part 1- Lipo batteries for Dummies... by a Dummy- technical stats of a battery

[Frank v B]

Mark Satin asked me a question today about batteries and I gave him a quick answer. 
I then realized we buy packaged planes (Apprentice, Tundra), teach people to fly but we don't really explain the "what", "where", "why" and "how" of Lipo batteries so people understand and not just follow instructions.

I will be publishing here a simple, non-technical explanation (what do you expect from a guy with a flip phone and 8 track RC radios) of batteries and how to pick one for your plane.
Please comment on the writing and correct any mistakes on this post.  I will edit it and publish it here.  My involvement will be to keep it simple using language no more difficult than "see Spot run".

The first draft will be published Sunday after dinner.  Feel free to make constructive comments.  Andy will handle all destructive comments... his specialty.

Frank

[Frank v B]

A change of plans.

Mark will proof read my article starting tonight.  If he understands it great.  If he doesn't, I will make it understandable.
As a special treat and challenge, I will ask Malcolm Cullen to proof read the final draft.  Malcolm has absolutely no problem telling me whether I have succeeded or failed failed miserably.
Hope to publish it Wednesday.  Stay tuned.

Frank

[Frank v B]

This will be split into 3 parts:

1)What do the technical ratings mean- using a 2200 mah, 3S, 20-40C example. Including  "What is Balancing"
2)How do I pick a battery for a new project.
3)How do I determine a power combination from scratch (motor, ESC, battery size).


Part 1-   What do the technical ratings on the label mean.

The picture is of a Venom battery.  The label reads "11.1 volt (3S), 2200 mah, 20 C continuous, 40C burst.  Suggested charge 1C. Max charge 3C." 

What do these numbers mean:

"3S, 11.1 volts" - Lipo batteries are made up of cells, each one with a nominal 3.7 volts.  To make up the voltages, they attach cells in series (therefore S).  The voltages will always be a multiples of 3.7 volts.

1S- 3.7 volts
2S- 7.4 volts
3S- 11.1 volts
4S- 14.8 volts

anything more than 4S and you can write this article.

"2,200 mah (milliamps or 2.2 amps)"- it measures the size of the gas tank.  If you change from 2200 mah to 4400 mah you will get similar performance for twice as long.  The only negative is the heavier weight and the bigger size.

"20 C continuous".  This means that the maximum discharge rate is 20 times the battery's Amp rating.  This battery can have a maximum discharge rate of  44 amps  (20 C x 2.2 amps). 
A safe way to find the maximum current draw of your plane uses is to use the Electronic Speed Control rating (ESC).  If your plane has a 40 amp ESC this 20C battery would be fine but approaching the upper limit.  The closer you approach this limit, the hotter the battery gets.  Hot is bad.

"40 C Burst".  This means that the absolute maximum this battery can take for 15 seconds is 88 amps (40 x 2.2).  The signal that you have exceeded this amperage draw is the white smoke of surrender.  The battery will swell and could blow.

"Suggested Charge 1C".  This means that when you are charging this battery it should be at 1 C or the amp rating.  In this case 2.2 amps.  That means it will be fully charged in about an hour. (60 minutes divided by 1C).

"Max Charge- 3 C."  This battery can be charged at a maximum of 6.6 amps (3 C x 2.2 amps) and would be charged in 20 minutes (60 minutes divided by 3C)


What is "Balancing".  This is making sure that the individual cells are at the same voltage.  Unbalanced cells accept a charge at different rates and draw down at different rates.  It shortens the life of the battery.

Balance charging- the balancing is done by the charger.  It reads all cells, picks the one with the highest voltage and charges the lower voltage ones to this level.  Then tops up all 3 until the battery is charged.

External balancing- this is a small device that plugs into the small white plug.  It reads all cells, picks the one with the lowest voltage and brings the others down to this voltage.

Estimated flight time  The quick and dirty way to calculate the flight time is 60 divided by the C rating.  If you discharge this 20C battery at its limit it will last  3 minutes (60minutes/20C).  A 90C battery sound terrific but that means it will last for  60 minutes /90 C or exactly 40 seconds!

In plain English:

1.Use batteries that match the motor with safe ratings (half the C rating)
2.charge at 1 C.  That means a 1 hour charge
3.I use an external balancer every 3 or 4 flights and do not use a balancing charger.
4.Something is wrong when a battery is too hot to hold.
5.If you want to find out how many cells in a battery,count the number of coloured wires on the balancing (white) plug minus 1.  A 3 cell battery will have 4 wires.
6.The maximum run time of this battery if drawn down at the 20C rating is 3 minutes (60 divided by 20C). 


End of section 1

[Andy Hoffer]

Hi Mark,

If @Frank v B had let his camera focus for him the photo might have looked something like this.   

If you would like to know more about Dutch masters, give me a call.

Andy

(Can't wait to see the photos for sections 2 and 3!)

[Frank v B]

Andy,

predictable!


From my original post "Andy will handle all destructive comments... his specialty. "

Frank

[GuyOReilly]

Thank you for "dummying it down" for the rest of us... me... 
Very informative and useful.
Looking forward to the next instalment.
Guy

[Frank v B]

Part 1 (cont'd)  "What do the technical ratings on the label mean?

