18650 battery pack

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Camerong

Member
Joined 2015
Hey everyone.
What do you guys think of building your own 18650 battery packs? Or is it better to just buy one with included bms and charger to suit..

I was thinking something like this

22.2V 25.2V 6*18650 2600mAh 6S Lithium ion Li-ion Battery Pack [6x 18650 6S 22V 2600mAh] - $38.20 : Lithium Rechargeable Batteries, Battery BMS, Pack Assembling

Li-ion Li-Po 25.2V 22.2V 2A 6S Wall Socket Battery Charger AC DC [25.2V 2A Lithium Battery Charger] - $17.20 : Lithium Rechargeable Batteries, Battery BMS, Pack Assembling

But it seems a lot cheaper to rip a laptop battery apart and wire 6 batteries in series and put a bms on it. Or is it not as simple as that?

I want to have a switch switching from the battery pack to 240 ac.

Can someone please send me an idea
 
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Foxx510

Member
Joined 2006
I don't see a problem with using laptop cells if that is cheaper. You do need to know what you are doing though with these - they don't respond well if mistreated as you are probably aware. Just don't try to solder to them - only use tabs or spot welding. Which bms are you considering? What is the load?
 
C

Camerong

Member
Joined 2015
Yeah I was thinking nicad but it's heavy and has memory loss after a while. It's going to be a portable speaker box and I would prefer it to be as light as possible.
Even if it cost me a bit more.

Just wondering how I could have one cord and be able to charge the battery and run it off the same cord for 240v ac.
 
A

AndrewT

R.I.P.
Joined 2004
I just bought a 22Ahr 3.7V battery pack. It weighs 462g
It has it's own built in charging system, so hopefully the USB 5V never damages it.
It also has a set of USB 5V outputs.
Use that into a DC to DC converter and you are go.

Building you own lithium battery charger is not easy.
 
F

Foxx510

Member
Joined 2006
Camerong said:
Just wondering how I could have one cord and be able to charge the battery and run it off the same cord for 240v ac.
Click to expand...

You'd need to limit the charge current to the cells(and the voltage, obviously) if you used the same plugpack to charge the cells and run the device. You don't want to be charging your cells at 5 amps or whatever the plugpack you use is. 1 amp would be about right.

Charging single lithiums is simple CC/CV charging. The trick managing your cell balance, over discharge etc. You need a decent bms for that.
 
C

Camerong

Member
Joined 2015
Ah ok right.
So I will would be much better off having two separate
Plugs one for running the device and one for charging.
I'm not too worried about that.
Just would have been convenient.

Also is the bms the only circuit that I will need on the safety side on charging?
 
F

Foxx510

Member
Joined 2006
Camerong said:
Ah ok right.
So I will would be much better off having two separate
Plugs one for running the device and one for charging.
I'm not too worried about that.
Just would have been convenient.

Also is the bms the only circuit that I will need on the safety side on charging?
Click to expand...

No you can do it with one plugpack, you just need to regulate the current and voltage appropriately.

I'd advise doing a lot more research if you are going to use a lithium pack. They will burn your house down if you get it a tiny bit wrong.

And don't use cheap chinese cells. Use Panasonic, LG, Sony or Samsung cells from a reputable dealer.
 
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C

Camerong

Member
Joined 2015
Will this work?
Don't laugh it's my first schematic lol.
And I haven't finished it but it could work right?
Feel free to change anything on it... actually please do haha
 

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C

Camerong

Member
Joined 2015
They stores I would like to buy from don't allow li ion batteries to be shipped to new Zealand so I'm good to have to make my own battery pack out of either laptop battery or import individual cells.
Also can anyone please look at my schematic and advise me if it will work or not. Thanks
 
infinia

infinia

Member
Joined 2005
your AC input scheme with the diodes isn't sound.
BTW you don't need the manual switch with the output diodes, if you can adjust either voltage to back bias the unwanted diode. Think of it as automatic switching when the battery V drops below a certain threshold.
I thought the question was BMS design choices? that's where knowledge and safety lays! understand individual 18650 cells completely 1st. Me, I only pick 1st tier brand names! (you know the ones that supply real engineering data sheets) Battery University web site is decent. Battery packs require new cells for best performance E.g. matching, old laptop battery pulls are for chumps.
They stores I would like to buy from don't allow li ion batteries to be shipped to new Zealand
Click to expand...
strange , but if you insist on building a custom pack find a new store. (please look into Lipo hobby packs). I get mine from HK >fasttech.com, air shipped to cali in ~10 days recently. BTW good code search word is "authentic +18650" muhaha
 
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C

Camerong

Member
Joined 2015
infinia said:
your AC input scheme with the diodes isn't sound.
BTW you don't need the manual switch with the output diodes, if you can adjust either voltage to back bias the unwanted diode. Think of it as automatic switching when the battery V drops below a certain threshold.
I thought the question was BMS design choices? that's where knowledge and safety lays! understand individual 18650 cells completely 1st. Me, I only pick 1st tier brand names! (you know the ones that supply real engineering data sheets) Battery University web site is decent. Battery packs require new cells for best performance E.g. matching, old laptop battery pulls are for chumps.

strange , but if you insist on building a custom pack find a new store. (please look into Lipo hobby packs). I get mine from HK >fasttech.com, air shipped to cali in ~10 days recently. BTW good code search word is "authentic +18650" muhaha
Click to expand...

Could you do me a huge favor and change what needs to be changed. :) .
Also thats where I was going to get the 18650s from I was going to https://m.fasttech.com/products/1420/10002357/3935802-authentic-samsung-inr-18650-30q-3-6v-3000mah
What do you think?
 
Ron E

Ron E

Member
Joined 2002
I have one of these, has never disappointed. Lasts for many charge cycles on my phone and some other usb devices. I sometimes use it to power my cheapo usb powered pc speakers for weeks at a time ;)

I also have a cheapo giveaway single 18650 battery power pack that self-discharges within a couple weeks.
 
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