Victron BMV-712 Settings

[TwoKozy]

Hoping you can help me out. Installed a Victron 500 shunt with a Victron BMV-712 Smart meter on 3/9/22. Watched a few you tube videos. Posted on the FR Forum. Tried contacting support with PIKE Industries where I got the system from on Amazon. No response.
Still not confident I have the settings correct for it to function properly. Absolutely sure my installation is correct.
First off let me tell you 99% of our overnights are in campgrounds with minimum E/W 30amp hook ups. We are in a 26'TT with 30A main. No inverter, no solar, no generator. Plans for all the previous mentioned features but not yet. Lithium batteries next step forward.
Anyways please if you have time and inclination look at my attached screen shots from our last outing where we had E/W for 4 solid days. Pictures from 5/9 which was start of day 4. Are my settings correct for two lead acid 120Ah batteries wired in parallel?
I tried to Manually synch the Victron with my phone app (a couple of times)but it doesn't show in the history. And nothing appeared to happen after touching the Synchronization button. So I don't know if it's synched at 100% or not.
Is there a way to do it with the meter buttons themselves?
Expensive investment of time (installation) and money for it not to be functioning. Or am I expecting to much?

[kcmusa]

2, 120ah in parallel should be 240ah battery capacity.
Take off battery’s start sync
Charge battery’s then set state of charge to 100%
Most everything else leave at default.

[Theo]

TK -

Based on my earlier post to you in March, you have made some good adjustments to your original settings. However, I would make the following additional adjustments:

Battery capacity: As kcmusa just pointed out, your (2) 120Ah rated batteries in parallel (on paper) produce 240Ah of battery capacity. However, for the sake of tuning the BMV-712, I have had the best results by entering in a value that is 90% of the specified battery capacity; in your case that would be 216Ah.

Charged voltage: You may have adjusted this a bit too low. In my earlier post I suggested this be set at 13.0, or about 0.2 volts below your actual float voltage. My earlier recommendation also assumed that your float voltage was 13.2V but I also posted how you could verify this voltage (see "Note:" in my earlier post).

Charge efficiency factor: You may also have your value of 85% set just a tad too high; I'd try 80% and see if that yields a more accurate result.

Glad to see you changed the Tail current to a much more reasonable 0.50%. However, you may want to actually verify your tail current by referencing the "Note:" in my earlier post.

I think that kcmusa's battery capacity recommendation (minus 10%) will make the biggest difference but please make the above changes (in red) as well. Also, have you considered adding a temperature sensor to your BMV? IMHO, it is much more useful than knowing the battery bank's midpoint voltage since the battery temperature (if available) is used by the BMV as an (optional) parameter in calculating the actual temperature-compensated SOC. Anyway, if I need the midpoint voltage to check on battery-balancing, I'll get out my multi-meter!

HTH

[TwoKozy]

Ok made the changes in red. TT has been sitting with both negative & positive battery switches open. Batteries down to 8.3V.; 0.0 A; 0W;-0.1Ah; 100%; INF h; showing full bar. All on the display.
See screen shot of my iPhone app!
Do not understand?

[rk06382]

Originally Posted by TwoKozy

Ok made the changes in red. TT has been sitting with both negative & positive battery switches open. Batteries down to 8.3V.; 0.0 A; 0W;-0.1Ah; 100%; INF h; showing full bar. All on the display.
See screen shot of my iPhone app!
Do not understand?

Default is to reset to 100% every time you power the Victron BMV-712 up.

[Theo]

Originally Posted by TwoKozy

Ok made the changes in red. TT has been sitting with both negative & positive battery switches open. Batteries down to 8.3V.; 0.0 A; 0W;-0.1Ah; 100%; INF h; showing full bar. All on the display.
See screen shot of my iPhone app!
Do not understand?

Obviously, something is wrong. Unfortunately, we may need to go back to basics, so please excuse the elementary questions. We need to verify a few things before we get too far into this:

(1) I'm not sure what you mean by "sitting with both negative & positive battery switches open"? Please describe this in more detail. Or, better yet, post photos of these switches.

