Basic questions about chargers and charging

givre

givre

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Hello :)
Very new to this world, learning and reading. I hope there is some patient people around here ;)
If you do have nice online courses/information/suggestion for someone just starting to learn about all of this, please don't hesitate to share.

Here are some questions or understanding I have about Battery Chargers and Testers
My references are more with Lithium (ion or iron)

Questions
Q1- How much voltage&current do I need to charge a battery pack ?
I can't find the information on how I calculate this on my own.
I understand it will be very specific to the battery pack, but I would like to see how i can plan on what kind of charger I will need.

In my specific case, I would like to charge my pack using the GRID (home plugs)
Or even let if connected to the grid and charge until I get a lost of power and I am sure the charge will be the most effective.
I was thinking of something like that :
https://www.amazon.ca/-/fr/Converti...VDDE2YM09E0&psc=1&refRID=4QQ3N5EHRVDDE2YM09E0

But will see what comes out of this post ^^

Example with the packs I have :
12S8P with A123 Batteries (ANR26650M1A) like this pack https://batteryhookup.com/products/...650m1a-in-12s8p-config?variant=35854917599394

Specs of the cells :
Nominal capacity and voltage : 2.3 Ah, 3.3 V
Internal impedance (1kHz AC) : 8 mΩ typical
Internal resistance (10A, 1s DC): 10 mΩ typical
Recommended standard charge method: 3A to 3.6V CCCV, 45 min
Recommended fast charge current: 10A to 3.6V CCCV, 15 min

So the pack is a 40V and 2250A. I don't know why they say 36V and it written on the pack 40V. Mine are all around 39.x volts

Q1a- How do I know how much voltage and current I need to put into a single pack (12s8p) to charge it ( minimal /maximal /nominal)
Q1b- If I had more pack in // does this change ? For example if I add like 5 packs in //
Q1c- When charging, I don't really understand what is important : voltage or Amps . Is it better to have a 12V charger with 10A or a 30V with 10A . Maybe I just don't see how voltage and amps are flowing into each cell of a pack and how current and/or voltage will flow.
Q1d- This is more a BMS question, but, when charging a pack with a BMS, does the BMS always has to seat in between the source of energy and the pack? This is so it can cut-off when needed ?
Q1e- I see a lot of people using a BMS to balance the state of charge but I don't see a lot of monitoring/logging solution. Why that ?
Q1f- Why is it considerate "safe" to balance 1s with X cells in // without going to monitor the state of each one cells ? Or this is just the "best" of what is is possible and there is no need to monitor every single cells and wait that the 1s become poor to investigate ?
Or is there any DIY project/PCB that can handle a good unitary cell voltage and a good amount of temperature sensors ? :)

Understanding / Assuming
U1- Charing a battery pack with x number of cell in parallel will result as 'as full as the first cell reach the maximum voltage'
Because once the first cell in parallel will have the max voltage (and let say a BMS will cut off), that will be the end of the charging for this cell pack.
That is why a BMS can monitor as many pack in // because he will only see series if all the 12s have their own connexion (all the 1s together, all the 2s together and so on)

U2- if I have a 3000w inverter and that I use at the maximum of 3000w continue on the 36v if I want to know the discharge current that will be passing in the BMS i can just do ( 3000w/36v = 83 Amps)

Thanks a lot for you help and valuable knowledge
Ben
 
Batteries have a 'max recommended voltage' (max v) that is the sum of the max v of cells in series. The specs at BatteryHookup for this cell (on their web page) shows this at 3.6v. You say 12s8p so it would be 12 * 3.6v = 43.2v would be max charge voltage.

To charge a battery, the charger must create voltage a little higher than the battery - else current won't flow from the charger to the battery. If you're battery is at at 12 * 3v = 36v, then a charger might start out at 38v to get X amps flowing into the battery. As the battery voltage rises to 37v, 38v, 39v ..., the charger will raise it's voltage to 39v, 40v, 41v, ... as well to maintain a constant current. This is the "CC" (constant current) portion of charging a battery. Once the charger reaches the maximum for your battery - e.g. 43.2v - then the charger will not go any higher and the battery will gradually get closer and closer to the 43.2v but the current will flow less and less because the voltage difference is smaller and smaller. This is the "CV" (constant voltage) portion of the charge.

If you look at the specs again - it says "Recommended Standard Charge" is 3a (per cell) "CCCV". "Recommended Fast Charge" is 10a (per cell) "CCCV". Notice the "CCCV"? - that refers the to "Constant Current / Constant Voltage' explanation above. For a 12s8p that would be 8 * 3a = 24a @ 43.2v and 8 * 10a = 80a @ 43.2v. 24a is 'standard' and 80a is 'fast'. Standard will lead to longer life than fast but its OK to do fast.

