# Did I Get The Wrong Controller?



## gregski (Sep 6, 2011)

Originally I planned on buying a 72 volt controller but because of money I settled for the Alltrax AXE 4834. The AXE is the model that is programmable. The 48 means it's a 48 volt and the 3 means it's 300 amps for those of you not familiar with the Alltrax brand. I landed one for around $150 bucks on eBay ( = score ! )

Anyway I would like to commute on my motorcycle conversion (Suzuki Katana GSX600F) however my top speed is barely 40 MPH with an average of 30 MPH just a bit shy of what I would feel comfortable with on busy city streets. My one way distance is just shy of 10 miles. I weigh a tad bit north of 200 lbs suited up.

I am currently running a 12 tooth front sprocket and a 47 rear. I just ordered a 13 tooth sprocket for the front and it should show up any day now. I know that gearing will help, but I am just trying to avoid any self imposed bottle necks.

When I bought this controller my logic went lie this. Why do I need anything more than the 300 amps if my MARS ME0709 motor is rated at 125 amps continuous and 300 amps peak. Right?

Well what I have learned during my two year conversion is that there is a set of heuristics or rules of thumb one must be aware of in the world of electricity. For instance what we call a 12 volt battery like you find in your car, is anything but, it's really a 13.6 battery and at 12 volts it's considered dead. And one would think at 6 volts it's 50% depleted... WRONG!

Also a 48 volt motor can be "over volted" to say 60 volts. OK, but a controller can not be "over volted" because it will cause a puff of black smoke. And word on the street is that a 300 amp controller may only be a 275 amp controller and a 400 amp controller really only a 350 amp controller, see where I am going with this? Some specs go one way, others the other, it's what keeps me up at night, LOL.

So considering the optimistic marketing specs of controllers would I get more umph out of the next model up i.e. the AXE4844 which runs up to 400 amps? Did I buy the wrong controller?

I know that ultimately I would like to go to the AXE7245 (72 volts, 400 amps) but that will be costly as I will need two more batteries, a different charger, a new solenoid, etc...


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## Guest (Sep 12, 2011)

Your controller is not really up to the task for street driven vehicles. Would be OK for a Golf Cart at Golf Cart Speeds. But for a street bike you should do at least 72 volts and at least 500 or more amps. Your motor should do 72 volts just fine as most of the time you won't be using that amount of power. Finding a good high amp low voltage controller is the problem. I try to educate folks before they go spending money before they really understand whats happening. Everyone is so eager to jump right in and assume but find out later they wasted the money and then have to sell the items and go out and buy the right stuff. There is lots to learn before you jump in. I was no different but I am different in that I want to educate. Can't educate if you go jump in and buy before you learn. It is a waste of money. 

You can still use your parts on some fun project like a lawn mower. Go with lithium batteries too. Don't bother with lead. It's dead. Bulky and low life. A small project is always a good way to start. A lawn mower is perfect. I started with a VW Ghia but should have started with a mower. Actually my first electric car was a really early Datusn Bluebird with an electric motor. I sold the car and the guy I sold it to is trying to make a killing. I sold it for $600 and he is trying to get $4000. Car and old baldor electric motor and home made adaptor with no clutch. The second was a Bradly GT that had an old Kaylor Electric Car kit installed in it. It was garbage. Learned a lot since those days. The VW Ghia was a success. The second was a 77 Midget that we improved and installed lithium and a nice high power controller. I then purchased a Nissan Leaf and we are planning two more. VW Bus and Buggy. Maybe another but that will be later. We are all solar here. Totally green. 

Pete


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## EVfun (Mar 14, 2010)

I think you are going to need a higher voltage controller. Permanent magnet motors have very predictable behavior, the voltage sets a hard rpm maximum for the motor. According to this source that motor is good for up to 72 volts and only turns 3050 rpm no load at that voltage. That means that it maxes out at about 2030 rpm at 48 volts. With a PM motor you have to pull the motor below that maximum rpm to make any power. 

You will need more voltage and you can't over-volt your controller without the magic smoke escaping. More amps will not increase the motor rpm, it will only increase the torque at lower speeds.


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## gregski (Sep 6, 2011)

gottdi said:


> Your controller is not really up to the task for street driven vehicles. Would be OK for a Golf Cart at Golf Cart Speeds. But for a street bike you should do at least 72 volts and at least 500 or more amps. Your motor should do 72 volts just fine as most of the time you won't be using that amount of power. Finding a good high amp low voltage controller is the problem. I try to educate folks before they go spending money before they really understand whats happening. Everyone is so eager to jump right in and assume but find out later they wasted the money and then have to sell the items and go out and buy the right stuff. There is lots to learn before you jump in...
> 
> Pete


Thank you Pete for taking the time to respond, you are spot on accurate, I did jump right in, [ahem] (like you - lol), though I did build two electric go carts for my kids before doing the motorcycle for myself. I find that I really don't learn until I try and do something. It's like trying to read a book on how to swim, I doubt anyone's put one down and dove into the pool and butterflied across, lol. 

Anyway I realize education costs, and that's how I justify my spending, plus building a 48 volt system that you can ride around the neighborhood on really builds your confidence, did for me. I think I can re use the controller on my kids third go cart as well as the charger so not all will be lost. Plus if I nailed it on the first try I would have not really learned much on my own, I would have just assembled a project very Lego like.

