Simplest battery monitor and shunt? Advice for non-expert

[profdant139]

I have seen references in various threads to shunts and battery monitors. I have searched the archives for a very basic "how to" and have come up empty. Youtube has some instructional stuff, but it tends to be fairly technical.

A little background info -- my battery sits in a box on the tongue of my trailer. I am not an electronics expert at all. What I am looking for is a fairly easy, fairly inexpensive way to monitor the capacity of my battery on a real time basis.

I'm guessing that I will have to install the monitor inside the trailer and run wires to a shunt installed on the negative cable near the battery.

In your opinion, which is the most basic and inexpensive monitor? Are shunts sold separately from the monitors? What gauge cable does the shunt/monitor require?

Thanks in advance for your advice and expertise!

[vermilye]

profdant139 wrote:
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.

I have a Victron solar controller (which is a 100/50). I had to add a Victron dongle to it to be able to read the device from my truck. I have read that the Smart Shunt produces fairly weak Bluetooth & requires the dongle as well. My old 100/30 didn't need one; neither does the 712.

As to a daily recalibration or sync, if the solar controller shows it reached 14.5V & the absorption stage runs at least 15 minutes, and it switches to float, I assume that the batteries (3 100 amp hour Battleborn lithium) are full. Most of the time, under these conditions, the Victron 712 battery monitor does an automatic sync, if not, I'll do it manually.

If I was really concerned, I'd test the batteries every year by running them down to the BMS low voltage shut off & note the number of amp hours used, but to be honest, I don't bother.

With lead acid batteries, it might be more important to know the true battery capacity, however I suspect that shortened discharge times before hitting low voltage would become obvious as the battery capacity drops. Not so obvious with lithium...

Hope this is helpful.

Jon

[jaycocreek]

StirCrazy wrote:

jaycocreek wrote:
SC

That's DC home,I like it better than the Renogy BT..

never heard of it.

Steve

It's called Renogy DC Home and it's in the app store for both Android and Apple..I like it better because the Bluetooth connection is much stronger and the layout I like better also..

Jayco

[StirCrazy]

jaycocreek wrote:
SC

That's DC home,I like it better than the Renogy BT..

never heard of it.

Steve

[jaycocreek]

SC

That's DC home,I like it better than the Renogy BT..

[StirCrazy]

jaycocreek wrote:
Another option if you don't mind dealing with .tenths instead of .one hundredths is the Renogy BT-1 or 2 bluetooth dongles that give a little extra in readings..From using it with my Victron monitor it is spot on to the tenth..



As well as a history page with stuff like total this or that used etc.

Jayco

did they update the App, I have never seen that screen before.

[3_tons]

Providant139 says, “how do you recalibrate a Victron”??

First off, ask yourself why you’d need to recalibrate??…The only answer I can think of is that several years of battery usage has passed, thus causing some normal wear and tear (e.g. normal irreversible sulfation with age, or other battery malady), but not really needed as a routine exercise…

Or, perhaps your confusing recalibration with re-synchronizations which typically recur passively at the end of every full charge cycle?

Either way, to do a recalibration, you might simply impute a presumed amount of capacity loss over time (say x amp/hrs worth of decline, per season??), and adjust the meter’s programmed capacity accordingly, or do an actual load test which (without a solid reason…) many might view as an a love of unnecessary labor…

Bottom line here is that even with a small amount of naturally occurring capacity decline, I seriously doubt you’d find a need to routinely recalibrate when as an alternative (say over a x year period?) you might simply choose to go no lower than 55% SOC instead of your previous 50% SOC…Reality is that (for flooded wet cells), shunt meters are just not that persnickety - JMHO after years of meter usage…

3 tons

[jaycocreek]

Another option if you don't mind dealing with .tenths instead of .one hundredths is the Renogy BT-1 or 2 bluetooth dongles that give a little extra in readings..From using it with my Victron monitor it is spot on to the tenth..



As well as a history page with stuff like total this or that used etc.

Jayco

[Gdetrailer]

Gjac wrote:
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.

DING, DING, DING, we have a winner!

No matter what battery you chose to use, they ALL degrade in capacity over time whether it has been used or not. Whether they are fully charged 100% or in some partial state of charge they ALL degrade in capacity.

Batteries are considered a "consumable" item, as such you use them and consume them until they no longer have enough capacity for your needs.

Meters are just there to monitor your progress and nothing more. Perhaps you might squeak out an additional one or two months more life with critical monitoring down to the last electron every second but in the end you still will have to replace the battery eventually.

Sometimes life works a lot better by not trying to helicopter and hover over things you cannot control?

I go camping to LEAVE technology behind, when I am camping, technology is the last thing on my mind, it no longer dominates and controls me when I am away from it and now able to concentrate on the beauty of this Earth around me.

Simply buy enough battery capacity to handle your needs for a specified time and supplement with some solar and/or generator as needed and don't sweat the small details in life..

[profdant139]

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.

[vermilye]

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.

[Gjac]

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.

[pianotuna]

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.

[3_tons]

“ 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

[FWC]

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!