Thread Tools
Sep 24, 2015, 05:08 AM
If it has wings it will fly...
ckleanth's Avatar
Quote:
Originally Posted by Aeroplayin
.....As Fitz always says, "you know the Germans always make good stuff."
they do sometimes cheat just a tiny bit...
Sign up now
to remove ads between posts
Sep 24, 2015, 06:27 AM
Registered User
Ohio AV8TOR's Avatar
Quote:
Originally Posted by Aeroplayin
"you know the Germans always make good stuff."
Ya just ask the CEO of Volkswagen................ah former CEO
Sep 24, 2015, 06:41 AM
They Call him Dead!
YellowJacketsRC's Avatar
Thread OP
So HV Lipos.....

All other things being equal, if we fly an HV lipo that is charged to 4.35 volts instead of 4.20 volts, would we expect the amps to go up, or down?

I ask this question from a practical, not a theoretical point of view. I know that amps drop as volts go up and Ohms stay the same. What I mean is, in practice HV lipos create more power than standard lipos when used on the same power system (This I know from everyday use of each). So are the HV lipos allowing more amps to flow? Or are the amos going down?
Sep 24, 2015, 06:45 AM
Registered User
Aeroplayin's Avatar
Quote:
Originally Posted by YellowJacketsRC
So HV Lipos.....

All other things being equal, if we fly an HV lipo that is charged to 4.35 volts instead of 4.20 volts, would we expect the amps to go up, or down?
All things being equal except volts....

Up Voltage
Up RPMs
Up Power-Out
Up Amps
Sep 24, 2015, 06:49 AM
Registered User
Aeroplayin's Avatar
Quote:
Originally Posted by ckleanth
they do sometimes cheat just a tiny bit...
Keeping this in mind, if my choices at this point are between a German motor and ESC and a Chinese motor and ESC, where would this comment make more sense?
Last edited by Aeroplayin; Sep 24, 2015 at 07:15 AM.
Sep 24, 2015, 07:29 AM
Can it fly? I'll try and see!
ryane67's Avatar
Quote:
Originally Posted by YellowJacketsRC
So HV Lipos.....

All other things being equal, if we fly an HV lipo that is charged to 4.35 volts instead of 4.20 volts, would we expect the amps to go up, or down?

I ask this question from a practical, not a theoretical point of view. I know that amps drop as volts go up and Ohms stay the same. What I mean is, in practice HV lipos create more power than standard lipos when used on the same power system (This I know from everyday use of each). So are the HV lipos allowing more amps to flow? Or are the amos going down?
The amps would go down if the load was changed accordingly, but since our motors turn a given RPM per volt, and the voltage is increasing if you change nothing else, everything else will increase alongside it.. the only way to pull the amperage back down while still using the same motor would be to reduce prop size.

Another good way is to greatly increase voltage and swap out the motor to a lower KV. I do this on my heli's.. Ive got a 450 size heli that runs 3s 2200 packs on a 3600kv motor.. with gearing, etc let's say I get about 3000 RPM on my rotor speed. I can take that same airframe, swap out the motor to one that's about 1800KV and run it on 6S, but keep the same headspeed, and my amp draw will be cut in about half.. same power(watts) though.. just delivered at higher voltage.
Sep 24, 2015, 10:07 AM
Registered User
Aeroplayin's Avatar

