Jbd bms not showing small devices running

[marcello]

Hi,
Let's say if I plug an usb light or something small like this, my bms still shows zero Ah consumed.
I think everything under 2 or 3Ah is not shown.
Does it mean if I let an usb light plugged during one month, the displayed battery SOC will still be at 100%? (Whereas we all know the battery will be flat dead)
Or maybe the bms still count the Ah but doesn't ahiw them?
Thanks

 

[740GLE]

Does it show the wattage being consumed? My 200A 4S JBD recognizes around 3-5W or usage.

How big of a battery bank is the BMS connected to?

5w on a 1200whr battery is much different from 5w on. 13,000whr battery.

Knowing the SOC in mainly voltage based it’s not the most accurate, a proper smart shunt is well worth the investment if you need to track each WHr.

 

[SeaGal]

You don't state below what power the JBD is not detecting - maybe you meant 2 to 3W?

The JBD's internal shunt is reputed to be quite accurate, though probably not as good as a Victron Smart Shunt.

I guess all shunts will have a minimum voltage that they can measure, which will represent a minimum current depending on their size. e.g. a 500A shunt will be less sensitive than a 2000A shunt.

I would not be worried if the JBD does not register a small discharge if that is the only load you are running - this is because it also will stop discharge when a minimum cell voltage is reached and prevent any damage to the cells.

 

[Tomthumb62]

Some small USB lights consume less than 0.5W. I think you’ll be hard pressed to find anything except for very expensive measuring tools to be able to accurately and consistently detect such a small current. Someone correct me if I’m wrong but I don’t believe even a good columb counter like the Victron smart shunt can do this.

 

[SeaGal]

I'd agree. 0.5W at 12v is just 42mA. IIRC, the most sensitive Victron Smart Shunt drops 50mV at 500A. So 42mA would represent a voltage across the shunt of just 4.2 uV - sounds hopeful to be able to accurately measure that amount above electrical 'noise'. Having said that, Victron's tech spec claims a resolution of +/- 10mA.

FYI: there is an old thread also relevant...

JBD BMS internal shunt accuracy

been suspecting that my jbd shunt is full of it so i hooked up the victron smart shunt, here's is what i see, anyone else experience something similar? (nothing is connected to the battery except bms -> victron shunt) first pic only has a DC POE switch + 4 poe cameras + access point hooked up...

diysolarforum.com

 

[marcello]

Hi guys thank you very much for your replies.

My battery is a 200ah one.

I think the bms doesn't show under 1ah consumption, I have to do some tests I only tried with usb lights . I think I also tried with a phone charging and saw nothing on the bms, but I can't recall well, have to do it again