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jpebeer avatar image
jpebeer asked

BMV-702: how to disable automatic sync

I find the automatic sync function problematic with a system where charging can be from multiple sources (charger, solar, windmill). I also want to monitor the full cycles of discharge/charge myself. So, I want to disable it. With a 12V system I tried to put the charged voltage to 20V, the tail current to 0.5% and the charge detection time to 50 minutes. The 702 still syncs to 100% SOC after getting close to full charge and sometimes earlier.

Does somebody know how to completely disable the auto sync?

BMV Battery Monitor
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3 Answers
JohnC avatar image
JohnC answered ·

Hi @jpebeer

I don't think that's possible via switch. It won't sync under those conditions, though 0.5%Tail isn't really very low (try 0.01%).

If you haven't tuned it, it may be returning to 100% naturally, even prematurely. Try reducing the Charge Efficiency so it won't do that. Depending on your batts and how far you draw them down, this may need to be quite low. Like I use 88% right now.

There's a Sync counter in History, so you could keep an eye on that too. Also you can set SOC to whatever you want as you go along, which might help your researching.

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jpebeer answered ·

Hi John,

Thanks for your comments. On my 702 it is possible to reduce the tail current only down to 0.5%. Is there a new firmware version allowing smaller tail currents?

I had a Xantrex before and it died. It did not have automatic sync and I felt this was better for a multi source charging system. Due to the changed form factor I had to switch to Victron.

Maybe I should suggest a firmware mod to include an on/off switch for the sync function, but I don't know how to do that and it seems that few people have a problem with this.

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jpebeer answered ·

I also need to add that it seems that the firmware of the 702 has a logic flaw. In the manual it says that sync occurs when the charging voltage exceeds the "charged voltage" and the charging current drops below the "tail current" during a time longer than the "charged detection time". Since I set the "charged voltage" to 20V, these conditions should never occur and the auto sync never happen.

Or, am I wrong?

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JohnC avatar image JohnC ♦ commented ·
@jpebeer

You're right, and that's why I said yours shouldn't sync anyway. Thanks for the feedback on the 0.5% Tail, correct again, that's a lower limit I'd never used, so I checked and confirmed. I suggested a reduction of that for a 'triple assurance' that an unwanted sync wouldn't happen.

A firmware issue is unlikely, these devices are rock solid. Not impossible, but may be confused with a natural progression to 100%. Which can be controlled with other settings.

Not sure why you find your BMV 'problematic' with multiple charge sources. It doesn't know where the charge is coming from, it just measures it. It does need tuning to the battery, and you really must go through that if you want to be able to look at it's SOC anytime with confidence. Otherwise it's just an Ammeter.

As for Feature Requests, you can make those here. Maybe preface your question title with 'Feature Request -' and select it as a 'Topic' too. I've a personal desire to have sync occur at a figure less than 100%. I haven't requested it because I know it would add another line to an already complex parameter selection process. Just sayin.

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kevgermany avatar image kevgermany ♦♦ commented ·
To add to @JohnC excellent replies. Auto synch is there to correct drift errors that are inevitable with a device like this.
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