Here is a way to understand it.
An analogy with Mark's car.

Analogy:

The battery we are using is a 3S, 11.1 volt, 20C continuous, 40C burst rating, Charge at 1C Max charge 3C.

Mark loves his car.  Comparing Lipo batteries and their quirks to Mark's car.

Picture the following:

- Mark's car has 3 cylinders  (3S)
- 3 gas tanks on top of the trunk, each holds 22.00 litres of fuel (Amp- capacity)
- One tank is connected to a fuel injector of one cylinder.  3 Cylinders, 3 tanks
- The tanks are full of fuel.
- The fuel line diameter is a percentage of the tank/battery capacity (C rating) let's say 2% for 20C, 4% for 40C
- The Electronic Speed Control (ESC) is the accelerator.

Here are the definitions:
Voltage: 11.1 Volts, 3S- three cylinders are operating at the same time.  You get the output of 3 cylinders for as long as the gas lasts.  All three fuel tanks draw down fuel at the same time.  All three cylinders work together for the same length of time.

C rating- The fuel line is 2% (20C) the diameter of the tank but it is way more than the engine needs to run full blast.  Even if we double the diameter of fuel line, the engine only consumes it at a rate it needs to give full performance.  Note: if your Apprentice flies for 10 minutes it is only drawing down the battery at 6C.  (solve for "X"  60/X=10, therefore "X = 6).

Charging: To make this analogy work, we can only refill the tanks through the fuel line which is 2% of the diameter of the tank.  If we fill it at an easy rate for 1 hour (Charge at 1C).  No problem.  We can speed it up it up to 3 C for 20 minutes but it requires a lot of pressure.  Greater than 3C it blows.... because it will. 

Another way to look at it.  If Esso's self serve stations used a fill hose that is 3 (C) times the diameter of the current hose do you think we would have problems?  They probably established a long time ago that the current diameter is perfect (1C).  An Indy car gets refuelled in 5 seconds.  Probably 90C and yes, very dangerous.

Balancing- What happens if two tanks of the 22 litre tanks are empty but one still has 2 litres in it.  A full charge would force 22 litres into all tanks.  The two empty tanks will be fine and full.  The 3rd tank will blow because you are forcing 24 litres into a 22 litre tank.  No go, she will blow.

Two ways of balancing:
balance charging- the charger reads all 3 tanks and finds out two are empty and one has 2 litres in it.  It puts two litres in each of the two empty tanks and it is now balanced and can safely accept the rest of the equal charge of 20 litres per tank so that all 3 tanks now have 22 litres.

External balancing- The electronic balancer plugs into the small white balancing plug.  It reads all 3 tanks and finds out two are empty and one still has 2 litres.  It empties the one tank that still has 2 litres in it and then the whole thing can safely be charged.

Flight time.  If Mark wants to drive further, he just uses larger gas tanks- instead of a 22 later tank (2200 mah) he can install a 44 liter tank (4400 mah. lipo) and get twice the run time at the same power setting.  The car's performance will be the roughly the same but it will weigh more and the tanks have to physically fit on the car. 
Example- A 2650 mah battery will run 20% longer than this 2200 Mah battery (2650/2200).  It will not make the plane go faster.

Testing: when I test a plane in my shop and the plane uses 3 or 4 cells, for safety sake I use a 2S battery (2 tanks of gas).  Only 2 of the cylinders will work but I just need to test whether it is spinning the correct way, to make sure the servos work, the functions are not reversed and to program the throws on the transmitter.  Purely a safety thing.

This also shows that if you plug in a 4S battery into a 3S ESC and motor, things "just ain't fittin".  The indication is usually the white smoke of surrender.


Frank

[msatin]

Thanks Frank!
Even I could understand Frank's 

[Frank v B]

Malcolm replied:

"For the first time, I understand what all the markings on a battery mean. Not that I will retain them, but do understand what you have written so well and will be able to use as a reference."

I used Malcolm as a proof reader because he is the ultimate in bluntly separating all information into two categories:
1) Need to know
2) Nice to know.

His mantra is "Just teach me what I need to know to fly safely and bring back a model airplane in one piece."  Anything beyond that just absorbs time and does not add to the experience.

Phew!


Malcolm promises to be back this summer once Covid is over.  He did not even fly once last year because of business commitments.


Frank

[bweaver]

Re: "Just teach me what I need to know to fly safely and bring back a model airplane in one piece."

Solution: Always take fast drying glue with you when go out to the field to retrieve your model airplane.

PS Frank, thanks for the information about the batteries. 
     Mark, I am so sorry to see you have such a complicated car. Try a Tesla, I understand they come with batteries.

[Frank v B]

Bruce,  re: your comment to Mark on Tesla

A Tesla has up to a 100 Kilowatt hour battery. 

In terms we try to understand:  375 volts (101 S!) and 267 amps.

Eye opening!

Frank

[msatin]

I would love a Tesla, but not sure how I would get a Tesla battery fitted to a balsa model.