Kenny'sID said:
I, decided on a 14s/10p pack...it'll fit nicely for both applications/bikes, and it's a little more than the 18AH which someone suggested here/elsewhere?
Question: Can someone please tell me how many AH the mentioned pack will be?
It will be 10 * the Ah of one cell. The "10" comes from the number of cells in parallel (10P). So if your cells were 2100 mah (2.1amp/hours) , you would have a 21 amp/hour pack.
Kenny'sID said:
How many mAh can these vary 100/200? more? Or is that not really a concern if I do the lay them out in a row thing from low to high and keep grabbing one from each end till I have what I need?
The standard is to use all identical cells. I have no idea what the reasonable work-arounds are if you don't do that. I'd think that not having well matched cells is generally considered a "bad thing." But others with more experience can probably give better real world, practical insight into that.
Kenny'sID said:
One more question: On the 36v ebay packs I just mentioned, there is no way to get those to work with a 48v system without tearing into them, nothing feasible anyway? right?
The general advice here seems to be to tear the packs apart and rebuild them to suit. There
are clear advantages to doing that. You can custom shape the battery pack for a better custom fit. You can customize the voltage and capacity. You can create very high voltages and amperage configurations.
But that's not what I did. I'm using a DC-DC boost converter - which is pretty non-standard. Bottom line is that it is working fine for me. I've been commuting 32 miles round trip through a hilly area with a 1000watt direct drive with no problems. I put about 540 miles on my bike in about a month. I use either five or seven packs wired in parallel. When I can stop working 12 hour days in a few weeks, I'll probably reconfigure into two groups of four packs in parallel. Five packs are enough to get me to work and back and then a few miles on one charge. But I've been using seven packs lately to put less strain on the batteries and to have more flexibility to take side trips and/or go faster on some days.
The boost converter hurts efficiency a bit - probably by 5-7%. I run mine set to a 54v output. Its real world power limit (delivered to the controller/motor) set this way is 1175watts (the battery draw peak is about 1250 watts). My 48v 13A controller pulls a maximum peak of 26A. When it pulls more than the converter can deliver, everything shuts down for about five seconds and then power self-restores. That's not good when accelerating through an intersection or beginning a hill climb. I resolved this problem by using my S-LCD3 display to limit the controller to 80% of its maximum output. I no longer get any shut downs from demanding too much power from the converter.
So the converter limits my max power by 20% and I'm losing about 5-7% of my battery capacity. But I like the modular nature of my system. If a pack misbehaves, I can just pull it out and test it (I can plug my 10s charger in and check the pack balance if I wire in a BMS bypass) and replace a pack if it isn't performing properly. On the road, I could just disconnect a failing pack and leave the others connected. As a newbie to ebikes, I've avoided the whole business of designing and welding or soldering packs together (weld or solder? Nickel strips or fuse wire? Make sure strips aren't just nickel plated. Solder or weld? Build a cheap battery welder? Holders or not? If holders, which ones? What about the BMS? It isn't rocket science, but it does take more time and effort than rigging up a wire loom for multiple pre-made packs and mounting a DC boost converter.
I think the DC boost converter is fine for a commuter ebike if the rider likes to pedal along a bit on hills and/or when accelerating from a stop. If you crave more performance, then you'll want more than the 20 amps and 1175 watts that the DC boost converter can deliver. I see there's a 50/30A converter that might deliver 1500 watts (more than my controller should pull). If that device is smaller, it might be better than the converter I'm using. But that converter will deliver about 4 amps more than my controller can handle. My bike will do over 30mph unassisted on the flats. It handles hills with up to about a 10% grade with only mild effort needed from the rider. I'm commuting 16 miles in about 45-50 minutes on the downhill run to work and in about 50 minutes to 55 minutes on the uphill run back home. I could probably go faster, but I've been tending toward conservative use of power.
BTW, perhaps the biggest negative with those 36 volt packs (from alarmhookup on ebay) is that they are based on 2150mah cells. You can get better energy density (size and weight) by using higher capacity cells or using LiPo packs in parallel. I'm intrigued by the 22.2v 10A LiPo packs. My main concern is the lower voltage (44.4v nominal vs. 48v nominal). I'd probably be inclined that direction before I'd build a battery pack myself. The 36v packs are economical, but do add a bit of weight if you want to go relatively long distance. The weight doesn't bother me a lot. After all, I could shed a lot of that weight by running four packs and recharging at work. But with a heavy hub motor, it can add up to be a fair amount of weight.