LiPo Batteries and ESC

[AReality]

Hi,

Do i need a LiPo battery protection device (I dunno what u call that) in my setup? Or I can just fly without it? Is it really necessary?

Where can I get one ESC that comes with that protection? Discharge not more than 15Amps. Anyone can recommend 1?


Thanks..

[Babylon5]

Happen to see your post. For RC model , lipos use in RC model for high current do not have protection circuit built in since the model draws amps.

You do not want the protection circuit to kick in and the model will shut down in mid flight resulting in the lost of any controls...short for crash.

I hope this will help.

[X34]

Hi,

Do i need a LiPo battery protection device (I dunno what u call that) in my setup? Or I can just fly without it? Is it really necessary?

Where can I get one ESC that comes with that protection? Discharge not more than 15Amps. Anyone can recommend 1?


Thanks..

Most ESC comes Lipo Ready. If u want to limit the amps to 15, just buy an ESC with max cont current of 15, if cannot find an exact one, u can get one that is about there.

[Babylon5]

Most ESC comes Lipo Ready. If u want to limit the amps to 15, just buy an ESC with max cont current of 15, if cannot find an exact one, u can get one that is about there.

Hi , Sorry to say buying ESC rated at 15 amps max will not limit the lipo to 15 amps.

It means if you exceed 15 amps the ESC may burn or be damaged.


For ESC always go for higher rating if weight and $$ is not a problem.
Higher ESC current rating means the ESC can accept higher current without damage.
Moreover it is more efficient and less loss because its "turn on" internal resistance of ESC is lower for higher rating ESC than lower rating ESC.

Note For some ESC at 60amps or higher ,may not come with Battery eleminating circuit (BEC) or may not support 3 lipo cells and lower so always ask and check before buying.

Cheers

[aeronautical]

hi i think what your looking for is the: Li saver. in the pic below.. i took it from rc forum. but i dont think you really need one.. anyway does that mean the same thing for a battery? like say a 1500Mah, 10C battery can have a max draw of 15 amps? so long as you dont draw more than 15 amps you wornt damage the batt? (provided you dont over discharge as well.)?

[X34]

Hi , Sorry to say buying ESC rated at 15 amps max will not limit the lipo to 15 amps.

It means if you exceed 15 amps the ESC may burn or be damaged.


For ESC always go for higher rating if weight and $$ is not a problem.
Higher ESC current rating means the ESC can accept higher current without damage.
Moreover it is more efficient and less loss because its "turn on" internal resistance of ESC is lower for higher rating ESC than lower rating ESC.

Note For some ESC at 60amps or higher ,may not come with Battery eleminating circuit (BEC) or may not support 3 lipo cells and lower so always ask and check before buying.

Cheers

Max current of 15 amps means anything more than that the esc will shutdown, not burn.
Oversize esc can cause damage to your battery and motor.

[X34]

hi i think what your looking for is the: Li saver. in the pic below.. i took it from rc forum. but i dont think you really need one.. anyway does that mean the same thing for a battery? like say a 1500Mah, 10C battery can have a max draw of 15 amps? so long as you dont draw more than 15 amps you wornt damage the batt? (provided you dont over discharge as well.)?

Most ESC in the market today has lipo cutoff, if your esc doesn't have lipo cutoff, than this device is helpfull.

[Babylon5]

Hi X34, not to sound rude but to keep the spirit of discussion let me explain to you why the ESc is rated 15amps and why some (not all) ESC cut off when it reaches the ratings.
When the ESC (or motor) is rated max 15 amps it means if you operate below this rating the ESc will function normally.
Why the ESC cuts off at maximun rated current (e.g 15 amps and above)because there is a thermal sensing device the shuts down the device when it reach a certain high temperature.
However this thermal sensing device do not response to the high current instantly. There is a lag. I have seen ESC burn when high discharge Lipo was use because of the current surge.

In addition, when the motor is stationary not receiving any electrical input, the internal resistance is low almost a shorted resistance. When you turn on the motor that instance, the intantaneous current like the speed 400 motor can reach 40-50 amps for a short duration. If the ESc cannot withstand this current spike it is likely to suffer damage.


Another thing you should know about ESC is that ESC runs hottest not at maximun throttle but between 30-60 percent of max throttle.
For explaination go to my thread http://www.daddyhobby.com/forum/showthread.php?t=15229

I hope this will help you and others reading this thread.


Cheers

[X34]

Babylon5, this is a forum, so it is not rude to put forth your discussion. we are all here to share info, sometimes we maybe right/wrong etc.. but we must remain open.

U mentioned about ESC resistance, can u elaborate on that? The only resistance I am aware of is the combine resistance of batt, wires, motor, connectors, ESC and quality of soldering.

I am not aware that the resistance is higher at part throttle. I agree ESC runs hotter at part throttle than full throttle because at part throttle the FET would be switching on and off, therefore, the FET heats up. At full throttle, the FET would be on all the time - cooler.

ESC overload protection is usually monitored at the input, the only time this fails is because the 3 phase wire has varying resistance. Or the motor phase unbalance. Under those condition, when u run the ESC to its max, it would burn.

[Babylon5]

Babylon5, this is a forum, so it is not rude to put forth your discussion. we are all here to share info, sometimes we maybe right/wrong etc.. but we must remain open.

U mentioned about ESC resistance, can u elaborate on that? The only resistance I am aware of is the combine resistance of batt, wires, motor, connectors, ESC and quality of soldering.

I am not aware that the resistance is higher at part throttle. I agree ESC runs hotter at part throttle than full throttle because at part throttle the FET would be switching on and off, therefore, the FET heats up. At full throttle, the FET would be on all the time - cooler.

ESC overload protection is usually monitored at the input, the only time this fails is because the 3 phase wire has varying resistance. Or the motor phase unbalance. Under those condition, when u run the ESC to its max, it would burn.

Hi X34, what I mean is the ESc has a minumun resistance stated inside their data sheet.
Somtimes the use the term, internal resitance or Inside impedance or minimun resistance. They all mean the same. This is the lowest resitance the ESc can be switch at max trhrottle.

eg RC smart ESC, the inside impedance

WK-WST-60A=0.0022ohms

WK-WST-40A=0.0033ohms

WK-wst-30A=0.0044ohms

WK-WST-20A=0.0066ohms

From this example you will notice that the higher rated ESC the 60amp has the lowest internal(inside impedance)resistance . It make sense because for higher rated ESC more MOSFET connected in parallel to carry more current
The total resistance RT is given as ...

1/RT=1/R1+1/R2+1/R3+....

Where RT is the total resistance and R1, R2 R3 ...represent the internal resistance of each mosfet.


You mention the the ESC feels hot in between throttle.
If the ESc is hot then there must be and average impedance inside the ESC. That is why it feels hot especially when you stay at half throttle setting.
ESC Heat=power= I square R where R represent the average real resistance of the ESC at the point of operation of the throttle control.

This is the simplest explanation


Cheers