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Zoom › Proper cut-off voltage? Let's figure this out...
10-22-2004 04:48 AM  13 years agoPost 1
iskoos

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Orlando, FL

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I have been working on that for a long time but really couldn't come up with something solid.
I do want to know safe cut-off voltage (per cell) for lipo packs.

Okay now this 3.0 volt/cell is like a rule in the book. Ask anyone, you will get this answer. But what is this 3.0volts/cell? Is it under load or NOT? Because there is a huuugggeee difference.
A pack that goes down to 3.0v/cell under load can easily put out 3.3-3.4 volts when it not under load.
When I was flying my Shogun with stock motor, stock lipo and stock ESC. The Evoflight ESC didn't have auto cut-off feature. It did have a red light that came on when the voltage drops 7.9volt. I was flying till the red light came on and then was charging it. Nothing happened to my lipo pack.
Then I bought TP 1320. Instruction manual strictly says set the low voltage cut off to 3.0v/cell under load NOT 2.9v or below. I do understand that they are the manufacturer and don't want to take any responsibility. Look at Castle Creation p-25 manual; it even says 7.2volts per 3-cell lipo pack. Now I know this is kind of too low but why did they say so.
I did some online research and found out that lipo packs can be discharged to 2.5v/cell under load (or 3.0v without load). So let's be more concervative and say 2.7volts or even 2.8volts per cell that makes the cut-off voltage (for 3-cell pack) 8.4volts.

I am not trying to justify something here if it is not true. I just want to know what the majority is doing.
Please give us your opinions on that. This is very important.

Thanks

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10-22-2004 06:25 AM  13 years agoPost 2
WreckRman2

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Orlando, FL

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I have mine set to 9.0v cutoff but honestly my packs loose enough power that the heli will no longer fly before the BEC kicks in.

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10-22-2004 06:30 AM  13 years agoPost 3
Glenn in Den

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Longmont, Colorado​area

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I'm using the new Kokam 15 C discharge 3S1P packs. I have two of them. I'm using the Phoenix ESC's recommended 7.2 cutoff and these 2000 packs are each taking an 1800 mah charge and NOT getting above 100 degrees so I would say it's working fine so far.




Glenn.

I'm not really an R/C pilot, I stayed in a Holiday Inn Express last n

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10-22-2004 06:32 AM  13 years agoPost 4
WreckRman2

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Orlando, FL

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Due to the ridiculous Monday only image attachments I've uploaded it to my site... the CC25 actually says use 9.0v for 3 cell Lipos. Look at the image:


http://www.rchangout.com/forums/att...tachmentid=6028

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10-22-2004 06:44 AM  13 years agoPost 5
Glenn in Den

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Longmont, Colorado​area

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Measurement under load is very, very different. I have a friend running the same plane and he was using a 6 volt cutoff by mistake and has not harmed his battery.

Follow the ESC makers recommendations and you should be fine. If you set for 9 volts when they tell you 7.2 you won't get much run time at all.




Glenn.

I'm not really an R/C pilot, I stayed in a Holiday Inn Express last n

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10-22-2004 11:22 AM  13 years agoPost 6
raptorbasher

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Bristol, England

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The manual has been updated, the paper manual which was included in my new cc25 has the recommended cutoff for 3 cells at 7.2 volts, but the PDF download now says 9.0volts. if this is due to problems they have encountered only they know, but I also wondered if this was under load or open cell voltages. I would say that this should be specified whenever these voltages are mentioned in instructions. I would guess by the wording that 'it is not recommended to discharge past 3 volts per cell' this is under load condition.

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10-22-2004 01:34 PM  13 years agoPost 7
iskoos

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Orlando, FL

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Due to the ridiculous Monday only image attachments I've uploaded it to my site... the CC25 actually says use 9.0v for 3 cell Lipos. Look at the image:
WreckRman2

I swear same manual that came with my CC P-25 says 7.2 volts. They may have fixed it as raptorbasher mentioned.

Either way I am not in favor of 7.2 volts. It is too low like I said but there is 1.8volts between 7.2v and 9.0v that's big difference. However, if the heli shows the signs of getting lazy and don't want to fly at 9.0v and below than there is no point to set it below 9.0v.
I did observe performance loss around 9.0v but it was not at the point where heli couldn't have enough power to fly. And with low voltage cut-off set to 9.0v, I can only put 1200mah into 1320mah pack. On theother hand, I used to put over 1600mah into 1600mah pack when my low voltage indicator light (when I was using stock brushed ESC) came on at 7.9volts.

Glenn in Den,

If your friend running airplane, I would say it is different, because you don't put that much load on the motor when you run airplanes. When it comes to helis, the load that the motors dealing with is much more.

I'll try to find the article where it says 2.5v/cell under load.

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10-22-2004 01:56 PM  13 years agoPost 8
iskoos

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Orlando, FL

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The article

Okay I found the article that says it could be discharged down to 2.5volts per cell.

here it is

It is the very last table.

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10-22-2004 03:02 PM  13 years agoPost 9
CRAZYKEV

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Cincinnati,Oh -​U.S.A.

