NZer on hybrid

Fuzzo

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May 19, 2009
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Hi all, I'm a recent pedal-electric convert, looking to do some mods to my bike. The information I've found here already was awesome, so I figured I should say so.

My vehicle is a Dyna - a basic chinese heavy 12V 200W brushed DC commuter using SLAs, but in a mountain bike frame. I'm pretty happy with the power performance, as I need the exercise and I know if I had more grunt I probably wouldn't bother to pedal at all. What I do want is more range, and preferably without increasing the weight - it's already a heavy bike with a heavy guy on it. My goal is the ability to ride it over the Waitakere mountain range to my favourite beach (I'm in Auckland), and back again. I managed to ride to the top of the range a few days ago, but the batteries were pretty much completely flat at the end, so I headed home, both pleased and disappointed at the same time. I need about double the battery life.

I know this means more Wh in my batteries - so I'm experimenting with setting up a NiMH pack. I'll be grateful for any pointers from anyone who has successfully done this, but really I'm just here to say cheers for the information I've already gleaned, and the inspiration provided by the dedicated resident 2 wheeled nuts.
 
Very nice intro, welcome aboard.
We like kiwis.:D

Jump right in, tell us about that plan to ride the range
and get over to that beach so I can live vicariously through
your tales in a part of the world my heart longs to visit.
All the best!
 
Cheers folks, I will put some notes and pics up of what I'm doing. What's the best way? Do I just start a thread and keep posting to that?

A few other chores will be getting in the way, my garage is being converted to an office to make way for a new baby, so I've got a ton of painting to do. But after that, I should have the mean lean workshop I've wanted for years, in which to work on my various projects.

The batteries are being couriered - 32 2.9Ah AA size - I'm figuring this gives me 32 x 2.9ah x 1.2v = 111.36 Wh, which more than doubles my existing 2 x 8ah x 6v = 96 Wh SLAs, and the plan is to wire them in parallel. But I'm nervous because this is mixing and matching battery pack types - SLA + NiMH might not like each other. Perhaps I'd be better off just switching between the packs when one is depleted - tips on how to test the performance will be much appreciated.
 
Nicads in parallel with the SLA's is a good thing, basically because you can reduce the puekert effect (which is basically the more current you demand from an SLA, the lower the capacity - ie. 7ah becomes 5ah at high current draw)

Are the AA's you ordered a high discharge variety? Because if they are only 1C then you can only draw 2.9A out or severly shorten their lifespan. I would recommend Sub's like used in tool batteries.

2 6V 8Ah SLA's is SFA - seriously. At 200W you are drawing ~20A, which derates your battey pack something serious (think 4.5Ah). Replacing the 2 sla's with just Sub C high discharge rate NiMh or NiCd would give you close to triple your range for the same (or less) weight. Replacing them with some serious chemistry batteries (like 14/18V Lithium tool batteries) would make this bike a totally different proposition.
 
Heath, I'm not entirely sure if they're high discharge. They were cheap, so I doubt it. But if I have 7-10 12V packs wired in parallel, each delivering 2.9A, won't that suffice to provide enough total current, without drawing more than the batteries are rated for, in the worst case that they are only 1C? I don't know, this is theory until I try it, unless anyone can enlighten me as to the flaw in that. Or is every cell in the whole array subjected to the same 20A draw? I don't exactly know how it works, it's been 21 years since my electronics classes at school :)

I've only ordered enough for 4 such packs now, so I can test the performance of the batteries before hooking them in.

I'm glad to hear that mixing and matching isn't a disaster, and might actually extend the range of the SLAs. I'm well aware that their total power is pretty weak, I get about 20km without pedaling, and about 30km if I'm giving the kind of output I can deliver all day long (which suggests it's probably about 100-150 Watts). Ultimately if I can build a decent NiMH pack, I'd like to dispense with the SLAs altogether, since they fit into a customized removable battery holder. It would be neat to put the new pack in there, rather than having them dangling from the frame in some kind of bag. Then I can keep adding more packs in parallel (I theorize) as I find them for a decent price, until the box is totally full. Then I might think about a stronger engine - but currently I'm happy with it - it's still meant to be a pushbike, with assistance, rather than a motorbike. The motorbike can come later.

My plan is to do my learning about electric vehicles on the bike first, before I launch into a motorbike or car project. Baby steps. This is NZ - it's not so easy to get hold of parts without selling the farm, so I'm doing my best to learn how to build this stuff. It's more fun too.
 
AA's are usually only good for 1c or so.

If you run several in series (to get 12V - 10 series) and several of these 12V packs in parallel would give you more current capabilities without sacrificing life due to overheating your cells. AA'a do allow you a much greater packing density due to their dimensions.

2900maH AA's are pretty rare, 2500 is about the max the chemistry in this size can do, regardless of the fantasies of marketing departments.

I'm in Aus, so getting bits here is pretty hard as well - you guys at least have scooterparts.nz (who don't like to answer aus email addresses - grr...)
 
Cheers folks, I will put some notes and pics up of what I'm doing. What's the best way? Do I just start a thread and keep posting to that?

Cheers back and yes, most certainly start a thread in electrics (or appropriate forum) that way you can keep adding to it...much better than here in intros.
 
Will do, Happy

Heath, I'm guessing 2900 is a puff too. That configuration was what I had in mind, a bunch of 10-series, all in parallel. The difficult part is how to recharge them. I presume I'm probably going to need a specialized NiMH charger rather than just hoping to use the existing 12V lead acid charger?
 
NiMh is harder to charge, simply because they cannot be charged with a 'dumb' SLA (usually constant voltage charging) -

NiCd can be charged with a constant current charger.

NiMh has to be charged with a delta V charger.
 
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