PDA

View Full Version : what makes a brushless motor burn out?


peterkron
03-09-2007, 06:59 AM
well thats my question. im wondering because i have a small fiego inrunnerthats rated at 5 amps max and im only using about 3.5 amps with a 2 cell so im wondering if i can go to 3 cells if i just stay under 5 amps without burning up the motor

JWilliams
03-09-2007, 03:36 PM
I wonder too. It has no connected parts so I presume that as more and more juice is run through it, the wires creating the magnetic field get hotter and hotter to the point where they melt and/or start to deteriorate, similar to how if a lightbulb rated for a typical lamp has a thousand volts put through it its filament will burn out from too much heat.

crash_out
03-09-2007, 03:58 PM
Over-revving is a common cause of brushless motors going out. Magnets can be thrown off by too much heat or speed. Generally anything that can cause a brushed motor to destruct can destroy a brushless motor as well. Too much current, too many watts, too much heat...Of course these are all problems caused by over-propping, over-celling, or inadequate cooling.

I've got a small Feigao (IPS replacement) on an Edge RC Pocket Combat Wing. I can't remember it's numbers, but I do know with a 3x2 GWS prop and a 3s ~550 mah Tanic it pulls slightly more than the rated 5 amps. In the air it unloads to a more reasonable level. I generally don't run my equipment that close to the ragged edge, but the performance increase with the 3 cell was so significant, I decided it was worth it.

If you're worried about it, try a smaller pitch or diameter prop, and think on it from there. I don't personally think the increase from a 2-cell reading of 3.5 amps would be damaging if only run briefly to get an idea of the amperage.

-n

peterkron
03-10-2007, 03:18 AM
thanks

skiman762
03-10-2007, 03:29 AM
you can put 100,000 volt through the lamp and it will be fine as long the amps don't exceed the limits
Remember it not the voltage that kills it the amps
But like it's been said rpm can cause problems

peterkron
03-10-2007, 03:33 AM
thanks again

Bob_CO
03-10-2007, 08:24 PM
im only using about 3.5 amps

Is that 3.5 amps WOT?

stroland
03-12-2007, 01:47 PM
wattage is what kills em. power(in watts) is volts times amps. to stay at the same power imput, if u rasie voltage then current has to drop.

pilotpete2
03-12-2007, 06:06 PM
you can put 100,000 volt through the lamp and it will be fine as long the amps don't exceed the limits

Be assured, that if you did that to a 120V lamp filament, the current would be about 800 times the current at 120V:eek::eek::eek:;)
Pete

ron_van_sommeren
03-12-2007, 07:21 PM
wattage is what kills em. power(in watts) is volts times amps. to stay at the same power imput, if u rasie voltage then current has to drop.Nope, only current. Or, if you like, power/wattage dissipated IN the coils and stator. But not power in or power out.

paranoia
03-12-2007, 07:38 PM
magnets, epoxy/enamel covering the wire, and bearings can all be damaged by the heat form the motor itself.

also low quality bearings can blow out

peterkron
03-13-2007, 03:35 AM
i see. and yes 3.5 amps wot static

paranoia
03-13-2007, 07:01 AM
every time the motor heats up it takes a bit out of the magnetic field strenght, so next time the motor will have to run harder and hotter to make up for the loss, and so on.....

better/costly motors should have more heat resistance magnets which should slow the rot.


so most new motors will run the same, ie super cheap motor vs costly motor on the bench

however the super cheap motor will fall off quicker and the costly will come through in the end.


so don't buy and cheap brand motor that is 2nd hand

JWilliams
03-13-2007, 04:26 PM
every time the motor heats up it takes a bit out of the magnetic field strenght, so next time the motor will have to run harder and hotter to make up for the loss, and so on.....

better/costly motors should have more heat resistance magnets which should slow the rot.


so most new motors will run the same, ie super cheap motor vs costly motor on the bench

however the super cheap motor will fall off quicker and the costly will come through in the end.


so don't buy and cheap brand motor that is 2nd handHow much for the average user does that really affect things? Noticeable loss after one hour? 10? 50? Has anybody plotted it in a way relevant to our application of these motors?

paranoia
03-14-2007, 01:05 AM
How much for the average user does that really affect things? Noticeable loss after one hour? 10? 50? Has anybody plotted it in a way relevant to our application of these motors?



don't know, but my hi-end mega motors are still flying strong after +2yr of service, i use a heat sink, (which keeps it cooler) which increases the life

on the flip side i had a razor heli2 motor which i overloaded every flight in a micro heli w/o a heat sink, and after about 6months i when from using 45% power to hover to using 70% to hover. i sold that motor off cheaply...


