what factor hp conversion?

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what factor hp conversion?

fred ungewitter
I'm aware that one cannot make a valid comparison between electric motor horsepower and infernal combustion engine horsepower, but is there a rule of thumb (or any other digit) that one can use to compare the two?

Let's say that you have a 5kw electric motor. Google says 1kw is anywhere from one and a quarter hp to one and a third. Taking the higher figure, that would mean that a 5kw motor is a bit more than 6 hp, say six and a half.

That's all well and good, but six and a half horses in ICE form isn't anywhere as powerful as a 5kw electric motor.

What would be a more practical way to look at this?  Let's say that one wants to have an electric motor to perform on a par with a 15hp diesel?  Would a 5kw electric do as well?

fred



     
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Re: what factor hp conversion?

Robert Johnston
On Thu, Jul 16, 2009 at 16:16, fred<[hidden email]> wrote:
> I'm aware that one cannot make a valid comparison between electric motor horsepower and infernal combustion engine horsepower, but is there a rule of thumb (or any other digit) that one can use to compare the two?
>
> Let's say that you have a 5kw electric motor. Google says 1kw is anywhere from one and a quarter hp to one and a third. Taking the higher figure, that would mean that a 5kw motor is a bit more than 6 hp, say six and a half.
>
> That's all well and good, but six and a half horses in ICE form isn't anywhere as powerful as a 5kw electric motor.
>
> What would be a more practical way to look at this?  Let's say that one wants to have an electric motor to perform on a par with a 15hp diesel?  Would a 5kw electric do as well?

Bear in mind that HP values for ICEs are peak value readings, whereas
HP values for electric motors are constant load values.

So while your brand new Shelby Mustang might have a 475HP engine,
you'll only actually get that 475HP at ideal revs, in ideal
conditions. For regular driving, and to hold speed, that ICE will be
producing something like 20-30HP, tops.
--
Robert "Anaerin" Johnston

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Re: what factor hp conversion?

Roger Heuckeroth
In reply to this post by fred ungewitter

On Jul 16, 2009, at 6:16 PM, fred wrote:

> I'm aware that one cannot make a valid comparison between electric  
> motor horsepower and infernal combustion engine horsepower, but is  
> there a rule of thumb (or any other digit) that one can use to  
> compare the two?
>
> Let's say that you have a 5kw electric motor. Google says 1kw is  
> anywhere from one and a quarter hp to one and a third. Taking the  
> higher figure, that would mean that a 5kw motor is a bit more than 6  
> hp, say six and a half.
>
> That's all well and good, but six and a half horses in ICE form  
> isn't anywhere as powerful as a 5kw electric motor.
>
> What would be a more practical way to look at this?  Let's say that  
> one wants to have an electric motor to perform on a par with a 15hp  
> diesel?  Would a 5kw electric do as well?
>
> fred

If the motor is rated as output kW the conversion is HP = kW x 1.34,  
so 5 kW = 6.7 HP.

1 HP = 746 watts

However, if the motor is rated as input 5kW, then you need to know the  
efficiency and power factor in order to calculate shaft BHP (brake  
horse power).  The formula is BHP = kW x 1.34 x pf x eff.  where pf is  
the power factor and eff is the efficiency.

It can be a bit confusing as HP and kW are both measures of power, but  
HP is normally used as a measure of a motors output, and kW can be  
used as input electrical power or output mechanical power.

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Re: what factor hp conversion?

Roger Heuckeroth
In reply to this post by Robert Johnston

On Jul 16, 2009, at 6:33 PM, Robert Johnston wrote:

> On Thu, Jul 16, 2009 at 16:16, fred<[hidden email]> wrote:
>> I'm aware that one cannot make a valid comparison between electric  
>> motor horsepower and infernal combustion engine horsepower, but is  
>> there a rule of thumb (or any other digit) that one can use to  
>> compare the two?
>>
>> Let's say that you have a 5kw electric motor. Google says 1kw is  
>> anywhere from one and a quarter hp to one and a third. Taking the  
>> higher figure, that would mean that a 5kw motor is a bit more than  
>> 6 hp, say six and a half.
>>
>> That's all well and good, but six and a half horses in ICE form  
>> isn't anywhere as powerful as a 5kw electric motor.
>>
>> What would be a more practical way to look at this?  Let's say that  
>> one wants to have an electric motor to perform on a par with a 15hp  
>> diesel?  Would a 5kw electric do as well?
>
> Bear in mind that HP values for ICEs are peak value readings, whereas
> HP values for electric motors are constant load values.
>
> So while your brand new Shelby Mustang might have a 475HP engine,
> you'll only actually get that 475HP at ideal revs, in ideal
> conditions. For regular driving, and to hold speed, that ICE will be
> producing something like 20-30HP, tops.
> --

I think it is more relevant to talk in terms of torque when comparing  
ICE and an electric motor.  Most people drive their ICEs at low RPM  
(under 3500 rpm).  The motor never even gets close to the peak HP of  
the ICE.  Good low end torque is what gives you decent acceleration in  
an electric car.  If you compare the torque curve of a series DC motor  
with that of an ICE you will find that the ICE has a steep curve and  
the motor will have a relatively flat curve.  All that low RPM torque  
is what makes an electric accelerate well.  Peak HP is going to limit  
your top speed, but do little for you on acceleration.


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Re: what factor hp conversion?

Doug Weathers
In reply to this post by fred ungewitter

On Jul 16, 2009, at 4:16 PM, fred wrote:

> Google says 1kw is anywhere from one and a quarter hp to one and a  
> third.

1hp = 746 watts.  That's the number I remember.

<http://www.google.com/search?hl=en&rls=en&q=1hp+in+watts>

Similarly, 1Kw = 1.34hp.

<http://www.google.com/search?hl=en&rls=en&q=1Kw+in+hp>

--
Doug Weathers          | "The Moon.  I've been there.  It's super!"
Las Cruces, NM, USA    |   - Astronaut Charles "Pete" Conrad
http://www.gdunge.com/ |

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Re: what factor hp conversion?

Bill Dube
In reply to this post by Roger Heuckeroth
A fun fact is that in Europe, a HP = 743 Watts (instead of 746 watts)

I guess the horses are smaller in Europe. :-)

Bill Dube'

At 05:22 PM 7/16/2009, you wrote:

>On Jul 16, 2009, at 6:16 PM, fred wrote:
>
> > I'm aware that one cannot make a valid comparison between electric
> > motor horsepower and infernal combustion engine horsepower, but is
> > there a rule of thumb (or any other digit) that one can use to
> > compare the two?
> >
> > Let's say that you have a 5kw electric motor. Google says 1kw is
> > anywhere from one and a quarter hp to one and a third. Taking the
> > higher figure, that would mean that a 5kw motor is a bit more than 6
> > hp, say six and a half.
> >
> > That's all well and good, but six and a half horses in ICE form
> > isn't anywhere as powerful as a 5kw electric motor.
> >
> > What would be a more practical way to look at this?  Let's say that
> > one wants to have an electric motor to perform on a par with a 15hp
> > diesel?  Would a 5kw electric do as well?
> >
> > fred
>
>If the motor is rated as output kW the conversion is HP = kW x 1.34,
>so 5 kW = 6.7 HP.
>
>1 HP = 746 watts
>
>However, if the motor is rated as input 5kW, then you need to know the
>efficiency and power factor in order to calculate shaft BHP (brake
>horse power).  The formula is BHP = kW x 1.34 x pf x eff.  where pf is
>the power factor and eff is the efficiency.
>
>It can be a bit confusing as HP and kW are both measures of power, but
>HP is normally used as a measure of a motors output, and kW can be
>used as input electrical power or output mechanical power.
>
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>Usage guidelines: http://evdl.org/help/index.html#conv
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Re: what factor hp conversion?

Roger Heuckeroth
1 hp (metric) = 735.5 Watts.

