Basics of brushless motors

http://www.cirrus.com/en/pubs/whiteP...ess_motors.pdf

OK, so it's not the ripple current itself that kills the ESC, it's the FET's inability to switch fast enough.

That makes sense. So it's not current killing the ESC at all, just substandard parts.

Hmm, water is quite a bit different than electricity. I have felt electricity and it is not wet. I can't wash my hair in electricity, and my water faucet works quite a bit different from my MMM.

All kidding aside, you have to factor amp spikes, in both directions. Heat and its effect on materials that conduct electricity is very important. Kinda like friction. If you do not factor friction into physics equations they are very simple, however we do not live in a friction-less enviorment so it is kinda important.

The battery has to be able to output a stable voltage at high current levels while also having low internal resistance to keep from getting hot, and also accepting a charge back from the regen brakes. The esc has the task of controlling the motor and ducting the electrons to and from the battery.

I am by no means in full understanding of how this stuff really works, but I do know that the battery is the single most important part of these brushless systems. I have experiemented with alot of different batteries and there is a difference.

Here is an excerpt from a review of the Castle Phoenix ICE controller, which can measure voltage ripple as part of it's data logging feature. The context is from the airplane/heli side of things, but regardless it sheds some light on voltage ripple and how low-spec and low quality batteries can cause problems.

"Battery Ripple Voltage: This is a really cool feature that no one else has implemented in an ESC. If you wanted to try and measure this any other way you’d need a lot of high-end lab equipment to do so. Basically, if you could graph the battery voltage between the pulses of the controller which happen tens of thousands of times a second, you’d be looking at a ripply line, not a flat line. As the controller allows energy to flow from the battery, the internal resistance of the battery affects (causes) the voltage to drop, even in that millisecond. This isn’t necessarily a bad thing when the battery and motor are properly matched, but it is a very good way to determine if, indeed, the battery is up to powering a particular application.

Generally speaking, higher discharge batteries will provide better performance and have less voltage fluctuation with changes in load, so lower ripple voltage. Let’s take this a bit further. The big capacitors on the controller are used to smooth out that ripply voltage. This is important because the FETS need to have a stable voltage or bad things can happen. The capacitors can only smooth out so much of this ripple. If the ripple exceeds the capabilities of the capacitors, you have a much greater chance of the controller letting go. This isn’t a defect of the controller, it’s just the physics. Use the ICE’s ripple voltage readings as a relative number. Try different packs in the exact same machine with the same gearing. Those with lower ripple voltage are the ones best suited for that application. The others may simply not be up to running that particular setup.

So, the ripple voltage measurements finally give you a scientific way to compare the C rating of a battery pack with other packs. This is something that consumers have needed for a long time. You are no longer at the mercy of the marketing guys’ declarations of C ratings. You’ll now have the ability to produce graphs that prove which packs are better!

If you happen to have a charger that displays battery internal resistance, this is also indicative of C-rating. Combined with the ripple current data you can determine if a particular battery is either up to the task for your application or starting to age.

Say you have a 500 size model and you’re running a 20C pack and have a 3D setup. You may very well see a big ripple. If you were to change the battery to a 40C rated pack, the ripple will decrease and the flight efficiency will increase. That 20C battery could be old, or just not up to the task for the kind of demands your power system is putting on it. It may fair better in an airplane application that draws less current, thereby allowing you to get some more life out of it.

The ripple will be more pronounced with a lower C‐rated pack in a high demand application, whereas the higher C-rated pack will reduce the ripple. To get a baseline, log when your battery pack is new and then check it periodically to monitor its health. You can also look at the wattage data and determine when the battery starts to head south, since the wattage will drop."

Dude, not to be a "freezebyte" but the 3rd person diatribe is not necessary. If you say "I" or "me" we will understand. Not the traxxas or savvy forum...

This is badass. May have to get one of these escs just for this feature. Make myself a bench testing setup with a ducted fan jet (big one) and a variable inlet to provide some resistance. Then I can test some packs and see how they really compare.

This does answer the op question quite well.

enough with this water crap. it is not the same, nice try though. you might be an expert in that area, congrats. when have you ever worked with REAL electricity? not this measily sub 600 volt stuff either. show me water that will seek a path to ground at all costs. is it going to jump out of your cup? no. if you stand too close to a full pool will the water arc out and hit you because you are dry no. show me a pipe which water will flow through that has a resistance value. show me a capacitor for water that will correct power factor(voltage lagging behind current). water in no way behaves like electricity other than the fact that it flows. sure electrons do the same but they dont flow through a pipe or hydrant or any of that. electrons flow due to a difference in potential. fluid dynamics are fluid dynamics for a reason, it fluid. electricity is electricity, it behaves in one manner, it wants ground, and wont do anything for you until you give it that. water will do whatever you tell it to in the vessel you give it. there are a few excelent posts in this thread, all with the same underlying theme. if the power is not there to be taken other componets will fail trying to make up for this, being subpar has nothing to do with it. heat is a byproduct of current, and will destroy things in a hurry. most obvious is the fact that when the voltage sags under load the three giant caps on the mmm will compensate for the voltage lagging behind the current, when they cant keep up other componets take the brunt of the excess current and fail. dont claim to know it all but believe me when i say i am alive today because i know how electricity works.:mdr:

Excellent, no getting around this info!!!

really just the proverbial tip of the ice burg. didnt even get into transformation, but should be enough to hilight most common charactoristics. on a side note, why spend good money on quality motors and speedos only to skimp on batteries. nevermind quality or price or whatever, but with low amp ratings? your electrical system is only as strong as its weakest componet. in no way am i conciously trying to be rude or anything like that just enjoy electricity and the things it has allowed for me in my life so far. will share what i know about it willingly in hope that it might interest someone as much as it has myself. not to mention the electric r/c car..........

Sheesh guys! lol.

The water analogy works for a very basic understanding of electricity. It works ok for the most part when dealing with DC, but falls apart very quickly with AC. And our ESCs running pulsed DC is effectively AC (no one said AC has to be a sine wave). So, it is very difficult to use the whole water example effectively.

In short, water pressure=voltage, restriction in a hose=resistance, water flow=current. That's about all you can do.

Slim: Actually, if you think about it. Water would "jump" from a cup if enough pressure is present. It would either blast a hole in the bottom (signifying breakdown of the "insulator" which is what happens with HV), or splash out. :wink:

all this arguing needs to stop. If you know facts state them. (thank you Linc, Arct1k, slim) If you are making an assumption keep it to yourself or preface your statment with, "in my understanding", or, "I think it works this way". But don't state assumptions as fact, and then argue to support your assumptions. That is pure ignorance.

Quite simply- We are at the leading edge of technology in our r/c world. What we see on a small scale will be seen in the future in full size cars. We have the best ESC's and best motors and we need the BEST batteries.

Using sub-par batteries is like putting wooden wheels on an f-1 car.

Let's stop the childish bickering and get back to sharing knowledge to help RCM and the R/C industry to grow, mmmkay?:yes:

first time i have smiled reading this thread:rofl: gotta get me one of those cups, could make my drinking that much easier if it eould just jump into my mouth:lol: was hoping the sine wave wouldn't come up but you caught me brian. interesting though how simmilar the two motors behave.

and yes i will play nice from now on guys:whistle:

This annoys me, firstly I do have specialised knowledge of fluid dynamics. My knowledge isn't in hydraulic's as such but in airflow, aerofoil, hullforms etc

Secondly while I was using an small (hydraulic) excavator today I realised my dismissal of the analogy was hasty & wrong, it is actually a reasonable analogy...especially when considering 'ripple current' and 'fluid hammer' for example

I thought of an excellent analogy between supercavitation & C ratings in cells if you want to keep playing with analogies :lol:

Never. 480 is as high as ThunderbirdJunkie has worked with. We are talking sub-30 volts here, though, so none of that has any bearing on this conversation. We are simply talking SIMPLE DC systems, such as what deliver power to the ESC.
You are aware that electricity only seeks a ground simply because it's charged, and it's going to something that's charged oppositely, right?
We are constantly surrounded by electricity whether we are near electrical devices or not. Is ThunderbirdJunkie going to get zapped to death just sitting here, typing this out? In theory, it could happen, should the power supply on his computer go kaput, but that's another conversation for another time.
Water under pressure will go to wherever the pressure isn't. That is all there is to it. Go turn on your hose; it's going to come out the end, right? Not flow backwards. The unpressurized end of the hose is the ground.
Absolutely, if it's charged (pressurized) properly
Funny thing about this. If everything around you is a high pressure water system, and you yourself are unpressurized, absolutely it will.
It's called mechanical resistance. Also known as friction.
Just another word for "pressure regulator".
Prove it.
Ah, metaphors are lost on you. If you don't understand anything about hydraulic systems why don't you spend your time learning about how they work rather than telling everybody how they don't work.
And fluids flow for the same reason. If there wasn't more pressure behind the fluid pushing it to where it was going, it wouldn't be going that way.

Anyway, done dissecting your post. It's fruitless and it will solve nothing. Your mind is made up, and you're choosing to, rather than explain what's going on, chide somebody for asking questions in an effort to understand this mystical "ripple current" that spikes and stuff, and more to the point, have somebody explain why it kills ESCs.
Thank God somebody understands the analogy. A very basic understanding of DC is all ThunderbirdJunkie is after, and why voltage spikes would come from being drawn, and why this
This isn't an alternator in a car, where (since it generates alternating current electricity) voltage must be regulated, the voltage is (for the sake of argument) constant under load from the battery (yes, everybody is aware of voltage drop, etc etc, no need to nitpick...), why would it spike from the battery?
What would cause two 7 cell batteries on a Flux to spike to the point that it would surpass the MMM's 6S 24ish voltage max? Two 8.4v batteries, 9vish fully charged, shouldn't jump past 24v?

Everybody seems to be hung up on the fact that electricity isn't water and ignoring the fact that there are legitimate questions being asked.

Remember...input voltage is DC. Doesn't matter what the output is, unless what's frying is the switching mechanism, which the more ThunderbirdJunkie reads on the issue, it seems to be the caps and the fets smoking themselves from not being able to switch fast enough to deal with the ripple current, which again, points to more of a hardware issue with the speed control rather than a battery issue.

Thought I would throw this in the mix. Power is not only from the battery.