# Article on Motor Voltage



## major (Apr 4, 2008)

ElectricSpeedShop said:


> Hello All, in my never ending quest to learn and share all I can about EV conversion knowledge I wrote an article about the importance of choosing your motor with the correct voltage for your desired use. Would appreciate any feedback on what I may have missed/ got wrong.
> 
> 
> 
> ...


I quickly looked at it. I could not get past this sentence. 


> Next you need to think about the voltage of your system.
> *Voltage is essentially the flow of your current through your system.*


Your definition of voltage is so wrong. 

Regards,

major


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## electro wrks (Mar 5, 2012)

Yes, you need to revisit the electricity/water flow analogy:https://learn.sparkfun.com/tutorials/voltage-current-resistance-and-ohms-law/voltage


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## brian_ (Feb 7, 2017)

The title of the article is misleading, because it doesn't seem to be specifically about motor voltage at all. Perhaps splitting it up would help...

sources of motors
system voltage
power
etc


From the blog post:


> Well torque and HP are both measures of power or the ability to do work.


No!
Please review the meanings of "torque", "power", and "work" (in physics), and note that "HP" is an abbreviation for "horsepower", which is just one specific unit of measure for power.

I don't think it makes sense to conduct a basic course in this thread, but for a start... you can apply torque to a shaft and be doing no work at all, if the shaft is not turning.

Once you have these basic concepts down, and have corrected your electrical understanding (the voltage and current issue identified above), you can make suitable connections between motor current and torque, and between electrical power input to the motor and mechanical power output of the motor.


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## brian_ (Feb 7, 2017)

Since there are substantial issues with the article, and it is essentially a draft which is being reviewed and improved, does it make sense to have it publicly posted as if it is a useful reference? If someone runs across it while looking for information, outside of the context of this forum discussion, they're likely to be confused and unintentionally misled.


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## brian_ (Feb 7, 2017)

Again from the blog post:


> Now let’s look at jumping up the voltage, staying within the same brand of motor.


You used performance charts for the AC-20 at up to 96 volts, then show a chart for the much larger AC-51 at 144 volts, and suggest that the difference is due to only the voltage! Please don't do this; if you want to show the effect of voltage, stay with the same motor; two different sizes of motor at the same voltage could be used to illustrate the importance of current to produced torque.


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## ElectricSpeedShop (Dec 4, 2018)

Thanks all! I will be making corrections tonight. Some of these I am ashamed I did not catch. Appreciate the fast feedback from this very knowledgeable crowd!


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## ElectricSpeedShop (Dec 4, 2018)

major said:


> I quickly looked at it. I could not get past this sentence.
> 
> 
> Your definition of voltage is so wrong.
> ...



I think this was a typo as the next sentence more correctly describes the current as the flow. Either way I will fix it, appreciate the feedback!


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## ElectricSpeedShop (Dec 4, 2018)

brian_ said:


> The title of the article is misleading, because it doesn't seem to be specifically about motor voltage at all. Perhaps splitting it up would help...
> 
> sources of motors
> system voltage
> ...



I will definitely have to research this more. My physics knowledge has not be tested in years! Appreciate the cliff notes!


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## ElectricSpeedShop (Dec 4, 2018)

brian_ said:


> Again from the blog post:
> 
> You used performance charts for the AC-20 at up to 96 volts, then show a chart for the much larger AC-51 at 144 volts, and suggest that the difference is due to only the voltage! Please don't do this; if you want to show the effect of voltage, stay with the same motor; two different sizes of motor at the same voltage could be used to illustrate the importance of current to produced torque.



Does the AC20 come in a higher voltage than 96V? I did not mean to imply the difference was only from the voltage but I understand how it could be interpreted that way. Certainly will clarify. Thanks. I included 3 AC20 to show the jump and then quickly jumped to larger and higher voltage motors to illustrate the impact. Will have to be careful in the future with that that might infer to someone. Appreciate the feedback!


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## brian_ (Feb 7, 2017)

A response posted to the blog entry says this:


> Bottom line is AC motors vs DC
> Are the best. higher voltage is more power with less amps and smaller wires. That is why all new electric cars use AC motors and 400 volts.


This person is confusing the somewhat separate questions of AC versus DC, and low versus high voltage. 

If you want to address that, you could explain that the operation of the brushes and commutator of a brushed DC motor put a practical limit on voltage. There are, of course, factors entirely unrelated to voltage which lead all production EV manufacturers to use AC motors.

Along with the AC versus DC confusion, this person sort of wanders toward another voltage-related point which is not covered in the blog entry: for a given amount of power, voltage and current are inversely proportional, so if you use more voltage (by selecting a different motor) you use less current. Of course, that would naturally fall out of covering the electrical basics as I suggested earlier.


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## brian_ (Feb 7, 2017)

ElectricSpeedShop said:


> Does the AC20 come in a higher voltage than 96V?


Yes. HPEVS doesn't appear to offer these motors wound for different voltages - they just publish performance charts for the same motor with various controller current limits and supply voltages. The performance charts look different at different voltages, even at low speeds where the performance is limited by current rather than voltage, because they test them with different current limits as well... sort of randomly, based on the controllers they happen to have on hand. It would be more useful if they just used one controller and ran tests with a high voltage supply at various current limits, then with the highest current limit at various voltage limits, the way serious motor manufacturers do.

Also, HPEVS charts show "battery voltage" and "current", which are actually DC link voltage and current (what is coming to the controller from the battery)... not motor voltage and current. If you're trying to understand how current results in torque or how more voltage is required for a given current at higher speed, these charts are confusing at best; I'm not convinced that "straight forward" is a valid statement about these measures in the charts.

I shouldn't criticize HPEVS performance data, because at least they publish extensive and useful performance data, unlike most (perhaps all) of the brushed DC motor sellers and many of the other small motor sellers. That's may be one reason they were picked as the example for this blog entry.

I've never seen an actual published maximum voltage specification for the HPEVS motors, but their suggested controller options and performance charts imply that at least 144 volts is permissible for all of the larger sizes (AC-20/23, AC-34/35 single and double, and AC-50/51), and at least 96 volts for the smaller sizes (because, well, no one uses more than 96 V on a golf car or small industrial cart).


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## brian_ (Feb 7, 2017)

brian_ said:


> From the blog post:
> 
> 
> > Well torque and HP are both measures of power or the ability to do work.
> ...





ElectricSpeedShop said:


> I will definitely have to research this more. My physics knowledge has not be tested in years! Appreciate the cliff notes!


Okay, but the text has been edited so it now says this:


> Well power is the ability to do work and your available torque will allow you do work faster in this case.


Still no: power is the rate of doing work, so more power (not torque) "will allow you do work faster".

I really think it's worth taking a step back and making a fresh start, rather than tweaking a phrase here and there.


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## ElectricSpeedShop (Dec 4, 2018)

Thanks I will have to look at it again when I have more than 5 minutes.


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