Victron BMV-712 Settings

[Theo]

Also, remember to relocate your BMV’s power wire. When you get your temp sensor, it should be attached to the same (+) terminal to which you’ve attached your (moved) BMV power wire. That should be the terminal with the 4/0 wire running to the positive disconnect switch.

Have you double-checked to make sure the taller GC2s will fit into your battery box with the lid closed?

I’ll be back on Wednesday and will check in to read your updates! Good luck!🍀

[JRHill02]

I have a Victron of the same model. I use it for an off grid system that powers everything in our home, shop, etc. But I have to ask, putting all the wiring and programming aside, WHAT DO YOU WANT IT TO TELL YOU?

I really appreciate a battery monitor and it is invaluable for our purposes. But know you can not lie to it (settings and battery characteristics). If you do then its data is worthless. I use the Victron as a day to day health-at-a-glance gauge. But it is another maintenance device. A battery monitor drifts over time - sorry, but its the nature of the beast. So even if you have it set up in perfection it won't be perfect some weeks or months down the road.

The way to dial it back to reality is to fully charge the batteries and reset the monitor at that point AND NOT DISCONNECT IT afterward. Then you can use the state of charge, hours remaining, etc. with some reliability. You can disconnect it but you need to know that it will not give you real world info until you fully charge the batteries and reset it again. Even then it will drift from reality in a given time from the last reset.

The standard for good data is to fully charge the batteries and reset it when the batteries are full and the specific gravity of the electrolyte is maxed. If you have sealed batteries or lithium the monitor still does great but you need to use it with the battery charging procedures in mind.

So I ask again, what do you want it to tell you?

[Theo]

Originally Posted by JRHill02

...{snip}But I have to ask, putting all the wiring and programming aside, WHAT DO YOU WANT IT TO TELL YOU?{snip}...

Well, for its application in the world of RVing, the data points I use the most are the SOC datum, the current datum and the Time-to-go datum. Some may use additional data points.

Originally Posted by JRHill02

...{snip}But know you can not lie to it (settings and battery characteristics). If you do then its data is worthless.{snip}...

However, Victron instructs us on how to modify the parameters to improve accuracy and to configure the meter for battery chemistry and other situations. This also allows us to be more realistic about manufacturers specs like Ah ratings. Just because a tech sheet says 215Ah doesn't mean that the battery you receive it is exactly 215Ah.

For good or for bad, as a rule-of-thumb, I've fallen into the habit of adjusting the Ah rating down by 10% for two reasons: (1) I doubt that the battery I receive will be exactly 215Ah and (2), by doing, so I give myself a smidge of a cushion. If this skews anything, it will be toward the conservative side of the spectrum (Time-to-go & SOC). YMMV.

Originally Posted by JRHill02

...{snip}A battery monitor drifts over time - sorry, but its the nature of the beast. So even if you have it set up in perfection it won't be perfect some weeks or months down the road.{snip}...

Good point. I'm assuming that's why Victron's app allows us to manually synchronize the SOC and execute a zero current calibration.

[Theo]

I did some experimenting with the shunt to answer some questions I'd been thinking about while I was away:

(1) Are electrons flowing across both terminals of the shunt if the chassis side of the shunt is disconnected;

(2) What is the current (parasitic) draw produced by the BMV-712?

I quickly realized that some common sense thinking regarding electron flow would both answer question (1) and negate a test to prove/disprove it! The answer to question (2), however, was easily determined.

Following is a description of the shunt and battery test conditions. Two 6V batteries are connected in series. The BMV-712/shunt battery-side is connected to the battery bank's negative terminal. The shunt's chassis side is disconnected. The BMV-712's positive wire from its B1 connector is wired to the battery bank's positive terminal. The BMV temperature sensor is connected to the battery bank's positive terminal with red & black wires running to the BMV’s B2 connector. Please note that the black wire of the pair is disconnected; only the red wire carries sensor info. To test, I used a Fluke 115 Multimeter in both the DC volts mode and the DC amperage mode.

In (Image 1) and (Image 2) below, I am measuring the volts between the positive terminal of the battery bank and each of the shunt’s terminals. At this point, you will realize the folly of my testing the chassis side of the shunt. Obviously, the circuitry of the multimeter is closing a circuit and, therefore, am “drawing” electrons across the shunt in the measuring process! Without the meter closing the circuit, it stands to reason that electrons would not be drawn across the shunt since there is an open circuit on the chassis side of it. Therefore, the current (electrons) will flow from the battery’s negative terminal to the shunt’s processor and back to the battery bank’s positive terminal through the BMV’s B1 port and its connected red wire. That is the closed circuit.


(Image 1) voltage on battery side of shunt


(Image 2) voltage on chassis side of shunt (Duh!)

The current does not flow across the shunt because the shunt’s chassis side is disconnected and, therefore, does not offer a closed circuit (beyond the B1 port) for electrons to return to the battery bank’s positive terminal. No electron flow, no current! In Image 2, it was the multimeter itself that was closing the circuit! Without the meter, no electron flow.

I happen to keep my BMV-712 running all the time when when the batteries are put back into the RV each spring. I have measured the parasitic draw of my rig to average ~0.23A (CO/LP detector & BMV-712). I wanted to know what part of that draw was due to the BMV. Image 3 shows that it is drawing only 0.009A (9 milliamps)! That’s only 1.5A a week. Therefore, my CO/LP detector still has a parasitic draw of ~0.22. In my case, disconnecting the BMV to save on parasitic draw won’t make a whole lot of difference.

(Image 3) parasitic draw of the BMV-712

[CHICKDOE]

Mr Theo, thanks for the experiment and confirming the 9 milliamp draw. I think I read somewhere that victron specs say 10 milliamperes so your experiment confirms their spec. I agree that is a small draw that will have hardly any effect over several months while in storage. But by being active and with the Bluetooth capability you can get battery status info at any time.

I don’t if they measure this small draw and deduct it from the battery state of charge. But it’s so small why worry about it. I just let the shunt figure out when the battery becomes fully charged again via the tail circuit parameters and it resets itself to 100% so any small drain that might have happened while in storage gets eliminated.

[Theo]

Originally Posted by CHICKDOE

...{snip}I don’t if they measure this small draw and deduct it from the battery state of charge. But it’s so small why worry about it. I just let the shunt figure out when the battery becomes fully charged again via the tail circuit parameters and it resets itself to 100% so any small drain that might have happened while in storage gets eliminated.

EXACTLY!

Since the meter showed a current flow, I'm guessing that the BMV processor is counting all electrons that power it AND the ones that go across the shunt; I don't believe there is the circuitry to allow it to deduct the electrons passing only through the BMV's processor. Of course, in this case, no electrons were going across the shunt so it's safe to assume that the 9 milliamps is strictly the BMV's draw.

[TitanMike]

Originally Posted by Theo

EXACTLY!

Since the meter showed a current flow, I'm guessing that the BMV processor is counting all electrons that power it AND the ones that go across the shunt; I don't believe there is the circuitry to allow it to deduct the electrons passing only through the BMV's processor. Of course, in this case, no electrons were going across the shunt so it's safe to assume that the 9 milliamps is strictly the BMV's draw.

Any current draw by the BMS is probably below the resolution limits of the shunt/meter.

Victron shows voltage resolution to be ×/- 0.01v and an accuracy of +/- 0.3%. That's a lot to ask of a 50mv 500amp shunt.

I solved all these miniscule power drain issurs by just camping more often. "Storage" for me is typically less than 3-4 weels before I sm back camping one way or another.

[JRHill02]

You have some really good input from others. I won't muddy the water too much. But after 11 years of 2 matched banks of Trojan RE16B's on a 48v system I learned a lot about FLA batteries. And I thought I knew AC and DC well. NOT. Two years ago when my 2nd bank was at end-of-life based upon SGs I bit the bullet and went with lithium (SimpliPhi, $$$$). It was one of the best investments I've made after the the original purchase/configuration.

Even on an off grid setup, using a battery monitor with lead batteries is a moving target on a day to day basis. But in an RV not used every day, what a PITB. That's why I harped on the SOC reset after a full charge. So here are a few other items to consider:

- Battery self discharge of ~5% per month. The Victron can't measure that. Only a full charge and reset properly done covers it.
- Battery health including matched blocks. No swapping in of newer batteries or of a different production lot. Your worst battery will bring the best one down to its level.
- Battery temp compensation is really cool for a monitor to use Peukert's law. But did you know its even more important for your charger to be temp compensated?
- Loading. That's both in and out. Use the batteries hard and charge them hard at intervals. Deep cycle batteries like to work hard. Light loads and slow charges are not your friend.
-Usable SOC. Yup, never lower than 50% For lead and that is stretching it. The bottom 50% isn't near what the upper 50% is but both make up the total amp hours of the battery specs.
- That's enough for now.

