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Hi Dink,Why do some motors have a small and others large wire for winding size(dia), and a high or low number of comutator segments? Second what does the number of winding segments mean? High v/s low.

The basic parameter (for the armature) is the number of series turns per pole which then determines the voltage speed relationship for a given magnetic flux per pole. One must also know the armature winding pattern to know the number of parallel circuits.

For a given flux and speed, the more turns, the higher the generated voltage. For a motor running on a fixed voltage, this means the more turns, the slower it turns. But also, the more turns, the higher the torque for a given current.

There is a finite space in the armature for the wire (turns), so when you increase the number of turns, you have to make the wire smaller. And the smaller the wire and the higher the turns, the higher the resistance, and lower the current capability.

So, few turns, large wire, high speed, high current. Many turns, small wire, low speed, low current.

The number of commutator segments (or bars) is chosen by the designer with various considerations, voltage being a primary factor relating to acceptable level of sparking. Often the number of comm bars is set equal to the number of slots in the laminated armature core. How that choice is determined gets into the magnetic structure and manufacturing process and cost benefit analysis which I think is beyond discussion.

Generally speaking, higher voltage motors have higher comm bar counts.

I hope that addressed your questions.

major

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1,626 Posts

But I'm interested to know one more thing about DC serie motor.

At a fix given current, maybe 1000A, what determines the capacity of a motor to sustain his max torque over the increasing rpm?

I read someting about resitivity of motor in ohm (mΩ) vs voltage given to the motor vs voltage produce by the motor, but it's not clear for me.

Also, the number of commutator segments can play a role?

Can you explain please.

I need to understand why a motor compare to another one fo the same voltage and the same Amp lose his max torque before the second.

Bellow, an exemple of torque lost at high rpm!

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406 Posts

But I'm interested to know one more thing about DC serie motor.

At a fix given current, maybe 1000A, what determines the capacity of a motor to sustain his max torque over the increasing rpm?

I read someting about resitivity of motor in ohm (mΩ) vs voltage given to the motor vs voltage produce by the motor, but it's not clear for me.

Also, the number of commutator segments can play a role?

Can you explain please.

I need to understand why a motor compare to another one fo the same voltage and the same Amp lose his max torque before the second.

Bellow, an exemple of torque lost at high rpm!

This is sort of two questions here..The ability for ANY motor to sustain a certain torque is a function of how much current it can withstand with out burning up! This has to do with the wiring and how thick the gauge the windings are. also the mass of the motor in its ability to disibate heat. Bigger motor usually can sustain larger torques due to Bigger and heavier winding and more mass for the Heat to go. Larger motors also tend to be more effecient too.

Now If your asking what does it take for a Series or SepEx to sustain torque in an increased RPM that has to do wit the Voltage accross it. The higher voltage with the same 1000 amps will run at a higher RPM. this is a linear realtionship for the most part.

Here is something to think about for given motor:

Volts equates to RPM

and

Amps equates to Torque.

Volts X Amps equals Watts

Torque X RPM/5252 equals Horse Power

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4,838 Posts

Just out of interest, what units are you using for torque in the last line, GT?Here is something to think about for given motor:

Volts equates to RPM

and

Amps equates to Torque.

Volts X Amps equals Watts

Torque X RPM/5252 equals Horse Power

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1,626 Posts

You need to use Feet-lbs!Just out of interest, what units are you using for torque in the last line, GT?

240 ft-lbs x 2500 rpm / 5252 = 114 hp

A torque-speed curve like the one you show depends on both the motor and controller, as has been discussed here in the usual congenial manner with regard to AC versus DC motors. For a series DC motor that "flat" part of the curve to the left is where the controller can put out enough voltage to push it's max current through the motor, which gives max torque. The fall off to the right is where the current through the armature is decreasing due to back emf of the motor increasing with speed. Back emf is also of course increasing with speed at the lower rpms to the left, but the controller can increase voltage to compensate (limited by battery pack voltage). If you want to extend the flat part out to higher speed, you need a higher voltage controller and/or a higher voltage battery pack that will give the same max current. More max torque requires higher max current.I need to understand why a motor compare to another one fo the same voltage and the same Amp lose his max torque before the second.

Bellow, an exemple of torque lost at high rpm!

Maybe major can add details on how motor design affects this.

Nice explanation on motor armatures major!

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7,791 Posts

Hi Yab,But I'm interested to know one more thing about DC serie motor.

