leon.davibe
Executive Member
- Joined
- Feb 3, 2009
- Messages
- 5,158
- Reaction score
- 2,202
If you decide to diy a lithium lifep04 battery
Take the effort to top balance it first
No you most likely did not get beautifully balanced cells because they all happen to be 3.21v or 0.01 volt separated cells
Trust me trying to balance them after the fact while in use though possible is going to be a schlep and way more time consuming
And no the bms/balancer isn't gonna ballance it
And no just connecting them parralel and leaving a few days isn't gonna do it too
You have to get them on the steep portion of the state of charge graph while parallel
ie 3.65 volt
so either connect parralel and buck converter and charge to 3.65v if you have a small amp charger this can take time ie even days
If you want to speed up the process you can use the inverter to charge the battery with bms don't make the build pretty as you will most likely take it apart again if you see you were indeed not lucky to have received magically balanced cells
Disconnect the balance wire plug from the bms
Connect the batteries in series
Connect the balance wires to cells normally black wire to negative and then next wire first cell positive next second cell positive rinse repeat untill done
Some bms that cab handle higher s count have different ways of connecting lowet s count follows their manual
Can do a safety check on the plug to make sure each pin increases by about 3v
Connect the negative wire link to the bms first , and then the balance wire plug can be plugged in if more than one plug do the one with negative first and the the next ie you work your way up from first cell to last ie some 16s hms have 4 plugs so first cell1-4 then 5-8 you get the picture
So later if you want to take apart
you work in reverse ie start with the plug connected to last cell and end with the plug with negative and the disconnect the main negative
At this point you can see if the bms powered on by itself by putting the tester on the negativ coming from bms to load and the positive terminal
connect inverter and take the voltage up gently
That way you can also see how the bms behaves and how badly out of balance the cells are
Start with a voltage close to the nominal 3.2v x S the cell count of cells in your battery
Then increase the voltage in increments
ie can do 1v at a time until some of the cells hit 3.35-3.4v on 48v system with smaller packs you can do smaller jumps if you like
The bms is your safety device
As soon as you hit 3.65 v on a cell
It will be evident how bad the balance is
At this point you can take them apart connect parralel and connect buck converter set to 3.65v and charge away
Once you have them all at 3.65 they are balanced some specs sheets say 3.75 no biggy whatever you want ad long as it is about 3.6v at least
Disconnect
And build battery
Take the effort to top balance it first
No you most likely did not get beautifully balanced cells because they all happen to be 3.21v or 0.01 volt separated cells
Trust me trying to balance them after the fact while in use though possible is going to be a schlep and way more time consuming
And no the bms/balancer isn't gonna ballance it
And no just connecting them parralel and leaving a few days isn't gonna do it too
You have to get them on the steep portion of the state of charge graph while parallel
ie 3.65 volt
so either connect parralel and buck converter and charge to 3.65v if you have a small amp charger this can take time ie even days
If you want to speed up the process you can use the inverter to charge the battery with bms don't make the build pretty as you will most likely take it apart again if you see you were indeed not lucky to have received magically balanced cells
Disconnect the balance wire plug from the bms
Connect the batteries in series
Connect the balance wires to cells normally black wire to negative and then next wire first cell positive next second cell positive rinse repeat untill done
Some bms that cab handle higher s count have different ways of connecting lowet s count follows their manual
Can do a safety check on the plug to make sure each pin increases by about 3v
Connect the negative wire link to the bms first , and then the balance wire plug can be plugged in if more than one plug do the one with negative first and the the next ie you work your way up from first cell to last ie some 16s hms have 4 plugs so first cell1-4 then 5-8 you get the picture
So later if you want to take apart
you work in reverse ie start with the plug connected to last cell and end with the plug with negative and the disconnect the main negative
At this point you can see if the bms powered on by itself by putting the tester on the negativ coming from bms to load and the positive terminal
connect inverter and take the voltage up gently
That way you can also see how the bms behaves and how badly out of balance the cells are
Start with a voltage close to the nominal 3.2v x S the cell count of cells in your battery
Then increase the voltage in increments
ie can do 1v at a time until some of the cells hit 3.35-3.4v on 48v system with smaller packs you can do smaller jumps if you like
The bms is your safety device
As soon as you hit 3.65 v on a cell
It will be evident how bad the balance is
At this point you can take them apart connect parralel and connect buck converter set to 3.65v and charge away
Once you have them all at 3.65 they are balanced some specs sheets say 3.75 no biggy whatever you want ad long as it is about 3.6v at least
Disconnect
And build battery
