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HelicopterBeginners Corner › Lipo and 80% confusion
01-11-2011 09:26 PM  7 years agoPost 1
CUJO

rrApprentice

San Angelo, TX

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I'm not sure if I understand the 80% rule about LiPos. I know I'm supposed to fly for a couple of minutes, charge my battery and see how much I put back in but I worry about the safe voltage for each cell or make sure I never have to charge more than 80% the capacity of the battery? I saw where you wouldn't normaly get into the danger zone as far as minimum voltage go but when figuring out my flight times am I supposed to assume not to go over 1760mA in a 2200mA pack?

Rappy 50 Titan, OS Hyper 50, Futaba 2.4 7ch.

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01-11-2011 09:33 PM  7 years agoPost 2
Hellsiege

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Colorado Springs, CO

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I use voltage of pack. If it's new I like to go to 3.5-3.7 range per cell and once the pack has 5+ cycles I'll go closer to LVC 3.2v Never had an issue this way and depending on pack brand have some packs with over 70 cycles or so on them and still chugging along fine.

I never understood the 80% rule myself, but then again I'm mostly nitro

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01-11-2011 09:34 PM  7 years agoPost 3
Heli 770

rrProfessor

USA.

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You have it right with No more than 1760mAh from a 2200mAh pack.

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01-11-2011 09:57 PM  7 years agoPost 4
Anthony.L

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Seattle, WA

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I supposed to assume not to go over 1760mA in a 2200mA pack?
Correct, nothing more to it. That's the 80/20 rule.

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01-12-2011 01:37 AM  7 years agoPost 5
fastflyer20

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N. Tonawanda, NY

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And you use mah because voltage is not an accurate indicator of capacity.

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01-12-2011 10:45 PM  7 years agoPost 6
Brokenwing II

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Watertown, NY

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So if I understand, I can fly my batteries down to 440 mah? Or does it mean I only fly 440 mah?

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01-12-2011 10:51 PM  7 years agoPost 7
Heli 770

rrProfessor

USA.

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If you have a 2200mAh pack. 440mAh should be remanding in the pack. Meaning you can use 1760mAh for flight time.

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01-12-2011 11:45 PM  7 years agoPost 8
Hellsiege

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Colorado Springs, CO

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Ok, if I shouldn't use voltage as it doesn't accurately measure pack capacity, how do you know how much you put back in? I know you can't go off what chargers say they put back in as some of that is lost in efficiency. For example, sometimes a pack will have a cell go slightly off wack. You'll know it as your charger sits there forever balancing / discharging (.1 / .2 amp rates like you see before they finish) to get that cell up to the voltage of others. During this time it's burning off energy from the cells that are already at voltage while charging the entire pack, yet this still adds to the "amp rating" that I put back in? So how do you know what you accurately put back in?

Are you saying if charging 2200mah pack and it gets to 1760mah put back in and the voltage is not up to 4.2 per cell do you stop your charger? Or does your charger stop based on the voltage of the total pack?

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01-12-2011 11:50 PM  7 years agoPost 9
Anthony.L

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Seattle, WA

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Yes, go on what the charger says how much MAH you put back into the pack during the charge.. Any lost to "efficiency" is inconsequential.

Chargers work on voltage, they charge the pack until each cell reaches 4.2v then they stop. If you run the pack past 80% don't stop the charge, just let it finish and next time adjust your radio timer to fly less.

You guys are really over thinking this one, some of you must be engineers. 80/20, very simple.

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01-13-2011 11:14 PM  7 years agoPost 10
Brokenwing II

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Watertown, NY

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Thanks Heli 770. That is how I understood it.

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01-14-2011 07:52 PM  7 years agoPost 11
bustedmp

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Shamokin, PA

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How important is the 80%? Reason I am asking is I had my heli out today for a bit. I have the timer set for 6 minutes. Nothing but hovering around and easy flying. I didn't hear the timer beep, and when i looked down at the screen I was 4:24 past the 6 minute mark. So 10:24 on a 4000mah 6s pack in my swift nx. I landed and disconnected the pack. the pack was pretty warm for being 30deg outside. I let it sit for 30 minutes before charging. The cells where all 3.77v which I am pretty happy with. The pack took 3468mah to come up to full charge. That would mean I used about 87% of the total capacity. I didn't get the data from the esc yet to see how eveything looked during that pack, but shouldn't the voltage have been lower being that close to fully discharged? I have the cutoff set for 3.5v per cell and think maybe I should change it to 3.7v or 3.8v. On my other packs when I stopped at the 6minute mark they where barely warm. Was this pack warmer due to being discharged more than the rest?

