BMS question

[Gunnar]

I am pretty new at this, and plan to switch from two 6v golf batteries to a diy lifepo4 setup. Will the BMS allow me to set the charge cutoff and discharge cutoff to I run my battery from say 10 percent SOC to 85 percent SOC? The BMS I am looking at is the 120a from overkill solar. If that won't work, is there one that will? Or, do I need a charger that can be set for this? I have a progressive dynamics 4060k charger in the trailer and an epever mppt for the solar panels.

Thanks in advance.

 

[Ampster]

The charger and charge controller will havevto be set a voltages that approximate 85% SOC. If you have an inverter it can be set for a Low Voltage Disconnect.

 

[Pierre]

I am pretty new at this, and plan to switch from two 6v golf batteries to a diy lifepo4 setup. Will the BMS allow me to set the charge cutoff and discharge cutoff to I run my battery from say 10 percent SOC to 85 percent SOC? The BMS I am looking at is the 120a from overkill solar. If that won't work, is there one that will? Or, do I need a charger that can be set for this? I have a progressive dynamics 4060k charger in the trailer and an epever mppt for the solar panels.

Thanks in advance.

Yes , indeed you can set this BMS to operate like that. Very flexible and easy to program. I have done quite a bit of testing on this BMs here —https://diysolarforum.com/threads/dgjbd-bluetooth-bms-a-short-review.5290/

 

[Ampster]

To be clear most people suggest relying on your charger to be the primary failstop and the BMS to be the fallback if the charger fails to stop charging. That way you get a two stage charge instead of the BMS cutting off Bulk (constant current) charging.

 

[Pierre]

To be clear most people suggest relying on your charger to be the primary failstop and the BMS to be the fallback if the charger fails to stop charging. That way you get a two stage charge instead of the BMS cutting off Bulk (constant current) charging.

I agree. I use the Victron Smart Charger with LFP charge profile as primary protection. That being said , if you want to stop charging at say 13,8v you will have to set this up in the BMS.

 

[Ampster]

He already has a charger and charge controller.

 

[Gunnar]

Thanks for all the replies. So now I have another question. If I wanted to upgrade my charger/converter do I need a new power center? It looks like the converter is integrated into my power center. If it's possible, is there one that will let me set the charger to cut off at 85 percent? Also, how hard is it to change to 24v setup, that still outputs 12v to the trailer? Last, I think you can get one that will also invert power and supply 120v to the trailer when on battery power. Can anybody recommend a unit that does all of these functions?

 

[Zil]

It is best practice to have the BMS as the last drop dead protection. Not to rely on BMS as the control. You need have a charge controller that can be set for proper Li charge cycles. You need another low voltage disconnect to manage the discharge voltages.

 

[Bob B]

It is best practice to have the BMS as the last drop dead protection. Not to rely on BMS as the control. You need have a charge controller that can be set for proper Li charge cycles. You need another low voltage disconnect to manage the discharge voltages.

Can you tell me a 120V converter charger for an RV that will do a proper lithium charge cycle? Does ANY charger know the individual cell voltages?

 

[Ampster]

Can you tell me a 120V converter charger for an RV that will do a proper lithium charge cycle? Does ANY charger know the individual cell voltages?

A Lithium charge cycle is very simple. Constant Current (often called Bulk) and then when voltage gets to set voltage switch to Constant Voltage (often called Absorb). The thing that makes Lithium more complicated is different chemistries have different voltages and different batteries have different amount of cells in series.
I can't answer your question but if you tell me more about your Lithium battery I can give you the tools to look for the correct converter charger.

What is chemistry? NMC or LFP?

How many cells in series?

 

[Bob B]

A Lithium charge cycle is very simple. Constant Current (often called Bulk) and then when voltage gets to set voltage switch to Constant Voltage (often called Absorb). The thing that makes Lithium more complicated is different chemistries have different voltages and different batteries have different amount of cells in series.
I can't answer your question but if you tell me more about your Lithium battery I can give you the tools to look for the correct converter charger.

What is chemistry? NMC or LFP?

How many cells in series?

LFP
Most of the RV converters I have seen ... with a lithium profile ... are just a constant voltage power supply. Some of them will do bulk for a set time frame and then drop to float ..... nothing very smart about charging based on time. The float level is normally higher than I like.
The best option seems to me to get one that has a constant voltage and shut it off with my Chargery BMS. That way, I can cycle the battery .... based on cell voltages, not pack voltage ... and set the range anywhere I want.
If I am boondocking and charging with a generator, I want the charge to be as quick as possible.

 

[Zil]

I have a programmable charge controller as well as a programmable mains charger. The proper charge for LiFePo4 is charge to full with constant voltage then stop. Turn the charger off. Start discharging the battery, don't let it at top voltage. My personal researched top charge is 3.47 V per cell. My CC charges to 13.88 volts and shuts off. I have many small loads that gradually take the battery back down to a 'good' level. Once a year or so I balance to 3.6 volts per cell.

 

[Pierre]

I have a programmable charge controller as well as a programmable mains charger. The proper charge for LiFePo4 is charge to full with constant voltage then stop. Turn the charger off. Start discharging the battery, don't let it at top voltage. My personal researched top charge is 3.47 V per cell. My CC charges to 13.88 volts and shuts off. I have many small loads that gradually take the battery back down to a 'good' level. Once a year or so I balance to 3.6 volts per cell.

I like your thinking.

 

[Bob B]

I have a programmable charge controller as well as a programmable mains charger. The proper charge for LiFePo4 is charge to full with constant voltage then stop. Turn the charger off. Start discharging the battery, don't let it at top voltage. My personal researched top charge is 3.47 V per cell. My CC charges to 13.88 volts and shuts off. I have many small loads that gradually take the battery back down to a 'good' level. Once a year or so I balance to 3.6 volts per cell.

What chargers do you have? I haven't been able to find an RV converter that does what you are describing.... what you are describing is what I intend to do with my Chargery BMS.

 

[Zil]

I have only programmed my solar CC. Tri-Star. it has a setting for high voltage disconnect parameter. I tricked it, it charges bulk and turns off at 13.88V. It will not go into float until 14 volts, so never. After I do my ProMariner I will post the results. You must have a charger that can be set to custom parameters with a computer connection.

 

[Bob B]

I have only programmed my solar CC. Tri-Star. it has a setting for high voltage disconnect parameter. I tricked it, it charges bulk and turns off at 13.88V. It will not go into float until 14 volts, so never. After I do my ProMariner I will post the results. You must have a charger that can be set to custom parameters with a computer connection.

Do you have a link? All I see for Tri-Star is SCC .... not 120V converter charger.