liveforphysics said:
oatnet said:
That C rate is useful for RC, not for EV's; if you actually discharge at that high C rate you will run out of current in 2 minutes. Dunno why LiPo FanBoys always throw the c-rate stat out there like it is gonna make your bike run faster/further.
If your 50v pack sags to 40v under load, you just threw away 20% of your packs energy into resistive loss.
If your 50v pack says to 49v under load, you just threw away 2% of your packs energy into resistive loss.
You schooled me here, I did not consider that when you are riding an exhibition bike with a 10c discharge and 6 minute run time, IR/sag really comes into play and significant current is wasted.
However, when one is commuting on a typical EV wath a 1c discharge and 60 minute run time, the discharge C=sag is small, so the current wasted is not as significant. For example, on the 20s LiFePO4 bike I rode to week this morning, I think that the resting voltage was 66v, and 64.3v under a 1.1c load, for a drop of .085/cell, so I guess I had 2.58% resistive losses through the pack/wiring/controller/motor.
liveforphysics said:
Likewise, RC LiPo can and does go 4-digit's on cycle life when treated right. More importantly, as a recreational user, I see under 100cycles per year on an ebike pack, even if it only was good for 300 cycles, it would last me 3 years into the future where I'm not going to want my old 3 year old battery tech anymore anyways, as things will be new and lighter and safer with more capacity for cheaper etc.
Seeing a 1000-cycle data point for HK LiPo would change my perception of lipo, I haven't seen folks posting that experience. Can you point me to someone who has demonstrated that? I'd expect you haven't experience that, as it would be 10 years of riding for you. :lol:
I remember reading one of your posts recently, where you mention that you have probably ridden less than 500 miles on an ebike despite being in the hobby for a few years. That makes sense, you like exhibition bikes, and as you stated you get more payoff from building, so you like spending more time under the bike than on it. You come up with some really cool stuff that we all love to see, but I assert that your duty cycle does not represent most of the folks here.
There is no 'right' answer for all builds, there are different 'right' answers for different builds. I wouldn't dream of suggesting that your bikes be powered like my commutor bikes are - our design criterea is totally different. However, you sometimes make recommendations to commuters based on your exhibition bike experience and assume it applys to everyone, when it may not, and I think this is such a case.
For example, I put a cycle a day or more on an ebike pack, either commuting, or errands, or riding along the beach. While your pack may die of calendar age before the cycles are used, 300 cycles is less than a year for commuters like me. Further, calendar age is important to me too - I have 4 year old LifePO4 bikes I built in 2007 that I still pull out and ride - even if there is a newer cooler battery, I don't want to replace the old one when the old one is just fine. I have other packs that I have repurposed onto new builds - why spend money on tomorrow's whiz-bang new chemistry to save 3lbs, when the old chemistry meets the discharge requirement just fine? I'd rather buy cells with enough cycles for a decade, and spend the savings buying/trying new motors.
liveforphysics said:
It's like buying a computer with a 10 year warranty or something, so what if you can still have it work 10 years from now? It's the last thing you would want to be using.
Great example. I have (8) computers scattered about my house, some 10+yo, some new. The old ones meet my needs just fine, they surf exactly as fast as the new ones. The only thing that dual quad-core does is give me bragging rights that my puter is fast, I don't use that extra horsepower. It would be different for a diehard gamer, we'd have different needs.
I can see how LiPo and chain/belt driven motors suits your needs very well, and how they are great for many applications. Can you see how my needs might be different, and LiFePO4 and hubbies a great fit for my them?
-JD
And I DO still have the original paperwork.
