FAQ

Oz18650

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I think there should be an FAQ for people who are new to all this.
DarkRaven made the following (very good) post.
I think it (along with other relevant info such as diagrams for "series and parallel")should go in an FAQ.
--
This is the notation for the configuration of the battery. S means Series, P means Parallel. xSyP means x cells in series (to get the desired voltage) and y cells in parallel (to get the desired capacity). If xS or yP is missing then it is either to be read as 1S or 1P respectively or it isn't important for what is meant to be said.

Examples:
- Car batteries are usually 6S lead acid batteries for a total voltage of 12V. A lead acid cell has a nominal voltage of 2V, 6x2V is 12V. There are no cells in parallel, so it is just 6S.
- Lithium batteries for small/medium RC vehicles are usually 3S or 4S, again no cells in parallel.
Technically these batteries can be called 3S1P, 4S1P and 6S1P. But that is not very common since the 1P part has no meaning in this case. Also, lead acid batteries are the reference when talking about 12V/24V/48V systems. They define these systems. That is why they are usually called 12V, 24V and 48V batteries instead of 6S, 12S or 18S.

- If someone says "Use a 7S battery" then there is no yP since this is not relevant in this case. It means you should use a battery with seven cells in series (of that given chemistry that is talked about, in this case lithium ion cells) and the number of cells in parallel is yet to be decided on available space, current draw and so on.

- Similar thing, "Use 90P packs" means you should take packs of 90 cells in parallel and add as many of them in series until you have the desired voltage.

- And finally, 7S90P as an example, is a complete electrical specification of a battery. It uses seven cells in series and 90 in parallel, so a total of 7x90 = 630 cells are needed. You know the voltage, it is seven times the nominal voltage of an individual cell, and the capacity, it is 90 times the capacity of the individual cell. Its energy is its voltage times its capacity and its maximum discharge current is 90 times the maximum discharge current of the used cells.

Did that became clear, more or less? It is not unusual that this is a bit confusing for people that are new to the business

And regarding you question about conversion losses from 24V to 12V: Not much is lost, the conversion efficiency of DC-DC converters is rather high so the losses are small. Efficiency can be as high as ~98% and is rarely under 90%. I usually use 95% as an example if no real figures are available.
 
Batteri University have a pretty decent database with above info :)
 
I've been thinking about a FAQ for some time. I'm glad that you like my explanation, this is certainly one topic for FAQs. Other ones are 3S/4S lithium vs. 12V, basic electrical units and their relation to each other and such things...
Sure, this is no rocket science and it certainly isn't something new, but it isn't helpful for people coming HERE that this information is available SOMEWHERE ELSE. I'm very familiar with people's inability and reluctance to search for something, espcially if they are new to the subject and don't really know what to search for. It is difficult to google something if you don't have the proper word for it.
 
DarkRaven said:
I've been thinking about a FAQ for some time. I'm glad that you like my explanation, this is certainly one topic for FAQs. Other ones are 3S/4S lithium vs. 12V, basic electrical units and their relation to each other and such things...
Sure, this is no rocket science and it certainly isn't something new, but it isn't helpful for people coming HERE that this information is available SOMEWHERE ELSE. I'm very familiar with people's inability and reluctance to search for something, espcially if they are new to the subject and don't really know what to search for. It is difficult to google something if you don't have the proper word for it.

I agree. It would be hard to summarize what is on the forum. But you do see a lot of questions being covered more than once. Its hard to know what to search for when you are new to a topic. Different people have different needs though.

Like the 3S/4S question comes up a lot. We do need a thread with a couple of examples so people get an idea of what they may wish to do.
 
For the basic basic stuff i think its good to. I would say such a page should be 1-2 A4 pages at most and cover the basic. That would solve alot of questions.
 
I started writing down stuff, comments/corrections/additions/suggestions for more topics are very welcome:

1. Definition of Battery, Pack, Module, Cell - What are they?

Battery:
The completed end product, a usable DC source for the intended application, made from a number of modules or cells, connected in series and/or in parallel.

