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Thread: Lithium Batteries (And Chargers) for Heavyweights

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    We used a single 6S (22.2V nominal) 8Ah pack in Coyote which was running two 24V, 800W scooter motors, and two electric actuators (I'd add a third actuator and a brushless motor in here too but the chainsaw saw such little use that it's negligible ) and usually only took about 3Ah out of a pack for a full three minute battle. The battery pack itself didn't have a footprint much bigger than a standard TV remote, and a little bit more in height.

    Obviously depends what you're running (Constrictor, right?) but you'll be able to go a lot smaller physically and a bit smaller in terms of Ah and still be more than fine. And prepare to save a ton of weight. We got our pack from Optipower (30% discount for FRA members) but plenty of people have had success with Hobbyking packs, as per both of Chris's links.

    In terms of chargers, I just use the same little chargers that I use for my featherweights but they're a bit weedy for a fast turnaround. Gary (PP3D) and several others use a quad charger (Reaktor I think it was called) from Hobbyking that is beefier with the right power supply behind it and can obviously do up to four packs at once. Not too sure on budgets as I haven't looked at them for a while, but there should be a few options on HK.
    Jamie McHarg
    RogueTwo Robots
    http://www.rogue-two-robots.vze.com

    With great power, comes great reliability.

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    Theo's Avatar
    Roboteer

    By Lithium Ion, do you mean Li-Fe? They have a lower power density and a bit less voltage per cell, and are a bit more expensive (not by much). Their biggest (only) selling point which makes them worth it to me is undoubtedly their safety. LiPos (if protected well enough) can be okay but if one does go wrong, you might get a repeat of Chompalot in a worst case scenario. Li-Fes are safer but not much else.

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    S is the number of cells in a pack. So 6s means there are 6 cells. To work out the fully charged voltage multiply this by 4.2V.

    C is a multiplier that tells you charge and discharge rates. 50C means that the pack can discharge 50 times whatever it's capacity is. So a 4000mAh pack with 50C discharge could in theory give you 200A. Charging is generally in the order of 1 to 3C.

    Jamie is correct that I use a quad reaktor charger. Excellent charger doing everything you would need with lipo batteries. Important thing being to balance charge keeping all the cells the same voltage and if you aren't going to use them for any length of time to put them into storage voltage which is about 60 to 70% capacity from memory.

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    No bother. They are a little more physically delicate than hawkers so a layer of foam packing is recommended but you will be astounded at how much more weight you suddenly have to spare.

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    Quote Originally Posted by Dom View Post
    Thanks Gary! I thought it was something like that.

    Shame they couldn't have used C for cells rather than S ... wtf ?!?!

    Then they could have used D for discharge which would have created plenty of opportunities for innuendo as per ISO standards for all things engineering.
    There is a reason for that (I used to work remotely for Hobbyking in my spare time). In the early days of Lipos you would see batteries that had cells in series AND parallel, as the individual cell sizes just weren't available to make high capacity battery packs. Therefore the cell count was "S" to say that the cells were in series. If the pack was doubled up, say, to increase the capacity, then it would also have a 2P rating. As this can still go on (but doesn't) then the naming nomenclature remains.

    By the way, you could count the number of Lipo factories worldwide on one hand, so your expensive Lipos quite probably have the same cells in as your cheap Turnigy batteries from Hobbyking do. This is one of the reasons why Turnigy batteries perform so well for the price- Hobbyking are absolutely massive and sell millions of them, so can afford to keep their profit margins really low.

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