At a fix given current, maybe 1000A, what determines the capacity of a motor to sustain his max torque over the increasing rpm?

At a fixed given current, the series motor will always have the same torque. Torque = Kt * Ia * Flux. Kt is a machine constant and is proportional to the number or turns in the armature.

In your plot, the torque is constant at 240 lb.ft. from 0 to 2500 RPM. This is obviously at the current limit of the controller, a constant current value. So, in the equation, Ia is constant, and Flux is constant, so the torque is constant.

Above 2500 RPM the torque falls off because the current decreases. And for a series motor, as Ia decreases, so does the Flux. Ia = (Vm - Eg) / Req. Vm = applied motor voltage, Eg = generated voltage in the armature, and Req is the equivalent series resistance of the motor.

Eg = Kt * Rad/s * Flux. Kt is the same constant as in the torque equation, numerically if metric units are used.

If you wrap your head around all these equations at the same time, you will see that as the motor speed increases, Eg increases, and unless Vm can increase, Ia will decrease and hence torque will decrease.

It is the resistance of the motor. And for these EV motors, is in the milliohm range. I tried to show how that plays into it with Req in the equations.I read someting about resitivity of motor in ohm (mΩ) vs voltage given to the motor vs voltage produce by the motor, but it's not clear for me.

For these EV motors (series wound and capable of 1000A), they have bar wound armatures instead of round wire wound armatures. Meaning that the armature conductors are rectangular copper ribbon. This makes for a robust motor having the conductor brazed or welded to the commutator segment, low resistance winding and mechanically secure assembly. In most cases, these bar wound armatures have a single turn coil and the number of armature coils equal to the number of commutator segments (bars).Also, the number of commutator segments can play a role?

So the armature constant, Kt, relates directly to the number of comm bars. This is generally true for the EV suitable motors you will encounter, but there are some winding tricks occasionally used which make that statement not universal

Hope that confused everyone

major

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4,838 Posts

Thanks Yabert.You need to use Feet-lbs!

240 ft-lbs x 2500 rpm / 5252 = 114 hp

I did a very quick mental calc while in classes today (ok shouldn't have been on here while studying ) and the numbers, using ft-lbs seemed bigger then I expected. That's a good thing, right?

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1,626 Posts

If I understand correctly , for the same voltage, the same current and same quantity of bar in the armature, a motor with less resitivity will be capable to sustain his max torque to a higher RPM.

So, because the the copper has a very little resistivity, the most resistive part of a serie DC motor is probably the brush and the brush contact area on collector.

If it is true, a motor with very large brush can tolerate more current and can also give his max torque at higher RPM. And in this case, with same controller, a bigger motor can probably give his max torque at higher rpm than a comparable smaller motor. (Example: Warp 11" vs Warp 9")

Am I right?

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7,791 Posts

I think you are placing too much concern on resistance (not resistivity, which is a property of copper). Motors of same size and basic design (comm bar count) will have resistance near enough not to make appreciable difference.If I understand correctly , for the same voltage, the same current and same quantity of bar in the armature, a motor with less resitivity will be capable to sustain his max torque to a higher RPM.

Yes, this does play a part in it and for simplification I just included this in the _Req_ for those equations. However, when doing detailed motor calculations, the brush drop (Voltage drop including brush and surface contact) is considered separately because it is a nonlinear function of current and surface speed. It is also dependent on the temperature, brush material, spring force, seating, humidity and sunspot activity.So, because the the copper has a very little resistivity, the most resistive part of a serie DC motor is probably the brush and the brush contact area on collector.

If it is true, a motor with very large brush can tolerate more current and can also give his max torque at higher RPM.

Generally speaking, the larger the total cross sectional area of the brushes, the higher current capability. At higher currents, like 1000 A, this might account for a volt or two difference between one motor to another of similar size. So in a hundred volt system, will mean little as to being able to carry maximum torque to high speed.

Not necessarily. Larger motors generally produce more torque. But generally run slower. And may not have higher power rating. There are just too many variables. It is unlikely you can find two motors of different sizes with all other design features similar to even make a comparison. You could do analytically, but I'm not up to it tonightAnd in this case, with same controller, a bigger motor can probably give his max torque at higher rpm than a comparable smaller motor. (Example: Warp 11" vs Warp 9")

For example, I think the Warp9 and Warp11 have the same size and number of brushes. The W11 would have a larger comm and therefore likely a slight advantage in short time base current overload capability. Other difference is, I think, the W9 has 49 slots and bars and the W11 has 25 slots and 75 bars. So the W11 has a higher Kt. Even though the W11 is larger diameter, I think the W9 has a longer core. But the W11 has a higher flux at saturation.