Pack/Module:
Subcomponent of the battery, the battery is made of packs/modules. This is "optional", the battery is not always devided in packs or modules.
Sometimes the word pack is also used for a battery (as in power pack).

Cell:
Subcomponent of the pack/module and/or the battery. This is the individual 18650 cell (or any other format) and the smallest component.

2. What is a serial connection (connection in series) and a parallel connection (connection in parallel)?

A serial connection is a connection of cells by putting one of their negative and one of their positive terminal together. The result is increased voltage across their non-connected terminals.
A parallel connection is a connection of cells by putting all of their negative terminals together and all of their positive terminals as well. The result is increased capacity across their commonly joined terminals.

3. Electrical units / Electrical characteristics of a battery - What is V (Volt), A (Ampere), W (Watt), Ah (Amperehour) and Wh (Watthour)? What is capacity and energy? What is their relation to each other?

These are some of the basic units in physics when it comes to electricity:

W: W is the common symbol for the unit watt. Watt is the unit of the wattage. The word wattage isn't commonly used, it is usually called power.
V: V is the common symbol for the unit volt. Volt is the unit of the voltage. Usual voltages for DC systems are 12V, 24V and 48V. The voltage dictates which devices can be used in any given system.
A: A is the common symbol for the unit ampere, often shortened to "amp" in the english speaking community. Ampere is the unit of the amperage. The word amperage isn't commonly used, it is usually called current.

These three units are related as power is voltage times current, W = V*A, more commonly described as P = U*I. P, U and I being common symbols for power, voltage and current (as opposed to W, V and A being the common symbols for their units, this isn't the same).
Also, these three physical quantites are instantaneous. That means they have no timely relation on their own. When applied over time and when this time is measured a relation of these units to time is created.
The voltage is an important property of a battery, so is the maximum amount of current it can deliver.

Wh: Wh is the common symbol for the unit watthour. A watthour is the combination of a power in watt used over time in hours or any other unit of time. However, hours are commonly used. Watthour is the unit of energy.
Ah: Ah is the common symbol for the unit amperehour. An amperehour is the combination of a current in ampere used over time in hours or any other unit of time. However, hours are commonly used. Amperehour is the unit of capacity.

Energy in watthours is commonly used to measure the usage of power, often in kilowatthours (kWh). 1 kWh = 1000 Wh. It is also used to describe how much energy a battery can store. This is sometimes used to describe how "big" a battery is.
Capacity in amphours is more commonly used to describe how "big" a battery is. This figure can be used to compare batteries of the same voltage.

The addition of a time factor doesn't effect the relation of these units. Just like power is voltage times current, energy (power over time) is voltage times capacity (current over time). Wh = V*Ah.

The units scale like most metric units, for example with the "m" prefix for milli (a thousandth). A milliwatt (mW) is therefore a thousandth of a watt, 1000mW = 1W. It works the same way with the other units.

It also works the other way, the prefix k for kilo (thousand) is especiallycommon for watthours. 1000Wh = 1kWh.

Please note that the units symbols are case sensitive and soare the prefixes as well. A milliamp is 1mA, not 1ma neither 1MA nor 1Ma. And a milliamphour is 1mAh, there is no other valid spelling. The lower case m is especially important as the upper case M is mega. Between m (a thousandth, 10^-3) and M (million, 10^6) are several orders of magnitude.

Example of prefixes using watt as an example:
1000mW = 1W
1000W = 1kW

Below m there is for micro, above k there is M for mega, but these and all consecutive prefixes are usually out of scope for what we are doing here.

4. Why are 12V, 24V and 48V widely used defaults?

These systems were defined ages ago through lead acid batteries. A lead acid cell has a nominal voltage of 2V, six of them in series make a 12V battery, twelve make a 24V battery and 24 make a 48V battery. 36V does exists as well, but is less common.
With the introduction and the widespread use of other chemistries, notably lithium based cells, this poses some challenges because their nomimal voltage doesn't always fit the existing 12/24/48V systems.