See:  http://en.wikipedia.org/wiki/Horsepower

On Jul 16, 2009, at 8:07 PM, Bill Dube wrote:

> A fun fact is that in Europe, a HP = 743 Watts (instead of 746 watts)
>
> I guess the horses are smaller in Europe. :-)
>
> Bill Dube'
>
> At 05:22 PM 7/16/2009, you wrote:
>
>> On Jul 16, 2009, at 6:16 PM, fred wrote:
>>
>>> I'm aware that one cannot make a valid comparison between electric
>>> motor horsepower and infernal combustion engine horsepower, but is
>>> there a rule of thumb (or any other digit) that one can use to
>>> compare the two?
>>>
>>> Let's say that you have a 5kw electric motor. Google says 1kw is
>>> anywhere from one and a quarter hp to one and a third. Taking the
>>> higher figure, that would mean that a 5kw motor is a bit more than 6
>>> hp, say six and a half.
>>>
>>> That's all well and good, but six and a half horses in ICE form
>>> isn't anywhere as powerful as a 5kw electric motor.
>>>
>>> What would be a more practical way to look at this?  Let's say that
>>> one wants to have an electric motor to perform on a par with a 15hp
>>> diesel?  Would a 5kw electric do as well?
>>>
>>> fred
>>
>> If the motor is rated as output kW the conversion is HP = kW x 1.34,
>> so 5 kW = 6.7 HP.
>>
>> 1 HP = 746 watts
>>
>> However, if the motor is rated as input 5kW, then you need to know  
>> the
>> efficiency and power factor in order to calculate shaft BHP (brake
>> horse power).  The formula is BHP = kW x 1.34 x pf x eff.  where pf  
>> is
>> the power factor and eff is the efficiency.
>>
>> It can be a bit confusing as HP and kW are both measures of power,  
>> but
>> HP is normally used as a measure of a motors output, and kW can be
>> used as input electrical power or output mechanical power.
>>
>> _______________________________________________
>> General EVDL support: http://evdl.org/help/
>> Usage guidelines: http://evdl.org/help/index.html#conv
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>> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
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Re: what factor hp conversion?

Joseph Ashwood
In reply to this post by fred ungewitter
--------------------------------------------------
From: "fred" <[hidden email]>
Subject: [EVDL] what factor hp conversion?

> I'm aware that one cannot make a valid comparison between electric motor
> horsepower and infernal combustion engine horsepower, but is there a rule
> of thumb (or any other digit) that one can use to compare the two?

A very rough rule of thumb on performance is an electric motor will deliver
2-3 times the performance per HP or KW, so to have roughly the same
performance as a 475HP Internal Combustion Vehicle would require roughly
200HP of Electric Vehicle. This does not take into account overpowering the
electric motor which almost everyone does.

This is based on very rough comparison in various environments, and your
experience will almost certainly differ.
                    Joe

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Re: what factor hp conversion?

Mike Golub-2
You might also think about what is meant by an ICE having 475 HP...

http://www.stealth316.com/2-calc-hp-et-mph.htm

MPH = 224 (hp/weight)^(1/3)

where MPH is the top speed of a vehicle in the 1/4 mile...

On Thu, Jul 16, 2009 at 5:49 PM, Joseph Ashwood <[hidden email]> wrote:

> --------------------------------------------------
> From: "fred" <[hidden email]>
> Subject: [EVDL] what factor hp conversion?
>
> > I'm aware that one cannot make a valid comparison between electric motor
> > horsepower and infernal combustion engine horsepower, but is there a rule
> > of thumb (or any other digit) that one can use to compare the two?
>
> A very rough rule of thumb on performance is an electric motor will deliver
> 2-3 times the performance per HP or KW, so to have roughly the same
> performance as a 475HP Internal Combustion Vehicle would require roughly
> 200HP of Electric Vehicle. This does not take into account overpowering the
> electric motor which almost everyone does.
>
> This is based on very rough comparison in various environments, and your
> experience will almost certainly differ.
>                    Joe
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
>
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Re: what factor hp conversion?

Evan Tuer
In reply to this post by Roger Heuckeroth
This is only used for car engine specifications - electric motors, if
they have a HP rating, work it out from 746 Watts per HP, as far as
I'm aware.


On Fri, Jul 17, 2009 at 1:44 AM, Roger Heuckeroth<[hidden email]> wrote:

> 1 hp (metric) = 735.5 Watts.
>
> See:  http://en.wikipedia.org/wiki/Horsepower
>
> On Jul 16, 2009, at 8:07 PM, Bill Dube wrote:
>
>> A fun fact is that in Europe, a HP = 743 Watts (instead of 746 watts)
>>
>> I guess the horses are smaller in Europe. :-)
>>
>> Bill Dube'
>>

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Re: what factor hp conversion?

