Budget 90ah 48v lifepo4 battery build (under a grand)

[oldrock]

Really enjoyed catching up on this thread. thanks Augie for sharing. I'm going to try building a pack and will go with same cells unless something becomes available.

[augiedoggy]

Thanks, I should update that I ended up going with this charger due to price and fast shipping. It does work perfectly so far and tapers off to a constant voltage charge as it approaches being fully charged.

https://www.ebay.com/itm/354540341250

[Pat911]

Can you wind the voltage down on that one Augiedoggy? There might be an internal pot that will allow you to.

[augiedoggy]

Originally Posted by Pat911

Can you wind the voltage down on that one Augiedoggy? There might be an internal pot that will allow you to.

I dont know.. im still not so sure ill ever use it. The mppt boost charger and solar roof panel charges very well and I can set my charging voltage to whatever voltage I want. But even so 3.65v is the fastest way to charge the cells fully. I guess I have to do more research if if its even in my advantage to charge to a lower voltage with a longer absorption time. Being grade b cells and with the type of heavy c rate loads the cells will see will it matter?
Right now it stops charging when each cell reaches about 3.64v and the pack is at 58.3v according to the bms app. the current going in drops long before that to such a low current the bms cant even sense it. this is because I have one cells that is a bit of a runner (cell 14) it reaches my protection point of 3.65v and then my bms relay opens, only allowing trickle charging through a resistor at that point.

I am waiting to get the pack in the cart and do some testing to see if I need to replace cell 14 or its just a bit of a runner when the pack is already charged and being topped off since it wasnt an issue when I was charging the pack from a lower state of charge.

[Pat911]

That’s exactly why you drop the charge voltage, to give any cells that are runners a chance to be balanced prior to the BMS going in to protection mode. By charging to 3.65v AND having 3.65v as your protection setting, one cell will always trip the charging prior to the charge controller actually finishing its job. Your BMS is now controlling end of charge, not the charger.

[augiedoggy]

Originally Posted by Pat911

That’s exactly why you drop the charge voltage, to give any cells that are runners a chance to be balanced prior to the BMS going in to protection mode. By charging to 3.65v AND having 3.65v as your protection setting, one cell will always trip the charging prior to the charge controller actually finishing its job. Your BMS is now controlling end of charge, not the charger.

Good point but I think I may have to restrict the voltage more than Id like to stop that cells from shooting up to 3.65v.. I had the voltage at an even 58v when using my mppt boost charger before the 20a charger arrived and it still tripped the bms. I guess I could try 57.6v and charge to 3.6v

[Volt_Ampere]

You might have to better balance the cells to get the charge process to complete without tripping the BMS. I always top balance.

[augiedoggy]

Originally Posted by Volt_Ampere

You might have to better balance the cells to get the charge process to complete without tripping the BMS. I always top balance.

I have top balanced them using the active balancer and leaving them on the charger for a couple days. one thing I have not tried is leaving the active balancer off with the charger on once they are all at 3.64v but they were all within .002v

[Volt_Ampere]

That sounds good.

[Pat911]

Once the pack is balanced you should remove/turn off the active balancer.

At the risk of telling you something that you already know, make sure your bus bars/links are torqued correctly and evenly. Any difference in terminal resistances can show up as unbalanced cells, but this would be more noticeable at higher charge/discharge currents.