More Voltage = Less Amp Draw?

[starscream]

Originally Posted by BP-Revo

Thats ok then. If I set "full brake" as neutral, but my EPA is set to 0, then the controller will still not receive anything further than its percieved maximum full brake, and all should be ok.

Yep, thats exactly how I had it configured and "Beep" the esc would randomly "reset" and off it went to the races and all the while I was doing the WOT dance and trying to get control of my truck back. It was startling to randomly see the wheels turn to pancakes or just flip on its lid as I gave it brakes. The only fix for this was to cycle the power on the esc and let it re-arm itself.

This was quite frustrating as the EPA should have prevented the esc from detecting the brake but unfortunately it did not.
I hope you have better luck than I did.

I'm eager to hear how it goes for you.

captain harlock ygpm

Originally Posted by captain harlock

I have it. It's good, but it thermals alot, although I used it in a 2wd 10th scale buggy( very light) with a 1920/8 and 10 GP3300mah. I even used a 12v fan and even that did not help alot.
IF, you are gonna use it with a 540 sized motor, then you probably need to feed the motor with lots of volts to cut down the amp draw. Even Mike Franz, an official of Kontronik's technical department, said that it isn't really made for use in cars, despite the fact that it has two types of car programs.
I found that it thermals alot when you apply brake more often. Probably if you use mechanical brakes, that'll keep the controller much cooler. Either than that, this thing is smoooooooooooooth.

Shucks. I hope it doesn't thermal. You're not the first person to tell me this though. I will be running 10S to minimise amp draw and hope that will be sufficient. At 30V (3.0v/cell) and 65A, that's 2000W - well within its ratings. I thought about getting an MGM controller, but the Kontronik is cheap enough to risk it. I'm into RC helis too and I know the Jazz will be useful for a future heli if it ends up on the shelf with this experiment.

Glad to know it runs smoothly. I've read old posts about it cogging. I guess that was with old firmware. Cool!

[captain harlock]

It coggs because its not strong enough to handle a motor in a rc car.

Make note that this thing only gives a 55amps continuous and 65-70amps surge. It isn't really a good choice for MTs.

[starscream]

Originally Posted by captain harlock

It coggs because its not strong enough to handle a motor in a rc car.

Make note that this thing only gives a 55amps continuous and 65-70amps surge. It isn't really a good choice for MTs.

In my experience, my lower amp esc work's most efficient with an appropriately geared automatic 2 speed transmission. For example, I have an esc that runs most efficent at ~35amps. The pwm kicks in after ~50amps or so but I don't notice the pwm kicking in when I use an automatic 2 speed tranny like the tmaxx or Revo trannies. Now, if I put this same esc/motor in my single speed losi 8ight the pwm kicks in very quickly as the amps spikes are much higher with the single speed so I am no longer considering using this esc for the 8ight. I plan to get some eagletree comps once I get my G2R back together. The auto two speed tranny is a great load buffer but you do sacrifice a percentage of the instant power capability of the higher amp esc's.

[BP-Revo]

I hope it works for me too. :p

I might tweak with the controller and adjust the subtrims or something so that the "neutral" the ESC will see when my throttle trigger is between neutral and full brake is just infront of full brake, but not enough to engage throttle (like in the little dead-band spot in between).

We'll see. My CRX seems to be very good about holding EPA adjustments properly.

yes simple ohms law. P=VI. 500wattts=50voltsX10Amps or 10voltsX50Amps. You get my drift.

[BrianG]

Gotta remember the resistance factor in there...

50v will only draw 10A if the resistance is 5 ohms. 10v will draw 50A with a 0.2 ohm load. Both do generate 500w.

[Serum]

Yes, that's the reason for a HV setup being more efficient.

[BrianG]

Yeah, I just want to make sure some people realize that simply adding more voltage on an existing setup will just increase current. You need to increase the motor winds quite a bit when you increase voltage if you want less current.

[BP-Revo]

Yea, for ~40,000RPM, I need a 20 turn 1530 motor, which is dang high (way higher than I had ever expected). But it should fly :D

Originally Posted by BrianG

Yeah, I just want to make sure some people realize that simply adding more voltage on an existing setup will just increase current. You need to increase the motor winds quite a bit when you increase voltage if you want less current.

and/or regear ... :)

[BP-Revo]

Not exactly...no amount of regearing will change the fact that most motors lose efficiency above 40,000RPM.

[Serum]

who said it runs above 40K?

And a setup with 85 percent efficiency can draw less current than one with 95 percent efficiency..

Why do you say motors loose efficiency above 40k RPM? Which motors exhibit this behaviour?

Motors run most efficiently when iron losses and copper losses are equal. Copper losses increase as torque load increases (current goes up), while iron losses increase when RPM increases.

Obtaining maximum motor efficiency is a balancing act of seeing how much torque you need, and running your motor so that its RPM is high enough to deliver the required torque after gearing and low enough to achieve an equal balance between iron and copper losses at these torque levels.

In e-heli world, high performance setups are chosen so that motors run just below their peak RPM where heat buildup increases exponentially due to iron losses. At that point the motor delivers the highest torque after gearing before copper losses become too high.

[BP-Revo]

Well maybe it isn't 40K but it sure as hell isn't as high as 100k...