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Old 12-02-2013, 08:27 AM   #1
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Default What happens if you run 6 cells on a 3 cell motor?

This is probably a stupid question, and has probably been covered elsewhere, and I already know the ansure but gonna ask any way.

What happens if you run a 6 cell battery and esc on a motor rated for 3 cells?

I know the motor is gonna overheat and die, eventually, but are we talking a ways down the road or gonna let the smoke out right now?

I realy wanna juice the hell out of a cheap hobbyking motor and see but if somone has allready smoked one I'll save the little bit of money, maby.

Thanks,
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Old 12-02-2013, 08:51 AM   #2
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Originally Posted by fpveric View Post
This is probably a stupid question, and has probably been covered elsewhere, and I already know the ansure but gonna ask any way.

What happens if you run a 6 cell battery and esc on a motor rated for 3 cells?

I know the motor is gonna overheat and die, eventually, but are we talking a ways down the road or gonna let the smoke out right now?

I realy wanna juice the hell out of a cheap hobbyking motor and see but if somone has allready smoked one I'll save the little bit of money, maby.

Thanks,
It all depends on the KV of the motor and what size prop your using and what the amp draw is, it can be done, but you cant overload the motor, also your ESC has to be rated for 6 cells, so, What size motor do you have, what is the KV/RPM of the motor and is your esc rated for 6 cells.

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 12-02-2013, 09:06 AM   #3
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Let me explain, I have a friend that loves his snot burners (glow) and sez He fly's "real" panes.. He's also a speed freak.. loves his reno racers..

I want to blow his doors off. I have a plane I don't realy like (a little orange parkzone) And several huge motors. I started to put a firepower 60 on it, but It's only a 400 kv motor. I could never swing enough prop to realy make use of the extra HP. Plus I'de have to run 2x 3 cells in series to run it.

Then I thought I could just double the battery in series in the motor that's in it that sound's a little weard at twice the voltage...once? I haave an extra 60 amp esc that is rated for 6 cell, not being used..
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Old 12-02-2013, 09:07 AM   #4
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Originally Posted by fpveric View Post
This is probably a stupid question, and has probably been covered elsewhere, and I already know the ansure but gonna ask any way.

What happens if you run a 6 cell battery and esc on a motor rated for 3 cells?

I know the motor is gonna overheat and die, eventually, but are we talking a ways down the road or gonna let the smoke out right now?

I realy wanna juice the hell out of a cheap hobbyking motor and see but if somone has allready smoked one I'll save the little bit of money, maby.

