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[Reaper]

Ok thanks, so what is everyone having the most luck with as far as controllers go?  I found a motor but cant seem to find a controller that I really like.

Hey man,

Like I said before, I am a newbie but from what I can tell on Evalbum and various other websites a lot of folks seem to like the Alltrax brand controllers.  They seem to be pretty solid.

[frodus]

yeh parallel the whole time. Extra motor will help with top speed, and accelleration, you have double the kW to play with!

How do you guarantee that each get the same current? Only one way.... 2 controllers, 2 motors, 1 big battery pack. You don't have twice the KW to work with, its still limited by the output of the controller. If its 400A, each motor "SHOULD" get 200A.... but if one motor has a different impedance, or is cooled at a different rate, more current will flow to one than the other. Its not a bad idea for racing, but not for something you drive on the roads for 30minutes.

Also, I'm not sure why anyone thinks that series is worse acceleration. Torque is current, speed is voltage. If you have your motors in series, you'll get ALL the current through both motors, but the speed will be limited. If you put them in parallel, you get 1/2 the current through each, but full speed.... eventually. There are gains to both, but with series, the issue of having unbalanced motors is negated, the current is the same through both, and neither will have unbalanced current... less cooling issues.

Also, even with motors the same design, the impedance varies quite a bit. Its essentially a short circuit, but its got a very low impedance (inductive mostly). One may be 1mOhm, the other is 2mOhm... that means the one motor could get 33% the other gets 66% of the current.  The one with the lower resistance gets more current. It doesn't take much of a difference at such low impedances to throw things off.

[Bogan]

I probly just explained it wrong, with parrallel you get a much higher top speed. The acceleration can be the same as for series (but it continues through double the rpm range) this is assuming the batteries/controller just deliver twice the total current (when pwm voltage adjusting is taken into acount the power used will be the same as for series), and acceleration is roughly double that for a single motor.
To have twice the kW to play with i was refering to the motors themselves, of course you need a controller and batteries that can deliver this much, series you have twice the acceleration over a single but half the top speed, parralell you have twice the acceleration and the same top speed.

Current balancing will not be perfectly the same for each motor (think i mentioned that somewhere) but i dont beleive it will be unbalanced enough for one to start engine braking the other so I cannot see how this slight unbalance will be detrimental to the running of the bike. If you are correct and one motor has double the impedance of the other then sure itll create problems but manufacturing this flawed sounds highly unlikely.

[frodus]

I have seen it with a couple motors... and not all motors are the same. Even just a little difference causes a difference in current. There's a difference in most motors out there even if they're the same. You just can't match brushed motors that well, too much resistance at the brushes. Contrary to what you might think, there are major differences in the consistency of Agni motors, as well as eteks.

You wouldn't THINK it'd matter, but its just like a resistor network, change the resistance of one resistor and the current flows to the one with least resistance. Its generally NOT a good idea to parallel motors for this very reason. If he wants to risk it, then carry on. I'm voicing my concerns, because they're real concerns, while yours are optimistic that it'l work.... because it seems like it should.

The time I've spent on elmoto, endless-sphere, EVDL, diyelectricar and working with Synkromotive and MotoCzysz and the discussion has come up a lot in the past couple years. There's no way to guarantee that it'l work besides one controller per motor each at full voltage.

[Bogan]

ok, i dont have as much experience with the real world applications, but at least the theory was sound!

[frodus]

I didn't mean to come off as know-it-all, that was not the intention.

I just don't want anyone to assume it'l be 100% right and then have problems. There are always 2 sides to things. Here, the sides are why it would be good, and why it wouldn't. There ARE pro's to parallel though... just as there are cons.

Now, there are people that have done it and get away with it no problem, but if there was a problem, the unbalanced current would likely be the culprit.

Now, since power is power no matter how you look at it, I'd say, if you want 2 motors.....get a 144V controller from kelly and do series, the current is balanced, and the motors get the same power they would.... just gotta build a taller pack with smaller bats.

[Bogan]

yeh, that probly a bette ride, if you can get a big enough battery pack into a bike, wouldnt be doable with lead acids, possibly doable with prius nimh's, definetely doable with flash lithium batterys. Btw frodus i am impressed with the prices for lithiums on your website.

[frodus]

We try to get VERY LARGE orders put together and get the pricing way down....

economy of scale

So far we're the lowest price for TS, Sky Energy and Headways in the US.

[Camaro]

frodus,
  What's your website? I'm interested in getting Li-batteries for my bike.

[HotRodHoose]

Ok, so now I should be thinking series and not parallel?  So if I run series am I still going to have a decent top end, or would I be better going with two motors and two controllers in parallel?  I would also like to check out your website as I am going with Lithium batteries now too.

[frodus]

frodus,
  What's your website? I'm interested in getting Li-batteries for my bike.

www.evcomponents.com

email me at travis@evcomponents.com and I'll help ya out.

[frodus]

Ok, so now I should be thinking series and not parallel?  So if I run series am I still going to have a decent top end, or would I be better going with two motors and two controllers in parallel?  I would also like to check out your website as I am going with Lithium batteries now too.

what voltage were you thinking for the motors? If you did 2 72V motors in series, you could throw a 144V kelly controller on there and be done. It'l have the same top end as 1 72V, but it'l get you there quicker.

You cannot parallel controllers. They won't switch at the same time (high frequency PWM). You would have One battery going to each controller. Each controller would be wired to its own motor.

[HotRodHoose]

Ok thanks, do you think that I will be able to achieve a top speed of about 75mph with two motors in series at 144V?

[frodus]

all depends on the motors and available peak power that the batteries can supply.

[HotRodHoose]

Ok, I plan on buying lithium batteries but who knows which one, batteries are hard to figure out, i mean lithium come so small and to get the big pack its a pain in the rear.