Now I really need to get a charger that puts out more than 50w. I have been taking my charger and packs to work and charging them while working so I don't have to waste 8hrs at home charging when I could be using them up.

The world is yours!

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01-14-2011 08:27 PM  7 years agoPost 12
Heli 770

rrProfessor

USA.

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You were probably close to 3.5V per cell when you landed, the batt packs will build up voltage after a flight when you let them sit. With Hyperion's you can run them down to 90%.

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01-14-2011 08:49 PM  7 years agoPost 13
bustedmp

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Shamokin, PA

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That thought crossed my mind as well, but I have the lv cutoff set to 3.5v and didn't have any indication that the esc went into protection mode. For the way I am flying right now, I think 8min per pack should keep me safe. I am going to drag my heli upstairs soon and get the data from the esc and that wil tell me what the voltage was during the flight.

The world is yours!

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01-18-2011 03:30 AM  7 years agoPost 14
bustedmp

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Shamokin, PA

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Ok I got a look at the data from the last pack I flew, and the voltage was 22.1v at the lowest point and that was at the end of the flight. I used 3.47 amp hrs out of a 4000mah pack over a period of 10min 24sec. My flying isn't near stick banging high amp draw of hot 3d. The peak current was 29.7a. I set my lv cutoff at 3.7v, and changed my timer to 8min. I think that should keep my packs safe until my skills get better.

The world is yours!

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01-22-2011 05:36 AM  7 years agoPost 15
bigdog714

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Rochester, MN U.S.A.

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What are you guys using for chargers? This is not rocket science, a good charger will tell you how much is in the pack when you go to charge it, no math required. The battery should always be balanced with every charge, once again a good charger with its matching balancer, with a data cable that communicates with the charger, they will charge your battery safely and perfectly every time, and it won't burn the house down! LOL

I used to fly 600 and 550 class electrics, on 6S 5000mAh lipos, with Castle ESCs, always flew gov. mode for a nice steady head speed of 2150rpm. I am no stick banger, but no slouch either, and after 4.5min. the packs would be around 20-24% depending on how I was flying. I have put three seasons on some of the packs I had with no loss of performance, and I fly almost every day during the season. I have always followed the 80% rule and timed my flights!

Some things to remember is that hovering is actually harder on the battery than flight, its a steady draw on the pack with minimal air flow. In flight the power level fluctuates with nice air flow, so you can actually fly longer if you fly nice easy figure eights.

Don't forget to match your ESC to your motor, this is commonly overlooked. The constant output of the ESC should match the continuous draw of the motor as close as possible. ESCs overheat when they are used as regulators, the speed of motor is controlled by the speed of the electric pulses from the ESC, and the ESC likes those pulses to be full power. A 35amp ESC is happiest running a 35amp motor, if the ESC is 50amp and the motor 35amps the ESC has to work harder trying to limit the power being delivered to the motor, make sense?

MD 800
Logo 600SE
Logo 14/500 Carbon
Ballistic 700
HD 500V2
Hirobo 50E
Avant 90E

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01-22-2011 12:49 PM  7 years agoPost 16
baby_zyklon

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Singapore

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Voltage, loaded or not, is not going to be accurate because it can vary with age and "c" rating. Modern lipo seem to keep their voltage high, unless you pull large amps.

Your peak amp draw was only about 7C. A good lipo will not even get warm with that sort of current.
Don't forget to match your ESC to your motor, this is commonly overlooked. The constant output of the ESC should match the continuous draw of the motor as close as possible. ESCs overheat when they are used as regulators, the speed of motor is controlled by the speed of the electric pulses from the ESC, and the ESC likes those pulses to be full power. A 35amp ESC is happiest running a 35amp motor, if the ESC is 50amp and the motor 35amps the ESC has to work harder trying to limit the power being delivered to the motor, make sense?
I do not agree. A 35amp esc might not actually be a good idea with a 35amp motor.

