NZer on hybrid

Discussion in 'Introduce Yourself' started by Fuzzo, May 19, 2009.

  1. Fuzzo

    Fuzzo Member

    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.

  2. Happy Valley

    Happy Valley Active Member

    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!
  3. az cra-z

    az cra-z Guest

    Welcome! Second what Happ said, we want pictures!!
  4. Fuzzo

    Fuzzo Member

    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.
  5. heathyoung

    heathyoung Member

    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.
  6. Fuzzo

    Fuzzo Member

    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.
  7. heathyoung

    heathyoung Member

    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 (who don't like to answer aus email addresses - grr...)
  8. Happy Valley

    Happy Valley Active Member

    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.
  9. Fuzzo

    Fuzzo Member

    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?
  10. heathyoung

    heathyoung Member

    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.
  11. Fuzzo

    Fuzzo Member

    Must get me one? I don't relish the idea of charging up 30 batteries in a standard charger every time I go for a ride.
  12. heathyoung

    heathyoung Member

    No, it isn't practical. To charge large NiMh packs too (especially in a series/parallel configuration) the parallel packs should be charged separatly.

    I know its a PITA but its doable with shottky diodes to isolate the packs - this allows you to plug in chargers for each pack, and charge each pack in isolation, but also allows the packs to combine and - more importantly - not to try and charge weaker packs (cell reversion - death to NiMh). I designed a setup like this that also did LVC on each pack using a Mosfet and a Zener diode.

    Don't get discouraged with this, I know its sounds complex, but its worth it.
  13. duivendyk

    duivendyk Guest

    How the current between two parallel batteries divides depends on their internal resistance.For instane if one has 0.1 Ohm and the other 0,075 Ohm resistance,and the first battery delivered 7.5 A,the other would supply 10A (7.5x0.1=10x0,075),not only that ,the discharge characteristics of leadacid and these other batteries are different also.So it all becomes a chancy proposition IMO.It would make more sense to 'homogulate' the batteries from an operational point of view,that is put a 6V Nicad in series with a 6V SLA and put the 2 12V batteries thus created in parallel.This would work better when using them,but might create problems charging them,unless you come up with some fancy switching arrangement (is doable and a good mental exercise).Hint : you can actually do it with a one double pole double throw switch
    Last edited by a moderator: May 21, 2009
  14. Fuzzo

    Fuzzo Member

    I don't really have a problem charging the SLAs separately to the NiMH. I just don't want to have to charge the NiMH packs separately from each other, if possible. My ultimate aim is to drop the SLAs, and use them for something else. But until I get my desired range, I'm keeping them!

    Heath do you have a diagram of what you did? I'm pretty sure I know what you mean, but then again...
    Last edited: May 21, 2009
  15. duivendyk

    duivendyk Guest

    To seperate the SLA's&NMH's from the composite arrangement SLA+ NMH in series.Imagine 2 parallel strings,each consisting of 2 SLA and 2 NMH batteries in series.At the interconnection point in the middle of each string put a double throw switch that allows you to connect to either the original battery(of the same kind) or to the one of the other kind in the other string,crossing over so to speak.So with a double pole 2 position switch in the middle ,you can either have 2 batteries of the same kind in series,or two of different types.So that is not all that hard to do.I know little about charging NMH or Nicads in parallel strings except that it's not a good idea.
    Last edited by a moderator: May 22, 2009
  16. Fuzzo

    Fuzzo Member

    If I'm understanding you duivendyk, you're suggesting I make the NiMH into 6V packs and string those in parallel to each other and in series to a 6V SLA each. What's the advantage to that over just having 2 12 volt packs, SLA and NiMH in parallel? I can see that it would balance the internal resistance better.

    I have never tried this, but my assumption was that 2 batteries of the same voltage in parallel should end up pretty much balanced in their depletion under load, as the load would draw more from the battery with the higher voltage. Is this not correct?
  17. duivendyk

    duivendyk Guest

    Your assumption is not necessarily true,not if the two battery types have different internal resistances.Do you remember a previous post in which I pointed out that if you put two dissimilar batteries,A and B with the same nominal voltage and the same AH capacity in parallel but which have different internal resistances the current drawn by each divides as follows :
    IaxRa= IbxRb or Ia/Ib= Rb/Ra, so if for instance Rb= 0.8 Ra then Ia= 0.8 Ib,so the B battery with the lower internal resistance gets discharged more quickly.Of course if that battery had a higher AH capacity lets say 25% higher this would havebeen fine&dandy
    The internal resistance of a battery goes up as it discharges in fact that how the battery condition manfests itself,the noload voltage does not change all that much but the voltageunder load plummets.It so happens that Nicads don't show much voltage change under load until almost fully discharged and then collapse (Nmh might be similar)
    So you can appreciate that if you come up with a series combination af A and B batteries you have a composite battery AB if you make another one you have two identical batteries they will share the load equally.Imagine two 6V SLA's in series and two 6V Nicads in series side by side if you cut the connections in the middle and crossconnected such shat the left top SLA is connected to the right bottom Nicad and conversely the right top Nicad is connected to the left bottom have created to identical composite batteries with (pretty much) identical internal resistances,and if you stick a double pole(2circuits) double throw (2 positions) switch in the middle you can switch back&forth between the both configurations.I must admit I'm not an authority on how to play this sort battery game,this seemed to me a way to play it safe.The other possibility would be to use them sequentially.You could ask SAFE, he has been mixing SLa's& Nicads and has a lot of practical experience messing around with batteries.Send him a PM and ask his advice,he seems pretty helpful.
  18. Fuzzo

    Fuzzo Member

    It's worth trying all of that, thanks JJ.

    Would another possibility be to tweak the resistance on the less resistant pack by adding resistors? I guess the aim is to have all of the batteries mostly depleted at the same time, so the bigger Wh pack needs to draw more current. How much more exactly can be both calculated in theory, and measured in practice.
  19. duivendyk

    duivendyk Guest

    That appears rather doubtful I'm afraid.In theory if the capacities were inversely proprtional to the internal resistances they would lose their charge at an equal rate.The discharge characteristics of different types of batteries are not the same and furthermore are also dependent on the discharge rate,nor is that dependency the same to the best of my knowledge.Looks like a can of worms to me.Throwing power away just to equalize relative discharge rates,somehow does not seem appealing.As I pointed out just by flipping that crossover switch you can switch configurations,alternatively you could do the alternating battery routine.You could put a diode in series with each battery (of one kind) to isolate them from one another,if you parallel them,so that they can't crossfeed .The best type would be a power Schottky diode (if such a thing exists),a silicon diode has close to 0.7V drop which is not insignificant ,the Schottky about half that.Again remember I am not the foremost battery expert on this forum probably,and I hate to pontificate about things I don't know a lot about.But you should also be aware there are people who have firmly stated opinions which are not backed up by either knowledge and/or experience, I'm sorry to say.You could start a thread on this subject,it could elicit useful info from members who have real-life experience with inter-mixing battery types.
    Last edited by a moderator: May 26, 2009
  20. Fuzzo

    Fuzzo Member

    Thx JJ. I'll search the site a bit before I charge ahead and start a thread on this. I can't work on it for a while anyway, while I'm still fitting out the garage, so I'm just collecting information and ordering parts at the moment. While I understand the crossover switch idea, I have to say that any arrangement where I can keep the wiring of the SLAs and the NiMHs separate appeals more, as it is likely that I will detach one or other pack at various times, perhaps to leave them somewhere to charge, while I continue to ride on the other pack.