>So the pack is a 40V and 2250A. I don't know why they say 36V and it written on the pack 40V. Mine are all around 39.x volts
12v, 24v, 36v, 48v, 72v, etc... are 'nominal' voltage - meaning the general voltage range you would expect from Lead Acid classic batteries. Custom DIY batteries don't always fit exactly in these but it doesn't matter - what matters is that the equipment you buy will operate for the voltage range of your battery.

For your 12s battery - you need a 12s lifepo4 charger (43.2v max) to be able to charge it to 100%. If you're charging via Solar panels, you should be able to find a charge controller that will let you set the absorb/float values to 43.2v. If you're charging via grid power... hmm... you may need to a power supply of some kind - maybe a boost board or a standard 0-60v power supply.

>Q1a- How do I know how much voltage and current I need to put into a single pack (12s8p) to charge it ( minimal /maximal /nominal)
Answered above.

>Q1b- If I had more pack in // does this change ? For example if I add like 5 packs in //
If you add 5 packs in parallel - then you would multiple the amps in / out by 5.

>Q1c- When charging, I don't really understand what is important : voltage or Amps . Is it better to have a 12V charger with 10A or a 30V with 10A . Maybe I just don't see how voltage and amps are flowing into each cell of a pack and how current and/or voltage will flow.
1) Voltage - you must not exceed the max voltage of a lithium-ion battery or risk fire. No problem charging a battery to less than it's max if that suits your needs.
2) Amps - best to stay the within the recommended specs. In your case standard = 3a/cell and fast =10a/cell.
NOTE: You'll find that a 43.2v @ 80a charger is quite expensive.... and/or A LOT of solar panels... so its not usually a problem of having a charger that is too strong amp wise :)

>Q1d- This is more a BMS question, but, when charging a pack with a BMS, does the BMS always has to seat in between the source of energy and the pack? This is so it can cut-off when needed ?
Yes

>Q1e- I see a lot of people using a BMS to balance the state of charge but I don't see a lot of monitoring/logging solution. Why that ?
Cost money to to log info - cheapest BMSs don't let you monitor anything. Middle cost offer iPhone monitoring. Expensive offer computer and integration monitoring.

>Q1f- Why is it considerate "safe" to balance 1s with X cells in // without going to monitor the state of each one cells ? Or this is just the "best"
1s = 1 cell. Not sure what "X cells" in 1s would be.

> is there any DIY project/PCB that can handle a good unitary cell voltage and a good amount of temperature sensors
Yes - if I'm understanding this thought I would direct you to "Stuart Pittaway" diyBMS as a solid example. Here's a youtube -
You should search this forum as well as I believe some members use Stuart and have quite advanced solutions.
 
Last edited:
Thanks a lot for you answer.
This is very clear and helps me a lot. :)

About the 1s my understanding is :
When there is 12s8p , there is 12 series of 8 cells in //
So 1s = 8 cells in my mind times 12

And the BMS will monitor 1 série of 8 cells to make sure they are at 3.6v (for example)
But there is basically 8 cells , not just one, and it is considered "safe" to do it that way

Now if there is 5 packs of 12s8p and 1 series is now made of 40 cells (5 series of 8 cells joined ) it's a lot of more cells but I understand the output will always be 3.6v and it is assumed that if there is less than that, some cells are not doing well maybe.
You can see the picture joined to make more visible :
1609975822072.png

Looks like in this kind of pack (and from what I have seen, they all do the same kind) 1 BMS of 12S will assure that all the packs are balanced even with 5 packs

Before I though that 1 BMS was required per 12s8p
But it seem that it commun to only have 1 BMS for the 5 pack in //
 
Thanks for the pic - looks nice!

I see 8 'batteries' of 12s8p instead of 5?

>So 1s = 8 cells
Agreed.

>Looks like in this kind of pack (and from what I have seen, they all do the same kind) 1 BMS of 12S will assure that all the packs are balanced even with 5 packs
>Before I though that 1 BMS was required per 12s8p
>But it seem that it commun to only have 1 BMS for the 5 pack in
Agreed.
 
So, a charger like this one is not suitable ?

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Even if that will take a long time (i imagine) using just 10A is it possible to charge the pack ?
Or do I really need something like you said a charger 43.2v @ 24a (standard)

Knowing that I will have a BMS 12S to make sure everything is well balanced while charging the pack. I think i will only need something that can give 43.2v Max

I'm still confused if a charger will work under the standard rating ?
Thanks again
 
Last edited:
givre said:
So, a charger like this one is not suitable ?

