DrkAngel said:
.27C draw resulting in 95% usable of rated Li-ion capacity!
And yes, if you looked, you would see that I have, multiple times, stated that my brush motor is 20%, or more, less efficient than a brushless motor!
Usually when people talk about efficiency, they are talking about the efficiency of the controller and motor, not how efficient the battery is. I don't even know if calling a battery 'efficient' is correct in the first place. See how i got confused there?
Also, 20amp discharge on a 20amp pack is not .27c, it is 1C.
DrkAngel said:
Yes, cruising speed! On the level! Only way to provide accurate comparison between different configurations!
Digital amp meter connected at battery tells the best story. But I tend to rely on battery capacity divided by miles motored, factoring in the maintained speed.
No, not really, you need to look at peak amps as well. In fact, all batteries should be chosen with peak amps in mind, not cruising amps.
This is so that you don't exceed the cell's discharge rating when taking hills or accelerating from a stop or lower speed.
If you watch your digital amp meter, you'd know that there is a lot of variance in amp draw.
DrkAngel said:
My 25.9v 31.2ah pack never exceeds 30amps, even full throttle from a dead stop, and ... it drops noticeably below 20 amps at 22mph+!
That's good, but you still need to design your battery pack around the 30 amp number. Often time the cycles rating is *much* lower than the discharge rating.
DrkAngel said:
Just looked up multiple manufacturers, product specs, for their 18650 Li-ion cells, they are rated at 1.5C continuous output ... and 1.5C charging!
For the Ultrafires?
That seems to conflict with every review of ultrafires i have ever seen on dealextreme and elsewhere.
They do not live up to their specifications in any way.
Even dealextreme puts big quotes around their capacity ratings.
Ahh, their site seems to be down so i can't even quote them..
But check this site:
http://lygte-info.dk/info/Batteries18650-2011 UK.html
The 3600's deliver less than 2500mAh at 0.2amp draw. More so around 2300mAh at 0.5amp draw. That means you are getting 33% less AH. So if you build a 40ah pack, you have in reality more like 26AH.
That's best case scenario, assuming these cells aren't actually worse than advertised.
DrkAngel said:
Li-ions might run 90% rated capacity at .5C.
SLAs run at 60% rated capacity at.6C. Rated capacity is at 20 hours! SLA = .05C
I've never heard of any battery exceeding a 90% rated capacity at .5C. 80% at 1-2C either!
Depends on the lithium cell's chemistry. The laptop cells you seem to be fond of have very low C ratings, often in the 0.5-1c range.
The reason you don't get all their capacity is that you are running them over their comfortable C rating and they are most likely turning some of that energy into heat because of it.
Lipo gives me 100% of it's rated capacity at the 7C i have been discharging it at lately.
Better lifepo4 cells like headways etc. give you 100% capacity at the 1C-2C also from what i have seen.
If you're okay with carrying around a 40AH pack and still getting low cycle life and bad voltage drop when you hit the throttle, go for it. I'm not stopping you.
I'm just saying that these batteries are not all that.