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stulana avatar image
stulana asked

BMV-712 measuring current, but no draw apparently charging or discharging battery

I've just hooked up the BMV-712 to my van's system that's been working well for months. I've got 2 LiPO4 Trillium batteries in parallel that solar charge with the Victron 100/30 Solar Charge Controller. I've also got a Battery-to-Battery Charger (Sterling 60amp) for cloudy days hooked into the system - its very plug-and-play. I've been using the Victron Connect app for a while and following the solar charging profiles. All has been going well and the 320 watts of solar keeps the batteries charged up very well (with minimal use over the winter). My question is: The BMV-712 measures about a +7 amp current (after I zeroed the current on the app) even when its dark. I have the Trillium batteries hooked up to the shunt's "battery" side. The other side of the shunt is wired to a negative bus bar that includes all negative loads in the system - including the starter battery (which I am using as my ground - the starter batter is then well grounded to the chassis). I am also monitoring the voltage of the starter battery with the BMV-712 via the +B2 input. If I was indeed drawing this much current into the Trillium house batteries for the last 3 months (from the starter) then my starter would be constantly discharged. This current is present when it's dark outside so its not the solar. Can you please help me figure this out?

BMV Battery Monitor
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8 Answers
spanner avatar image
spanner answered ·

Is shunt wrong way around - ie battery and load connected to the wrong ends ?


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stulana avatar image stulana commented ·

Thanks Spanner... I don't think so. The Shunt's inputs (UTP cable and B1/B2) are facing down - my house batteries are connected to the left side and negative bus bar is connected to the right side. From all the diagrams they have sent me, this seems right.

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spanner avatar image spanner stulana commented ·

Seems weird - the info you've provided indicates that there is a 7 amp plus load and no charging, is this a correct statement - can you take a photo of your shunt?


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stulana avatar image stulana spanner commented ·

I'll send a photo soon. The other weird thing was that the monitor measured the 7 amps load even while the positive on/off switch was in the "off" position (while I was wiring things up). I'm wondering if I have a ground "leak" of current, but I'm just guessing as this isn't exactly my area of expertise.

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stulana avatar image stulana spanner commented ·

Hi spanner: Just now, I attached a photo to another message in this thread. If you wouldn't mind having a look, maybe you can unravel my mystery.

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spanner avatar image spanner commented ·

Ooh - if you take off the neg to the starter battery - is there something on your system wired to chassis ground??

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stulana avatar image stulana spanner commented ·

No. I was assuming that if I was wired to the neg of the starter (which is then grounded), I would be all good. Maybe my assumption was wrong.

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spanner avatar image spanner stulana commented ·

ok - possible some thing push / pull between the 2 batteries and common -ve, almost got to pull all the fuses / isolators and switch them back on 1 at a time until the culprit is identified !


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stulana avatar image stulana spanner commented ·

I've given this a good try. Disconnecting everything and reconnecting one at at time. Nothing. No change to the read out whatsoever. I've even turned on multiple appliances at once expecting a change in the current read out - no change at all. Appliances worked just fine. I'm starting to think the ammeter is broken.

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seb71 avatar image
seb71 answered ·

When you zeroed the shunt, did you disconnect everything from the battery (except the shunt itself)?

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stulana avatar image stulana commented ·

Thanks very much seb71! I just tried this, but it didn't work. Still measuring around 7-8amps of current. Even when I disconnect the battery bank entirely (on both pos and neg sides) from all loads (except the shunt), it still measures the same current. I've posted a photo. Have a look at my wiring and see if something jumps out at you (if you wouldn't mind!).img-5965.jpeg

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img-5965.jpeg (7.9 MiB)
img-5964.jpeg (310.6 KiB)
seb71 avatar image seb71 stulana commented ·

So you disconnected the negative wire between the shunt and the negative busbar.

Disconnected the positive wire from the battery pack.

Then in VictronConnect you entered the BMV battery settings and you did "Zero current calibration" (clicked/taped that button).

After that the shunt still shows 7.73A going into the battery.


If the above is accurate, most likely the BMV is defective.

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Unrelated:

Modify the wiring of your two batteries in parallel so that the negative wire that goes to the shunt is connected to the negative terminal of one battery and the positive wire that goes to the fuse and battery switch is connected to the positive terminal of the other battery.



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stulana avatar image stulana seb71 commented ·

Thanks again! Yes, all that info you wrote is correct. My unorthodox parallel wiring could be the cause? I tried it to save wire runs, after double checking with an electrician, but can easily change it. Maybe I'll start with that. Next, if that doesn't work, I may try to ground the load side of my shunt to both the common neg bus bar AND add a grounding cable to the chassis close by.

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stulana avatar image
stulana answered ·

Also, with the system up an running, I attached a large load via my inverter (about 800w at 120v) - the current readout from the shunt changed minimally, but the load was clearly getting power. I'm a bit baffled. Can these shunts be faulty?

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spanner avatar image
spanner answered ·

Doh - possibly got it got it, your lithium is charging your starter battery through the shunt where are the +ves of your lithium

wired?

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stulana avatar image stulana commented ·

My intention was not to charge my starter with my lithium house batteries - hopefully that's not happening. The positive from the starter is through the B2B charger (gated), but negs are all common. The positives from my lithium house battery bank go to a bus bar on the left/bottom of the photo I posted (except the small pos from lithiums to shunt). This weird amp draw is present even when all pos & negs are disconnected from lithiums.

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spanner avatar image
spanner answered ·

interesting - the +ve supply to the shunt - where is it wired onto, should be direct onto the battery - cant quite see on the pic, the other +ve on the shunt is this for your starter battery voltage?


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stulana avatar image stulana commented ·

Initially, I had the +ve supply from the lithiums to the shunt directly on the lithiums. Then I changed it to just downstream (about 6" away). I've wired the batteries in parallel, but in a weird way, maybe that's the issue - after double checking with an electrician, I connected pos to pos and neg to neg, but the take off wires come off the same battery (a bit unorthodox). And yes, the other +ve on my shunt is from the starter battery measuring voltage.

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hmcintyre avatar image
hmcintyre answered ·

Hi, I was wondering did you ever sort this issue out? As we are having the same issue! @stulana

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stulana avatar image
stulana answered ·

Hi, I did finally sort it out after replacing the shunt (which wasn't the problem). The UTP cable was bad. As soon as I replaced that, it all worked just fine. Hope this helps.

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hmcintyre avatar image
hmcintyre answered ·

@stulana Thank you so much for your advice! We had a faulty UTP cable also, all is working now. I had a very happy bloke today in the van! lol

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