# What AC motor to replace a Diesel engine



## Alfonso(MX) (Apr 11, 2015)

Hello, I hope some one here can help me out. I´m on a project to convert a Bus using a 190hp, 700 nm Torque diesel engine to electric. 
My first though was to get an electric motor with the same power and torque, but is seems that it will be too much, but because such an electric motor is quite expensive.

I want to calculate how smaller I can go with the e motor without loosing performance vs. the diesel. We are planning to keep the gearbox.

Gearbox: 1st 6.7, 2nd 3.81, 3rd 2.29, 4th 1.48, 5th 1, 6th 0.73. Final drive 6.14
Diesel engine: 700 Nm torque from 1400 to 1600,
190 Hp @2200
I have calculated the "normal" acceleration" to be 25 sec. from 0-60km/h.
Wheel radius is 22in.


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## Hollie Maea (Dec 9, 2009)

Alfonso(MX) said:


> Hello, I hope some one here can help me out. I´m on a project to convert a Bus using a 190hp, 700 nm Torque diesel engine to electric.
> My first though was to get an electric motor with the same power and torque, but is seems that it will be too much, but because such an electric motor is quite expensive.
> 
> I want to calculate how smaller I can go with the e motor without loosing performance vs. the diesel. We are planning to keep the gearbox.
> ...


Closest match I can think of is an Evo AFM-240-4, driven by a Rinehart PM150dx inverter.

No clue what the motor costs (let me know!) but the inverter is about 7 grand or so.


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## jwiger (Oct 18, 2014)

Depends on your drive cycle. A lot of times you can get away with half the HP in an EV conversion and get decent performance (I may be wrong, and hopefully some will correct me). That torque range is at a low RPM. You could easily find a motor that spins twice that speed and use lower gears multiply your torque. I just checked evtv.me and Jack is still listing his custom dual Warp11 motor $10k

That would certainly give you the torque your after. 

Also, Bigfoot 20 is electric, you could research the motor supplier they use. That would be a lot more money though.


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## madderscience (Jun 28, 2008)

The systems are somewhat rare and older, but if you could lay your hands on an Azure AC90 / DMOC645 system it might be a pretty close match. 630nm motor torque and 110kw, or about 150hp. Given the motor will be able to make peak torque over a much wider RPM range than the diesel would have, you would probably be OK, but you would definitely want to keep the transmission, or maybe be able to get away with a 2 speed axle.

However I can't imagine they ever probably made more than dozens to maybe a couple hundred of these systems, and you would have to be willing and able to deal with older, community-supported tech since the original manufacturer is no more.

They made a few thousand total of the smaller AC55/DMOC440 systems like what I have. FWIW mine has been reliable so far over 14000 miles and 2+ years driving.


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## Yabert (Feb 7, 2010)

Hi Alfonso
If it's a project a little bit ghetto/low cost, I suggest you to simply use two used 11'' forklift motors connected together with a 1000A controller(water cool). That will give you over 700 Nm of torque and plenty of continuous power.
You can also take a look to use few used Chevy Volt or Nissan Leaf battery to power the thing.

On the other hand, if it's more like a professional project, maybe contact TM4 or Balqon (by example).


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## dcb (Dec 5, 2009)

ac ghetto would be 3 ac24ls, in parallel in a "pyramid" connected to a central shaft via ~2.5:1 reduction, feeding the transmission input.

And a diy controller, with seriously modded power stage, and lots and lots and lots of lithium batteries (and a way to charge them ), 336v battery pack and wye should keep the 1000a igbt's safe. you will burn through 180ah in an hour of continuous duty (80hp). That would be like THREE 24kwh leaf batteries you need to source.


AC motors need higher rpms to make good power, so 3 ac24ls's and ~2.5 reduction will put you nearly on target for 690nm, and put peak power at about 2200 rpm @ 189hp.

significant mechanical and electrical skills will be required. Scrappiness and lots of patience would help.

the ac90 looks more straightforward though ($3k on ebay, don't really know what an ac 90 should look like, so buyer beware) http://www.ebay.com/itm/AZURE-DYNAM...TOR-/170895516018?hash=item27ca2aa172&vxp=mtr, couple stats here: http://www.electricautosports.com/node/314 but it will come up a little short on power with the dmoc 645, and it is usually recommended to buy the controller preconfigured with the motor as a set, as there are a crapton of variables, and you need a can controller (and maybe a parameter file).

Edit: I salvaged a copy of the ac90/dmoc645 spec sheet from the bowels of the internet and attached it here for posterity, they have a picture of a truck in it so that is a good sign  Looks like it was meant to bolt straight to the driveshaft, but that would feel like starting off in 5th gear... good luck with the adapter and coupler. Consider also bolting directly to the driveshaft and upping the rearend ratio to like 10:1 or something. No transmission losses and less shifting may leave you in about the same performance zone.


