They can explode or catch on fire for no apparent reason. Always charge where such a fire won't cause massive damage. Compressing the cells is good. Putting all of them inside of some kind of metal can is good.
24s BMS for LiPo Battery
- Thread starter pbrownhg
- Start date
I am working on buying a battery charger for this lithium-ion pack. I am looking at a 10amp charger configured for Lithium-ion. CC/CV 5% of CC cut-off. They are asking about the option of 100.8V @ 4.2V/cell or a 99.6 @ 4.15V/cell. The charger is from evassemble. I do not know what the best answer is here????? Is this typically "on the fly" adjustable, or factory set?
dnmun
1 PW
you can adjust it later if you wanna change the final voltage. it requires the full voltage 4.2V/cell (100.8+)to balance the pack under the BMS but if you don't want it to reach full voltage, just turn off the charger when it reaches the voltage you want.
i recommend not charging the battery until you need to use it. leaving a battery charged 24/7/365 is how they end up with short life cycles.
i recommend not charging the battery until you need to use it. leaving a battery charged 24/7/365 is how they end up with short life cycles.
dnmun
1 PW
then just leave it at 100.8V if you don't wanna change it.
My battery is 90% built and by the end of the weekend I should be ready to start balancing. If I am going to use the HCX-D131 balance board, what is better, to charge first or discharge first? I was going to use a few light bulbs to discharge.....Maybe a better question should be, now that the battery is together, what is the next step?
I have taken pictures and will post soon if there is interest.
I have taken pictures and will post soon if there is interest.
dnmun
1 PW
when you charge it up the first time it will not balance. you need to use a big 2-5 ohm power resistor to soak up the excess charge on the high cells.
i used several soldered together to get to about 12 ohms and i had the power resistor on jumper wires with alligator clips so i could clip onto the terminals of the high cells as it was pushing higher ahead of the others and kept doing that as much as i could to keep them from going to HVC but eventually it hit HVC and i had to cycle it again. but i was able to make it get to within about 80mV by the end of the second cycle.
if you are using only the balance board and have removed the power board then it will not hit HVC. it will just overcharge since there is no way to shut off the charging current.
i used several soldered together to get to about 12 ohms and i had the power resistor on jumper wires with alligator clips so i could clip onto the terminals of the high cells as it was pushing higher ahead of the others and kept doing that as much as i could to keep them from going to HVC but eventually it hit HVC and i had to cycle it again. but i was able to make it get to within about 80mV by the end of the second cycle.
if you are using only the balance board and have removed the power board then it will not hit HVC. it will just overcharge since there is no way to shut off the charging current.
izeman
1 GW
if you have an rc charger you can bring every single cell to the very same level (the highest one, as charging mostly is much faster then discharging) by setting your charger to single cell charge mode and charge through the balance wires. with 20awg you can easily do it with 3-4 amps. this should bring every cell to the same level quite fast and you don't need to sit next to it all the time. after all cells are at the same level connect the bms and do a full charge to a slightly higher voltage then the whole pack's final top charge voltage. this will give the lower cells the chance to catch up while the high ones are pulled down to your balance voltage. that's it.
ARod1993
100 W
pbrownhg said:
That's actually a pretty good deal as far as I can tell; would you be able to give us more information?
wesnewell
100 GW
At 27 cents per wh, I'd call it a hell of a deal. Wonder what the catch is. Shipping cost?
Side note: I used to get email notifications when somone replied to my posts...That did not happen this time. I will check my settings.
I am also trying to attach pictures of the battery pack in the "upload attachment section". They are jpegs, but it gives the error message "invalid file" I will be happy to post progress of the build, but just have to figure it out.
I am quite happy with the cells. There is a shipping premium. These are the same cells that Gianni, (italian contact) purchased, As a total the cost, it was about $55.90 usd/cell.
Dennis, you may have to dumb it down for me a little. I understand about the soldering together of resisters to get the 12 ohms and a higher wattage, but not understanding how if I have some cells at 3.8V and others at 4.15V, I can use one resistor to slow down multiple cells that are higher. I know just enough to be dangerous.
If I use the HCX-D131 balance board, can I put a load of 8-9amps to draw the battery down to the lowest cell being about 3.5V and then add the charger with 10amps giving the BMS a chance to balance the cells? Can I draw and charge at the same time? I must admit, I don't know exactly how the BMS board works. Does it balance cells by diverting current to unbalanced cells during the draw and charge processes, or does it manage balance at the upper and lower ends of the cell voltages? I do have an RC charger, so maybe this is the easiest method?
Phil
I am also trying to attach pictures of the battery pack in the "upload attachment section". They are jpegs, but it gives the error message "invalid file" I will be happy to post progress of the build, but just have to figure it out.
I am quite happy with the cells. There is a shipping premium. These are the same cells that Gianni, (italian contact) purchased, As a total the cost, it was about $55.90 usd/cell.
Dennis, you may have to dumb it down for me a little. I understand about the soldering together of resisters to get the 12 ohms and a higher wattage, but not understanding how if I have some cells at 3.8V and others at 4.15V, I can use one resistor to slow down multiple cells that are higher. I know just enough to be dangerous.
