# Mythbusters: Higher voltage motor = more powerful motor



## meanderingthemaze (Jan 25, 2010)

I guess this question is part theoretical, part practical. Can anyone explain what the limiting factor is in the power any given motor can produce?

Looking at the basic P=IR statement, I suppose with the same current flowing, higher voltage would produce more power. 

But then there's the practical side. How much power can you get out of a certain voltage on a motor? And what would be the design considerations to maximize power in a motor at a fixed voltage?

The reason this question came up is that I'm doing an pickup AC conversion and so there are only so many options out there. Azure Dynamics small AC motor ~156V is not powerful enough (I hear), so most people would recommend the higher ~320V motor. Recently I just heard about High Performance Golf Carts who makes a 96V AC motor that is more powerful than AD's ~156V motor. And it's much cheaper!

So can anyone help me understand this? This is probably just Electric Motor 101.


----------



## Georgia Tech (Dec 5, 2008)

meanderingthemaze said:


> I guess this question is part theoretical, part practical. Can anyone explain what the limiting factor is in the power any given motor can produce?


Well the biggest thing is the the amount of power you supply it! Namely the batteries and the controller...yes the Motor DOES have I^2 R losses that play but they are not as much a factor as the first 2.



meanderingthemaze said:


> Looking at the basic P=IR statement, I suppose with the same current flowing, higher voltage would produce more power.


No it is I squared R that equals power but that is really Heat related loss. Power in the motor is really (Voltage * amps) - I^2 R


meanderingthemaze said:


> But then there's the practical side. How much power can you get out of a certain voltage on a motor? And what would be the design considerations to maximize power in a motor at a fixed voltage?


Well the highest Brushed motor is about 350 volts and that a motor sepcially built to go this high...Like it having interpoles. High current motors Have big Brushes wires and Coils with Thick wires. 
There is alot that goes into having a high perfomance motor...Do you want a High RPM motor? High Torque? 


meanderingthemaze said:


> The reason this question came up is that I'm doing an pickup AC conversion and so there are only so many options out there. Azure Dynamics small AC motor ~156V is not powerful enough (I hear), so most people would recommend the higher ~320V motor. Recently I just heard about High Performance Golf Carts who makes a 96V AC motor that is more powerful than AD's ~156V motor. And it's much cheaper!
> 
> 
> So can anyone help me understand this? This is probably just Electric Motor 101.


The basic rules apply for AC motors also, but there might be other details that are specific to AC motors...for one AC motors RPM is not totaly based on voltage alone but Phase frequency as well....any way if the AC 96 volt motor SYSTM has more power than It pull more current..


----------



## meanderingthemaze (Jan 25, 2010)

D'oh

I meant to say P = I*V. Don't know where my brain was.

So, I guess my major question is whether the operating voltage of an (AC) motor necessarily correlates to the max practical power of the motor. (By power I mean the ability to do more work, where more power means you can do more work, heavier lifting, faster acceleration, better climbing speeds, etc.) 

Or is it just a coincidence that most higher power motors are also higher voltage?

Is my question too general or broad to have a specific answer? 

This seems like the very first question one must consider when planning a conversion. What power requirements must I have to get 0-60 in 10 secs, or climb those big hills on my street, or just to keep up with traffic in a metropolitan city, etc. But everywhere you look you see conjecture and projecture(I think I made that one up). It's hard to get a straight answer. Of course once I do the conversion I can share the empirical data on my application, but it's a lot of money to gamble on. Do you just trust the HP charts of the manufacturer? 

If so, how much HP would you need to move a 3000lb vehicle at 70mph, and to accelerate 0-60 in 10secs, or climb a 10% grade.

Thanks for the reply.


----------



## gor (Nov 25, 2009)

meanderingthemaze said:


> D'oh
> 
> ....
> 
> ...


you can do some exercising and find it out:
http://buggies.builtforfun.co.uk/Calculator/index-imperial.html

or make a bit of search and find answers on most of your Qs


----------



## rmay635703 (Oct 23, 2008)

meanderingthemaze said:


> I guess this question is part theoretical, part practical. Can anyone explain what the limiting factor is in the power any given motor can produce?
> So can anyone help me understand this? This is probably just Electric Motor 101.


