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Principles of DC electric controllers, and the use on GTs


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#1 wvbuzzmaster OFFLINE  

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Posted March 19, 2011 - 05:16 AM

Ok, as some of you may know I have done at least one electric conversion and working on another (still). Well, I have finally done so other tests to better understand controllers and motors for the current project, using the Electric Springfield (first conversion) as the test subject. Turns out I was wrong about what a controller does to vary the motor speed, because using the multimeter on the motor leads from the controller it immediately reads 24v (system voltage) however the motor speed still varies. This means that it is amps that vary, and some controllers have modified electric signals to make it more interesting, but the simple ones (and I will confirm this) vary the amps, contrary to my original belief, of volts. This is important for any electric conversion theory.

Most controller manufacturers say to go triple the motor's amp rating on the controller's amp rating, but I believe for our needs the controller's amp rating should be fine matching the motor's amp rating, if not slightly higher for simple sakes. The reason I believe this is because if you go with high amps and you use a plow and it requires more amps than the motor is rated for and your controller can deliver, you could prematurely burn out your motor. Using a golf cart in your theory is not the right move unless you plan to use the entire golf cart system.

There is a lot more information in this that should be added and or confirmed, however, I have yet to learn it all myself, and if anyone can add to any of what I have said so far, go for it, just as long as you confirm your information first. Doug, I know you will read this and I hope you can add some of your experience and knowledge from the Massey and the Sears to the information bank of this thread. I hope with this thread to create a basic guide for selection of parts for anyone interested in converting a GT to electric. Proven applications are good starting points.
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#2 DH1 ONLINE  

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Posted March 19, 2011 - 03:26 PM

Well I'm no real expert on EVs, motors and controllers but I'll tell you what I know.
Controllers for Permanent magnet and series wound DC motors work on the principle of "pulse width modulation" to vary the speed or power of the motor. Think of a switch being turned on+off many many times a second. If the switch is on 25% of the time and off 75% of the time then only 25% power is being delivered to the motor. They use Mos-fets inside the controller to do this, turn them on and off thousands of times a second, the more mos-fets the more power it can deliver.
The output voltage stays the same but the power or amps changes just like Casey says.
There are many different kinds of motors, some DC motors use field weakening to change there RPMs how that works??? There are also AC motors, 3 phase motors and again how those controllers for those motors work???
DC motors, series wound motors produce maximum torque at 0 rpm where the AC motors are more like a gas engine, they have a power band.

My electric Sears is basically a battery pack, motor and a switch, a 12 volt starter/generator that is fed 24volts, the motor gets hot and I'm sure that a full charged battery pack could cook it with continuous non stop running before the batteries died.
My Electric Massey is a 36 volt motor, 36 volt battery pack and a 36 volt 200amp controller, it works great.

Sizing the controller to the motor, this is what I did.
The motor has 45amp continuous and 275amp peak ratings.
The controller has 80amp continuous and 200amp peak ratings.
I was under the impression that the controller should be double the amp rating of the motor, but which amp rating do you double?
I doubled the continuous rating, my reasons were that even thou the controller can't deliver the max amps the motor can draw it will still deliver almost double the continuous rating of the motor, if you do that for a long enough period of time you will damage the motor.
The 500amp controller almost doubles the 275 rating and it delivers 200amp continuous, yes I would have more power but more stress on the motor. Also something to consider is how long the battery pack can deliver high amps for.
As it stands now with the 200amp controller, if I drive up to a wall, put the trany in 4th, top gear, mat the pedal, full power the wheels sit there and spin, if the belt doesn't slip. I got to try this with my gas powered Massey's some day.

Anybody sees where I'm wrong or knows more please say, I'd like to know more about this stuff.
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#3 wvbuzzmaster OFFLINE  

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Posted March 19, 2011 - 05:08 PM

Doug, I messaged Kelly Controls, LLC a while back about controller sizing and they told me that the controller peak current (amps) should be about triple the rated amps of the motor, so I would assume the continuous load in your case. However, as you know controllers are sized in certain current intervals in which you have to choose from, therefore I believe you picked the best of both worlds on your controller, above and below. Your motor was actually a golf cart motor if I remember right, therefore you could have gotten away with a stock sized golf cart controller which most are rated at 275 amps stock. Personally, I aim for the continuous amp rating of the motor (Springfield has 34 amp motor, 40 amp controller), because the difference between a golf cart and a tractor is abuse level, and golf carts get more abuse, tractors get the use. Therefore the tractor is more often seeing continuous strains; rather than a golf cart which sees bursts of hard on the throttle, and then off. This does not mean golf cart motors are bad for conversions, but I have found that 90% of golf cart motors have no front support bearing, and an internal splined shaft, due to design. I know you (Doug) are having that issue right now.