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## Alfonso(MX) (Apr 11, 2015)

thanks everyone for your help....


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## jwiger (Oct 18, 2014)

I can't believe I forgot about this. Take a look at http://www.transpowerusa.com/

They have their own design controller/charger. And use two Fisker Karma motors, they get 400hp and plenty of torque to move an 80,000 pound truck.


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## Alfonso(MX) (Apr 11, 2015)

Thanks Jwiger didn´t know of that company. The main problem of some great motors is availability. I don´t wan´t just to find one motor like if it was a treasure. I want an stable source. 

Will try to find out about those Fisker motors, but last I heard is Fisker went bankrupt and is reorganizing.

I don´t discard using two "small" motor to make up the torque needed, just as transpower is doing it. 

thanks


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## dougingraham (Jul 26, 2011)

Alfonso(MX) said:


> Hello, I hope some one here can help me out. I´m on a project to convert a Bus using a 190hp, 700 nm Torque diesel engine to electric.
> My first though was to get an electric motor with the same power and torque, but is seems that it will be too much, but because such an electric motor is quite expensive.
> 
> I want to calculate how smaller I can go with the e motor without loosing performance vs. the diesel. We are planning to keep the gearbox.
> ...


The goal is to find a suitable motor. Not strictly speaking to find something that can do what the Diesel does. 190HP is 142 kw. The only thing HP does is to limit your top speed. It is the torque that matters. 700 nm is 516 ft-lb. The diesel is horribly limited in this regard because that torque is only found between 1400 and 1600 rpm. It tapers off quickly on both sides of that rpm band. It would be helpful to have a torque plot vs rpm.

For the record you can get the Horsepower by combining three of the HPEVS/Curtis packages. Three combined would give over 250 hp. And combining three of the AC-75 would give 3*170 ft-lb = 510 ft-lb or 691 nm. And this is flat from 0 rpm to 2500 rpm and down to half that at just over 4000 rpm. The diesel probably runs out long before that. If I punch in your numbers in my spreadsheet at 2500 RPM for 44 in diameter tires I get the following:

Gear/Speed (MPH)/Thrust in lbs
1st/8/11440
2nd/14/6505
3rd/23/3910
4th/36/2526
5th/53/1707
6th/73/1246

This all looks reasonable. No idea what the top speed would be but certainly somewhere around 90 mph. First gear is probably not necessary at all. Max acceleration would probably use a shift point 10-15% above the above speeds.

So you can get the torque to match the diesel with three of the budget AC setups paralleled. Whats does this bus weigh and I can do some acceleration estimates.


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## Hollie Maea (Dec 9, 2009)

jwiger said:


> I can't believe I forgot about this. Take a look at http://www.transpowerusa.com/
> 
> They have their own design controller/charger. And use two Fisker Karma motors, they get 400hp and plenty of torque to move an 80,000 pound truck.


Any clue who made those motors for the Fisker, and if they are still in production? Kind of looks like an Axial Flux design. I'd love to see a torque curve...


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## Alfonso(MX) (Apr 11, 2015)

Hello Doug...

Thanks for your comments, they are interesting and helpful. The fact is that city buses here are limited to 40mph as top speed. Therefore and based on what you say Hp is not an issue any more, it should be all about torque.

This is another option I just though and would appreciate your opinion. If a get a 150nm Torque motor, and use a reduction gear ratio 5:1 before the transmission that would give me 750 Nm of torque when connected to the transmission. If that motor speed up to 10,000 rpm, then transmission would be reeving at 2,000 rpm (tops), really similar to what "it was designed for" with the diesel engine. 

In this case, we would have to drive the bus using all the gears all the way to 5th or 6th to reach 40mph, but the big advantage would be using a very small motor to move a very big vehicle. Also, less amps and voltage. 

Top speed would never be an issue, as those buses are not aloud to be driven at highway speeds.

I´m rigth?


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## dougingraham (Jul 26, 2011)

Alfonso(MX) said:


> This is another option I just though and would appreciate your opinion. If a get a 150nm Torque motor, and use a reduction gear ratio 5:1 before the transmission that would give me 750 Nm of torque when connected to the transmission. If that motor speed up to 10,000 rpm, then transmission would be reeving at 2,000 rpm (tops), really similar to what "it was designed for" with the diesel engine.


Simplistically yes. The problem is you need to match the torque curve of the motor to the application. That 150nm is not going to appear all the way to 10krpm. It might be flat up to 3000-4000 RPM and then it will taper off as the RPM continues to rise. When you divide the rpm by 5 you get the torque amplified by 5 but the point when the torque starts to fall off is divided by 5 as well. So that 3000 to 4000 rpm becomes 600 to 800 rpm with it falling off at that point. I am afraid that this is probably not what you want.

Matching the motor to the application is the whole trick. You will need someone to do this for you in order to get a good result. Making a selection like this would be outside of my comfort zone by a good margin.

Best Wishes!


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