motor/kv/ system question
 

imagine the following 2 scenarios, the goal of both is to move a 12 pound monster truck at the ridiculous rate of 55mph or so, both systems at 6S, and BOTH SYSTEMS HAVE THE MOTOR SPINNING THE SAME SPEED, AND SAME VEHICLE SPEED:

1) 2200kv motor with a whatever-size-you-want pinion, but throttle epa turned way down, truck goes 55mph

2) lower than 2200kv (1700kv??) motor, same size pinion, epa @ 100%, truck goes 55mph

the question - regardless of what you may think about running a monster truck at these speeds, are there any differences between these 2 setups? In other words, is the motor, battery, or esc working harder in either system? My guess is that the motor in both setups should run the same temp, but I'm lost from there.

HELP!

why?
:neutral:

Option 2 - more effecient lower temps...

Motors have an effeciency curve IIRC using EPA is not ideal...

Yes option 2 will have lower temps but i don't think that it will be lower by much. Probably by 1 C??? The kv difference isn't all that much.

eh thats like a 1y vs a 2.5d... Amost 33% more KV's in the 1Y... ie 37.7k RPM vs 48.8K RPM

Quite a difference...

Well then any idea about the temp diff for that 33% kv diff?

Well I have both motors, 6s batteries, an eagletree and a temp gun

hmmm only one problem - my pinion is set screw is stripped on the 2.5D on the the revo...

When I get a spare day I'll let you know...

Speed controls aren't as efficient at less than full throttle. ESC would have more heat with throttle end point turned down. A 1515 2.5d on 6s will get you to 55mph easily as long as you have a smooth finger, otherwise you'll wind up on your lid, same with a 2200kv motor.

you simply wouldn't want to run a brushless setup with your epa turned down. As stated before it's rough on the esc and causes heat. You wouldn't buy a corvette and unplug 2 spark plugs, it just doesn't make sense.

Yeah, they barely run as it is!

Is the EPA setting relative to the kv rating of the motor?

case 1: A 4000 kv motor at 4S EPA 100%. Motor has max efficiency at 40k rpm. The rotor will be turning at 59.2K rpm which obviously is going to heat up the motor and possibly over work the esc.

case 2: The same motor at 4S at EPA 67.5%. Assume that the motor is running at 40K rpm which is at the max efficiency rpm. Motor will be running cooler and not overloading the esc.

Will the above be true?

its just a silly backwards way of doing things. you first figure out what batteries you will run, then match your motor kv to that. If you're overvolted get a smaller battery, don't turn your epa down to compensate.

Here's an idea: 2200kV motor at 100% EPA going 70mph. :neutral:

Other than that I'd use the second option. Compensating with EPA seems a bit backward to me also.

well, the question has been asked "why", and it's real simple; see my other thread!!

Now that u mentioned it, will it work well by compensating with EPA values down?

Will it cause any damage to the system? Will the esc work harder with a lowered EPA setting to meet a specific range of motor rpm? I mean as compared to the same rpm range of a system with 100 EPA but with lower cell count. If the motor to be used is identical in both setups.

I was thinking that as long as the motor is being operated at its recommended range of RPM for good efficiency, the cell count or epa value doesn't matter. Please correct me on this. Thanks.

Any explaination as to y it is not recommended to compensate by reducing EPA values other than that the esc could be working harder?

I can't give you a technical explanation, but partial loads on the esc are what heat it up. Allowing the esc to be "wide open" and just flow power is less stressful on it. Turning down your epa effectively makes your esc a partial load at alll times and isn't good for it. I wish I could give you technical terms and what not, but this is my farmboy answer.

Sums it up pretty well in my opinion, although I liked the vette analogy better. :D

I would go over to the 2000 kv 80mm medusa first. Or if you have the money the 1521 series neu.

Why does an ESC run cooler at WOT than at partial throttle? Simple; fewer on/off pulses. To get variable power, the FETs switch on and off. However, a FET does not switch on and off instantly - there is a ramp up and down. This ramping is where the power is lost as heat. When at partial throttle, the ESC sends more of the on/off pulses to limit the average voltage. Think of it this way, if the ESC is 10% of the time "on" and 90% of the time "off", the motor will see an average of 10% of the battery voltage. At WOT, the ESC is sending full battery voltage, so there are no on/off switching cycles (well, not counting the switching between the phases).

I hope that made sense.

FYI, there is no difference between setting the EPA at something less than 100% and not using the full throttle trigger throw. So, you can have the EPA set at 100%, but if you are only using 1/2 the throttle trigger throw, it's the same amount of losses as setting the EPA at 50% and using full trigger throw.

If the setup is too fast, reduce gearing (will increase torque), get a lower kv motor (may increase torque), or reduce battery voltage.

Hi there. thanks for the explaination. Correct me if I am wrong. So you mean that there is some actual pwm switching of the fets when powering each phase to vary the power delivered to each motor phase right? Doesn't the esc just rotate the magnetic field to get variable speeds by just switching the fets just on and off without pwm?

Yes, there are two stages of FET switching. One stage is the rotation of the magnetic field, but then those are PWM chopped to regulate the power.

Oh I see. That explains everything. Thanks alot really.