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01-22-2011 01:16 PM  7 years agoPost 17
Wimbledon99

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UK

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Don't forget to match your ESC to your motor, this is commonly overlooked. The constant output of the ESC should match the continuous draw of the motor as close as possible. ESCs overheat when they are used as regulators, the speed of motor is controlled by the speed of the electric pulses from the ESC, and the ESC likes those pulses to be full power. A 35amp ESC is happiest running a 35amp motor, if the ESC is 50amp and the motor 35amps the ESC has to work harder trying to limit the power being delivered to the motor, make sense?
Using a larger ESC than necessary will NOT harm the ESC. It will only supply what the motor is asking of it! It will cost more, and weigh more, but will probably run cooler and may also have a larger BEC in it (the Battery Eliminator Circuit, which supplies Xv for your receiver).

Obviously, you have to get a brushless ESC for a brushless motor, or a brushed ESC for a brushed motor. They cannot be mixed. Then you normally choose an ESC which is rated for a bit more current than the motor is rated for. Go for 15% to 25% more than the motor rating -- maybe more if the ESC is going to be placed where it won't get good cooling.

3D?? No - just another input error!!!

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01-22-2011 01:26 PM  7 years agoPost 18
Heli 770

rrProfessor

USA.

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I must be missing something!
Why would a larger Amp. rated ESC have a harder time limiting power to the motor? When did this happen!

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01-22-2011 02:12 PM  7 years agoPost 19
Pistol Pete

rrProfessor

Seffner, FL

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A 35amp ESC is happiest running a 35amp motor, if the ESC is 50amp and the motor 35amps the ESC has to work harder trying to limit the power being delivered to the motor, make sense?
Why would a larger Amp. rated ESC have a harder time limiting power to the motor? When did this happen!
think EFFICIENCY!

~~Enjoying the hobby one flight at a time~~

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01-22-2011 03:20 PM  7 years agoPost 20
bigdog714

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Rochester, MN U.S.A.

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I read allot! Castle Creations has written a lot of technical information on the importance of matching the ESC to the motor. The ESC is designed to deliver a constant flow of the amperage it is rated for, that keeps them running cool. An over sized ESC causes over heating because it is now a regulator, look it up!

I don't pull my info out of mid-air, I always do plenty of research before I make a statement. There is also a Finless Bob video where he shows you how to setup the gov. on a 85HV. In the video he also explains the importance of matching the ESC to the motor as explained to him by the engineers at Castle Creations, its not Bob's opinion!

I have had 32 electric helis, and used other ESCs besides Castle, and after doing the research they all make the same recommendations. Match the motor to the ESC!

To simplify things all that the ESC is, is an electric valve that interrupts the power flow between the lipo and the motor. The valve has two positions, open, and closed, there is no half open or 3/4 closed, its full open or full closed. The speed in which the valve opens and closes, or pulses, adjusts the speed of the motor. The ESC doesn't regulate the power like a rheostat on a light switch, every pulse is a 35amp pulse on a 35amp ESC because it is design to deliver 35amps. So if the motor is 35amps the ESC is operating normally as it was designed. If the ESC is 50amp and the motor is 35amp, the valve has to work harder to limit the 50amp pulses to the 35amp motor causing more heat. It has been tested, proven, and written, believe it or not, its your money flying around not mine!

Granted a 50amp ESC with a 35amp motor is not the worst scenario, it is a setup that will probably give you plenty of mishap free flights, but be aware that it may cause premature ESC failure or motor burn out! It will be in direct correlation to the quality of the two components, a Castle or Jazz ESC with a Neu motor will probably be less likely to fail, maybe never?

Here is another one that always stirs things up. Internal BECs have come along way in the past couple of years, 3-5amps is more the norm these days. The one problem that still exists is that the more voltage in, the less amps output by the internal BEC, usually signified by a rating of 3-5amp(example)output. Align ESCs, specifically the 35amp, I believe they were the L,GL,and GX, I may be off on the syntax. Anyway the internal BEC cannot handle the electrical system of a 450 heli, especially with a 4S lipo. Pilots experience brown outs and loss of signal with 2.4g systems and cant understand why, always ruling out the possibility of it being the BEC because "Align makes the ESC for their 450 helis, it says so in the manual" The manual, which was written by the engineers that designed it, also states that the BEC can only run 3 analogue or 2 digital servos! Lets see 4 digital servos, a gyro, and a RX, on a 4S lipo, I don't see the problem?

MD 800
Logo 600SE
Logo 14/500 Carbon
Ballistic 700
HD 500V2
Hirobo 50E
Avant 90E

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HelicopterBeginners Corner › Lipo and 80% confusion
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