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Old Jan 24, 2013, 01:11 PM
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Again, they're talking continuous, not pulses. If they were all on all the time, the motor wouldn't turn at all. At any given time, 1 phase is +v, 1 is -v, and the other is 0v.

See here:
http://www.rcgroups.com/forums/showp...postcount=2661

The first pic is WOT, and you'll notice that that phase is still switching on and off constantly. And clearly from other scopings, the real number exceeds the numbers that are used for the ratings (which are the same as you get with a wattmeter).


If you look here, you can see all 3 phases at once:
http://www.rcgroups.com/forums/showthread.php?t=1166779
You'll notice that worst case scenario is where 2 phases are "on" and the 3rd is "off". (The graphs look inverted, but that's normal. Up is off, down is on).

This pretty much establishes a good definition of a 2/3 duty cycle, if you ask me. If you average 3 parts with one being zero, then you get:
continuous input amps(wattmeter) = 2*(pulse amps) / 3

The pulses have to be higher than the average if only 2 out of 3 of them are on at any given time.

Taking CC at their word is not enough for me. If they can show measurements or theory to back what they say, it's just more heresay in my eyes.
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Old Jan 24, 2013, 01:17 PM
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Quote:
Originally Posted by dav3uk View Post
A pulse cant be a straight line, its not a pulse.

If you had straight line input to all 3 phases the motor would stop.........or am I missing something here

Dave
I think he meant the draw would look like a straight line, as in the exact instant phase 1 shuts off phase 2 opens and the exact instant P2 is off P3 goes full. This would mean 100% on at all times and the current would be a straight line.

-Brian
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Old Jan 24, 2013, 01:21 PM
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Old Jan 24, 2013, 01:32 PM
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From what I understand about the brushless controllers, they are basically 3 phase DC switches with 2 phases conducting at any given moment. The third non-conducting phase is measured for zero crossing of back EMF for timing reference of the next pulse. So the FET's do see full battery voltage and current on their conducting phase. A 12 pole motor (which the parkzone BL15 is) will need each phase conducting 6 times per revolution, and yes, all portions of the circuit will have to be able to sustain the full voltage and current whether it be low throttle or full throttle in short. Like was said before, the current measuring device will only represent an average reading that it sees and not the full current/voltage that is actually introduced to the ESC/Motor.
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Old Jan 24, 2013, 01:37 PM
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Originally Posted by Retiredtech View Post
What? Let me ask this question. Who should one believe; one of the most trusted ESC companies that engineers, builds, tests, and sells these switched ESCs; or someone blowing smoke on a user thread? Are you trolling??

RT
I'll believe the measurements, which is what I keep posting. It's pretty clear that the FAQ is massively simplified so they don't confuse customers. I'm not saying nobody there knows it, I'm just saying what you are posting on the FAQ is just somebody's opinion with no supporting evidence given.
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Old Jan 24, 2013, 01:41 PM
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Originally Posted by kalmon View Post
I think he meant the draw would look like a straight line, as in the exact instant phase 1 shuts off phase 2 opens and the exact instant P2 is off P3 goes full. This would mean 100% on at all times and the current would be a straight line.

-Brian
But that's averaged over time, which is not what we're talking about here. We're talking about the pulse peak current, which as I said before, is quite a bit higher than that.

CC is saying each phase is averaging the full current, and this is true. They aren't saying anything at all about the actual peak currents seen on each phase. It's also true that each phase has a 2/3 duty cycle, on average (it's on 2/3 of the time), so there is equivalence there that CC is talking about. However, the non-averaged current is at least 1/3 more than the average.
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Old Jan 24, 2013, 01:42 PM
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Quote:
Originally Posted by jtaylor996 View Post
This pretty much establishes a good definition of a 2/3 duty cycle, if you ask me. If you average 3 parts with one being zero, then you get:
continuous input amps(wattmeter) = 2*(pulse amps) / 3

The pulses have to be higher than the average if only 2 out of 3 of them are on at any given time.

Taking CC at their word is not enough for me. If they can show measurements or theory to back what they say, it's just more heresay in my eyes.
Did you read Bruce Abbots post that you linked?

summary:
Full throttle: watt meter shows7.45V and 1.3A, oscilloscope showed: 2.3Amps
"Half" throttle: Watt meter shows: 7.5V and 0.95A, oscilloscope shows: 3.2 amp peaks!

That's real life independent measurements that back up Castles claims.

-Brian
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Old Jan 24, 2013, 01:46 PM
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Actually, CC is claiming that it should read 1.3A at all times.
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Old Jan 24, 2013, 01:51 PM
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This just about sums up things (directly in response to Bruce's pics above):
http://www.rcgroups.com/forums/showp...2&postcount=61

Quote:
Originally Posted by vintage1 View Post
NoFlyZone: That's why I simply muttered the magic spells, and forebore from laying down the law. because..

Bruce: Nice pictures! Even I didn't think there would be sinusoidal ringing !

muidaq: Er, yes, in spades.

The so called 'current ratings of your average ESC are actually no more than an educated guess on the part of the manufacturers, and more than one ESC that works perfectly at - say - 30A on one motor has let the magic smoke out at 25A on another motor. Bruces waveforms begin to show how this can be so.

