I’ve never discharge them below 3.6V per cell. You could feel the difference with drones when the cell voltage fell below 3.8V almost instanly. Between 3.6 and 3.7 they were getting really sluggish. That was a clear sign for a battery change.
I’m holding to the same habits here in the esk8 hobby as well. 3.7V is preferably the lowest point one should go, 3.6V being a rare exception. Going lower will degrade the performance and can cause bigger risks of damaging the cell…which will over time inflate or even be prone to catch fire. I store my lipos @3.8V per cell.
I used to charge my 3S drone packs with 2C without any issues whatsoever. Then I f*ed up (2 times actually) and did a deep discharge to around 2.8-3V. The cells started to puff right after that.
It was similar with my first esk8 build where I was foolish enough to count on the ESC to do a cut-off. But I never even had a chance to charge those (brand new) batteries more than once. The board stopped but it wasn’t the ESC. The batteries were at 2V I’ve managed to recover the packs but they are quite puffed now and had to remove 2 cells after few more charges because they died.
In my experience, it is the discharge that kills it. Fast charge away, ain’t noone got the time to wait for a ride I only slow charge at night.
Exactly
I look at the charging situation like this: we’re in a year 2017 and we utilize 2-5A chargers for BMS to fully charge our esk8 in like 3-4 hours? Even electric cars can be charged up quicker…and have times bigger batteries.
Because “it’s more convenient” to hook up the board to a charger and then wait 3 hours. I disconnect the batteries in series, connect them in parallel and hook it up to my charger. 1-2 min of work tops. 28 minutes later I’m riding again.
And if I for example keep another two packs of 2x4S 5000mAh charged (1 hour of charging time for both together) I drop them in my lipo safe bag and then in my backpack and off I go. And when my Drok shows around 65% of charge after like 12km I know I’m close to 3.7 - 3.8 V per cell. I swap the lipos and that way I can theoretically ride for 3x12km and I’m being very, very conservative with my batteries on a single motor setup. That’s almost 40 km of range @ around 15km/h average (we have below average quality of asphalt on the city bike trails).
Somewhere in this forum @Namasaki talks about this. Saying that it’s unwise to go for a 2p pack since balancing the cells of such battery is not completely accurate.
Why?
Because the cells are packed as groups of 2, meaning the balancer sees two cells as one cell.
Hi @Namasaki
Just to have an understanding of how to use lipos with a BMS.
When you buy 5 fresh 2s lipos for your 10s build. Do you first have to balance every battery individually using a lipo balancing charger?
Or can you just install all 5 and hook them up to the BMS and let him do the job?
@Namasaki is there any ratings I have to be aware of for the E-switch? I have that BMS, can I use the illuminated push button switch that came with my SPS switch?
@Namasaki My 10S BMS from Bestech has overcharge protection of 4.28V - as you have same model do you think I can let it charge to this number or keep an eye on voltage meter and disconnect it at around 4.1V? In specs it’s says Balance charge 4.2V - does it mean it will start balancing at this voltage only ?
You could always connect the LED on the switch using different ways:
connect LED pins to the BMS outputs with a resistor in series. Calculate resistor value like this:
R=Vin-2V/I, where Vin is your battery voltage, I is 0.02A
And use closest resistor you can find to the calculated value. You don’t have to be extra accurate about it. For example, using 10S pack it would be like R=40-2/0.02=1900Ohm which means 1.8kOhm or 2.2kOhm resistor.
connect LED to the ESC or receiver 5V outputs. Calculate resistor values using same formula, but use 5V as Vin. Depending on the LED type, it might not light up on 5V. Test it on the bench
The overcharge protection is set at 4.28 by default to allow some headroom. Balancing starts at 4.2v
If your cells drift during discharge and then if you undercharge them, the bms will not balance them.
If you continue this way so that your cells drift too far out of balance, your battery could reach a point where it will not fully charge and the bms will not be able to balance the cells.
How the bms works is like this:
When your pack reaches 42v and the charger stops charging (green light) the bms will then trim down the highest cells to balance them with the lowest cells ending up with a total voltage below 42v
How much under will depend on how well matched your cells are and how evenly they charge and discharge.
The more balanced and matched(internal resistance) your cells are, the closer you will be to 42v
Thanks! By trimming you mean that BMS will discharged highest cell, voltage then will drop below 42V, charger will come on again to top up missing voltage ( of the lowest cell ?) until all are balanced?
Chargers do what is called constant current / constant voltage charge.
If empty battery is connected it will start charging using pre set constant current. The battery voltage will slowly rise as the battery charges. When the charger voltage level is reached, it will slowly reduce current and it will go into the constant voltage mode meaning it is charged.
I’m glad you asked.
Voltage is like pressure
Current is like flow
If the voltage (pressure) from your charger is greater than the voltage (pressure)in your battery.
The voltage will continue to flow into the battery.
Once the voltage in the battery is equal to the voltage from the charger then the flow stops because the pressure is equal.
The the flow stops the green light comes on
Yes but best to remove the charger, let the cells balance down and then put the charger back on to fill it up again.
Better yet though is to leave it below 42v
Bestech designed it that way to help prolong battery life
So lets say i have a 10s setup. Then when i connect my Charger , it can feel that the voltage is under 42v ? So when it starts to charge , it’s start with lower voltage than 42v ? Or starts in 42v, and can feel when the battery level is the same ?
Hi are you running a hub setup? If not I’m not sure if the batteries will help as much as you would like. Also what esc are you using the vesc tops out at 60amps with cooling.
I’ve managed to recover the packs but they are quite puffed now and had to remove 2 cells after few more charges because they died.
I only slow charge at night.
I look at the charging situation like this: we’re in a year 2017 and we utilize 2-5A chargers for BMS to fully charge our esk8 in like 3-4 hours? Even electric cars can be charged up quicker…and have times bigger batteries.
Because “it’s more convenient” to hook up the board to a charger and then wait 3 hours. I disconnect the batteries in series, connect them in parallel and hook it up to my charger. 1-2 min of work tops. 28 minutes later I’m riding again.
And if I for example keep another two packs of 2x4S 5000mAh charged (1 hour of charging time for both together) I drop them in my lipo safe bag and then in my backpack and off I go. And when my Drok shows around 65% of charge after like 12km I know I’m close to 3.7 - 3.8 V per cell. I swap the lipos and that way I can theoretically ride for 3x12km and I’m being very, very conservative with my batteries on a single motor setup. That’s almost 40 km of range @ around 15km/h average (we have below average quality of asphalt on the city bike trails).