# What is a controller and why do I need one?



## order99 (Sep 8, 2008)

Nope, got it in one. Controllers come in handy. You can control all your power settings through one, trading power for fuel economy like a carb on a combustion engine. The main thing they do of course is to keep you from stripping out your gears, blowing out your motor or snapping your spine as the motor tries to go from 0 to 'infinity' RPMs when you flip the switch!

Some turn of the century EVs i've seen used variable resistor technology to control the juice. Others-mostly from the 70s and early 80s-use contactor-driven switching to cut batteries in and out of the circuit...12V, then 24V, then 48V for example. The modern ones 'pulse' the current, cutting in and out at x per second, thereby feeding the motors variable power from a non-variable source. The 'pedal'(or thumb throttle, or handgrip) is the Potentiometer, which feeds the necessary input to the controller like the lever on a carb.

If you want to get any more technical than that you'll have to wait more more experienced Posters-until I found this Forum I used to think you were supposed to test battery current with a screwdriver between the posts...


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## major (Apr 4, 2008)

chiques said:


> I "think" it's a device that regulates the voltage and current going to the propulsion motors through a variable pedal of some sort.


Hi chiques,

Your thinking is correct. To expand a bit....Electric motors are basically single speed machines. Yeah, that speed depends on the load. But if you have a fixed load, and connect the DC motor to a fixed voltage, like a battery, it will run at a fixed or constant RPM. Not quite what you'd want for your EV. So, the primary function of the controller is to regulate speed. With DC motors, this is done by varying the voltage to the motor.

Also, when starting the DC motor from zero RPM, simply connecting it to the battery, like with a switch, will cause a large inrush of current. And with series DC motors, the inrush of current will cause a very large torque output from the motor. This results in too great of a stress on the electrical and mechanical components connected to the motor, and in the motor itself.

So a secondary function of the controller is to manage current, called current limit. I say secondary, but really it is a needed function. This current regulation is also accomplished by the controller by controlling the voltage to the motor. But the controller needs to be able to sense the current to do this. Usually, with modern PWM controllers, this is all built in. All you need to do is give the controller a signal from the throttle pedal. This is normally done with a potbox. So a few millivolts or milliamps from the pot (variable resistor) can control lots of volts and amps via the controller. Somewhat like an amplifier.

Hope that explained it somewhat.

major


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## chiques (Mar 9, 2009)

order99 said:


> ...I used to think you were supposed to test battery current with a screwdriver between the posts...



LOL!




I appreciate the detailed responses. I think I can grasp the functionality of a "controller" now.

Thanks a bunch!!!


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## Will-E (Apr 20, 2009)

Hi Major,
Thanks for such a clear and understandable description of a controller as you posted in reply to Chiques. I have a question regarding the controller and its relationship with the voltage of the motor. I have my eye on a 36/48 volt 12" 200 pound motor from a forklift. Would a 48 volt controller be enough to power a EV comfortably . Does a larger controller allow the motor more power?
Thanks
Will-E


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## Guest (Apr 23, 2009)

Will-E said:


> Hi Major,
> Thanks for such a clear and understandable description of a controller as you posted in reply to Chiques. I have a question regarding the controller and its relationship with the voltage of the motor. I have my eye on a 36/48 volt 12" 200 pound motor from a forklift. Would a 48 volt controller be enough to power a EV comfortably . Does a larger controller allow the motor more power?
> Thanks
> Will-E


There should be no reason other than timing and good brushes that would prevent you from pumping in 144 volts and 550 or more amps with that big 12" motor. Most motors can handle that kind of power. Just not for hours on end. That is why the forklift is 48 volts. At that voltage it will run full out just about all day long without a hiccup. With high voltage and high amps you are limiting the time at that power level but most of the time you only need a few seconds anyway to get you up to speed. After that you can cruise along just fine. Clean it up and put in new brushes and get the timing just right and get a nice controller that can handle 144 volts and at least 500 amps. More if you can get one. The higher the voltage you use the less amps you will need to cruise along in your ev. I use 72 volts and 550 amps and a 9" GE motor. I can go to 144 or 156 volts if I want. I want! : ) 

I will be upgrading soon. 

Pete : )


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## Will-E (Apr 20, 2009)

Pete, Thanks
sweet conversion
great site
very inspiring


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## major (Apr 4, 2008)

Will-E said:


> Hi Major,
> Thanks for such a clear and understandable description of a controller as you posted in reply to Chiques.


Hi Will-E,

You're welcome.



> I have a question regarding the controller and its relationship with the voltage of the motor. I have my eye on a 36/48 volt 12" 200 pound motor from a forklift. Would a 48 volt controller be enough to power a EV comfortably?


Comfortable? Probably. Maybe not to fast.

The motor size sounds like enough for a mid size car. But you may find that with the available controllers limited to 500 amps, that 48 volts will not provide enough power for ya. Meaning limited speed. *P*ower is *V*olts times *A*mps. So the most you can get from that system is P = V * I = 48 * 500 = 24000 watts = 24 kW. Which would get you about 24 hp, roughly. And that is like the maximum not considering any battery sag, which could easily knock you down 30 percent. And that 500 amp rating for the controller is a peak. For steady driving, the current rating may be down to less than 200 amps. Then, P = 48 * 200 = 9.6 kW or about 10 hp. So can a car with a 16 or 17 hp power plant be comfortable for you? And a cruise power of about 10 hp? Not at highway speeds. But it might get you around on surface streets below 35 mph.