5. What lithium configuration do I use for 12V? 3S or 4S?

Neither. This is the major case described under No. 4 where the chemistry prohibits the effective use within the 12V system:
3S lithium batteries have a range of ~9.0V when empty to 12.6V when fully charged.
4S lithium batteries have a range of ~12.0V when empty to 16.8V when fully charged.

The 12V system usually ranges from ~10-11V to ~15V. 3S is too low, you will have early cutoffs and can't use the full capacity of the battery. 4S is too high, when fully charged you will force some devices into their overvoltage protection or simply destroy them.
Lithium cells fit the 24V (7S) and 48V (14S) systems nicely so 24V is the minimum you should use. If you need 12V, you can either use a DC-DC converter from 24V to 12V or use lithium iron phosphate cells (called LiFe, LiFePo or LiFePo4). They have a lower nominal voltage of 3.2V and therefore a 4S configuration will fit the 12V system.

6. What does S and P stand for? What is xS, yP or xSyP with x and y being numeric digits?

This is the notation for the configuration of the battery. S means Series, P means Parallel. xSyP means x cells in series (to get the desired voltage) and y cells in parallel (to get the desired capacity). If xS or yP is missing then it is either to be read as 1S or 1P respectively or it isn't important for what is meant to be said.

Examples:
- Car batteries are usually 6S lead acid batteries for a total voltage of 12V. A lead acid cell has a nominal voltage of 2V, 6x2V is 12V. There are no cells in parallel, so it is just 6S.
- Lithium batteries for small/medium RC vehicles are usually 3S or 4S, again no cells in parallel.
Technically these batteries can be called 3S1P, 4S1P and 6S1P. But that is not very common since the 1P part has no meaning in this case. Also, lead acid batteries are the reference when talking about 12V/24V/48V systems. They define these systems. That is why they are usually called 12V, 24V and 48V batteries instead of 6S, 12S or 18S.

- If someone says "Use a 7S battery" then there is no yP since this is not relevant in this case. It means you should use a battery with seven cells in series (of that given chemistry that is talked about, in this case lithium ion cells) and the number of cells in parallel is yet to be decided on available space, current draw and so on.

- Similar thing, "Use 90P packs" means you should take packs of 90 cells in parallel and add as many of them in series until you have the desired voltage.

- And finally, 7S90P as an example, is a complete electrical specification of a battery. It uses seven cells in series and 90 in parallel, so a total of 7x90 = 630 cells are needed. You know the voltage, it is seven times the nominal voltage of an individual cell, and the capacity, it is 90 times the capacity of the individual cell. Its energy is its voltage times its capacity and its maximum discharge current is 90 times the maximum discharge current of the used cells.

7. What is MPPT and PWM on solar charge controllersand what is the difference? What is better? What should I go for?

To understand this you need to know that solar panels work basically like a power supply. By design they have a sweet spot where they work at their highest possible efficiency. For solar panels this is called their maximum power point. Power is voltage times current, see 3. if you are not familar with the concept.
Without any load the panel will be at its idle voltage, assuming there is decent sunlight. This is usually called their open circuit voltage, or Uoc for short.
When putting a load on the panel, i.e. drawing current to charge a battery, the voltage will drop while the current goes up. With power being voltage times current you see that both effect the power output of the panel. Very high current will lead to very low voltage. As a result the total power will be very low as well.

Uoc is the open circuit / idle voltage, Imp is the current at maximum power (point), Ump is the voltage at maximum power (point). Imp*Ump is the maximum power, Pmax or Pmp. This is usually the rated power for the panel.
For a "12V panel" rated for 100W it will, for example, look like this:

Uoc = 23.2V
Isc = 6.2A
Ump = 17.5V
Imp = 5.71A

Sometimes mpp instead of mp is used.Isc is the short circuit current which is of no relevance at this point.

