Batteries Charging Routine
- Thread starter Az.
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Looking at your graph, the last hours charging (90-150 minutes) is unproductive. Very little Ah is gained and the battery wont be balancing anyway . You could stop the charger early at the 90 min point if you want or are in a hurry. Get into the habit of feeling the charger temperature. When it gets cool, its an indication that the battery is nearly charged. Its the diode's curve that causes the problem. If you could get a high power zener diode to work at 1 volt 's this would not happen.
Anyhow, your are nearly ready for Hack number 2, which will prevent any anxiety you may have about your cells going out of balance and you will be ready for 2000 or more long and anxious free enjoyable spins with that battery.
not necessarily. We don't know for certain until Stuart tests the battery using his discharge rig like he did last time. The reason for it is we don't know how much fast charging distorts the distribution of the Lithium ion inside the anode. It's this distortion that causes poor performance (lower voltage than expected) when discharging.
the last hours charging (90-150 minutes) spreads the Lithium ions inside the anode.
Using your roast chicken analogy, if you roast the chicken in the oven at 120C for 2-3 hour, it'll be cooked.
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Indeed not.
I have not done a discharge test using the diode charge hack, and I will wait for the 1A charger to arrive.
Does anyone else have any practical examples or tests and results they have done where eBike batteries, preferably 10Ahr and less, have been discharged to say 3.0V per cell whilst measuring the Ahr capacity then charged back up to 4.1V per cell, the charge stopped, either at the first 4.1V point or when the CV charge drops to a few mA ?
Well, over 3 years ago I started this experiment:
www.pedelecs.co.uk
That pack has been in constant use and only charged to 41V (as are all my 36V packs). Even after 3 years and hundreds of cycles, all banks are in a similar balance as they were at the start. If I can take the pack into the lab tomorrow I will give a more precise update.
Charging pack to 41V experiment
Some people think it's a good idea for cell longevity to only charge to 4.1V instead of the normal 4.2V. However, when you have a pack of cells, only charging to 41V may cause balance issues as the BMS in many cases does not start balancing until about 41.5V. Anecdotal evidence from some on this...
www.pedelecs.co.uk
That pack has been in constant use and only charged to 41V (as are all my 36V packs). Even after 3 years and hundreds of cycles, all banks are in a similar balance as they were at the start. If I can take the pack into the lab tomorrow I will give a more precise update.
On most chargers of 2A rating, all that it means when the green light comes on is that the current draw has dropped below 100mA and it is then in constant voltage mode at that point, rather than constant current. The green light does not mean that the battery is "fully charged".
In my experiments with what is happening during the balance process, this does not occur until 4.18V / bank is reached. In the process, some banks may be driven over 4.2V per cell, while the lower voltage banks catch up. It seems BMS are generally set up to cut out at 4.25V per bank, but I have not risked pushing things this far.
In terms of capacity difference between 41V and 4.2V per cell, it's a difference of about 7 to 8% in my experiments.
In my experiments with what is happening during the balance process, this does not occur until 4.18V / bank is reached. In the process, some banks may be driven over 4.2V per cell, while the lower voltage banks catch up. It seems BMS are generally set up to cut out at 4.25V per bank, but I have not risked pushing things this far.
In terms of capacity difference between 41V and 4.2V per cell, it's a difference of about 7 to 8% in my experiments.
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As for putting a diode in series with the charger, to drop the output, I'm not sure it's a good idea. When I tried it some time ago, it caused the output to go way higher than 42v! The charger is constantly monitoring the output and adjusting it accordingly...I didn't try it under load, I didn't want to risk it, but then I discovered how easy it is to modify the voltage divider on the 431 voltage reference IC found in almost all chargers:
www.pedelecs.co.uk
www.pedelecs.co.uk
For some time I have been charging at 3A as 2A just did not give me enough turn around time, especially in the winter. Recently I bought a 5A charger and have been using that - also modified to 41V output (I will post a report on this when I get time). Is that a lot of current? For a 15 Ah pack, with 6 cells per bank, this is less than 1 A per cell. Bear in mind if you have a USB bank, the charge current is likely to be at least 1A/cell.
2A 42V chargers cost next to nothing. Most of them don't seem to give the correct voltage output anyway (on a calibrated DVM) so someone like @StuartsProjects with a lot more skill than me should be able to do this no problem.
Mikes eBikes 3A charger
I picked up one of these recently and thought I'd give it a once over. It looked quite compact, came with a fan, already had an XT60 connector and I could do with something that charges a bit faster than my SANS chargers. It uses a PSU PCB company that also makes the PSU boards for the Vruzend...
www.pedelecs.co.uk
Tuning cheap 42V charger
A while back I bought a couple of cheap 42V chargers as spares, so I could have one at work, at home etc. I got two for just under £10 each. They are quite a lot smaller than the SANS charger and looked good: However, when I checked the output, I was disappointed to see that it was nearly...
www.pedelecs.co.uk
For some time I have been charging at 3A as 2A just did not give me enough turn around time, especially in the winter. Recently I bought a 5A charger and have been using that - also modified to 41V output (I will post a report on this when I get time). Is that a lot of current? For a 15 Ah pack, with 6 cells per bank, this is less than 1 A per cell. Bear in mind if you have a USB bank, the charge current is likely to be at least 1A/cell.
2A 42V chargers cost next to nothing. Most of them don't seem to give the correct voltage output anyway (on a calibrated DVM) so someone like @StuartsProjects with a lot more skill than me should be able to do this no problem.
On the charger I was using the green light comes on when the current drops below 280mA. In the case of the 42V charge it takes a further 45mins for the current to fall to zero.
Whilst you can keep an eye on this with an in-line charge\discharge monitor, it would be good if chargers had a extra 'really finished' charge indication.
The two hailong batteries I gor for my mountain bike conversion each came with a charger. Nice charger, alluminium case with screws and a fan so you can hear when it goes green. So I have a spare, might take one too bits to see if it can be adjusted.
what you mean by really finished?
The LED turns green when the charging voltage is 42V AND the current is below 100 milliAmps.
On the charger in question the green light comes on when 280mA is flowing.
Then about 0.13Ahr goes somewhere over the next 45 minutes .............
Some of that will go on charging, some will be bled away on the balance resistors.
What is the current rating of your chargers? 280 mA transition to green seems quite high for a normal 2A charger. All the ones I've had tend to go green around 100 mA. Even my recent 5A charger goes green at around 240 mA.
I guess the 280mA may be due to the 5AH. I never had a small capacity battery except a Bosch tool battery sometime ago for my Brompton but that had its own charger. I am learning from Stuart's observations.
My thoughts too.
But look at the current fall off for the 41V charge, same sort of currents but twice as long. At what voltage would the balancing normally start ?