July 12, 2015 electricbike.com – Amazing new 18650 cells for E-bike batteries in 2015 – LiPo is for high performance enthusiasts, but the charging systems are too cluttered and complex, and although many LiPo users can assemble a pack together cheaper than a pack made from 18650 cells, a LiPo pack that is used daily to a full discharge/charge cycle will likely only last for one years riding season. In 2014, Samsung made a real splash in the E-bike DIY world when they began selling the 20R cell. 2015 was the turning point for E-bikers who want an easy and reliable battery pack with good performance, long life, and still have decent range. Samsung decided to release a cell that had 20% more range than the 20R cell, but only had to give up a small amount of its ability to crank out the amps. When Samsungs newest high performance cell made its debut (the 25R), Panasonic introduced more range instead of more current. They developed their now-famous “B” cell 3400-mAh Panasonic NCR18650B, which was the result of Panasonics relationship with the Tesla electric car company.
Look carefully at these three Samsung cells, and the capacity along with the current they can put out safely, and see the relationship between the two: 20A-2500mAh, 15A-3000mAh, 10A-3500mAh. New technology has dramatically increased the capacity of these 18650 format cells, but the more current you want, the less capacity they can hold. The three cells listed here are all from the same company, using the same chemistry.
I am going to list several models of 18650 cells below that I think will soon become available to build battery packs from, and that I believe will become the most desirable cells to use on an E-bike.
Highest Current – 3000mAh ICR18650HG2 LG-Chem, 2500mAh INR1865025R Samsung, 2500-mAh, ICR18650HE4, LG-Chem – these cells are the current replacement for LiPo in high performance E-bikes. All three are rated for 20A continuous per cell (and some web-sites list their temporary peak capabilities at around 35A! I am reluctant to list peak amps, because…the few places that do that do not agree on the amount, and they don’t list for how long the “peak” amp-draw is, or what temperatures they reached before they stopped raising the amp-draws. With either of these cells, a tiny 5P pack (only 60 cells if configured for 12S/44V) can put out 100A! If you are only drawing 60A as a peak during acceleration, and maybe 20A during a cruise-phase…a pack like this will not even get warm, and should last a very long time.
MAX Capacity that still has Great Current – The 10A per cell options are – (3500mAh, NCR18650GA Panasonic-Sanyo), 3500mAh INR18650MJ1 LG-Chem, 3200mAh NCR18650BD Panasonic, 3200mAh INR18650MH1 LG-Chem, 2900mAh NCR18650PF Panasonic. With 10A of current per cell, a 5P pack can provide 50A continuous, but at a higher capacity. It would be reasonable to expect temporary 75A peaks from a 50A continuous pack, as long as there were frequent cruise-phases when you were only drawing 20A to maintain your top speed, so the pack could cool down.
2016 re-evaluation : 3500mAh INR1865035E Samsung – All the information I had available in 2015 indicated this was a 10A cell. It has a higher capacity, but for long life, I am now calling this a 6A cell. Its a good cell, just not able to put out 10A continuous without getting hot. 3400mAh NCR18650B Panasonic – same story here. This is a great cell, but for longer life you should limit it to 6A per cell, otherwise it will get too hot. This is the cell used by the Tesla car company in 2015.
Conclusions – If you can fit a large battery pack in your frame, you don’t need to pay top dollar for the high-current 25R, HE4, HG2, or 30Q cells to get high amps out of the pack. As an example, if you increase the parallel strings from 5P to 6P, and you use the high capacity 3500mAh GA cell, a 12S / 44V pack at 6P will give you an incredible 21-Ah of range, and it will do that with only 72 cells! A 6P pack of GA cells at 11A per cell would be 66A continuous, and peaks at roughly 90A.
Be aware, when I say about a cell that it provides 10A, you can have one or the other. If you calculate the range you need and then you hit the throttle hard and often to get max amps, the pack will not deliver the full rated range. The rated capacities of all of these cells are tested in a lab at a 2A per cell drain, or less.
