Sanwizard
Solar Wizard
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Since shipping costs are way up, Always bundle in 1 or 2 extra cells as spares with a cell order shipment. They come in handy for a quick swap out item.
BMS MOSFETs Explained
- Thread starter upnorthandpersonal
- Start date
martyfarkle
New Member
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- Oct 5, 2020
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- 27
What is the best way to limit the charge controller to keep the SOC between 20% and 80%, never going above that or below that?
As I understand, the LifePo4 cells like that range but don't like both extremes.
The reason I ask, is that I use very little electricity during the day and would like my panels to supply that, 2X250w, my battery pack is a 24 V, 280 amp hour, with my usage of both panels it continuously charges the battery, up above 80%, going to the full capacity that the charge controller is set to.
I want to continuously operate within the 20 to 80% range, to keep the battery healthy. Otherwise it'll constantly be up to 90% or more.
Can I change the settings on the charge controller to make it, force it, to operate between the 20% and 80% range? Or is this not good for the whole system.
As it is, I have turned off the charge on the BMS, charge MOSFET, to stop the battery from receiving a charge yet using the panels to supply all my needs, and allow discharge from battery if it should come to that during the day.
As I understand, the LifePo4 cells like that range but don't like both extremes.
The reason I ask, is that I use very little electricity during the day and would like my panels to supply that, 2X250w, my battery pack is a 24 V, 280 amp hour, with my usage of both panels it continuously charges the battery, up above 80%, going to the full capacity that the charge controller is set to.
I want to continuously operate within the 20 to 80% range, to keep the battery healthy. Otherwise it'll constantly be up to 90% or more.
Can I change the settings on the charge controller to make it, force it, to operate between the 20% and 80% range? Or is this not good for the whole system.
As it is, I have turned off the charge on the BMS, charge MOSFET, to stop the battery from receiving a charge yet using the panels to supply all my needs, and allow discharge from battery if it should come to that during the day.
It's not so much that LiFePO4 doesn't like 100% SoC, it's that they don't like to be kept at a high voltage. They need to be able to settle.
I regularly use my cells at 100% to 0%, and have been for four years now without issue.
That said, if you want to keep them between percentages, you need a shunt (something like the Victron SmartShunt or similar) and base charging/discharging off of that. It won't work at all with voltages.
Alternatively, in your case, you could just put the float voltage of your charge controller at 3.375V per cell (which will allow the cell to settle) and charge to 3.45V per cell or so, while keeping it there for some time to finish absorption. Once every few months, do a charge to 3.55V per cell to balance them. This still has the potential to charge to 100% (just takes longer) but because of the lower voltage, you lower any stresses as well.
I regularly use my cells at 100% to 0%, and have been for four years now without issue.
That said, if you want to keep them between percentages, you need a shunt (something like the Victron SmartShunt or similar) and base charging/discharging off of that. It won't work at all with voltages.
Alternatively, in your case, you could just put the float voltage of your charge controller at 3.375V per cell (which will allow the cell to settle) and charge to 3.45V per cell or so, while keeping it there for some time to finish absorption. Once every few months, do a charge to 3.55V per cell to balance them. This still has the potential to charge to 100% (just takes longer) but because of the lower voltage, you lower any stresses as well.
I have bin using the charging MOSFET to stop my solar charger from toping up my battery when I am not on the move, there is only some minor draw from the battery during the night when there is no solar power, is this ok or is this bad for the BMS (MOSFET)? @upnorthandpersonal (JBD Smart BMS 4S Lifepo4 200A)
Technically, you shouldn't rely on the BMS for day to day operations. It's a safety device, the last line of defense, the thing that tries to protects the cells at all cost. In principle, you should control the charge controller by not allowing it to charge. Some charge controllers don't like it when they are not connected to the battery but do have solar connected.
I would prefer to just have a disconnect at the solar input of the charge controller when you don't want to charge batteries. That said, if your charge controller has no issues with the BMS disconnecting, and you're ok with a BMS being used in this way, it likely won't be an issue. It's just not best practice.
I would prefer to just have a disconnect at the solar input of the charge controller when you don't want to charge batteries. That said, if your charge controller has no issues with the BMS disconnecting, and you're ok with a BMS being used in this way, it likely won't be an issue. It's just not best practice.
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