[somanywelps]

Originally Posted by Plamenator

A dual commutator is actually a longer one.
Normally commutators accomodate 8 brushes in 4 rows.
A longer one can take 12 or 16 brushes (still in 4 rows but 4 in a row).

This is done in order to spread the current and in some cases results in lower commutator and brush temperature. It can be done if arcing is a problem or if amps per sq.mm of brush surface were over the norm.

Making it longer has 2 drawbacks:
1) More brushes mean more friction so if arcing/amps were not a problem initially, going to 16 brushes actually heats up the commutator.
2) A longer commutator experiences more centrifugal force and is more prone to exploding.

Actually our K13" DirectDrive was with 16 brushes initially.
We reduced those to 8 and shortened the commutator to achieve higher continuous rpm.
Result was very good.
But this was an interpoled motor to start with so it never had arcing problems.

Does this have anything to do with why your 9" 220V has such a high RPM rating?

[Bowser330]

Originally Posted by Plamenator

A dual commutator is actually a longer one.
Normally commutators accomodate 8 brushes in 4 rows.
A longer one can take 12 or 16 brushes (still in 4 rows but 4 in a row).

This is done in order to spread the current and in some cases results in lower commutator and brush temperature. It can be done if arcing is a problem or if amps per sq.mm of brush surface were over the norm.

Making it longer has 2 drawbacks:
1) More brushes mean more friction so if arcing/amps were not a problem initially, going to 16 brushes actually heats up the commutator.
2) A longer commutator experiences more centrifugal force and is more prone to exploding.

Actually our K13" DirectDrive was with 16 brushes initially.
We reduced those to 8 and shortened the commutator to achieve higher continuous rpm.
Result was very good.
But this was an interpoled motor to start with so it never had arcing problems.

The #2 drawback is sort of a catch-22...the whole point to add the extra comm would be to add more collector bar to brush interaction points to spread the power out so there is less chance for arcing....meaning you can increase the voltage of the motor and thus the rpm of the motor....but the catch is...the extra weight of that added assembly increases the centrifugal forces which can lift the bars and destroy the motor...

I guess i don't see why with the extra comm & brushes the motor couldnt draw full amperage at least up to its redline...Warp9 5500rpm?

[Plamenator]

Originally Posted by somanywelps

Does this have anything to do with why your 9" 220V has such a high RPM rating?

Not really - it can go that high because it is much smaller in diameter than the 10/11" commutators.
Technically, if we make it a 16 brush comm, redline rpm will fall but biggest factor is smaller comm.

[Plamenator]

Originally Posted by Bowser330

I guess i don't see why with the extra comm & brushes the motor couldnt draw full amperage at least up to its redline...Warp9 5500rpm?

I guess only George Hamstra knows
It depends a lot on the commutator construction.
If you do it properly 5500rpm can be continuous rather than peak...or should I say "burst" (Chinese battery producers seem to like that term a lot heheh).

[Bowser330]

Originally Posted by Plamenator

Technically, if we make it a 16 brush comm, redline rpm will fall but biggest factor is smaller comm.

So you are saying that the extra weight of having a longer commutator will cause the motor's "redline rpm" to be decreased due to the additional weight affecting the centrifugal forces and lowering the speed at which the comm. bars may lift and cause armature destruction....is that correct?

http://kostov-motors.com/tractionmot...13directdrive/

The K13 looks like a serious machine!
240V = 4450rpm, what is the redline of this motor with the smaller comm.? 5,500rpm?

What would the redline have dropped too if you have left the longer comm. with 16 brushes?

[somanywelps]

Originally Posted by Plamenator

Not really - it can go that high because it is much smaller in diameter than the 10/11" commutators.
Technically, if we make it a 16 brush comm, redline rpm will fall but biggest factor is smaller comm.

Sorry to bother you, but in another thread you mentioned that the 6800RPM nominal of the 9" 220V was ok, but 8000RPM was an acceptable temporary peak redline. Did I interpret that correctly?

That would involve higher than 220V?

[Plamenator]

Originally Posted by Bowser330

So you are saying that the extra weight of having a longer commutator will cause the motor's "redline rpm" to be decreased due to the additional weight affecting the centrifugal forces and lowering the speed at which the comm. bars may lift and cause armature destruction....is that correct? YES!

The K13 looks like a serious machine!
240V = 4450rpm, what is the redline of this motor with the smaller comm.? 5,500rpm? IT WILL INCREASE A LOT OF COURSE BUT WILL REDUCE MAX AMPS IT CAN HANDLE.

What would the redline have dropped too if you have left the longer comm. with 16 brushes?
NO IDEA - WE HAVE NEVER DONE SUCH TESTS WHICH ARE QUITE COSTLY GIVEN THEIR DESTRUCTIVE NATURE

See my replies in quote above.

[Plamenator]

Originally Posted by somanywelps

Sorry to bother you, but in another thread you mentioned that the 6800RPM nominal of the 9" 220V was ok, but 8000RPM was an acceptable temporary peak redline. Did I interpret that correctly?

That would involve higher than 220V?

Did I not mention 8000 is "unofficial" in that post?
We have only tested 6800.
I suppose 8000 will also hold as peak but cannot back that up by real data

You can have 8000 at 220V if amps are less than nominal.
Motor can operate at 250V as far as commutation is concerned.
Problem is 250V implies nominal rpm that I am not comfortable with.

[somanywelps]

Originally Posted by Plamenator

Did I not mention 8000 is "unofficial" in that post?
We have only tested 6800.
I suppose 8000 will also hold as peak but cannot back that up by real data

You can have 8000 at 220V if amps are less than nominal.
Motor can operate at 250V as far as commutation is concerned.
Problem is 250V implies nominal rpm that I am not comfortable with.

Understood, my car is nothing more than a parts list at this point

Primary objective is to make sure I don't wind up blowing up something.

[Bowser330]

Plamenator, can you please give us more information of the K11 Alpha?