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

BTW - This diagram DOES NOT show the shunt's fused power wire which should run directly from the positive terminal [A] to the shunt's B1 port.


(3) Is your shunt connected "directly" between the battery's negative terminal [B] and the chassis? By directly, I mean that there is nothing but the shunt connected between the negative terminal and the chassis ground. No other negative wires are connected to this path?

(4) It would help greatly to see photos of how your batteries are connected and how your shunt is directly connected between the negative terminal and the chassis. These photos will be of great value in helping us remedy your issue.

[TwoKozy]

Absolutely sure all are wired correctly. Just as your diagram shows.
Except there is also a power cable to the shunt (B1 to Terminal A) from the positive battery terminal that you show going to the RV Charger. So the Victron BMV-712never loses power.
2 12volt 120Ah batteries wired in parallel.
The TT came with a keyed battery disconnect switch from the factory. This is wired to the positive(RED) side of the battery bank after the break away brake switch. Turn it off and take the key out to disconnect.
I recently installed a on/off rotary style disconnect between the load side of the shunt and the chassis to nullify ALL power from the batteries. Except the Victron 500mA shunt.This is in answer to your #3 question.
I put it between the green negative cable and the chassis frame on the TT tongue. You can see the 4/0 cable with green tape on the right of the picture before I added the rotary disconnect switch to the TT tongue metal. Drilled and tapped the chassis bolt to replace the tek screw ground installed by the factory.No other negative cables attached from battery terminal B to bolted chassis ground on TT tongue metal.
Sorry can't post more pictures. TT a couple of miles away in storage. Will take some tomorrow but I've dressed the cables out pretty well and not sure how revealing they will be.
You can see inside the shunt 6x6x4 plastic box that I installed the spare red #22awg cable from that box to the battery box but taped off each end. If I do install a temperature cable I can use that as a pull string.
Thanks for all your input. Can't figure out why it doesn't work properly-unless I've never really synched it when fully charged?
But at 8.3v it shouldn't be showing 100%.

[Theo]

TK -

First of all, you need to verify the voltage in your battery bank using a multimeter! If it IS indeed 8.3V, you are damaging your batteries and need to charge them IMMEDIATELY! FLA batteries should never be allowed to drop below 12.00V @ 70º(f). I repeat, CHARGE THEM IMMEDIATELY! If you have to, bring them home and hook them up to a charger.

[Theo]

TK -

Second, you need to understand the electrical import of rk06382's post. By turning on the "Battery starts synchronized" setting, it means that each time current to the BMV-712 is removed (by turning-off your negative disconnect switch) and then reapplied (by turning-on your negative disconnect switch on), your SOC will be forced to read 100%.

What is not evident is that even though the shunt is visually wired to the positive and negative battery terminals, if the shunt is not grounded to the chassis, no current flows and the BMV will lose power.

That would account for the 8.3V reading but with 100% SOC! More on circuits in the next post.

[Theo]

Now that we've figured-out what caused your 8.3V to read as 100% SOC, let's quickly/simply review how a battery generates current (moves electrons) through a wire. Bear with me on this one, please!

Electrons emanate from a battery's negative terminal and are "attracted" by positive ions inside the battery through the battery's positive terminal. Without a path connecting the negative and positive terminals, no electrons flow and, thus, there is no current (your BMV reset problem). Similarly, if a wire is connected between the terminals (DON'T DO THIS!) but it is cut, no electrons will flow and there is no current. It does not matter where on the wire (circuit) the "cut" takes place; an open circuit results and no electrons will flow.

Therefore, your two disconnect switches are redundant. In fact, the negative disconnect switch just boogered-up your BMV's reading!

I know what you are trying to achieve here, but there is a less error-prone way of ensuring no unneeded current flows by examining your how your positive disconnect switch is wired. But first, there are a few circuits to which you might consider keeping current flowing:

(1) your CO/LP detector;
(2) your radio (in standby mode to keep station settings);
(3) and, especially, your RV's electronic emergency brakes.