Aaron Richardson
In reply to this post by Mike Golub-2
This seems like a good way to compare ICE and EVs.  However, I would
think this does not apply to a car that reaches its top speed before
reaching .25 miles.  How far does it take for most EVs to reach their
top speed?

Aaron
 


On Thu, 2009-07-16 at 20:58 -0800, m gol wrote:

> You might also think about what is meant by an ICE having 475 HP...
>
> http://www.stealth316.com/2-calc-hp-et-mph.htm
>
> MPH = 224 (hp/weight)^(1/3)
>
> where MPH is the top speed of a vehicle in the 1/4 mile...
>
> On Thu, Jul 16, 2009 at 5:49 PM, Joseph Ashwood <[hidden email]> wrote:
>
> > --------------------------------------------------
> > From: "fred" <[hidden email]>
> > Subject: [EVDL] what factor hp conversion?
> >
> > > I'm aware that one cannot make a valid comparison between electric motor
> > > horsepower and infernal combustion engine horsepower, but is there a rule
> > > of thumb (or any other digit) that one can use to compare the two?
> >
> > A very rough rule of thumb on performance is an electric motor will deliver
> > 2-3 times the performance per HP or KW, so to have roughly the same
> > performance as a 475HP Internal Combustion Vehicle would require roughly
> > 200HP of Electric Vehicle. This does not take into account overpowering the
> > electric motor which almost everyone does.
> >
> > This is based on very rough comparison in various environments, and your
> > experience will almost certainly differ.
> >                    Joe
> >
> > _______________________________________________
> > General EVDL support: http://evdl.org/help/
> > Usage guidelines: http://evdl.org/help/index.html#conv
> > Archives: http://evdl.org/archive/
> > Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
> >
> >
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Re: what factor hp conversion?

Zeke Yewdall
I suspect many of the less performance oriented ones require much more than
a quarter mile to reach top speed.  I know that my lower powered ICE's can
take a mile or more to reach top speed sometimes (top speed being around
60mph or so).

Z

On Fri, Jul 17, 2009 at 8:30 AM, Aaron Richardson <
[hidden email]> wrote:

> This seems like a good way to compare ICE and EVs.  However, I would
> think this does not apply to a car that reaches its top speed before
> reaching .25 miles.  How far does it take for most EVs to reach their
> top speed?
>
> Aaron
>
>
>
> On Thu, 2009-07-16 at 20:58 -0800, m gol wrote:
> > You might also think about what is meant by an ICE having 475 HP...
> >
> > http://www.stealth316.com/2-calc-hp-et-mph.htm
> >
> > MPH = 224 (hp/weight)^(1/3)
> >
> > where MPH is the top speed of a vehicle in the 1/4 mile...
> >
> > On Thu, Jul 16, 2009 at 5:49 PM, Joseph Ashwood <[hidden email]> wrote:
> >
> > > --------------------------------------------------
> > > From: "fred" <[hidden email]>
> > > Subject: [EVDL] what factor hp conversion?
> > >
> > > > I'm aware that one cannot make a valid comparison between electric
> motor
> > > > horsepower and infernal combustion engine horsepower, but is there a
> rule
> > > > of thumb (or any other digit) that one can use to compare the two?
> > >
> > > A very rough rule of thumb on performance is an electric motor will
> deliver
> > > 2-3 times the performance per HP or KW, so to have roughly the same
> > > performance as a 475HP Internal Combustion Vehicle would require
> roughly
> > > 200HP of Electric Vehicle. This does not take into account overpowering
> the
> > > electric motor which almost everyone does.
> > >
> > > This is based on very rough comparison in various environments, and
> your
> > > experience will almost certainly differ.
> > >                    Joe
> > >
> > > _______________________________________________
> > > General EVDL support: http://evdl.org/help/
> > > Usage guidelines: http://evdl.org/help/index.html#conv
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Re: what factor hp conversion?

fred ungewitter
In reply to this post by fred ungewitter
An interesting response. I didn't need the direct conversion figures, since I had a pretty close approximation to them already, but the answers I've selected is the closest to what I understood to be valid.  It's the torque that matters and is especially useful in my need for information.

