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Old 09-19-2021, 11:20 AM   #1
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Battery Readings with Smart Shunt

I am a bit confused. I installed 2 Battleborn batteries and a Victron shunt. I think I have all the settings right, including manually setting the SOC at 100% when the batteries were fully charged to 14.4. I confirmed they were fully charged as there was next to no current going into the batteries and the voltage read 14.4.

I unplugged the trailer for several days and the battery voltage has dropped to 13.28v yet the SOC is still at 100% even though it has lost over 1v since full charge. It would seem to me that the SOC should be something less than 100%?
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Old 09-19-2021, 11:42 AM   #2
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The way I understand is your "charged voltage" is used (along with tail current and time) to determine when the SOC calculation will automatically sync. It is not used to calculate SOC as the battery starts being used, that is a mathematical calculation determined by current removed over time. I think your surface charge just stabilized to a "resting" voltage of 13.28 over the resting period and since no measurable current was taken from the battery it is still fully charged. The recommended settings for charged current are the same for all 12 volt battery types, 13.2 and by setting yours to 14.4 I believe all that accomplishes is a delay in the SOC calculation synching back to 100%. You won't gain anything by that delay as it was fully charged at 13.2 and the rest is just a surface charge that would disappear anyway as soon as loading occurred. Voltage dropping as current is drawn is the reason why the standard volt meter that Airstream supplies is inaccurate during use and why the shunt uses mathematical calculations instead.
In regards to your charged voltage setting, the instructions don't go into much detail other than saying 13.2 works for all batteries however some of the battery manufacturer's including Victron recommend 13.8. (see answer #2 in attached link to Victron forum) It still won't affect your SOC reading on the downhill side though as it is only used during the sync to 100% if my understanding is correct.

https://community.victronenergy.com/...-settings.html
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Old 09-19-2021, 12:06 PM   #3
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Also I found no need to manually sync mine and I also left the "battery starts sync" switched to "OFF". Once installed I just loaded them down to 80%, then recharged. Once my "charged" parameters were met it automatically synched to 100%. Since there is zero load detected when my batteries are at rest with the battery switch turned to "OFF" I don't expect the Smart Shunt will keep track of any self discharge which is of no concern since I keep them on a Smart Charger anyway. Self discharge is one of the reasons why the Smart Shunt must regularly self sync which always requires a discharge of at least 90% followed by a full recharge. If you leave "battery starts sync" "ON" it will sync when connected regardless of battery SOC and if they were connected without charging first the SOC could be inaccurate (until the next discharge/charge).
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Old 09-19-2021, 12:31 PM   #4
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Hi

If your battery is at 13.24 and the device shows 100%, there is a problem somewhere. Roughly speaking 13.4 to 13.5V is in the >= 90% range. Anything below that very much should show as having discharged.

On the first picture, the device believes that 0.1AH has been consumed. At the same time, there is a 0.13A current flowing out of the battery. Wonder what's going on .... hmmm ....
Under settings you have a "current threshold" setting of 0.1A. You told it to ignore 0.1A and it's doing exactly what it's been told. It's ignoring the parasitic drain of your trailer.

I'm only guessing here. Let's say "several days" works out to 5 (again just a guess). That would be 120 hours. At 0.13A that's 15.6 AH. More or less 8% down from 200AH. Since this is a mighty small current compared to what the 500A shunt is designed for, your guess is as good as any in terms of what the real number is. It could be twice that. It could be half of that.

Some math:

The shunt puts out 50MV at 500A. At 100uV / A, the 0.1A reading is 10uV on the wires. That's a good gracious small voltage to be measuring on a simple device like this.

This still does not explain the low voltage on the battery. I'd go back and see if somehow a wire got missed and there is a circuit that runs past the shunt.

Bob
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Old 09-19-2021, 02:02 PM   #5
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Bob, How can we assume anything is wrong when we don't know more about the .13 load? We don't know if it has been there for days or minutes. If I switch on my battery switch I will see a small load similar to that and at the same time my voltage will drop slightly. We can't assume current has been flowing for days nor can we assume that the voltage readout is 100% accurate while a load exists. The small load may drop the voltage reading a 10th or so, Battle Born's own site shows 13.4 as being 99%. We also don't know if a load was used shortly before the measurement was taken with no time for the voltage to stabilize.
Assuming the .13 load has been there for days it would show a drop of roughly 1% SOC every 15 hours. Since the SOC shows 100% and the Smart Shunt is obviously seeing the .13 in the snap shot the more likely scenario is that the load has not been present for days, since the SOC during discharge is measured by current not voltage and we know it is seeing the current. If the circuit was wired outside of the shunt negative side the current would not show up on the display.
As far as the current threshold, it would not ignore the .13 load as it exceeds .10, this is proven by the fact that the .13 is showing on the display. IMO the threshold is there for line noise.
Now if there is a load smaller than .10 I could see it taking the SOC down without the Smart Shunt's knowledge.
I suggest the OP, as a first step, to wait till all loads disappear from the Smart Shunt display even if it means disconnecting something. The display should then show zero current, zero watts and time remaining as infinite. Once this displays wait a period of time for the voltage to recover on the battery then see what the voltage reading is. We can't get an accurate voltage reading when a load or a charge is present, or was recently present.
As a second step I would disable the current threshold and look for a small, steady draw that the setting may be hiding.
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Old 09-19-2021, 03:02 PM   #6
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I was curious about the current threshold and if it is possible as Bob mentioned that it could be ignoring enough to make a difference so I disabled mine and connected to the shunt. Interestingly it fluctuated between .0 and +.01 while plugged into my Smart Charger which was in "Storage" mode at the time and supplying no voltage. When I unplugged the Smart Charger the current fluctuated between .0 and -.01 which I believe is the stated draw of the Smart Shunt of <1ma. So in my case the draw is negligible and would take a minimum of around 10 days to deplete 1% of a 200 ah bank as a guesstimate and who knows how much less than 1ma the draw is? It is of no concern to me as I keep the Smart Charger on it anyway which will initiate a charge when needed but if you store for an extended period with no charger you may want to add a disconnect for the Smart Shunt or for any other loads that may bypass the battery switch, in my case there are none so my only parasite is the Smart Shunt itself. If you use a disconnect that includes the Smart Shunt you will want to switch "battery starts sync" to "OFF" otherwise as soon as you power up the shunt it will sync to 100% regardless of the SOC of the batteries.

