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Thread: Time limit

  1. #1

    Default Time limit

    This may read out as stupid but if you have a brushed motor with limits at 12 v on a lipo battery. The lvc at 3.5 on 3S which gives you 10.5 and lipo will be 12v, how much time can boat be run before you can safely bring it in? Lipos are fairly new, thanks for your time in answering! Boat is a 27" roundnose, made from a kit I put together ( bought ).

  2. #2

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    There are too many variables to be able to give an accurate answer to that question. The primary one being the capacity of the lipo. We would at least need to know that.
    All you can do is run it for a set time, maybe two minutes if the pack is around the 5000mah size, & then check the voltage/capacity remaining in the pack. If there is still say, 50% left run it for another minute and check it again. Repeat until there is still 20% -25% capacity left in the pack.
    Never run a pack below 20% capacity left or you will damage the packs.
    Here's a chart that will help.
    Lipoly Voltage vs. State of Charge 2S - 6S Packs.JPG

    A cell checker is the best way to monitor your packs after each run.
    Without fail, the first thing I do when I pull a boat from the water is check the battery.
    It will measure pack voltage & capacity, and individual cell voltages & capacities.
    https://www.offshoreelectrics.com/pr...emp-eossentry3

  3. #3

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    Paul, I had typed a whole bunch and errored but to lazy to type it over. The chart told me I have only 84 or so juice to play with and time running won't be much. Thanks for your help.

  4. #4

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    The voltages in that chart are resting voltages, dont forget that in use the load will bring the voltage down below that temporarily, and it will take some time for the pack to recover back to its resting voltage.
    Paul "tug Killer" Upton-Taylor, Cat lover.
    FastElectricBoats.co.uk

  5. #5

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    Paul is absolutely correct.
    If the cells are run down to about 3.5V each under load, the resting voltage will come up to around 3.7V/cell in a few minutes.
    But I don't understand what you mean by you only have 84 to play with. 84 what?
    What size battery do you have?
    A 5000mah on a setup suitable for a 27" hydroplane should run for around 4 minutes. But that will depend on your motor size & kv, & your prop size.
    Tell us your lipo size, motor size & kv rating, & the prop you have.
    It will make it so much easier to answer your original question more accurately.

  6. #6

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    This is the second time I typed a response to tell you everything I did and more. I'm teed off now and lets forget I posted, have a good day! They say I wasn't legal to post but I signed in with name and password and log in and they say i'm illegal. Thanks for your help and will put a outrunner 2836-2700 on 3S in and with such a long flex, i'll drop down to a 632 and my guess of rpm will be around 26000 for me. Again thanks gentlemen! This has happened more times than I like and will cease posting and just read. I've been in this hobby since 95 and love it. Been nice typing with you people!

  7. #7

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    Norwest, it looks to me that a simple question was asked about a number you mentioned such as 84 , yes what is that suppose to represent ? surely i hope you didn,t take any offence about this simple ask. i know its 8.4 volts hey.

  8. #8

    Default

    That sounds like a good setup, you should get somewhere in the region on 4 minutes on a 3s 2200mAh if it is running nice and loose.
    Paul "tug Killer" Upton-Taylor, Cat lover.
    FastElectricBoats.co.uk

  9. #9

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    I have to do some cutting where m/mount is supposed to be by 1 3/4" toward the transom. No wonder my head was screwed on backward. There was no room in the inn for 3S 2200 lipo.

  10. #10

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    Actually i take that back, I missed that it was 27", I was incorrectly assuming from the motor size and cell count that it was closer to the 20" range, I would say it is undersize for a 27". You have more chance with an x435 than an X632, but a 36mm 2000ish KV motor and 4s 5000mAh pack would be more apropriate.
    Paul "tug Killer" Upton-Taylor, Cat lover.
    FastElectricBoats.co.uk

  11. #11

    Default

    Thanks for replying. I worked on the motor mount and moved it more to the transom. I put the 2700 in with 2 3S just to find out the cg and was way off, so your suggestion is most likely in the ball park. I'm giving the neck and back a rest. I have a motor that size and a 2030 too. I'll find out more tomorrow.

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