question

drumond avatar image

BMV is showing a small load even when the sun is out

Hello,

In my rv, I have 3 solar panels linked to a Victron MPPT, a Lifepo4, a BMV 702, different things such as cctv, monitors, leds.

The CTTV and monitors are turned on 24/7.

When the battery is on float mode the voltage stays around 13.48V and the current amperage is 0.

The problem is the consumed ampers go from 0 to -1.6A each time the battery is fulled and return to the float mode (after the two hour absorption mode).

I don't know if there is a way to change the settings to have 0 instead of -1.6A.

I tried to change the tail current, 4% 5% 6% it is always -1.6A each time after the absorption.

Does it have to do with the fact the CCTV cams and other items are working full time?


What can I do?


Regards.

BMV Battery MonitorTemperature Sensor
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3 Answers
Justin Cook - Bay Marine Supply USA avatar image

@drumond, if the CCTV and "other items" might have a total draw of 1.6A, then yes, I think it's very likely that it has to do with that.

Tracking consumed energy from -and energy put back into- your batteries is exactly what the BMV is supposed to do, so if you have loads connected and running, it will start tracking them as a negative (showing current out) as soon as the battery has completed its charge cycle, since the power consumption counter is reset when the battery is charged - Ah consumed is how much you've consumed since reaching 100% SOC.

It sounds like the BMV is doing its job... technically you could tell it to ignore that consumption, but then that risks throwing all its other calculations off, which could lead to significant inaccuracies in the future.

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Ok thank you but why does the MPPT float with -1.6A, couldn't it charge a little higher in float mode to erase these -1.6A. The sun is shining outside and instead I have to deal with this useless draw of 1.6A. It would be better if the MPPT could understand what it is happening and see that floating with -1.6A is not a clever thing to do...

@drumond, the controller is floating based on battery voltage, not current draw... it can't see current out, it can only see battery voltage. If your current out isn't significant enough to drop the battery voltage, the MPPT can't tell it's even happening.

Regardless of a higher float voltage, it's still not going to "erase" the draw your equipment is pulling; if you have a SmartSolar MPPT you can of course change your float voltages through the app, but nothing's going to erase the draw of your equipment. When your running equipment draws down the voltage enough, the controller will kick back into charging, but a single amp or so isn't enough draw to keep it in absorption or bulk modes for very long.

Again, the BMV's sole purpose in life is to measure in/out current from your batteries, so the fact that it's showing the in/out current isn't something that I'd recommend trying to work around... and keep in mind that 1.6Ah consumed is not the same thing as SOC. If you're consuming 1.6Ah of energy with your CCTV and cameras and such, you need to know about that, and the BMV needs to know about that to calculate an accurate SOC.

Leslieanne avatar image

Hi Drumond,

I will try to put this simply another way. At end absorbtion your battery will be at say 14.2 volts. Your set float voltage is lower, say 13.5 volts. This is for the health of your battery. After absorb the battery has to discharge a little. This is the -1.6 A that you observe going into your loads, until it has dropped to 13.5 V. Once it reaches 13.5, then current into battery and current out will be similar and average 0 volts, as you indeed observe.

If you were to set float volts = absorb volts, then you would see an average 0 volts on the Bmv right from end of absorb, but the health of your battery would suffer.

In summary, your system is behaving exactly as it should. Don't worry. Be happy!

Cheers, Leslie

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Please excuse the three instances above where I wrote "volts" instead of "amps" when describing current shown on BMV!!!!!...and I was trying to clear up some confusion.....

drumond avatar image

Ok thank you all!!


There is just one concern now, I think my idle hourly consumption should be a little more than 2 amps, maybe 2.5A, because I think I lose 2.5 per hour every night. I will have a look at that this night. The absorption phase takes currently two hours, do you think I should have -2.5*2=-5A instead of -1.6A in float when the sun if shining?


Thank you.

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