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Safe ESC Lipo Cutoff Voltage for Today's Standard

red_z06

rrProfessor

Dumont, NJ

The typical standard auto lipo cutoff is set somewhere around 3.0-3.1v for ESCs. This was based on yesterday's standard on safe lipo voltage of 3.0v per cell. Although the cell does not receive immidiate damage, it has been shown that repeated use to this voltage will shorten useful battery life.

I time all electric flights so there is 20% reserve in the pack when the alarm goes on for me to land. But, once in a while you either forget to set the time or simply blow through the timer and are met with the lipo cutoff of ESC. At this cutoff, the pack has much less than 10% reserve left and gets much hotter even for the same flying as the pack has to pump much more current to compensate for the dropping voltage.

I have been testing a safe cutoff voltage for ESCs (CC mainly due to adjustability). For heli setup, current sensitivity should be set to insensitive or disabled. I set the cutoff to 10v for 3s or 3.33v per cell. With this setting, with slow cutoff (current limit to maintain 10v under load), your 3s pack will see 10.8-10.9v when the cutoff occurrs. This is a much safer level for the pack leaving 15-20% reserve that you are looking for. Obviously, if you land before this occurrs, even better.

For most beginners practicing (except inverted), there is enough time for you to safely land when the safe cutoff starts to slow down the blades.

For other ESC's that do not have voltage selection, go with high cutoff. If the document does not specify what that voltage is, do a hover test until it kicks in and wait 5min or so for the pack to stablize then measure the pack voltage (no load). If it is 10.8 or above, you can fly until cutoff occurrs without worry.

What I also found is that, at higer cutoff voltage, due to 20% energy still in the pack, the amount of time you have to bring the heli in is much greater than for the lower cutoff.

www.JustinJee.com

08-07-2008 Over year old.
HOMEPAGE  
MrMel

rrProfessor

Lidingo, Sweden (GMT+1)

Unfortunally it depends totally on what battery you have and what Temps are outside, it will make a huge difference just 10 degree celcius difference.

If you have a TP or FP pack and set the cutoff for that, and then get an outrage or desirepower you will overdischarge your pack severly.


What we need is a good Fuelguage, non-intrusive would be nice (clamp on would work) with several means of notification, it should have a way to change the throttle level (for .90 sized where you cant see or hear any beeps or small LED's)

Gone fishing..or hunting..or something
My site: http://heli.dacsa.net - VBar videos and more

08-07-2008 Over year old.
red_z06

rrProfessor

Dumont, NJ

Yes you are right. As more lipos with 30c packs are introduced, 10v cutoff will mean lower than 10.8v. If the cutoff occurrs at 10.5v (still much better than at standard cutoff) for the 30c packs, then the cutoff needs to be adjusted up to 10.3v for 3s packs.

Again, use the primary means to limit the flight but this should come in as a good safty backup. When the cutoff occurrs in CC, at this high setting is that it feels like you just switched to normal from idle up and still flyable with ample time to land.

www.JustinJee.com

08-07-2008 Over year old.
HOMEPAGE  
frebou

Key Veteran

Montreal / Canada

I've been doing this kind of test last winter with my CC esc and I was sooooo happy I was about 1 feet of the ground when it started pulsating!!! the tail was all around 2-3 seconds after the protection came in!

have they upgraded their software since then?

BEAM - Beautifully Engineered Action Machine

08-07-2008 Over year old.
HOMEPAGE  
red_z06

rrProfessor

Dumont, NJ

frebou:

It sounds like you either had gov mode or did not set the cutoff to soft. CC gov mode goes bad when you lose head speed. If you are in fixed mode and cutoff disabled, it would not pulse or die. Becuase it is trying to keep the loaded voltage above 10v, it just starts to limit the current. It very much feels like getting out of the idle up into normal.

Correction:

I meant to say

CC gov mode goes bad when you lose head speed due to gov gain not liking the lower speed. If you are in fixed mode and current limiting disabled and soft cutoff set, it would not pulse or die.

www.JustinJee.com

08-07-2008 Over year old.
HOMEPAGE  
paintball_kidz

Veteran

Surrey, BC Canada

What about anti-puff lipos like airthunders? would continual over discharging it make its life shorter?

08-07-2008 Over year old.
Rob_T

Elite Veteran

..

frebou:

It sounds like you either had gov mode or did not set the cutoff to soft. CC gov mode goes bad when you lose head speed. If you are in fixed mode and cutoff disabled, it would not pulse or die. Becuase it is trying to keep the loaded voltage above 10v, it just starts to limit the current. It very much feels like getting out of the idle up into normal.
That's exactly what happens when you enable the "soft" low-voltage cutoff feature in Castle ESCs. The other choices are to disable the low-voltage cut-off or set it to "hard" in which case the motor will stop dead rather than pulse. (At least that's been my experience on 5 different Castle equipped helis.)

Personally I always set the low voltage cut-off in my helis as a last line of defense, and use a timer as my primary way to protect my batteries. For planks I set the low voltage cutout at a voltage that will protect the battery more as dead sticking is much easier and my flight times are more variable.

08-08-2008 Over year old.
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Safe ESC Lipo Cutoff Voltage for Today's Standard

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