Thanks,
Maybe my understanding isn't perfect, but voltage determines the rpm of the motor. Not taking into account any drag the motor will have (prop, gearbox), of which will increase amp draw, a motor will have a top rpm at a given voltage. kV determines the rpm of a motor per volt, and at some point, the motor can't be pushed with any more voltage before it just converts to heat, and burns up the motor. A motor is rated by wattage, comprised of amperage and voltage. If the wattage is maxed by a product of the volts and amps, the motor is at its peak. To a certain degree a motor will decrease in amp pull if voltage is increased, and vice versa. Typically lower kV motors deal with higher voltage levels to achieve rpm, and higher deal with less volts and more amp draw. Low kV is much more efficient, and you can usually increase voltage up to a level of high rpm where it will have much less heat than a high kV motor will have at less voltage. If your motor is a max of 3s, it is not a low kV motor, and is likely a small motor too, in itself will not handle heat as well as a larger motor, simply because it will struggle motor to turn a prop or whatever it is powering, and it will max out in amp draw. To put it simply, increased voltage will max out the rpm, and going over than max voltage will not see a significant rpm increase, if any, and the motor will burn up very quickly, probably as fast as throwing too large of a prop on a plane. 6s is typically for larger planes with larger motors and bigger props, where volts easily allow the motor to turn the prop. If you are looking for all out speed, you will want a high kV motor, 2-3s and a small prop. Amp draw will be very high, and you will need a high C rating battery. I may not be 100% accurate as I am relating to my understanding of rc cars, as I am new to planes, but the principles will be similar. You could potentially have a lower kV motor with higher voltage, and this would in theory be more efficient, but the concept of weight comes into play, something that has a greater effect on flight. A lower kV motor is at times a larger motor and a higher voltage battery weighs much more. Put this into play and you will be stressing the motor a lot more with this, causing a lot of heat issues.
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Old 12-02-2013, 09:16 AM   #5
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Btw: the motor in it is an eflight 15 1t's a 950kv 540 watt it's rated for 3-4 cells. I have a 60 amp 6cell rated esc i'm not using..if it won't smoke the motor right away, I'll give it a shot..it's a 70mph plane now twice the voltage should make it scream or burn. I undestand ohms law and I undersand how kv works. what I don't fully understand is how brushless motors and esc's work..I would think doubling the voltage (providing the esc is rated for it would double the rpm. and possably overheat the windings and or throw magnets. My knowledge of motor windings is limited to slot cars when I was a kid.. If you took smaller wire and rewound the little motors the slotcars would go lot faster, but they didn't last long.
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Old 12-02-2013, 09:18 AM   #6
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Originally Posted by fpveric View Post
Btw: the motor in it is an eflight 15 1t's a 950kv 540 watt it's rated for 3-4 cells. I have a 60 amp 6cell rated esc i'm not using..if it won't smoke the motor right away, I'll give it a shot..it's a 70mph plane now twice the voltage should make it scream or burn.
Why not try 4s first and see how hot the motor gets. RPM will be more or less maxed out at 4s, any more voltage will only turn into head, plus the fact 6s is much more weight, so your plane may become slower
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Old 12-02-2013, 09:30 AM   #7
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Originally Posted by fpveric View Post
Btw: the motor in it is an eflight 15 1t's a 950kv 540 watt it's rated for 3-4 cells. I have a 60 amp 6cell rated esc i'm not using..if it won't smoke the motor right away, I'll give it a shot..it's a 70mph plane now twice the voltage should make it scream or burn.
There are 4500 kv motors out there that use a 3 cell lipo, but the prop has to be small or the EDF has to be small like a 55mm, your 950kv motor on 6 cells is no where near that as far as KV and rpm goes, it would be like running a 2000kv motor on 3 cells, you cant use the same prop that you are now using, you will have to use a smaller Diameter prop and less pitch to keep the amp draw reasonable,

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Old 12-02-2013, 09:33 AM   #8
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Originally Posted by thepiper92 View Post
Maybe my understanding isn't perfect, but voltage determines the rpm of the motor. Not taking into account any drag the motor will have (prop, gearbox), of which will increase amp draw, a motor will have a top rpm at a given voltage. kV determines the rpm of a motor per volt, and at some point, the motor can't be pushed with any more voltage before it just converts to heat, and burns up the motor. A motor is rated by wattage, comprised of amperage and voltage. If the wattage is maxed by a product of the volts and amps, the motor is at its peak. To a certain degree a motor will decrease in amp pull if voltage is increased, and vice versa. Typically lower kV motors deal with higher voltage levels to achieve rpm, and higher deal with less volts and more amp draw. Low kV is much more efficient, and you can usually increase voltage up to a level of high rpm where it will have much less heat than a high kV motor will have at less voltage. If your motor is a max of 3s, it is not a low kV motor, and is likely a small motor too, in itself will not handle heat as well as a larger motor, simply because it will struggle motor to turn a prop or whatever it is powering, and it will max out in amp draw. To put it simply, increased voltage will max out the rpm, and going over than max voltage will not see a significant rpm increase, if any, and the motor will burn up very quickly, probably as fast as throwing too large of a prop on a plane. 6s is typically for larger planes with larger motors and bigger props, where volts easily allow the motor to turn the prop. If you are looking for all out speed, you will want a high kV motor, 2-3s and a small prop. Amp draw will be very high, and you will need a high C rating battery. I may not be 100% accurate as I am relating to my understanding of rc cars, as I am new to planes, but the principles will be similar. You could potentially have a lower kV motor with higher voltage, and this would in theory be more efficient, but the concept of weight comes into play, something that has a greater effect on flight. A lower kV motor is at times a larger motor and a higher voltage battery weighs much more. Put this into play and you will be stressing the motor a lot more with this, causing a lot of heat issues.
Its Motor KV and Voltage that Determines the RPM of a motor, not just voltage alone.
a 1000kv motor will turn 10,000 rpm with 10 volts, a 2000kv motor will turn 20,000 rpm with 10 volts under no load,

