DIY Lithium 18650 Battery 5 part video

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[Benjahmin]

Nice shout Soundwave, I'll probably never build one but it's good to know. The part about chargers was particularly useful.

 

[Deleted member 4366]

That was a really good walkthough about how to build a battery and how it works. Every ebiker should watch all five; however, there was one thing he said that was misleading:

Charging your battery to 90% will not extend it's life. You must always charge to 100%. The idea for 90% is for different types of batteries, i.e. those without a BMS or with special balancing BMSs. Yours needs to be charged to 100% for the balancing to work.

 

[IR772]

This is what experts say.

Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles.

On the negative side, a lower peak charge voltage reduces the capacity the battery stores. As a simple guideline, every 70mV reduction in charge voltage lowers the overall capacity by 10 percent. Applying the peak charge voltage on a subsequent charge will restore the full capacity.

In terms of longevity, the optimal charge voltage is 3.92V/cell. Battery experts believe that this threshold eliminates all voltage-related stresses; going lower may not gain further benefits but induce other symptoms. (See BU-808b: What causes Li-ion to die?) Table 4 summarizes the capacity as a function of charge levels. (All values are estimated; Energy Cells with higher voltage thresholds may deviate.)

 

[D8ve]

This is what experts say.

Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles.

On the negative side, a lower peak charge voltage reduces the capacity the battery stores. As a simple guideline, every 70mV reduction in charge voltage lowers the overall capacity by 10 percent. Applying the peak charge voltage on a subsequent charge will restore the full capacity.

In terms of longevity, the optimal charge voltage is 3.92V/cell. Battery experts believe that this threshold eliminates all voltage-related stresses; going lower may not gain further benefits but induce other symptoms. (See BU-808b: What causes Li-ion to die?) Table 4 summarizes the capacity as a function of charge levels. (All values are estimated; Energy Cells with higher voltage thresholds may deviate.)

But an expert in post 3 said... you need to go full voltage to let the bms work otherwise the cells can drift out of balance and that really life limits things.

 

[IR772]

Post 3, was that the one by D Trump ?

It is common knowledge that if you only CC your batteries as the cheap Chinese lamp chargers do, ( d8veh best light style, funny that ) you get 80 - 90 % capacity but the batteries last much longer as you do not peak the batteries voltage.

I could post in there that orange batteries are better than green ones, would that be correct as well, and before you ask of course they are !

All a BMS does is peak each cell. In peaking the voltage of each cell via the CC then CV element each cell gets to maximum voltage and reading this very respected and unchallenged source, that will reduce the life of your cells.

The worst that will happen if you do not balance the cells is that the battery operates at the performance of the worst cell not the best. Works for bike lights and stacks of other devices that you do not notice without a BMS.

But I could be reading it incorrectly and looking for green cells in the future for my replacement batteries.

 

[anotherkiwi]

I have a Samsung celled 10.4 Ah battery that is down to 80% capacity after 18 months. I put that down to drawing massive Amps on long steep climbs regularly rather than charging to 42 V. If you look further into online docs on battery life you will find that asking too much from a battery is going to stress it probably in a worse fashion than charging to max volts. Of course if you do both...

If the batteries were sold with intelligent chargers where you can set the final charge voltage I would agree with you IR772 - I would probably have set final charge voltage to 41.5 V. But they aren't and it isn't really important because even having gotten only 18 months use from my battery it is still much cheaper than buying bus tickets to cover the same mileage. A battery is a wear part just like tyres and brake pads and those selling electric bikes should come clean about it with realistic life cycles.

Now I use Lipo so I do charge and discharge within the reasonable limits (4.15 - 3.65 V per cell) and the battery is correctly dimensioned to provide the Amps I need at 1C or less.

 

[Deleted member 4366]

Nobody is arguing that charging a single cell to 90% won't extend its life, but we're using batteries, not single cells. That's the difference between how a scientist (theory) sees it and an engineer (practice).

 

[Benjahmin]

Touchet varlet!

But according to Prof Brian Cox scientists never get it wrong

 

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[Rohloffboy]

Slightly of topic, but the latest EVTV video gives quite a good insight into EV batteries, the Friday 13th January 2017 ( sorry can't do the Linky thing) episode gives a talk on a stripped down Tesla battery, which of course is stuffed full with 4000 odd 18650 cells.

 

[awol]

I like the idea of having a go at this for a future project.
This is a good video too, by the same guy.
Anyone know where to get those triangle shaped nickel plates?

 

[craiggor]

The KFF thread on endless sphere is worth a read.

 

[Deleted member 4366]

Here's my version. Note the burn on my forefinger.

 

[D8ve]

Here's my version. Note the burn on my forefinger.

Tich tich wearing a watch...

 

[anotherkiwi]

So far I have only managed ceiling high sparks All the burning was done to a jumper on the bar stool...

 

[Deleted member 4366]

Tich tich wearing a watch...

Yes. There's a reason. I never take it off for anything. It's been on my wrist for about 5 years. I should really start a separate thread about it: The best watch in the world. They're difficult to find, but they do come up used on ebay from time to time. This is my second one. The first got hooked off my wrist at sea in a freak accident after I'd worn it for about 10 years, and I mourned it more than losing my wife.

It's a Casio Tough Solar Wave Ceptor. You never need to take them off, nor touch any setting. They always keep perfect time. You can wear them in the sea, in the bath, shower, etc (totally waterproof). The time changes automatically when the clocks go back. There's no battery to replace.Basically, put it on your wrist and never need to touch it thereafter - just look at it to see the correct time. One should last you an entire lifetime!

Only get the one with the metal strap because plastic straps fail in about 12 months.

No other watch comes close.