Battery types are really important. If I got forced into lead again I would only use flooded batteries. Why? I can monitor them with both voltage and SGs and that is what's really important. With sealed lead batteries you have only voltage and a load tester. In addition, charging stages of sealed batteries is crucial to their life. Bulk, Absorb and Float all adjustable to the battery specs They are different critters than flooded lead.

With just two 6v semi deep cycle batteries I'd not blink at changing them out yearly compared to dealing with under performance when you need them. Actually a pair of golf cart batteries would be better and of course they are more expensive. Properly charged and maintained you might get two or three years life from some T105s.

[JRHill02]

Originally Posted by TitanMike

Any current draw by the BMS is probably below the resolution limits of the shunt/meter.

I respectfully disagree. The shunts are relatively accurate. The battery wiring/connections, maintenance, health and overall age are much more of a debate than the shunt.

Are we speaking of precision, accuracy or trueness?

[TitanMike]

Originally Posted by JRHill02

I respectfully disagree. The shunts are relatively accurate. The battery wiring/connections, maintenance, health and overall age are much more of a debate than the shunt.



Are we speaking of precision, accuracy or trueness?

My comment was only in regard to the ability of the monitor to read the miniscule current drawn by a battery's BMS.

A shunt typically "drops" only 50mv at the fully rated current of the shunt. On a 500 amp shunt that means it will show a voltage drop of 0.0001 volts for a 1 amp draw. One BMS manufacturer states their BMS only draws 0.000025 amp which would translate to far less voltage than the "resolution" published by Victron.

By my calculations the example BMS will draw around 325 Microwatts or appriximatelly 1/4 watt hours per month.

I agree that shunt accuracy is great. It's just hard for a 500 amp shunt to accurately read low level currents.

That's why small currents are read without shunts.

[TwoKozy]

Traded my two 12v SRM-12 Group 24 batteries for two 6v GC2 batteries. Hope to gain more AH.
Yesterday I installed two new Duracell SLIGC110 Ultra BCI Group GC2 6V 215AH in series onto the tongue of my TT. They showed 12.4v or 80% when energized.
See attachments.
Also changed all the battery wiring from #8 to #4 cables.Not 4/0.
At the positive disconnect switch I moved the load wire (with 40a in line fuse) to the load side of the switch leaving only the TT electric brakes and positive cable from the positive side of the positive battery on the line side of the keyed disconnect switch.

THEO as per your #44 post the negative chassis disconnect switch needs to stay closed(load side of shunt to chassis) for the BMV 712 Smart to function correctly.Thanks for all that work you put it to that clarification.

Also you suggested using the red temperature cable only for the Victron temp sensor?
The Victron 712 wiring diagram clearly shows the VICTRON dual cable with the fused red conductor going to B1 and the black conductor terminating at B2 of the shunt.They are both crimped to the same 3/8 flat blade lug at the positive battery terminal.With the blue shrink tube. See attached photo.

I am waiting to bring my TT home on Sunday and having the batteries charge for two days before manually setting the SOC to 100%.
This will be from a 20a 120v garage circuit thru my 30A 120v shore power cable.
Have changed my settings to:
BATT. CAP. 193AH
CHARGE VOLTAGE 13
BATT. STARTS SYNCH. OFF

As you can see with the battery pictures (no awards for lighting) I used #4 automotive battery cables for the positive and negative terminations. The main cables came with a 3" #12 accessory connector which I have spared off. Also the original two red fused conductors that came with my Victron shunt are installed between my battery box and shunt box but safed off at each end.
Will post again when all is up and running correctly

[emm-dee]

Originally Posted by Theo

(2) Have you correctly parallel-connected your two 12V batteries? BTW, they ARE 12V, right? Below is the preferred method:

Thanks for posting the graphic. I had another thread going looking for that info. Even Victron’s 36 page manual provides no guidance when working with pure parallel systems.

And, along with advice from a aircraft guy who has years of experience with aviation DC and AC systems, I got the auto shunt installed. Works fine.

[Theo]

Originally Posted by TwoKozy

...{snip}The Victron 712 wiring diagram clearly shows the VICTRON dual cable with the fused red conductor going to B1 and the black conductor terminating at B2 of the shunt.They are both crimped to the same 3/8 flat blade lug at the positive battery terminal.With the blue shrink tube. See attached photo.{snip}...

