EVBiker2000 said:
Well, I know it sounds irrational....but I'm really serious....I really don't want to be constantly tearing apart my battery packs every other week. LIPO has too many headaches for a technology that only lasts for 300 charges. It's not that I'm not a tech nut or a garage hacker...I love that. But I like to fully understand what I'm working on...don't like this "black magic" aspect of LIPOs.
Well, LiPo is a relatively cheap way to get high-C-rate batteries for ebikes. If you really want to know all about them and understand them, there is probably enough information here on ES to overload most people (including me) if gone thru too quickly. :lol:
Right now it's kind of scattered, but there are people working on gathering up that info and condensing it into technical and FAQ threads in the various sections of ES, to help cases like this.
"Irrational" or not, it is your own decision to make; I think that we all just want to be sure you're making an informed one.
If you do decide to get rid of the LiPo, I definitely could use it (and could almost afford it at your offered price :lol: ).
I'd actually go for a homemade battery. Say 1.2V NiMH AA batteries configured in a series parallel combo. At least if I constructed it I would fully understand all it's limitations.
Although those limitations are fairly severe, unfortunately. Just about all NiMH cells I've used new or otherwise are over-rated by their manufacturers, especially if they end up in high-C rate applications like ebikes. The AA cells are some of the worst in that respect, though C and D are bad enough.
I've been using D and F cell NiMH, and it can barely run my bikes, with a 48V (sometimes 60V) 13Ah pack, or a 36V 9Ah pack. Even given that these packs are well-used and abused, even a bit damaged, they do pretty well, but for my very heavy cargo bikes (DayGlo Avenger and CrazyBike2) they have a hard time putting out the current (at least 2C) without major voltage sag while I'm trying to accelerate into or out of traffic, even with me pedalling hard to help.
With my basic commuter The Velcro Eclipse, the little 36V 9Ah pack just about works ok, but has short range because of the hefty current draw on acceleration if i don't pedal (whcih I prefer not to as my knees are bad).
I'm sure they'd perform a bit better with undamaged new packs, but even then I'd really need to parallel them (which makes things complicated) for better C-rate.
I also have some sub-C cells from powerchair packs, which are significantly better for high-discharge apps than AA cells, and they can't do it on the cargo bikes. Maybe on The Velcro Eclipse they could; haven't tried that. But without heavy pedalling they can't even start up CrazyBike2's old brushed powerchair motor thru-the-gears setup from a stop (though they work once I get going) (haven't tried the hubmotor yet, but expect it to be worse).
I have a bunch more sub-C Dewalt packs I have yet to take apart to salvage the good cells from (NiCD instead of NiMH IIRC). They might fare better than the powerchair packs, if there are enough of them still good.
Also, NiMH can be charged in series as long as you control the current.
Yes, but it can't (safely) be charged in parallel, so if you use series/parallel strings, you have to remember to unparallel them before charging.
I've charged NiMH packs with as little as just an adjustable-current-limit lab power supply, so it *can* be simple.
However, LiPo can be charged the same way, as long as (like NiMH or anything else) you don't set the power supply for any higher than the max normally-charged voltage per-cell times the number of series cells. You just dont' get the balancing act during charge that way. But if you don't discharge the cells too far each time, then recharging them this way works fine and unless there's a bad cell or they're really inconsistent among the cells in the pack, they probably won't get out of balance for some time, if at all.
Something like this....place 6 NiMH AA's inline in 1/2 in PVC (or maybe copper because of heat).
You'd want to use metal if you intend to balance charge them (which creates the heat). If you don't do the balance charging, and arent' using them at high C-rates, you could get by with the plastic, but I'd still stick a thermal sensor or Klixon thermal breaker inside there with them, if you go with plastic, in case something goes wrong.
The catch with metal is that vibration will eventually rub off the outer paper or plastic labelling of the cells, and once it happens to two of them then they'll short thru the case, albeit probably intermittently. As that happens, they'll essentially short-circuit across however many cells apart they are. If they're sequential, just one of them. If they're end cells, then five of them.
You'll get wierd behavior of the pack, and have to take it apart to troubleshoot.
I know this happens because I have a Stanley LED flashlight with aluminum tripod legs that hold the batteries, and I use AA NiMH in there. Eventually the thin plastic wore out on them, from vibration just being carried around on the bike occasionally. Killed one cell totally, overheated it till it leaked.
Had to take the leg apart to push it out with a tool from the other end, as it had swollen and could not be tapped out like usual.
Add some spring type connectors on the ends, and so you then have a 7.2V 2.3 AHr battery that can be charged without disassembly and no need for balance connectors.
Keep in mind that it won't be a 2.3Ah stick at the C-rates you'll be using them at, most likely. Unless you parallel a LOT of them, my guess is you will not even get a third of that. Even in that 20lumen LED flashlight, I don't get the rated Ah of the cells (some 2Ah, some 2.3Ah), perhaps half to three quarters of that. (calculated based on the draw from the LED, rather than directly measured by a wattmeter).
Also be careful which springs you use. If steel, they'll add resistance to the pack circuit, and cause heat at higher current draws. Maybe not a lot, but it still wastes power. Plus be careful of the springs de-springing
so that they no longer fully compress the stick of cells together, and then you get intermittent disconnects on some sticks during vibration or bumps, causing higher draws on other sticks in parallel with them. There is a thread on how to make a solderless battery pack using various types of springs and boxes and whatnot, somewhere here on ES. I can't remember for sure, but I think the member that wrote it starts with an "L".
It's got a lot of useful info that relates to this type of setup.
