Hi all . . . there are some heated discussions going on in a couple of "Private" Facebook Groups I'm in, about fully-charging a new Li-ion battery-pack and then letting it go "Flat" for three times to "Condition" it as per -
Cyclotricity instructions.
My guess is that the BMS cuts out power to the motor when it determines the voltage in the pack is getting to low, (rather than 0% Flat) but that I don't know, so I'm asking the experts here if they know . . thanks.
Also some are saying it's bad for the battery to leave it on the charger over-night, and my assumption was that the transformer part in the Mains-lead had some electronics, and a relay, which cut off the supply once the battery-pack was charged.
Others are saying it's the BMS which cuts off the power-supply to prevent the pack becoming over-charged, and not the intermediate box in the mains-lead.
Some are buying expensive electronics to stop the battery being charged beyond 80%, so am I being blind in just leaving mine plugged in overnight?
Thank you for any guidance . . .
my current eBike
In the (few) chargers I have looked at, the charger switches "down" to a "holding voltage", once the maximum charge has been reached.
For this post, I will consider only 36 volt nominal Li-ion batteries, for them, it has been in my experience, pretty exactly 42 volts, though this value also depends upon the accuracy of the volt/Multi meter used...that causes further arguments with some, because they do not know the accuracy of the charger, or the accuracy of the meter!!
If the charger is unplugged from the battery, you will measure 42 volts on the output plug from it, pretty accurately, with a reasonable meter.
The same can be said of the battery, which will be 42 volts or close to...
This tells me that in the case of the chargers I have owned (both for 36 volt li-ion batteries, with a 2 amp charge) and used, that the charger is responsible for the stopping of the charging.
Faster charging reduces the working life of the battery and if needed quickly, a better alternative is two batteries. This (if the second battery can be carried onboard), allows a battery to be discharged when power is dropped, and replaced with the seond one. But make sure that you have a bike that the battery can be easily and swiftly replaced on the street, with no tools needed. Not all can I believe....
Sadly though, the cheap chargers, if left connected, still charge at a few milliamps (I forget what I measured some time ago), not enough to increase the battery voltage, but just to be "ready" if the charge drops over time, to sense that and recharge again.
Contrary to the opinion of some here, I believe that this is really bad for the long term life of the battery.
Any Li-ion (and some other chemistries) have a limited number of charges, before the battery starts to lose capacity, and this small leakage current tend to "use up" some of these possible charge cycles, reducing the total working life of the battery.
This is a much discussed phenomena, that some of the non engineers here do not accept for some reason! I cannot explain why they do not accept it.
What I use to charge my batteries is a cheap 24 hour timer, one with a tiny synchronous electric clock motor, and I judge the length of charge needed and set the clock to turn off at a particular time.
To prevent it turning on again, I rewire the tiny motor so that its power comes from "after" the timer on/off switch, effectively a) removing all power from the charger and simultaneously b) turning itself permanently off, to prevent charging again in 24 hours.
If the battery is not going to be used for a period exceeding say 4 weeks, the same timer can be used to reduce the charge time, so as to achieve say around 35 volts for storage purposes.
But as batteries self discharge, some faster some slower, a volt meter needs to be used to keep and eye on the charge level, and top up when needed.
But only fully charge again when the battery is to be used again.
"Letting a battery to go flat" as you worded it, would in the case where good quality cells are in use, take months. The best way is to go riding and recharging when "empty" or just before, and the capacity will normally improve with each ride quite significantly in the first 10 charges, less so after that.
The BMS, as far as I can tell, is in "charge" (pun intended) of the battery to even out the charge between banks of cells, and to prevent a normal charger charging, if the battery dips below a certain minimum level, around or just under 30 volts, charging is thereby completely prevented.
This is a safeguard to prevent a battery getting damaged and possibly catching fire, as they are almost impossible to put out by normal means. They usually need to be bodily thrown in a bath of water, or a lake or a stream for some hours to cool down... Generally including the bike as well!
A hose may slow down the reaction, but generally it will not stop it completely and they can easily burn for 12 hours in some cases. YouTube is a good source of video about e-bike battery fires....These batteries are not something for an amateur to play with or to attempt to repair....Be warned...
You can see what this Dutch guy has done wrongly, he has two batteries on the bike, one, slightly pulled out of the socket above the rear wheel, and another on the down tube! Guessing only (I don't speak Dutch, but I can read it), he mixed up his polarities, but its just one of several possibilities, a short circuit is another!
You can hear the cells popping and reigniting the fire!! HORRIBLE!!
The smoke is also a health hazard too!
This guy has a reasonable "take" on e-bike batteries:-
regards
Andy
I hope this helps further.
