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Thread: Fuse Selection Advice

  1. #1
    James Williams's Avatar
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    James Williams
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    I've been looking into using Lipo batteries for Neophyte & have encountered a problem trying to find a suitable fuse.

    The battery I'm looking at getting is a Turnigy 5000mAh 5S 30C at 18.5v. As of right now the total stall current for my drive & weapon motors is 129.2A. (2x 18v drill motors @ 62A + actuator @ 5.2A).

    From my understanding having read what people have said on here the fuse needs to be slightly higher than the max draw of the machine but below the max burst current of the battery, which I've calculated as 150A. I've tried looking online for 130A fuses but the only ones I can find are either rated at much higher voltages (such as a 130A/80V one I found on Farnell), or ones with very limited information (such as on ASAP electrical).https://www.asap-supplies.com/anl-fuse-714434

    If anyone has any ideas where I could get a suitable fuse or if I'm making a mistake somewhere I would appreciate it.

  2. #2
    Redirect Left's Avatar
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    Adam
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    The maximum continuous current that battery can draw is 150A, I can confirm that (5.0Ah x 30C) - the burst is higher than this, but must be in short periods of time (usually no more than 15 to 60 seconds, depending on battery). Refer to manual or page you bought it from, for details of the burst.

    For the Team Death heavyweight, we're using strip fuses & mega fuses (the same as these but bigger, and supporting up to a lot more amps (these things ; https://www.ebay.co.uk/itm/191925440181 - ebay for 'strip fuse' or 'midi / mega fuse' and you'll find them - commonly used in vehicles so they're closer to the voltages we use in bots)
    We're also using several fuses. Each motor has its own fuse (so they can't blow themselves), and there is a master fuse of 200A (on a battery with 202.5A max draw) which if blown will kill the entire bot. As long as you have a master fuse of the correct rating you should be fine, but if you want extra peace of mind, you can fuse motors individually as we're doing. We have 60A fuses for each motor.

    eBay is often your best friend, as you can find some deals on there that are good, and more tailered to your exact needs. If you need it, someone is probably selling it on there - often at cheaper prices than a hardware shop.
    Last edited by Redirect Left; 20th May 2018 at 18:44.

  3. #3
    James Williams's Avatar
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    James Williams
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    Thanks Adam for replying. Are you sure about the current? Unless I'm misunderstanding something it seems to contradict what it says in the build rules.

    7.8.3 FusingA fuse rated below the maximum burst discharge of the battery MUST be fitted. The maximum burstdischarge current is calculated by multiplying the C rating by the capacity. E.g. 25C 2200mAh = 55 Amp

  4. #4
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    Paul Withers
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    There are two 'C' ratings of lipo batteries. There is a constant discharge and a peak (or burst) discharge.
    For example, this 5000mAh, 5S battery has a Constant Discharge of 30C and a peak discharge of 40C for 10 seconds. Therefore, the maximum constant current is 150A (30C x 5Ah) and the maximum burst current is 200A (40C x 5Ah).

  5. #5
    James Williams's Avatar
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    Ah, thanks for clearing that up Paul.

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