it’s really unnecessary…

3 tons

profdant139 wrote:
My guess is that if you have lithium batteries, you don't have to worry about this phenomenon.

Bottom line -- if actual battery capacity is a moving target, then an amp/hour counter may provide a misleading over-estimate of the remaining juice. And if I have to indulge in guesswork, I can just whip out my cheap old-school multi-meter, measure the voltage, interpolate state of charge, and call it done!

Actually the problem does exist for Li. If pair of brand new Li batteries are compared when one sits of the shelf for 5 years and the other is in use for 5 years, the (never used) shelf unit may have pretty much the same capacity left as the one that was used.

My bottom line was to use just voltage. But I do have a larger bank that most rv'ers. If I had a champagne budget, I'd go with smartgauge.

The Victron gauges are excellent, because they do a peukert calculation (unlike the trimetric).

I guess it comes down to whether there are issues of running out of power or not.

Dan in reading your posts and looking at the beautiful photos you always post with them, I believe while all this technology that was posted here while very informative, someone that likes to boondock like yourself, I would just get 2 6v GC batteries with 230amp hrs and not worry about an expensive way to monitor them. Just check voltage when you get up each morning and go hiking for the day and take some more photos. 230 amp hrs will last you a week before you need to recharge.

While long term tracking is useful, and, since the amp hour capacity of lead acid batteries drops over time, even the Victron or other shunt based battery monitors will need recalibration over the years.

That does not make them useless. During a trip the day to day usage & replenishment is where a shunt based monitor shines. You can easily determine whether your solar has put back enough that you are comfortable using a high current device such as a microwave, toaster, etc. If you are recharging with a generator, you can see when your converter switches to absorption and save running the generator for hours just to put a few amp hours back in the batteries.

I have used both voltage measurements and shunt based monitors, and am far more comfortable dry camping with the Victron monitor. I've gone as long as 91 days without hookups, relying on solar. Without a good method of tracking the battery conditions, that would have been near impossible.

Jon, your style of camping is fairly close to mine, so your comments are particularly persuasive. How do you recalibrate the Victron? Is it difficult? Do you have a bluetooth-equipped monitor?

Thanks in advance.