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  1. #1
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    Question Slash 4x4 LiPO C-Rating

    I am a new to Electric RC and just got a Slash 4x4 RTR to bash. I wanting to use LiPO's and I am having trouble understanding what specs I should look for.

    C rating this refers to a lipos maximum discharge rating, and is a multiple of its capacity. For example: A 20c 5000mah pack can put out 100amps. Choosing the right capacity and C rating is important and should be based on how many amps your motor can draw at maximum load. The Velineon® 3500 Brushless Motors draw 320amps at peak current levels. So, I should select a battery that can supply at least 300amps continuous? Generally though, the motors pull a continuous current of about 10-20amps or thereabouts.

    I plan on using at a min 5000mah packs. Based on the formula above I need a 50C or 60C rated packs (expensive).

    Do you really need that high C-rating?

    7.4v or 11.1v LiPO's?

    What are the good LiPO brands?

    What are the LiPO brands to stay away from?

    Thanks in advance for your help!
    Last edited by Radman; 02-03-2010 at 05:50 PM.

  2. #2
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    Anything over 25 c is overhead and wasted on the velinion system.

    A 5000 mah 2s 7.4 lipo will power you for around 30 minutes and will charge in under an hour. I recently bought one of these tenergy hardpacks Just 50 bucks. Seems to be a quality battery. You can spend anywhere from 29.95 to over 100 bucks on a simalarly sized battery. If you decide to buy from the site I linked do a google search for all-battery coupons. I got free shipping.

    The 3s 11.1 batteries IMO are a little too much for this vehicle and are reserved for special applications like monster trucks, high speed runs and guys that can never have too much juice.

    While the velinion system and the drivetrain are designed to handle this setup running anything at it's maximum capacity shortens it's useful lifespan.

    Hope this answers your question.
    Last edited by PanicRev; 02-03-2010 at 06:09 PM.

  3. #3
    RC Turnbuckle Jr. asheck's Avatar
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    In reality, a battery accurately rated at 50 amps will be capable of running the VXL. But IMO you want a 80amp rating, so at least a 4000 mah 20c.
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  4. #4
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    bought an ebay 4000mah 11.1 15c battery and it flat won't work. Initally takes off then lvc kicks in. This is with a 70 deg room temp battery too.

  5. #5
    RC Turnbuckle Jr.
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    Quote Originally Posted by caseymou
    bought an ebay 4000mah 11.1 15c battery and it flat won't work. Initally takes off then lvc kicks in. This is with a 70 deg room temp battery too.
    That is odd. I have run my Slash 4x4 for 10 minutes on a 2800, 20C 2s pack before the LVC kicked in.

  6. #6
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    Ive run about 10ish mins on a 20c 3200mah. That was before I just bought all new batts though. I added 2X 20c 5000 1X 25c 5200 and 1x 20c 4800 to the arsenal. Truck runs great on all of them, but I think the 4800 may be a bit tired.
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  7. #7
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    I agree. Might be a bad pack too. Currently Slash is my only electric I can test it on. Voltage seems good when checking. I'll probably try to cycle batt next.

  8. #8
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    Quote Originally Posted by caseymou
    bought an ebay 4000mah 11.1 15c battery and it flat won't work. Initally takes off then lvc kicks in. This is with a 70 deg room temp battery too.
    I bet its an early LVC problem, unless you have other lipo packs that work great

  9. #9
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    Understanding LiPos
    Lipo batteries are very different from previous generation batteries and understanding how they work, and especially how to charge them, is the key to getting the best performance.

    Series
    Individual Lithium Polymer cells have a nominal voltage of 3.7 volts (vs. 1.2volts per cell for Ni-Cds). Cells are wired in series to give the following pack voltages:

    1 cell = 3.7 volts
    2 cells in series = 7.4 volts
    3 cells in series = 11.1 volts

    Parallel
    Unlike Ni-Cd and Ni-MH cells that self-discharge when wired in parallel, LiPo cells can be hooked up, charged and discharged in parallel with no detrimental effect. Wiring two LiPo cells in parallel doubles the capacity (more run time), plus an important advantage of wiring in parallel is that each cell only sees half the total current.

    3S 2P
    A battery pack that has three cells in series (giving 11.1 volts) and 2 of these 3-cell packs are wired in parallel is commonly referred to as a 3S, 2P (3 series, 2 parallel).

