Weird battery charge readings

4ncar

So...6v flooded, bmv 712, running generator w/separate battery charger. Why am I reading a discharge? I have tried battery switch on & off. While switch on, I get .25a discharge, switch off 0. I have everything off in the trailer except the co2 sensor. The charger is putting voltage to the batteries but no amps, how weird. If I plug into truck, I get voltage & positive amperage (7-8). All in all I haven’t moved from 64%SOC all morning.

Any thoughts?

4ncar

Edit: I THINK I have a synch issue. Stand by while batteries rest...😅😬

That was the case! Out of sync! 30 minutes rested batteries read 12.78v. Reset to 100%

Sharon_is_SAM

@4ncar - I just spent the last week reviewing the nuances of the BMV, Victron’s recommended settings for solar and AC charging, our WFCO converter issues etc.  I know @TomCanada and @Dutch061 are all over this, but this is what I concluded.  On solar, the Victron recommendations are doable and make sense.  The object is to get the BMV to adjust to 100% SOC based on absorption voltage and a 5-6% tail current.  Unfortunately, due to the wacky WFCO programming, on shorepower, our AGM batteries won’t see bulk charging and the SOC won’t be accurate. (Thanks @rh5555).  I read a few marine websites and they revealed that using multiple charging sources (AC, solar, and alternator) messes with the battery monitor SOC.  The best recommendation that made sense and this is what I have resorted to - isolate the battery, charge it fully using a smart charger, let it rest.  Then sync,  then do a Zero Current Calibration.  I plan to do this after a trip to have a fresh start the next time around.  I am not sure what is the best answer if you have installed solar and plug in somewhere.  We had a persistent + current that would not clear until I did the zeroing.  To zero, you need to make sure there is no current flowing to the battery, so turn off the battery switch and disconnect solar.  I know we have been looking at 100% SOC when it was under charged.  

4ncar

I have all sources at my disposal, but in varying degrees. I’m full timing now, so I don’t have the benefit of a “home base” to fall back to to plug-in at. This week, for instance, I have zero shore power, but have solar, generator & truck. How I got so far out of sync is curious, but last week was a combination of solar, truck & shorepower. 

Separately, and I know this was being discussed elsewhere, but the variance between voltage & load from the bmv & the mppt controller is curious. Mainly load. Why is there a negative draw(as expected say) on the bmv, but the solar controller shows a positive load in the “battery” section of the app? 

I suppose I keep playing...

TomCanada

@Sharon_is_SAM do we expect any current draw from inverter (in off mode) or CO2 converter with battery switch off?  

Sharon_is_SAM

The inverters are wired directly to the battery and is not impacted by the battery switch.  Even if nothing is plugged into the wired outlet, the inverter itself apparently has it’s own background draw.  It must be turned off to prevent any current draw.  Plenty of owners draining their batteries if they forget to turn off the inverter.  The CO/LPG detector are off with the battery switch, assuming you are not hooked to shorepower or geni.

Dutch061

@4ncar , I would need to know what the Battery settings are under the BMV-712 in order to give you much guidance but the short version is this.

How it is currently set up, specifically these 3 settings are where the problem is.

Charged voltage
Tail current
Charged detection time

Based on your battery voltage of 13.74 it is my expectation tat the batteries are fully charged but it never met the criteria in order to synchronize or reset the Time since last full charge etc.

The way it works is that in order to reset - synch you have to meet the Charged voltage with Tail current UNDER the % specified for the Charged detection time. 

I can't say that I have this exactly sorted out but here is where mine is set and at least in my backyard testing it seems to do what I expect.

Charged voltage is set to 13.6 
Tail current is set to .5% which equates to 1.12 Amps with 2 x 6 volt Harris AGM
Charged detection time is set to 5 minutes

You have your settings, most like the Charged voltage set to a level that it is not obtaining and therefor not resetting - synching. My issue was it was set too low and doing a false reset - synch.

If I could set the Tail current lower than .5% I would, but that is the bottom. This is based on the Total Ah available from the batteries being used.

