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Old 03-01-2019, 10:56 PM   #1
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2018 30' Flying Cloud
Anchorage , Alaska
Join Date: Sep 2018
Posts: 204
BMV-712 Setting

I have a 2018 Flying Cloud with a WFCO 9855 converter. According to their website, it uses 13.2 V float, 13.6 V absorption, and 14.4 V bulk charging voltages. I just replaced the dealer killed SRM-24 batteries with some 6 V golf carts from Costco as a temporary fix on my way to lithium. I also added a Victron BMV-712.
Weíre now at our first campsite going on the new batteries. Over the course of around 24 hours we used 96 Ah of our 210 Ah total. The BMV seemed to track all that fine. At that point we hooked up our 2000 W generator to the shore power connection to charge. Unfortunately the converter doesnít seem to go into bulk and only around 10 A /120 W ever flows into the batteries. I donít remember the exact voltage. It was thirteen point something. Anything going on in the trailer reduces that 10 A. After about 5 hours, around 50 Ah had gone back into the batteries, but suddenly the BMV said 100%.
So all that gets me to the question on the BMV settings. It uses the charged voltage (default is 13.2), tail current (default 4%), and charged detection time (default 3 minutes) to decide when the batteries are full. 4% of my 210 Ah batteries is 8.4 A for the tail current it is using. I can see how we could have easily been down to that while making dinner since every 12 V thing you use was reducing the batteryís share of the ~10 A the converter was producing. Should I set tail current lower? If 8 A is flowing into the battery, that doesnít seem very full.
Victron says to set the charged voltage 0.3 V below the float voltage, which would be 12.9 V. I donít quite get how a value below the float voltage is ever going to happen as long as the converter is on though. On another thread on here someone else said to set it above float not below. What are other people using for this number? Are my settings fine and the converter is the problem, do my BMV values just need adjusting, or what is going on?
Any thoughts are appreciated.
Thanks.
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Old 03-01-2019, 11:53 PM   #2
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2018 25' Flying Cloud
Portland , Oregon
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I use my BMV712 with a lithium bank so Iím not a great source of wisdom on settings for yours but it does seem like the battery monitor doesnít know what the capacity of your battery bank is for starters. Iíd verify itís set to whatever number you want to use for that.

The converter seems to be in the dark as well. I donít know how you set that. If you are compemplating up grading the inverter and charger sooner than later you might consider the Victron multiplus.
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Old 03-02-2019, 09:48 AM   #3
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2018 30' Flying Cloud
Anchorage , Alaska
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The battery capacity is set to 210 Ah. Everything tracked fine on the state of charge going down and coming back up until it got to seventy-something percent and the next time I checked it a few minutes later, it had jumped to 100%. I think itís an issue of the values for Charged Voltage and Tail Current being met, so the BMV considers it full. Whether the values being met is the problem or the settings of the values themselves, I donít know.
The multiplus is a great suggestion and what I am 95% leaning toward when I add the lithium. Right now Iím on the road and figured rewiring for the multiplus while living in the trailer wasnít feasible.
This morning I hooked up the generator again and it is charging at 12.8 A and 13.09 volts, per the BMV-712. The SeaLevel indicates 13.4 V, which Iím guessing is because it takes the voltage closer to the converter and thereís 0.3 V of line loss.
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Old 03-02-2019, 10:02 AM   #4
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It does seem you are right that the charged voltage setting is getting met prematurely on the BMV so it figures everything is charged. Since the BMV is just for giving you a state of charge indication, and not controlling the charging process in your setup, you could experiment with increasing the charged voltage setting on it slowly until the BMV matches what the charge controller is doing. If the BMV indicates 100% charge about the same time the charge current drops to float then youíve found that magic place.
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