This thread is privately moderated by Ron van Sommeren, who may elect to delete unwanted replies.
 Jan 02, 2012, 05:45 PM Registered User Sweden, Gävleborg County Joined Jan 2004 853 Posts www.powerditto.de I think this was the original name. Loks like Ralph has seperated the speed planes from the other info.
 Apr 18, 2012, 07:16 PM Lost but making good time Joined Nov 2008 1,345 Posts Ron, This question may not have a place on your "sticky" but I can't find an understandable answer so I'm taking a chance. If it's out of place just disregard my question. What happens to an outrunner when you use more battery cells in series to power it than the number outlined by the manufacturer. I know the rpm increases, and I've been told you can destroy the motor. Why and how does that happen with to high a voltage? Regards, Hankg
Apr 18, 2012, 07:48 PM
Why not Delta?
Sacramento, CA
Joined Jun 2003
1,713 Posts
Quote:
 Originally Posted by hankg What happens to an outrunner when you use more battery cells in series to power it than the number outlined by the manufacturer. I know the rpm increases, and I've been told you can destroy the motor. Why and how does that happen with to high a voltage?
Unless you apply voltage high enough to break insulation (that would be probably in kilo-Volts) nothing will happen. Of course the rpm may exceed max rpm for bearings, and balancing quality or motor might explode from centrifugal force. But we are talking extreme here. The other limiting factor would be current running through the wire. Even if motor is unloaded at high rpm it will get enough load from the bearing and wind resistance that might exceed the max current for that design. The last part is the frequency of the alternate current powering the motor. Because of iron losses at high frequency it will heat the stator, and because of surface current effect it will reduce the maximum current that wire can handle.

So in short the real limiting factors for the motor are:
- voltage if high enough to break the insulation (unlikely),
- rpm for bearings, vibrations and centrifugal force (possible),
- current which may generate more heat in winding than the cooling might remove (most common)
- high switching frequency which reduces motor's efficiency (unlikely)
Apr 19, 2012, 11:48 AM
homo ludens modellisticus
Netherlands, GE, Nijmegen
Joined Feb 2001
13,618 Posts
Quote:
 Originally Posted by hankg ... This question may not have a place on your "sticky" but I can't find an understandable answer so I'm taking a chance. If it's out of place just disregard my question. ...
I will delete these posts later Hank, and/or move them to a new thread if you start one. I do this every now and then, to keep this sticky lean and mean.

What Richard/Rysium said

Volts jolt, current kills. And current wants to go up squared with voltage, increase will be higher than one would expect. I have made this very simple table which lists the effect of one/two extra cells on current:
http://www.wattflyer.com/forums/show...945#post594945
http://www.wattflyer.com/forums/show...red#post591620

And since copper losses (=heat) go up squared with current (Pcopper = I² Rcopper, copperloses go up with voltage^4! E.g. double voltage gives 16 times more copperlosses, worst case.

Also: motor power wants to go up cubed with voltage.

Vriendelijke groeten Ron
diy motor tipsDrive Calculator
diy motor groupCumulus MFC
• Get a life ... get a Watt-meter!!! •
Last edited by Ron van Sommeren; Apr 21, 2012 at 01:58 PM.
Apr 21, 2012, 08:30 AM
homo ludens modellisticus
Netherlands, GE, Nijmegen
Joined Feb 2001
13,618 Posts
Quote:
 Originally Posted by rysium ... Because of iron losses at high frequency it will heat the stator, and because of surface current effect it will reduce the maximum current that wire can handle. ...
Skin effect does not come into play here Richard, frequencies are not high enough.
Quote:
 Originally Posted by rysium ... - high switching frequency which reduces motor's efficiency (unlikely)
And low switching frequency also reduces motor efficiency.
Quote:
 Originally Posted by hanzie That's Dutch, it means something like 'best regards'
Are you a member of www.modelbouwforum.nl too?