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Old 12-02-2013, 09:33 AM   #9
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Originally Posted by CHELLIE View Post
There are 4500 kv motors out there that use a 3 cell lipo, but the prop has to be small or the EDF has to be small like a 55mm, your 950kv motor on 6 cells is no where near that as far as KV and rpm goes, it would be like running a 2000kv motor on 3 cells, you cant use the same prop that you are now using, you will have to use a smaller Diameter prop and less pitch to keep the amp draw reasonable,
If would think that if that motor is getting 70mph, it must be getting fairly hot. It is already being pushed, and it is not meant to be an extremely fast motor.
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Old 12-02-2013, 09:40 AM   #10
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Originally Posted by CHELLIE View Post
Its Motor KV and Voltage that Determines the RPM of a motor, not just voltage alone.
a 1000kv motor will turn 10,000 rpm with 10 volts, a 2000kv motor will turn 20,000 rpm with 10 volts under no load,
Yes naturally, I was just referring to the particular motor. It is the voltage that will determine that rpm, and once it is maxed it is maxed. A higher kV and less volts is the way to go for more speed, of course with the negative of having a higher amp draw and much less run time. With the Power 15, 4s will deliver the max theoretical rpm, as whatever prop is being used may be already maxing out the motor, and any more volts will just destroy it. Heat is the key to determining how good your setup is. If you are burning up at 3s at 70mph airspeed then 4s will burn the motor to nothing. To get any more potential speed, a smaller prop and 4s is the only way, or changing the whole setup to a new motor with a high kV.
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Old 12-02-2013, 09:41 AM   #11
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Originally Posted by thepiper92 View Post
If would think that if that motor is getting 70mph, it must be getting fairly hot. It is already being pushed, and it is not meant to be an extremely fast motor.
70 mph is Nothing, I do 70 mph with micro motors, drawing 20 amps at 220 Watts.
the E Flite 15 motor can be pushed a lot, they are underated, but you have to be Reasonable on pushing them. its really a 40 size motor

40 size Equvilent Brushless Motor Combo
Similar to an E-Flite Power 15
Motor Specifications:
  • Li-Po Battery: 3 / 4 cells
  • Max efficiency: 80%
  • Max efficiency current: 18 - 30A (>75%)
  • No Load Current / 10V: 2.1A
  • Max Current: 40A / 60 sec
  • Dimension: 35 x 36mm
  • Shaft 4mm
  • Weight: 132g / 4.6oz
  • Max Watts: 600W
  • Continuous Watts: 480W
  • Recommend ESC: Grayson Hobby 50Amp OPTO w/ 5Amp BEC
  • Recommend Prop Range: (see below)
      • 2820-04 (Sport Verison) - 3S Lipo - prop range 9x6
      • 2820-05 (Mixed Use) 3S Lipo - prop range (10x5, 10x6, 11x6)
      • 2820-06 (3D ) 3S Lipo - prop range (12x5, 12x6, 13x8)
  • Recommended Model Weight: 35oz

