• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Help! Motor Amp draw question

mayan

Well-known member
#1
If my motor mentions that the current load is 40A using a 12x6 prop on a 2-4S lipo does that mean I need a ESC that has at least 60a to be on the safe side from burning an ESC? If I plan on using a smaller prop would that draw more amps or less amps?
 

Zetoyoc

Well-known member
#4
If my motor mentions that the current load is 40A using a 12x6 prop on a 2-4S lipo does that mean I need a ESC that has at least 60a to be on the safe side from burning an ESC? If I plan on using a smaller prop would that draw more amps or less amps?
your current will not be the same between 2s and 4s batteries as your statement suggests.. Somewhere you are missing some data. likely the 40a is on the 4s but if you run 3s with the same setup you will draw fewer amps. the others are still correct. you'll want a bit of overhead on your esc for the max current you plan to draw . It could also be that your motor is rated for a max of 40a so your prop and battery combo shoudl not pass that limit. id clarify what the data says before committing to a setup. my 2cent
 

FoamyDM

Building Fool-Flying Noob
#6
what they are saying... what this means is with the suggested max prop size/pitch and Cell count combination, it will pull a max Amp, This case (40). Then If the it's about overall resistance to spinning really. and every element of that plays a factor. if the pitch increases, either reduce the diameter, or use a lower cell count. If you lower the Cell count you can increase the Blade Diameter or Pitch. your best bet is to test and measure the flow.

my 1408 Tachyon spinning the 3x4.5x3 pull 14.5A on 4 Cell, However at 3 Cell, I can expect somewhere closer to 12A. This is below and the pitch of the blade I plan to use is 3x3x3 and I can expect a draw of 10A this i enough margin to safely use the 12A Escs I have with it. I have used this same setup on another craft, and i can run them well ventilated all day long.
 

FoamyDM

Building Fool-Flying Noob
#8
Well it doesn’t have much more information than what I provided unfortunately :(. Check it out I might have missed something.
https://a.aliexpress.com/_dSM9fzD
look for the same motor on other sites... sometime the other sites, will actually present a more comprehensive table.
Remember the 40A is for use with the 12x6 on a 3cell bat. if you use 4S.... a 45A will not be enough. and likely not a 50 either. look at other similar motors to see reletively how much the Amp draw jumps between cell counts, and props/pitch. it will give you a ball park.
 

Zetoyoc

Well-known member
#9
there is another number to consider that isn't listed. The motors max rated wattage. or even max amp draw. you can get the same wattage via more volts fewer amps or the other way round. just because you can put a 4s on the motor and not fry your esc doesn't necessarily mean your motor is going to like it :) look at other sites data. but the best data is the data in hand with a wattmeter and temp gun. incremental changes and compare.
 

whackflyer

Well-known member
#10
It looks to me that on 3s with a 12x6 you'll be pulling 40 amps. I'd go with a 60 amp esc so you have the capability of using 4s later.
View attachment 161067
I'd agree with @Cookie. My Durafly Tundra motor is similar with a 12x6 also and had a 40a esc for 3s operation. I have ran it on 4s a few times but only short full throttle bursts. The ESC was also out in the open where it could cool well. Be safe and go with a 50 or 60a.
 

The Hangar

Well-known member
#11
I'd agree with @Cookie. My Durafly Tundra motor is similar with a 12x6 also and had a 40a esc for 3s operation. I have ran it on 4s a few times but only short full throttle bursts. The ESC was also out in the open where it could cool well. Be safe and go with a 50 or 60a.
With my rimfire motor 45 amp is the recommended esc but I’ve been using a 40 amp just cause I don’t want to buy another esc...
 

Wildthing

Well-known member
#12
Easiest way is to pick up a watt meter gauge, that way with any cell battery and prop you will know what that combo is pulling and then you can put in the right size of esc. Or if your esc that you have isn't big enough you can always prop down or drop some cells to get to what you esc can handle. Best cheap little tool everyone should have.
 

Hai-Lee

Old and Bold RC PILOT
#14
I have observed quite a large number of damaged ESCs which have caused not only Loss of control but also fires both in the air and on the ground. An ESC comes with voltage and current limits as part of its specification but one thing not specified is the ESC's cooling requirements.

You should always take the manufacturer specifications as the ABSOLUTE MAXIMUM that the ESC can handle safely. When selecting the propeller for the installation you should not allow the maximum current to be exceeded. So, when changing the battery fitted you should swap out the propeller as well. When going from 3S to 4S you should reduce the Propeller diameter, the propeller pitch, or both!

In addition you need to be aware that as the battery voltage increases you should pay more careful attention to the cooling of both the ESC and the battery. Where an ESC is cheap and has an onboard SBEC the BEC will actually generate far more heat with higher battery voltage, and due to over temperature protection it could even shut down the power rail to the Rx. This can and does result in a total loss of control.

Where pushing the ESC to its limits regularly I would recommend that you consider a separate UBEC for the electronics/control. The output drivers on the ESC that control the current supplied to the motor can become very hot and this in turn can also trigger the over temperature protection feature of the BEC and again can/will result in a total loss of control.

If you use an ESC that can supply more than enough current safely to the motor you run into another issue and that is the motor's ability to handle the current and the heat it generates. If you fail to adjust the motor load, (the propeller diameter/pitch), you can actually cause the motor to overheat. This causes the insulation on the motor windings to be heated greatly, (it becomes darker in colour over time), until the insulation fails totally, (it becomes charcoal). At this point the windings are no longer properly insulated and short circuits can easily develop.

A shorted winding can cause the current supplied by the ESC to spike way beyond its normal supply amperage and the ESC can still fail! The motor must not be overheated if at all possible. Ensure that the motor also has adequate cooling, (as a minimum).

In summary the propeller is the key item in not only the plane's performance but also in the life of the motor and ESC especially when increasing the cell count of the flight battery. Ensure that the ESC and the motor get sufficient cooling. Finally the throttle use is another factor in the temperature and current used by the motor and passing through the ESC. Allowing time to cool the motor and ESC between high speed runs can really help in averting a failure when the motor and ESC are operating at their absolute limits.

When under propped a motor and ESC will last for years but over prop them and their life can be as little as seconds!

Just my thoughts!

Have fun!
 

Wildthing

Well-known member
#16
I have observed quite a large number of damaged ESCs which have caused not only Loss of control but also fires both in the air and on the ground. An ESC comes with voltage and current limits as part of its specification but one thing not specified is the ESC's cooling requirements.

You should always take the manufacturer specifications as the ABSOLUTE MAXIMUM that the ESC can handle safely. When selecting the propeller for the installation you should not allow the maximum current to be exceeded. So, when changing the battery fitted you should swap out the propeller as well. When going from 3S to 4S you should reduce the Propeller diameter, the propeller pitch, or both!

In addition you need to be aware that as the battery voltage increases you should pay more careful attention to the cooling of both the ESC and the battery. Where an ESC is cheap and has an onboard SBEC the BEC will actually generate far more heat with higher battery voltage, and due to over temperature protection it could even shut down the power rail to the Rx. This can and does result in a total loss of control.

Where pushing the ESC to its limits regularly I would recommend that you consider a separate UBEC for the electronics/control. The output drivers on the ESC that control the current supplied to the motor can become very hot and this in turn can also trigger the over temperature protection feature of the BEC and again can/will result in a total loss of control.

If you use an ESC that can supply more than enough current safely to the motor you run into another issue and that is the motor's ability to handle the current and the heat it generates. If you fail to adjust the motor load, (the propeller diameter/pitch), you can actually cause the motor to overheat. This causes the insulation on the motor windings to be heated greatly, (it becomes darker in colour over time), until the insulation fails totally, (it becomes charcoal). At this point the windings are no longer properly insulated and short circuits can easily develop.

A shorted winding can cause the current supplied by the ESC to spike way beyond its normal supply amperage and the ESC can still fail! The motor must not be overheated if at all possible. Ensure that the motor also has adequate cooling, (as a minimum).

In summary the propeller is the key item in not only the plane's performance but also in the life of the motor and ESC especially when increasing the cell count of the flight battery. Ensure that the ESC and the motor get sufficient cooling. Finally the throttle use is another factor in the temperature and current used by the motor and passing through the ESC. Allowing time to cool the motor and ESC between high speed runs can really help in averting a failure when the motor and ESC are operating at their absolute limits.

When under propped a motor and ESC will last for years but over prop them and their life can be as little as seconds!

Just my thoughts!

Have fun!
All that info is right on the money but you still need the tool to read the amps.
 

mayan

Well-known member
#17
Thanks for all the answers so far.

Easiest way is to pick up a watt meter gauge, that way with any cell battery and prop you will know what that combo is pulling and then you can put in the right size of esc. Or if your esc that you have isn't big enough you can always prop down or drop some cells to get to what you esc can handle. Best cheap little tool everyone should have.
How do you set this up? Have pics? I have one but have no clue how to set it up.
 

Wildthing

Well-known member
#18
Thanks for all the answers so far.


How do you set this up? Have pics? I have one but have no clue how to set it up.
The watt meter gauge hooks up inbetween the battery and your esc, when you power up the motor it will now show you how many watts, amps and even volts . Sorry no pictures but I will see what I can find for you. This is a link to one of the cheapest watt meters I found last night.

https://www.aliexpress.com/item/32792450766.html
 

Wildthing

Well-known member
#20
I made a quick video showing my test setup.

Perfect :)

Now for you guys and just to test the amps and watts plus you have your motors mounted into power pods and don't want to remove the motors each time for testing. Build yourself a mount that you can securely clamp to the table and the power pods fit into it and lock into place. You need access to the battery minimum so you can hook the meter inline.