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Old Mar 03, 2004, 07:57 AM
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Apex, NC
Joined Jan 2002
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CC ESC 9V Cutoff for 3S LiPo Battery?

I just started flying a CC Phoenix 25 ESC with a HiMaxx motor on a 3DX with an ETech 3S 1200 LiPo battery.

Normally I would fly until it would not hover with the brushed setup. The battery would take 1,000+ MHa charge.

With a 9V recommended cutoff on the CC ESC the 3DX nearly crashed when it was in a strong hover and the ESC cutoff. The battery only accepted an 840 MHa charge.

My understanding is that it does not hurt to run the battery below 9V under load, but it is a big no-no if it is pulled down below 3V per cell when resting.

I am ready to set the LVC to the next lower level to avoid a crash.

Is this ok?

Victor
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Old Mar 03, 2004, 09:18 AM
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The Phoenix-25 manual tells you to use the 7.2V cutoff setting with 3 cell Li packs ...
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Old Mar 03, 2004, 09:37 AM
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Snohomish, WA
Joined May 2000
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Once the USB programmer comes out, you could program any level you want but I believe it says in the manual that softcutoff is recommended for helicopters so they don't fall out of the air like yours did.
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Old Mar 03, 2004, 09:54 AM
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There was a post from castle creations that said the 7.2v setting was a typo,just go to the soft cutoff,that works good.................Dennis
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Old Mar 03, 2004, 10:16 AM
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United Kingdom, Bracknell
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Quote:
Originally posted by Dennis Everett
There was a post from castle creations that said the 7.2v setting was a typo
Hacker controllers cut at 7.8V for 3 cells, so 7.2V doesn't sound that outrageous. The current Phoenix-25 manual (from the website) says to use 5V cutoff for 2 cells, 7.2V for 3 cells, and either 9V or 12V for 4 cells. Are those all "typos" then?
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Old Mar 03, 2004, 10:28 AM
Nimble with Gimbals
San Diego, CA
Joined Apr 2003
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Short answer: Yes

Long answer from Thunder Power:

Quote:
<1) What is the recommended ESC cutoff setting (7.2 or 9 volts)?

9V is perfect. It leaves a nice cushion of 5-10% in the packs which is excellent. Using 7.2v is ONLY a last resort - if you fly to this cut off more than once you will ruin your 3 cell packs. Using 9v you can fly to the cut off all the time and will get excellent battery life and longevity.
and

Quote:
The 3v per cell limit is under load. We recomend no lower than 2.9v per cell under load. Typically, this will only happen near the end of the flight or if you are pulling too much current.

9V soft cutoff works wonderfully. Treat your batteries well and they'll thank you with more cycles in the long run and you'll mitigate the chance of cell imbalance.
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Old Mar 03, 2004, 10:46 AM
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Olathe, KS
Joined Aug 2003
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Use soft cutoff...that way you will notice a decrease in performance before anything happens.
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Old Mar 03, 2004, 11:18 AM
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The original question related to 3S Etec 1200s rather than Thunder Power cells. I don't know what current Victor is pulling, but I do know that a fully charged 3S 1200 pack only gives 9.8V at 8.5A (I measured it with my Hacker B20 setup). So a 9V cutoff is going to start activating very soon, which is exactly what Victor observed. I've only had the 7.8V cutoff on my Hacker ESC operate once in flight, and the pack was at 9.6V when I checked it straight after landing (over 3V per cell) so I'm happy with that.

IMO - with Etecs in a low power setup 9V is probably OK. In a high power setup the voltage drop under load will make it operate too soon. This would obviously be less noticeable with a soft cutoff, but you'd start losing power very early in the flight.

I have a new Jeti Advance ESC with "automatic" Li voltage cutoff (and selectable hard/soft mode), it will be interesting to see how that works out!
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Old Mar 03, 2004, 02:49 PM
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I cant speak for others,but i know i read a post that was answered by i think Pat at cc and it said it should be 9v,i also talked to him at the ama convention in Ontario,and asked the same question and his answer was the same,all that being said,a lot of people are posting the fact that they are useing the lower cutoff voltage and seems to work ok,so you "pay your money and take your chances"when the programer comes out i think i will lower mine a little..Dennis
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Old Mar 03, 2004, 03:58 PM
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AFAIK battery charge state - for any chemistry - is assessed by the resting voltage, not voltage under load (which depends on what load you're putting on it at the time). But obviously an ESC can only respond to voltage under load, so the aim is to set a cutoff that will leave you with over 3V per cell, resting.

For any cell count this 'ideal' cutoff voltage will vary, depending on your application!

For 3S in my high power setup, Hacker's 7.8V cutoff is fine because it leaves a resting voltage of 9.6V. But in a low power setup that would discharge the same pack to a much lower resting voltage, quite possibly below 9V. 9V cutoff under load will always be safe (which is why some manufacturers recommend it), but may give short flights by cutting when the pack is only partially discharged.

With a $$$ pack like say a Thunder Power 8000 you would probably want to be pretty conservative, but IMO not with a relatively cheap pack like 3S Etecs. As Dennis said, all down to personal choice
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Old Mar 03, 2004, 04:11 PM
Measure twice, cut once!
Milton Keynes, UK
Joined Jan 2003
43 Posts
Wow - the Ezone is an amazing resource.

My first serious LiPo test was last night with an Etec 1200 2S1P and a CC ESC with the cutoff set to 6 volts. I too found the ESC cutting off at around 8 amps (the cells were not quite fully charged but were at about 7.6 volts when measured soon after). This worried me as I'd like to try to hover the plane (a Depron Ultimate from the Foamies section). Just imagine getting into trouble and firewalling the throttle only to have the motor cut!

Tonight I logged onto the Ezone to research this and found this thread in seconds.

I think I'll try the soft cutoff option first (rather than reduce the cutoff to 5 volts) as it would appear give

a) The best protection for the cells
b) The same symptoms I've found with 8 cell Nicads - i.e. you slowly run out of sensible flying power well before the BEC kicks in.

Any thoughts from the more experienced LiPo users?

Hugh
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Old Mar 03, 2004, 08:55 PM
Nimble with Gimbals
San Diego, CA
Joined Apr 2003
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Hugh:

This is a safe approach and still offers you plenty of flight time. I've been using 9V/soft on my 40" Yak 54 and I couldn't be happier with it. I can fly without worrying about discharging my batteries too much yet still get excellent flight times.
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Old Mar 03, 2004, 09:03 PM
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have you ever considered that the lipo wasn't very capable of handling those amps?
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Old Mar 03, 2004, 09:11 PM
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Apex, NC
Joined Jan 2002
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My mistake. 7.2v cutoff is the recommended setup for a 3S LiPo. Soft cutoff looks like the way to go.

Thanks,

Victor
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Old Mar 03, 2004, 09:58 PM
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Brisbane Australia
Joined Nov 2003
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Victor,

If you are reading 7.2v cut off from the CC manual then it is a typo and should / has been changed to 9v. Lots of traffic on this in the CC forum.

Soft cut off provides the protection and the insurance that you need with 3D - you will almost always have some power available. Hard cut off should be used on low draw set ups as stated above.


As Wako stated you also need to ensure that the cells you are using are rated for the current draw you need. Nothing will protect a cell that is being used outside it's capability.

Michael
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