Generally voltage aside the amount of power a motor can generate is mainly dependant on its weight, more copper = bigger heatsync.

It is possible to have a very small motor generate a high level of power but the smaller it is the less time it will do so before damage.

In other words watts give power the bigger the motor and the more cooling you can get the more watts you can dissapate. That is why my little 6 3/4" can technically operate at 96v and drive my mini van to 65mph but it also fails if driven this way for more than a brief period of time.



meanderingthemaze said:


> If so, how much HP would you need to move a 3000lb vehicle at 70mph, and to accelerate 0-60 in 10secs, or climb a 10% grade.


 Quite a bit, it is generally acceptable and actually more economical to allow the vehicle to slow a bit on inclines (even if you have the power), also a 3000lb vehicle if aerodynamic only requires about 10hp on flat ground to go 70mph (think boattail) but if not aerodynamic this number can jump exponentially at 70mph. 

In other words WHAT SPECIFIC vehicle are we talking? A s10 pickup, a car, a mini van?


----------



## meanderingthemaze (Jan 25, 2010)

rmay635703 said:


> Generally voltage aside the amount of power a motor can generate is mainly dependant on its weight, more copper = bigger heatsync.
> 
> It is possible to have a very small motor generate a high level of power but the smaller it is the less time it will do so before damage.


OK, so this is very helpful in understanding the design consideration.



> In other words watts give power the bigger the motor and the more cooling you can get the more watts you can dissapate. That is why my little 6 3/4" can technically operate at 96v and drive my mini van to 65mph but it also fails if driven this way for more than a brief period of time.


So, even if I find a motor that is capable of doing what I want, it doesn't mean it will hold up to the test of endurance of normal use.



> In other words WHAT SPECIFIC vehicle are we talking? A s10 pickup, a car, a mini van?


1969 Datsun pickup L521, ~2150 lbs curb weight


----------



## rmay635703 (Oct 23, 2008)

meanderingthemaze said:


> So, even if I find a motor that is capable of doing what I want, it doesn't mean it will hold up to the test of endurance of normal use.


Oh it will just make sure you get a large enough motor, I would estimate a good 10" or 11" forklift motor could probably do it for your little truck, its much better not to drive 70mph though. My motor is about as small as they come and it will drive my mini van up to 65 at 96v but it falls apart because its simply too small and overheats, the key is to keep your motor within its rated power output, once you find a decently sized motor, get the model and brand and post it here and the wise veterans will tell you its capabilities. Your truck is fairly small so you should be golden without burning your motor.



meanderingthemaze said:


> 1969 Datsun pickup L521, ~2150 lbs curb weight


[/quote]
That is one of the better pickups to convert to electric, lighter is always better in electric. Is that pickup about 4 feet wide or so? If so it may be moderately aerodynamic as pickups go due to low frontal area, might consider lowering it a tad to gain better aero a good site to look at on that front is ecomodder.com. Also a front air dam, belly pan and maybe an aerocap would help matters more.

Many of the electric folks will convert something and forget that you can gain a lot of range and speed by overinflating tires and improving aerodynamics.

Good Luck there are many here who know much much more than I, but I would say that is an excellent choice for an EV pickup!


----------



## meanderingthemaze (Jan 25, 2010)

Well, I really appreciate the info and help.

I did a little homework before choosing that car, but it's obviously not as aerodynamic as the Tesla. But pickup seemed like the easier conversion, since this is my first.

I don't have the link for the motor I'm looking at but some other people on the forum have used this companies' motors. They just came out with a new one that's 50HP, at 96V.

I'll post when I get back to my home computer.

Thanks.

