# Building a four cell battery pack. How to charge it?



## roxtar (Sep 7, 2009)

I want to build a sealed 4x18650 battery pack. The question is how to convert a charger to work with the two leads I'll have coming out of it.


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## adrenalnjunky (Jul 28, 2007)

So you're wanting a pair of separate 2 cell packs sealed in the same housing? 

Youll need a charger that can charge 2 separate packs in that situation. 

Sent from my DROID RAZR using Tapatalk 2


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## roxtar (Sep 7, 2009)

No, I'll be using one 4 cell pack; sealed with one lead going to the light.
I need to be able to charge it without removing/separating the assembly.

However, I'm pretty sure I've figured it out. I'll be using the cable and connectors from Magicshine.Action-LED-Lights - 1m Extension Cable so this charger Action-LED-Lights - 1.8A Magicshine Charger should just plug into the pack.


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## adrenalnjunky (Jul 28, 2007)

Just for clarification - the pack is 4 cells, but wired in what fashion? 4S1P or 2S2P? (14.8V or 7.2V) that makes a big difference on if that charger will work for you.

It's still a little cloudy how you are planning on connecting the pack to your light - most batteries have one connector coming out of the pack, which plugs into the light, or into a charger when charging is required. from your description it almost sounds like you were intending to hardwire the pack to your light, which would have made charging much more difficult.

Using the Magicshine cables/connectors is a good plan - I just converted all my lights over to using the MS connector myself.


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## roxtar (Sep 7, 2009)

It's the battery pack for this project:
http://forums.mtbr.com/lights-diy-do-yourself/very-easy-xm-l-build-805894.html
This is the holder, wired for 14.8V:
14.8V 4 x 18650 Battery Holder Case Box with Leads - Worldwide Free Shipping - DX
I'll be cutting the MS cable; connecting one end to the battery pack and one to the light, with the connector between them. That way I can disconnect the battery pack and plug it into the MS charger.


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## adrenalnjunky (Jul 28, 2007)

That was my fear - the Magicshine charger is not going to work for you in this configuration. 

you have a 14.8V battery pack, but the MS charger is only 8.4V output - it is designed to charge the Magicshine 7.2V packs (although they are 4 cells, they are wired in series/parallel. 2S/2P). 

you'll need a charger that outputs 16.8V to fully charge 4 cells in series (14.8V pack).


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## adrenalnjunky (Jul 28, 2007)

It is 2X the cost of the MS charger - but this would work for your 4S pack - it is about the cheapest charger I can find that can charge a 4S pack, and has the versatility to do 1-3 cell packs as well:

All-Battery.com: Tenergy 1-4 Cells Li-PO/Li-Fe Balance Charger


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## roxtar (Sep 7, 2009)

adrenalnjunky said:


> That was my fear - the Magicshine charger is not going to work for you in this configuration.
> 
> you have a 14.8V battery pack, but the MS charger is only 8.4V output - it is designed to charge the Magicshine 7.2V packs (although they are 4 cells, they are wired in series/parallel. 2S/2P).
> 
> you'll need a charger that outputs 16.8V to fully charge 4 cells in series (14.8V pack).


Wrong charger or wrong battery wiring?
Should I be using 14.8 in this application? I based my charger idea from the fact that the MS808 uses the same LED as I'm using for this project.
Action-LED-Lights - MJ-808E, 4 mode 1000* lumen bike light 
I then assumed their four cell battery pack would be the same voltage as mine, hence being able to use the same charger.
Where did my thinking go wrong?


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## roxtar (Sep 7, 2009)

adrenalnjunky said:


> It is 2X the cost of the MS charger - but this would work for your 4S pack - it is about the cheapest charger I can find that can charge a 4S pack, and has the versatility to do 1-3 cell packs as well:
> 
> All-Battery.com: Tenergy 1-4 Cells Li-PO/Li-Fe Balance Charger


That will work with four separate cells but how would I wire it to work with my connector setup?
Also please comment on my post above. Should my battery pack be wired in this configuration?


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## adrenalnjunky (Jul 28, 2007)

the 808 used the same LED, but a driver that allows a lower voltage pack to be used. I would guess that the 808 driver is allowing input to be a little lower than 6volts on a partially depleted pack. Magicshine batteries are 4 cells wired in a series/parallel combination, 2 groups of 2 series cells, wired in parallel, would give you a 7.4v, 4800mah battery. (Magischine calls it a 8.4V battery because a 3.7V li-Ion cell, hot off the charger is 4.2V. 4.2*2=8.4)

The battery holder you linked to would wire those 4 cells all in a Series connection - that would take the 3.7V per cell and add them all together. So if your batteries at 2400mah for example, that would yield a 14.8V 2400mah pack. 

