# AC Motor Stupid Question



## rochesterricer (Jan 5, 2011)

The motor isn't the expensive part, the controller is. Especially as volts and amps go up. Tesseract has talked about this several times on here.


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## Sunking (Aug 10, 2009)

OK higher voltage less current should not cost more than low voltage high current units? It is the high current that gets expensive. But I am talking motor cost here. 

Whats a Curtis say 350 amp 144 volt model cost? 200 volt version if available should not be much more if even more. So I don't get that part. 

Are you saying the higher voltage controllers do not exist?


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## rochesterricer (Jan 5, 2011)

I wouldn't say high voltage is cheap, from what others like Tess and Major have said.

The Curtis is a bit of a different animal due to being analog and being subsidized by things like forklift sales. I also think I remember folks saying it is difficult to get higher voltages out of that analog architecture. 

Higher voltage controllers exist, but they aren't cheap.


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## major (Apr 4, 2008)

Sunking said:


> I must be missing something.
> 
> Controllers?
> Mechanical Interface?
> ...


I guess I'm missing something. Why do you think high voltage equipment is less costly? The 350A, 144V Curtis comes out to 50 kW, right? O.K. So that is peak. Industrial drives are rated for overload at 150% to 200%. So price out a NEMA induction motor and VFD with that rating in a 230 VAC package and you're looking at like $8k. On top of that, try putting that industrial package in your cart 

There are special high voltage motors and drives available in power dense packages for spindles and such. Price those out. 

High voltage doesn't make things less costly. The opposite is true in many cases, like with the battery. Dealing with a hundred series cells and associated BMS isn't trivial. Neither is the hazard that comes along with HV.


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## subcooledheatpump (Mar 5, 2012)

To get good power from an industrial motor, you really need to drive it beyond it's rated frequency. 

For example, you could take a standard 10 HP industrial motor rated 60 Hz and 240 volts AC, and drive it at 240 Hz and come up with 40 HP. Only one problem, then you need to come up with 240 X 4 volts or 960 Volts AC. You end up needing a battery voltage of 1357 Volts. The real issue here, a standard low voltage motor doesn't have insulation that can withstand that sort of voltage.


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## Sunking (Aug 10, 2009)

major said:


> I guess I'm missing something. Why do you think high voltage equipment is less costly?


Well that is why I asked, but to answer your question an industrial motor for a given HP, the wiring gauge is smaller and lighter. A 10 HP motor on 48 to 60 volt battery where I am looking takes 150 amps vs 35 amps @ 220.

Secondly higher voltage motors are a much larger market, thus the motors are readily available from many manufactures and lots of competition is all I was driving at. 

I am not knocking the lower voltage motors, I am an EE but I do not specialize in motors and controls other than how it applies to water pumps, fans, and HVAC. Bu tI have tons of experience with battery plants, generators, distribution, emergency power etc as it applies to telecom and solar energy.

I am building a LSV and do not want to use DC motors unless the economics prohibit me from using AC. To get a 1000-lb vehicle up to 35 mph if my calculations are correct is going to take about a 8 to 10 constant HP with 40 peak. Still fuzzy on that one. It can be done with DC series or shunt, but such a motor is around $700 plus another $500 to $600 for the PWM controller. Or around $1200. I will gladly pay up to $2000 to go with AC so I don't have to crawl up hills and get the extra mileage. 

So back to my other threads I need some help with calculations. I contacted two people from this forum who deal with the products but as of yet they have not gotten back with me. So if you are out there and got a minute please advise.


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## major (Apr 4, 2008)

Sunking said:


> Well that is why I asked, but to answer your question an industrial motor for a given HP, the wiring gauge is smaller and lighter. A 10 HP motor on 48 to 60 volt battery where I am looking takes 150 amps vs 35 amps @ 220.


The wiring is a fairly small portion of the system cost.



Sunking said:


> Secondly higher voltage motors are a much larger market, thus the motors are readily available from many manufactures and lots of competition is all I was driving at.


Maybe, but that does not appear to be an overriding factor. The cost of equivalent performance high voltage AC motor drive systems appear to be higher than the low voltage Curtis-HPEVS.