    C Rating
    LiPo cells are also commonly given a C or current rating. This is the maximum average recommended discharge current for the cell. For example, the Thunder Power 1900mAh packs have a 6C rating. To determine the maximum recommended discharge rate multiply the capacity times the C rating. 1900mAh x 6C = 11,400. So the maximum recommended discharge rate would be 11,400mA or 11.4 amps. If your application has a higher amp draw, remember that LiPo cells can be wired in parallel, and with 2 cells in parallel each cell sees half the total current. With 3 cells in parallel, each cell see one third the current.

    By wiring packs in a combination of series to get the voltage and parallel to achieve the capacity and individual cell current to an acceptable level, LiPo cells can be used to power nearly every type and size of model.

    Charging
    Charging LiPo batteries requires a very different charge method than other types of cells. It's imperative to use a charger designed specifically for LiPo batteries, and with most LiPo-specific chargers it's necessary to correctly select the cell count (1, 2 or 3 cells) manually. Fortunately, several good chargers are available through FMA. Astro Flight, plus many other companies including E-Flite and Thunder Power, will be releasing inexpensive LiPo-specific chargers within the upcoming months. These chargers give a constant current charge rate at 75% the cell capacity until the pack voltage reaches 3.6 volts per cell. This charges the pack to about 80% of total capacity. At this point the charger switches to a constant voltage charge rate of 3.6 volts per cell to top off the battery. To charge a fully depleted pack typically takes about one and a half hours.

    Serious Safety Issues
    If LiPo batteries are improperly charged they can cause an explosive fireball. Our staff recently tested the effect of improperly charging LiPo cells and the results were dramatic! We cannot over-emphasize the importance of using a charger specifically designed to charge LiPo batteries, and to be positive that the manual cell count (if the charger has one) is correctly set for the specific battery being charged. If you use a good quality LiPo charger, these batteries are totally safe.

    LiPo Do's and Don'ts
    Do: Only use a charger that is specifically designed to charge LiPo batteries. Using other types of chargers can cause an extreme fire hazard!


    Do: LiPos don't develop memory or voltage depression characteristics like Ni-Cds. Do charge them without the worry of cycling or discharging them.


    Do: Store LiPos at least partially charged. LiPos will maintain their performance levels over time, even during non-use, much better than Ni-Cds and there's no need to cycle them.


    Don't: Use any type of charger that is not specifically designed to charge LiPo batteries. Using non-LiPo-specific chargers can cause an extreme fire hazard!


    Don't: Fully discharge your LiPo battery pack. Most speed controller have a voltage cut off that will prevent over-discharging the battery. Discharging a LiPo beyond it's critical minimum voltage will cause damage to the battery.


    Don't: If you have a crash and the battery is damaged, don't put the battery in your car or house immediately after a crash. It's possible that a chemical reaction can take place in the damaged battery that could cause a fire. Put the battery in a safe place for a least one hour.
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  10. #10
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    Thanks for the info.

    What pinion and spur gear do you use for 7.4V LiPo's

  11. #11
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    pretty much the same as you would use for a 7.2V
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  12. #12
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    nimh in parallel!

    maxson??

    Parallel
    Unlike Ni-Cd and Ni-MH cells that self-discharge when wired in parallel, LiPo cells can be hooked up, charged and discharged in parallel with no detrimental effect. Wiring two LiPo cells in parallel doubles the capacity (more run time), plus an important advantage of wiring in parallel is that each cell only sees half the total current.

    Does this mean that my god sons minirevo can use nimh batteries in parallel?
    Would you be so kind and elaborate?

    Cheers

    Jussi

  13. #13
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    JHAAS, You are right about the lipo batteries being run in parrallel. NI-MH batteries can be ran in parrellel or series. Parrallel, it would give you more run time, so 2 2500 mah nimh batteries will essencially give you 5000mah of run time. 2 2500mah nimh ran is series will give you 14.8 volts. So if your god son wants to go faster run them in series, if he wants to get longer run times then run them in parrellel.

  14. #14
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    Does this mean that my god sons minirevo can use nimh batteries in parallel?
    Would you be so kind and elaborate?


    Last edited by radicalray; 02-04-2010 at 12:40 AM.

  15. #15
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    What pinion and spur gear do you use for 7.4V LiPo's
    Stock gearing is fine for bashing and most tracks.

  16. #16
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    i got a shippement from HK today (some heli stuff including some ***** 2200mah 15c 3s lipo's that way barely anything...if i ran em in parallel i could get 66amps out of em for 4400mah at 157grams each so 314 total....or run my 30c 5kmah 3s at 394 grams.....but i wonder if everything would hold up or not
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