If you wired your same 4 cells in a parallel only connection -you'd have a 3.7volt, 9600mah pack



If you are using the driver mentioned in the Easy XM-L thread, then it has a minimum input voltage requirement of 6v. Under load, a partially discharged 2S pack might sag to less than 3.0v per cell, which would cut power prematurely in theory. I haven't read that whole thread to determine what people have actually seen in real world usage. 

the original poster of that project used a 4S (14.8v) pack because you could use cheap batteries that don't have the highest capacity or specs, but get good performance still. I dont' think they intended for the pack to be sealed making the removal of the batteries impossible. I'm sure he was planning on taking the individual cells out for charging in the inexpensive 18650 chargers that are out there.


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## roxtar (Sep 7, 2009)

adrenalnjunky said:


> I dont' think they intended for the pack to be sealed making the removal of the batteries impossible. I'm sure he was planning on taking the individual cells out for charging in the inexpensive 18650 chargers that are out there.


Yea, this project was designed to charge the cells individually. I want to be able to seal them and charge the pack as a whole (if possible).
I don't mind paying $20 for a charger but isn't the one you linked designed to charge four individual cells? What would be the best way to adapt it to work for my plan?


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## mtbikerTi (Jan 15, 2004)

Get one of the "4 button" universal chargers, like This. That way you can charge pretty much any battery you'll ever have. Note that most of those style chargers require a DC power supply, but those aren't usually hard to find (I use an old computer power supply for mine).


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## adrenalnjunky (Jul 28, 2007)

The charger I linked to is a battery pack charger that can charge packs that are configured 1S - 4S.

You just need the appropriate connector to put on it to plug into your battery pack for charging.

for the sake of clarification - let me make sure that I'm explaining what the pack designation means.

A battery pack's voltage depends on how many cells it has in Series - that's the "S" in the configuration description. Cells in Series combine their Voltage to create a pack with a higher voltage.
Using a 3.7volt Lithium Ion cell like an 18650:
1S = 3.7volt pack
2S = 7.4v
3S = 11.1v
4S = 14.8v

The "P" designation is then how many cells are paralleled together. Parallel cells combine their capacity, but the voltage remains the same. 
Using an example of a 3.7volt, 2400ma 18650:
1P = 3.7v, 2400ma (this would be a single cell.)
2P = 3.7v, 4800ma (2 cells)
3P - 3.7v, 7200ma (3 cells)
and so on.

Then you can combine the 2 configurations to achieve whatever voltage & capacity you need. 
2S2P would be a 4cell pack made up of 2 groups of seriess, then combined in parallel as int he pic below. Assuming a 2400ma cell, this would make a 7.2v, 4800ma pack. (note, the red and black "wires" in the picture are not connected together in this example, they are crossing over each other. )


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## adrenalnjunky (Jul 28, 2007)

mtbikerTi said:


> Get one of the "4 button" universal chargers, like This. That way you can charge pretty much any battery you'll ever have. Note that most of those style chargers require a DC power supply, but those aren't usually hard to find (I use an old computer power supply for mine).


I fully endorse the Turnigy as well - I own one. I linked to the cheaper one earlier, just as a cost function, and it would do 1-4cell packs.


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## roxtar (Sep 7, 2009)

Thanks for all your help, guys.
I just ordered the Turnigy charger.


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## Ottoreni (Jan 27, 2004)

*Nice diagram .... 1 question*



adrenalnjunky said:


> The charger I linked to is a battery pack charger that can charge packs that are configured 1S - 4S.
> 
> You just need the appropriate connector to put on it to plug into your battery pack for charging.
> 
> ...


 Thanks for the great "real" diagram. Two questions.
One, I have read about these having a balancing wire.... is this necessary?

What would be a good holder for this cell pack.

Many Thanks!


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## MtbMacgyver (Jan 23, 2007)

This is actually the best way to wire to wire a 2s2p pack. If you don't connect the parallel cells together, then they won't stay in balance.