Vriendelijke groeten Ron
 Apr 30, 2012, 06:47 PM Registered User USA, MA, North Westport Joined Feb 2010 33 Posts I just rewound my 73 gram omega using 30awg wire three strands 9 turnes dlrk 12pole and it worked but I dont know what my kv or anything about how I should prop it can you help?
 Apr 30, 2012, 06:51 PM homo ludens modellisticus Netherlands, GE, Nijmegen Joined Feb 2001 13,618 Posts I try to maintain this sticky as a FAQ, your question and the answers will be deleted. Better start a new thread for your question, more viewers/anwswers too. Win-win Vriendelijke groeten Ron • diy motor tips • Drive Calculator • • diy motor group • Cumulus MFC • • Get a life ... get a Watt-meter!!! •
Aug 09, 2012, 02:30 PM
low tech high tech
Southern Vermont
Joined Feb 2007
3,029 Posts
Quote:
 Originally Posted by Ron van Sommeren Removing windings from used motors. Saw the 'winding heads' of, warm in oven and pull the windings from the slots. Pictures: http://www.eschmidt.de/galerie/wicklung/index.htm
 Aug 09, 2012, 05:07 PM Registered User Sweden, Gävleborg County Joined Jan 2004 853 Posts Things like that happens after seven years
 Aug 09, 2012, 06:20 PM low tech high tech Southern Vermont Joined Feb 2007 3,029 Posts I know. I was hoping for replacement with a corrected link or a pointer to other useful unwinding tips, or deletion of the dead link so searches for unwinding info don't land on it as primary. As well as deletion of my post. Now these 3 posts. Thanks!
Aug 16, 2012, 01:31 AM
Duh
grain valley mo, or about 25 minutes east of kansas city
Joined Jan 2004
600 Posts
Quote:
 Originally Posted by hankg Ron, This question may not have a place on your "sticky" but I can't find an understandable answer so I'm taking a chance. If it's out of place just disregard my question. What happens to an outrunner when you use more battery cells in series to power it than the number outlined by the manufacturer. I know the rpm increases, and I've been told you can destroy the motor. Why and how does that happen with to high a voltage? Regards, Hankg
it's not the increase in rpm or voltage that destroys it but rather the increase of amps/watts pulled from the increased resistance from turning the prop faster. creates heat faster than the motor can shed it causing the coating on the winding to burn off thus shorting the winds out causing more amps until you let the magic smoke out, then it runs no more. typically you can get away with it if you reduce the prop size but sometimes it takes a drastic size reduction and some motors are allready such a high kv that they are allready pushing the heat/cooling curve allready. best to use an amp/watt meter if you are going to play with running higher volts than recommended and remember that it's the watts that burns it up not the amps, it takes fewer amps at higher voltage to get the same watts as higher amps at lower volts. volts times amps equals watts, thats why you have to reduce the prop size so you do not exceed the max watts, thats when the heat gets excessive. hope I haven't confused you more.
Aug 16, 2012, 02:06 AM

South Africa, GP, Pretoria
Joined Jul 2003
599 Posts
Quote:
 Originally Posted by crashawk ... it's the watts that burns it up not the amps, it takes fewer amps at higher voltage to get the same watts as higher amps at lower volts. volts times amps equals watts, thats why you have to reduce the prop size so you do not exceed the max watts, thats when the heat gets excessive.
Crashawk
I can't agree with your statements above. It IS amps that causes a motor to heat up and burn the windings.
Look carefully at this formula: R x I² = copper loss.
R (or Rm) is the resistance in one phase of an outrunner motor. So, amps squared times the Rm is what causes the primary loss in a motor, i.e. the main source of heat.
In outrunners, iron loss is usually much smaller than copper loss and can also be calculated: Io x volts, where Io is the no-load current.

Christo
 Aug 19, 2012, 10:57 AM Registered User United States, GA, Alpharetta Joined May 2011 37 Posts hi there, i would like to ask about number of windings, if BL motor specification state 14turns (12 teeth,14 magnets) , does it mean total number of turns on one line (on all 4 teeth), or number of turns on one tooth, please ?
 Aug 19, 2012, 10:58 AM Unicorn (Cordova)Memphis, TN Joined Jul 2002 1,815 Posts Turns on one tooth