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Old 12-02-2013, 09:43 AM   #12
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Originally Posted by CHELLIE View Post
70 mph is Nothing, I do 70 mph with micro motors, drawing 20 amps at 220 Watts.
the E Flite motor can be pushed a lot, they are underated, but you have to be Reasonable on pushing them.
Haha well I stand corrected. 70mph certainly sounds fast to me.
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Old 12-02-2013, 09:48 AM   #13
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Have you tried it before? I'm not saying your wrong because I clearly don't know but it's been my understanding that kv goes up by the volt untill the motor fails..hence, a 1000kv motor runing on 4 volts would run at 4000rpm and at 8 volts would run 8000 16 volts 16,000 and on from there until the smoke escapes ... ... Am I misunderstanding how that works?
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Old 12-02-2013, 09:49 AM   #14
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I would try a APC 6 x 5.5 prop on 6 cells and check the amp draw

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Old 12-02-2013, 09:53 AM   #15
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Originally Posted by fpveric View Post
Have you tried it before? I'm not saying your wrong because I clearly don't know but it's been my understanding that kv goes up by the volt untill the motor fails..hence, a 1000kv motor runing on 4 volts would run at 4000rpm and at 8 volts would run 8000 16 volts 16,000 and on from there until the smoke escapes ... ... Am I misunderstanding how that works?
I am Known to push motors to there limits and then some only burned up 1 motor so far use the 20 second test, run a motor at WOT with a given prop, after 20 seconds shut it off, if you can hold onto the motor with your bare hands, then your ok, if not drop the prop and pitch size down,

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Old 12-02-2013, 09:56 AM   #16
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Originally Posted by fpveric View Post
Have you tried it before? I'm not saying your wrong because I clearly don't know but it's been my understanding that kv goes up by the volt untill the motor fails..hence, a 1000kv motor runing on 4 volts would run at 4000rpm and at 8 volts would run 8000 16 volts 16,000 and on from there until the smoke escapes ... ... Am I misunderstanding how that works?
Thats correct when using the Motors kv, also prop size and load on the motor is another consideration

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Old 12-02-2013, 10:07 AM   #17
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Ok, I'll give it a shot and let you know how it goes.. I'm a notoriously bad pilot and the odds of a 36" wingspan foam plane plane landing after a 120mph flight is remote anyway..
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Old 12-02-2013, 10:10 AM   #18
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Originally Posted by fpveric View Post
Have you tried it before? I'm not saying your wrong because I clearly don't know but it's been my understanding that kv goes up by the volt untill the motor fails..hence, a 1000kv motor runing on 4 volts would run at 4000rpm and at 8 volts would run 8000 16 volts 16,000 and on from there until the smoke escapes ... ... Am I misunderstanding how that works?
Yes that is correct, when a motor is rated for 2s-4s, it likes 2s and 3s and 4s is the max, At 4s, however, the motor maxes out, meaning that it is done. At 4s, it will draw the least amount of amps for the rpm, which technically is easier on the battery, but you are maxing out the rpm. As Chellie said, get the the max point with the prop. You can try 6s quickly, see how the rpm changes, but compared to how much more volts you are putting in the rpm will not increase much, although Chellie probably knows more about the Power 15 than I. For me though, I would stick to the max voltage and try to peak the performance with what prop I use, and finding ways to make the plane lighter. I am new to plane stuff, but I have always maxed out my motors on rc cars. 80mph is quite impressive for an rc car, especially one that has the torque to pull wheelies at 50mph. My ways were to always deal with gearing more than anything, allowing the use of a mid kV rating (3400kV in the case of the car) and getting the best of both worlds. Of course I put the max voltage, but I never go past that voltage, but rely on the conversion of the rpm of the motor, meaning the gearing, and for the plane, the prop used. Props and gearing do remarkable things, far more important than trying to get the most volts, and easily adjustable just be decreasing diameter and pitch to where the motor is running as hot it possibly can. The stuff that I have learnt with land rc I will put into planes once I am able to fly better, and I will no doubt be pushing things to the limit.
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Old 12-02-2013, 10:51 AM   #19
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with 22 volts at 1000kv = 22200 and 5.5 pitch prop = 115.63 mph prop pitch speed - aircraft drag

with 22 volts at 1000kv = 22200 and 6 pitch prop = 126.14 mph prop pitch speed - aircraft drag

http://www.pgam.ca/airspeed.htm

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Old 12-02-2013, 10:57 AM   #20
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Many motors will actually tolerate a 1 step up in pack S rating ... but care with prop size.

