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Thread: AC vs DC

              
   
   
  1. #1
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    AC vs DC

    For motorcycles as far as I can see reversing is a non-issue and regenerative breaking doesn't really help much either. Given this it seems like a lot of the benefits of AC motors don't really apply to electric motorcycles and I'm wondering if the added cost is really worth it. Specifically I am looking at comparing motenergy and HPEV motors for use in an electric motorcycle.

    Any information would be very helpful. Thanks.

  2. #2
    Electric Warrior CaptainKlapton's Avatar
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    It really depends. Are you including PMAC/BLDC motors in the "AC" category? Or are you just comparing brushed DC to induction?
    What models do you have in mind?
    "Never let schooling interfere with your education."
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    Senior Member jonescg's Avatar
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    In my mind, AC motors (BLDC, PMAC and ACIM) all win hands down. They can all be liquid cooled because the bit that gets hot is the bit that's stationary. They have no electrically conductive parts rubbing on anything and are able to be made completely waterproof. Sure, regen and reverse are not needed on a bike, but good luck finding a DC motor small enough, light enough and reliable enough to take the place of an AC.

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    Seņor Member podolefsky's Avatar
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    In general, I agree with Jones. There's a reason every major electric car and bike manufacturer uses AC. As with all things, it depends on your budget and expectations.

    If you're comparing Motenergy to HPEVS, then you're air cooled either way. In that category, the main performance advantage to brushless versions is that they can run higher voltage, so with the same current rating you get more power. If you're running 72V, then a brushed ME1003 will has nearly the exact same torque and power as a brushless ME1115. The advantage to the brushless is basically lower maintenance.

    If you have a higher voltage pack, then the brushless motors win...as long as you also have a high voltage controller.

    So...you also have to look at the controllers - what voltage and current will they do? The HPEVS AC-20 comes with a 650A, 130V controller. That's gives you more power than most of the Motenergy AC packages (although the high current Sevcon size 6 is very close, if you can find one). But, that's only if your battery pack can supply that voltage and current.

    If you're looking for bang-for-the-buck, the ME1003 / Alltrax is hard to beat. It's not going to build you a race bike, but it will be plenty of fun and under $1000 for the whole kit.

    On regen - true, it doesn't give you that much back in energy, but I still like it. Mostly for the "engine braking" feel. I've ridden my bike plenty both ways, and I like having regen kick in off-throttle. But, if I were on a budget I wouldn't pay an extre $1-2k for it.

    I love my AC-20, and once I upgrade to a 100V pack I know I'll like it even more. But it wasn't cheap.
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    Senior Member Athlon's Avatar
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    I prefer AC for safety , when a DC controller fail it fails ON , when an AC controller fails it fails OFF.

    In one case you will have your bike going to full speed , in the other your bike will stop.

    with 4 quadrant DC controller is a little safer because for having trouble you need two mosfet shorted ON not just one , but still possible

  6. #6
    Seņor Member podolefsky's Avatar
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    I should say also that I'm using an ME1003/Alltrax 7245 on my KZE. I won't have regen, but that's OK. I decided the extra money for AC wasn't worth it for this build. It will have plenty of power for street and highway use, and to be honest brush maintenance is virtually a non-issue. With the kind of miles put on your typical elmoto, you could probably go a couple years before you need new brushes (and when you do, it's about $30 and an hour of work).
    - Noah Podolefsky -
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  7. #7
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    I am planning on using either the AC-12 with the 350A controller or the ME1003, either way I will be using a 72V system. This system is mostly city driving with about 2.5km of highway twice a day so I will not need any more power than those two motors will supply. I'm not currently considering PMAC or BLDC because from what I have seen neither of those is worth the extra cost in my build.

    For the controller failure deal, a circuit breaker and contactor should make the DC controller "failing on" a non-issue shouldn't it?
    Last edited by ruairdhri; 06 July 2014 at 1222.

  8. #8
    Seņor Member podolefsky's Avatar
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    Think about which one will fit your frame with batteries and other things installed. They're different shapes. The AC-20 fits my GSX well, but not my KZE. The ME1003 fits the KZE and not the GSX.

    Yup, your contactor will act as a safety valve, if you set it up so it's easy to switch off in an emergency.

    You want a fuse, rather than a circuit breaker, unless you can find a 300A DC circuit breaker. That *might* save you, but not necessarily. It depends on what speed the motor is going when the controller fails. If it's above a certain RPM, you won't pull enough amps to blow the fuse.

    Not to dismiss it outright, but as far as I know it's pretty rare for a DC controller to fail completely on. Of all the things that can go wrong on a motorcycle, that one is pretty low on my list of concerns. There are ways that an AC system can fail with wide open throttle (like if the throttle itself fails).
    - Noah Podolefsky -
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