The comparison on which I'm working involves a diesel ICE of about 15 hp, and diesels are pretty torquey.  I'm thinking that a 5kw electric would probably be a good match.  What say you all?




________________________________
------------------------------

Origina Message: 8
Date: Thu, 16 Jul 2009 19:36:03 -0400
From: Roger Heuckeroth <[hidden email]>
Subject: Re: [EVDL] what factor hp conversion?

On Jul 16, 2009, at 6:33 PM, Robert Johnston wrote:

> On Thu, Jul 16, 2009 at 16:16, fred<[hidden email]> wrote:
>> I'm aware that one cannot make a valid comparison between electric  
>> motor horsepower and infernal combustion engine horsepower, but is  
>> there a rule of thumb (or any other digit) that one can use to  
>> compare the two?
>>
>> Let's say that you have a 5kw electric motor. Google says 1kw is  
>> anywhere from one and a quarter hp to one and a third. Taking the  
>> higher figure, that would mean that a 5kw motor is a bit more than  
>> 6 hp, say six and a half.
>>
>> That's all well and good, but six and a half horses in ICE form  
>> isn't anywhere as powerful as a 5kw electric motor.
>>
>> What would be a more practical way to look at this?  Let's say that  
>> one wants to have an electric motor to perform on a par with a 15hp  
>> diesel?  Would a 5kw electric do as well?
>
> Bear in mind that HP values for ICEs are peak value readings, whereas
> HP values for electric motors are constant load values.
>
> So while your brand new Shelby Mustang might have a 475HP engine,
> you'll only actually get that 475HP at ideal revs, in ideal
> conditions. For regular driving, and to hold speed, that ICE will be
> producing something like 20-30HP, tops.
> --

I think it is more relevant to talk in terms of torque when comparing  
ICE and an electric motor.  Most people drive their ICEs at low RPM  
(under 3500 rpm).  The motor never even gets close to the peak HP of  
the ICE.  Good low end torque is what gives you decent acceleration in  
an electric car.  If you compare the torque curve of a series DC motor  
with that of an ICE you will find that the ICE has a steep curve and  
the motor will have a relatively flat curve.  All that low RPM torque  
is what makes an electric accelerate well.  Peak HP is going to limit  
your top speed, but do little for you on acceleration.




------------------------------
End of Original Message: 8



     
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Re: what factor hp conversion?

Zeke Yewdall
Depends on what the rated torque and rpm of the diesel and the electric
motor are....

On Fri, Jul 17, 2009 at 1:37 PM, fred <[hidden email]> wrote:

> An interesting response. I didn't need the direct conversion figures, since
> I had a pretty close approximation to them already, but the answers I've
> selected is the closest to what I understood to be valid.  It's the torque
> that matters and is especially useful in my need for information.
>
> The comparison on which I'm working involves a diesel ICE of about 15 hp,
> and diesels are pretty torquey.  I'm thinking that a 5kw electric would
> probably be a good match.  What say you all?
>
>
>
>
> ________________________________
> ------------------------------
>
> Origina Message: 8
> Date: Thu, 16 Jul 2009 19:36:03 -0400
> From: Roger Heuckeroth <[hidden email]>
> Subject: Re: [EVDL] what factor hp conversion?
>
> On Jul 16, 2009, at 6:33 PM, Robert Johnston wrote:
>
> > On Thu, Jul 16, 2009 at 16:16, fred<[hidden email]> wrote:
> >> I'm aware that one cannot make a valid comparison between electric
> >> motor horsepower and infernal combustion engine horsepower, but is
> >> there a rule of thumb (or any other digit) that one can use to
> >> compare the two?
> >>
> >> Let's say that you have a 5kw electric motor. Google says 1kw is
> >> anywhere from one and a quarter hp to one and a third. Taking the
> >> higher figure, that would mean that a 5kw motor is a bit more than
> >> 6 hp, say six and a half.
> >>
> >> That's all well and good, but six and a half horses in ICE form
> >> isn't anywhere as powerful as a 5kw electric motor.
> >>
> >> What would be a more practical way to look at this?  Let's say that
> >> one wants to have an electric motor to perform on a par with a 15hp
> >> diesel?  Would a 5kw electric do as well?
> >
> > Bear in mind that HP values for ICEs are peak value readings, whereas
> > HP values for electric motors are constant load values.
> >
> > So while your brand new Shelby Mustang might have a 475HP engine,
> > you'll only actually get that 475HP at ideal revs, in ideal
> > conditions. For regular driving, and to hold speed, that ICE will be
> > producing something like 20-30HP, tops.
> > --
>
> I think it is more relevant to talk in terms of torque when comparing
> ICE and an electric motor.  Most people drive their ICEs at low RPM
> (under 3500 rpm).  The motor never even gets close to the peak HP of
> the ICE.  Good low end torque is what gives you decent acceleration in
> an electric car.  If you compare the torque curve of a series DC motor
> with that of an ICE you will find that the ICE has a steep curve and
> the motor will have a relatively flat curve.  All that low RPM torque
> is what makes an electric accelerate well.  Peak HP is going to limit
> your top speed, but do little for you on acceleration.
>
>
>
>
> ------------------------------
> End of Original Message: 8
>
>
>
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Re: what factor hp conversion?