If I use the HCX-D131 balance board, can I put a load of 8-9amps to draw the battery down to the lowest cell being about 3.5V and then add the charger with 10amps giving the BMS a chance to balance the cells? Can I draw and charge at the same time? I must admit, I don't know exactly how the BMS board works. Does it balance cells by diverting current to unbalanced cells during the draw and charge processes, or does it manage balance at the upper and lower ends of the cell voltages? I do have an RC charger, so maybe this is the easiest method?
Phil
dnmun
1 PW
if you have a group of cells adjacent to each other which are higher than the rest of the pack then you can put the light bulb across all of those high cells together and your light bulb will draw higher currents because the voltage is higher and it will drain all of the cells down together that are high. i have done that to entire sections, almost half a battery at a time to bring the pack closer to balance so the BMS can function to balance it before it goes to HVC and shuts off the charge.
when the BMS is balancing, the charger current is down to the lowest level it delivers at the constant voltage CV. for this BMS the balancing current is 4.2V/25 ohm or about 175mA so that is the amount of current that can flow around the cell that is above the balancing voltage. the lower cells below the balance voltage continue filling with charge at that 175mA rate.
when the BMS is balancing, the charger current is down to the lowest level it delivers at the constant voltage CV. for this BMS the balancing current is 4.2V/25 ohm or about 175mA so that is the amount of current that can flow around the cell that is above the balancing voltage. the lower cells below the balance voltage continue filling with charge at that 175mA rate.
Just to clarify....The BMS is balancing anytime the battery curcuit is closed, whether charging or discharging, but at a very slow pace, so only small corrects can be made when charging with 10A because at 176mA, it takes a long time to even curve the slightest imbalances. If this is correct, then I don't fully understand the quote below...."it requires full voltage 4.2V/cell (100.8+) to balance the pack under the BMS"....
dnmun said:
izeman
1 GW
you charger will need to go in "balance charge mode" at the end of your charge. there is no way that this bms can "compete" with the regular charging current. so you charge with your 10a+ and at the end the charger switches from CC to CV and reduces the current as it reaches it's final voltage.
i removed the daughter board from my "emc style/kingpan" charger which did shut the charger off once it reaches the final voltage as a LIPO safety feature. so now it doesn't shut off and keeps charging with 0.15a which is slightly below the bms's balancing capability.
so even if the battery would be quite unbalanced the charger would be able to keep the higher cells at 4.2v (balancing current is higher then charging current) so the lower cells can catch up.
after some charges all my cells are PERFECTLY balanced within 5mv.
i removed the daughter board from my "emc style/kingpan" charger which did shut the charger off once it reaches the final voltage as a LIPO safety feature. so now it doesn't shut off and keeps charging with 0.15a which is slightly below the bms's balancing capability.
so even if the battery would be quite unbalanced the charger would be able to keep the higher cells at 4.2v (balancing current is higher then charging current) so the lower cells can catch up.
after some charges all my cells are PERFECTLY balanced within 5mv.
I must admit, I still don't fully understand how the nuances of the BMS board works. Maybe by messing around with some of the suggestions given, I will connect all the dots and get it.
One main question...Can I draw on the HCX-D131 board and charge through the board at the same time? And if so, what is happening in the balance leads during this time? Is current flowing from cell to cell attempting to balance?
One main question...Can I draw on the HCX-D131 board and charge through the board at the same time? And if so, what is happening in the balance leads during this time? Is current flowing from cell to cell attempting to balance?
dnmun
1 PW
no, do not discharge the battery while charging it. if it goes to HVC then you have to discharge it down to 4.05V.
very few people understand how a BMS works so you are in the majority.
very few people understand how a BMS works so you are in the majority.
izeman
1 GW
sure you can charge and discharge at the same time. i have my CA running during charge to check voltage.
and yes. you don't really understand how balancing works
there is no distribution of charge between the individual cells. during charge ALL cells see the very same current, as the current is applied to negative and positive of the battery. because of ohms law the current every cell sees is the same.
so all cells charge, or none does. the bms can only turn on or off charging for ALL cells.
so what can happen: during charge one of the cells (measured through the balance wire) one cell may reach high voltage cut off (eg 4.29v) while others are still below that value. to avoid damage to this cell the charging stops. after the cell is discharged to a certain level, charging starts again.
if a cell is above 4.20v (balance voltage) it's getting pulled down to 4.2v with the internal resistors. the balance/bleed runs through the balance wire and is transformed into heat in the little resistors on the board. this current is NOT transferred to the other cells.
i hope this helps.
and yes. you don't really understand how balancing works
there is no distribution of charge between the individual cells. during charge ALL cells see the very same current, as the current is applied to negative and positive of the battery. because of ohms law the current every cell sees is the same.so all cells charge, or none does. the bms can only turn on or off charging for ALL cells.
so what can happen: during charge one of the cells (measured through the balance wire) one cell may reach high voltage cut off (eg 4.29v) while others are still below that value. to avoid damage to this cell the charging stops. after the cell is discharged to a certain level, charging starts again.
if a cell is above 4.20v (balance voltage) it's getting pulled down to 4.2v with the internal resistors. the balance/bleed runs through the balance wire and is transformed into heat in the little resistors on the board. this current is NOT transferred to the other cells.
i hope this helps.
