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Electronic / Battery pack query

(5 posts)
  • Started 12 years ago by Smudge
  • Latest reply from alibali
  • This topic is not resolved

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  1. Smudge
    Member

    Quick question for the electrical experts... OT except that I'll use the info when I get around to wiring up my homebrew deathray LED lights!!

    I'm aiming to replace a knackered ni-cad battery pack in a lightweight hoover (told you it was OT!)
    Currently (geddit) it has four 1.2v 1300mAh sub C cells wired in series.
    Am I better to use 6 x 1.2v 1700mAh Duracell AA nicads from Tesco wired series parallel to give me the required 4.8v and a larger 3400mAh,
    or,
    Should I buy four of the original type from somewhere like here and replicate the original pack ?( http://www.batteriesplus.co.uk/acatalog/1.2V_NiCd_Sub_C_Rechargeable_Tagged_Batteries.html )

    Advice?

    (edited for mong spelling!)

    Posted 12 years ago #

  2. Smudge
    Member

    Forgot to add, the wallwart charger for it pushes out 7.5v and 150mA

    Posted 12 years ago #

  3. Arellcat
    Moderator

    For series-parallel, wouldn't you need 8 cells run 2x4 to provide both the required 4.8V and the desirable doubling of the single cell capacity?

    I can't see how you could achieve it using 6 cells, as you could have either 3.6V and 3400mAh or 2.4V and 5100mAh. Running a 4.8V/1700mAh pack in parallel with a 2.4V/1700mAh pack would actually provide only 2.4V.

    The main problem is ensuring the cell voltages and capacities are as well matched as possible, if you're trying to squeeze every last electron out of the system. Otherwise, going cheaper and worrying less about total pack lifetime is probably the better option.

    When I built a second battery for my old Vistalites, I modified a Vapextech 6V pack that used 4300mAh sub-C cells, and gave me an instant doubling of runtime compared with the original battery. How about one of these, Smudge?

    Posted 12 years ago #

  4. Smudge
    Member

    DOH! I checked what batteries would fit in the compartment (9 x AA's but only the tagged C's) drew myself a little diagram to remind me how it goes, added all the numbers up for eight AA's then wrote 6 in my question (rolls eyes), sorry! You are of course quite correct (blushes)

    I *could* modify a pack like the vapextech one but there's only really space in the battery compartment for four of those cells, my thinking was that using double A's would allow me to buy them over the counter tomorrow rather than having to mail order, and any amp hour increase would be a bonus, of course I have a vague memory that smaller cells don't handle high draw tasks as well, and the charge time should be increased by a factor I can't remember(!) but maybe viable...?

    Posted 12 years ago #

  5. alibali
    Member

    Smudge, It's not usually a good idea to put cells in parallel.

    Also, if your Duracells are "normal" batteries you will need some kind of holder for them since it's not usually possible to solder wires on to cells due to the metal types and the heat involved.

    The tagged cells look the best bet to me.

    BTW, I recommend this site for battery tech. Fill your boots with battery charging, cell connections, strengths and weaknesses of chemistries etc.

    Posted 12 years ago #

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