# What motor and amperage should I use?



## joamanya89 (Feb 13, 2012)

Hi,I'm trying to convert a Mitsubishi Lancer, because it is not a heavy car, and also I like it and it has enough space for the batteryes.

My question is what kind of motor should I use? I've seen a FB1 4001A or a Warp 9 (they are almost the same), as you see I'll use a DC system.

Are those ok for my car? or is to much?

And then I would like to have a range of 200km - 240km with one charge and be able to drive at 90km/h - 130km/h.

So what amperage should I use? Because I was thinkin to do it with lithium batteryes but those may be to expensive...


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## frodus (Apr 12, 2008)

You'll need lithium (and lots of it) for that range.... lead just won't cut it. The thing would weigh as much as a tank. You're looking at a pack that is at least 38kwh worth of batteries, give or take a few percent.


I'll expand:
Amperage isn't really as important at this point in the design phase, Watt-Hours determines range. Estimate that a car like that is going to be ~300wh/mile give or take a little depending on many factors.... but it's close. Then say ~125mi (200km). 300wh/mi * 125mi = 37500watt-hours. If you need 240km, that's 150mi * 300wh/mil = 45kwh.

Speed is limited by Voltage in a DC system, acceleration is limited by torque. Top speed is limited by HP, which is a factor of volts and amps. I think you're well below what a 11" motor could produce, and if you have a pack big enough with decent quality batteries, current won't be an issue. 130kmh should be possible, but it depends on the voltage you run at, and the gear ratio of your transmission.


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## joamanya89 (Feb 13, 2012)

Thank you very much!
Can I ask here about where's a good place to buy the lithium batteryes?

Because, I'll have to import it, and that's not an easy issue.
Calculating that W= amp(i) * volt, I suppose that W/h= a/h * volt so there is a balance between A/h and Volt.

For example: I can get my 37500W using 375V * 100A/h, or using 144V * 200A/h.

So, in my first example I will have my 37.5KW on my energy storage, but if I use 144V *33a/h (that would be 3C discharge capacity isn't it?) I'll have 4752 W moving my motor, so what you have said is that I'll have a range of 200km + or - but a speed that my motor can give me with 4752W, did I understand it well?

And the controller it's what is gonna regulate the Volts that goes to the motor?


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## frodus (Apr 12, 2008)

Please use correct units. Kw is power. Kwh is energy. We're talking about energy. Also amps and amp hours are different.

100Ah * 375V = 37,500Wh of energy
200Ah * 144V = 28,800Wh of energy
Completely different energy packs.

Also, 3C discharge on 100Ah cells is 300A. 2C is 200A. It's a multiplier of the Ah capacity of the cell.

If you have a 100Ah pack at 375V, and you discharge at 3C, that's 300A. The voltage will sag a little bit, lets say 12%, so down to 330V. That would be 99,000Kw of power. With a 37kwh pack, you should have no problem with power using 100Ah cells that can discharge at 3C. But realize, discharging at 1C would give you 37kwh of energy. Discharging at 3C, you'd need a larger pack to get 37,500kwh out. The higher the current you discharge, the less energy you get out of the cell.... so expect to get a larger pack to get 37kwh out. Something with at least 20% more energy at 1C.

Basically, you're going to be spending a lot of money on this vehicle to get that range, so be sure you are sold on the idea, because it's a lot of work and lots of time.

The controller regulates voltage and current to the motor, yes.


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## joamanya89 (Feb 13, 2012)

I apologize for my mistake in the units, obviously I didn't know the difference.

Could you tell me, what volt and amperage may you use on these case?
Or perhaps, I should change my goals on these car a bit?


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## frodus (Apr 12, 2008)

Start by looking at prices of lithium. Right now, things are ~$1.25 per Ah. 100Ah is ~$125, and you'd need ~118 batteries @3.2V to get ~375V, so 118 * $125 = $14750 just for batteries, then add motor, controller, some sort of battery monitoring or management system to monitor the pack and a charger, contactor, fuses, cabling, DC-DC..... it's going to be well over $20k USD.... plus shipping and import fees.

100Ah batteries should be ok at that voltage, but it boils down to what motor you're using. It'l be about the same cost for batteries, but if you have a 144V motor, then you should go for a 144V pack and batteries that are ~260Ah.


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## joamanya89 (Feb 13, 2012)

Ok, but I can't expend that money just on batteryes, so, for example I'll leave the clutch, I've been told that I can get more speed using less W, so the speed wouldn't be a problem.

