A week with the Victron BMV-712...mystery discharge?

[Ruck_and_Roll]

Last week installed the BMV-712. Finding it fairly nifty. I ran through each of fixtures and was able to determine their power usage...cool. Turning camper master switch off showed no discharge....cool (nothing mysterious is draining my battery). Plugging into shore power and pulling out master switch shows battery charging....cool.

Everything seemed to be working as expected until I plugged into truck power later in the week (finally got this wired up). Car is on and shows + charging. Everything seems to making sense....Until I turn the truck off.

Now battery monitor is showing
-1.0 amps (when atwood plug is connected)

Now it even gets stranger, I disconnect the atwood plugs and I'm seeing around -0.5 amps. This is consistent. Master power is "off," and/or master power is "on" (and everything is turned off), both show around -0.5 amps. Turned off/on master fuses. Went camping this weekend. Consistent -0.5 amp draw when nothing is powered on and/or master switch is off the whole time.

All the electrical components seem to be stock:
Converter: Iota IDP-30 (no IQ4 or IQ-AGM)
Battery Seperator: Sure Power 1314/1315 (can't tell which model number as it is packed pretty tight)

So needless to say I'm a little confused. Any comment on the following hypotheses?
-Battery monitor itself is using about -0.5 amps (seems unlikely particularly as it showed '0' discharge for the first 3-4 days I had it installed)
-I somehow damaged the battery? Batter is a cheapie. It is a FLA 75AH that came with the camper. He stated it was new. Thursday morning I did notice the propane alarm going off after plugging into shore power. Could the batteries have cooked and somehow become damaged to a slow discharge?
-Other scenario?

I guess there are technically two concerning issues; 1. being that battery is discharging around -0.5 consistently and 2. that the discharge seems to be a little higher when plugged into the truck (and truck is off).

 

[Vic Harder]

Look in the BMV manual for the zero current calibration - https://community.victronenergy.com/questions/20193/bmv712-how-to-do-a-zero-current-calibration.html

Also, it isn't unusual for current to flow FROM the camper batteries back to the truck battery when you first turn off the engine... that would be a -ve current flow. If it gets too serious, the battery separator will kick in and disconnect the two systems.

 

[veryactivelife]

As far as the alarm going off, there are 2 things (other than a failed alarm) that most often set it off. One is very high humidity and the other is off gassing from the battery. You don’t mention if you have solar so I’ll assume you don’t. If your FLA battery is not in a vented compartment and/or some distance away from the alarm then that could be the problem. Even with my AGM batteries located in a compartment vented to the outside I had alarm problems due to overcharging with my solar system. After replacing the solar charge controller with a Victron which allows for custom battery profiles the alarm problem went away. In short it’s probably battery related in some way.

Regarding the BMV question I defer to Vic. He’ the resident expert here on all things electrical.

Dean

 

[Ruck_and_Roll]

Thanks Gentlemen-

Dean, it is a FLA battery in a non-vented space. Vic, I did do the 0 calibration reset.

So I did actually do the "zero caliberation" by removing the load from the shunt and hitting the calibration button. It is now showing '0."

So I am actually even more confused than before. I think another question would be can you caliberate the BM with a multimeter to detect amperage? I know how to check voltage across the battery leads but I am not sure how to detect current draw. I've been learning all of this on the fly.

Here are my updated current working theories:

1. Battery isn't actually discharged/discharging, but the monitor got miscaliberated somehow when I plugged into truck or some other activity. Supporting this theory is that it was caliberated to 0 with "master off" until I:
a. Plugged into shore power overnight, woke up the next morning, my alarm was going off (did not check the monitor for amp draw that morning)
b. Plugged into the truck

2. Battery is discharging
a. When I charged the battery through shore power, somehow cooked the battery and the monitor is detecting a low discharge, (not sure if this possibly, considering nothing is technically 'on' except the battery monitor)
b. possibly thinking this is relating to propane and CO monitors being 10 year old. Maybe there current state or that they were activated to draw more battery power when they were set off? I am replacing both for safety purposes obviously.

Clearly, I need to do more troubleshooting.

Best, Luke

 

[Vic Harder]

Luke, thanks for "hanging in there" and puzzling this out. OK, so you did a zero current calibration? Awesome. To confirm/check with your multimeter, it needs to have a DC current option. If it has that, you need to insert it into the circuit. That means literally opening the circuit between the battery -ve terminal and the BMV's shunt, and putting the meter in there. Now it can read the current going through the shunt.

If the BMV is reading zero, so should your MMeter.

Now, onto the battery SOC reading. I am sure that you noticed when setting the zero current, that there is a button right next to it for "Synchronize". What this does is tell the BMV what 100% charge is. This bears some explaining... I was with two friends who recently went solar with my recommendations, and their BMV was way off on what 100% was

If you were to hit that button when the battery was actually only 50% charged, and then used it for an hour or two, the BMV might indicate 90% charged, when in fact it is really only 40% charged. Unfortunately, if you were then to fully charge the battery, the BMV will NOT ready 150%. 100% is as high as it goes. So, when are you actually at 100%?

Safest bet is to have NO load on the batteries (totally disconnected) and then charge the batteries with solar and/or battery charger for a a few days. THEN hit the synchronize button. This SOC now becomes the reference point for 100%.

Note that you may need to do a sync periodically. I noticed yesterday that mine were indicating 100%, but still accepting 5A of charge. I set my "fully charged" state in the MPPT controller as having a .7% "Tail Current".... meaning .07 * AH of battery. That's less than 2A in my case. SO, the MPPT is still charging a fully charged battery? Not likely. So my BMV was off, and needed to be resync'd.

I hope that helps.

 

[Ruck_and_Roll]

Very helpful Vic, I really need to do more troubleshooting. Lately, I have been too busy camping to work on some of these issues. I am going to try this out this weekend.