Most RV smoke detectors are battery-operated these days, but check to be sure. If no batteries, then that is another circuit to which power should remain.

Using my BMV-712 amps (current) display, I know that in my RV, with the positive battery disconnect off, the parasitic load is only about 0.20A at any given moment. That's only about 4.8A a day. That is the draw from my CO/LP detector, my emergency brakes (hopefully, always zero draw) and my A-frame jack (rarely on). I have rewired my radio's standby circuit with an on/off switch so I can choose whether I want to preserve presets or not.

The problem with using a second, negative disconnect is that turning it on can be forgotten by you or your co-pilot. If that is done, you'll have no emergency brakes should the trailer become disconnected. And, I believe that most, if not all, states require emergency braking capabilities.

Also, if the negative switch is forgotten, you won't be able to charge your batteries with the RV's charger. And, obviously you'll unknowingly reset your BMV without having recharged your batteries!

[TwoKozy]

OK, so you believe that having the rotary negative cable disconnect switch between the shunt and the chassis ground is the cause of the misreadings?
I realize the outcome of forgetting to turn back on before using the TT, but I only plan to use this switch when in long term storage. (As with the keyed positive cable disconnect.)
This was installed to hopefully keep me from having to remove the batteries to the charger in my garage. But will do so today. After pictures and individual battery readings with my multimeter.
What do you think of me leaving them hooked up in parallel while charging with a 12 volt three step charger?
We are planning a cross country trip after Memorial Day.

[CHICKDOE]

I have the victron smart shunt and I was concerned about it drawing the battery down while in storage. So I was considering putting the disconnect between the battery and the shunt as you did. However, I did not and I put it after the shunt so the shunt is always connected to the battery negative terminal and to the positive terminal via the small 12+ wire. It turns out the shunt draws so little power that I can leave it for months without any appreciable battery drain. Plus there is another huge benefit to wiring it this way. I can drive over to the bad trailer and get the battery status on my phone via their app without even having to get out of the truck. This is great! You can easily check battery status and you’ll see the shunt does not drain the batteries.

As far as the possibility of towing with the batteries disconnected because I forgot to turn the disconnect switch back on I have what I consider a fail safe. I must use the front legs to raise the trailer when we hook up. To do this I must have the batteries connected. So I can’t even hook up unless I put the batteries back on-line. This works for me.

[Theo]

Originally Posted by TwoKozy

OK, so you believe that having the rotary negative cable disconnect switch between the shunt and the chassis ground is the cause of the misreadings?...{snip}

TK -

By turning the negative switch off, you have opened the circuit and cutoff the flow of electrons that would have powered the BMV. I know your intention was to eliminate parasitic draw, but that can be done (better) by rewiring your positive switch. More on that later; for now, get your batteries charged so you can determine if any damage was done to them by letting the voltage drop to such a low value.

To check their voltage in the battery box, connect the + probe to the battery terminal to which you have your BMV power wire connected and the - probe to the battery terminal to which your black 4/0 cable is attached.

When you bring them back to be charged, connect the charger clips to the same two terminals.

I would also turn-off the BMV's "Battery starts synchronized" setting. That will prevent your SOC from resetting to 100% due to an open circuit being closed by turning on your negative switch.

[Theo]

Originally Posted by CHICKDOE

...{snip}So I was considering putting the disconnect between the battery and the shunt as you did.

CHICKDOE -

Actually, TK didn't do that. His negative disconnect is between the shunt and the ground...which would be fine if he had not turned on the "Battery starts synchronized" setting!

This caused the BMV to automatically be set to 100% SOC as soon as the negative ground was reconnected...no matter what his true SOC actually was. Hence, it forced the BMV's SOC to read 100% when the actual battery bank voltage was only 8.3V.

[wharfrat48]

Your original post indicated you camp with hookups 99% of the time, what draw is on your battery bank to bring it down to 8 volts. You also mention lithium, solar, invertor, and generator are all on your to do list, is that because you plan to start boondocking much more?