Then the range would become my only issue.

I know that I'm bothering you, but it's my first convertion, and will need to import it all, so I wanna be sure about everything, so could you please explain me again what you said before, about the difference between W and W/h and also, if I've got X W/h how does the motor expend it, cos I've got a bit confused before...


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## major (Apr 4, 2008)

joamanya89 said:


> ...., so could you please explain me again what you said before, about the difference between W and W/h and also, if I've got X W/h how does the motor expend it, cos I've got a bit confused before...


Hi Joam,

W/h is a non-unit  Wh is a unit of energy. It is pretty confusing to the beginner. Maybe you can learn here: 
http://www.diyelectriccar.com/forums/showthread.php?t=669&redir_from=668 

Regards,

major


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## joamanya89 (Feb 13, 2012)

Thank you verry much!


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## Ziggythewiz (May 16, 2010)

top speed is directly related to Volts, more volts will give you more speed and is more efficient, so you want to go as high as you can here (limited by battery space, and motor/controller/and charger limits)

range is related to Volts*ah so adding volts (cells) and ah (bigger cells) will give more range.


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## major (Apr 4, 2008)

Ziggythewiz said:


> top speed is directly related to Volts, more volts will give you more speed ........


Hi Ziggy,

This statement isn't necessarily correct. It is true if the motor, controller and gear ratio are fixed (cannot be changed). However, top speed of a particular vehicle is determined by the power delivered to the wheels. That power can originate from many combinations of motor designs, controller ratings and battery configurations (voltage and amperage). A 100 volt, 500A system could easily outpower a 300V, 100A set-up and yield a higher top speed with the appropriate gear ratio in the same vehicle. So more volts doesn't necessarily give you higher top speed 

Regards,

major


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## joamanya89 (Feb 13, 2012)

But, if I'm going to keep the clutch, couldn't I get an smaller motor, or perhaps a FB1 4001 but of 96V? I mean, the clutch and the gears are made to get a better performance with not much energy, so perhaps with an smaller motor, I can handle less batteryes and get the same speed?


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## major (Apr 4, 2008)

joamanya89 said:


> But, if I'm going to keep the clutch, couldn't I get an smaller motor, or perhaps a FB1 4001 but of 96V? I mean, the clutch and the gears are made to get a better performance with not much energy, so perhaps with an smaller motor, I can handle less batteryes and get the same speed?


The clutch doesn't have anything to do with it. Multiple gear ratios can enable you to achieve faster acceleration and therefore use a smaller motor. This doesn't affect the battery size. It takes the same energy to accelerate the vehicle either way.


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## frodus (Apr 12, 2008)

Gears are made to convert high torque low RPM to low RPM, high torque.... they don't convert low energy to high energy, that stays the same.

You still need a motor with a certain power to maintain a certain speed or accelerate at a certain rate.


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## joamanya89 (Feb 13, 2012)

I appreciate everything you guys have explained me and taught me, it is not easy for my to get these information in my country and even harder is in my lenguage.

Thank you again!


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## joamanya89 (Feb 13, 2012)

frodus said:


> Gears are made to convert high torque low RPM to low RPM, high torque.... they don't convert low energy to high energy, that stays the same.
> 
> You still need a motor with a certain power to maintain a certain speed or accelerate at a certain rate.



So is there any scale (an easy one) to know + or - what kind of motor do I need?

And if I use a smaller motor, perhaps I wouldn't have more speed, but if the motor needs less Volts, aren't the batteryes going to last any longer? so I could get more range?


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## frodus (Apr 12, 2008)

Easy? This isn't going to be "easy", not even close.

You'll need to do some work. You need to do some calculations to see how much power you need to get your vehicle fully loaded up to the speeds you want. Then work backwards. Get a motor that can handle that power, get a controller that can handle that motor, then design a battery pack that can supply the current and voltage that is required to the controller. You basically need to engineer it.

Read this:
http://www.diyelectriccar.com/forums/showthread.php/want-build-ev-do-starti-6441.html

Read all of it's links. Read, read and read some more.

We can't tell you what you're going to have to choose becuase you've given us nothing to go by. If you want help, start a post called "joamanya89's electric [insert model of car here]"

What you will want to post is: 

Your skill level with auto mechanics and fabrication
The range you are hoping to get (how many miles/charge)
What level of performance you are hoping to get
How much money you are willing to put into your project
What parts you've already considered, if any.
Then keep everything related to your questions inside that thread. It makes it easier for people like Major and myself to figure out what your goal is, what vehicle you're doing. If I have to jump between threads to figure out what you're doing, I'll likely just skip answering questions altogether.


