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Thread: Dual motor setup, what have we learned?

              
   
   
  1. #1
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    Dual motor setup, what have we learned?

    Just wondering if those who have been paying attention or done this type of thing have any insight into what it takes to have a dual motor setup. The Agnis only need one controller, but how much of a pain is it to get 2 motors and controllers dialed in? Is one controller better and easier than 2? I'm think the KISS method applies.

    Also, what are the real differences to running motors parallel or in serial? And how might that affect the battery cells?

    Here's what has been going through my head. I'm thinking of a dual Motenergy motor setup with a max of 75kW going to both motors, or 37.5kW each. Now, do the motors care how the 37.5kW is delivered to each of them? Because it could be (well any combo, but) 187.5v at 200A or 93.75v at 400A at each motor. For some reason I have it my head that the higher voltage lower amp way of doing things would mean down the line there would be less stress put on each individual cell in the battery pack. I could just run 2 of these motor kits, but it would seem to be cheaper an easier to run one controller.

    Lets look at that for a second. Say I ran the dual Sevcon setup. How much of a pain would that be? And then, I could only get 84v out of the Sevcon, so I would be running about 450A per motor, which is well within Sevcons 550A. What performance difference would I notice between those 3 different voltage/amp combos? Obviously it would be for a race bike so that has to be taken under consideration.

    Ok, I've boiled it down. Wire the motors for serial or parallel? And, within a power (kW) limit is more voltage or more amperage better? Then, I can start thinking about this hypothetical bikes controller.

    Thank you for any insight you can provide. And apologize if I am rehashing old subjects.
    Rich
    Last edited by jazclrint; 03 January 2012 at 2223.

  2. #2
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    I'm running dual sepex, dual Navitas 500A on my bike. If I ever get it done, I'll let you know how it is.
    "We realize that we have not answered all your questions and in most cases, our
    answers have only served to produce more questions for which we have no answers,
    leaving us as confused as before. However, (we believe) we are now confused on a
    much higher level and about much more important things than before."

    1978 Suzuki GS550 - 48V 60Ah Pb-A, Alltrax 4844, Etek-RT
    1997 Suzuki Katana 600 - 18s8p (~72V, 40Ah) 30C Turnigy Lipo, Navitas 500A with D&D Sepex

  3. #3
    Senior Member SplinterOz's Avatar
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    Yes the motors will care. It is the Amps that produce heat so if you run in series they get the same amps.
    This means that in Series you will have to have a controller that delivers twice the voltage the motors want an in parallel twice the amps the motors can handle.
    SplinterOz
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  4. #4
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    Running a PMAC in series might be tricky to get right, you'd need to make sure they were both in phase.
    "We realize that we have not answered all your questions and in most cases, our
    answers have only served to produce more questions for which we have no answers,
    leaving us as confused as before. However, (we believe) we are now confused on a
    much higher level and about much more important things than before."

    1978 Suzuki GS550 - 48V 60Ah Pb-A, Alltrax 4844, Etek-RT
    1997 Suzuki Katana 600 - 18s8p (~72V, 40Ah) 30C Turnigy Lipo, Navitas 500A with D&D Sepex

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    Quote Originally Posted by SplinterOz View Post
    Yes the motors will care. It is the Amps that produce heat so if you run in series they get the same amps.
    This means that in Series you will have to have a controller that delivers twice the voltage the motors want an in parallel twice the amps the motors can handle.
    Ok, so that confirms one thing for me. But I would argue that with either set up each motor is getting the same volts and amps. So, in the case you stated, wouldn't it actually be the controller that cares?

    Whether you double the voltage and put them in series, or double the amps and put them in parallel, is the performance different in either configuration? I don't think it would be, but that is why I am asking. It would just be down to which way puts less stress on the controller and cells?
    Last edited by jazclrint; 04 January 2012 at 0004.

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    Quote Originally Posted by Tony Coiro View Post
    Running a PMAC in series might be tricky to get right, you'd need to make sure they were both in phase.
    Do you see enough of an advantage running them in series, to be worth it? I was already thinking this imaginary race bike would have to spend a serious amount of time on a dyno to get the motors balance, after seeing what Ripperton found on his bike.

  7. #7
    Senior Member SplinterOz's Avatar
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    Sorry what I was meaning was that if you overvolt a motor it will spin faster and beyond its design parameters. If you over amp a motor it will heat up and fail, the failure will depend on the style of motor. In the Australian TTXGP we had failures of both Brushed and Brushless dual motors.
    Now if you can get the same KW with lower amps then the motor will run cooler for the same power. So you really want to divide the current (run them in parallel) rather than divide the volts (running them in series).

    As we all have said it is a package controller, battery and motor.

    The first motor you pointed to is a ME0913 PMAC Motor from Motenergy. It already is really two motors in one. It has two sets of coils wired in parallel pushing one set of magnets. This motor has been modified by Zero and Ripperton to improve cooling (among other things). Note that Ripperton's left coil kept burning up due to a mis-alignment of the coils causing more AMPS on one side. It is designed to run 96 volts, Ripperton is running his at about 140volts.

    Now if you put two of these in series you will need to find a PMAC motor controller capable of around 192volts or more to spin it up to speed. Finding a controller that can deliver 192 volts may be difficult.
    If you run them in parallel you need a controller that with a voltage range of 96 volts to 144 volts but delivers 250 amps continuous (single motor rated at 125 amps continuous).

    So as a package the motor should be happier with less amps and it is easier to find a controller with voltages under 150volts than above.

    Hope that makes sense.
    SplinterOz
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    http://rgelectric.wordpress.com/

  8. #8
    Senior Member SplinterOz's Avatar
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    Quote Originally Posted by jazclrint View Post
    Do you see enough of an advantage running them in series, to be worth it? I was already thinking this imaginary race bike would have to spend a serious amount of time on a dyno to get the motors balance, after seeing what Ripperton found on his bike.
    Cool I see you are following Daniel (Ripperton). Note in his DIY thread you will see the controllers not liking the higher pack voltages.
    Last edited by SplinterOz; 04 January 2012 at 0042.
    SplinterOz
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  9. #9
    teddillard
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    I've been trying to collect links with information on this:
    http://evmc2.wordpress.com/2012/01/0...s-dual-motors/

    I'm for now just interested in PMDC motors, and the conclusion I came to is that it's not worth the trouble. If you want more motor, just run a bigger motor (if it's available - which is the problem).

    Most of the good information is on the Jozzer's post on Agni tuning. Along with an Agni shop manual.
    http://endless-sphere.com/forums/vie...711&hilit=agni There are a bunch of other random posts and some other threads on this on ES, I'm still researching.

    The bottom line for me is that when you run two motors in parallel, the entire system has to be perfectly matched. Cedric Lynch himself picked out parts off the shelf, put a couple of perfectly matched motors together, and when they went into the bike they eventually blew up. That sealed it for me. If Lynch himself can match up motors and they still get melted, the I don't have much of a chance. Running two controllers, though possibly helping address this issue, seems to me to be too much additional hardware.

    This, again in my opinion, has been proven out on the track. A few years ago everyone was trying to run dual Agnis or even triples (who was that.. I can't remember? MotoCzysz?). Now they're running bigger liquid cooled AC. It seems pretty obvious that trying to run dual motors, although cool from a tech standpoint, was more of a bandaid than a long-term solution. At least for PMDC.
    Last edited by teddillard; 04 January 2012 at 1313.

  10. #10
    Senior Member protomech's Avatar
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    Yeah, MotoCzysz ran in 2009 with three Agnis.

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