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Old May 02, 2014, 10:06 AM
Registered User
Calgary Alberta
Joined Apr 2004
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rewinding - for lower amps?

Hey folks,

Quick question - trying to sort out a power solution for a scratch build design... A10 cartoon fatty (modified jorgen design) - going edf and bringing the size way down...

But - started planning on a pair of 28-35mm fans from a f86 or umx habu - but realized a 50-55mm would "fit" the nacelles better...

However planes designed for 2-3oz of thrust each, and about 8amps each... Hard to get from 50-55mm edf's... Most are 10+oz and 16-20amp... I'm planning to use 2s batts (but 3s may be an option)

So - question is can I rewind (or use an off the shelf?) motor to spin the fans slower and draw less amps - in the bigger size edf?

Speeds not as much of a factor - more looking for the scale power for low level turn n burn...

Anyone able to point me in a direction?
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Old May 02, 2014, 04:23 PM
MigLovin'
Sanford, FL
Joined Dec 2008
71 Posts
Without trying to dive too far into the decisions or science behind your build, I think I can give you a simple answer to your question. Yes, as I'm sure you know, you can simply drop a motor with lower kV into your fan system and get less amps, as well as less thrust. Problem is, you will likely have a hard time finding any data on what this motor/fan combination will produce as far as thrust/amps. A watt meter will come in extremely handy for your trials. If you run into the problem of not being able to find a compatible motor, you can absolutely re-wind a motor to get a kV that fits your needs. Judging by your question, I would assume that re-winding is also something new to you, so be sure you know what you're getting yourself into. Here is a link in the event that you decide to attempt a re-wind.
http://www.bavaria-direct.co.za/models/motor_info.htm

You can also find high quality wire at the site I will list below:
http://www.gobrushless.com/shop/inde...ef=magnet+wire

Good luck!
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Old May 02, 2014, 04:53 PM
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Philippines, NCR, Pasig City
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i would not recommend rewinding the motor to get a lower kv the main reason is because edfs have low thrust per weight (of the whole assembly) and because of this reducing the thrust just makes it worse..
Keep in mind that you don't need to go full throttle all the time right? extra power can't be bad if you are adding those 55mm fans
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Old May 02, 2014, 08:14 PM
Good Better Best quest.
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Australia, VIC, Cranbourne East
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How about just trimming the fan blades down in size?
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Old May 03, 2014, 04:56 AM
Su-27's Rule!
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Philippines, NCR, Pasig City
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Originally Posted by olmod View Post
How about just trimming the fan blades down in size?
he does not need it smaller just lower amps the whole idea of the shroud is to increase efficiency, cutting the blades smaller could potentially destroy the edf
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Old May 03, 2014, 05:29 AM
Jack
USA, ME, Ellsworth
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If you have a Delta terminated motor now and rewind it and terminate it Wye it will have fewer turns to attain the same Kv.

With fewer turns, larger wire can be used thereby lowering the resistance in the windings.

And the Wye terminated motor will have better torque and lower current draw.

The factors for changes in Kv, torque, and current draw when changing a motor from Delta to Wye and vice versa are:

Wye to Delta = increased by a factor of 1.73

Delta to Wye - decreased by a factor of 0.58

So, yes, you can rewind a motor to lower the current draw.

Jack
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Old May 03, 2014, 07:12 AM
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Australia, VIC, Cranbourne East
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Originally Posted by Su-33 View Post
he does not need it smaller just lower amps the whole idea of the shroud is to increase efficiency, cutting the blades smaller could potentially destroy the edf
True not for the faint hearted but one may be able to fit a different fan with fewer blades or lower pitch as far as rewinding goes good luck if its an inrunner they are bears.
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Old May 03, 2014, 02:34 PM
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Calgary Alberta
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Yeah, just not a lot of great options for this oddball scenario...

Wound a couple outrunners back in the early days of CDROM brushless (crap was it really a decadeago?) So its not foreign - but haven't done it much.

