ESC Current Output Testing

[hotrod6107]

Here is an interesting video from RC Review on YouTube. If nothing more to shed some light on how much current you can get out of some popular ESCs and BECs.

https://www.youtube.com/watch?v=NYqDSJaSX4A

[Jim85IROC]

Interesting that the Mamba X put out more current than the Castle BEC. I'm glad I ditched my BEC when I installed my Mamba X into my Bomber.

[Xx Losungen xX]

Not an accurate test at all.

He should be measuring for voltage drop as well as current drawn.

Also, more volts does NOT equal more current, his electrical theory is incorrect.

If he did this test properly, I bet you'd see the Mamba X dropping more voltage over the BEC resulting in the higher current being drawn.

The end result is that the power, or work being done is the same on both, but the BEC is more efficient over the Mamba X.

[twade984]

Originally Posted by Xx Losungen xX

Not an accurate test at all.

I watched the video the day it came out, and it’s been bugging me ever since. I don’t claim to be great with electrical, but from my understanding, the bec (internal, or external) does not “put out” amperage. The load (servo in this case) draws the amperage. The draw should depend on physical resistance to servo, voltage being supplied, and built-in electrical demand of the servo.

Amp rating of the bec (internal or not) just indicates what it can tolerate, and as electronics work, they get hot, heat increases resistance, resistance increases voltage drop, and lower voltage causes a drop in output (servo torque in this case). And I’m sure at some point those factors may cause esc to not work properly, or possibly fail altogether (internal bec).

I’m probably wrong, but I really hope someone with real knowledge chimes in with a more informed explanation.

[Xx Losungen xX]

Originally Posted by twade984

I’m probably wrong, but I really hope someone with real knowledge chimes into this thread.

You are more right than wrong, in a round about way, your understanding is correct.

Your understanding is superior to the author of this video in fact.

My knowledge on the subject of electrical theory IS REAL knowledge btw

[twade984]

Originally Posted by Xx Losungen xX

You are more right than wrong, in a round about way, your understanding is correct.

Your understanding is superior to the author of this video in fact.

My knowledge on the subject of electrical theory IS REAL knowledge btw

maybe I'm just missing the point to the video. Maybe it's just meant to be a visual demonstration.. i don't know. I do enjoy his videos, and I'm not trying to talk shit. Just trying to understand better.

[Prescott John]

I saw that video too, and was thinking that showing voltage drop along with the amps draw would have been more informative. The other thing I wonder about is how long can an ESC maintain the currant supply.

[tuxstang]

Good video but missing a point ... knowing how much amps the BEC can deliver is great but when brown-out happen on the trail, it's rarely with just the servo running, but when both the servo and motor are taking their toll on the ESC ...

[Xx Losungen xX]

Originally Posted by twade984

yeah, I didn't mean to imply no one else could have real knowledge on the subject, but mostly everyone is random names to me here. I don't know who actually knows what they are talking about.



maybe I'm just missing the point to the video. Maybe it's just meant to be a visual demonstration.. i don't know. I do enjoy his videos, and I'm not trying to talk shit. Just trying to understand better.

I meant it as a joke mate, words on a screen, hard to decipher sometimes hehe.

[Xx Losungen xX]

Originally Posted by Prescott John

I saw that video too, and was thinking that showing voltage drop along with the amps draw would have been more informative. The other thing I wonder about is how long can an ESC maintain the currant supply.

If he measured voltage drop, he'd more then likely see that the servos are doing the same amount of work (power/watts) and that the rise in current is due to the voltage drop. Which actually means that circuit is less efficient.

The way his video is produced, he seems to think that the BEC, esc etc. produces current and the higher the better, that's just completely false.