If you begin shopping for loose individual 18650 cells, and you find advertisements for 4200-mAh cells that put out 30A per cell…they are lying (Trustfire, Ultrafire, etc). An authentic Ultrafire cell is not horrible, but again, there are lots of counterfeits. Buy some samples of the cell you think you want to use. Set-up a current-drain pulling the same watts that the cell is rated for, and if it is too hot to hold in your hand after 5 minutes, its a fake. It may even look exactly like an authentic Samsung, Panasonic, or LG cell. Once you find a trusted vendor, only buy cells from them.endless-sphere forum about Samsung INR18650-32E / 2015 : This seems like a perfect cell for our e-bikes.. 3C max (10/3.2), maybe 1.5C continuous & in the 200whr/kg+ club. Probably best to use these cells @1-1.5C, always cut the C rate of a battery into 1/4-1/3rd of what it’s rated for, for optimal use. I’d run it at 90% SOC to extend it’s life and discharge it on 1-1.5C. Probably will get 500+ cycles doing that. If you have a big pack, each cycle can go pretty far. The specs PDF says 500 cycles is at 1C, 300 cycles is at 2C. Samsung 29E is declared at 500 cycles at 1C dow to 70%, not 80%. So they are basically the same, performance wise (both are 2C continuous, and 3C peak). Cycle life wont be a problem, same goes for LG MH1. But Samsung seems to be the cheapest one (panasonic be and lg mh1 are more expensive), so if you don’t need a crazy discharge current, it’s a way to go! Samsung 32E at 10A not so good as as Panasonic BE and LG MH1. LG MH1 and panasonic BE are the best compromise between capacity and performance, if you don’t mind the price.
How to make a lithium battery last as long as possible – keep the battery cool by charging at a lower rate, and also don’t charge to 100% all the time. Professor Jeff Dahn from the Dalhousie University in Canada is the only research University in the world that has a contractual research relationship with Tesla’s battery department, and Tesla could have partnered with any University they wanted. Tesla gives an 8-year battery warranty, prof. Dahn tells us how, in a 73min video lecture. HOT is BAD – bad chemical reactions are worse at higher temperature. The Amount of TIME when hot is BAD – the time of exposure, is really the bad actor here, in the failure of these cells at elevated temperature. Amount of TIME at HIGHER VOLTS is BAD – the biggest issue is the time spent at highest voltage. Negative electrode (anode) plating & “Secret Sauce ” additives – there’s a 20-fold increase in cycle life, just with a few percent of a few magic ingredients. For Long term storage, use low volts at low temps.
The GM Volt battery charges to eighty percent, just 4.03 for that cell. The more time you spend at higher voltage, the worse.
Drain your battery pack to 3.5V per cell, and store it in a cool area. Not necessarily a refrigerator (although that would actually be OK), but at the minimum, some place that is NOT warm. You might not want to put it in a freezer, because it would have very bad voltage sag until the battery warms to room temperature. Also, definitely disconnect it from the controller, and also disconnect it from the charger.
Avoid Heat – Whether charging, or during a ride, avoid as much heat as possible in the battery. If you are drawing max amps often it may “work”, but you will NOT be getting the maximum possible life-cycle from that pack, due to the resulting heat. There are two ways to reduce heat in a battery pack system design. First, use a larger battery pack than you need. You might only “need” a very short amount of range on your particular commute, but a bigger pack will run cooler, since each cell is less stressed at a lower amp-draw per cell. The next way is use cells with higher amp-rating than you need. You can buy a pack of the same physical size, but with a higher amp-rated cell, and it would run cooler. The Tesla cars and the Chevy Volt both have an on-board battery pack cooling system to help stabilize pack temps at a reasonable level.
Charging. There are some days when you want to recharge your battery as fast as possible. For example, the Luna Advanced charger has the ability to charge at 5A, or at 3A. If you charge at 5A, the battery will charge faster, but if you charge at the lower (and slower) 3A rate, the 3A charging rate will also leave the battery pack less warm, the cooler the battery is, the better. The Grin Tech Satiator also has the ability to adjust the charging amp-rate.
Don’t charge to 100% (4.20V per cell) The amount of extra charge you get from charging to 4.2V per cell, instead of 4.1V is very small, and has very little effect on your range. You may think that charging to 100% will give you the maximum range possible, but it trades a significant amount of pack life for a very small amount of extra range. The Luna Advanced charger, and also the Grin Tech Satiator both allow users to charge their packs to 80% (4.05V per cell), 90% (4.1V), and also 100% (4.2V).
In the graph above, there are 17 graph squares (of range) between 4.2V and the cutoff at 3.3V. You only have to give up 1/17th of the charge to gain double or triple the battery pack life in months. I have not charged any of my ebike battery packs to 4.2V since I found this out.
Also, if you ride only on the weekends, it would be more ideal to leave your pack half-empty during the week, and only charge it an hour or two before the ride. However, I know this is not practical. If you feel you need to charge the battery pack immediately after a ride, charge it to only 80%, and then let it cool off before you ride, or before you charge it more. Then, just before you want to ride, charge it up to 90% to get a little extra range. Of course, if your battery pack is large enough you never NEED to charge it to more than 80%. If your ebike commute is short and you also have a large battery pack don’t charge the pack every day. If you can take several rides throughout the week, but only need to actually charge once a week? This would mean your pack is spending less time at the highest voltage. Lead-acid batteries need to be topped off completely, and as often as possible, lithium does not. For long lithium battery life big packs rule and try to keep them cool.