Its more the huge battery and huge jump in thrust - which then requires a bunch of reinforcing - thats keeping me from wanting to just use an off the shelf 50mm Im shooting for near umx size (24" ws- but wanting 18" if I can hit weight targets)
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Old May 03, 2014, 07:04 PM
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manuel v's Avatar
Mexico, BC, Mexicali
Joined Aug 2004
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Quote:
Originally Posted by AndyCold View Post
Hey folks,

Quick question - trying to sort out a power solution for a scratch build design... A10 cartoon fatty (modified jorgen design) - going edf and bringing the size way down...

But - started planning on a pair of 28-35mm fans from a f86 or umx habu - but realized a 50-55mm would "fit" the nacelles better...

However planes designed for 2-3oz of thrust each, and about 8amps each... Hard to get from 50-55mm edf's... Most are 10+oz and 16-20amp... I'm planning to use 2s batts (but 3s may be an option)

So - question is can I rewind (or use an off the shelf?) motor to spin the fans slower and draw less amps - in the bigger size edf?

Speeds not as much of a factor - more looking for the scale power for low level turn n burn...

Anyone able to point me in a direction?
What motor do you have?
Please post the link to them.

They are of this type?

http://www.rcgroups.com/forums/showthread.php?t=1185976


Manuel v.
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Old May 05, 2014, 12:39 PM
MigLovin'
Sanford, FL
Joined Dec 2008
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Originally Posted by jackerbes View Post
If you have a Delta terminated motor now and rewind it and terminate it Wye it will have fewer turns to attain the same Kv.

With fewer turns, larger wire can be used thereby lowering the resistance in the windings.

And the Wye terminated motor will have better torque and lower current draw.

Jack
Not true, delta current travels through two wires instead of one on each lead. Two pieces of smaller gauge can actually add up to more cross-sectional area than a single larger strand in most cases. If you have the same kV for a motor with Star as you do for one with Delta , the amount of torque will be the same. Torque is merely associated with lower kV, and so you are making the mistake of associating with a lower kV termination. Where did you get your information, Jack?
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Old May 05, 2014, 02:19 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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http://www.bavaria-direct.co.za/models/motor_info.htm

"..DELTA vs STAR (WYE)

For the same number of turns and wire thickness:

DELTA gives 1.73 higher power and amp draw than STAR
I read it on the Internet, it has to be true!

DELTA Kv (RPM) = 1.73 higher than STAR Kv while the Kt (torque) = 1.73 lower

With a STAR connection, 1.732 less turns need to be wound to get the same power (and Kv) as with DELTA..."

I read that early in my winding learning phase and when I tried the same motor both ways (with a Kv as the target, not the number of turns) I was just as happy with the Wye wind as with the Delta wind based on flying it.

And it always seemed that the Delta motor, at the same Kv, drew more current and used up batteries faster.

I don't think you can call me wrong until you have tried it both ways. Have you done that? Don't make the mistake of just comparing a 10 turn Delta wind to a 10 turn Wye wind, that does not make any sense. What makes sense is to base the comparison on using the same prop and targeting the same "perfect for the prop" Kv.

Jack
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Old May 05, 2014, 07:26 PM
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Australia, VIC, Melbourne
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Originally Posted by jackerbes View Post
And it always seemed that the Delta motor, at the same Kv, drew more current and used up batteries faster.
Motor theory does not support this, though with RC escs odd things can happen.

if you wind the same stator for the same Kv with both Y and D optimised for fill the results should be the same.

How did it seem, do you have test results (and no flight time is no good, way to many variables)?
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Old May 05, 2014, 08:49 PM
Jack
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Originally Posted by desertstalker View Post
Motor theory does not support this, though with RC escs odd things can happen.
I'm not strong on motor theory. I rewind and test and use motors and will admit that a lot of the conclusions I make about motor performance is subjective. But I also have a lot of data to support increases in input power over the original winds. But I have never taken a dLRK Delta motor and rewound it to a dLRK wind again but for the same Kv with a Wye termination.