Amazon.com: Adjustable DC Power Voltage Converter AC 110V-220V to DC 0-48V Module Switching Power Supply Digital Display 480W Voltage Regulator Transformer Built in Cooling Fan: Electronics

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Even if that will take a long time (i imagine) using just 10A is it possible to charge the pack ?
Or do I really need something like you said a charger 43.2v @ 24a (standard)
Click to expand...

That is a fairly standard power supply and is not suitable for charging batteries, because the LiIon battery will suck more than 10A and trip the overload protection of the power supply... or burn it out... or worse.

12S LiFePO4 is roughly equal to so-called "36V" systems. Unfortunately there are not many chargers or inverters made for that voltage.
You may want to look into rewiring the cells to a 8S configuration ("24V" system) or 16S configuration ("48V" system).

Here is a charger & inverter that should work with your 12S (36V) battery. But I warn again: you will continually run into the issue of not finding devices that work with 36V.
www.aliexpress.com

90.47US $ 17% OFF|72v 60v 67.2v 84v Li-ion Lipo 48v Lifepo4 Lithium Battery Charger Curren Adjust 2a 5a 10a 12a Fast Charge Ebike 12s 16s 20s 24s - Chargers - AliExpress

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Hi,
Thanks @ajw22 .
Yes I have heard that 36V is not the best case, but at least I get something to start with. I thought about changing the configuration too, but at the end I will keep the configuration and make the best out of it.

That is a fairly standard power supply and is not suitable for charging batteries, because the LiIon battery will suck more than 10A and trip the overload protection of the power supply... or burn it out... or worse.
Click to expand...
How Can I calculate that ? Is there a ways to know
Because as said @OffGridInTheCity about the charging possibility: 24a is 'standard' and 80a is 'fast'
What if I charge with less than 24A and how low I can go.

You mentioned that a pack will suck more than 10A but the charger above si 12A max .
Or it's because it says : suit for 20AH to 120AH Li battery

Thanks
 
>So, a charger like this one is not suitable ?
>https://www.amazon.com/Adjustable-Converter-110V-220V-Switching-Transformer/dp/B0777MH681
Agree with @ajw22. Also - a power supply is CC (constant current) and does not have the electronics for CV (constant voltage). This is why a 'power supply' is not the same as a 'charger'. Charger's have extra smarts to do the CV at a specific top voltage compatible with your battery.

Some "Bench" power supplies - like this one - https://www.amazon.com/3-Digital-Pr...ords=0-60v+power+supply&qid=1610035309&sr=8-4 - may have "CC/CV" capability. Notice this in the description:
C.C & C.V.MODES AUTO CONVERSION-It's easy to adjust your desired voltage and current with coarse and fine turning knob. The constant voltage and current mode automatically switch over with load changes.

But I've not personally used one of these - so maybe others can advise.



>What if I charge with less than 24A and how low I can go.
Yes, you can charge by less amps. You can calculate the 'how long'. Let's say you buy a 5a charger at 36v (nominal). Then 5a * 36v = 180watts. If you charge for an hour, that's 180watt-hours. Your 12s8p has 8 in parallel (e.g. 2300mah * 8 = 18,400mah) times the voltage (40v nominal) which equals 736watt-hours. 736wh/180wh = 4.1hrs to charge your 12s8p. This is approximate - will be less for if not charging 100% and there's extra time for the CV portion of the process if you go for 100% charge - but will be 4-5hrs for a 5a charger @ 36v.

Its pretty much linear - so double the amps and it will take 1/2 the time.
 
Excelent :)
That make sense, I kind of guessed that the CC and CV has a lot to do with the charger. Thank you .

Appreciate a lot your explanations guys
Enjoy your day
 
I was wondering something.
If I do have a BMS in front of the pack 12s8P , Do I really need special charger that is Lithium specific 12s ?
Or just having a power supply that is 110 AC to 43V DC with CC-CV is enough and goes to the BMS for balancing is a good option?

because something like this : https://www.amazon.ca/EV-PEAK-1350W-Charger-Battery-Screen/dp/B01D4PORJW already has a BMS kind of thing built-in . I feel it is not useful in my case as I will have a BMS attach to the pack.
But this one can reach 25A and it's a quick way to see if a pack is balanced
 
A BMS's primary function is to disconnect the battery from the load (so current stops flowing) IF....
1) A cell'v voltage is too high or too low.
2) A cell is too hot or too cold.
3) There is too much current flow to the load (or charging)
-------------
4) A nice to have is that the BMS will balance the cells
-------------
5) Another nice to have is the BMS will report on what's happening so you can see it / make adjustments.