EDIT: I just found a link. I believe this is the same motor. But this isn't the link for the manufacturer's site, this is a vendor. Scroll down to the end and look for the AC-50 motor/controller combo.
http://www.thunderstruck-ev.com/AC_drive_performance.htm


----------



## meanderingthemaze (Jan 25, 2010)

OK, so here is the link to the manufacturer's site, and it appears it is the same motor as the above thunderstruck link.
http://hpevs.com/drive-systems/ac-50

Looks like they may have developed this motor specifically for my type of application.

Any opinions?


----------



## Evilsizer (Jan 25, 2010)

kinda surprised at no response yet... i would think that AC-30 would be more then enough. it prolly has about 2x the torque of the 4cly in it..


----------



## rmay635703 (Oct 23, 2008)

Many of us are DC forklift motor folks only. I know nothing of AC (well not quite but close enough)

Also to give a decent answer to his question we would need to know the CDa of the vehicle and driveline/wheel friction/ Then its just plug and chug at 70mph.

Because it is a pickup things get rather muddy above 45mph.


----------



## Bowser330 (Jun 15, 2008)

rmay635703 said:


> Many of us are DC forklift motor folks only. I know nothing of AC (well not quite but close enough)
> 
> Also to give a decent answer to his question we would need to know the CDa of the vehicle and driveline/wheel friction/ Then its just plug and chug at 70mph.
> 
> Because it is a pickup things get rather muddy above 45mph.


rmay's right...aero really starts to make a difference in higher speeds...weight is what will get you at lower speeds...

As others have mentioned, there are considerable gains to be had by blocking off the front grill and other air inlets, lowering, installing belly pan, smaller side mirors, etc. definitely check out ecomodder.com


----------



## rmay635703 (Oct 23, 2008)

Evilsizer said:


> kinda surprised at no response yet... i would think that AC-30 would be more then enough. it prolly has about 2x the torque of the 4cly in it..


I really don't know of any electric motor within the realm of reason that can drive a 2000lb+ vehicle up a 10% grade at 70mph continuously.

He would have to be willing to give up a little and that motor to me is perfectly workable but again as to what grade it could maintain speed is a big unknown. Aero is another big unknown.


----------



## meanderingthemaze (Jan 25, 2010)

I guess I was a little misleading in my wishlist, rmay.

I don't need all of those things at once, but rather I would like to be able to drive on flat ground at 70mph, drive let's say 25mph at 10% (very rare case). And 60 miles range in somewhat ideal conditions but not perfect (ie: mild slopes but mostly flat, 30-35mph average, with some but not a lot of stop and go). 

I think I'm comfortable with the design, price may dictate whether I get the beefier or the smaller motor.

BTW, ecomodder is a very cool site, I plan on implementing some of those techniques to increase aero. 

Thanks for the input.


----------



## tomofreno (Mar 3, 2009)

> I don't need all of those things at once, but rather I would like to be able to drive on flat ground at 70mph, drive let's say 25mph at 10% (very rare case). And 60 miles range in somewhat ideal conditions but not perfect (ie: mild slopes but mostly flat, 30-35mph average, with some but not a lot of stop and go).


 I think it would be difficult for the Curtis 1238-7501 controller/HPEVS AC50 with 36 LiFePO4 cells (115V nominal) to do this for your 2150 lb curb weight pu. The thread "SwiftE" in the Builds and Conversions forum gives some performance numbers for this controller/motor in a small car. You can use one of the ev calculators on line or the spreadsheet referred to as evcalculator at electricnevada.org to estimate performance. I used the later with some guesses of 0.4 drag coeff, 22 ft squared frontal area (maybe too small), 2150 curb weight (final ev weight around 2500 lb) and got about 1.3C current draw up a 10% grade at 30 mph. That is using 36 180Ah cells, so 1.3C is about 234A. The controller may well overheat if you do that for very long, but short climbs would be no problem. At 70 mph on flat ground the above parameters give about 1 5/8C, or 293A. The controller will overheat if you do that for very long in summer temperatures. It also wouldn't be too good for the cells to pull that high of continuous current regularly. It would be better to go to larger Ah cells. You may be able to prevent overheating of the controller by adding a large heat sink and fans. The 180Ah/115V pack would give around 70 mile range at 35 mph for the above vehicle parameters. Top speed would be around 80 - 85 mph, but acceleration will be anemic over around 50 mph. The AC24LS Wye connected (high voltage) would give a bit better acceleration above around 50 mph, but lower acceleration at lower speeds (AC50 has more torque than the AC24LS at lower rpm, less at higher). Do some research to determine your truck's parameters and compare motor/controller combinations.


