[major]

Originally Posted by IamIan

What I stated is correct, current and resistance are the drivers of electrical heat ... Voltage doesn't matter.

Hi IamIan,

So what you're saying is that voltage is irrelevant

Just as I disagreed with Drew when he said that torque was irrelevant, I disagree with you that voltage is irrelevant. But maybe I should start another thread.

Ever notice the similarities between the expressions for electrical and mechanical power?

Pe = V * I or (Watts = Volts * Amps)

Pm = T * S or (Watts = Torque * Angular Velocity)

In the mechanical case, Drew chooses to use Power and Angular Velocity. Then says Torque is irrelevant. But when he defines the Power and Angular Velocity, he has defined Torque.

And you have done the same with your logic. Looking at "electrical heat", it is power. So when you say all you need is the current and resistance to determine power (electrical heat), you are correct, however by defining resistance and current, you have defined the voltage. You could have just as easily figured the electrical power (heat) by using voltage and current (making resistance irrelevant?) or by using voltage and resistance (making current irrelevant?).

My whole point here is that because you can have torque without power, it certainly cannot be considered irrelevant. And, as a sidebar, in your electrical heat example, you can have voltage without power, so it would be wrong to consider voltage irrelevant.

Regards,

major

[DavidDymaxion]

Don't forget, if you PWM you get less average voltage. 100 Volts with a 10% on / 90% off PWM means you'll get on average 10 Volts. Armed with this knowledge, you'll see you get the same heat numbers and no mysterious differences.

Originally Posted by IamIan

The Ohms has to stay the same.
So a 1 Ohm resistance ( not reluctance , or impedance, etc. ) when exposed to a 10 VDC electrical source can drawl up to 10 Amps... If we supply a conventional 100V electrical power source it would go up to 100 Amps... but Amps are just the average flow of electrons... so we use a PWM power supply to put out 100V at 1 Amp to the 1 Ohm circuit...

Now both are passing 10 Watts of power through the 1Ohms ... but it is well known and well documented that even at the same power ... the 10 Amps of higher current will always produce more heat at the same resistance... the 100V at 10 Amps will produce the same heat from that 1 Ohms of resistance as 10V at 10 Amps.

Amps of current drive the heat... Voltage effects power... but Voltage does not directly effect the heat at all... heat generation from electricity is a product of the resistance and the current... Voltage is not involved.

If 100% of the power was converted to heat than both the 1 Amp and the 10 Amps would both supply the same amount of heat as both have the same amount of power ... but that is not what happens... the heat is driven by the amps not the volts or the net power... which shows that more of the power is not lost to heat when one has higher voltage.... which turns out to be 100% correct... this is a very old very well known phenomenon of current and heat generation.

------------------


The major flaw with the spring example is that there is no energy conversion with the spring while it is held stationary ... and there is no energy flow over time while it is held stationary... if you had both of those with the electrical motor it to would have zero power at zero RPMs.

In the spring example... it is not because there is 0RPMs that there is no power... there is no power because there is no energy conversion ... and no flow of energy over time.

That same thing is not true for the electrical motor... In the electrical motor there is energy flow over time... and energy conversion... either of which mean you have power even at 0 RPMs.





That's allot of periods...
But I still disagree.... even if I also still say it is just an academic discussion.

Now I will grant you... that if you want to just ignore the power at 0 RPMs for one reason or another... fine... but weather you want to ignore it or not... there is power there.

Even if you begin to exclude lots of things ... like when you say mechanical power you are also ignoring any perpendicular motion ... if at 0RPMs the electric motor caused the whole vehicle to move perpendicular to the rotational axis ... by the excluding rules of mechanical power that motion doesn't count and it would still give a result of 0 even if the whole EV is moved at any acceleration or speed you like, because as soon as you say mechanical power you exclude all perpendicular motion ... which just shows how silly it can get when you start to just exclude things... Mechanical power also excludes any vibration that is perpendicular , etc... it is just a way of ignoring lots of things that are actually there.

If you want to ignore it fine... but it is still there.

-----------------------

An other way to see that there is power at 0RPMs is the 'Instantaneous Power' ... Instantaneous Power is power with no time and no movement... ie 0RPMs because it is instantaneous and it would take at least some time to move, at any speed .... there is even 'Instantaneous Mechanical Power' ... or mechanical power without any motion and without any passage of time.

But that is even more academic than we have already been.

----------------------

I still hold that... it doesn't matter... find the rating for your components under the conditions you will use them... including pulling out on a hill from a stop... use torque or power... whatever makes you happy... if you like it easier and just want to ignore the power at 0RPMs... go ahead... I don't see how it will effect 99% of the EV builders either way... do it however you want... if you don't know enough about it.. ask others who have done conversions and or read up and or pay someone to do it.