cwah said:
Lifepo4 is heavier (we all knew that) but it still has several benefits against us18650v3 and even more against generic lithium:
I wouldn't consider generic lithium-ion cells because they are, in my view, not appropriate for e-bikes. Most cells have to high internal resistance so the voltage drops too much, when really using them. The only cells, I would consider for ebikes in 2013 are the V3 and the VTC4 Sony cells.
cwah said:
- it outperform any lithium cell on winter conditions. Other cells have a lot of sag and increased resistance
No, it doesn't. The Sony cells drop a lot less when faced with colder temperatures. With generic chinese Li-Ion cells, you'd be right, not with the Sony cells, though.
Also, you will never, even in the coldest winter get a higher W/kg with LiFePo4 than with the Konions.
But then again, most people charge their "small and portable" Sony packs in their house and don't leave them outside on the bike in winter.
I would consider leaving the battery pack outside at -10°C and then going for a bike ride for over an hour a very special application.
With a pack that doesn't weigh 7kg, but considerably yes, it's no problem to bring it inside to charge and have a warm battery that you connect to your bike in winter. Depending on the padding of the pack it will take longer than most winter bike rides for the temperature to drop.
So, in real world applications, even in winter, I don't see myself going LiFePo4.
cwah said:
- his lifecycle and calendar life are proven. A lot of manufacturer are lying about their cell. But with lifepo4 we buy reliability. Not saying your cells are not reliable. It's just that it hasn't been proven yet.
Sony Konion cells have been around for a long time and their calender life etc has been proven time and again. What puzzles me, is why this forum has been so resistant. Are they not available in the US?
The datasheet for the V3 cells states a drop in capacity of 10% after 500 full (!) cycles, at 5C discharge 4.2V down to 2.5V. I don't know anyone, who would do an equivalent to that over a time of 3-4 years. And even at 90% capacity, the cells have a much, much better weight to capacity ratio than any LiFePo4 cell out there.
On a side note: even if you had done these 500 full cycles over a period of 3-4 years, within that time, there will be a new, even better battery technology with even higher capacity and discharge. Just like a few years ago A123 were the way to go, and now they're outdated.
cwah said:
- it's cheaper than the new 18650 cells. If you can sell them at the same price as sun-thing29 on ebay then we can say there isn't any price difference. It's not the case yet.
I don't know the prices they charge for LiFePo4 cells, but mind you that when importing to Germany, you have transportation costs from China, for shipments over 150€ value (that is purchase price + shipping costs) and on top of that another 19% VAT.
I buy all my ebike related parts from China or Hong Kong. And there's always a risk that you don't receive anything, or you get subpar quality. And in case of failure, you're faced with a real problem. I wouldn't know, what to do either, when I have a pack, where one cell was damaged.
On the other hand, I had a Konion pack, that was physically damaged so one cell bank was broken. I opened the pack, exchanged that bank, balanced the pack, and it's back in full operation with just 3 days downtime and costs of less than 50€.
cwah said:
There are reasons lifepo4 are still used and purchased over lighter cells.
I understand why, you would choose them over cheap, or knock-off Li-Ions, but not over quality Li-Ions, sorry.
cwah said:
If I were to invest 500usd on cells for my cargo bike, choosing lifepo4 would give me proven reliability and increased capacity over lighter cell.
That I would have to calculate.
And it will probably depend on your personal risk evalutation.
For me, using a battery technology that requires additional electonics to work properly, is a risk in itself. Buying from Asia is another huge risk over buying from shop in your own country, where warranty rules apply.
On top of that you'll have to look at custom's and VAT charges. shipping time etc. That's a lot different from a pack that you'll get within 48h and that runs completely care-free.
Without conceding that the total cost of ownership of a LiFePo4 pack would be lower thatn a Konion pack, I would not sacrifice that much weight on a vehicle, just to save a few bucks because nowhere on the bike will saving weight ever be easier than there.
But hey, that's what the forum is for. Sharing different opinions and view points.
Maybe, I'll make you a nice pack some day and you'll be convinced