This is whereMPPT comes into play, itstands for MaximumPower Point Tracking. That means the solar charge controller will search for, or"track", the maximum power point of the connected solar panels, i.e. the current where the panels operate at their highest efficiency. Imagine it's like trial & error, monitoring the power output while adjusting the current and then locking the current where the power is the highest.

PWM on the other hand stands for Pulse Width Modulation. Instead of looking for the maximum power point there will be pulses of voltage, resulting in a current. That means the voltage is turned on and off, sometimes very quickly, and for different periods of time. This is what is usually called the duty cycle, a value in % that show for how much of the time the output is activated. 50% could mean 1ms on, 1ms off. 1000ms = 1s, so we are talking about very short periods of time.

PWM is generally cheaper to implement. All cheap solar charge controllers will use PWM technology. The problem is that this is very inefficient and with that you will never use the maximum power (or even close to that) of the panel. MPPT is more expensive, but more efficient.

If every penny counts, then you have to stick with PWM. But if possible you should always choose an MPPT solar charge controller.

8. How to read the specification of solar panels?

See 7., it is explained as the introduction to MPPT and PWM.

9. What size of wire / fuse wireshould I use?

Size of the wires depends on the intended load. Once the load is known then the wires can be sized. There is no general rule and no definitive answer as it all depends. You should always go for the next biggest size after you've done the sizing to have some margin, not only for expansion, but also for safety.

For fuse wires at cell level it is a bit different. While choosing big wires will always work in case of doubt, fuse wires have to be very small to fuse at the desired curent but don't fuse under normal operation.

For used cells with low current per cell we are looking at something in the region of 34AWG to 30AWG, 0.02 to 0.05mm.
For new cells with higher current per cell we are more in the 24AWG range, 0.2mm.
It is also important to look at the number of cells in parallel as this is what fuse wire will protect the pack from, to keep the rest of the parallel cells from dumping huge currents in to shorted cells.

10. I want a 1kWh battery, what do I do?

This is just a matter of simple maths.

A 1kWh battery can have all kind of different physical sizes/shapes and electrical configurations, there is no standard or THE single solution for this.
If you have, for example, 2000mAh 18650s then each of those stores 7.4Wh of energy and you need 136 of them (1000/7.4 ~ 136) for a 1kWh battery. 136 in parallel will give you a 1kWh battery with a nominal voltage of 3.7V.
If you want higher voltage, and you probably will, you have to put them in series as well. 7s is a typical minimum for a LiIon battery. 136 cells can't be evenly distributed over 7 packs in series, you then need 140 cells for a 7s20p setup. That will give you a battery with a nominal voltage of 25.9V (7x3.7V) and a capacity of 40Ah (20x2000mAh) which results in 1036Wh (25.9Vx40Ah).
And this is just one example, there are plenty other possibilities. For example you then have to figure out what your load is going to be and if 20p is enough to handle the current and if the runtime is what you want.

11. What's all this about the different chemistries?

This whole topic has a backpack full of naming issues, not only because people use it wrong or simplify it, but also because the manufacturers not always state the complete chemistry and because there are "in between / hybrid chemistries" which are a mix. Also some terms overlap with other ones.


The absolute baseline is the term lithium cell.This is always correct, but not always very precise. Depends on whether this kind of precision is important.