This is why most road worthy EVs go to higher voltage batteries. To get more power, you need more voltage, or more current, or both.



> Does a larger controller allow the motor more power?
> Thanks
> Will-E


Yes, up to a point. The system consists of the batteries, controller and motor. Any one can be the power limit. That 200 pound motor will probably take all any controller can throw at it. But the controller can only put out what it can get from the battery.

Regards,

major


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## AlterPower (Sep 5, 2008)

order99 said:


> -until I found this Forum I used to think you were supposed to test battery current with a screwdriver between the posts...


Nice! Thats how we build flashlights up here in the north country!


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## Will-E (Apr 20, 2009)

Ok. My next question is theroretical and maybe stupid all at the same time. Please bare with me....I'm a carpenter.....wood is my medium.
Can I run my Will-E ('46 jeep willy) with my newly aquired 36/48 volt 12" 200 lb Clark forklift motor with a -AXE ALLTRAX Motor Controller 7245- 72 volt controller for "regular back road to the grocery store" type use with an additional "reserve" battery bank that is activated with an additional foot pedal (say.... all the way to the left of the clutch that has a primary "on" switch up on the dash for extra safety....kinda like batman)that will add the additional voltage as wanted/needed (with propper dioding(if that is a real word)) will this allow for the additional voltage needed to produce more power/speed/tourqe. I ask this in my quest for cost savings around the more expensive high voltage controllers. My project has yet to be fully sanctioned by the CFO (The Wife) and all savings possible put me that much closer to completion.
Thanks
Will-E
Aka
Luke


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## ngrimm (Oct 19, 2007)

Will-E said:


> Ok. My next question is theroretical and maybe stupid all at the same time. Please bare with me....I'm a carpenter.....wood is my medium.
> Can I run my Will-E ('46 jeep willy) with my newly aquired 36/48 volt 12" 200 lb Clark forklift motor with a -AXE ALLTRAX Motor Controller 7245- 72 volt controller for "regular back road to the grocery store" type use with an additional "reserve" battery bank that is activated with an additional foot pedal (say.... all the way to the left of the clutch that has a primary "on" switch up on the dash for extra safety....kinda like batman)that will add the additional voltage as wanted/needed (with propper dioding(if that is a real word)) will this allow for the additional voltage needed to produce more power/speed/tourqe. I ask this in my quest for cost savings around the more expensive high voltage controllers. My project has yet to be fully sanctioned by the CFO (The Wife) and all savings possible put me that much closer to completion.
> Thanks
> Will-E
> ...


I think what you are referring to is a bypass contactor like some of the Curtis 120x controllers employ allowing a higher current than normal. Not sure if it is a very efficient solution power wise. Also I don't think they let you switch to a higher voltage though. Possibly by using the bypass, for higher amps (don't think any Alltraxmodels supports that) you could get by with 72 volts resulting in lower rpms by using more of your transmission's gears. Do a search for "bypass contactor" on the evalbum and you'll see what I mean. Good luck. Norm


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## High Tension (Apr 29, 2009)

*Re: What is a controller and why do I need one? And..... *



gottdi said:


> There should be no reason other than timing and good brushes that would prevent you from pumping in 144 volts and 550 or more amps with that big 12" motor. Most motors can handle that kind of power. Just not for hours on end. That is why the forklift is 48 volts. At that voltage it will run full out just about all day long without a hiccup. With high voltage and high amps you are limiting the time at that power level but most of the time you only need a few seconds anyway to get you up to speed. After that you can cruise along just fine. Clean it up and put in new brushes and get the timing just right and get a nice controller that can handle 144 volts and at least 500 amps. More if you can get one. The higher the voltage you use the less amps you will need to cruise along in your ev. I use 72 volts and 550 amps and a 9" GE motor. I can go to 144 or 156 volts if I want. I want! : )
> 
> I will be upgrading soon.
> 
> Pete : )


Hi All. I'm learning fast too from this, thank you. 

Now, I've heard about 'timing'... I can understand the importance of that with an Infernal Combustion Engine. Please can you elucidate regarding timing an electric motor? 

Is it simply a matter of altering the position of the brushes around the armature, and, like ICE engines is this constantly changed somehow according to rpm/load or are the brushes merely advanced or retarded to a fixed point more suited to faster running if e.g. a motor originated from a fork lift? My thanks in advance!


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## Guest (May 9, 2009)

*Re: What is a controller and why do I need one? And..... *

Advancing is for the same reason an ICE is advanced. As the speed increases the mechanical parts can transfer power only so fast. Advancing is used to over come some of the limitations of mechanical parts. Advancing helps the high end but takes some away from the low end. It helps keep arching to a minimum which will burn brushes and commutators if left unchecked. Low speed at high voltage will usually do fine but crank on the juice and you get arching. Advance it and get more speed and less arching. 


Pete : )

That is the best I can explain. I am sure someone else can do that better as they know the proper mechanics of the electric brushed motor at speed.


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