Contrary to what seems logic ... upping volts in actually usually increases amps as well ...

If I run my speed PKJ (3800kv 450 Westor) on 3S ... I draw about 55A .. if I put a 4S in - I draw over 70A on same prop.
The motor is actually rated at max 40A and 3S !!But it survives.

My F15 with 3200kv 250 heli motor ... on 3S draws 30A ... on 4S draws 40A

These are well over design levels but illustrates the problem you face when increasing power ...

Speed is not only rpm - but Pitch as well ... but they both incur serious demands on power supplies.

I've cooked so many lipos, esc and motors in my Need for Speed campaign than I care to admit !!

Nigel

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Old 12-02-2013, 11:07 AM   #21
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Nigel is right another way to go is to up the pitch on your prop and reduce the Diameter and use the same battery size that your now using, 8 or 9 pitch prop should get you into the 100 mph mark on 4 cells, you may have to cut down a larger prop and balance it.

4 cell lipo, 1000kv motor @14000 rpm + 8 Pitch prop = 106 mph i would start with a APC 8x8 prop if amps is ok, go to a 8x9 prop. est speed with 9 pitch prop on 4 cell is 119.32 mph

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Old 12-02-2013, 11:53 AM   #22
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This is my general workbook ...

I don't usually hand this out - but Need For Speed has been run for so long now ... it's old hat ...

The purpose of the spreadsheet is to create my own base to estimate likely speeds based on KV vs LiPo vs Prop ...

It's based on pushers ... the PKJ principally so it will need 'tweaking' for another model ... the EDF section is for my two T45's ... the 50mm and 64mm

It hasn't been updated for quite a while ..

But it shows the disparity between increases ... I admit it misses out an important section - AMPS !!
TBH - I wasn't too bothered about that as all I wanted was to calculate speed to break my own 222 pusher and 140 EDF records !!

You may amend / modify as you need......

Nigel


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222kph PKJ,EDF Concorde, Mini4,Mig3,T45,PKJ twin,ME109,Edge540,Cessna182,Skymaster Biplane,F15,F16,Badius,Ultimate,SE5,Qbee10,450 Heli,V911,J3 Cub Founder 9x forum: http://groups.yahoo.com/group/Flysky_RC_radio/
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Old 12-02-2013, 12:11 PM   #23
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Originally Posted by thepiper92 View Post
Yes that is correct, when a motor is rated for 2s-4s, it likes 2s and 3s and 4s is the max, At 4s, however, the motor maxes out, meaning that it is done.
Nope, that's not how it works at all. The motor will keep revving faster as you increase the voltage and it will do so basically without limit until you find the point where the motor fails structurally due to centrifugal forces ripping it apart.

However, as RPM increases you will need to reduce prop size in order to keep the motor Amps within limits.
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Old 12-02-2013, 12:33 PM   #24
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Originally Posted by JetPlaneFlyer View Post
Nope, that's not how it works at all. The motor will keep revving faster as you increase the voltage and it will do so basically without limit until you find the point where the motor fails structurally due to centrifugal forces ripping it apart.

However, as RPM increases you will need to reduce prop size in order to keep the motor Amps within limits.
This is the problem with E motors ... unlike wet-fuel motors they have no real rpm limit except physical failure of construction.

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Old 12-02-2013, 05:38 PM   #25
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Default Ok unless I'm misunderstanding. It's yes, no, maybe?

I don't even know why I ask anything on the internet anymore. If you wait a few hours you will get 15 contradictory responses. I'm just gonna wire 2, 3 cell, 2200 mah bat's in series, hook it to a 3 cell motor and crank it up till it smokes...

I'll let you guys know how it works out...
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