LiIon is often usedfor all lithium chemistries with a fluid electrolyte and 3.6/3.7V nominal voltage, that covers basically all cylindrical cells. If you want to bemore precise then you have todifferentiate between their chemistries. Most common ones are lithium cobalt / LiCo / ICR cells, usually found in laptops, powerbanks and so on. Then there is lithium manganese / LiMn / IMR which, unlike the ICR cells, are high drain cells for powertools and similar applications. They were superseded, sort of, by (and now fasten your seatbelts) lithium nickel manganese cobalt / LiNiMnCo / INR cells. This is a hybrid chemistry, not hard to figure out why. These are the main three chemistries, obviously some manufacturers also vary the amounts of the respective element in the mix. Samsungs ICR cells aren't chemically identical to the LG ones and also almost every manufacturer makes several different cells of each type.
There are more chemistries beside these three, a notable one is Teslas lithium aluminium chemistry which is like INR but swaps manganese for aluminium. It is called NCA.
Lithium iron phosphate / LiFe / LiFePo / IFR cells belong to the aforementioned ones technically, but are often handled separately because of their lower nominal voltage of 3.2V.
All of them come in cylindrical forms, LiFe is also often in prismatic forms. The other LiIon chemistries come in prismatic forms as well, but not as often as LiFe.

Lithium polymer cells always come in pouch form. They use similar chemistries with cobalt, manganese and so on, but their electrolyte isn't fluid. It isn't completely solid either but a semi solid gel. Basically it is a kind of plastic. They have the advantage of being lightweight and can easily be built in any shape you need.

LiIon: Refers to all of them, specifically ICR, IMR and INR, nominal voltage 3.6V-3-7V, usually cylindrical cells, sometimes prismatic
ICR: LiIon, made to provide highest capacity for applications where runtime is important but high current discharge isn't
IMR: LiIon, high drain cells for applications with high discharge currents
INR: LiIon, like IMR with some of the benefits of ICR while not losing IMR qualities completely

LiFe/LiFePo/LiFePo4/IFR: LiIon, but often mentioned separately because of lower nominal voltage of 3.2V, cylindrical and prismatic cells

LiPo: Like the other LiIons, but separated from them by their semi solid electrolyte, always in non-standard pouch cells
 
Well done. You must be technical writer :)

A few points:
Should add in mA as well. Also, make a point that it is mA, not ma, kWh, not kwh, etc, etc.
Make a distinction between xSyP and yPxS. This is especially useful when building a single pack with either of these configurations. A 7s10p is 7 cells in series and 10 series in parallel. A 10p7s is 10 cells in parallel with 7 of these connected in series. (or did I get that backwards? see, it's even confusing to me :p )

Adding:

What is MPPT and PWM charge controllers?
- MPPT is Multi Point Power Tracking. This charger tracks along the voltage/current curves of the supplying generator (usually Solar Panels) to achieve the greatest Wattage output and most efficiency of the generator.
- PWM is Pulse Width Modulation. This charger will actually pulse power into the batteries, like a hammer hitting a nail. The charger varies the pulses depending on how full the battery is charged to. Note, it changes the duty cycle of the pulses, the duration of a pulse, not how many pulses in a given time. So, it is like On for 20ms, Off for 20ms, On for 20ms, Off 20ms, etc. Or, On 40ms, Off 10ms, On 40ms, etc...

What gauge wire should I use?
- Always use the size larger wire than for your required load amperage requirements. Measure all your devices current draw and go above those measurements

What size wire should i use for a fuse?
- 30 awg is the largest size that is recommended at the cell level. 34 probably better.


Now, granted, there needs to be more than what I'm saying here. I'm not a writer or a technician manual compliler :p
 
Technical writer? Not at all! :D
However, I'm a technician if you like. I'm working in IT as a server administrator. That sometimes involves writing down stuff for people who don't have a clue! :D

You made some good points, I'll think about how to incorporate them!
 
I would say it might be to much text and images is needed for detailing out especially series and paralell stuff.

When defining a 3s vs 4s you cannot just say its between volt xxx and yyy. You need to include the type of cell and the individual voltages. For instance my Lithium packs in 3s dont go above 10.8V :) Lithium as such is so wide today and include so many types.

I would also say that xSyP should be XsYp. Ie small letters and not capital. I dont have any ref for that though but thats how it looks on all tech sheets i read when it comes about lithium.

ie 14s80p as an example. And as Korishan said the s vs p or p vs s order is important and am image is a must...
 
