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What is a “250 watt continuous” motor? (DC variable speed)

Discussion in 'Electrics UK' started by ericmark, 2 Sep 2021.

  1. ericmark

    ericmark

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    I have an electric bike, the question is if it's an e-bike? The hub is marked 350 watt, however it seems most hubs can give over 250 watt, it is the continuous which matters, I know on steep hills it trips out, I assume on over heat, which to me means it can't deliver 350 watt on a continuous basis.

    Reading reports it seems most hubs can produce over 250 watt, what is important is the continuous which clearly since battery powered can never be continuous, but the question is how long is continuous?

    My wife's e-bike will with a 250 watt rated mid mounted i.e. through the gears climb steeper hills than my 350 watt bike will climb, I have learnt I need to stop at the cemetery and wait a few minutes before trying to ascend the last 50 yards to my home, or it will trip out, however my wife can simply go for it and get home, so she seems to have more power than me.

    So does it matter if the hub is marked 350 watt, when one knows it can't give that power continuously?

    OK I can travel 16 miles to Welshpool and back without any real problem except for final 300 yards, but fact wife's can do last 300 yards and mine can't without a rest to me means it has less power.
     
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  3. RandomGrinch

    RandomGrinch

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    Could it be the battery over heating and entering a protected mode rather than the motor?
     
  4. ericmark

    ericmark

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    Not a clue, but if I wait at bottom of hill, it then does whole hill, so motor unable to deliver 350 watt continuously.
     
  5. RandomGrinch

    RandomGrinch

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    36V hub?
    A 36V, 13Ah battery should be able to deliver a continuous discharge of 15A - 20A
    And a controller may be able to handle 100A
    So should be over the 10A needed.
    Have you any specs?
     
  6. ericmark

    ericmark

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    No specs, thought it was an e-bike when bought, it may be an e-bike, it was only latter I saw the 350 watt on the hub, which does not mean really 350 watt, as it is the controller which limits the power.
     
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  8. RandomGrinch

    RandomGrinch

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    Last edited: 2 Sep 2021
  9. Master of None

    Master of None

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    It could be that your bike is sold in other countries but is limited to 250w in the UK. Its well known that a lot of UK bikes can be modified to 500w or so using software.
    If your wife's bike has a crank mounted motor I assume it is likely a more expensive bike so may have better management hardware / software.
    If it cuts out at least you know it has some sort of motor / battery monitoring and protection.
     
  10. Keithmac

    Keithmac

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    Mid mount is far better for climbing hills (I have both).

    Hubbed is quieter and more suited to flatter roads imho.

    Legally you cannot run continuous 350w, the mid drive can take advantage of the rear gears/ hub as a torque multiplier.

    Apples to oranges unfortunately comparing the two, both good at different things.

    I built the first bike from an old frame, TSDZ2 Mid Drive, Nuvinci 360 rear hub, 15ah 36v battery.

    I've got 2 GTECHs as well (MK1 and MK2), ideal commuters with the carbon belts!.

    20210831_085816.jpg 20210624_083944.jpg
     
  11. ericmark

    ericmark

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    Did look at G-tec, I am too heavy to ride one, weight limit rather low. I think the mid motor is far better, less noise, and drives through the gears so torque is increased on the hills, but it needs a special frame, at least for the Bosch fitted to wife's bike, and it means no gears at the front as a special belled crank gear, so think her's is 7 speed, where mine is 21 speed, not that it is really 21 speed as there is a lot of over lap, but without a dynamometer one can't really know the output of any motor. I remember at collage having to work it out, 2πNT/33,000 but god knows what it is today with metric system? Funny how one remembers formula. I note many quote volts x amps x power factor, which clearly is a problem as no idea of the power factor, and they are AC motors, it must be less than DC volts x DC amps and we know battery is 48 volt at 12 Ah so 250 watt = 2.3 hours running time, I get well over that time, so clearly the motor uses well under 250 watt on a continuous basis. And of course there must be losses, so even less at the wheel.

    My wife's bike seems to use more of her battery than mine uses of mine on the same run, so sure my motor in real terms has a lower output to hers. However since my system continues to give assistance after 16 MPH it is clearly not to spec required in UK, although CE marked and bought before we left the EU. It seems the 5 power ratings are in real terms maximum speed ratings, and at level 3 it is approx 16 MPH, there is a menu that allows some changes, all I have done is change from km to MPH, there are 17 options, and option 2 swapped to MPH. However the instructions do not say how to set up, so bit of a guess that it's similar to others found on internet. It seems likely number 5 which I think is power assist may change it to 3 options instead of 5, or 7 which it seems is speed measuring magnets in motor, but since not sure what they do, I am leaving well alone.
     
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