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## joamanya89 (Feb 13, 2012)

Ok, I'm new at this forum, so I didn't know that I could do that.

About my level I'm an engineering student, so the electric wouldn't be a problem, the mechanical perhaps yes.

I'll do that post you've told me, but you will have to pardon me for my english, as you see I'm limited at the tecnical lenguage


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## GizmoEV (Nov 28, 2009)

joamanya89 said:


> I'll do that post you've told me, but you will have to pardon me for my english, as you see I'm limited at the tecnical lenguage


You are doing quite well so keep at it. You might try google translate or something when you can't think of the English word you are after. I do not know how good Google Translate is at technical language, however.


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## sokon (Sep 15, 2011)

Hello joamanya89

I am a newbie on the matter, just like you 
still I will try to give some input.

It seems to me that your aimed range is rather ambitious, in particular for a first conversion. AFAIK the larger dc motors are not exactly the most efficient ones. Given your range expectations, maybe you should give efficiency a bit more weight in your "motor choosing procedure". However, the most efficient motors tend to be quite expensive (it would be helpful to know your budget for the whole conversion).

There is no way a clutch or a gear box (or for that matter any mechanical system) could improve your range (assuming the drive train was not completely bad/inefficient design to start with) since those systems do not add any energy to your car (worse even, any gearbox will transform some of your energy into heat..).

rgrds,
sokon


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## GizmoEV (Nov 28, 2009)

sokon said:


> AFAIK the larger dc motors are not exactly the most efficient ones.


Electric motors aren't like ICEs where larger is often less efficient. The opposite is more often true. An 11" is more efficient than a 9" which is more efficient that an 8" and so on. You don't want too small of a motor. Erring on the big side of things is much better and might even be more efficient. I believe major alluded to this in an earlier post.


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## sokon (Sep 15, 2011)

> Electric motors aren't like ICEs where larger is often less efficient. The opposite is more often true. An 11" is more efficient than a 9" which is more efficient that an 8" and so on.


My statement didnt rely on that assuption, it is rather about what I remeber having read. I think remembering that the typically used DC motors have (peak) efficienties in the range of 80-85%. See for example
http://www.evolveelectrics.com/PDF/NetGain/ImPulse 9 Spreadsheet.pdf

Here is an example of an efficient yet small and affordable motor
http://www.jobymotors.com/public/views/pages/jm1s.php

(of course, this motor is not suitable for a car, but it makes a nice motor for a small motorbike imo)

Here is examples of a efficient motors that also have many other nice properties (powerdensity etc) which is likely are expensive though (I dont know their price)

http://www.enstroj.si/Electric-products/emrax-motors.html

http://www.evo-electric.com/products/electric-motors/


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## GizmoEV (Nov 28, 2009)

But now you are comparing a DC motor suitable for a car with quite different purpose and a different type of design. That is an illogical comparison for the purpose of motor size selection.


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## sokon (Sep 15, 2011)

> But now you are comparing a DC motor suitable for a car with quite different purpose and a different type of design. That is an illogical comparison for the purpose of motor size selection.


the two larger motors are certainly suitable for cars imho. I quote the spec sheet of the evo AF130 motor:

"AF type electric machines combine high performance with low weight and size, ideal for electric and hybrid electric vehicles..."

And EMRAX on its website says about its motor:

"EMRAX motors are suitable for electric vehicles - EV,... "

The small motor was rather an example that small motors can be very efficient while still affordable.

What is illogical in comparing different type motors? What do you even mean by the term "illogical"? I am just showing some options...(yea, not knowing his budget makes it difficult but more info seems better)

rgrds,
sokon


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## GizmoEV (Nov 28, 2009)

sokon said:


> What is illogical in comparing different type motors? What do you even mean by the term "illogical"? I am just showing some options...(yea, not knowing his budget makes it difficult but more info seems better)


The question is about appropriate motors for a road going EV. You said that smaller motors were more efficient. I countered that that wasn't generally the case. You said smaller motors were more efficient by showing a motor which wouldn't work in his road going EV. That is what is illogical. Selecting a motor outside of the implied parameters given by the OP doesn't help him out. He says he is thinking of converting a Mitsubishi Lancer and considering a 9" size motor. Anything that wouldn't move his car at a reasonable pace and be able to keep it going at the speeds he wants is an illogical comparison.


