Making a 12v 4s battery pack from 18650

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Old 09-16-19, 05:32 PM
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Making a 12v 4s battery pack from 18650

Hi, I have around 20 18650 battery just sitting around, so I thought of making a 4s 12v(well more like 12-16v battery depends on charge).

That should be fairly easy overall, just looking for some advices to make it as good as I can.
One thing I would like to try is avoiding soldering as much as I can, especially with the 18650 batteries themselves, I'm not sure where I've heard that, but if I remember correctly soldering straight onto a 18650 is not very healthy for the battery due to the heat(like here for example: https://www.youtube.com/watch?v=0sj5DvG-qPI)

Now I believe that with the proper soldering skills and tools, soldering the 18650 batteries might not be an issue, but in my case both my soldering skills and soldering tools are fairly bad, and that's mainly why I'd like to avoid that if possible.

I thought about a solution for that, and thought about getting 5 of these 4 slots holder:
https://www.aliexpress.com/item/3282...chweb201603_52

The wires are very very thin, so I believe I'll replace that, but the general idea here is that I'll simply get 5 of these, and then wire them up in parallel, so each slot holder is going to be ~12v(more like 14-16), and when wiring them in parallel each cell will increase the amps.

What do you guys think? Will that do the job? Would that be a good idea?

I'm also plan on using a bms for that, I already own the following 4s bms:
https://www.aliexpress.com/item/3296...27424c4dbx6fs0

That's probably a bit of an overkill, but that seems like it should work just fine.

Are there any other recommendations? Something I'm not doing properly?
Thanks for the help!
 
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Old 09-16-19, 08:16 PM
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Those cells are 3.7v so you would need to use four in series for a nominal pack voltage of 14.8v.
 
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Old 09-17-19, 01:07 AM
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Yes I'm aware of that, but that doesn't really answer any of my questions
 
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Old 09-17-19, 04:29 AM
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Making a battery pack is super easy. I assume your 18650's are used/old. Have you checked to verify that you have enough good battery cells?

You asked if it will do the job??? You did not tell us why you are making the battery pack so we can't tell you if it will do the job.

No, you really can't solder well to 18650. Their end caps are plated steel. Most battery packs use welded connections and devices use a spring loaded battery holder.

You linked to a battery management board. Do you know how to wire/connect it? Do you know how to power the board for charging? Their wiring diagrams really aren't that accurate and seem to miss a really important part for cell balancing.
 
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Old 09-17-19, 07:28 AM
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Well actually the batteries should be rather new, most batteries I've checked are with around 4-4.2V, so that's rather good.

By "do the job" I'm not referring to how well it will perform for my needs(which is simply using 12v battery in the field for powering 12v stuff that uses an average of 0.5-1AH), what I'm referring to, is if what I described is the correct way to make it, which is getting 5 pcs of the 4 slots holders I've shared, each 4 slot is connected in series, so that gives me 12v(well not really 12v but ok), then simply connect each "4 slot cell" in parallel to stay on 12v, but increase the capacity.

I'm aware of the issues with soldering 18650, that's why I'm looking for a rather solder-less solution to go with
As for the bms, no, I don't "know" how to wire it, but I believe that by watching some videos and looking carefully on the board I'll manage to get it working, do you have any other 4s bms that you recommend? (I'll need to order that from either aliexpress or ebay).

I do plan on getting a seperate balance charger by using something like this:
https://www.aliexpress.com/item/3281...chweb201603_52

I also plan on wiring the battery pack in a way that the plus is coming from one side, but have the negative coming from the other side, that way the flow is going through all the batteries, and doesn't focus on 1 cell by drawing power from the "bottom" batteries.
 
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Old 09-17-19, 09:36 AM
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Are your 18650 protected or unprotected? You can get away with a little less care by using protected cells and rely on the batteries internal circuit board to protect the cell.

The batteries voltage in storage often does not tell you if it is still good or not. A battery can show a healthy voltage while at rest but quickly die under load without ever delivering anywhere near it's rated storage capacity. If using old cells the original packs were probably discarded because they no longer worked so you're likely to have at least some bad cells that should not be used.

I normally make up battery packs using LiPo "soft" batteries and use three cells to power 12 VDC items. The voltage is slightly high (12.6) when freshly charged but most of the time is about 11.1 volts which is OK for most electronic items. I don't use four cells because electronics are not damaged by lower voltage but higher voltage can hurt them. Four cells fully charged in series can provide about 16.8 volts with 14.8 volts most of the time.

If using old cells in serices it's a good idea to match them into groups according to their internal resistance. Each series of 3/4 batteries should be as closely matched as possible.

You are planning five parallel groups of three or four batteries in series for a total of 15 or 20 cells. Best is to balance charge all the cells. With the board you linked that will require you to charge each series of 3/4 cells individually. That will make charging your pack pretty slow and tedious 5 charging cycle process.
 
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Old 09-17-19, 10:06 AM
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Awesome comment, thanks!!
I believe the batteries are not protected, since I don't actually know, I'd much rather think of it as unprotected than protected.

Most the the equipment I'll be using requires 11-16V, with 11-12V being sometimes too low, so I'd rather use the 4s pack.

I'm actually intend to use a balance charger like this one:
https://www.aliexpress.com/item/3281...chweb201603_52

I believe this way I could charge the whole battery pack evenly in one go?
Thanks for the tip regarding each cell balance, that is something I'll definitely do.
 
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Old 09-17-19, 01:02 PM
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those newer vehicle jump starter packs are fairly inexpensive not sure its worth the trouble of building your own when you can buy one for 40 bucks already designed to be used as a power pack.
 
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Old 09-17-19, 01:21 PM
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I'm not really sure that a 12v battery with 10AH for a price I could simply get around 40-75AH battery would help me all that much though, and I already have some batteries I could use.
 
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Old 09-17-19, 01:38 PM
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there not all 12 volt some go much higher like 16 or 19 volts for powering other devices would atleast look at them and then add up all your components and time to build one thats probably going to be a lot less capacity.
 
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Old 09-17-19, 01:51 PM
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I don't really need more than 12v though, and the price I'm paying for that doesn't seems to be worthy to me when I could simply use what I already have.
 
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Old 09-18-19, 05:11 AM
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I use four button chargers like that all the time and they can work well. Selecting the balance function for each charge will help keep your pack more in balance. The down side is that balance charging takes longer than normal charging.

If you look at other, similar chargers you will see that many also have a temperature sensor. That temp probe can be attached to your battery pack and if the pack overheats during charging the charger will automatically turn off.

The issue for you is that charger can only balance 6 cells. You will have 20. You can use that charger treating each of your series strings as one cell but it will not be balancing the cells in your series string. To the charger each of your series strings will appear to be one big cell.

Using protected cells will provide some protection against over charging an individual cell. But, when the cell's protection kicks in it will open the circuit and prevent the other cells in that series string from charging. Whichever cell comes up to full charge fist determines when charging stops and the remaining cells in that string will be under charged.

There are chargers similar to what you linked but they are capable of charging 2 or 4 batteries at once. That is 1, 2, 3 or 4 batteries of up to six cells. Choosing a 4 channel charger would allow you to balance charge up to 48 individual cells. It's a lot of wiring but it is possible if you want the best performance.

 
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