Yes, DC systems are less costly than the AC systems. But it is not the voltage level that causes this discrepancy. It is what it is no matter what the reason.

Call the guys at Thunderstruck Motors. I bet they'd be happy to sell you a system and talk about your application. Note: I have no financial interest or business connection with them, or anyone else. But they have provided excellent service and sales to me.

major


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## Duncan (Dec 8, 2008)

Putting my tuppence worth into this conversation

I think (for what its worth) that DC motors are less expensive because they have been made longer and in larger numbers (for mobile use - forklift and the like)
The machinery is paid for - engineers have had decades squeezing the price

AC - other than stationary mains AC - is new to the game

A


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## Sunking (Aug 10, 2009)

major said:


> Call the guys at Thunderstruck Motors. I bet they'd be happy to sell you a system and talk about your application. Note: I have no financial interest or business connection with them, or anyone else. But they have provided excellent service and sales to me.


THX Major you have never steered me wrong. I am not trying to debate anyone, this is just one area I have never crossed over into before electrically. I know the fundamentals and math, just not the application. Batteries I know up and down, power train lacks.


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## Sunking (Aug 10, 2009)

Duncan said:


> Putting my tuppence worth into this conversation
> 
> I think (for what its worth) that DC motors are less expensive because they have been made longer and in larger numbers (for mobile use - forklift and the like)
> The machinery is paid for - engineers have had decades squeezing the price
> ...


THX Sir. 

I have a friend who is an EE for BNSF. We have chatted a few times on Traction Motors. Up until about 1980 DC motors rained king of rail roads. Not today though as 3-phase AC Induction is taking over as it save railroads big bucks in both energy and mechanically. Energy is a no brainer as AC motors are more efficient and can be finely tuned to the power source of a diesel engine. What suprised me sort of is maintenance cost. AC motors are cheap to build and last longer which I knew. But the big maintenance issue is BRAKES. DC traction motors REGEN fades as the train stops requiring more braking. AC motors REGEN brakes does not fade until the train has almost come to a complete stop. 

From what I can ascertain, 3-phase AC induction motors will take over industrial applications requiring high power. Even mega sized Coal Shovels are switching over.


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## Caps18 (Jun 8, 2008)

The DIY market is more geared towards what companies are selling as kits or 'grouped' components. I didn't do much research into higher voltage because it didn't seem necessary. And Netgain and HPEVS are at the sub 200V range.

The problem for me is with the battery. Getting enough small batteries hooked up to get up to 300+ Volts seems like a challenge. Getting 48 batteries hooked up to get to 130V is enough work as it is.


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## PStechPaul (May 1, 2012)

My own limited experience with EVs (a lawn tractor), and my general knowledge of various motor types, has convinced me that AC is the way to go even for a small vehicle, and certainly for larger ones. I think the reasons for DC motor preference among the DIY community are familiarity, experience, source of inexpensive fork-lift type motors, and simpler, cheaper controllers. I am using three phase AC motors of up to 2 HP and an industrial VFD, and the cost of both (from surplus sources) was less than $150. I have used and plan to develop DC-DC converters so that battery packs of 48 volts or less can provide the 300-600 VDC needed for industrial VFDs and motors, and it should be possible to achieve a 2x power boost by using 120 Hz. Insulation is much cheaper than copper, so there is a cost advantage to higher voltage. So I think I can get a system for about $100/HP, and thus a reasonable passenger EV conversion with 30 HP would cost about $3000 (plus batteries of course). 

High performance AC motors for cars are more expensive because they are specially wound for lower voltage and inverter duty, and the magnetic material of the rotor and stator is more expensive because it must be thinner and more efficient at higher overclocking such as 240-400 Hz. Also the frames and shafts are made for better fit in automobile frames. And the VFDs are specially made for the unique environment of vehicles as well as the special requirements for driving as opposed to most industrial loads. Industrial motors and VFDs are produced in huge volume in a competitive industry which greatly lowers costs, and there are many available as surplus and fixable junk.


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