I would check yours and see where you are at, if there is a bigger draw then you can lower the threshold and let the Smart Shunt count it.

Keep in mind if you do this and say the SOC on the display drops to 95% and you charge back up you won't get an automatic sync to 100% since the SOC did not drop below 90%, in that case you would have to sync manually, you would still have the incoming current though which theoretically should replace the deficit on the SOC display. Or just add a Victron Smart Charger and let it keep you at 100% automatically without fear of over charging.
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Old 09-19-2021, 03:12 PM   #7
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Quote:
Originally Posted by ITSNO60 View Post
Bob, How can we assume anything is wrong when we don't know more about the .13 load? We don't know if it has been there for days or minutes. .......
Hi

Well, in the original post, the batteries start fully charged and then things go into storage for "a couple days". There is no data provided that anything has changed. The easiest assumption is that it's been pulling the indicated current over the entire period.

There's also the cumulative discharge total shown in the first picture. If more has been pulled from the battery since the last reset, the shunt missed it.

Bob
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Old 09-19-2021, 03:39 PM   #8
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Hi

Well, in the original post, the batteries start fully charged and then things go into storage for "a couple days". There is no data provided that anything has changed. The easiest assumption is that it's been pulling the indicated current over the entire period.

There's also the cumulative discharge total shown in the first picture. If more has been pulled from the battery since the last reset, the shunt missed it.

Bob
Yes, that's my point. We know the shunt didn't miss it because it shows up on the display as current being drawn so we know the shunt sees it but it doesn't add up to enough on the total which tells me the load can't have been there for days. What we really need is an accurate resting voltage before we can go any further.
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Old 09-19-2021, 04:57 PM   #9
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Originally Posted by uncle_bob View Post
Hi

Well, in the original post, the batteries start fully charged and then things go into storage for "a couple days". There is no data provided that anything has changed. The easiest assumption is that it's been pulling the indicated current over the entire period.

There's also the cumulative discharge total shown in the first picture. If more has been pulled from the battery since the last reset, the shunt missed it.

Bob
Yes, the trailer switch is in the Store position and I have disconnected the propane detector as well. I am assuming that the 0.13A draw that the shunt continues to show is possibly from the subwoofer and the shunt itself. To be more precise the "couple of days" is actually 3 full days. I have checked the draw several times and it is always 0.13A - 0.14A.

As far as wiring goes, I have a 4" 2.0 neg cable from the most negative battery lug to the battery side of the shunt and all other negative cables are hooked up to the draw side of the shunt. All the positive cables, except the small positive cable for the shunt, are hooked up to the opposite battery's positive lug.

I am going to start the process again by fully charging the battery, and synchronize to 100%. I will keep an eye on it in the next several days and see what happens.
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Old 09-19-2021, 05:22 PM   #10
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Can you go into history and look up the cumulative discharge and last discharge? I'm wondering if somehow it synched and cleared the "ah consumed" total on the home page.
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Old 09-19-2021, 06:35 PM   #11
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I will certainly have a look at this when I am able to return to the trailer in the next day or two and I will post a photo. I think something went amiss and caused the SOC to return to 100% even though there clearly was a drawdown of over 1A from the full charge of 14.43A at the start.

I have started again and the resting voltage after being off the charger for 60 minutes was 14.02A
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Old 09-19-2021, 06:44 PM   #12
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For interest, here is my BB install into the factory battery box, including the shunt and the 60A fuse for the Victron 12-12-30 DC-DC charger.
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Old 09-19-2021, 06:46 PM   #13
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Will look forward to that. If that load is indeed consistent and you are storing with no charger you'll need to disconnect it, if not you'll be losing 25ah per week. If you go back in a day or so you should see about 3.5 ah consumed on the home screen for each 24 hours.

If for some reason power was interrupted to the Smart Shunt with the "battery starts sync" switched to "ON" it would reset the ah consumed to zero and set the SOC to 100% regardless of the actual SOC.
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Old 09-20-2021, 06:31 PM   #14
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Here are the latest readings after sitting for 24 hours. Unlike the previous readings after sitting for 3 days, these readings look to be normal now. Brian, you called it, 3.5ah consumed in 24 hours.

The only puzzling thing is the time remaining is still 10d 0h. If my calculations are correct, it would take about 57 days to deplete the batteries at this rate?
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Old 09-20-2021, 07:04 PM   #15
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Looks like you got it figured out. The 10 days seems to be default maximum, mine never exceeds 10 days either. When you put a decent size load on it the time remaining will drop but it will always go back to 10 days when the remaining time is 10 days or greater.If the load drops to zero the 10 days will change to "infinite"
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