# how fast is 48v?



## arklan (Dec 10, 2012)

im sure this has been asked before but i searched the forum and google and couldnt find an answer..
i wanna know how fast a car weighing approx 700kg (including driver) will go at 48v
i ask because i was thinking to get a scrapped forklift and just transfer the whole lot to the car without modifying anything
i read the entire forklift thread and couldnt find the answer there either
i think there was a calculator somewhere for weight x volts = speed somewhere but i cant find it


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## rwaudio (May 22, 2008)

arklan said:


> im sure this has been asked before but i searched the forum and google and couldnt find an answer..
> i wanna know how fast a car weighing approx 700kg (including driver) will go at 48v
> i ask because i was thinking to get a scrapped forklift and just transfer the whole lot to the car without modifying anything
> i read the entire forklift thread and couldnt find the answer there either
> i think there was a calculator somewhere for weight x volts = speed somewhere but i cant find it


Not very fast!
I have a 1350kg car on 300v and it's simply awesome.
I drove the same car on a few different voltages through the build (the car would have been lighter on less batteries but I don't have exact weights)

150v the car was kind of fun, I could keep up with traffic easily including speeds of 110km/h 

100v the car was responsive and good at low speeds but I had to use 5th gear and it took awhile to reach 110km/h I probably would have topped out around 115-120km/h as my top speed but can't imagine how much longer it would have taken to go that fast.

The difference between 100 and 150v was incredible. The difference between 150 and 300v is beyond words.

Obviously a forklift motor can only handle so many volts, however I doubt you would be happy on 48v unless it's a neighbourhood vehicle that never has to go faster than 50-60km/h


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## subcooledheatpump (Mar 5, 2012)

Any car at any weight at 48 volts will go exactly 0 mph. 

You need current and voltage to get to power, to get a vehicle to move. 

What motor? what controller? what about the batteries? how much current can the batteries discharge?


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## favguy (May 2, 2008)

OK, Without much more information we can't let you know anywhere near accurately, but whatever motor and controller you choose, I'd guess that 48 volts on a 700Kg vehicle will give you about 30mph maximum on the level and it will take you a while to get there


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## Woodsmith (Jun 5, 2008)

Given you are using the whole set up from a forklift truck then depending on the size of the truck there could be the potential for a lot of amps to be drawn creating enough power to move quite a few tons of loaded forklift about at walking speed.

In a car you may not be able to have as much battery pack as the forklift and so there will be a limit to what the controller can deliver to the motor. Then, regardless of gear ratios, you won't have much top speed nor remaining acceleration when it is near the top speed.

Post up some details of the forklift truck, the controller, the motor, any other data plates that might be there and we may be able to give some more meaningful information.



As an aside, my tractor runs on 48V, has a Curtis controller that could deliver 350A and has a top speed of 10mph. Changing the gearing may bring that up to nearer 20mph but would be unneeded.

I am developing my next EV, the EVan-Tricycle, with a 40mph top speed and using a 72V 350A Curtis controller. I have no idea if that will get it to 40mph comfortably and hold it there on hills, but I am only using what I have to hand.
If it can't give me the performance I need (I need it to get to 40mph promptly, while loaded up, and up a hill and then keep that speed even with a head wind) then I will increase the voltage and get another controller.


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## trukr (Mar 17, 2013)

MD Juan makes a vintage stamped steel military ejeep with a 4KW motor 48V sysstem.
Their 13 passenger ejeepney is only 7KW with a 72V pack.

There is also a number of etrikes in the philippines that all run 4KW. They are usually 6 passenger shuttles between the airport and the town of puerto princessa. I think this was a joint project between the parts group of MD Juan and Leo Motors.

It will move you. Physically, NOT emotionally.


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## major (Apr 4, 2008)

arklan said:


> im sure this has been asked before but i searched the forum and google and couldnt find an answer..
> i wanna know how fast a car weighing approx 700kg (including driver) will go at 48v
> i ask because i was thinking to get a scrapped forklift and just transfer the whole lot to the car without modifying anything
> i read the entire forklift thread and couldnt find the answer there either
> i think there was a calculator somewhere for weight x volts = speed somewhere but i cant find it


Here's a classic 48V conversion. http://forkenswift.com/ 

How fast CAN a 48V EV go? I suppose you could build it to go highway speeds or faster. It wouldn't be practical and your money would be better spent using a higher voltage system. But there are 48V classes in NEDRA (electric drag racing).

For 48V EVs, think golf carts


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## poprock (Apr 29, 2010)

subcooledheatpump said:


> Any car at any weight at 48 volts will go exactly 0 mph.
> 
> Correct me if I am mis-interpreting your answer, but not so. As well as the forkenswift that Major mentioned my Subaru L series with a 36v motor running 48v hit 50k (30mph) on local roads .


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## Coley (Jul 26, 2007)

My first setup in my 1991 Yugo was a 5 HP motor and 48volt. It was capable of 45 - 50mph for 15 miles.