[Alka]

I don't understand why there would be a voltage drop with a switch mode regulator . That is what they are designed to do. Keep the voltage stable regardless of input voltage and current draw. I use a number of switch mode regulators in many designs and you can bet if the regulator does not maintain its voltage and up to its rated maximum current as specified in its data sheet then the whole lot goes back to the manufacturer as defective.
If you feed a servo directly from a battery then there will be a voltage drop at the battery because it has internal resistance. Otherwise if I make a 5 amp switch mode regulator that is set to 6v for example. It puts out 6v at 1 amp at 2 amps or 5 amps. If it doesn't its either designed wrong or the manufacturer is lying in their datasheet and they will sure hear about it!
It would have been nice to know what voltage each of the BECs were set at though since. I would hope that they are set to the same output level or its not much of a test.

[Jim85IROC]

Originally Posted by Alka

I don't understand why there would be a voltage drop with a switch mode regulator . That is what they are designed to do. Keep the voltage stable regardless of input voltage and current draw. I use a number of switch mode regulators in many designs and you can bet if the regulator does not maintain its voltage and up to its rated maximum current as specified in its data sheet then the whole lot goes back to the manufacturer as defective.
If you feed a servo directly from a battery then there will be a voltage drop at the battery because it has internal resistance. Otherwise if I make a 5 amp switch mode regulator that is set to 6v for example. It puts out 6v at 1 amp at 2 amps or 5 amps. If it doesn't its either designed wrong or the manufacturer is lying in their datasheet and they will sure hear about it!
It would have been nice to know what voltage each of the BECs were set at though since. I would hope that they are set to the same output level or its not much of a test.

I had a similar post earlier then deleted it because I didn't have time to elaborate at work. Because these are constant voltage outputs, I'm guessing that they utilize a current limiting buffer on the input of the rectifier specifically to protect the circuit. On the cheaper ESCs with linear rectifiers, I'm more inclined to think they allow the voltage to sag specifically to avoid the cost of a current limiter.

[Xx Losungen xX]

Would love to see the source stating the BEC and mamba X are switching regs and what the specs are. Note that I only mention these two above.

I already know the pro bec is a switching reg.

What are the tolerances on the 1080s bec?

Where are you guys buying switching regs with 0% tolerance? The best I've gotten my hands on are around 0.5%, built or bought.

Crappy Chinese no name bulk ones can be upwards of 10%, have tested some as high as 20%.

[Alka]

Pretty sure you will see switching regulators in all of these. I don't know why they would use a linear one since switch mode regulators are so cheap to make and produce much less heat and take up less board real estate for the same power output.

I can provide no sources for this. I am only making a guess as to their designs. It would be like seeing a carburetor in a modern car.

I am not saying there are perfect loss free devices but the output of a voltage regulator will be within tolerances that the manufacturer states.

[Steve g]

So I've seen a few of his videos, which i enjoyed, but I've got one question. How does the amperage go up when the voltage goes up?
Let's focus on the servo as just a dc motor. I am an electrician, so I know electrical theory and practice, at least in ac. Take a 3 phase ac motor, hook it up to 208v, and it draws say 32 amps. Take this same motor and hook it up to 480v, and it'll draw less then half of what it would on 208. Why? Well power equals amps times volts (P=IE). The motor will produce the same power ( watts) on either voltage, so increasing the volts decreases the amps.
Take a dc motor, 3 phase (brushless) or single (brushed), and suddenly its the opposite? Seems like it from his videos on servo testing. Well how about our brushless motors? Take a 3500 kv motor, like a puller pro rated for 4s, run it on 2s and everything is cool and happy, throw it on 4s and things start to heat up. Now why is that? Seems like the motor is making more power (watts) which is more heat. In theory it should have the same wattage on 2s and 4s, which to me it doesnt seem to be the case right? Same with the servos, increase the voltage and it gets warmer faster, and also has more power. So what am I missing here? I don't know much on dc motors other then these rc motors, so I'm looking for someone to point me in the right direction here...

Sent from my SM-G970U using Tapatalk

[Xx Losungen xX]

Originally Posted by Steve g

The motor will produce the same power ( watts) on either voltage, so increasing the volts decreases the amps.
Take a dc motor, 3 phase (brushless) or single (brushed), and suddenly its the opposite?

The opposite seems to be what's being suggested here, I've personally never come across ANY circuit that breaks ohms law myself.

