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batteries with homework board? — Parallax Forums

batteries with homework board?

TutTut89TutTut89 Posts: 10
edited 2006-03-07 23:46 in General Discussion
I know that it is recommended that you do not use anything but a 9v battery with the homework board, but could i use rechargeable AA's instead because 9v batteries are quite expensive. I was thinking about using 2, 3, or maybe 4 rechargeable nimh batteries. Is this a wise thing to do? I am hoping that there wouldn't be a risk of messing up the board.

Comments

  • gibbmangibbman Posts: 98
    edited 2006-03-07 04:01
    You can, I suppose, but it might get a little big for most projects. Since rechargeable batteries (AA) only put out 1.2V each, you would need between 6 and 8 of them to power your board. (7.2 - 9.6 volts). By the time you buy the rechargeables and the charger, if you don't have it, those 9V batteries don't look so bad. They would need to be connected in series, so you would need to arrange for battery holders, either 2 three-packs or four packs, and wire them properly (+ to - between them). But yes, I'm sure it would work. You should also get the ones with the 9V-type connector for the board end.
    Jim

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  • TutTut89TutTut89 Posts: 10
    edited 2006-03-07 04:18
    Don't worry - I have plenty of rechargeables since that is all i like use. So if I were to use 8, which would give out 9.6v, it wouldn't fry the microcontroller? And with the extra power, would i have the possibility of destroying something like a servo that plugs into the Vin? I'm not scared of trying it, I just want to make sure so this venture doesn't cost me more than I planned on spending. (Which is just $4 for a battery holder and snap connector from radioshack)
  • Tom WalkerTom Walker Posts: 509
    edited 2006-03-07 14:45
    Keep the ratings of all of your components in mind. The voltage regulator has to dissipate the "extra" power (above the 5v it is regulating down to) as heat. If you are driving servos off of the Vin line, their life will be significantly shortened (perhaps to seconds) because they are designed to be driven by 7.2 volts. If rechargeables are your choice, I would recommend not going higher than 7.2v (6 cells)...but that's just my opinion [noparse]:)[/noparse]

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    Truly Understand the Fundamentals and the Path will be so much easier...
  • Jeff DegeJeff Dege Posts: 85
    edited 2006-03-07 17:07
    I picked up a used dual bench supply on Ebay.

    At the time, I thought it was something of an extravagence, but I've never regretted it.
  • TutTut89TutTut89 Posts: 10
    edited 2006-03-07 22:50
    So would that mean it be more efficient to use 5 AA's since it would give out 6v and there is less extra power given off as heat?
  • Jeff DegeJeff Dege Posts: 85
    edited 2006-03-07 23:38
    Every voltage regulator has a dropout voltage - a minimum voltage drop across the regulator. For the LM7805, for example, this is 2.0 Volts.

    In other words, a 7805 won't generate 5V output on a 6V input. It needs at least 7V input.
  • TutTut89TutTut89 Posts: 10
    edited 2006-03-07 23:46
    Awesome- thanks for all help everyone!
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