Active FW


Getting back to high load synchronicity, the question about Active Freewheeling came up again, so here is some info I put together on the topic. I have plagiarized a bit here because I did find some spot-on comments online that helped me understand this a little better the way it was written, so I kept some of these bullet points the same hoping it will do the same for you.
  • A motor uses voltage from our battery source to produce rotational energy.
  • As the motor rotates, the magnets and coils also produce voltage in the same way a generator does.
  • This generated voltage is known as back EMF (electro-motive force) that travels back to the ESC.
  • The ESC can measure this voltage and use it to predict the RPMs of the motor and time switching.
  • But spikes in the voltage can occur when energized coils have their voltage and current source switched off by the ESC's FETs.
  • These spikes can be severe enough to smoke the FETs, and therefore, the ESC.
  • There are two ways manufacturers use to protect the ESC from these spikes.
  • They as designated as passive and active freewheeling (FW).
  • Passive FW defines the use of an intrinsic body diode to block the back EMF spikes, and is the most common method used to protect against these damaging spikes.
  • Active FW defines the use of a second FET in place of the diode (mosfet conduction), which is considered to be a better configuration.
  • The advantages are that an FET acts as a controllable diode, and can be turned on and off by the ESC's micro-controllers.
  • The reason this is better than passive is because a controlled configuration means a lower "on" resistance, which translates to less power dissipation during active "on" sequence as opposed to the diode's passive control.
  • A secondary result is a cooler running ESC.
  • AFW requires FETs on both the forward and back sides of the motor power circuit, so they are only found on high-end controllers.
  • Most of the standard ESCs, as we know, have only one bank of FETs.
  • One bank of FETs means that the design configuration allows back EMF/current from the motor to flow through a built-in diodes of the same input FETs.
  • The difference is between 1v of drop across the diode versus 0.1v of drop across the second bank of FETs.
  • Freewheel happens inversely to the throttle curve, so 100% throttle is 0% freewheel and 10% throttle is 90% freewheel.
  • So Active FW translates to a 10 fold reduction in freewheel voltage, which is a significant efficiency increase as you use lower throttle values.
  • This means that if you are running 160A at 50% throttle, the input current is now only 16A.
  • Which means it's the most efficient and coolest way to run partial load systems.
  • So the idea is to use an Active FW ESC, turn on freewheeling, and turn off brake mode.
  • Brake mode slows the motor because the voltage coming back from the motor uses energy that can otherwise be used as rotational inertia, so Brake mode should always be programmed out for our application.
  • Just because there is a Brake mode, it doesn't mean the ESC has Active FW.
  • This concept of Active FW is also called Active Rectification and you can learn more about this by searching for both.
There is also a video on youtube explaining it.

So far, I know that all Kontronik (German), all YGE (German), all Mezon (German), and HeFei's King Kong III (Chinese), and the copyking's dup of the YGE, YEP (Chinese), all have Active FW. When I say Mezon, I do NOT also mean SPIN or SPIN Pro. Caslte also does not. My understanding is that Graupner HV does too, but I can't confirm this yet. Matt, do you have a link to any confirmation on this (or anyone)?

The problem I have with the Chinese ESC's is that they reverse engineer everything (well, most everything), and the problem with that is you don't always get it right when you do this with electronics. I've seen this in my industry a lot. I've read in some instances where there was loss of commutation with YEP that disappeared when Active FW was turned off. Probably more than one issue with that ESC, tho, because there is nothing more efficient than actively controlling back EMF.

Feel free to add to this, or to the list of AFW controllers.
Sep 24, 2015, 11:15 AM
Huckin around the Shire
Enterprise7's Avatar
Openhobby told me what they call Cool FETs are the same as active freewheeling.

http://www.openhobby.com/front/produ...00000000&sort=
Sep 24, 2015, 11:17 AM
3D? I only got two thumbs!
So, ESCs with AFW should have slightly more power available at full throttle too because they aren't dropping voltage across the diode?
Sep 24, 2015, 12:05 PM
Registered User
Aeroplayin's Avatar
My understanding is that the lower throttle setting, where the FETs are working the hardest, is where the freewheeling has the most influence. The spikes occur when the FETs close (bad word but just an analogy), and they close more often at lower settings, limiting voltage, and therefore power to the motor. AT WOT, much fewer closed cycles occur, developing much fewer current spikes. I'm refraining from saying that there are no closed cycles at 100%, but I guess that's a possibility too. I just don't know. But AFW's greatest advantage is off of WOT, and incrementally more so as throttle settings decline.

