Very interesting Setup from Mega Motors

[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.

[coolhandcountry]

I think this was discussed one time before on voltage and amp draw.
With the same resistance. ( same motor on same gearing)
If you go from 3 cells to 6cells which is twice the voltage.
The amp draw will go up roughly double.
A light bulb with more voltage will burn brighter.
I know cause i have done this. It won't last long though.

[Serum]

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

[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.

[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

[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.

[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.

[GriffinRU]

Originally Posted by 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.

You will get better efficiency overall with higher voltages. All losses associated with resistance goes down with the current.

Power loss = Sum[I^2*R(x)],
where R(x) resistance of:
- motor
- wires
- connectors
- FET's
- Cap's
- Batteries
- ...

Going really high in Voltage is not good as well :) There are obvious reasons and electrical.

Artur

[BrianG]

Doh! How could I forget wiring losses! :007:

[Nick]

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

[glassdoctor]

Serum, I probably missed your post.. I skipped a few posts on the first page, sorry. I'm sure you tried to make the same point as me.

We are having some difficulty making it clear to sleebus and maybe some others....

Please guys, don't get this confused with changing motors, and/gearing with a change in voltage. That's a different subject.

Try again:

A motor DOES draw more amps with higher voltage, under the same load.

Sleebus, let's use that motor in the picture you talk about as an example. It doesn't have a built-in current limiter that forces the motor to only draw the rated 1hp, or 746 watts. That is only a rating on what the motor can do within spec, without self-destructing or stalling, etc. Each motor has a limit to what it can do, for both short cycles and continuous duty.

If that motor produces 1 hp at 110V, then it would indeed produce more power at higher voltage. But at some point it will burn up, literally. That is why we have different motors that are designed to run at higher voltage. They are a different wind, and draw less amps and turn a lower rpm per volt. So when this "high volt" motor is run at the higher voltage, it can produce the same hp at half the amps. It's a DIFFERENT motor.

I wish you were right sleebus, because we could have our cake and eat it too. :004: