Solar Power activates JK BMS when in sleep mode, bug or feature

[Hans Kroeger]

Bug or feature? The JK-BMS can be set into its sleep mode by pushing a button for 5 Seconds. In sleep mode it's power consumption is close to zero. It also goes automatically into sleep mode, if a cell voltage drops below the "Power Off Voltage", which I set to 2.6 Volts.

By chance I learned that the application of an external "charge" voltage which is somewhat higher (some 1.8 V) than the actual battery voltage, the BMS wakes up and enters its normal mode.
Personally I consider this to be a bug. If I turn Off the BMS intentionally (pushing a button) I don't want the BMS to switch on automatically if my Solar System delivers a charge voltage. With no load being present, it will finally charge the Battery until SOC = 100%.
This is exactly what I try to avoid at long rest periods, because of the accelerated aging of the cells by the high SOC.
From my perspective, it is OK if the BMS wakes up from its standby mode, after a "Power Off" event.
However, after it was turned off by pushing the Off button. it should stay in its sleep mode until the button is pushed again.
Comments are welcome.
Cheers Hans

 

[BentleyJ]

JK-BMS has separate charge and discharge controls so you could disable charging but that wouldn't prevent the BMS from waking up and becoming a parasitic load.
The other choice is to reduce the charging voltage set point on the solar charge controller to 3.35 to 3.40V per cell. This is low enough to significantly reduce the "cycling-aging" effect but will keep your batteries topped up while the BMS is in full power mode.

 

[Hans Kroeger]

JK-BMS has separate charge and discharge controls so you could disable charging but that wouldn't prevent the BMS from waking up and becoming a parasitic load.
The other choice is to reduce the charging voltage set point on the solar charge controller to 3.35 to 3.40V per cell. This is low enough to significantly reduce the "cycling-aging" effect but will keep your batteries topped up while the BMS is in full power mode.

Thanks for your comment!
The lowest voltage I can set at my solar cc is 13.9 V / 4 = 3.48 V per cell.
If I discharge my battery such that the voltage at rest is 12.2 V or more, this may be just high enough to avoid the unintentional switch on of the BMS. This assumes, that the switch on voltage is 1,8 V above the Battery voltage. I have no idea if this is true over temperature, for all units......
Disabling the charge MOSFET is no good idea. In case the BMS is activated by the Solar voltage, it will discharge the battery down to 2.6 V cell voltage, and then go to sleep mode. From then on it will be discharged further on, whenever the solar voltage activates the BMS. Even worth the Switch Off delay at 2.6 V is a Minute or more.
As a consequence, the battery will be overdischarged.

Note: I am not speaking for myself, because I can set my combined integrated Votronic charger (mains, solar, alternator) such, that it turns off solar power once I am hooked up to the msins. Being connected to the mains, I will set this charger to 12.8 V constant voltage. There will be no unintentional activation of the JK-BMS.

 

[glamsland]

Anyone tryed this "Smart Sleep On" setting? What do this setting do?

Is this the same as turning off the bms with long-press on the button?

 

[upnorthandpersonal]

Bug or feature? The JK-BMS can be set into its sleep mode by pushing a button for 5 Seconds. In sleep mode it's power consumption is close to zero. It also goes automatically into sleep mode, if a cell voltage drops below the "Power Off Voltage", which I set to 2.6 Volts.

By chance I learned that the application of an external "charge" voltage which is somewhat higher (some 1.8 V) than the actual battery voltage, the BMS wakes up and enters its normal mode.
Personally I consider this to be a bug. If I turn Off the BMS intentionally (pushing a button) I don't want the BMS to switch on automatically if my Solar System delivers a charge voltage. With no load being present, it will finally charge the Battery until SOC = 100%.
This is exactly what I try to avoid at long rest periods, because of the accelerated aging of the cells by the high SOC.
From my perspective, it is OK if the BMS wakes up from its standby mode, after a "Power Off" event.
However, after it was turned off by pushing the Off button. it should stay in its sleep mode until the button is pushed again.
Comments are welcome.
Cheers Hans

Originally, this was the only way to turn the BMS on - there was no button. Personally, I don't consider it a bug. The sleep mode is there to protect the battery from discharging further than it should due to the power draw of the BMS. If solar then appears, I want the BMS to turn on again so it can now charge to almost depleted battery.

Keep in mind that the BMS is a safety device, not something that should be used to control charge. That's your charge controllers' job. You can set the charge controller to a float voltage below the settling voltage of the cell (say, 3.375V or below) and charge to 3.45V with a short absorption time. That way, you won't overcharge the battery and the controller will go into float mode almost immediately after sunrise.

 

[glamsland]

I ask this question becouse i'm looking for any ways to try to save some power. Here in norway its getting dark now in november, and at my off grid cabin its wery low chargig ang to high resting power consuption from the inverter/charger (epever up 3000hm10022) its about 30watt/h just having the cc on without inverter running. So my batteries are slowly drained..

The up invrter are for bigger setup it think.. i'm planning swapping this with a single charge controller and a inverter. Then the power consuption will go drastic down..

 

[upnorthandpersonal]

I ask this question becouse i'm looking for any ways to try to save some power. Here in norway its getting dark now in november, and at my off grid cabin its wery low chargig ang to high resting power consuption from the inverter/charger (epever up 3000hm10022) its about 30watt/h just having the cc on without inverter running. So my batteries are slowly drained..

That's one of the reasons I wanted a CC that turns itself off when there is no sun. I'm not sure about that 'smart sleep' setting, I have older versions that don't have it. You can always have the BMS sleep kick in at 3.0V so it prevents discharge below that. It's not like we get a lot of power here in the north during winter to even have the CC on...