I guess a good (or poor) way to explain this is to go back to my ceiling fan and water hose analogy that got a lot of criticism. But consider shooting water (EMF) from a hose with a constant valve setting (voltage) through a rotating ceiling fan (ESC's FETs). The more water that gets through, the faster the plane's motor and prop on the other side rotate. The blades contact the water, splashing it away, limiting the water that gets through. The space between the fan blades is always constant, so the only way to limit the volume of water is to speed up the rotating fan. The faster it rotates, the more times the blades interrupt the flow, so when the plane's motor is rotating at 10% of it's potential RPMs, 90% of the water is contacting the fan blades, and splashing all over the place. Electro-Chaos. When the fan stops, no blade is contacting the water so 100% flow means 100% throttle. No splashing = no current spiking. So although the motor is working harder at WOT, the fan blades get a rest.

Just a simple analogy, and FETs, EMF, and current are not really represented well this way, so please just take it as a simple illustration. Like trying to explain relativity using the guy reading a book in a moving train passing another guy on the station platform, at night.
Sep 24, 2015, 12:32 PM
Registered User
Aeroplayin's Avatar
Quote:
Originally Posted by Enterprise7
Openhobby told me what they call Cool FETs are the same as active freewheeling.

http://www.openhobby.com/front/produ...00000000&sort=
I hate when they do that... like when Hobbyking uses the term "Active RPM Control". Made-up terminology is usually a marketing smoke screen. Like Turnigy implies the battery cell company Tenergy, and Nano-Tech implies the A123 Systems' trademarked LiFePO4 "nanophosphate technology". Cool FETs could mean it, but I wish these companies would just say what they mean, and then do what they say.
Sep 25, 2015, 01:49 AM
KE Spins make me dizzy.
I wonder if O.S has AFW on their speed controllers. It says as one of their features is "cooler running - the latest generation FETs"
Sep 25, 2015, 10:52 AM
Registered User
Aeroplayin's Avatar
Quote:
Originally Posted by Sabin
I wonder if O.S has AFW on their speed controllers. It says as one of their features is "cooler running - the latest generation FETs"
Since they don't come right out and use a term that has marketing benefits -- THIS ESC HAS ACTIVE FREEWHEELING -- then I'd say no. I say this because I'm under the impression (and I could be wrong) that the number of mosFETs will manage heat differently too. I know that the ESC I'm looking at now has more than the YGE and both have Active FW.
Sep 25, 2015, 12:28 PM
aka JetMan Joe
MCSGUY's Avatar
The newer FET's offer higher power density meaning each Fet can carry more current then older fets. Unfortunately instead of using the same number of fets and offering an ESC with more heatroom they (at least CC) use less fets because it's cheaper and they can. The higher power concentration caused Castle to add heatsinks which were not necessary in the older Phoenix line.

Joe
Sep 25, 2015, 01:00 PM
Registered User
Aeroplayin's Avatar
Quote:
Originally Posted by MCSGUY
The newer FET's offer higher power density meaning each Fet can carry more current then older fets. Unfortunately instead of using the same number of fets and offering an ESC with more heatroom they (at least CC) use less fets because it's cheaper and they can. The higher power concentration caused Castle to add heatsinks which were not necessary in the older Phoenix line.

Joe
What about the number of FETs? My understanding is that the ESC I'm considering now has more than YGE and also has AFW like YGE. It sounds like we now may need to consider New versus Old mosFETs too?

So we now need to consider:

How old are they (is there some design date or version that will designate this or is "Cool Running" a real designation)?
How many are there (what are the options you know of because my understanding is that more run cooler)?
Is Active FW an option (on or off is usually the programming options)?

Is this correct?


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question RC kits for experimenting with flight control systems SubZer0 DIY Electronics 15 Feb 25, 2015 04:15 PM
Wanted left wing for extreme flight yellow and black 74 yak hondaboy92hatch Aircraft - Fuel - Airplanes (FS/W) 0 Sep 29, 2011 10:18 AM
Discussion Extreme power systems & Royal Evo 12 rbehrends Radios 5 Oct 11, 2007 05:55 PM
Discussion Battery for Logo 10 - Thunder Power "eXtreme" 5S 4600 or Flight Power 5S 3700? WeatherB Electric Heli Talk 6 Jan 25, 2007 11:29 PM