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NiMh or Lithium Polymer ? — Parallax Forums

NiMh or Lithium Polymer ?

ichoelichoel Posts: 17
edited 2010-08-05 01:32 in Robotics
which one do you choose to supply your boe bot? NiMh or Lithium Polymer ? Or does anyone has another option ? Pls, i need recommendation here! I have 3 servos, 1 hm55, 2 ping, 1 lcd, and some IR.

Post Edited By Moderator (Joshua Donelson (Parallax)) : 10/23/2009 4:26:54 AM GMT

Comments

  • WhitWhit Posts: 4,191
    edited 2009-01-28 03:13
    ichoel,

    Putting a subject on your posts will help those who can help respond. The NiMh work well, but you need an extra AA. See the BOE-Boost for an easy way to do this.

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    Whit+


    "We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
  • SRLMSRLM Posts: 5,045
    edited 2009-01-28 03:42
    I'd stay away from the LiPo batteries since nasty things can happen if you drain them too far or overcharge them. I like using the 7.2 v rechargeables from RC car types. You have to come up with a connector though.
  • ichoelichoel Posts: 17
    edited 2009-01-28 22:01
    yeah sorry guys, i just forgot to put the subject. btw, what type of rechargable battery do you mean SLRM ?
  • dandreaedandreae Posts: 1,375
    edited 2009-01-28 22:58
    You can either of two types·with the Boe-Bot Boost.· The Boe-Bot Boost·allows you the ability to add an extra battery.· Most rechargeable batteries are 1.2v which is not enough voltage when it comes to the BASIC Stamp.· Here is a link for more information:

    http://www.parallax.com/Store/Robots/RoboticAccessories/tabid/145/CategoryID/22/List/0/SortField/0/Level/a/ProductID/455/Default.aspx

    Dave





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    Dave Andreae

    Parallax Tech Support·
  • WhitWhit Posts: 4,191
    edited 2009-01-29 00:15
    ichoel said...
    yeah sorry guys, i just forgot to put the subject. btw, what type of rechargable battery do you mean SLRM ?
    Just so you know, since you made the original post you can always go back and edit it to add a subject line.

    Bean (Hitt Consulting)·on the forums also sells a 5 cell AA battery holder on his website. It fits nicely in the BOE-Bot chassis. You can find it here.



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    Whit+


    "We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

    Post Edited (Whit) : 1/29/2009 12:21:11 AM GMT
  • SRLMSRLM Posts: 5,045
    edited 2009-01-29 02:00
    RC hobby shops like 'Hobby People' and 'Hobby Town' among others sell lots of different kinds of battery packs. I got some 3Ah NiMH 7.2 volt batteries for about $30 recently. They're in a single package, not separate like AAs.
  • ichoelichoel Posts: 17
    edited 2009-01-29 03:50
    I wanna know consideration you take choosing the battery, more voltage or more ampere ? Ex : 6 V 2700mAh or 7.2 V 2100 mAh . Which one is gonna last longer ?
  • kwinnkwinn Posts: 8,697
    edited 2009-01-29 04:42
    6V x 2700mAh = 16.2 Watt hours. 7.2V x 2100mAh = 15.12 Watt hours. In theory the 7.2V battery will provide more energy, but there are other considerations. It also depends on the discharge rate and voltages used by the equipment. Adding voltage conversions will reduce the efficiency.
  • daveedavee Posts: 35
    edited 2010-08-03 16:10
    given the same voltage, lith-poly will give you more running time than NiMh, will be lighter (also contributes to longer run) and is more expensive. NiMh usually can support higher amperage loads than liPoly. Both require chargers designed for their use. I recently went through this exercise with a bot I'm building. I settled on NiMh primarily because I wanted hi current drain for te motors.

    As such, the cost was about $340, counting the charger. liPoly would have almost been double that. the 13K battery weighs about the same as a 7ah gel cell but will run almost twice as long.

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    Dave Evartt

    People don't hate computers, they just hate lousy programmers.

    http://wehali.com
  • W9GFOW9GFO Posts: 4,010
    edited 2010-08-03 17:50
    davee said...
    given the same voltage, lith-poly will give you more running time than NiMh

    I'll have to disagree with that. Running time will depend upon the capacity (mah) of the battery, not the chemistry. LiPo's will have a higher energy density than NiMH so for a given physical size the LiPo will have a higher capacity.

    Also, there are LiPo's that are rated for 40c continuous discharge. I don't know of any NiMH that can support that high of a current drain.

    My favorite battery for the Boe-Bot is a six cell RC pack like SRLM describes except I remove one cell to make it a 6 volt pack. Very few servos are intended to be run at more than 6 volts.

    Rich H

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    The Simple Servo Tester, a kit from Gadget Gangster.
  • Spiral_72Spiral_72 Posts: 791
    edited 2010-08-03 21:00
    My two cents:

    For what you are doing, weight really isn't an issue. I'd use a NiMh pack no question. LiPo packs require too much care in dealing with them. Shorts often fry the pack, you have to be concerned with cell balancing so to not over-discharge one cell, cost more....Naaaaah. For energy density, LiPo's are the trick, but NiMh are pretty forgiving to abuse. You can get some pretty small 2500mA NiMh packs if you need that much. 1500mA packs are a dime a dozen, and quite small!

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  • John AbshierJohn Abshier Posts: 1,116
    edited 2010-08-03 22:13
    Jameco has a charger and batteries that provide 1.6 volts each. Haven't tried them.

    http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2115821_-1

    John Abshier
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-08-05 01:32
    NiMh all the way . there way more forgiving .

    I have used TONs of the Duracell 2650mAH AA cells for robots Ham radio stuff and the like . not a single failure yet .

    Peter KG6LSE

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