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Why are DC motor modifications so costly?

17K views 46 replies 11 participants last post by  bjfreeman 
#1 ·
I read an article that Black Currant's siamese 9" motors were 10,000$....

Seeing as 9" Series motors can be found in junkyards for a few hundred dollars each, I am wondering what the other 9,500$ is for...even purchased refurbished/new for EV normal use they can be purchased for 1,600$ each, so 2X = 3,200$...so to siamese the motors and upgrade them further costs...6,700$?? I found a link advertising "Jimpluse9" for ~5000$ in 2008. Did the price really double in 3 years?

I have been searching the web for details as to what exactly is done to the motors to upgrade them for drag racing durability, it seems the "tricks" aren't being discussed very openly, I guess to keep the advantage and the price mark-up with the motor builders...

1: Advanced timing
2: Insulation (liberal nomex paper wrapping)
3: External cooling/blower fan
4: Newer better "Heavy Duty" Brushes
5: Additional Kevlar banding
6: Higher temp wiring
7: Higher rpm bearings
8: Higher voltage terminals
9: Field Weakening
10: Add brushes
 
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#6 · (Edited)
hahaha good point...I don't think that's even possible and definitely not reliably with only 10K$....

Major, everyone knows you know your motor tech...

Is there really some kind of magic that goes into the siamese impulse 9's?

If the cost is really driven by the machining & assembly time/labor to siamese the motors then I will understand that, I am more interested in knowing the specific motor upgrades, bearings, terminals, kevlar, latest brushes, etc (the list above) is that really it?

For example, I know what a dual armature is, I've seen the pictures showing two armatures on a single shaft, each with their commutators on the far ends....


however, I have not been able to find a good picture on the web of a "dual commutator", which Netgain has advertised...can you help describe that to me? Also, how does that help the voltage handling of the motor?

I found this picture but I am not sure it helps much...
 
#9 ·
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.
 
#19 ·
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.
 
#21 · (Edited)
It was inspired by my Z4 conversion.
Maybe you know that K11" 250V only handles 210A continuous at 250V.
This was irritating me a lot so we made this motor that is something like 50-53kW/230V/5600rpm/90Nm continuous. For overload purposes one can use a 250-288V battery so rpm stay high under overload conditions.

I was also unhappy with the standard shaft mounted fans as ventilation was rpm dependent. I.E. if you have 1/3 of nominal rpm, your ventilation is like 3 times weaker. Further the standard fans tend to make lots of whining noise at 4000+ rpm. So we re-introduced the specially shaped back flange that you see on the picture to allow forced air cooling to pump more air through the motor.

As this back flange makes it impossible to use it for mounting, we added machined platforms with threads in the motor case so one can hang the motor on those - there are 4 platforms/8 threads in total.

The motor can also come with an SKF sensor bearing producing 80 pulses per revolution - it is automotive class (used in car ABS systems) and is extremely reliable and maintenance free (unfortunately Soliton/Zilla cannot read it :confused:).
 

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#25 ·
Planetmotor-can you post more info about this motor in its own thread or maybe on this one: http://www.diyelectriccar.com/forums/showthread.php?p=288288&posted=1#post288288

I am really curious about it. Will it handle 1000Amps for any length of time? Do you have the motor performance graphs? Etc...
No performance graphs for the moment as I am still wondering how to market it. I.E. be realistic or adopt the methods of our competition and claim a ridiculous figure like 288-300V :)
 
#40 · (Edited)
I looked At DC motors but could not find one in the 150KW range that was used in the EV world. The DC traction motors faced lot of maintenance, commutation and flash over with other associated problems during operation
Over and above, the DC traction motors have low kW/kg ratio which made the traction drive very uneconomical
I researched more and found three-phase squirrel-cage (induction) AC traction motor on inverter supply made the traction drive most economical with high kW/kg ratio and also reducing the unsprung mass on the axle
Aluminium die cast rotor bars are used since 1930

The greatest advantage of using aluminum alloy rotor bars in the three-phase squirrel-cage A.C. traction motor is high starting and running torque (i.e. more tractive effort), improved starting power factor and weight reduction, thereby reducing the cost of machines and achieving high kW/kg of the traction motor.
There is an increase in starting torque by more than 25% with significant improvement in the torque – slip characteristics, power factor during starting goes up to about 0.75 whereas for conventional induction motors the power factor is in the range of 0.35 to 0.45 during starting.
I also noticed that poles were an important part of determine Torque. The more Poles the more Torque. Adding Poles reduces the RPM for a given frequency this is easily compensated for in the PMW control. Poles are the number of sets of three-way electromagnetic windings that a motor has. Each set of Poles bring make how far the rotor has to move to be under the influence of the next set of poles, hence more torgue
 
#42 ·
The DC traction motors faced lot of maintenance, commutation and flash over with other associated problems during operation
If you abuse them, yes. If you keep within (or at least reasonably close to) specs, no.

There's a few hundred SepEx-powered EVs in Sweden that were imported during the 90's and about half of them are still operational. Most (all?) of the other half were scrapped due to battery and electronic problems (there's been a bit of scavenging to keep as many as possible rolling), don't know of a single one that was scrapped due to motor problems and brush maintenance isn't really a huge maintenance concern as well.

If you, for example, regularly push 1kA through a WarP 9" odds are that something's gonna break eventually, which isn't really surprising considering it's about 4 times the rated current...

Kindly fine tune your opinion to more realistic levels.
 
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