I have found great motor sources can be floor scrubbers which are 36 volt and usually have 3/4 or 1 hp gear motors on the brushes. There are also larger models of floor scrubbers including ride on which do have larger drive motors (usually not reduction drive motors). Some industrial equipment has AC to DC converting controllers to run DC motors and can be good sources for motors. Usually you can get away with running higher volt DC motors on lower volts (DC), they just run slower and you may not get to see the full potential of the motor due to the volts going down, the amp requirement to match the power will go up. Here are the equations and conversions you will normally need in a conversion when shopping for motors and sometimes deciding wire size (sometimes).

Volts X Amps = Watts
Watts / Volts = Amps
Watts / Amps = Volts
1 HP = 746 Watts

I hope this thread will grow into a powerful knowledge base for those considering, or in the middle of their electric conversion project.

#4 ducky OFFLINE  

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Posted March 19, 2011 - 06:16 PM

Just to clear things out here a little guys.
1. Motor speed varies by the voltage supplied.
On a series wound motor measure the voltage drop across the field and armature as they are series. As the motor speed up you will see the the voltage drop increase to near battery volts appox 95% (SCR Controlled system) then a contactor (aka 1A) is closed to bypass the controller and full battery volts are supplied to the motor. As the load is increased the amperage will rise to a point were the control card will drop out the 1A contactor to prevent motor damage and amperage control is returned to the controller and it has the ability to limit the amperage to prevent motor damage. This is programmed into the controller depending on the motor it is driving.
2. Motor torque is relative to amps, as the motor is loaded speed slows and amperage increases to pull the added load.

Doug to address your question on "Field Weakening" it is used to speed up the motor under low load condition to increase travel speed. There is an addition contactor and resistor in the system. The contactor is "NC" (Normally Closed) during normal operation. When the amperage level and/or time are met that is programmed the to the controller this contactor will open and the field current is then routed though the resistor and the motor will speed up. you should not employ field weakening when there is not a load on the motor. i.e. wheels jacked up. The motor will overspend to the point centrifugal force will cause the armature to destroy it self.

You have probably heard of "Regenerative Braking" when exploring this subject. It is used to slow an EV vehicle when the accelerator in released. It consists of another contactor and a diode that basically turn the more into a generator and returns this energy to the battery. Let me know if you want more on "Regen" and I can put more out on that. It is not of much use except in an automotive application where you would have to amount of decel that would return any amount of current to the battery to be beneficial.

I'll and some info on SEM "Separately Excited Motor) and AC technology if you would like. Let me know.

George, I also would like to get some EV Info and Training manuals uploaded. Could you add an EV Conversation manual section?

Edited by ducky, March 19, 2011 - 06:35 PM.
Typo

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#5 wvbuzzmaster OFFLINE  

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Posted March 19, 2011 - 06:29 PM

Ducky, that is good information, have to ask though, is that "NO (Normally Closed) a misprint?
Also the manual section might be nice, and those that have done conversions can draw our wiring schematics for others to see, and help them in their efforts.

#6 ducky OFFLINE  

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Posted March 19, 2011 - 06:34 PM

Ducky, that is good information, have to ask though, is that "NO (Normally Closed) a misprint?
Also the manual section might be nice, and those that have done conversions can draw our wiring schematics for others to see, and help them in their efforts.


Thanks you are on the ball.
Yes (NC) I will go back and edit.

#7 caseguy OFFLINE  

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Posted March 19, 2011 - 06:56 PM

...There are many different kinds of motors, some DC motors use field weakening to change there RPMs how that works???


Field weakening is only used to allow a DC motor to go beyond it's "base speed". Base speed is the normal operating top speed (the speed that is on the nameplate) when the armature voltage is at it's rated peak and the field current is also at it's rated peak. If you lower the armature voltage while the field current is at rated peak, the motor slows down. if you lower the field current while the armature voltage remains at rated peak the motor will spin fasted than it's base speed, but the torque also decreases proportionally as the speed increases above base speed. In the "normal" operating range of motor speeds, the speed is varied by changing the armature voltage.

There are also AC motors, 3 phase motors and again how those controllers for those motors work???


AC, both single phase and 3 phase motor controllers (also called variable frequency drives or VFD's) vary the speed of the motor using pulse width modulation (PWM). As you may already know, AC current is generated in a sine wave. VFD's use DC current and modulate the pulse width to create a varying voltage level. The result is an "artificial" sine wave. The speed at which the modulation happens can be changed to "simulate" AC sine waves of different frequencies. The generated RPM's of an AC motor are governed by the frequency of the input current, so when the frequency is varied the resulting output RPM's of the motor vary proportionally.
If you want a more in depth explanation Click Here
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#8 ducky OFFLINE  

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Posted March 19, 2011 - 07:11 PM

Field weakening is only used to allow a DC motor to go beyond it's "base speed". Base speed is the normal operating top speed (the speed that is on the nameplate) when the armature voltage is at it's rated peak and the field current is also at it's rated peak. If you lower the armature voltage while the field current is at rated peak, the motor slows down. if you lower the field current while the armature voltage remains at rated peak the motor will spin fasted than it's base speed, but the torque also decreases proportionally as the speed increases above base speed. In the "normal" operating range of motor speeds, the speed is varied by changing the armature voltage.