----------



## meanderingthemaze (Jan 25, 2010)

Tom,

Thanks for bringing my attention to your post. WOW. Your efforts to document the experience are just so commendable. Great work and thank you! 

I see that I will be able to get close to what I want, but perhaps my wishes are a little out of reach in our current state of the EV market. We are all watching for "the next best thing" to come out. And I believe that HPEVS' AC50 motor is one thing that has filled a much needed niche in this realm of DIY'ers. 

But of course, our product wishlist is still not fulfilled. We need someone to produce a higher voltage controller to work with it. Plus, we need better and cheaper options to a Lion/BMS system. We need better automotive solutions to things like regen braking alerting the brake lights, etc. that would be considered essential in a production vehicle.

These are all possible, and perhaps inevitable with enough time, but in the mean time, it's great to have this community in which to foster ideas and share solutions.

As far as my conversion goes, I'm going to have an extra 300-400 lbs and worse aero than you, but drive less freeway miles than you, my ratio being closer to 80street/20freeway.

I think with a little extra work and tricks, I can increase aero on the truck. And I don't need quite the range you do, so I am going with lead acids (with the plan to upgrade to Lion on next battery replacement in hopefully 3-4 years).

As far as acceleration is concerned, I'm a little disappointed in the results you reported, but basically I was shooting for something comparable to my 4-cyl '96 Toyota Corolla, which if I punch it, can do about 0-60 in 10 secs. Anyway, getting to 50mph is the most important range for acceleration when getting onto freeways in my area, so perhaps it will be satisfactory after all.

I've pretty much ruled out the Azure systems due to price and reports of poor performance (in the case of the AC24) or overly heavy system (in the case of AC55). Like I said, I think the HPEVS' AC50 fills that middle ground we have needed in the AC world. It's really a shame that Curtis is holding out on their end, because that would make this system practically ideal for most conversions.

In my area it doesn't snow, and can get into triple digits in the summer, so I'll have to look into a cooling system of some sort. 

Sorry for asking again, but I was up until 2am last night reading your SwiftE thread and it was a lot of information. What was your final battery pack voltage? 115V? Since your last discussion with HPEVS, what was the upper limit of the voltage they recommended with the Curtis?

Thanks


----------



## tomofreno (Mar 3, 2009)

> What was your final battery pack voltage? 115V? Since your last discussion with HPEVS, what was the upper limit of the voltage they recommended with the Curtis?


 That's correct 115V nominal, 3.2V/cell. Upper limit is about 130V, actually about 134 I think, but haven't tested it. Yes, the AC50 would be much more useful if there was a higher voltage and higher current controller available for it. Higher current to give higher torque and acceleration below the "knee" of the torque-speed curve (more than the present 90 ft-lb max at 550A), higher voltage to give more available torque above the knee. It would give good performance for a Corolla sized car then. Several months ago HPGC (HPEVS) said they were working with someone on a higher power controller. Not sure what the status is. Thanks for the comments on the thread. I had a lot of frustration trying to find real data on performance when deciding what motor/controller to use, so wanted to help rectify that. Nothing like real measurements.


----------



## meanderingthemaze (Jan 25, 2010)

Well, you did a good job. Hopefully we can find more Tom's out there to do the same. Then if all the information could be gathered onto one site such that you wouldn't have to spend so much time sifting through things to find.

Hopefully, by the time I'm ready to put the motor in, they'll have figured out a new controller.


----------