And like this if you want a balance connector


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## pucked up (Mar 22, 2006)

Would it be safe to run a light with a 4S2P as long as the driver can handle the voltage? So you'll have a 14.8V , 4800mAh pack. So if a 4S 2400mah pack gives you a 3hr run time the 4S2P will double it?

Also can I use two of these holders soldering the 2 black wire to each other same with the red wires to make a 2S2P?










And to keep them in balance I still have to connect the parallels together?


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## roxtar (Sep 7, 2009)

So, the one I have (in pucked up's build thread) would be a 4S1P, correct?

OK, I guess that would just be called four cell in series :idea:


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## MtbMacgyver (Jan 23, 2007)

pucked up said:


> Would it be safe to run a light with a 4S2P as long as the driver can handle the voltage? So you'll have a 14.8V , 4800mAh pack. So if a 4S 2400mah pack gives you a 3hr run time the 4S2P will double it?
> 
> Also can I use two of these holders soldering the 2 black wire to each other same with the red wires to make a 2S2P?
> 
> ...


Yes, as long as the driver is rated for the voltage you can use a 4s pack. Yes, if you double the capacity of the pack, you will get twice the runtime. Sometimes you may actually get slightly more than double, because you're discharging the cells at a lower current and the capacity of a battery drops at higher discharge rates.

Yes, it's possible to use that holder, but you'll need to connect more than the 2 red and black pairs together. You'll also need to make the parallel connection between the pairs of cells as you mentioned, which will be a pain since the holder doesn't have a lead for that connection.

Personally, I'm not a big fan of battery holders. I think they introduce too many reliability issues and also end up being too much work in the long run if you start switching cells around and have to keep track of the history of a bunch of individual cells. I find that buying qood quality cells with solder tabs and building up a permanent pack with a protection PCB ends up being less work and more reliable over time.


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## adrenalnjunky (Jul 28, 2007)

I'm a fan of packs as well. But If you want a holder instead, Batteryspace sells them with PCB's installed, so you don't have to run protected cells.

Li-Ion 18650 Battery Holders with PCB

Notice they do offer 4S1P, 1S4P, and 2S2P options for 4 cells.


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## adrenalnjunky (Jul 28, 2007)

roxtar said:


> So, the one I have (in pucked up's build thread) would be a 4S1P, correct?
> 
> OK, I guess that would just be called four cell in series :idea:


correct.


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## CdaleTony (Jun 21, 2005)

adrenalnjunky said:


> I'm a fan of packs as well. But If you want a holder instead, Batteryspace sells them with PCB's installed, so you don't have to run protected cells.
> 
> Li-Ion 18650 Battery Holders with PCB
> 
> Notice they do offer 4S1P, 1S4P, and 2S2P options for 4 cells.


Wish they had a 2S3P holder... Thing is I have a bunch of Keeppower 18650's here already---It'd be nice to have a 2P or even 3P holder to pop them into for rides..

Thought my magicshine and geoman replacement pack run a solid 2.5 hours on high already...I wonder if 2S2P keeppowers would outlast that....

And since the batteries are protected would I need a PCB, or would it be redundant?
Thanks
CDT


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## pucked up (Mar 22, 2006)

adrenalnjunky said:


> I'm a fan of packs as well. But If you want a holder instead, Batteryspace sells them with PCB's installed, so you don't have to run protected cells.
> 
> Li-Ion 18650 Battery Holders with PCB
> 
> Notice they do offer 4S1P, 1S4P, and 2S2P options for 4 cells.


Don't know why that place charges soooo much for shipping. Or maybe they don't like business from Canada. A $15 part and then charge $25 to ship it? Frack them!


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## roxtar (Sep 7, 2009)

Sorry, more noob questions.

OK, 

18650 batteries wired 4S1P into Trailteck connector-check
Turnigy Accucel 6 charger-check

Now, can I just build leads for the charger with the matching Trailtech connector and charge the pack that way or do I need to wire the batteries differently, with a separate connector, for charging?


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## random walk (Jan 12, 2010)

CdaleTony said:


> Wish they had a 2S3P holder... Thing is I have a bunch of Keeppower 18650's here already---It'd be nice to have a 2P or even 3P holder to pop them into for rides..


A member here used to sell unwired 6-cell holders that I configured for 2S3P. I had bought a Magicshine 1400 lighthead during the battery recall debacle, and have used this pack successfully as a substitute.

Unfortunately his website says they're no longer selling them (luminousdiy dot com).


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