esbjorn avatar image
esbjorn asked

BMV-712 discrepancy vs voltmeter

My BMV-712 display 13,26V but voltmeters (2 different) display 13,51.
How do i get the correct value of BMW?

BMV Battery Monitor
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hour avatar image hour commented ·

I feel like I've seen quite a few of these threads lately and thankfully ordered some 1A fuses of the appropriate form factor the other week. I just got around to swapping the fuse out yesterday. Was previously ~0.08v below the voltage that two multimeters displayed. It's now 0.04v below. The BatteryProtect voltage and BMV voltage finally match, but they're still incorrect. So continued diddling with the BMV will just put it out of sync with the BatteryProtect.

Thing I really dont get, is despite joining / unjoining / creating new / yadaya VE Smart Network from the BMV, my SmartSolar 75/15 always shows a wildly different voltage when charging. If it's in float for a bit then the SmartSolar will read identical (or 0.01v) different than the BMV. Under charge though the BMV will show something like 13.58v where charge controller shows 13.40. I continue to check, and it always says it's actively receiving temperature and voltage data from the VE network.

Is the 'Battery->Voltage' in the SmartSolar page on app supposed to always match the BMV's 'Output->Voltage' when it's properly receiving information over the network? Or is it normal to observe a difference when a beastly bulk charge is underway? If it's normal, then what kind of arithmetic is being done to warrant displaying 13.40 on the charge controller and 13.58 on the BMV?

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2 Answers
sir-raoul-duke avatar image
sir-raoul-duke answered ·

I have this same issue. Mine started a bit differently though, in that the voltage was shown fluctuating all over the place and giving errors. So I started troubleshooting.

It's the included fuse holder. It's garbage. I have three of them. One with the temperature monitor, and two that came with the Victron 712. Use your voltmeter on the end of the positive lead that attaches to the 712. There's significant voltage drop in two of mine, and one that's completely faulty.

I bought this thought Amazon. I thought, no biggie, these things happen. I'll email Victron to let them know ... turns out that's not possible, as they have no tech support contact.

Then this morning I had a significant issue with the MPPT 75/15, where it ran at an unbelievable 15.7 volts after being connected, despite 14.4v being set as the Absorption voltage. And there's no way to limit the max voltage output. Thank god I've isolated this bank from my RV electrical system or I'd have some vehicle issues from that voltage spike. The voltage spike killed some of my "12v" equipment.

Needless to say, after all of these issues, I'll never buy Victron again, and I have some free equipment for anyone that wants this junk.

If Victron had a means of contact, that wasn't "contact your dealer" (I'm an Engineer, what help will Amazon really be giving me in this?) I'd have been able to feel okay. But no means of contact? That's a sign of not caring.

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ commented ·

Hi @Sir Raoul Duke, indeed we do not offert direct end user support.

We do care though, and my belief is that building up a room full of support engineers on phone or email is not the way to go.

Instead, we have a trained network of dealers and distributors. Also your buy from Amazon: that was through a dealer. Not Amazon, but someone else. So its Victron -> Dealer -> Amazon -> You. And that dealer will be equipped to help you & is responsible to help you.

Please check the documents closely; there ought to be a name of the “seller” on one of them. If not; drop the serial number here and I can look it up for you.

With regards to the voltage drop, please check the fuse. We’ve inadvertedly shipped the BMV-712 with a 100mA fuse for a while. It needs to be a 1A fuse.

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rainerb avatar image rainerb mvader (Victron Energy) ♦♦ commented ·

Hi mvader (Victron Energy Staff)

Is this an official recommendation or necessity to replace the fuse?

I bought my BMV712 about a month ago and there is also only a 100mA fuse installed in the cable and not a 1A fuse.



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wkirby avatar image wkirby ♦♦ rainerb commented ·

The 100mA fuse measures about 6Ω which presents too much of a Voltage drop between the battery + terminal and the shunt. This causes the BMV to read a lower Voltage than the actual battery Voltage.
A 1A fuse presents a much lower Voltage drop, which negates the error.

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ rainerb commented ·

Yes; it will take a while for all stock to flush through.

