# Basic question: What is the importance of amps - when referring to a controller?



## stealthE (Jan 31, 2016)

I am a complete newbie, lol.

Say I was looking to buy a AC50 motor and curtis 1238 controller operating at 650 amps..... (96 volts)

What would happen if I used a 1000 amp controller or a 500 amp controller?

What does the amps for the controller affect?


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## Vanquizor (Nov 17, 2009)

roughly amperage equates to the torque output- double the amperage will be close to double the torque all else being equal (although often there are other considerations)


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## stealthE (Jan 31, 2016)

so is 144v @ 500 amps (curtis 1239) inadequate for a 3000lbs car? I am not building a rocket....but i dont want to merge the freeway at 60kph lol


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## Vanquizor (Nov 17, 2009)

I guess that depends on what the rest of the system looks like and how long your merge ramp is.

If you are thinking direct drive then hopefully your merge lane is really long and really down hill.

From your other questions I'm guessing this is for converting a stealth with an AC-50/51... in that case if you keep a trans and row the gears you can probably get 0-60 in ~20 seconds which would put you on pace with a loaded mail truck. Probably a bit of a nuisance in rush hour traffic but not terrible if you keep your head up and use all the throttle. Certainly fine for less traveled roads or rural settings.


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## piotrsko (Dec 9, 2007)

ARE the 1000 amp controllers AC? Bet they are Dc. Different motors then.

Traditional wisdom says 746 watts is 1 hp. So 96 v at 500 amps is like 70 hp

How will the vehicle do on that hp?


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## onegreenev (May 18, 2012)

stealthE said:


> I am a complete newbie, lol.
> 
> Say I was looking to buy a AC50 motor and curtis 1238 controller operating at 650 amps..... (96 volts)
> 
> ...


What kind of car? For a street DC setup you want at least 96 volts and 600 plus amps. You will also need at that level the manual transmission that comes with the vehicle to make use of the gearing to get your higher speeds. If you go with a higher voltage system you can forgo super high amperage. The simple AC setups you can get from HPEVS will allow up to 144 volts and 400 amps. You'd still need a transmission but with the AC setup you could use an automatic as well. If you want a real serious system you need to go for the expensive AC systems or you can double or triple up the simple HPEVS systems and build a super sweet system that will not only kick ass but will cruise all day long. Then you need to build a good battery system for your setup. Will you have the room? What chemistry to use? Those are questions you need to look at. 

What car do you want to use? Is it a car you have experience driving and like? Don't go run out and buy a sports car just because you think its cool unless you have experience driving one for the purpose you want the electric car. Most would still use the car for commuting to work and back and daily things. I had purchased a Porsche 914 and know that many convert them to electric. I'd agree that they are a great vehicle to convert but for a daily commuter and all around get around vehicle they are not. For fun and occasional driving they would be great. Lightweight, strong, and would be a great candidate for a dual HPEVS system. Find what you want first. You do need to know if you like the vehicle and if it can hold the requisite amount of cells for your driving needs. Do not go Lead Acid. Period.


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## Sunking (Aug 10, 2009)

piotrsko said:


> ARE the 1000 amp controllers AC? Bet they are Dc. Different motors then.


Motors come in both DC and AC. Any EV uses DC batteries as there is no other way to carry around stored electric energy. The difference is a DC motor uses a DC controller. Most DC controllers use PWM type controllers. PWM = Pulse Width Modulation. 

AC motors use a Controller which is a form of an Inverter which changes DC to AC.




piotrsko said:


> Traditional wisdom says 746 watts is 1 hp. So 96 v at 500 amps is like 70 hp.


True in theory, but is not real. No motor either AC or DC is 100% efficient, nor are any controllers 100% efficient. There are also losses in wiring and connections. AC motors are the most efficient, but even the most efficient over all system is on the order of 80%, so that theoretical 70 hp is only around 55 hp at the shaft. 

Keep in mind you cannot compare electric motor hp to an internal combustion engine. Although there is no direct conversion from a ICE to electric motor, but as a general rule a it takes roughly a 1 HP electric to replace a 3-4 hp gas engine. 

Gas engines are rated at maximum peak hp at some given RPM rating, but cannot sustain that power for a long period of time. Example hop in your car and floor the accelerator and do not let up on it. In a short period of time you will burn up the engine. Electric motors are rated for continuous power. Catch is most electric motors can produce 3 to 4 times their rated HP for short period of time. 

Good example one that I know is a Honda Civic sedan uses a 157 HP motor. At cruise on a flat, level, paved surface at 65 mph requires 18 hp. All the extra hp is for acceleration. Assuming the same weight and vehicle would require roughly a 40 to 50 HP electric motor with like RPM operating characteristic.

So to wrap it up say we have a gas engine with a hp of 100 hp at 5252 RPM with 100 foot pounds of torque would require a 25 HP AC electric motor of like RPM's. In fact the electric would out accelerate the gas engine because it can be set up as Constant Torque from 0 RPM to 5200 RPM. HP is not the entire picture. 

As an old saying goes HP is for car sales, and torque wins the race. HP is a function of RPM and Torque. HP = T x RPM / 5252. A gas engine only produces maximum torque (acceleration) in a very narrow band of RPM's. Some electric motors produce flat torque from 0 RPM to as high as 10,000+ RPM. In electric motors voltage is related to RPM and Torque is current. Higher Voltage = Higher RPM, and Higher Current = Higher Torque.


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## Soulless (Jan 24, 2016)

<---taking notes. good read. This helped me get a better idea of what kind of set up i'd like to aim for


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## twright (Aug 20, 2013)

I have another data point for you: My 2000 Ford Escort (2600 lbs) has the following:

1.) Netgain 9" DC motor
2.) Open Revolt 500 amp controller
3.) 44 100 amp hour Lithium Iron Phosphate battery cells

Here's what it will do:

1.) 85 mph
2.) 50 miles at 0% State of Charge (or 40 miles, safely)

YMMV


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