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[mKlRivPwner]

So I've been doing some searching and it seems like everyone is doing a DC motor.  Is there a reason?  Is it that AC motors cost too much?  Or is there some drawback that prevents AC motors from being usable?

Basically, what I'm trying to understand is what are the benefits and drawbacks of AC versus DC motors?

[frodus]

well, as far as I know there's really only one setup for electric motorcycles with AC.... thats the HighPerformanceGolfCart AC motor and curtis combo, at least hobby level.


AC:
Pros:
No brushes
typically a higher RPM range than DC
typically smaller cables to motor (but 3 cables instead of 2)
regen is just part of the package
efficient

cons:
cost
complexity of system/controller
not many "packages" on the market
large controllers
flux must be induced in the armature, so torque is not as "instant"

DC
Pros:
cost is low
lots of controllers and motors to chose from
instant torque at 0rpm

cons:
brushes (but they don't wear out quickly)
lower efficiency (although there are high eff DC motors)
Not all DC motors have regen, and not all controllers offer regen


essentially for most people, its cost.

[skadamo]

Frodus, let me know if I am making generalizations here but one thing I learned from TTXGP is DC motor failures result in a locked up rear wheel. I believe this is not as likely with AC motors?

Of course these were race conditions and the motors may have been pushed beyond their limits. Sounds like that is what did the E1pc in. Also, see :45 into this video when the eRockit entry goes down...

ttxgp practise run

[mKlRivPwner]

If one were to start out DC, how much would have to be swapped to get AC?  And where could I find a DC motor that supports 72-84 Volts?

[frodus]

Frodus, let me know if I am making generalizations here but one thing I learned from TTXGP is DC motor failures result in a locked up rear wheel. I believe this is not as likely with AC motors?

Of course these were race conditions and the motors may have been pushed beyond their limits. Sounds like that is what did the E1pc in. Also, see :45 into this video when the eRockit entry goes down...

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Any motor could technically lock up. The main problem being that the armature flies apart. The agni's seemed to have a problem with being overheated and the magnets would come loose and lockup, or the armature would come apart. They were being overstressed and run into their limits. AC motors are less likely to have this happen.

[frodus]

If one were to start out DC, how much would have to be swapped to get AC?  And where could I find a DC motor that supports 72-84 Volts?

you'd have to replace the motor/controller to go from DC to AC. Thats about it.

DC motors that go 72V-84V, I'd look at a sepex combo (D&D and a sevcon), or an Advanced DC or D&D series wound motor with a Synkromotive, Curtis or Kelly controller.

I have a Synkromotive controller and Advanced DC K91 motor. I ran it before at 72V, it'l be running at ~100V after my lithium upgrade.

[mKlRivPwner]

Thanks for the info!  Plenty to think about.

Still wishing for an AC system, and maybe with the right gearing, a little ingenuity, a lot of luck, and a good salvage yard, I'll be able to get something together on a budget (even if it means sacrificing some batteries and range).

[frodus]

efficiency is marginally higher. Maintenance on brushed is minimal (you might go 100kmiles before replacing).

I'd say get a bike first. whether DC or AC, you need a bike. Then work from there.

AC is not a budget project component.... and you can do just as good using series or sepex and a little more battery capacity.

[mpipes]

Travis,

Have you ever seen any issues with DC controllers flaking out? After reading on metric mind about what happens in a DC controller when it fails, it seems AC would be a safer bet for people building commuters and driving in traffic.

On the other hand, I'm also sure the reputable controller makers have a pretty low failure rate to the point it may not be much of an issue anyway.

I'm planning out a project right now and actually have budgeted for an AC system, but am also wondering if there really is much advantage over DC for a project like mine - ~300lb vehicle, 230lb rider, 45MPH cruising speed, somewhat hilly terrain (45MPH climbs in the 1-2 minute range, nice downhills for coasting).
As far as safety, I have thought about wiring a switch into the brake that would open the motor contactor whenever sitting in traffic or at lights/stop signs, along with an LED indicator that would warn me of a fail condition before I let loose of the brake lever. Am I being paranoid?

[frodus]

I've never used another controller besides a Synkromotive.... its a different type of controller, it fails OFF. I've heard of ONE failing on, not sure what happened, but it was logisystems and it was a prototype. Most controllers never fail while they're running and those that do, don't fail off. Its not much of an issue.

As far as a system for you, there's no need to do AC for your needs, you could do a sepex motor/controller and get even higher speed, and regen for half the cost of an AC setup.

as far as a switch to disable... don't need to disable the contactor, that should be only tied to the key switch, kill switch and an emergency switch on the gas tank. You can disable the keyswitch input on the controller though. I think its a bit paranoid, because you would disable the controller every time you brake. Controllers don't draw much current at rest and don't fail ON when they're not ON. If they're off, it won't just short circuit and go full ON. If anything goes wrong thats what your kill switch and emergency switch are for.

[mpipes]

Thanks for the info Travis.

Well, saving $1500 on a motor/controller means a battery/BMS upgrade