Do we have someone who volunteers and is qualified beyond Microsoft Paint to make some pretty pictures? :)
 
You mean like this?

3s4p Battery (or is that 4s3p?)


image_grvdpp.jpg

image_xhngzp.jpg
 
Neither is 3s4p, that much I can tell :D

Do you really think we should differentiate between XsYp and YpXs? Do you want to use this to show whether a battery has been built series first or parallel first? I've never seen YpXs in use.
XsYp has been used for quite some time, especially for setup that were wired in parallel first although the series connection is mentioned first in the notation.

If we want to do this then we have to define which one is which. No matter what we choose, your pictures show the same thing :)

I guess this is what you want to show?

image_zukamu.jpg


The first one, 4p3s, is four parallel strings of three cells in series. And the second one is the other way around, it is three cells in series four times paralleled.
It took me 5 minutes or so to find the proper wording, this is really confusing and I think it makes everything even worse since it is almost the same :D
Especially since 3s4p is well established for the left example.

Let's take another example, you know my powerboard. I will use a 7s30p setup but I will take seven modules of 30p and put them in series. Is this 30p7s then because I parallel them first?
 
Yeah, I typed it backwards.

The difference between the two makes a huge difference on what kind of bms system you use. In a XsYp configuration, 1 bms can handle the whole thing. In a XpYs system, you a need a separate bms for each series. Or at least a more complicated bms setup.
 
Yes, I know, but does it justify an own category? Or am I missing something here? Is it already a thing to differentiate between 3s4p and 4p3s? I think it isn't and we are making stuff up. But I could be wrong, don't know. What I do know is that it might be too late now because XsYp is well established for what we now want to call YpXs.
 
Yeap it makes a huge difference actually
For instance i got 14s80p as packs but those could also be represented as 2p14s if we count all those 80p as a single cell :) (Just to make it more difficult)
or even better they are 2p14s80p (not sure if you can put it that way and i dont think we should get into it either)

Im dis-qualified for paint so i cant draw up images for it :)

darkraven: Both your images look the same but its hard to say since there is lines missing?


image_nimmua.jpg
 
Hi All,
To KORISHAN : what is the software you have used for your last battery drawing (yellow cells) ?
Thanks.
 
They aren't missing, I left them out intentionally as we all know they are there :)

You've done it the other way round now. The top one should be 3s2p and the bottom one 2p3s. See what I mean? This is confusing and pointless, because while there is a difference it doesn't justify its own category. Also it is very hard to figure out what is what because as a battery it is the same.
 
Dark no you read it backwards :) For instance i got 14s80p packs. That is 80 cells in paralell and then 14 of those in series ;)

And this is important
Because on a 80p14s you would need 80 BMS runs meanwhile on a 14s80p you need 1 BMS run.

Another example the packs i bought are 4s100p. They have 4 cells to meassure.
100p4s would have been 400cells to meassure. Quite a difference
 
Why would you read this backwards? That's what I mean, there is no way to tell which is which. Because it is the same thing. I know that you need to monitor more cells when you do the series connections first. And this is a fact, yes, but it isn't important. This is rather the reason why almost nobody is doing this.
 
Its not read backwards and its easy to tell which is which. (Atleast for me)

14s80p measn that you got 14 packs in series that have 80 cells each.
80p14s would read that you got 80 packs in parallell that have 14 cells in series.

For me that have been doing RC packs for big drones and other big things last 10 years almost now that have been a big deal in when for instance buying and building packs.
Quick example: https://hobbyking.com/en_us/multistar-high-capacity-6s-16000mah-multi-rotor-lipo-pack.html
This battery consist of 6 packs in series that each have 2 cells in series. Actually 12*8Ah cells :)

And yes its quite important on how you hook it up when you want it to be balance charged or run a bms to it. Atleast for me it is.
 
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