Hi Dink,

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

 

Yes it does. I may have some more later. I need to process this first. So it all comes down to building the strongest magnetic field you can at a given speed or rpm range? Kind of like the camshaft in an ICE building cylinder pressure?

 

I like your answer Major. It's realy clear!

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

 

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!

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.

Maybe major can add details on how motor design affects this.
Nice explanation on motor armatures major!

 

It's always a pleasure to read your great explanation Major


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?

 

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.

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.

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.

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.

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.

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")

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 tonight

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

 

It seem you are right Major! (see picture). Maybe it's more 25 slots and 50 bars.

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..

 

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.

 

Which bit confuses you?

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).

 

yabert i think I see from your photos...you have the one piece brush design i was told by the people at warfeild to MAKE SURE that this was upgraded to the 2 piece brush design...this would then be like the WARP 11.

 

Is it a big disavantage to have one big brush hold with two spring compare at 2 brush with one spring on each?
I assume the same area of brush contact (2x1 = 1x2).

 

Major,
how do you have an armature design that has a different number of Commutator bars and a different number of armature slots?
How does this work?

what advatages does this have over the same number bars and same number slots? like 49 and 49 in the GE 11?

 

Major,
how do you have an armature design that has a different number of Commutator bars and a different number of armature slots?
How does this work?

2 coils per slot. 1 coil per comm bar. 25 slots * 2 coils/slot = 50 coils. Minus one dead (unconnected) coil = 49 coils for 49 comm bars. Dead coil keeps spacing and balance. Odd number of comm bars needed for 4 pole wave armature winding.

I had thought (never having seen one) that it was 25 slots and 75 bars, using 3 coils/slot. I think GE also makes an 11 incher using 65 slots and bars. And maybe other designs as well.

what advatages does this have over the same number bars and same number slots? like 49 and 49 in the GE 11?

Some pros and cons for each way. Existing tooling plays a big part in the choice. For high volume production, equal bars and slots are probably best, for both design and process.

major

 

You can see.....

Warp 11 have 25 slot in armature, but 49 bar comm.

I would like to know the difference rpm and torque of each motor at same voltage and current!..

 

You can see.....

Warp 11 have 25 slot in armature, but 49 bar comm.

I would like to know the difference rpm and torque of each motor at same voltage and current!..

Hi Yab,

So both motors have 49 bar comms. They both use single turn armature coils and wave winding. So they would have equal Kt values for those equations in my post #9.

But, both the speed and torque equations include the term _Flux_. And we do not know the Flux values for these motors, so it is impossible to draw an accurate comparison of performance from the information at hand.

Both motors use steel although we do not know the exact type. But we could assume that the saturated (maximum) flux density would be the same. To get a ballpark comparison, measure the steel armature core diameter and stack length. From this, calculate the cylindrical surface area. For a comparative ratio between the two, just use ratio of D*L, one to the other. The larger D*L will have more Flux at saturation, meaning more torque/amp on overload.

Back down at non-overload conditions, it is much harder to draw such conclusions. The field coils turns (mmf) come into play and a host of other design features like air gap length (distance between pole face and armature surface), pole pitch, etc.

Gross estimation: Same comm bar count, same size = about the same speed torque current voltage relationships.

Regards,

major

 

In a recent AC vs DC motor thread Daniël posted up about the motors used in his awesome boat project, and Paul was able to pull up some of his photos.

That got me curious to see and read the rest of the boat thread and from there i found that Major had identified the motors as having 2 Turns per coil, and that he had actually invented and made a small fortune on this multi-layer winding back in 1979, see post here.

Now i'm curious about these winding--was there a patent on the multi-turn winding, i would be interested to read it and probably others would too.

 

Small fortune = $1.00

https://patents.google.com/patent/US4270065A/en?inventor=Jeffrey+Major&oq=Jeffrey+Major