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I have read that 2.5 volt also which would be under load so that ads up to 7.5V. I have my voltage cut off set for 7.2 on my cc25, but I also am using lipo alarm that starts to beep at 9.4V. Once it starts to beep I know I had better get it back in for landing. Before it even starts to beep I can tell that the heli is loosing power. I only have the cutoff set as a precaution so I don't totally wax a battery.

Iskoos,
Like90 has these lipo alarms for $39 and they only weigh 3.9g. Just know you live close to them buddy.

My view on this is that the heli doesn't perform all that great below 9v so I just bring it in.

Kevin

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10-22-2004 03:40 PM  13 years agoPost 10
iskoos

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Orlando, FL

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Yeah Kevin,

The guy showed me that lipo alarm when I was down there last weekend. It is really a tiny thing and won't add much to total weight. I may consider getting one for myself.
Is the beeping voltage programable or only 9.4volts?

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10-22-2004 03:50 PM  13 years agoPost 11
WreckRman2

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Orlando, FL

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Like I said on mine though... it looses enough juice that it will no longer fly before the BEC kicks in, even at 9.0v so I don't think we have to work about much with the Shogun.

If you were running something that put a very high load on the battery then you would reach the 9.0v before the battery was actually dead.

And yes the 9.0v cutoff is with a load... you are flying when the BEC would cut it off so that means it has to be under loaded conditions. It's kinda hard to get a 3s1p pack under 9.0v unless it's under a big load.

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10-22-2004 03:52 PM  13 years agoPost 12
CRAZYKEV

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Cincinnati,Oh -​U.S.A.

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Iskoos,

You can change the voltages, but I haven't messed with that part of it yet. Them make a usb cable for it that is like the castle creation setup except that it talks to the lipo alarm through a light diode. It also stores 46 minutes of voltage info, But you would have to get the cable to down load it. I like using it because that cc25 cutoff even at soft cut still pulses the motor pretty hard. You can also program the lipo alarm manually. Check out http://www.customidea.com for hr-poly.

Kevin

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10-22-2004 04:48 PM  13 years agoPost 13
playfair

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Rochester, NY

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Isn't the battery manufacturer better qualified to set the rules?

From the Thunder Power website:
Charging & Safety Pamphlet (included with all batteries)
under "Caring For Battery", section 4:

"Do not discharge battery to a level below 3V per cell under load."

'nuff said.

Fortunately, the head spead does noticeably slow as the pack drops from 11v, so why risk an already volitile battery?


The sky is our canvas

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10-22-2004 05:18 PM  13 years agoPost 14
iskoos

rrKey Veteran

Orlando, FL

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playfair

Of course, they will say 3.0volts. They are the manufacturer and they don't want to be getting called up by hundreds of people that have ruined their packs by pushing them too low. If the safe cutoff voltage 2.7volts (for example) they will call it out 3.0volts just to be on the safe side. It is just like how speed limits work. If you want to get the drivers going 50 mph, you post 45mph sign cause you know they will add at least 5mph on it. This is just an analogy.

Well, actually I haven't flew my brushless upgraded Shogun outside so I can't tell how it feels as voltage drops. It may be very true that once the pack gets down to 9.0v, it is not enjoyable anymore. But what I realized that ESC cut off doesn't give you enough time to land the heli safely if you are more than 7'-8' off the ground (especially in FF).
While hovering in the garage yesterday, ESC initiated the soft cut-off (wasn't very soft to me though) and I barely landed the bird. If I had been at 10' or above, it may have not been a nice landing.
Here lies my main argument. It just doesn't make lot of sense to set the cut-off voltage to 9.0v while you still have enough power to safely land the heli. I don't know you but with my light wooden blades I am not getting a good auto rotation from my Shogun.

CRAZYKEV, I liked the idea that it stores voltage info. I will check the link you provided thanks.

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10-22-2004 07:26 PM  13 years agoPost 15
ericfly

rrApprentice

Cornwall, UK

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I'll go with Iskoos. I set my cut ESC cut off to well below 9v. I don't want the heli dropping out of the sky at 9v.

I have been flying mostly with a FP Hummingbird and have only just got into flying the zoom.

I flew the HB with an indicator that comes on at 9v and when the battery is getting low this comes on when you load the motor quickly. A couple of seconds later it goes out again as the load on the motor declines (it has an hysterisis of approx 0.2v).

With the cut off set at 9v I would have curtailed my flying time as I don't stop flying until the indicator comes on for more than a few seconds.

I have flown the HB with this set up for several months and my Li-Polys are fine.

I have new batteries for the Zoom, with higher current discharge capacity. I will be fitting the same indicator to the Zoom and following the same practice (provided that I can see the indicator! ).

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10-24-2004 04:43 AM  13 years agoPost 16
kaptkaos

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Miami FL

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I have had the Heli fall out of the sky by following the recommendations.
I set the LVC on Helis to the lowest, 6 volts, I set a soft cutoff, and I set sensitivity disabled. I tuned the motor with low timing, the right pinion, 8T, and a large TP1900 Gen 2 battery.
Now it doesnt overheat, overamp, or fall out of the sky anymore.

As soon as I feel the power is getting weaker, i bring it in.

I cant have it dump on a heli like I do with my plane. I fly my plane to the 3rd dump sometimes when I am having fun.

If you give a Chimp a gun, and the Chimp shoots, DONT BLAME THE CHIMP!!!!

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