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  1. #1
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    Max Lipo cells on EVX2 ??

    I just built a brushed 3903 from scratch with my son. We are using the EVX2 ESC and I have to get some batteries for the truck. I was looking at the EVX2 specs and they indicate 16.8V max and the ability to take 4S Lipo batteries. However, when reading the specs on the Traxxas E-Maxx 3903 page, it says 2S 7.4V Lipos only. Is it because the EVX2 is wired in series (a pair of 2S Lipo packs) rather than parallel (a pair of 4S Lipo packs) or is the wiring of the EVX2 in parallel so that I can use a pair of the 4S to max the voltage and extend the run time? I don't want to fry something and the Traxxas web site is contradicting.

  2. #2
    Marshal ksb51rl's Avatar
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    It is rated for two 2S packs. The series connection is made internally, but the BEC side is not supposed to be able to handle more than a 2S or 7C pack. Two 4S packs in parallel should not be an option.

    How would two 4S packs in parallel increase voltage or run time over two 2S packs in series?
    Alt-248 on the number pad =

  3. #3
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    two 2s LiPo is the max the EVX-2 should be powered with. As ksb51l said, the ESC internally makes the series connection. So you have two 8.4v going in and 16.8v coming out of the ESC.

    Is your EVX-2 the newer version with built in LVD? if not, you'll need to pick up a $2 LVA and use it on the BEC side.

  4. #4
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    I will look at getting two 2S Lipo packs then.

    How would two 4S packs in parallel increase voltage or run time over two 2S packs in series?
    Two 4S packs in parallel wouldn't increase the voltage, but would double the run time. The packs in series would double voltage and do nothing to the run time.

    2 x 2S 7.4V @ 5000mAh in series = 14.8V @ 5000mAh
    2 x 2S 7.4V @ 5000mAh in parallel = 7.4V @ 10000mAh
    2 x 4S 14.8V @ 5000mAh in parallel = 14.8V @ 10000mAh

    I was hoping the ESC was internally wired in parallel so I could use 2 x 4S @ 5000mAh and double my run time while maximizing the ability of the ESC to handle 16.8V.

    Can a person make a parallel wiring adapter (as I have done on my MMM) and use one of the EVX2 ESC battery connectors rather than both (capping one off)? Then I'd still be supplying 14.8V and be able to increase my run time by getting 2 5000mAh packs.

    Is your EVX-2 the newer version with built in LVD?
    Yes. I just purchased it.
    Last edited by mikanda; 02-27-2013 at 11:51 AM.

  5. #5
    RC Turnbuckle Jr. JimmyNeutron's Avatar
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    Capping and connecting a parallel adapter is possible, but the max voltage would be 2S or 7 cells, as stated in post #2.
    Whatever it is I just typed... could be wrong.

  6. #6
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    A pair of 2S Lipo packs it is then. Thanks for the help everyone.

  7. #7
    RC Turnbuckle Jr. JimmyNeutron's Avatar
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    I have seen as high as 9200's... but that was a while ago. SPC does have 8200's that fit.
    Whatever it is I just typed... could be wrong.

  8. #8
    Marshal ksb51rl's Avatar
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    Quote Originally Posted by mikanda View Post
    I will look at getting two 2S Lipo packs then.



    Two 4S packs in parallel wouldn't increase the voltage, but would double the run time. The packs in series would double voltage and do nothing to the run time.

    2 x 2S 7.4V @ 5000mAh in series = 14.8V @ 5000mAh
    2 x 2S 7.4V @ 5000mAh in parallel = 7.4V @ 10000mAh
    2 x 4S 14.8V @ 5000mAh in parallel = 14.8V @ 10000mAh

    I was hoping the ESC was internally wired in parallel so I could use 2 x 4S @ 5000mAh and double my run time while maximizing the ability of the ESC to handle 16.8V.

    Can a person make a parallel wiring adapter (as I have done on my MMM) and use one of the EVX2 ESC battery connectors rather than both (capping one off)? Then I'd still be supplying 14.8V and be able to increase my run time by getting 2 5000mAh packs.



    Yes. I just purchased it.
    The fallacy in your premise is specifying an arbitrary 5000mAH limit. A 2S 10,000mAH pack will be the same size as a 4S 5000mAH pack. In which case, two 4S in parallel is equal to two 2S in series.
    Alt-248 on the number pad =

  9. #9
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    Quote Originally Posted by M n M View Post
    two 2s LiPo is the max the EVX-2 should be powered with. As ksb51l said, the ESC internally makes the series connection. So you have two 8.4v going in and 16.8v coming out of the ESC.

    Is your EVX-2 the newer version with built in LVD? if not, you'll need to pick up a $2 LVA and use it on the BEC side.
    How can u find which side is the BEC side ?

  10. #10
    RC Turnbuckle Jr. JimmyNeutron's Avatar
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    It is usually the side with the red tag.
    To double check, just hook one battery up and try to turn on the ESC. If it lights up for a split second and then powers down, that is the BEC side.
    Whatever it is I just typed... could be wrong.

  11. #11
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    Is it possible to run the truck with 1 battery? I have a 2S Lipo that I connected to one of the battery leads (the one with the red tag) but the truck will not go. The transmitter is bound, the throttle setup has been completed, servos steer, solid green lights all around. When I hit the throttle nothing happens (except the EVX2 light goes out when the throttle is applied). The motors are new and were broken in two days ago. Any suggestions? Do I have to run a pair of packs in this thing?

  12. #12
    RC Turnbuckle Jr. JimmyNeutron's Avatar
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    It is going to run very slow with just one pack...
    You will need to loop the other connector; similar to the one below but with a TRX female.

    Whatever it is I just typed... could be wrong.

  13. #13
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    Quote Originally Posted by ksb51rl View Post
    The fallacy in your premise is specifying an arbitrary 5000mAH limit. A 2S 10,000mAH pack will be the same size as a 4S 5000mAH pack. In which case, two 4S in parallel is equal to two 2S in series.
    That's true, but they only make packs so big. 2x 2S 10000mAh in series is still less that 2x 4S 10000mAh in parallel. All I'm saying is that packs in series increases voltage and in parallel increases capacity. I own 2x 4S and would have rather used them instead of purchasing two new larger capacity 2S Lipos just to get the same end result.

    It is going to run very slow with just one pack...
    You will need to loop the other connector; similar to the one below but with a TRX female.
    Thanks for that. I did some more research last night and figured that out. I made a jumper and it is now working. I'm okay with slow until I can afford another Lipo pack. The operator is 7 years old...
    Last edited by mikanda; 02-28-2013 at 10:38 AM.

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