Iridetheshortbus
New Member
I ran out of battery unexpectedly last night and after charging fully today these are my values. Should the cell voltage be higher? Is cell 4 with in range of the other three or should I rebalance? 
Are these values normal?
- Thread starter Iridetheshortbus
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Iridetheshortbus
New Member
I wasn’t aware I needed charge more. Good to know. So if I’m pushing 30amps into the battery it will automatically limit it lower when fully charged?
BentleyJ
Solar Wizard
Yes, its called tail current. When the cells reach full charge at 3.5V per cell (14.0V) The potential of the cell itself resists the flow of current and amperage drops off rather sharply. This how charge controllers know when to switch over from Absorption mode (constant voltage charging) to No Charge or Float depending on the selection of 2 or 3 stage charging.
KITROBASKIN
Solar Enthusiast
Thinking we need more information.
Some people here have no problem with your charge settings. How did you come about choosing those values?
Some people here have no problem with your charge settings. How did you come about choosing those values?
Iridetheshortbus
New Member
Choose? Those are the values that the battery’s displaying while charging. I didn’t choose them they are a byproduct.
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rodrick
Free energy enthusiast
Don’t rely on the bms state of charge displayed it is about as accurate as the weather forecast to truly know what the charge level is you need to install a shunt
Iridetheshortbus
New Member
Yea I definitely know not to blindly trust the bms soc anymore, Can you recommend any shunts? A wireless connection is preferred.
I assume I’d attached the shunt between the battery positive and positive bus bar?
rodrick
Free energy enthusiast
Victron smart shunt about $130 Bluetooth and ve direct ready I have 3 personally and love them
What was the state of charge displayed and cell voltages just before cut off? Heavy load?
Iridetheshortbus
New Member
Happened over night, so can’t be certain. Everything looked normal at 8/9pm with over 100amps left on the battery but at 6 am the battery was dead. I know from 12am-6 the only draw on the battery would have been a heater pulling at max 4-5amps.
My best guess is that the 15-20amps I was using during the day for a long period had yet to be fully reflected on the bms soc
Since recharging to 100% I’ve had no issues.
I wish I could have my overkill solar bms send me a notification when I reach a certain percentage or amp/hrs remaining.
What kind of heater only takes 4-5 amps DC? More likely, it's 4-5 amps @ 120VAC, which is 37.5-47 amps @ 12.8VDC.
Iridetheshortbus
New Member
A diesel heater uses that much power and it’s only 4-5 amps with the fan blowing full, most the time it’s 1-2amps.
In the end more capacity is needed. Although if the BMS indicated more charge remaining than it had it may have implied skipping the evening recharge was OK. Honestly I would spend the monitor money on a second battery.
Maybe keep closer tabs on voltage etc to verify the charge level as the evening progresses and what is left in the morning.
Maybe keep closer tabs on voltage etc to verify the charge level as the evening progresses and what is left in the morning.
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Iridetheshortbus
New Member
This was an only a one time thing I rarely run my battery so close to empty. Was stuck in single digit weather for a couple days.
Definitely have made it a bed time routine to check the battery levels.
Iridetheshortbus
New Member
Here’s an update, I’ve been letting the battery fully charge and one of my cells is off from the others. Should I look into do a top balancing?
BentleyJ
Solar Wizard
162mV Delta, yes its time to top balance or add a 2A to 5A active balancer.
Iridetheshortbus
New Member
So I currently don’t have a power supply so would you suggest getting one to top balance or would the active balance be the better route?
BentleyJ
Solar Wizard
Cell #4 is high but the voltage didn't run away and trigger an over voltage alarm which is a more serious situation so I wouldn't recommend getting a separate power supply. A separate active balancer is the way to go because it will keep things in line at every charge cycle.
Is important to select a model with a Voltage based trigger that can be set at 3.4V. The balancer should only be active when the first cell hits 3.4V.
I'm using a JK-BMS brand active Bluetooth balancer but it doesn't have the above feature. Maybe the new models do? Funny thing is their BMS's with balancing built-in does have the feature.
Andy at Off-Grid Garage has posted MANY BMS and balancer YT videos if want to do some research. If the newer JK brand 2A balancer doesn't have the feature maybe try Neey. Sorry, I'm not up to date on all the choices at the moment.
