Choosing battery Ah based on my current usage

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yoyoman

1 kW
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Jun 9, 2008
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477
Location
San Diego, CA
I've been riding my Crystalyte 408 bike to work for the past week. I just added the Watt's Up meter and have started recording the values.

The first column is the category, 2nd - to (day 1), 3rd - from (day 1), 4th - to (day2)
Ap 22.24 21.95 21.71
Vm 33.12 9.24? 34.49
Wp 825.8 769.2 762
Wh 125.6 101.0 117.7
Ah 3.535 2.812 3.295

The first day was with one set of SLAs, and the second day is with a different set of SLAs. I hate carrying 27+ pounds of batteries!

I have a 48V ping pack, but even those 20 pounds seem unnecessary for my ride. I take different routes going and coming to minimize the amount of uphill riding on the 7 mile ride. I would like to carry less weight, and so I'm considering Bosch fatpacks, which are just under 3 pounds each for 2.2Ah.

From my stats, how many packs would I need?
 
thanks. Mathematically, the 4.4Ah is obviously enough, but I wasn't sure how much of it was usable. Will my amp usage be the same with the Lithium vs SLA?
 
I bet you use slightly less current because I bet the fatpacks don't sag volts as much as the SLA so you'll be more energized, but who knows until you do it. You'll definitely be able to get 4.4ah out of the fatpacks.. it's a fairly conservative rating based on 40.5v charge.. if you take them to 41v or 42v you'll get a little more range at the cost of cycle life, but even at that you'll get 100s of cycles, which is quite a long time if you do like a cycle a day. Not bad for $100.

My commute is 7.5mi and climbs 1,600ft and this morning I used exactly 5ah @ 75v (high 60s under sag). I also use konions like the fatpacks... awesome cell... very tolerant of abuse. :wink:
 
hmm, since my "current" needs are low, perhaps I should sell my expensive 48V ping pack and go for the fatpacks. Sure the power is nicer, but I prefer to travel light.
 
wow, 2 fatpacks in parallel are that strong! Man, I should sell my ping pack asap and go to the fatpacks!

I rode again to work and used 3.526Ah. I probably would use more battery power during the ride, but I am always worried about the climb towards the end of my ride. I don't want the voltage sag to start too soon, or else that climb is going to be more difficult.
 
yoyoman said:
wow, 2 fatpacks in parallel are that strong!
Click to expand...

Believe it... having said that.. they won't last 1,000s of cycles like the ping pack claims to that's for sure, but they're so cheap who cares! :mrgreen:

EDIT: Here's a photo of the single fatpack I was using temporarily to power my 504 motor that you may want to check out. 1,000+ watts output no problem. 80wh so only a few miles, but it was enough to get to town and back at least 2-3 times. :D

http://endless-sphere.com/forums/viewtopic.php?f=6&t=9691#p161424
 
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