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aaronmiller avatar image
aaronmiller asked

BMV 712 soc full too early

Hi,
Setup is a Century Marine flooded lead acid under the bonnet of my 4wd, charged by a Redarc BCDC 1225D. I am working on the assumption that the redarc knows what its doing and when its showing greater than 13.6v and or 3 amps going into the battery, the battery is not full.
When using the default settings for Peukert and charge efficiency, soc is indicating that the battery is full whilst i am still seeing 10+ amps going into the battery so i know its nowhere near full.

The general advice from victron suggests that doing a sync will help ensure the accuracy, but it seems that unless the soc drops to below i think its 60% then a sync will not occur. The problem with that is the soc from day to day doesn't go below an indicated 85%.
The only usual thing running is the 12v 47l fridge.

Is the 712 behaving as usual, or should i be tweaking the Puekert and charge efficiency figures?

battery charging
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3 Answers
klim8skeptic avatar image
klim8skeptic answered ·

What charge profile (volt) have you set the redarc to?

What charged voltage have you set the bmv to?

Has the redarc done a "full" charge cycle? (boost>absorb>float)

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aaronmiller avatar image
aaronmiller answered ·

Redarc is set to profile A (14.6)

bmv to 13.1

yes many times, this has been ongoing since installed 6+ months ago

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klim8skeptic avatar image klim8skeptic ♦ commented ·

Hi Aaron.

I would definitely look at bumping up the charged voltage a little, have a look at page 12 of the manual. https://www.victronenergy.com/upload/documents/Datasheet-BMV-712-Smart-EN.pdf

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aaronmiller avatar image aaronmiller klim8skeptic ♦ commented ·

Hi,
Float on the bcdc is 13.3, it is suggested to set the charged voltage to 0.2 below float in the manual?

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klim8skeptic avatar image klim8skeptic ♦ aaronmiller commented ·

Hi Aaron.

Charged voltage should be set just below the absorption voltage.

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aaronmiller avatar image aaronmiller klim8skeptic ♦ commented ·

Ok will do,
but I don’t think that will solve the problem. That will effect whether the bmv syncs or not, but as I typically only draw down the battery by around 10% each day and then it charges back up the battery doesn’t get low enough for a sync to occur.

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Justin Cook avatar image
Justin Cook answered ·

@aaron.miller, a couple of thoughts:

1: Are you certain that no chargers or loads are bypassing the shunt? If a load (such as your fridge) is connected directly to the battery rather than the NEG attached to the "loads" side of the shunt, the BMV would be reporting 100% SOC much sooner than is actually the case because it can't "see" the outbound current of the load.

2: Is the Ah capacity of your battery set correctly in the BMV?

3: How long have you had the BMV connected? When you first connect it, the default option is for it to think that it's starting out at 100% SOC, so if you were actually at 60% when you connected it and you didn't set it accordingly, it will think that 60% is 100% until it learns better (usually 5-6 discharge/charge cycles).


I kinda think that option 1 or 3 are the most likely causes of this behavior, but if you check everything out and it's not any of the 3, definitely report back to us... I'm always super curious about unexpected behavior in these.

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aaronmiller avatar image aaronmiller commented ·

Hi,
1. there is only 1 cable attached to the negative post which is the cable coming from the battery side of the shunt

2. battery has 100ah capacity and is set in the unit

3. I have had the unit for around 2 years, it has been in the current car for 6 weeks. I relocated the head unit, when I reconnected the data cable from the shunt, the battery symbol was flashing and soc was at 0%. The battery was charged by a 240v charger with the negative clamp on a earth point and the soc showed 100%
since then the battery has cycled daily, the fridge runs 24/7 and the car has been run long enough maybe 10 times to the point that the bcdc has gone into float.
With both the previous car and this car, the soc has always returned to 100% at least an hr before the bcdc goes into float.


the cabling in the car has the following setup.

negative cables from the bcdc and solar Anderson plug go to an earth point on the body inside the engine bay approx 10 cm from the cars main earth point

the negative wire from the fuse box in the rear of the car, goes to the negative post on the start battery. A negative wire goes from the negative post on the start battery to the load side of the shunt.

Aaron

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