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C-cells and BOE-Bot — Parallax Forums

C-cells and BOE-Bot

MacGeek117MacGeek117 Posts: 747
edited 2006-01-19 12:31 in General Discussion
How would I mount 4 C-cells instead of AAs on a BOE-Bot?
RoboGeek

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Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-12 17:18
    If the stand-offs are high enough between the chassis and the BOE you could mount a "C" battery holder there.· I have seen people mount 7.2V R/C Battery Packs in there before.

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  • MacGeek117MacGeek117 Posts: 747
    edited 2006-01-13 21:52
    I am trying to think of ways to make the batteries last longer, and I think this is the best way.
    RoboGeek

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    There are·3 kinds of people in the world,

    the dreamers, the do-ers, and the "Oh, what's this button do"-ers.
    Formerly bugg.
    www.parallax.com
    www.goldmine-elec.com
    www.expresspcb.com
    www.startrek.com
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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-01-14 14:19
    RoboGeek,
    Using C cells is a good way because you can easily buy rechargible replacements and they really can add a lot.
    In a pinch, you can get quite a bit more from Alkalines that from Nicads. So the 'C style' provides a flexible choice that other formats will not.

    I have a litium 7.2cell [noparse][[/noparse]which can carry quite a lot of power and recharge quickly], but I bought an extra and overcharged it on my 3rd time.
    Sadly, I wasted about $20USD for so little use. Litium also doesn't like a complete discharge. It is more optimal for electric airplanes where you really need to reduce the weight to power ratio.

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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-14 18:21
    The problem with using rechargeable batteries in standard packages like AA and C are that they don't have the same voltage as their alkaline counterparts so when you replace the alkalines with them you can find yourself browning out earlier since the voltage going into the Stamp Module is already below 5 volts.· If you wanted to use rechargeable batteries you really should have 5 cells just to get back to the 6 volts you should have.

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  • MacGeek117MacGeek117 Posts: 747
    edited 2006-01-15 03:27
    Well, I'm definitely not going to use NiCads, if anything NiMH or Renewal. I am going to use alkalines (Duracell!) because of the higher voltage. i am just doing this for the greater current rating. My BOE-Bot seems to least only about ~1-2 weeks on AAs. Thanks for all the help, guys!
    RoboGeek

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    There are·3 kinds of people in the world,

    the dreamers, the do-ers, and the "Oh, what's this button do"-ers.
    Formerly bugg.
    www.parallax.com
    www.goldmine-elec.com
    www.expresspcb.com
    www.startrek.com


    Post Edited (RoboGeek) : 1/15/2006 3:31:01 AM GMT
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-15 04:38
    Remember, NiMH batteries are 1.2V as well.

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  • bulkheadbulkhead Posts: 405
    edited 2006-01-15 07:56
    1-2 weeks isn't bad for battery life. I would suggest just sticking to alkalines. If you want the same 6V provided by 4 alkalines, you would need 5 rechargeable batteries. Most chargers that charge AA's charge in groups of 4, so the 1 battery in the 4+1 would have to be charged separately (and probably, will perform differently from the other 4, shortening all of their battery lives).

    If you want to spend more, you could get a peak detection charger, and that way, you could charge all 5 cells at once (in series), but that's quite a bit of money just for not having to change batteries every few weeks.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-01-16 08:23
    While the little 9 volt batteries are very convienient for quickie work, they are probably the worst economic value in terms of output per $.

    C and D cells are better values as it really doesn't take much more to manufacture a C or D cell than a AA, but the capacity grows geometrically with the diameter.

    Something about economies of scale.

    I tried to figure out a way around the BasicStamp voltage regulator with NiCads and NiMH, but while four are 'rated at 4.8volts' that can easily go about 6 volts on a full charge. Also, the BasicStamp is programed with its Brownout circuit somewhere around 4.5volts. So you are struggling with too high causing damage and too low quickly shutting down.

    About the only thing that can be done is to accept using the extra battery and go through the regulator. Still, you will easily get double the time or more from the Alkalines. The rechargilbes never last very long. They serve a different user.

    You could add a 5.0 Volt low dropout Switching regulator to get 80-90% efficency rather than 70% efficency from the on-board regulator.

    At some point it is really a question of how hard you can squeeze an orange? And why?

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  • bulkheadbulkhead Posts: 405
    edited 2006-01-17 03:58
    Kramer, actually, four rechargeable batteries will only read around 6 volts on a full charge under NO load. As soon as you start actually drawing power from them, you will see that the voltage of each one will read around 1.15-1.20 volts.

    Using C or D batteries may be a good idea, since they will last much longer, but they are large (I cant imagine a boe bot with 4 D cells).

    The only advantages to using rechargeable batteries are the higher current capacity (you can discharge rechargeables faster than you can discharge alkalines) and the fact that you can recharge them (probably saving money in the long run).

    However, they will probably be more trouble, since you need to find a way to charge 5 or 1+4 at a time. Plus, when they run out, you have to actually recharge them.
  • BeanBean Posts: 8,129
    edited 2006-01-17 11:58
    And don't forget that the BOE-Bot is going to use more power to haul around those larger C or D cells.

    Bean.

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  • GadgetmanGadgetman Posts: 2,436
    edited 2006-01-17 13:11
    Why not add a DC-DC step-up chip in there?

    http://www.maxim-ic.com/PowerSupplies.cfm

    Then you could make do with two AA, C or even D cells.
    (It may be advisable to use NiCad or Ni-mh, though, as you'll be drawing more current from them)



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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-01-18 14:54
    So, you are saying that I am overly cautious about the high voltage of using 4 cells and I can go ahead with an 'unregulated' four pak of NiCad or NiMH batteries?

    Sounds good.

    I am expecting Parallax to come up with a 'low voltage/low power' BasicStamp soon. One that runs on a 3.3volt regulator. Of course, the logic attached to it will have to adapt, but it will greatly stretch those battery powered applications whilst keeping the speed.

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  • GadgetmanGadgetman Posts: 2,436
    edited 2006-01-19 11:02
    My BS1 runs OK from a single CR2032 3V cell.
    (Draws less power than when operating at 5V, too)

    All it takes is to cut a single track...
    No, I'm not saying which one as I don't want to be blamed when some clutz destroys his BS1/2...

    Also, not all BS1's may be able to operate that that voltage.

    Anyway, several Parallax employees have earlier thated that a low-voltage model is NOT being considered. First of all, the demand isn't very large, and second, none of the Appmods would work with it without some sort of interfacing. (Expensive)

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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-01-19 12:31
    That BS1 is a PIC, not an SX-Ubicom. So is the BS2 [noparse][[/noparse]which draws only 2ma]. But the newer and much faster Stamps are running at 75ma and higher.

    There is a big savings in power without any drop off in speed by using 3.3volts as the regulated voltage. Not only is the current consumption less, the total power consumption is less. And, you have less problems with possilbe EMI from the high clocking speed. And, it runs cooler.

    By the way,·someone offered me a Christmas present this year and I asked for a BS2 because it does only draw 2ma. For solar powered devices, it doesn't get much better.

    I still have to check out that 4 pak for safety. It seems that D cells are a bit larger and top heavy, but the C cells are a good weight to power ratio without upseting the Bot.

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    Post Edited (Kramer) : 1/21/2006 5:09:16 PM GMT
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