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  1. #1
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    Radio battery mod

    if you're still buying 8 batteries almost every time you wanna run your car, then read this

    you probably saw people put lipos or nimh batteries instead, but that's not really good idea. here's why:

    li-po - they have less capacity compared to li-ion. but they have a higher C-rating. so it's good for your car's motor but it's senseless for your radio. and you have to use something to not let it overdischarge.

    nimh - beside that it's something vintage it's still pretty expensive because you still have to buy 8 of them. and the recharging time is not good compared to li-ion or li-pol

    here's what i did:
    i took 3 14500 (AA) 3.7v 900mah li-ion batteries with protection and a charger

    look:

    needless to explain anything.
    it's really simple and easy to do by anyone. no soldering is needed.

    it worked fine and i wasn't afraid of overdischarge because this batteries have a PCB.
    but every time before going out, i was have to check the batteries and recharge them if needed.
    I should had to do something with this

    now i decided to use 4 batteries (same as before)

    circuit:


    have no time to make it pretty

    it should just work after all, no one will see what's inside

    in typical application lm3914 measure voltage from 0 to 1.25v
    it took some time to make it measure 13v to 16.5v that i was needed.

    i took 4 full and 4 empty batteries and a lot of resistors
    My mini E-Revo.net and the BIG ERevo.net

  2. #2
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    finally it works fine:


    and finally:

    can't make a good photo, but it shines really cool bright red
    i also have a green bar - maybe for the next 2.4ghz radio

    now i easily see when it's time to recharge
    My mini E-Revo.net and the BIG ERevo.net

  3. #3
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    Nice mod .... especially the pack gauge on the top!!

    Why not just purchase a 1600 mAh LiFe transmitter pack? http://www.amainhobbies.com/product_...=Product-Feeds

  4. #4
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    the price is significantly higher
    and also:
    1) You will need a LiFe specific charger to charge the pack (NiMH, NiCD or Li-Poly only chargers WILL NOT WORK!)
    2) You must not discharge the LiFe battery pack below 3.26V per cell during the break in period or below 2.5V per cell after break in.
    so + you'll need to buy a charger at least
    will it worth it? :-\
    My mini E-Revo.net and the BIG ERevo.net

  5. #5
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    I'm just using rechargeable Eneloops in my Tx and I recharge through the charge plug already built into the Tx with a wall-wort charger. The Eneloops are low discharge AAs.

    I understand the $$$. Like I said ... nice mod. It's good to see someone getting into electronics!!

    Bob
    Retired Electrical Engineer

  6. #6
    RC Turnbuckle Jr. danielhr77's Avatar
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    Nice mod!!! I like the LED bargraph on the top... I might do it too...

    Quote Originally Posted by Evgen
    li-po - they have less capacity compared to li-ion. but they have a higher C-rating. so it's good for your car's motor but it's senseless for your radio. and you have to use something to not let it overdischarge.
    Well, actually, you already saw my LiPo mod thread... The LiPo I'm using has 1450mAh compared to the 900mAh of your LiOns; and the C-rating is only 1C, perfectly designed for this application... Also, the 1 LiPo is cheaper than 3 LiOns...

    He Who Dies With the Most Toys Wins.

  7. #7
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    yes, your mod is pretty good too, but that batt have more mah because it's much bigger (almost all the space in the bottom) than 3 my and it has no protection. i can put 2x4 and get 1800mah (and it's a 4s, not 3s )

    anyway, the idea of the first mod is to be easy - simply put standart AA size li-ion on it's place and put one wire.

    the second mod is not as easy, but really usefull.
    My mini E-Revo.net and the BIG ERevo.net

  8. #8
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    Wow, that is a great mod you have done there, especially the battery meter.

    By the way, if you were to charge those 14500 batteries with your RC lipo charger(s), what is the maximum *C charge rating can it be charged at? also a recommended C charge rate?

    I've got one of those chargers for my 18650 but it can only do like 450mA. It's sloooow~

  9. #9
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    i don't know, i just use two of this chargers
    14500 charges to full in a hour
    18650 is almost 3-times bigger so with same charging current it should take at least twice longer i guess :-\
    Last edited by Evgen; 03-07-2010 at 03:13 AM.
    My mini E-Revo.net and the BIG ERevo.net

  10. #10
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    Evgen:

    Important question...

    What is the maximum voltage these TQ3 radios can handle? I noticed that your full red bar charge was like 16.35v ?

    Do you know if one of those new 2.4GHz Link radios can handle 2S LiPo? There aren't any small size LiFePO4 to make a 6.6v.

    I hope you get yourself a one of those latest 2.4GHz LINK radios and mod it

  11. #11
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    i don't know about maximum, but there's voltage stabilization at around 9v as i remember. so 10-20v input voltage should not hurt it.
    i have no any 2.4ghz model yet. but since it requires only 4-batteries 2s should work just fine
    i'm tracking ebay for a nice price for a new black 3ch model. and once i get it, i'll mod it too of course

    here's 14500 (AA-size) LiFePO4 450mAh
    but it actually: " Item is temporarily sold out."
    My mini E-Revo.net and the BIG ERevo.net

  12. #12
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    I know you've said you don't have any Traxxas 2.4GHz radio system yet but I am wondering if you have plans to purchase one soon?
    going for the 2.4GHz Link on eBay seems to be around $60 range.

    Anyways, I would really like to see your LiPo battery mod work on Link 2.4GHz Traxxas radio.

    Hope to see your thread about it soon!

  13. #13
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    What did i cost to do this mod? And where did you get all the parts. Do you have a parts list on hand. I would like to try this mod for myself. Thanks

  14. #14
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    which mod? the battery or indicator?
    links to batteries and charger is in my first post.
    LM3914 and led bar i've got from local shop (7806 and bunch of resistors i had have before) 7806 can be replaced to 7805 (or LM1084-5.0 but pins order is different)
    you can also find them on ebay:
    7806 or LM1084
    LM3914
    led

    but if you'll use this indicator on different batteries with different voltage, then you'll have to tune it by resistors yourself
    Last edited by Evgen; 04-08-2010 at 11:36 PM.
    My mini E-Revo.net and the BIG ERevo.net

  15. #15
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    by the way, i've made some changes.
    added 3s2p battery pack for approx 1800mAh total capacity

    two diodes is for battery packs do not charge each other all the time
    and the led bar graph is also corrected for the new voltages (now it's approx 9.6v to 12.6v)
    My mini E-Revo.net and the BIG ERevo.net

  16. #16
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    Thanks very much for the reply. If i have any more questions i will be sure to contact you. I think i am going to do just the wire mod right now and try to get the led bar graph going a little later.
    Thanks

  17. #17
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    I can see the mushroom cloud from here! I'll just keep feeding it double AA's!!!
    I drive my jato with my eyes closed!!!!!

  18. #18
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    some video of this led bar in action
    http://www.youtube.com/watch?v=G28EuD5VVO4
    My mini E-Revo.net and the BIG ERevo.net

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