And yes, for the product to operate within specification, the fuse needs to be replaced.

Sending out a proper communication about that fell through the (? Whats the english word?). My apologies. I’ll make sure we send it soon.

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ben avatar image ben ♦ mvader (Victron Energy) ♦♦ commented ·

"Cracks." :-)

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wkirby avatar image wkirby ♦♦ ben ♦ commented ·

:) That's the word he was after. :)

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robinjay avatar image robinjay mvader (Victron Energy) ♦♦ commented ·

Just received my BMV-712.

The fuses in the two red wires read about 6 ohms.

The fuse in the temperature sensor (for BMV-702/712) also reads about 6 ohms. There is also a yellow tag on the sensor that says "Caution BMV 702 only!".

What gives? My first Victron purchase.

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wkirby avatar image wkirby ♦♦ robinjay commented ·

The 6Ω reading is due to 100mA fuses being fitted. This was an error in manufacturing and has been corrected. Of course it will take some time for the erroneous ones to flush through the market. Swap those 100mA fuses out for 1A fuses.

The yellow tag stating BMV-702 only is from before the BMV-712 was available. It's to alert people not to use the temperature sensor on a MultiPlus which uses a different type of sensor.
The sensor you speak of will work just fine on a BMV-712.

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robinjay avatar image robinjay wkirby ♦♦ commented ·

Packing list shows Victron products shipped from Victron in Thomaston, Maine. If I call them, will they send me the correct fuses (3 of them)?

The Quick Installation Guide doesn't mention the BMV-712.

Yellow label on the temp cable should be corrected as well.

On-line supplier had no idea about the fuse issue.

Thanks for the reply.

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ robinjay commented ·

Hi, @robinjay

I’ll make sure they do. Thank you.


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esbjorn avatar image esbjorn mvader (Victron Energy) ♦♦ commented ·

I switched from 0.100mA to 1A, but there was no change. This cable is with temperature.
Also tested 2 other signle cable 0,100mA with the same result.
I took the cables and tested on a BMV-702. They all worked with the right volt.
So the question remains: why different volts on BMV-712

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wkirby avatar image wkirby ♦♦ esbjorn commented ·

That's perculiar. Is it possible to temporarily swap the BMV-712 unit in to the place of the 702? This wil help to rule out cabling / wiring isues on the 712 side. It's the RJ12 cable that I am wondering about, perhps it has a bad connection or termination.

The caveat is that the 702 will loose its current Ah and SOC readings, so don't do the above if you don't want to loose that data.

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esbjorn avatar image esbjorn wkirby ♦♦ commented ·

I haven't tested RJ12 yet - the only thing left.

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esbjorn avatar image esbjorn esbjorn commented ·

Same result with both RJ12 :-((

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wkirby avatar image wkirby ♦♦ esbjorn commented ·

That's not expected behavior then. I suspect the unit is faulty / not calibrated correctly. Have it replaced by whomever you bought it from.

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esbjorn avatar image esbjorn wkirby ♦♦ commented ·

So it may be! It seems like a discrepancy of 0.2 volts and that says Victron MPPT 100/30 also on the battery voltage.

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esbjorn avatar image
esbjorn answered ·

Thanks for your reply. I will measure the red 12v and see if the fuse is incorrect.
I also use the Victron regulator (100/30), but have not had problems, but I would like to have a simple device that counteracts power spikes - I have a booster (Votronic 25A), which gives power spikes sometimes, when it closes charging from the car alternator

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sir-raoul-duke avatar image sir-raoul-duke commented ·

You're welcome. I think you'll find success in checking the cheap fuse holder, and replacing.

Given the amount of current that a 2000 watt sine wave inverter can draw there is no great way of equalizing voltage. And devices that do (victron has one such device) reduce system efficiency. The correct way is for the manufacturer to to build devices that are voltage limited - this makes complete sense. I realize that this is probably an algorithm that is running on connection, but anytime a 12 volt system is approaching 16 volts, that's just plain bad design!

And please look at your suppliers, Victron. 3 of 3 faulty fuses? That doesn't look good.

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