Batteries Lipo math explained

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tommyboy660

Member
Ok so I would like to know the math for lipo batteries in detail if anyone could please tell me I would be very thankful. Ie if I own 3qty 3.7v 1s1p 30c 950mah lipo batteries and combined them all in parrellel would I end up with 1qty 11.1v 3s1p 30c 2850mah lipo battery or would I end up with 1qty 11.1v 3s1p 30c 950mah lipo battery? Please explain why and how you get there for understanding thanks.

If I wanted to end up with a 11.1v 3s1p 30c 2850mah lipo battery what size & how many 1s1p lipos would I need to use, once again please explain on how to come up with your answer. Thank you Tom

Disclaimer: by answering any of the questions I nor anyone else holds anyone at any fault or blame for anything done using any info gotten anywhere from this post or site or from anyone. So u have 0 reasons to wirry of anything, other than if you do have the knowledge and dont share then your just holding me and anyone else back from furthering our knowledge base of lipo batteries which in turn makes it safer in all aspects when you have the proper knowledge.
 
Tony

Tony

Staff member
It depends on how you wire them. If you wire your 950's in parallel, you would add each of your mah for the 3, so 2850 mah. But, if you wire then in series, then you would add up the voltage, and the mah would stay the same.

To get 2850 3s1p, you would need a total of 9 cells. 3 wired in series, then take that 3x3 pack and wire it in series with the other two 3x3 packs. You will end up with a 3s3p battery.

Lets say the below is a single cell...

_

Now, lets look at your 3 batteries in parallel

_
_
_

Now, lets look at them in series

_ _ _

Remember, the right side is positive, the left side is negative, or vice versa. Think of those lines as a AA battery.

If you wire them...

_
_
_

then you will have 3.7 volts, but 2850mah.

If you wire them in series like this...

_ _ _

then you will still have 950mah, but 11.1 volts.

now, you are wanting to take that 11.1 volts, and add up the mah to 2850, it would look like this...

_ _ _
_ _ _
_ _ _

Each of them running horizontal is run in series, each running vertical is run in parallel. You would run the parallel first, THEN run them in series.

I hope this makes sense. If not, I will try to get something that does.
 
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tommyboy660

Member
Oh wow yes that make perfect sense tome now thanks Tony. So these packs that we buy, i opened one up and it was a 3s1p 2200mah 11.1v pack and it had what it looks to be 3 long cells in it that make it up, so are each one of these cells just 11.1v and 733mah each to make that up or vise versa 3.7v and 2200mah each to make it up? Where would you find either of those 2 cells if you where in the market to build your own lipo do you know cuz i have been on places like hobby king but they dont have anything close to either of the 2, the largest single cell ive seen was the 950mah.
 
Tony

Tony

Staff member
They are 3.7v cells with 2200mah. And I have no idea where to get single cells. Never looked since you can get full packs cheaper than you can build them.
 
T

tommyboy660

Member
Ya thats what i just found out, so my lipo battery building has ended before it begun. I had the thought of possibly building a lighter cheaper higher powered lipo that would work with my heli but after just looking those up found out what you just said, its better off to just buy them pre made lol. hobby king after all does sell 3.7v 2200mah bare single cells but yes it would be more expensive to build my own than to buy one even if i didnt include the time it would take. I got 2 3000mah 3s1p batteries that are the same wieght as my 2200 mah lipos and just about identical on size to off ebay for only $50.00 for both and there 30c so there is no way i can beat that price. thanks for your help though
 
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xokia

Active Member
One thing that's missing or maybe I missed it in the explanation is that when you wire them in parallel the C rating also goes up but it does not double with each additional cell.

When wired in series the C rating will drop. But like above each additional battery doesn't drop the C rating in half.
 
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Stambo

Stambo

Well-Known Member
xokia said:
One thing that's missing or maybe I missed it in the explanation is that when you wire them in parallel the C rating also goes up but it does not double with each additional cell.

When wired in series the C rating will drop. But like above each additional battery doesn't drop the C rating in half.
Click to expand...
Why not?
When studying for the electrical part of my trade exams I was always taught that 2 similar batteries in series would double the voltage and maintain the capacity and 2 in parallel would double the capacity, (C) and maintain the voltage.
All tests I have done since then (35+ years) have borne this out.
What has changed?
 
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xokia

Active Member
Stambo said:
Why not?
When studying for the electrical part of my trade exams I was always taught that 2 similar batteries in series would double the voltage and maintain the capacity and 2 in parallel would double the capacity, (C) and maintain the voltage.
All tests I have done since then (35+ years) have borne this out.
What has changed?
Click to expand...
The equivalent series resistance has changed (ESR)

Each battery has it, when you put them is series you add the ESR which reduces overall C rating.

If you put them in parallel then the ESR reduces by the equation 1/(1/ESR + 1/ESR + 1/n) where n is each additional battery beyond the first 2. It's just the parallel resistance equation I'm sure if you're studying you remember that equation. Since the ESR drops the C rating will increase

You can find calculators online to calculate the C rating from the ESR. You are correct that two wired in series the capacity stays the same and the voltage doubles. And you're also correct that putting them in parallel the voltage stays the same and the capacity increase. The C rating isn't a measure of voltage nor capacity.

*edit*
When looking for an ESR meter that could check individual cells I ran across this video which has a really good explanation. Its pretty simple stuff just over looked by many. I'm tired of buying cells and expecting the manfucaturer to give me real data. The C rating stuff is such hocus pocus BS. Manufacturers should publish the ESR of their batteries, but I guess they could fudge that also. I want to be able to measure each cell individually and know if I have droopy cell so I can return it before ever using it. And also be able to really judge if battery x is better then battery y. Being a geek I like data more than personal feel.

In the video below they use ESR and IR interchangeably so don't get confused with out boring you with technical details consider them the same thing.
Product Spotlight: ESR Meter - YouTube
 
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