A charger that does balancing (as you show above) will 'sort of' act as a BMS in that it will do some balancing as it charges and if properly matched, won't allow a cell to get over charged and won't push too much current in.
However - this will do nothing during discharge (current, temp, cells voltage) or ongoing balancing.

Its true that in some applications a balancing charger is sufficient - like an ebike or a drone if you take care not to let tje ;pad get to hi or the battery too hot or run down to far manually.

What's the goal of this battery?
 
givre said:
If I do have a BMS in front of the pack 12s8P , Do I really need special charger that is Lithium specific 12s ?
Or just having a power supply that is 110 AC to 43V DC with CC-CV is enough and goes to the BMS for balancing is a good option?
Click to expand...

For my ebike batteries that i build, i use the ANT-BMS you can get it in a few different flavours..

10s-24s with different discharge upto 300A peak
7s-20s which is available in different discharge upto 400A peak

The advantages of this is that it has bluetooth connection so that you can set parameters.

you can also connect an LCD that displays the cell Voltages, Amp draw etc.

The down side is and i havent pushed this to see if it can get anymore but charge Amps i have had at 12A max
 
The goal of this first build is just to have a backup system with some Kwh available for house appliances in case of an outage .
This is why I just want to be able to charge it from the grid and have it ready when I will loose power. And if the power does not come back before it's become empty, too bad :D

Something very simple as a first way to learn.

That is why I don't really mind if it takes a long time to charge
The system will not be over used at all
But I still like the idea of running a couple of appliance at the same time ( TV, computer , lights and eventually a kettle but not necessarily )
And mostly have fun doing it
 
givre said:
The goal of this first build is just to have a backup system with some Kwh available for house appliances in case of an outage .
This is why I just want to be able to charge it from the grid and have it ready when I will loose power. And if the power does not come back before it's become empty, too bad :D

Something very simple as a first way to learn.

That is why I don't really mind if it takes a long time to charge
The system will not be over used at all
But I still like the idea of running a couple of appliance at the same time ( TV, computer , lights and eventually a kettle but not necessarily )
And mostly have fun doing it
Click to expand...
From having Power outages here over the last few months, My advice is to build it to be able to power the highest load.. which would be the Kettle.

I have lots of part built and completed battery packs that i can use and have quite a few lower power inverters so that i can power the same but couldnt ever power my kettle until i recently bought a 3kw inverter.

The only potential issue you have with Lithium cells is having them laying around fully charged, i would advise to build something that you can add t0, but rather than have it sit around, i would have it powering something and charging so that it is in good condition.
 
The only potential issue you have with Lithium cells is having them laying around fully charged, i would advise to build something that you can add t0, but rather than have it sit around, i would have it powering something and charging so that it is in good condition.
Click to expand...
Yes, that is something I have in mind too. But I'm far away to understand how to do this ^^ So I will have time to think about it . Thanks for your advise.
I was thinking of having the 3kw inverter also ;)
 
givre said:
Yes, that is something I have in mind too. But I'm far away to understand how to do this ^^ So I will have time to think about it . Thanks for your advise.
I was thinking of having the 3kw inverter also ;)
Click to expand...
The easiest way to look at it is like you have a battery that you use every single day, like ebike pack, if you have the 3kw inverter and a shed/room that you work from, use it to power your loads

just be mindful that if you plug in a 4 way extension to a 3kw inverter and use the full 3kw, you are right on the limits of the cable... especially here in the UK, we have 240v and 10A rated cables so that would mean 2300W is the max i would be happy putting through it.

Not sure what the ratings are for your extension leads but i would be mindful of that.
 
I wanted to avoid to discharge/charge too much. So my plan is to use it like once every month for example just to make sure everything is in a good condition and fully charge.

Here in Canada we have 110v but I don't know how is the rating of a 4way extension, thanks for that.
 
I am sure that once a month maybe twice a month would be ok. if you go with the ANT BMS, you can set the charge and Discharge Min and Max

It lets you set the BMS to cut power at Cell level... so each 1s would be monitored to say 3.1v and cutoff and then charge would be set to 4.1v and stop there. that would use 80% of charge but give the cells a much better lifetime.
 
If max charge voltage is as example 3.6V you shall never ever have something above this. Not at the battery terminal. You only do this thing on lead acid where you do bulk/float.

You compensate so that at the battery terminals its 3.6 MAX... At the charger it could potentially be 3.62 due to losses in wiring but thats it.
This is IMPORTANT for lithium. Never ever over charge.
 
Sorry these 3.2v cells?

To correct the info for the Ant BMS you can set the cells charge and discharge voltage to LVC and HVC that your cells require
 
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