AC, both single phase and 3 phase motor controllers (also called variable frequency drives or VFD's) vary the speed of the motor using pulse width modulation (PWM). As you may already know, AC current is generated in a sine wave. VFD's use DC current and modulate the pulse width to create a varying voltage level. The result is an "artificial" sine wave. The speed at which the modulation happens can be changed to "simulate" AC sine waves of different frequencies. The generated RPM's of an AC motor are governed by the frequency of the input current, so when the frequency is varied the resulting output RPM's of the motor vary proportionally.
If you want a more in depth explanation Click Here


You got it Case guy. Much more detailed explanation.

Thanks

#9 DH1 ONLINE  

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Posted March 19, 2011 - 07:25 PM

Just to clear things out here a little guys.
1. Motor speed varies by the voltage supplied.
On a series wound motor measure the voltage drop across the field and armature as they are series. As the motor speed up you will see the the voltage drop increase to near battery volts appox 95% (SCR Controlled system) then a contactor (aka 1A) is closed to bypass the controller and full battery volts are supplied to the motor. As the load is increased the amperage will rise to a point were the control card will drop out the 1A contactor to prevent motor damage and amperage control is returned to the controller and it has the ability to limit the amperage to prevent motor damage. This is programmed into the controller depending on the motor it is driving.
2. Motor torque is relative to amps, as the motor is loaded speed slows and amperage increases to pull the added load.

Doug to address your question on "Field Weakening" it is used to speed up the motor under low load condition to increase travel speed. There is an addition contactor and resistor in the system. The contactor is "NC" (Normally Closed) during normal operation. When the amperage level and/or time are met that is programmed the to the controller this contactor will open and the field current is then routed though the resistor and the motor will speed up. you should not employ field weakening when there is not a load on the motor. i.e. wheels jacked up. The motor will overspend to the point centrifugal force will cause the armature to destroy it self.


Thanks Ducky and I've heard that before, the only way the electric sears works is by doubling the motors voltage which gave it more speed and amps so it could move itself along.

The best source for info and examples of what other people have done is
>EV Photo Album: Our Electric Cars on the Web

If I was going to do another EV conversion with or without a controller I would go for this motor
>ME1004
It has a 1" shaft similar to what you find on a vert or horiz shaft gas engine.
Has a 48volt 200amp continuous rating 12.9hp and a 400amp peak rating 25.7hp.
Enough power to move the tractor and drive a mower deck. It has being used many times without a controller to do this with gear and hydro tractors. Something to consider at least.

If you look at GE Elec-Trak E20, I5 or New Idea EGT200 you will find they use a contactor type controller.
3 steps resistive different amounts
1 step direct connection motor to battery pack
3 steps of field weakening

Max power or torque was with direct connection no field weakening and max speed was the last step of field weakening. I wonder how many people thought max power was with the pedal all the way down when really it was 1/2 way down.

Edited by DH1, March 19, 2011 - 10:39 PM.
spelling


#10 ducky OFFLINE  

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Posted March 19, 2011 - 10:29 PM

Interesting Doug.
I have never ran across F/W on the contactor/resistor systems. I am pretty much talking about the forklift industry. It should work as you explained with another contactor and resistor. I guess we never needed that on our Class II & III lift trucks. What our manufacturer did was use 1A for the high speed.
Our resistive drive were designed to be cost effective for the consumer. With the introduction of more refined (more battery life) systems such as the Curtis controller we were able to do all this with out contactor and be able to give the motor just the amount of power it would need at any operating condition.

By the way Nice motor. I tend to scourge and have a nice collection for future projects. The problem I will have is getting the power off the shaft as they vary widely from short to splined shafts.

#11 DH1 ONLINE  

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Posted March 19, 2011 - 10:38 PM

When it comes to electric motors and control systems for them there are so many different kinds and ways to do it, at least that's what I find.
Curtis makes a controller and pot box just for the Elec-Traks but how they do it, the field weakening part???. It's suppose to be a more efficient setup that gives more run time by eliminating the loses of the resistors.

#12 ducky OFFLINE  

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Posted March 19, 2011 - 10:47 PM

When it comes to electric motors and control systems for them there are so many different kinds and ways to do it, at least that's what I find.
Curtis makes a controller and pot box just for the Elec-Traks but how they do it, the field weakening part???. It's suppose to be a more efficient setup that gives more run time by eliminating the loses of the resistors.

Yes Doug
With the advent of solid state we have made some really big advances in EV.
I also have saved a few Curtis, GE and Danaher controllers from the junk man as well.
Now I just need to find the time and live long enough to get all this done.

#13 DH1 ONLINE  

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Posted March 20, 2011 - 08:37 AM

Yes Doug
With the advent of solid state we have made some really big advances in EV.
I also have saved a few Curtis, GE and Danaher controllers from the junk man as well.
Now I just need to find the time and live long enough to get all this done.


Well judging by what I see on the 4855 project of yours if you do make an EV it's really going to be something.
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#14 ducky OFFLINE  

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Posted March 20, 2011 - 09:47 AM

Thanks Doug
Glad you like the 4855.




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