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Dominic avatar image
Dominic asked

State of Charge never gets reset - BMV700 with MPPT 75/15 and 110W Solar panel

Hi, Sorry if this is a common question, I'm very new to Solar and trying to learn. I'm very impressed with my Victron gear but there is 1 problem.

I watched the Victron video explaining to change the BMV settings and have done so however the SOC detection still doesn't seem to be working...hope someone can offer some advice.

Setup:

120Ah "Fusion" brand battery

110W Solar Panel

BMV 700

MPPT 75/15

0.8A load

VenusOS on a Pi 3B+ with 2 x USB to VE Direct cables

The battery seems to be charging fine, I can see bulk then absorption then float phases. Unfortunately the SOC never gets reset at all, it just gradually declines until it's zero.

I haven't changed anything on the MPPT, it's by default at Factory default "Gel Victron deep discharge 2".

The BMV I have these settings:

Battery Capacity: 120Ah (I changed this)

Charged voltage: 13.5V (I changed this)

Tail Current: 4% (default)

Charged Detection time: 3m (default)


I set the charged voltage at 13.5V because I can't find the battery stat for this on the manufacturer's details so I looked at the average figure during absorption phase, 13.8. Based on this I set charged voltage at 13.5, 0.3 below absorption rate per video instructions here:

https://www.youtube.com/watch?v=4ReljfO3k6M

I guess I must have misunderstood something, can anyone help?

Thank you.




BMV Battery MonitorSOC
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3 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Is the BMV wired correctly?

If the SOC only goes down until 0% even if the MPPT is charging I guess that the (-) of the MPPT is connected directly to the battery instead of to the "load/charger" side of the shunt.

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Dominic avatar image Dominic commented ·

Thank you, I agree the cabling doesn't look correct that my friend did. This diagram looks right and will be easier for us to follow. Would you mind checking it is correct please?

solar-panel-install-1-panelmpptbattery-monitor-pdf.jpg

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solar-panel-install-1-panelmpptbattery-monitor-pdf.jpg (318.8 KiB)
klim8skeptic avatar image klim8skeptic ♦ Dominic commented ·

All loads and charger negatives must go on the "Loads/Charger" side of the shunt. You watched the video?

shunt.png

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shunt.png (140.6 KiB)
Dominic avatar image Dominic klim8skeptic ♦ commented ·

Isn't that what's depicted in this diagram?


Sorry I feel like I'm not doing very well here.

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Dominic avatar image Dominic Dominic commented ·

Ah you modified it, thanks.

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Dominic avatar image Dominic klim8skeptic ♦ commented ·

Just so I'm really clear, is it like this?


bmv-wiring.png

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bmv-wiring.png (422.9 KiB)
klim8skeptic avatar image klim8skeptic ♦ Dominic commented ·

Looks ok for the charging side.

Dont forget the loads negative wiring also go to that side of the shunt.

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Dominic avatar image Dominic klim8skeptic ♦ commented ·

My friend is going to re-wire this, final diagram with some load examples....


1, Low current load wifi gear will be attached to the solar charger load ports.

2. High power draw items such as a fridge would be connected to the positive on the battery and the right side of the shunt.

Really appreciate the advice.

Hopefully we've got this right end to end now?


bmv-solar-cabling.png

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bmv-solar-cabling.png (443.8 KiB)
Dominic avatar image Dominic Dominic commented ·

Can confirm cabled up as above and now all working fine, SOC is getting reset and can see the devices in Victron Connect.


Thanks for the help klim8skeptic and Matthias

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tedwad avatar image tedwad Dominic commented ·
Just a quick question - I'm about to add my BMV battery monitor and need to add the invertor cabling. Looking at the above - I would wire the same - from the battery (+) and the shunt (-)? As its in my shed - the chasis would be the invertor?
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klim8skeptic avatar image klim8skeptic ♦ tedwad commented ·
Have a look at the above diagram. Substitute the fridge for your inverter.

Dont forget to properly fuse your wiring.

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tedwad avatar image tedwad klim8skeptic ♦ commented ·
Thank-you. Thought that was the case. Do I need to fuse between the battery and inverter?
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klim8skeptic avatar image klim8skeptic ♦ tedwad commented ·
Yes.


The fuse needs to protect the cable between the battery and inverter.

The fuse should fail before the cable catches fire, should something bad happen.

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tedwad avatar image tedwad klim8skeptic ♦ commented ·
thank-you feedback very much appreciated
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Dominic avatar image
Dominic answered ·

Photo of the install

20210213-092243.jpg


20210213-092243.jpg (3.0 MiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Well, that is a new way to mess up the shunt's wiring. A star for effort.

BMV quick install guide.

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Dominic avatar image Dominic klim8skeptic ♦ commented ·

Yes, I reviewed the cabling guide, he's cabled it wrong by the looks of it.

This video was also useful

https://youtu.be/MRljOaTdc3s


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Dominic avatar image
Dominic answered ·

These are the graphs from VRM portal

bmv-soc-not-working.png


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