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Old 07-13-2018, 11:59 AM   #1
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Victron BMV 712 setup

I'm having difficulties with settings on my Victron. I have two 6 volt AGM Trojans and am unsure what to use for the full state of charge setting. I set the capacity to 117 amp hours, but when I get to a point of say 50 amp hours used, the voltage seems lower than it should be (like 12.2 or 12.1 volts) and the percentage of state of charge is really high like low 90s.

Should I just reset the monitor, fully charge the batteries and just put in the capacity only and let the monitor figure out the rest?

Thanks,

Joe
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Old 07-13-2018, 12:17 PM   #2
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Hi

1) Did you wire things correctly? Everything *except* the lower battery - terminal goes to one side of the shunt ( = low side). The *only* thing that goes to the other side of the shunt (= high side) is the battery. Charging cables, inverter cables, power to the rest of the trailer all to to the low side.

2) Does the shunt readout make sense? There are two possible shunts you could use. There are settings for both of them in the menus. If the shunt does not match the setting, the readings will be way off. Simple test is to turn on a Fantastic Fan and see if the current goes up by about 2 amps ( and not by 20 or 0.2).

3) If you have 6V AGM's, shouldn't the amp hours of each one be around 200 or more? If so, 200 ( not 110) would be what you put into the 712 as the "full" capacity.

4) The monitor power leads should go directly to the battery. The 712 should read the same thing that a multimeter does. If the multimeter says 12.1V, that's what you should see on the 712. If not, check the power wiring.

If your batteries are at 12.1V and the temperature is anywhere near normal, they are at the "stop using" point. That's true regardless of what the 712 thinks. The device will reset to "battery full" when it sees the charge current fall below a pre-set point. There is no need to do anything wacky to get it synchronized (assuming things are wired correctly).

Lots of fun !!!!

Bob
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Old 07-13-2018, 01:15 PM   #3
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Do you have a load on the batteries at that point? Try taking all loads off and see what voltage you are at.
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Old 07-13-2018, 02:04 PM   #4
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I'll echo Uncle Bob's comment-- I haven't seen and Trojan 6-volt AGMs with less that 200 amp hours, why did you set yours at 117?
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Old 07-13-2018, 05:00 PM   #5
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Quote:
Originally Posted by fran&frank View Post
I'll echo Uncle Bob's comment-- I haven't seen and Trojan 6-volt AGMs with less that 200 amp hours, why did you set yours at 117?
My typo. I meant 217 for battery capacity. I do have a minimal load but it's normally just the fridge, propane detector. I'm just wondering if I just set the capacity to 217 and nothing else at default if the system will do the rest.

Also I read AGMs can discharge at or a bit lower than 12.0 volts with no real issue.

Thanks,

Joe
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Old 07-13-2018, 06:42 PM   #6
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I had similar issues with mine I installed a few weeks ago but was more an issue with the solar charging reseting back to 100 before it was possible based on the AH used and charged via portable suitcase. Seems like it's closer to reality after raising the charged voltage setting. One of the things they tell you in the troubleshooting as I recall.
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Old 07-13-2018, 07:07 PM   #7
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Something is off if your state of charge is showing 90% with 217Ah as the capacity and 50Ah used. You should be showing about 77%. Double check everything as Bob mentioned above, as well as the values you've entered into the monitor.
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Old 07-14-2018, 06:59 AM   #8
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Hi

Indeed there is no single magic voltage that instantly kills lead acid batteries. The issue is accelerated aging of the batteries. You get far fewer discharge cycles before they die when you go to lower voltages. Since the actual voltages are temperature dependent, things get even more complex. Go out in the full sun in the desert and your voltages may all be a half volt lower. Sit out in the freezing snow and the voltages are likely a half volt higher.

One of the cute things a full Victron setup will do is look at a temperature probe and adjust everything so it works out over temperature. No more massive over charging batteries in the summer. No more killing deep discharges in the winter. Yes, this involves a bit more than just putting in a 712...

Bob
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Old 07-15-2018, 10:05 AM   #9
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Quote:
Originally Posted by AlinCal View Post
I had similar issues with mine I installed a few weeks ago but was more an issue with the solar charging reseting back to 100 before it was possible based on the AH used and charged via portable suitcase. Seems like it's closer to reality after raising the charged voltage setting. One of the things they tell you in the troubleshooting as I recall.
Yeah, that's what I was hoping to find out; what others might have put into the settings for their SOC for 2 6-volt AGMs. I currently have 13.3 volts but not sure if that's what I need in there. According to the manual, all I really need to put in there is that 100% SOC and the battery capacity.

Joe
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Old Yesterday, 07:04 AM   #10
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Hi

First some background:

A pretty typical charge profile for any lead acid is to run constant current up to some magic voltage in the 14.2 to 14.6V range. Once you get there, you dwell a bit and drop back to around 13.6 volts. If and when the current drops below some set point ( and possibly a timer expires) you fall down to around 13.2V.

The gotcha with most chargers in RV's is the current set point on the 13.6V stage. The charger does not know if current is going into the battery or a load. If the set point is something like a half amp and the RV pulls 1A all the time .... in never drops back. Putting a BMV 712 into the loop with the charger takes care of that.

Now your case:

Since you aren't playing with a charger and just working with the BMV, most of that really does not matter. Stand alone the monitor pretty much does not care what the charger does. It looks for a low current limit and declares the battery to be full. Since it *knows* about current into the battery independent of loads, it does a good job at this.

So ....

If everything is wired right and you only get to 13.3V, you have a problem with your charger / converter. If it's not getting to the right voltages, you are running with mostly empty batteries. The history log on the BMV will show you what's been going on.

Bob
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Old Yesterday, 09:46 AM   #11
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Quote:
Originally Posted by wareaglewalt View Post
Yeah, that's what I was hoping to find out; what others might have put into the settings for their SOC for 2 6-volt AGMs. I currently have 13.3 volts but not sure if that's what I need in there. According to the manual, all I really need to put in there is that 100% SOC and the battery capacity.

Joe
I'm using two T105's (not AGM). I've got the following in my settings:
Battery capacity: 225Ah
Charged voltage: 13.2V
Tail current: 4.00%
Charged detection time: 3m
Peukert exponent: 1.25
Charge efficiency factor 94%
Current threshold: 0.10A
Time-to-go averaging period: 3m


I'm using a PD4655 as my charger. Yours may need different settings.

Note, my charger settles in at 13.31V so the 13.2V charged voltage is below this, but maybe I should set it a bit higher based on the manual (0.2V or 0.3V above the float voltage for the charger). It is however working well so I'm not adjusting it yet.

I also adjusted the charge efficiency factor to 94% based on info I found for the T105.

I don't have a midpoint monitor installed between my two batteries, but since you are having issues I'd check the voltage across each of them to ensure they are very close to equal both when charged and when partially drained. There may be a bad battery in the mix.
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