Castle have produced a simplistic explanation that isn't actually correct at all, but its more correct than the simple-think most people have, so its better than nothing!

The actual answer to 'how hot will my ESC get?' is a nice function with about 6 unknowns..its a time integral of the instantaneous current squared, over a cycle, times the resistance of the switching FET(s) which depends on the motor resistance, the pack resistance, the smoothing capacitor on the ESC baterery wires, the resistance of those wires, the resistance of the pack, the resistance of the connectors, the inductance of the motor, its lead out wires, and the battery wires, and the parasitic capacitance of the FETS and the motor, the motor timing, the motor RPM, and ..probably a few other things I haven't actually thought of. Probably throw in the quality and nearness to saturation of the stator iron work as well.. Oh, did I mention ambient temperature and airflow over the ESC? silly me! Better throw in production spread on all the components as well..could be +-50% easily..

Its the sort of problem that even seasoned professional circuit designers tend to solve by saying 'er, let's just test these to destruction against a range of motors, and derate by 50% and call that safe' Or less experienced 'test against one motor, for 10 seconds, it didn't break: Add 50%, That's its rating'

Needless to say, the former approach costs money, and that is reflected in the price of SOME of the higher priced ESC's one may buy. Others simply have expensive LABELS on them.

Its one reason why I argue with my colleagues who say 'I've run that at 38A' and I say 'it says 25A on it, I wont run it over 20A'

I know far too MUCH about this. To rely on anything it says on the packet.

Bruce's pictures give the inkling as to why..
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Old Jan 24, 2013, 02:04 PM
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Quote:
Originally Posted by jtaylor996 View Post
Actually, CC is claiming that it should read 1.3A at all times.
I understand the this is very oversimplified as your other quote from "vintage1" clearly shows, however:
Castle claim that the motor will see 50% more at full then at half...
2.3A actual from oscilloscope +50% is
2.3 * 50% = 1.15 + 2.3 = 3.45amps ..... I'd say that 3.2 is pretty darn close to 50% more.

I think the original intent of this has been lost though, I was merely trying to show why not to use that beautiful 4 bladed prop and throttle management. I think that has been thoroughly explained....maybe a little to thoroughly.....

I would love to continue the discussion as I always love to learn more about the way things work. Feel free to PM me or even start a ESC thread and link me to it. I just don't want to derail the P-47 thread any more.

-Brian
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Old Jan 24, 2013, 02:07 PM
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Ok, to summarize this conversation so far (which I think is necessary at this point):

There are at least 2 kinds of ratings and failures for ESCs:

1. Hi current (peak) burn out. Happens instantly from way too much current going through a single pulse.
2. Hi temp burnout. Happens over time from heat dissipation.

The ratings the manufacturers give are in regards to #2, and (should be) based on destructive testing. These numbers are at least 30% lower than what is actually seen in #1.

If you use a severely undersized ESC, you'll run into #1, as it's just not designed for that current and will short (I'm guessing burn out the FETs).

If you moderately undersize your ESC, then it'll just get too hot and you'll run into #2.

You're reading #2 with your watt meter. If you turn the throttle down, it goes down and looks OK. However, it's still not OK to use an ESC undersized and just keep the throttle down, because you'll run into problem #1. If it weren't for #1, this would probably work fine, as you're keeping the heat off the ESC and motor (newton's laws of thermodynamics right there), but that has nothing to do with problem #1 because it's not a heat thing.
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Old Jan 24, 2013, 02:40 PM
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Originally Posted by jtaylor996 View Post
44A static on the stock motor may be ok. In the air, that's only 40A, which is a common enough rating for a lot of similar sized motors. The pain in the butt is not knowing what it can actually handle since there are no specs.

I've been having a lot of success lately with exceed rocket 3020 motors in 3d planes. The 950kv version is rated for 44A. I also use an 860kv version to swing a larger prop. The cool part is that they are only ~$20!

I'm getting 550W+ out of them on 3s. Just food for thought in case your BL15 does go out.
I'm using 3 of the 3025s', J. So far they are doing fine and I do like the pricetag. In fact I am running one in my PZ P-47.
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Old Jan 24, 2013, 02:49 PM
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Fun and educational discussion, Guys. I agree totally with the esc needing to be sized up. We people need to be sure and learn something new everyday and increase our understanding about how things work.
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Old Jan 24, 2013, 03:22 PM
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Anyone have a Parkzone P-47 box and packing foam they want to give me/sell me? I just got orders to Japan and am trying to figure out how to get this guy safely packed and shipped! Wonder if parkzone would sell me just the box?
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Old Jan 24, 2013, 03:28 PM
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Originally Posted by Barrett_G View Post
Anyone have a Parkzone P-47 box and packing foam they want to give me/sell me? I just got orders to Japan and am trying to figure out how to get this guy safely packed and shipped! Wonder if parkzone would sell me just the box?
There is a guy on eBay that sells parkzone stuff I bought a box for my extra t-28 from him.just search a parkzone micro and you will see one of his planes. He always writes eBay across the front of the box so he should be pretty easy to find.im sorry I don't remember his name. But if you call them they are real easy to deal with.
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