Roger Heuckeroth
In reply to this post by fred ungewitter
Any chance of getting the torque curves for both the diesel and the  
electric motor?

Sent from my iPhone

On Jul 17, 2009, at 3:37 PM, fred <[hidden email]> wrote:

> An interesting response. I didn't need the direct conversion  
> figures, since I had a pretty close approximation to them already,  
> but the answers I've selected is the closest to what I understood to  
> be valid.  It's the torque that matters and is especially useful in  
> my need for information.
>
> The comparison on which I'm working involves a diesel ICE of about  
> 15 hp, and diesels are pretty torquey.  I'm thinking that a 5kw  
> electric would probably be a good match.  What say you all?
>
>
>
>
> ________________________________
> ------------------------------
>
> Origina Message: 8
> Date: Thu, 16 Jul 2009 19:36:03 -0400
> From: Roger Heuckeroth <[hidden email]>
> Subject: Re: [EVDL] what factor hp conversion?
>
> On Jul 16, 2009, at 6:33 PM, Robert Johnston wrote:
>
>> On Thu, Jul 16, 2009 at 16:16, fred<[hidden email]> wrote:
>>> I'm aware that one cannot make a valid comparison between electric
>>> motor horsepower and infernal combustion engine horsepower, but is
>>> there a rule of thumb (or any other digit) that one can use to
>>> compare the two?
>>>
>>> Let's say that you have a 5kw electric motor. Google says 1kw is
>>> anywhere from one and a quarter hp to one and a third. Taking the
>>> higher figure, that would mean that a 5kw motor is a bit more than
>>> 6 hp, say six and a half.
>>>
>>> That's all well and good, but six and a half horses in ICE form
>>> isn't anywhere as powerful as a 5kw electric motor.
>>>
>>> What would be a more practical way to look at this?  Let's say that
>>> one wants to have an electric motor to perform on a par with a 15hp
>>> diesel?  Would a 5kw electric do as well?
>>
>> Bear in mind that HP values for ICEs are peak value readings, whereas
>> HP values for electric motors are constant load values.
>>
>> So while your brand new Shelby Mustang might have a 475HP engine,
>> you'll only actually get that 475HP at ideal revs, in ideal
>> conditions. For regular driving, and to hold speed, that ICE will be
>> producing something like 20-30HP, tops.
>> --
>
> I think it is more relevant to talk in terms of torque when comparing
> ICE and an electric motor.  Most people drive their ICEs at low RPM
> (under 3500 rpm).  The motor never even gets close to the peak HP of
> the ICE.  Good low end torque is what gives you decent acceleration in
> an electric car.  If you compare the torque curve of a series DC motor
> with that of an ICE you will find that the ICE has a steep curve and
> the motor will have a relatively flat curve.  All that low RPM torque
> is what makes an electric accelerate well.  Peak HP is going to limit
> your top speed, but do little for you on acceleration.
>
>
>
>
> ------------------------------
> End of Original Message: 8
>
>
>
>
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> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
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Re: what factor hp conversion?