Some speculation on my part there. I have never seen the Warp11 up close and personal. I have seen the W9, but not used it much.

If your goal is to take the torque at current limit higher in motor RPM, increase battery voltage. And figure out a way not to zorch it

major

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1,626 Posts

After all this learning (thanks), I have more ability to seach a powerfull forklift motor for an street EV aplication.

And after all this explanation I realise the best forklift motor for high torque at high rpm for a 1000A/156v configuration was the GE 11" motor I found few weeks ago.

Large diameter for high torque, large brush for high current and 49 big cumm bars for sustain high torque at high rpm.......

Unfortunately, it need new flange on both side and it's lot of money in material and machining.

So, one more time, thanks Major.... this thread can probably help many other guys to find the best forklift motor for street EV.

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4,838 Posts

Which bit confuses you?I have been reviewing this post and previous ones I have posted,and need some help understanding. I understand what the commutator is and it's segments, but the windings confuse me.

The armature has comm segments that are connected to copper windings that are on the core of the armature. If you take out an armature you can trace the route of the thick copper conductors on it.

As the armaure rotates the brushes contact certain segments of the comm causing a magnetic field to form in the energised coils.

The frame of the motor houses, typically, four big coils of copper conductors. These are the field windings. They are energised constantly when the motor is running and provide a magnetic field that is fixed in location to the frame.

The magnetic field in the armature is attempting to align with the field windings but because they are not physically aligned the force generated 'pulls' the armature around. However, as the armature is pulled around to align with the field windings the brushes then begin to break contact with that armature winding and moves to make a connection to the next one. And so the process begins again and the armature is pulled around further.

In a series motor the copper conductors used in the armature and the field windings are very big and have few turns. This allows the same amount of current to be carried by both the fields and the armature windings.

With a shunt motor the field coils are made up of many more turns of much thinner conductors as they don't have to carry the current that passes through the armature. They are wired in parallel to the armature.

Anything more complex will need to be answered by those more knowledgable then me (they will probably correct any errors in my post too).

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7,791 Posts

Hi Dink,I have been reviewing this post and previous ones I have posted,and need some help understanding. I understand what the commutator is and it's segments, but the windings confuse me.

The commutator (which is made of segments or bars) only conducts current from the stationary world to the rotating armature and switches that current in direction at the appropriate time and position. The commutator actually adds nothing to torque or power production in the motor, and in fact loses torque and power in friction and voltage drop.

The windings in the armature are what do the work. More specifically, the portion of the winding in the steel core (magnetic path). The windings are the coils and are connected to the commutator, each end of the coil to a comm segment or bar. The armature coils (windings) can be loops (turns) of round wire inserted into slots in the steel core of armature, or, as in the picture above, can be single turns (called hairpins) of copper rectangular conductors (sometimes also called bars) inserted into the armature core slots.

Hope that helps,

major

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406 Posts

After all this learning (thanks), I have more ability to seach a powerfull forklift motor for an street EV aplication.

And after all this explanation I realise the best forklift motor for high torque at high rpm for a 1000A/156v configuration was the GE 11" motor I found few weeks ago.

Large diameter for high torque, large brush for high current and 49 big cumm bars for sustain high torque at high rpm.......

Unfortunately, it need new flange on both side and it's lot of money in material and machining.

So, one more time, thanks Major.... this thread can probably help many other guys to find the best forklift motor for street EV.

This last photo, is the GE 11 that I have. I SWARE it looks EVERY bit the same as a WARP 11 motor.. they both have the SAME internal specs too..

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.. they both have the SAME internal specs too..

Not exactly.............

GE 11": 49 bars and 4 big brush (4 poles).

Warp11: 25 bars and 8 brush (4 poles).

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7,791 Posts

I suspect it has 25 slots with a 49 bar comm. 2 coils per slot.Not exactly.............

GE 11": 49 bars and 4 big brush (4 poles).

Warp11: 25 bars and 8 brush (4 poles).

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406 Posts

The GE 11" does infact have 8 brushes two per pole...at least mine does...Not exactly.............

GE 11": 49 bars and 4 big brush (4 poles).

Warp11: 25 bars and 8 brush (4 poles).

I was told that the Warp 11 had 49 bars as well who told you it only had 25?

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