Very interesting Setup from Mega Motors

[Serum]

Yeah glass, that's what i am saying.............

[sleebus.jones]

Originally Posted by glassdoctor

10v at 100A= 1000W
20v at 50A= 1000W
100v at 10A= 1000W

This is true, obviously.... but you can't apply it backwards to our cars and say that a given motor will put out a constant 1000W, therefore, if you run it on more volts, the amps will go down.

Ah. So, this manufacturer is lying on their motor dataplate:



As much as has been argued otherwise, a motor is a constant power device, and the proof is right there in the picture. As voltage goes up, amp draw goes down. If it didn't, then if you ran this motor on 208v, it would magically become a 3.5 HP motor, which is not possible. When you run it on 208v, it draws less power. It's not able to do any more work (which means horsepower, which is equivalent to 746 watts) than it was on 110v, which is exactly why the amp draw goes down. The motor power is set by the design, not the voltage.

Either I'm wrong, or someone changed the laws of Thermodynamics while I was sleeping.

Sleebus

[MetalMan]

The motors we use in RC will never run at constant power.

On the previous page you mentioned after BrianG's that Ohm's Law has nothing to do with this. In fact, it does. The motor has a resistance that is constant for the most part. If you do not change the gearing when increasing voltage, then the resistance is constant. You cannot use constant power to determine the amp draw, as the only thing that would be close to determinging the MAX power is the battery, but the only possible way for you to be running at constant power is if you were running at full throttle the entire time and the speed/terrain/acceleration/battery voltage were also constant.

So, since power is not constant, the amp draw will increase as voltage increases (assuming a fixed load, IE same gearing). If you use higher voltage AND the load decreases (smaller pinion or larger spur) then the amp draw decreases.

[GriffinRU]

Originally Posted by sleebus.jones

Ah. So, this manufacturer is lying on their motor dataplate:
Sleebus

I will explain later, below is more confusing then helping. SORRY

Ther is a difference between this motor and motors we use in RC.

This motor power determines by induction of the motor windings and once they saturated there is no more power, but you can burn it :)

In our case we have constant magnet inside and we can drive coils until saturation (if there is a core) or until meltdown, obviously there is no need to get more magnetic power then constant magnet has...

Artur

P.S. It is very simple "how it works"
Cool link and more models on the side bar

[Serum]

Sleebus, read my post.

(http://www.rc-monster.com/forum/show...4&postcount=27)

And if you look closer to the picture of that motor, it has got TWO setting, one for high and one for low voltages.

Please stop being sarcastic sleebus, this is just a discussion, nothing changed while you where sleeping, that motor always had two settings.

[sleebus.jones]

Originally Posted by Serum

Sleebus, read my post.

(http://www.rc-monster.com/forum/show...4&postcount=27)

And if you look closer to the picture of that motor, it has got TWO setting, one for high and one for low voltages.

Ah! Well, I must admit, I did not see any such setting. I'm squinting at it now, and I honestly can't see what you are talking about, but I do trust you that it's there. That would explain why the motor is acting so weird electrically.

Originally Posted by Serum

Please stop being sarcastic sleebus, this is just a discussion, nothing changed while you where sleeping, that motor always had two settings.

I'm just trying to inject a bit of humor. I shoulda put a ;) at the end. Sorry that I came across as a jerk.

Sleeb

[BrianG]

Originally Posted by sleebus.jones

Ah. So, this manufacturer is lying on their motor dataplate:



As much as has been argued otherwise, a motor is a constant power device, and the proof is right there in the picture. As voltage goes up, amp draw goes down. If it didn't, then if you ran this motor on 208v, it would magically become a 3.5 HP motor, which is not possible. When you run it on 208v, it draws less power. It's not able to do any more work (which means horsepower, which is equivalent to 746 watts) than it was on 110v, which is exactly why the amp draw goes down. The motor power is set by the design, not the voltage.

Either I'm wrong, or someone changed the laws of Thermodynamics while I was sleeping.

Sleebus

Sleebus, I can see where you might be coming from with the whole "work" thing, but there are assumptions made which are incorrect.

Motors are not constant power. The power listed on a motor tag will be at the nominal rated voltage. Actually, they usually list this power as "VA" which takes power factor (basically an efficiency factor) into consideration, but I won't go into that. If you double the voltage, you WILL increase current and power by a substantial amount. Maybe not exactly double because of the change in rpm (therefore beack EMF, ie: resistance), but close.

Most dual voltage (120v/240v) AC motors I've seen have alternate sets of windings/connections for the optional voltage; or if three phase, you can hook the windings in wye instead of delta or vice versa. And that's what the little diagram on the right looks like - a way to wire the windings for higher voltage. The motor windings would not like it if you tried to double the current going through them. So, the alternate wiring was designed to increase resistance enough so the power remains the same with higher voltage.

Besides, how could a passive device be constant power? The resistance would have to change. The only way for a device to be a constant power device is if it had active circuitry to read the voltage and be able to adjust its resistance to develop less current to generate equal power.

Ohms law is Ohms law, and it works - always. It gets a little more complicated than simple Ohm's law for AC motors because you have to take in drive frequency, rpm, and winding inductance (which changes the voltage to current phase angle).

[GriffinRU]

Much better link then "howitworks"

So, nobody tried mega motors?

Artur

[coolhandcountry]

Look on the right side. It says low voltage then right below it has high voltage.

[Serum]

Yeah, on the right of that picture.

[starscream]

Originally Posted by Serum

Cool!

This motor/mount is really awesome!!!

About the current draw;

Plain simple;

If a car is geared for 40 mph on 3S lipo, the current draw will be higher than that same car geared for 40 mph on 5S.

But.... It's rather uncommon to increase the number of cells to get more runtime... If you use more lipo's you obviously need more power. If you need more lipo's to get more speed, the current(A) will also increase.

The numbers they are talking about don't mean nothing to me. The current they take varies a lot. weight of the vehicle, maxximium amount of power the batteries can deliver before their voltage will drop, gearing, and the power they take under acceleration.

I am consistantly able to get 3+ minutes more runtime from my 6S setup geared for 30mph than my 5S setup gear for 30mph. This obviously proves that current is reduced with higher voltage.

Yes, higher voltage will decrease your current (assuming you adjust your gearing to match speed). I think it is unfortunate that people do not use more efficient setups to achieve longer runtimes. I would love to adopt an 8S setup but I can not find a suitable esc for the job (w/ 4 pole motor). I tried the castle HV110 but it doesn't work well with a pistal grip TX.

[Serum]

You are using the cells to get more runtime. Not for more speed. (30mph vs 30mph)

So the statement is correct.

[coolhandcountry]

By dropping the gearing down on motor. You change the torque load on
motor and also changes the amp draw. Also with more voltage on a motor
you don't have to run as hard so the amp draw is not as bad. If the truck
will flip over at 750watts. The higher voltage will make the truck flip with less
throttle input.

When you got to 5s you stated you changed the gearing.
You are adding more current avilible with another cells as well.
If some one has an eagle tree. It would show up better.

[BrianG]

I too noticed increased runtime with more cells, but that turned out to be simply that you are into the throttle less to achieve the same speed. The max power with a higher voltage setup is higher, so you don't need to push the batts as hard to get the speed you want. There is some savings with higher rpm since there is a little more "resistance" so that helps too.

[Nick]

That square heatsink looks ugly, is it for sitting flat or something?