tomw
In reply to this post by fred ungewitter
As someone pointed out, electric motor ratings are constant power, peak (momentary) power may be 3 times higher (mine is 17 HP/52 HP at 96V).  To compare an ICE and electric motor I think it helps to look at available power as a function of vehicle speed.  Power is the product of torque and motor shaft angular velocity (which of course vehicle speed is proportional to, depending on gear ratios).  An electric motor typically has higher torque available at lower rpm, but it is limited by the current the controller can supply.  As a result, both series DC motors/controllers and AC motors/controllers have about contant max torque available at lower rpm, then decrease above some rpm (3000 for mine).  So the power increases about linearly with increasing rpm, goes through a max at rpm slightly above the "knee" of the torque-speed curve, then decreases with increasing rpm.  

In contrast, an ICE as low torque at low rpm, and reaches a max at high rpm (6000 for the ICE I removed from my car).  It also has low torque at low rpm and reaches max torque before reaching peak power (3000 for my former ICE).  People many times report stronger acceleration with an electric motor compared to the ICE it replaced.  I think this is at lower speeds, less than 50 mph say, where the product of the electric motor torque and shaft radial velocity (power) is higher than the ICE.  The ICE typically has more available power at higher speeds if it's HP rating was higher than the PEAK HP rating of the electric motor.   The ev "calculator" (spreadsheet) at electricnevada.org has power versus speed graphs like this for several different motor/controller combinations.

Tom

fred_dot_u wrote
I'm aware that one cannot make a valid comparison between electric motor horsepower and infernal combustion engine horsepower, but is there a rule of thumb (or any other digit) that one can use to compare the two?

Let's say that you have a 5kw electric motor. Google says 1kw is anywhere from one and a quarter hp to one and a third. Taking the higher figure, that would mean that a 5kw motor is a bit more than 6 hp, say six and a half.

That's all well and good, but six and a half horses in ICE form isn't anywhere as powerful as a 5kw electric motor.

What would be a more practical way to look at this?  Let's say that one wants to have an electric motor to perform on a par with a 15hp diesel?  Would a 5kw electric do as well?

fred



     
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Re: what factor hp conversion?

Jeff Shanab
In reply to this post by fred ungewitter
My best friend used to work for a small engine shop. It was known that
for portable compressors, washers,pumps, and tractors that If you were
replacing an electric motor with a gas one the HP had to be 3 times the
HP rating. I don't know if it scales well.

Basically the difference is one of convention. They rate ICE at peak
which occurs at one rpm and load. But it can often do close to that
continuously once there. (In some cases even this is a lie. My
mitsubishi was rated at a point you couldn't even obtain, low hp motors
often are. I have heard that the newer Ford Mustangs are rated below
their max to keep some lawyers happy and meet quotas)

An electric motor is rated in continuous, what you can give it forever
with adequate cooling. But it is capable of giving a lot more and at a
lot of different rpm points for shorter periods.

I think the electric motor is a better match for accelerating the load.
More torque at the beginning when you needed it to get the mass moving
and less needed to cruise. The hybrid manufactures realized this pretty
quick.

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Canadian "Daily Planet" clip of KillaCycle

Bill Dube
In reply to this post by Zeke Yewdall
Just got a link to a Discovery Channel clip about the KillaCycle that
has been airing in Canada for awhile:

<http://watch.discoverychannel.ca/clip195298#clip195298>http://watch.discoverychannel.ca/clip195298#clip195298

Bill Dube'

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Re: Canadian "Daily Planet" clip of KillaCycle

ROBERT GOUDREAU
Any news on your AC drive Bill ?

On Mon, Jul 20, 2009 at 1:12 PM, Bill Dube <[hidden email]> wrote:

> Just got a link to a Discovery Channel clip about the KillaCycle that
> has been airing in Canada for awhile:
>
> <http://watch.discoverychannel.ca/clip195298#clip195298>
> http://watch.discoverychannel.ca/clip195298#clip195298
>
> Bill Dube'
>
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