With 72 volt and an 8 HP motor I like it better. now i can get a ticket.!!


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## Woodsmith (Jun 5, 2008)

poprock1 said:


> subcooledheatpump said:
> 
> 
> > Any car at any weight at 48 volts will go exactly 0 mph.
> ...


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## Ziggythewiz (May 16, 2010)

Yeah, with enough current any voltage at the right gearing can go any speed.

It's all about total power vs weight and drag.


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## mnikhilesh (Jan 10, 2013)

Don't know if you are still looking for answer but I will try to make it little more clear.
First you need to know the maximum power available to you. Simply multiply voltage to the max current you will have. Say you have 250 Amps then power available to you is 250x50 = 12.5 kW. Now assume your battery pack and controller is capable of providing this much current and I am leaving gearbox at the moment then calculating maximum speed is simple. 
{(1/2)x1.25x(Front area of your vehicle)x(drag coefficient)x(velocity)x(velocity)} + {0.01x(mass of vehicle)x10} = 12500x0.9 
(assuming 90% efficiency for overall energy conversion)

->Front area of your vehicle is the front area, I am assuming it to be around 2.7 square meters.
->drag coefficient is how much resistance your vehicle shape is giving to air. this link will give you fair idea of the value for different vehicle shape. http://development.part20.eu/en/wp-content/uploads/2009/08/aerodynamics2.jpg
I am going with 0.45 for the purpose.
-> mass is 700 kg.
Solving the equation gives velocity = 23.3 m/s = 83 kmph.
This is the theoretical maximum speed, but most likely you will not reach this speed because of motor and gearbox designs. 
Designing with brush type motor is most simple. For this type of motor there is given rpm per volt rating. Say your motor says 71 rpm per volt. So maximum rpm = 50x71 = 3550 rpm. Now look for gear ratio for each gear (also accounting for ratio in differential). Divide that ratio to 3550 and you have maximum speed in each gear.
Say my differential ratio is 5:1, and gear ratios are 
1st - 5
2nd - 3.66
3rd - 2.33
4th - 1
Than wheel rpm in each gear will be 
1st - 3550/(5x5) = 142 rpm
2nd - 3550/(5x3.33) = 213 rpm
3rd - 3550/(5x1.67) = 425 rpm
4th - 3550/(5x1) = 710 rpm
Now if radius of your wheel is say 0.23 meters
than maximum speed in each gear will be (v = rpmx2xpixradius of wheel/60)
1st - 142x2x3.14*0.23/60 = 3.42 m/s = approx 12.3 kmph.
2nd- 213x2x3.14*0.23/60 = 5.13 m/s = approx 18.4 kmph.
3rd- 425x2x3.14*0.23/60 = 10.23 m/s = approx 36.8 kmph.
4th- 710x2x3.14*0.23/60 = 17.09 m/s = approx 61.53 kmph.

You don't need to chew all this if you cant. Just let me know if you want to clarify anything.

Cheers


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## DavidDymaxion (Dec 1, 2008)

I ran my Porsche on 48V for a while. Many folks that rode in it commented they were surprised how good the acceleration was, but you had to row through all 5 gears to hit 40 mph! It was about like the old VW bugs, yeah they felt kind of fast in 1st gear. It was fast enough for city use, but not fast enough for highway or serious hill climbing. When I did an all-out effort it hit 55 mph on level ground. It would go 40 mph comfortably, and climb ~5% grades at about 25 mph. I had 2 strings of Optima batteries, so my internal resistance was pretty low. My car weighed about 1100 kg.

A very rough (but easy!) formula is:

0.5 * Amps * Volts = rwhp

There is a conversion factor for going from kW to hp, but it turns out that is comparable to driveline and electrical losses.

So for my car it was:

0.5 * 1500 A * 48 V ~= 36 rwhp

Given the speeds, I could believe it was around 36 hp (which was comparable to an early VW bug).



arklan said:


> im sure this has been asked before but i searched the forum and google and couldnt find an answer..
> i wanna know how fast a car weighing approx 700kg (including driver) will go at 48v
> i ask because i was thinking to get a scrapped forklift and just transfer the whole lot to the car without modifying anything
> i read the entire forklift thread and couldnt find the answer there either
> i think there was a calculator somewhere for weight x volts = speed somewhere but i cant find it


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## sammyleal (Aug 1, 2016)

I'm doing a little conversion using 48V. I'm overvolting a 24V SepEx motor, Curtis Controller 500A.

Initially I'll be testing with SLA (Mass is 800kg)

If the performance is good for commuting, I'll buy some Chinese LiFePo4.


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## rmay635703 (Oct 23, 2008)

My comutacar gets into the 40's with 48 volts and my Miles zx40 hits the 40's at 48 volts.

Historically there was a classic efficient belt CVT car that used the CVT to control its speed it would go about 55mph

So it's doable just doesn't accelerate very well


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