[CHICKDOE]

But if the negative disconnect is after the shunt (on the load side of the shunt) then the shunt should be powered at all times. Unless the small 12+ wire from the shunt did not run directly to the battery positive terminal and instead ran to the load side of the disconnect he has on the positive cable. If this was the case operating the positive disconnect would also turn power off to the shunt.

I do not have the synchronize upon connection option turned on. Instead there are settings for tail circuit amps and voltage (or was it time)? Anyway when the charging amperage falls below this threshold for the specified period of time the shunt then set the he SOC to 100%.

[Theo]

Originally Posted by CHICKDOE

But if the negative disconnect is after the shunt (on the load side of the shunt) then the shunt should be powered at all times.

I am assuming (and you know what that means!) that the BMW monitors the current running across the shunt and and not the current running from the battery side of the shunt to the battery's positive terminal. If that is indeed the case, since the current does not travel across the shunt, no amps are registered by the BMV's coulomb-counting algorithm. When the ground is then restored, a significant state change across the shunt is suddenly detected and, with the "Battery starts synchronized" setting set to on, this presents an effective "battery started" state to the BMV and the SOC is reset to 100%.

When I get a chance, I will test this hypothesis out on my rig. If I disconnect the ground side of the shunt and the BMV stays powered-on but shows zero amps for the current, this would confirm the hypothesis. I'll report back to this thread.

Originally Posted by CHICKDOE

I do not have the synchronize upon connection option turned on.

Excellent. If you have a negative disconnect, that's the proper setting!

Originally Posted by CHICKDOE

Instead there are settings for tail circuit amps and voltage (or was it time)? Anyway when the charging amperage falls below this threshold for the specified period of time the shunt then set the he SOC to 100%.

According to the BMV-712 manual:

"...the BMV resets to ‘fully charged’ when the following ‘charged parameters’ are met: the voltage exceeds 13.2V and simultaneously the (tail-) charge current is less than 4.0% of the total battery capacity (e.g. 8A for a 200Ah battery) during 3 minutes."

(of course the parameter numbers will/should be different for a LiFePO4 battery bank)

[CHICKDOE]

[QUOTE=Theo;2737658]I am assuming (and you know what that means!) that the BMW monitors the current running across the shunt and and not the current running from the battery side of the shunt to the battery's positive terminal.

there must be some current flow across the shunt at all times that it is active. the current flow is through the large cable to the battery negative and then through the small plug in cable to the battery positive. this current has to be there as it would be used to keep the performance numbers in memory and to power the bluetooth capability. but this current is in the milliamp level and as such i don't know if it can show on the display as i think the display only display current in 1/10's of an amp. a milliamp is still two orders of magnitude smaller than what the display can show. i don't know if the shunt can sense this small of a current.

[Theo]

Originally Posted by CHICKDOE

{snip}…there must be some current flow across the shunt at all times that it is active…

We’ll, not necessarily. The negative connection to the BMV’s processor could be on the battery side of the shunt and not on the ground side. So, the electrons would flow from the negative battery terminal to the battery side of the shunt, through the processor circuitry and then back to the positive terminal through the fused power wire. The circuit doesn’t NEED to flow through the shunt in order to power the processor and the display.

[TwoKozy]

I agree with CHICKDOE. The negative disconnect is inline with the load side of the Shunt and the chassis ground bolt therefore it still gets constant power to the BMV 712 Smart from the positive red conductor to the B! terminal supplied by Victron. If it effects the load reading is a good question.
But is part of my checklist when picking up my TT from storage and then is on constantly. Nothing will work without it closed.
I have attached photos of my battery wiring and disconnect switches.
The batteries are wired in parallel and read 8.28V from negative load terminal to positive load terminal across both.
When completely disconnected the Green battery measured 8.28v.
The black battery measured 9.24v when isolated with no conductors.
I have both in my garage (Las Vegas = Ave Temp 90 something!) charging one at a time.
We have two weeks before our second cross country trip. hopefully all will be resolved by then.
Another battery question.While at my MIL's house we will only have power from a 20A/120V AC circuit. will this allow the WFCO8955 converter enough power to charge the batteries? No other major power loads will be in use.
Thank you all again for your time and input.