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  1. #1
    RC Enthusiast
    Join Date
    Jan 2012
    Sedalia, Mo.

    New Batteries.... Wanna do it right!!

    OKAY, I just unpack the batteries from a couple of Christmas presents... I have (2) Traxxas 7cell 3000Mah batteries and want to make sure I charge them correctly as to get the BEST preformance expected from NiMH batteries.... I have a few questions

    1. the manual with my ONYX 245 says this size battery should be charge at 5.0v.... everything I have read elsewhere (here for example) says 3.0v i.e. MAH / 1000 = Charge voltage who is right??

    2. is there a break-in or setup period for these batteries..... whats the correct charge/discharge pattern if one is necessary? AND if not running the vehicle how can I discharge them if needed?? My charger doesn't have discharging feature...

    3. Can I charge today(Thursday) and use say (Saturday or Sunday).... whats up with storing them... charged/discharged...etc.

    Sorry for the NOBO questions just trying to learn it right the first time.... Hoping to charge the packs and maybe reinstall them before wrapping to open during our Christmas celebration on Saturday... if not no big deal...just wanted them RTR when opened.....
    Last edited by T.ScottSmith; 12-19-2013 at 02:28 AM.
    I Just got my 1st Traxxas Slash VXL 4X4!!!

  2. #2
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
    Join Date
    Oct 2009
    Alma, MI
    1) It seems you have voltage and amperage mixed up. 7 cell packs should be charged at 7 cell voltage. The amperage is mAh based... and NiMH max out at 1C which would be mAh/1,000. If you want longer pack life charger it at half of that.

    2) The way I treated my NiMH is to fully charge, and then fully discharge-- almost. You do not want to deplete the pack until it cannot move the RC, but stop using it when it starts to be noticeably slower. I also store my NiMH fully charged and in a cold environment. Breaking in a pack can be done in the RC... just go really slow and make no sudden movements for the first few cycles. If you want to discharge it out of the RC, you can hook up automotive light bulbs to it or build a discharger like this.

    3) Part of this is answered in #2. You can charge up and then use it a few days later, but I would top it off first.
    Whatever it is I just said... I could be wrong.

  3. #3
    RC Racer
    Join Date
    Aug 2013
    1. For your 3000 mAh NiMH: charge at 3.0A. It can be charged at a little higher rate up to 3.6A if you really need it to charge in a shorter time, but this risks overheating the battery and causing more venting which would shorten battery life. If you want the batteries to last longer, then charge at a lower rate, typically 1.5A (half normal charge rate). In general, it is best to stick to the battery manufacturers instructions rather than the generic recommendations provided in your charger manual (which makes 1 recommendation at charging at 1.2C, then in a later chart says charger your 3000-5000mAh batteries at 5A (faulty instructions in my opinion))

    2. It may take up to 5 charge-discharge cycles for the batteries (and new motor) to get broken in. Basically try to make the 1s 5 runs gentle runs -- avoid straining the systems with many rapid accelerations from stop and many rapid decellerations (braking) from high speed. The rapid accelerations draw more current from the battery (burst current) then running at a constant steady throttle (average current). After the break in period, then have it all you want.

    Batteries also get more strain when trying to provide current when the battery is starting to get depleted at <40% capacity (which basically means they are getting to nominal voltage so don't run until the battery is drained during the break in period. Stop when the truck starts to slow down and the lights start to go out when you accelerate. When you charge your 8.4v 7 cell battery to peak it will have around 9.8v (1.4 v/cell) when you get to about 40% capacity, you'll be a little above nominal voltage of 8.4v. Stop, let the battery cool, then recharge to full, then put the battery into storage.

    3. I store all my NiMH at full charge. All NiMH will lose voltage every day, even when not used sitting on a shelf. It is most important not to let the batteries discharge to empty while in storage. After a couple weeks, NiMH battery voltage may be down, but still usable. If below nominal voltage, charge to full before use. If above nominal voltage, then I just run until down to nominal, stop, let it cool, then charge to full. If I haven't used the NiMH in a month, I'll check to see where the voltage is and top it off before it gets down to nominal.

    NiMH will usually stay at ambient temperature during the bulk of the charging cycle, but once it gets to near full (last 2 minutes of charging) it will start to warm up. I will usually stop the charging manually at that point to avoid the heating phase (which basically means the NiMH is gonna vent internal gases which basically means its losing part of its chemistry which will eventually shorten battery life).

    A good learning resource is battery university

  4. #4
    RC Qualifier
    Join Date
    May 2013
    Hey Dementor I been reading about Nimh on the site (should learn more about them) After reading this I have one concern about not letting to discharge empty when not in use. I three 7 cells 3000mah batteries and the last time I used 2 of them was maybe last November, the third one I think in August.

    So what you are saying is this will shorten the battery life as well?
    Did you say Traxxas?

    Yes with or without lipos.

  5. #5
    RC Racer
    Join Date
    Aug 2013
    Overdischarging any battery (NiMH or LiPo or Li-Ion) is bad for the battery and wills shorten its life. The lowest safe discharge level is arround 1v/cell. NiMH will progressively lose charge over time. If you store it at discharge level, it may eventually fall below 1v/cell after a month or two. If you store it fully charged, it may maintain the charge above 1v/cell for a couple months.

    Bottom line is with any rechargeable battery, check it every 1-2 months to make sure it still has at least nominal voltage. Top off NiMH, Recharge LiPos back to storage voltage levels of around 3.85 v/cell.

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