I have always changed to a better wind and in many cases those were Wye terminated to get the Kv I wanted. The attached image shows how that works for the DAT-750 motor. All my rewinds there went from dLRK-D to Half Parallel dLRK-Y and it changed the DAT-750 from a 78g motor rated at 135W to a 80g or so 400W or so motor.

Quote:
if you wind the same stator for the same Kv with both Y and D optimised for fill the results should be the same.

How did it seem, do you have test results (and no flight time is no good, way to many variables)?
The results will not be the same. The Wye motor will (or can at least) have less resistance in the windings because it will have fewer turns and can be wound with larger wire.

I'll say it again. If you start with a dLRK wound Delta terminated motor, as we do in almost every case, you could get the same Kv with a little more than half the number of turns. And that is what makes room for larger wire.

I guess I could make a point to take a new motor, leave the wind the same, change only the turn count to match the Kv, and try to verify the theoretical differences listed on the Motor Building Info page (the lower current and equal thrust or better thrust using less capacity).

But like most of us that get mildly addicted to re-winding and turn into "man knitters" of motors, I have always found it better to change to another wind too. So that sort of contaminates the direct comparison you asked about.

The only cases where I did not change to another wind was a couple of 9 arm stators where there is really only one winding option. But even there I get better motors simply because of the single strands wind and my better workmanship at laying on turns evenly.

Jack
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Old May 05, 2014, 10:01 PM
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Australia, VIC, Melbourne
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Quote:
Originally Posted by jackerbes View Post
The results will not be the same. The Wye motor will (or can at least) have less resistance in the windings because it will have fewer turns and can be wound with larger wire.
Current flow in a Y and D motor is different. For the Delta, the phase wires leaving the motor link only 1 phase (1 set of windings). Y windings link 2 phases.



If each phase has resistance 1 Ohm (high I know) then the overall resistance of a delta motor is 0.67Ohm (1 and 2 ohm in parallel) between any two phase leads. The same windings connected in a star (or Wye) pattern will have a resistance of 2 Ohm between any two of the phase wires. This is all static, the nature of a motor changes things but you get the idea.

So a Delta wind motor while having more winds per tooth has a similar overall resistance becase it connects fewer teeth together. (otherwise simply changing from D to Y would yield more than a 50% increase in power handling which simply does not happen.

It is possible there are small differences in power capability due to the geometry of the motor allowing a little bit thicker wire on the Y winding but no where close to what you seem to be suggesting is possible (owtherwise why do most motor manufacturers wind delta (surely they could sell more expensive motors wound Y if there was such a benefit).
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Old May 06, 2014, 05:44 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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So these statements are not correct? Not being at all interested in or knowledgeable about electric motor theory, I have always taken them at face value.

"..DELTA vs STAR (WYE)

For the same number of turns and wire thickness:

DELTA gives 1.73 higher power and amp draw than STAR
I read it on the Internet, it has to be true!

DELTA Kv (RPM) = 1.73 higher than STAR Kv while the Kt (torque) = 1.73 lower

With a STAR connection, 1.732 less turns need to be wound to get the same power (and Kv) as with DELTA..."

Just out of curiosity, have you ever rewound a motor? Or tried changing both the wind type and termination on a Cheap Chinese motor.

I probably should have mentioned that I was also changing the wind type in those cases where I saw increases in power so I was seeing the effects of that also.

I don't think the makers of these average quality and inexpensive motors are that interested in making and selling better motors. I think they more just try to make the things that people are buying and hope to capture those sales.

How many buyers of brushless outrunners do you think would shop for and choose motors by the type of wind or termination they had?

If I can take an inexpensive motor and increase the power by 50% to 100% by changing to another wind type, why couldn't they make and sell a motor more like mine? Try to buy a motor with a Half Parallel wind or a multiple part motor with a YY or YYY wind, you won't find one.

Jack
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