Batteries Charging Routine
- Thread starter Az.
- Start date
Isn't whether or not your cells have consistent chemistry also a lottery?
I'm all for reducing green waste. Sadly there don't appear to be many small "Smart" BMSs which can be programmed to balance at a given voltage. IIRC @saneagle posted a link to this one when I enquired:
28.54￡ 30% OFF|8s 10s 13s 16s Jikong 36v 48v Circular Ant Jbd Smart Jk Bms Lifepo4 For 50ah 18650 Lithium Ion Battery Pack With Canbus Board - Battery Accessories & Charger Accessories - AliExpress
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Although I'm a big believer in:
" If it aint broke, don't fix it! "
...if I wanted to install a BMS that large (if one was available for 10s) I'd have to cut out a section of my shark/dolphin/blocky mollusc battery case, then cover over the gap and the protuding BMS with a custom moulded piece of plastic and waterproof.
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On a recent holiday, 4 of us were out cycling the Kennet and Avon tow path. There waqs along run of locks just outside Devizes so a long haul uphill. I noticed that my brother in law had dropped way behind, so we stopped. When he caught up he was complaining that his motor had 'broken'.
Checking it over for him I found that it was turned off, so I took the **** and turned it on. That's when it became obvious that his battery was empty. He swore blind he had charged it before they came away. On further questioning he said, ' Yeh I left it 'till all the bars showed on the display, then I turned it off'.
Despite having explained before that this was not the thing to do, and explaining again, I still don't think he's got it. He see's all bars - battery's full ain't it. He'd never seen the charger led change colour so wasn't looking for it. Also he was looking for it to be 'empty' before charging - like a car tank !
His behaviour does explain his comments about lack of range.
This is possibly fairly typical of the level of understanding most of the public will have. Of course, like most men, he had not read the instructions, mainly 'cos he's dyslexic, but would it help?
He hadn't bought his charger with him but, fortunately, one of mine was the right plug and polarity. So he got a free 4 hour demonstration of how to do it. This is when he said,' I didn't know it took so long'
Checking it over for him I found that it was turned off, so I took the **** and turned it on. That's when it became obvious that his battery was empty. He swore blind he had charged it before they came away. On further questioning he said, ' Yeh I left it 'till all the bars showed on the display, then I turned it off'.
Despite having explained before that this was not the thing to do, and explaining again, I still don't think he's got it. He see's all bars - battery's full ain't it. He'd never seen the charger led change colour so wasn't looking for it. Also he was looking for it to be 'empty' before charging - like a car tank !
His behaviour does explain his comments about lack of range.
This is possibly fairly typical of the level of understanding most of the public will have. Of course, like most men, he had not read the instructions, mainly 'cos he's dyslexic, but would it help?
He hadn't bought his charger with him but, fortunately, one of mine was the right plug and polarity. So he got a free 4 hour demonstration of how to do it. This is when he said,' I didn't know it took so long'
The safe zone for your 36V battery is 31.5V to 41.5V. You only need to knock 0.5V off to be very safe, that's equivalent to 5% of its capacity or taking the bike out to ride for a few minutes. For me, the safe practice is to charge only when you know you are going to use the bike on the same or next day.
I have checked a couple of batteries using the fan driven load.
The tests are specifically designed to represent real world practice, the battery is charged to 42V and the capacity measured down to 32V at a load of 2A. Then the battery is charged to 41V using a diode combination in series with the 42V charger output. This allowed the charger to complete constant voltage charge on the battery and the final charger voltage was 41.04V.
Hoverboard 4Ahr battery.
Charge to 42V, capacity 3658mAhr
Charge to 41V, capacity 3360mAhr (91.8%)
Hailong 11Ahr battery.
Charge to 42V, capacity 10494mAhr
Charge to 41V, capacity 9604mAhr (91.5%)
The tests are specifically designed to represent real world practice, the battery is charged to 42V and the capacity measured down to 32V at a load of 2A. Then the battery is charged to 41V using a diode combination in series with the 42V charger output. This allowed the charger to complete constant voltage charge on the battery and the final charger voltage was 41.04V.
Hoverboard 4Ahr battery.
Charge to 42V, capacity 3658mAhr
Charge to 41V, capacity 3360mAhr (91.8%)
Hailong 11Ahr battery.
Charge to 42V, capacity 10494mAhr
Charge to 41V, capacity 9604mAhr (91.5%)
You've shown 8.2% capacity between 42v and 41v. That's impossible, so your measurement method or procedure is flawed. Every single charge discharge chart done by professionals show that the capacity between 41v and 42v is around 3.5%. I got the same as that twice using two different methods. One reason for the difference is that the bleed resistors open as the voltage approaches 42v, so the power from your charger goes to heat instead of charging. If you use a conventional charger, it steps down the current to very low too, so nearly all the current goes to heat. I keep telling you that that method is invalid, but you just keep repeating it. Why? You can only measure the capacity by discharging, any method that involves measuring the charging energy is invalid because not all the energy goes into the cells.
It's a discharge test, not a charge test??
Discharge curves are produced under load. They do not stop at 4.1 V/cell and wait for the battery to equilibrate. Capacity under open circuit conditions between 4.2 and 4.1 V is not something they are interested in showing.
The capacity of a battery is de facto how much it can discharge under load, since it's impossible to discharge without one.
Nope, that's nonsense. You'd get a different answer every time, depending on the size of the load (in terms of what you would measure between 4.2 and 4.1 V - the discharge curve is highly non linear in this region and what you see under load is highly impacted by the size of the applied load).
If you want to know the state of charge of a battery at any point by measuring its voltage, it has to be the OCV. This involves waiting for it to reach an equilibrium if power has been taken from it.
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The guy that does the testing for lygte suggests a wait for up to one hour for cells to reach equilibrium in link below. He gives a figure of about 10% loss of capacity when cell is charged at 4.1v for the cell he tested.
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Your results are not far off what most research is showing as for example below. (3v - 4.1v @ .2C) Its also interesting to note that the higher capacity cell suffer more loss of capacity when charged at 4.1 volt.e.g the Samsung 36G has less capacity than the 35E when charged to 4.1v. This has also been observed on endless sphere.
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Glad to hear it.
The advantage of that cheap load tester, is that its easy for an ebike owner to carry out thier own load tests so they can decide for themselves how much capacity they loose with thier setup if they chose to charge to 41V only.
I use a water heater element from a 9 kw electric shower. At 5.5 ohms with all elements in parallel, it draws about 7 amps or less for 36v but I can disconnect some of the elements for a slower discharge. I can put it into a bowl of water if it gets too hot.
Very interesting... vapour cloud explosion: by the time smoke alarms go off, it's too late... and I've made a mental note to cover my eBikeBatteryHomeRuinationPreventerator®™© with wood and/or rubber (or lightweight [non-flammable] ceramic?), to avoid being permanenty killed by arc flash electrocution while I'm chucking said box containing my ebike battery out of the window, once the temperature activated horn goes off at 30-ish degrees Centigrade (winter) or 40-ish degrees (summer). In the very unlikely event it ever happens, I won't be running away to watch my home go up in flames, I'll be throwing the damned thing out!
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I'm gambling I'll have enough time to throw my battery with slightly elevated case surface temperature out of the window. Actually, I'll be lowering my battery down on a chain... in case it's a false alarm, and to avoid causing an explosion - I don't want it hitting the ground at high speed.