I see myself needing to tweak the Charged detection time to a level higher than 5 minutes, but feel pretty good about the other 2 settings. I will need to camp to determine this but I am a few weeks out from being able to go again due to other family matters that need to be attended to.

Brad

P.S. Turn off the Solar Charging under the battery settings in the MPPT, turn off the master switch and make sure everything else is off. Go under the Battery settings of the BMV-712 and yo can manually zero the current. I have never zeroed mine but it always shows zero with everything off.

The only other thought would be if you have the Shunt installed incorrectly.

4ncar

@Dutch061: good stuff. It looks as though the charged voltage was set way too high; I believe I got that info from battery mfg at time of install. My real world reading obviously makes more sense. Length of time is set to 3 minutes. I do not understand tail current. Can you provide “reader’s digest “ explanation?

other tips I will try in 2 days, when I expect to be running low(er).

were you trying to explain why bmv & solar controlar show different readings at the end?

Dutch061

No, I was trying to explain how to zero the current draw within the BMV-712 under the Battery settings. If you are going to zero this, you need to make sure nothing is flowing in or out, which is why I mentioned turning off the Solar Charging and master switch. If there is zero current flowing, you should read zero current on the BMV-712. Also check under the Battery settings to make sure that the Current threshold is set to 0.10 A which is the default setting.

As per Victron, they recommend setting the Charged voltage at .2 volts below Absorption voltage which with AGM batteries is 14.2. I tried that and if the batteries are fully charged my PD9260C convertor puts out 13.6 volts; which is why I set it to 13.6 because it would never reset - synch. Sitting in my backyard and looking at it now, it appears that it is functioning properly based on my settings but I will want to further test when I am able to go camping in a few weeks. Even with sun on the Solar Panel, it would not reset - synch. 

In the test results that @TomCanada had shared with me, I am certain his would have worked properly with 13.6, Tail current at .5% and Charged detection time higher than 3 minutes. As mentioned, I may raise the Charged detection time to 10 or 5 minutes if I need to.

My main goal is that I don't ever want a false reset - synch, I would much rather deal (only if I have to) with a situation like you had where the reset - synch wasn't happening even though you were charged. Ideally, it would avoid both error modes. 

It is important also to note that under the History tab of the BMV-712 there is a synch count but more importantly (at least to me) is Time since last full charge. The synch counter doesn't always index (I haven't researched as to why) when the batteries reach a full SoC but the Time since last full charge always does. 

May I ask what you had the Charged voltage set to? 

Thanks!

Brad

TomCanada

It's definitely all about tradeoffs...

I'd rather never sync with converter-only cases than potentially sync early on solar.  I don't think I'll ever have a case where I don't have at least *some* solar to top me up and allow a sync in the case the converter has already charged me overnight, so I'm not too worried about that case.. So I choose the 14.2V/4% settings.  If I know my battery is fully charged w/ the converter (perhaps at night?) and I don't want to wait for the next day's solar top-up to synchronize me, I can always do a manual sync.

If you would rather ensure you sync with your converter every time, the 13.6V/0.5% settings may work for you - but you can/will sync prematurely on sunny days when the sun goes behind a cloud.. (in my case, I dropped from 14V @ 7A to 13.58V @ 0.9A when a cloud came by - which would've caused a premature sync with 13.6V/0.5% settings)

No perfect solution unfortunately - sadly like with all things, ignorance is probably bliss here - but I'm in way too deep for that

4ncar

@Dutch061: charge voltage WAS set at 14.2. Again, I have flooded 6vs, not agm. At this juncture I’m not sure if the 14.2 was a factory setting or if the battery mfg suggested it, I don’t recall it’s been 9 months or so. Either way, 13.74/6 is the highest my batteries get to, so there it is now set to. Is .5% tail ok for the lead acid battery?

Currently, I have insufficient watts in solar. I need another 100w to make the system more sustainable. I’ll be landing in Florida to mooch dock  in a month, at which time I’ll order another panel before I head out again.

phil

Dutch061

Gents,

As mentioned, I will need to do some more evaluating when I get a chance to actually camp. I may have to adjust my Charged voltage but I am thinking that it will likely be more related to Charged detection time.

Brad