So you are saying I need more volts as well as amps? I agree that my motor will do 72 volts as it is rated for 72 volts, but what about the 500 amps that you are recommending sending down it's throat, the specs say the motor can do 300 amps tops, that's what has me confused?

Again thanks for you reply


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## drgrieve (Apr 14, 2011)

Can you measure how many amps you are using now?

In any case volts equals rpm which is your top speed and amps is acceleration

So if you want to improve your max speed more volts. Want to improve the time to get there more amps


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## major (Apr 4, 2008)

Hi greg,

What battery are you using and what voltage do you see at 30, 40 mph?

major


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## gregski (Sep 6, 2011)

EVfun said:


> According to this source that motor is good for up to 72 volts and only turns 3050 rpm no load at that voltage. That means that it maxes out at about 2030 rpm at 48 volts.


How did you come up with 2030, is it as simple as taking 2/3 (.66666666) of 3050? I'm good at over thinking the simple stuff, lol


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## gregski (Sep 6, 2011)

major said:


> Hi greg,
> 
> What battery are you using and what voltage do you see at 30, 40 mph?
> 
> major


UB12550 sealed lead acid 55 Ah


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## EVfun (Mar 14, 2010)

gregski said:


> How did you come up with 2030, is it as simple as taking 2/3 (.66666666) of 3050? I'm good at over thinking the simple stuff, lol


That is right. A permanent magnet motor is that simple. The constant for that one appears to be 42.3 rpm per volt. That is the no load rpm, to get some power you have to pull the rpm below that point. As you load the motor to pull the rpm down the amps will quickly shoot up to make the needed power.


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## BigAlum (Jun 12, 2008)

Soooo - can a PM motor controller be used in a series-wound situation? From my looking around and studying some of the Curtis manuals, it appears this COULD be done using an external F-N-R switch and bypassing the internal bridge. Am I out to lunch?


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## frodus (Apr 12, 2008)

Depends on the motor controller, but most likely you can use a PM controller on a series wound motor without any problems. The F-N-R doesn't really matter, you just have to wire up the motor the same as you would for any series wound application.

What motor and controller do you have? Maybe start a new thread and tell us about it.


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## major (Apr 4, 2008)

BigAlum said:


> Soooo - can a PM motor controller be used in a series-wound situation? From my looking around and studying some of the Curtis manuals, it appears this COULD be done using an external F-N-R switch and bypassing the internal bridge. Am I out to lunch?


While you're out to lunch, post the link to the manual about the F-N-R switch, bridge and bypass, please  It is not clear what you're talking about and you can't reverse a series wound motor the same way as a PM motor.

major


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## BigAlum (Jun 12, 2008)

OK, I hope this kinda clears up my rambling: No manual for this train of thought, but my understanding is that a pm motor controller (such as the Curtis 1237-series I have) controls forward and reverse internally through a "full-bridge" circuit, switched by a low-current logic input. By "bypass," I mean to simply run the controller in forward mode only and switch for F-N-R through an older (golf cart style) high-current switch, since I happen to have one. I'm looking at a quick, inexpensive go-kart application for the (young) grandsons. And that happens to bring me to another point of question - Since I also have several sep-ex motors (about 2HP each) besides the old golf cart motor, what's the effect of trying to treat this type of motor as series-wound? Seems this could be done exactly the same except that the amperage may need closer scrutiny because of the smaller windings... Thanks for all your input!


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## frodus (Apr 12, 2008)

Oh, sorry about that. You're right.... just missed a small detail on terminology.

That's not just a normal PM controller, it's a 4-Quadrant controller. It would work in forward, but because it's a series motor, it'd run the same direction if the controller was commanded to go reverse. Running in FWD only would work, and then do a reversing contactor.

As far as sepex, you could treat it as a PM motor and just give the field windings a fixed voltage supply. Just be careful it's the right voltage.


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## major (Apr 4, 2008)

BigAlum said:


> OK, I hope this kinda clears up my rambling: No manual for this train of thought, but my understanding is that a pm motor controller (such as the Curtis 1237-series I have) controls forward and reverse internally through a "full-bridge" circuit, switched by a low-current logic input. By "bypass," I mean to simply run the controller in forward mode only and switch for F-N-R through an older (golf cart style) high-current switch, since I happen to have one. I'm looking at a quick, inexpensive go-kart application for the (young) grandsons. And that happens to bring me to another point of question - Since I also have several sep-ex motors (about 2HP each) besides the old golf cart motor, what's the effect of trying to treat this type of motor as series-wound? Seems this could be done exactly the same except that the amperage may need closer scrutiny because of the smaller windings... Thanks for all your input!


Hi BigA,

We kinda hijacked this thread from gregski but I guess it still is about wrong controllers  

O.K. Use the 1237 for series or sepex motor in the forward only mode? Would work, but it may have problems regulating current due to the lower resistance motor. PM motors typically have a higher resistance armature. Worth a try IMO.

You can use a sepex as frodus explained. But not by wiring the sepex field in series with the armature. The field resistance would be way too high and the armature would get little voltage under load so would turn very slowly and burn up the field rather quickly.

Regards,

major


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## BigAlum (Jun 12, 2008)

Thanks, guys! This all helps me understand things a little better.


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