TK,
I bought my temp sensor 3-years ago and several months after I installed the BMV-712. The temp sensor came without an inline fuse on the red wire. It was in an opened package that was stapled shut; perhaps it was pilfered! So, I kept my original power wire in place and used the temp sensor's red wire to connect to B2. We've both accomplished the same thing, but I wish I had received a temp sensor with a fuse!

Nice job on the install! Everything looks proper, including the BMV settings. Please let us know the result!

[TwoKozy]

Started this thread weeks ago. Trying to close it out with a smile.
Got our TT home yesterday. Parked in front of the house, plugged into the 20a/120v garage outlet. Let the new 6V GC2 batteries charge for 20 hours till Victron BMV 712 Smart read:
State of charge 100%;
Voltage 13.67V;
Current 0.47A;
Power 7W;
Consumed Ah 0.0Ah;
Time remaining - ;
Relay State Open.

Unplugged the TT from shore power. Let the BMV settle for 2-3 minutes.
Pressed the Synchronize SOC to 100% tab in Battery Settings.

Nothing significant happened! Is it an electronic behind the scenes function? Should I have seen a blip or tab go grey? How am I assured it registered? Am I expecting too much from the App?
In the history window under Charge it is registering all zeros. Is this because it is plugged into shore power again?
Thanks in advance for your replies.

[Theo]

Originally Posted by TwoKozy

...{snip}Nothing significant happened! Is it an electronic behind the scenes function? Should I have seen a blip or tab go grey? How am I assured it registered? Am I expecting too much from the App?{snip}...

The only thing you should have noticed is that the SOC on the Status tab changed to 100%.

Originally Posted by TwoKozy

...{snip}In the history window under Charge it is registering all zeros...{snip}

Yup! should be all zeros...for now. Bear in mind that I DO NOT have a solar setup, but both my "Total charge cycles" and "Number of full discharges" read zero. Each time your BMV automatically (not manually) synchronizes, the "Synchronizations" field will update by one. Also, after your BMV synchronizes, the "Time since last full charge" field will be reset to zero and then will start counting the elapsed days and hours.

Originally Posted by TwoKozy

Is this because it is plugged into shore power again?...{snip}

Nope. See above. However, when you plug back into shore power, your "Current" field on the Status tab should be a positive number (no minus sign). This means that instead of current flowing out of the battery (minus sign), current is flowing into the battery from the charger/converter (no sign).

You should leave the shore power off for, say, five days with both disconnect switches closed (so current is flowing) but with everything turned off. During that time, look for:

(1) the "Current" field value being a negative value;
(2) the "Time since last full charge" field being updated with the elapsed days/hours.

The value in the "Current" field will be your parasitic draw with both disconnects closed. This simulates your parasitic draw when camping. I expect this reading to be somewhere between -0.20A to -0.80A. Record this first value for later.

After the five days have elapsed, check the "Time since last full charge" field. Does it display approximately the proper elapsed value? It should.

Finally, open both disconnects to "stop" the current flow. Now check the "Current" field in the BMV. It probably is not zero. You will see a negative value that is less than the first value you recorded. This is your true parasitic draw with the disconnects open, simulating the draw when your rig is in storage. This value (call it Ap) can then be used mathematically to forecast how many days your battery bank will last in storage before it nears 50% depth-of-discharge with both disconnects open:
(Battery Capacity/2) / (Ap * 24)

[TwoKozy]

Theo, ChickDoe, etc,
Victron BMV 712-Smart seems to be functioning well. Day 14 of our cross country trip and we have spent 4, not consecutive, nights boon docking. Batteries,2) GC2, are holding their own. Propane refrigerator, water pump and hot water heater only big items on full-time.

History states deepest discharge -23Ah.
Cumulative Ah drawn is -119Ah.
Still all zero's in the CHARGE category.

The only settings I've changed are the Charged Voltage and Tail Current.
A Victron video states to have the:
Charged voltage from 13.2v to 12.9 volts. (-3 from rated)
Tail Current at a factory setting of 4.0%. You have suggested 0.50%. I went with 2.0%.

Next step get a couple of lithium batteries and a swap out the converter to a full lithium charger or get an inverter/charger for them? That I could install closer to the batteries.....for another day and thread?

I'd like to thank the Forum for all the advice and shared knowledge that came out of this thread.

Safe Travels to all.