Batteries Charging Routine
- Thread starter Az.
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Have you, or anyone else, charged a battery, from low, to 41V, stopped the charge and then tested the capacity ?
No. I always charge my battery until the LED on the charger goes green for about 5 to 10 minutes. If I check the voltage of the battery after disconnecting the charger, I usually read 41.3V to 41.5V.
can someone figure out why Stuartsproject got only 106 minutes in discharging time when charging to 41V while he got 135 minutes on the same rig when charging to 42V?
I can't think of any reason.
His data:
Rest volts 41.7.
41V, 0.01Ahr,0min
40V, 0.384A,10min
On the face of it, between 41V and 40V his battery gives 10 minutes, 7.4%, roughly in line of expectation but why such a discrepancy between two charging methods?
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There are so many noise factors. This is what I was talking about in the other thread. You can't trust any measurements or test results unless you have proven the repeatability and reproducibility of the measurement method. A general clue to something wrong with it is when the results are inexplicably anomalous or implausible.
That can give very unpredictable results. The battery voltage will almost certainly start to fall unless the charge current is very small. There is a difference between (1)setting the charger to 4.1 volt/cell and (2)interrupting the 4.2v charger at 4.1v/cell. In the former case, the charger raises the voltage under limited constant current and then exposes the cells to 4.1 volt/cell (constant voltage) until the charge current tapers down. This saturates the cells to 4.1 v.
In the latter case, the cells wont even be at 4.1 volts EMF due to battery internal resistance and they wont be exposed to the constant voltage and certainly wont be saturated at 4.1 v.
I have tried to explain this by drawing in green lines in the drawing below. In this rather extreme example to illustrate the problem of a quick charging setup, interrupting the 4.2 charger at 4.1 volts only gives 60% charge. (The severity is high because the charge rate is high, = 1C)
If a 4.1 cell charger was used in this case instead of interrupting the 4.2 charger, the voltage slope (red line)would start to plateau at 4.1v instead of 4.2 and the plateau constant voltage/floating and saturation would take place without interruption at this 4.1 voltage.
I hope this explains. (Its the only diagram I could quickly find)
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that depends on the BMS in your battery. Passive balancers use bleed resistors and start balancing when your battery is mostly full.
Modern BMSes have active balancers that use a series of switches to shunt the charge from the cells with most charge to more depleted cells when the battery is not being used. It's rare that you have to do anything yourself.
I am trying to establish when to finish process of charging battery. I wish it was so simple as red light - charging, green light - charging is finished.
you have already got it with your charger. There is not much justification not to use it in the recommended way. Years ago, BMSes and chargers were not very good so people had to look for ways to improve the process but those precautions and workarounds are no longer necessary. Things like switch on the mains before connecting the charger to the battery, open the charger and adjust the output voltage, buy special charger to revive completely flat batteries etc. are no longer needed. Chargers have current limiter, BMS has overcharging protection, passive balancing makes way for active balancing etc. My bag battery for example is as quiet as a mouse when you plug in the charger or the controller.
I do understand that just stopping the charge at 41V does not complete the charge in the sense that the constant voltage part of the charge, where the current tails off to zero is missing. The balancing, if needed, is also missing.
With the battery I was testing, 24% of the total charge in occurs from 41V to 42V.
And once the constant voltage charge starts (at 41.8V) there is 7% of the total charge in added, so if you do just stop the chage at a particular voltage, your missing out on this amout of charge.
So it appears that quite a bit of charge is added to the battery between 41V and 42V and its a lot more than just a couple of percent.
Could be time to power up my adjustable voltage and current battery charger.
With the battery I was testing, 24% of the total charge in occurs from 41V to 42V.
And once the constant voltage charge starts (at 41.8V) there is 7% of the total charge in added, so if you do just stop the chage at a particular voltage, your missing out on this amout of charge.
So it appears that quite a bit of charge is added to the battery between 41V and 42V and its a lot more than just a couple of percent.
Could be time to power up my adjustable voltage and current battery charger.
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...which is a very simple black brick with only one small red/green light. Manufacturer recommends to leave battery on charge for 24 hours. It is much longer than simple process of charging. I was told it is to rebalance cells, so rebalancing must take place after battery is fully charged.
Bike is 6 months old.
There must be a reason why manufacturer asks for 24h charging time. I just don't quite see one.
To tell the truth I didn't charge battery for so long... I chickened out
Stuart, try this experiment .
1. Charge your battery to 4.1v and immediately disconnect charger and immediately record the voltage. Wait 1 hour without turning on bike and record the voltage again.
2.Go for a spin on your bike and run down your battery. Enjoy.
3.Charge your battery fully to 4.2 v. Make sure charger green light comes on. Disconnect charger and record the voltage immediately. Record your voltage again 1 hour later. Make sure that bike is not turned on during this period.
Report back with the 4 voltage readings.
Yes, it is not a recommendation for routine charging. Just few 24h charges upon receiving battery and once every few months.
Can you elaborate what happens during so long charging process? I was under impression BMS should terminate charging process once battery is fully charged.
24 HOURS?!?!? I'd only do that with the battery charging on a long handled shovel sitting next to an open window. Also arm length welder's gloves, welding mask, fireproof overalls and temperature activated siren on the battery.
It does, but balancing can still mean that any cells below the optimum charge level can be topped up from those fully charged. Doing that can result in the mean charge being slightly below optimum and the charge recommencing with the red light coming back on to top up that slight shortfall.
Hence that extra charge time on rare occasions to allow this to happen.
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