i should start recording my numbers in excel, i would check my motors is with a wattmeter, with a given setup. Then record the date setup and amp/volt draw. but i don't have many cheap motors left, i have sold them off, and replaced them with aveox and mega, axi motors :)

i still have one or two justgofly outrunners.... i think outrunners do stay cooler anyway, and they tend to be installed in better vented areas. Because the outter case is moving you can't install stuff to close to them.

skiman762
03-14-2007, 01:44 AM
Well my old trusty 14 dollar beater must be a fluke it's still pulls like it was new and I'm not very nice to it either

skiman762
03-14-2007, 01:51 AM
Not sure if motors are like generators in that the power output is only limited by there ability to cool themselves I would think so as the heat builds the electrical resistance goes up and more amps are required to make the same power
sounds good anyway

aircruiser
03-18-2007, 06:14 PM
I read somewhere too that brushless motors cant go under water like brushed motors can...so dont nose dive your planes into the lake ya hear? :)

socal swimmer
03-18-2007, 06:54 PM
brushed motors can go underwater?

are you sure?

wouldnt the water short out the motor (causing burn out)?

JWilliams
03-18-2007, 07:05 PM
brushed motors can go underwater?

are you sure?

wouldnt the water short out the motor (causing burn out)?Apparently some people break their brushed motors in with the thing dunked. I don't understand it, either. That's why I stick to brushless :)

WaldoXerxes
03-18-2007, 07:20 PM
I'm sure I read somewhere that brushless motors were pretty resistant to water. They had crashed planes into water, but still managed to power them back to shore, and once thay had dried out, there was nothing wrong with them.

aircruiser
03-18-2007, 10:14 PM
Yep I break in my brushed motors underwater. You just put some leads on it to a AA battery and let it run til its done. The water will turn a semi-transparent dark grey and thats all the crap you are getting out of it. I also have waterproofed my R/C trucks and run them through mud and underwater and they do just fine!

ron_van_sommeren
03-19-2007, 07:14 PM
Both can run under water. Brushless even better because they don't have brushes.

Vriendelijke groeten ;) Ron
• diy motor building tips & tricks (http://www.rcgroups.com/forums/showthread.php?t=240993)
• diy brushless motor discussion group (http://www.yahoogroups.com/group/lrk-torquemax)
• Drive Calculator (http://www.yahoogroups.com/group/D-calc/) download & discussion group
• int. E fly-in & diy outrunner meet (http://home.hetnet.nl/~ronvans/), Aug.26 2007, Nijmegen, the Netherlands

aircruiser
03-19-2007, 10:49 PM
Are you sure brushless can?

I know they can get a little wet but seeing as they dont use brushes, you'd think that water would screw up something..

pilotpete2
03-19-2007, 11:13 PM
Wet brushless motor, no problem. Wet ESC, not so good:o:p
Seriously though, this only applies to fresh water, salt water, not so good.
Pete

paranoia
03-19-2007, 11:59 PM
A brushless motor has no live contacts and will run in water / sail water eg.

however it will still rust

pilotpete2
03-21-2007, 09:10 PM
If your brushless motor winds up in the salty brine, immediatly get it into fresh water and rinse well, spin dry on gentle:D, hope for the best.
Pete

B.L.E.
03-24-2007, 08:39 PM
High temperatures is what kills motors regardless of what causes the high temperatures. Inadequate airflow, high altitude, high ambient temperatures, and overcurrent all cause high temperatures. When flying on a 104 F (40 C) summer day, you might consider lowering the maximum current and/or duty cycle to keep the motor's temps within limits. If you are flying off of snow, you may be able to push the motor a little more without overheating it.
Deciding what the motor's maximum current should be is a little like deciding exactly what altitude outer space starts at. It's not like the air suddenly stops and the vacuum of deep space suddenly starts. It's like answering the question "how long does a car last?" Well, first you have to define what you mean by "worn out".
If you have to push your motor to the ragged edge to get the performance you need, do yourself a favor and get a bigger motor.

Joe 1320
04-02-2007, 11:54 PM
Yes, brushed motors can run under water. Note I said "can". It depends on the voltage. Once the voltage gets high enough, it overcomes the resistance in the water and a short occurs. At low voltage levels brushed motors will work under water just fine.

aircruiser
04-03-2007, 01:09 AM
electric underwater:

http://www.youtube.com/watch?v=Oz7XKpGkbfU

*note* not me, someone else I know from another site.

BlazerB52
04-03-2007, 01:16 AM
This is a little long but explains very well in the middle ogf the post what happens to a motor to burn it up.

http://www.rcgroups.com/forums/showpost.php?p=7157040&postcount=35

worldraft
04-06-2007, 03:08 AM
If I may put in my two cents, :( the rules are that electricity and water donít mix in the same way that drinking and driving donít mix! Some will say ďI drink and drive all the time and Iím still hereĒ, well there are exception to every thing. With this said a motor can be run under water if the water is contaminants free (distiled water). It is not the water that will burn the motor itís the impurities in it, itís as speed doesnít kill, and itís the sudden stop that does it. I donít care what any body says you donít put a toaster in the bathtubÖ..SO :o

pilotpete2
04-06-2007, 05:05 PM
The conductivity of tap water can vary quite a bit, but is generaly quite low. Our well water measures a DC resistance of about 4 Meg ohm making it possible for many low voltage DC devices to work while submerged. This is also why dunking a lipo in a bucket of salt water does not work to discharge it for disposal.
Now your toaster is 120Vac:eek:, you'll end up "toast" with that scenario;)
The reason for breaking in a brushed motor under water has to do with seating the brushes, and was usually done with one or 2 "D" cells at most.
Cheers,
Pete

JWilliams
04-07-2007, 02:26 PM
The conductivity of tap water can vary quite a bit, but is generaly quite low. Our well water measures a DC resistance of about 4 Meg ohm making it possible for many low voltage DC devices to work while submerged. This is also why dunking a lipo in a bucket of salt water does not work to discharge it for disposal.
Now your toaster is 120Vac:eek:, you'll end up "toast" with that scenario;)
The reason for breaking in a brushed motor under water has to do with seating the brushes, and was usually done with one or 2 "D" cells at most.
Cheers,
PeteIt's not the water but rather its impurities that conduct, right? So, I could sit in a bath of pure distilled water and have a power extension directly hookd into a socket dunked in the bath and be ok, right? I believe I've seen people cool regular desktop computers by fully dunking them in mineral water, actually :)

pilotpete2
04-07-2007, 04:06 PM
It's not the water but rather its impurities that conduct, right? So, I could sit in a bath of pure distilled water and have a power extension directly hookd into a socket dunked in the bath and be ok, right? :)
Wellllllll, I dunno, just so happens we have no distilled water around the house, when I gets some I'll Ohm it out. If you want to do the 120Vac tub test, just make sure your life insurance is paid up:eek:.
Now as to the Dunkin computer thing, I don't know, I do know there are water cooled systems for processors, but submerging a switcher power supply:confused:
I don't think so.;)
Pete
BTW, I only do brushless in my planes:)

Bill G
04-09-2007, 07:45 AM
http://www.wattflyer.com/forums/images/icons/icon1.gif what makes a brushless motor burn out?
Sometimes just simply using it does.:D

If its a 12mm Feigao motor, its destined to burn out since the day it was made.

When you make a yarn ball of windings, cram them in a small space against the case, and then drive in a tapered anvil to obtain clearance for the shaft magnet, you have a short caused by an insulation breach just waiting to happen.

Both can run under water. Brushless even better because they don't have brushes.
You know Ron, I think a lot of folks actually think that the ball of electricity which traveled down the Christmas tree chord and fried the cat on "National Lampoons Chrismas with Chevy Chase" can actually happen that way.:D

Bill

ElectricFlyGuy
04-09-2007, 07:52 AM
You want to know what burns out a brushless motor?:eek: Just hook up the batteries direct! TOAST, and I don't mean bread:D .Never hook up a battery directly to a BRUSHLESS just to TEST it(poof),BUT, YOU can hook a battery directly to a BRUSHED MOTOR all you want. Take care, Scott.;)


http://www.wattflyer.com/forums/images/icons/icon1.gif what makes a brushless motor burn out?
Sometimes just simply using it does.:D

If its a 12mm Feigao motor, its destined to burn out since the day it was made.

When you make a yarn ball of windings, cram them in a small space against the case, and then drive in a tapered anvil to obtain clearance for the shaft magnet, you have a short caused by an insulation breach just waiting to happen.

Bill

worldraft
04-09-2007, 11:17 PM
Your Right distilled water does not conduct at all, :) but make sure it is pure distilled water:confused: .

pilotpete2
04-09-2007, 11:57 PM
You want to know what burns out a brushless motor?:eek: Just hook up the batteries direct! TOAST, and I don't mean bread:D .Never hook up a battery directly to a BRUSHLESS just to TEST it(poof),BUT, YOU can hook a battery directly to a BRUSHED MOTOR all you want. Take care, Scott.;)
yup, applying DC across one phase will make a very effective brake:D
No ESC, no commutation, no turney, just smokey:)
Pete