The servo (load) in this test is identical.

If applied the same voltage across all tests, the load will draw the same current across all tests.

In this test, the current is different across all tests, which means the voltage is as well, it's just a fact, actually it's a law.

I'm very curious how it's being suggested that this very simple and basic law somehow does not apply here.

It's quite obvious to me here that the voltage is NOT the same across all tests at FLA, otherwise FLA would be exactly the same.

[Xx Losungen xX]

Originally Posted by Alka

I don't understand why there would be a voltage drop with a switch mode regulator.

A switch mode regulator, ANY voltage regulator for that matter won't work without dropping voltage.

It's exactly what it's designed to do.

If I have an EMF of 12 volts and want to regulate it at 6 volts, I'm dropping 6 volts to do so.

Originally Posted by Alka

If you feed a servo directly from a battery then there will be a voltage drop at the battery because it has internal resistance. Otherwise if I make a 5 amp switch mode regulator that is set to 6v for example. It puts out 6v at 1 amp at 2 amps or 5 amps.

You're saying that if you make 5 amp switch mode regulator that it does not drop voltage to maintain 6v?

The only way that would happen is to have an EMF of 6 volts, which would make your regulator pointless.

Originally Posted by Alka

It would have been nice to know what voltage each of the BECs were set at though since. I would hope that they are set to the same output level or its not much of a test.

Isn't this the exact point I made?

Except that what matters is what the actual observation says and not it's intended or designed output, and since it won't be a rise in voltage, it'll be a voltage DROP, would it not?

[Alka]

Originally Posted by Xx Losungen xX

A switch mode regulator, ANY voltage regulator for that matter won't work without dropping voltage.

It's exactly what it's designed to do.

If I have an EMF of 12 volts and want to regulate it at 6 volts, I'm dropping 6 volts to do so.



You're saying that if you make 5 amp switch mode regulator that it does not drop voltage to maintain 6v?

The only way that would happen is to have an EMF of 6 volts, which would make your regulator pointless.
Isn't this the exact point I made?

Except that what matters is what the actual observation says and not it's intended or designed output, and since it won't be a rise in voltage, it'll be a voltage DROP, would it not?

So this is what you meant by voltage drop? I don't even think it's relevant to know the starting voltage of the battery as it doesn't mean anything here.

I really think we have our wires crossed on this one.. a voltage regulators output (buck) is lower than the voltage fed into it yes..

So if he is using a 28v power supply or a 10v battery what would knowing that help?

Edit : reading back at your older posts I think I understand you want to see a comparison of efficiency . I apologize if i got you backwards.. we would also need to know the current draw at the source but this would be nice to know!

[Xx Losungen xX]

Is he not testing efficiency?

Is he not concluding that higher observed amps are better?

Can we not agree that given the simplest of all electrical laws that higher current implies a voltage drop?

Do we not both know that a higher voltage equals a higher efficiency? Ie. Due to losses etc.

If we are agreeing on those above, then we should be able to agree that yes, I am looking for the same test, efficiency but with accurate results?

If we STILL agree, what are we missing? Voltage Drop!

If you agree with my last sentence, wtf have we been talking about?!

[Alka]

Originally Posted by Xx Losungen xX

Is he not testing efficiency?

Is he not concluding that higher observed amps are better?

Can we not agree that given the simplest of all electrical laws that higher current implies a voltage drop?

Do we not both know that a higher voltage equals a higher efficiency? Ie. Due to losses etc.

If we are agreeing on those above, then we should be able to agree that yes, I am looking for the same test, efficiency but with accurate results?

If we STILL agree, what are we missing? Voltage Drop!

If you agree with my last sentence, wtf have we been talking about?!

No, I don't think he is testing efficiency or even trying to. It looks like he is testing weather the BEC can handle the full load of a servo of a powerful servo without limiting current.

Higher current does not imply a voltage drop . The current output can be fixed to a certain level by design and very simple circuitry.

To get efficiency we would need to know watts at the source vs watts used by the servo. The difference would be watts wasted BY the bec.