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## sokon (Sep 15, 2011)

> You said that smaller motors were more efficient.


Really, did I? where?

I said that the large *DC* motor are not the most efficient ones. This does not imply that smaller motors are more efficient however. It could also mean that (large) *AC *(also BLDC which run on AC afaik) are more efficient.

My mistake was maybe not to be to clear about what I really meant, it is that the large DC motors that are typically used for diy conversions or discussed in that thread (like netgain or forklift motors) are neither very efficient nor do they have a very favorable power to weight ratio. I also posted a link to a netgain spec sheet to make clear what I was pointing at. This seemed problematic to me as the thread starter aims at a long range conversion.



> You said smaller motors were more efficient by showing a motor which wouldn't work in his road going EV.


Again, I didnt say that small motors are more efficient at any time! I gave three motors two of which are perfectly suitable for EVs and a small one to show that there *exist *(http://en.wikipedia.org/wiki/Existential_quantification)
small yet efficient motors. That is by no means a way to say that in general small motors are more efficient than large ones!




> That is what is illogical.


I might know very little about EVs but of logic, you can believe me, I know quite a bit more than the average person on the road.



> Selecting a motor outside of the implied parameters given by the OP doesn't help him out.


Again, I gave three motors, one of which was not suitable for a car but good enough to make my point mentioned before.



> Anything that wouldn't move his car at a reasonable pace and be able to keep it going at the speeds he wants is an illogical comparison.


u think none of the motors I quoted would be able to move a lancer at a reasonable speed?

rgrds,
sokon


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## GizmoEV (Nov 28, 2009)

From the original post:


joamanya89 said:


> My question is what kind of motor should I use? I've seen a FB1 4001A or a Warp 9 (they are almost the same), as you see I'll use a DC system.
> 
> Are those ok for my car? or is to much?


This set the parameters. He is wondering about a 9" DC motor and whether its size is appropriate or if it is too much. For the size of car he is doing they will be just fine.

You said:



sokon said:


> AFAIK the larger dc motors are not exactly the most efficient ones.


Within the parameters given that statement is not correct and within those parameters it does imply that smaller motors are more efficient.



sokon said:


> My mistake was maybe not to be to clear about what I really meant, it is that the large DC motors that are typically used for diy conversions or discussed in that thread (like netgain or forklift motors) are neither very efficient nor do they have a very favorable power to weight ratio. I also posted a link to a netgain spec sheet to make clear what I was pointing at. This seemed problematic to me as the thread starter aims at a long range conversion.


That is the fun part about trying to communicate. Your link to the spec sheet still didn't make it clear to me that you were trying to step outside the original parameters.



> I might know very little about EVs but of logic, you can believe me, I know quite a bit more than the average person on the road.


Your knowledge of logic is not what is in question and never was. It is a statement you made which is in question. Furthermore, don't forget that many of the people who post on this form might just fall into the same category that you place yourself in. In any case, this isn't about who is right, it is about what is right. Always view it that way and you won't get your feelings hurt.



> u think none of the motors I quoted would be able to move a lancer at a reasonable speed?


And now we are back to what I said not being taken the way I intended so that makes us even, right? I obviously didn't state it very well. That'll teach me to respond with an iPhone where it is harder to proofread things. None of the motors you quoted are a member of the set of motors in question, however.

What I was trying to say was that given the type of motor the OP was asking about it is illogical to bring up a totally different type of motor. The motors you referenced are not in the set. Within the size of DC motors which might be considered for a DIY conversion and available on the general DIY market bigger motors are not less efficient. Regardless, what ever motor is chosen, the efficiency comparisons need to include the motor and controller as a set. AC induction motors are more efficient than Series DC motors of similar capability but when the controller efficiency is factored in the difference isn't that great. When I was checking into whether I should go with AC or DC in an S10 conversion the overall difference in efficiency was 1-2% if I used a Zilla controller with the DC system. For the 100-150 mile range I want that translates to at most 3 miles difference in range.

There are other things the OP can do to improve range which cost significantly less than going with a slightly more efficient motor system.


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## sokon (Sep 15, 2011)

Yea, lets agree that we became victims of thepitfalls of natural language^^

wish you a nice week end! And a successfull conversion for the threadstarter with whatever motor he will finally decide to go with...


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