Drone batteries in series vs parallel
Drone batteries in series vs parallel- What does this really mean? How does someone determine what 4S3P 34-50C burst 1600 mAh really means? What do all of these strange battery ratings really mean? Where do I start when trying to select the best battery? What should a noob do?
This is confusing!? I don’t know where to begin! Help! Which battery do I need for my QAV250?
Every pilot has been there. The world of batteries can be a very daunting one. Where to start? This post hopes to help.
So you want to build a 3d flying, first-person view acrobatic robot AKA “DRONE” or “Quadcopter”
Well you need to make sure that you pick the right battery. Lithium with it’s extreme need to loose it’s electron and become stable makes it perfect for batteries. Lithium-ion or lithium-polymer are the only choices for the QAV250, Other batteries are too heavy at the same power output levels.
The anatomy of the battery
We have established that we need to use Lithium-ion batteries for our quadcopter.
Lithium batteries consist of cells. Inside each cell there is a cathode, anode, and electrolyte. Without going into too much detail, I will tell you that:
- Each cell of a battery has a voltage dependent on it’s core metal.
- So, An alkaline reaction makes 1.5V per cell
- A lithium reaction makes 3.7V per cell
- A Lead acid reaction makes 2.2V per cell.
- A Nickel Cadnium makes 1.2V per cell.
Rechargeable Battery Chemistries
(rotate to view if viewing on iPhone)
|Chemistry||Cell Voltage||Energy Density (MJ/kg)||Comments|
High/low drain, moderate energy density.
Can withstand very high discharge rates with virtually no loss of capacity.
Moderate rate of self discharge.
Reputed to suffer from memory effect (which is alleged to cause early failure).
Environmental hazard due to Cadmium – use now virtually prohibited in Europe.
|Lead Acid||2.2||0.14||Moderately expensive.
Moderate energy density.
Moderate rate of self discharge.
Higher discharge rates result in considerable loss of capacity.
Does not suffer from memory effect.
Environmental hazard due to Lead.
Common use – Automobile batteries
Not usable in higher drain devices.
Traditional chemistry has high energy density, but also a high rate of self-discharge.
Newer chemistry has low self-discharge rate, but also a ~25% lower energy density.
Very heavy. Used in some cars.
|Lithium ion||3.6||0.46||Very expensive.
Very high energy density.
Not usually available in “common” battery sizes (but see RCR-V3 for a counter-example).
Very common in laptop computers, moderate to high-end digital cameras and camcorders, and cellphones. & QUADCOPTERS 😉
Very low rate of self discharge.
Volatile: Chance of explosion if short circuited, allowed to overheat, or not manufactured with rigorous quality standards.
A single cell
[wolf_column col=”col-6″ first=”yes”]That Alkaline AA battery in your remote control is 1.5V.[/wolf_column]
[wolf_column col=”col-6″ last=”yes”]
Those little Lithium Ion button watch batteries like the CR2032 are 3.6V!
This is because of the chemistry that lies within.
Each of these batteries, the AA battery and the CR2032 battery are one cell batteries.
That is a very large voltage difference between those 2 chemical reactions….
It turns out that that Lithium technology packs the most volts per cell of all to the batteries, and it is a secondary battery, which is good news for quadcopter pilots because it is RECHARGEABLE.
We can look at the chart above and know that Lithium Ion has 3.6V per cell.
If I have a 1 cell Lithium Ion battery, I can count on it being around 3.6V. But what if I need more voltage?
drone batteries in series vs parallel
The parallel and series phenomenon
[wolf_column col=”col-6″ first=”yes”]If you connect 2 AA batteries together in series, you end up with 3v[/wolf_column]
[wolf_column col=”col-6″ first=”yes”]If you connect 2 Cr2032 Batteries together in Series you end up with 7.2V. The above picture is representative of 2 cells in series.[/wolf_column]
If you still need more voltage you can keep going like this, and connect 3 Cells in series.
A crazy example of what is possible when connecting lots of batteries in series.
We could continue in this fashion forever if we wanted to get more voltage. In the following video, a guy connects 244 used 9v batteries together in series to create a 2000v 244S1P battery.
What about the second part of the number? Sure a single cell battery is a 1s1p battery. (1 series 1 parallel) We can connect batteries in parallel to increase the amount of power available. The example below shows batteries wired in a 1s3p configuration (1 cell in series, 3 cells in parallel)
Why would we want to do this? This configuration allows us to create very high amp ratings. If each cell can output 1 amp, then the packs wired in parallel like this will create a 3 amp output.
Putting it all together
Electricity can be doubled in voltage, and halved in amperage, and the power stays the same.
It’s Ohms Law.
OK, so the volt guy is pushing, and the amp guy is getting pushed by the volt guy, and the ohm guy is pulling on the amp guy causing resistance.
THE CURRENT VOLT AND AMP ARE ALL INVERSELY PROPORTIONAL!
To calculate the power of something you have to multiply amps times watts.
This means that I can get the same amount of power from 7.2Volts and 1 amp as I can from 3.6v and 2 amps.
Combining series with parallel to make super batteries.
So really powerful batteries will have multiple cells in series such as a 2S3P battery. A 2s3p battery would have 2 cells of 3 batteries in parallel.
This is how we can achieve high voltage, high power lithium batteries.
So when you are buying a 3S battery lithium battery, you can know that the battery is 3 cells and you can calculate the voltage by knowing the chemistry of the cells.
Go to part II of this post:
[su_button url=”http://quadquestions.com/blog/engineering/qav250-c-rating-explained/” style=”flat” background=”#187e19″ wide=”yes” center=”yes” icon=”icon: level-up” desc=”Battery C Rating Explained”]Go to part II of this post [/su_button]