Introduction: DIY Battery Pack for FPV (recycling 18650 Cells From a Laptop)

Old laptop cells can hold a charge long after your laptop goes kaput. Here's how to recycle those cells to make a general-purpose battery pack!

This battery pack is good for things like RC planes, quadcopters, FPV, and more (if your cells have the correct C rating)! It has a nominal voltage of 11.1v (equivalent of 3 cell), and has a capacity of 2700mAh. The weight is 143 grams, and flight-time on my 250 quadcopter is 4-7 minutes. The cells of the battery pack will determine the capacity and C rating of your battery pack; so you can use the techniques in this instructable to build better battery packs by using better cells.

This battery pack is also very safe; the balance connector makes sure that the cells do not get overcharged, and the shrink-wrap makes sure that the battery cells are not short circuited.

Step 1: Materials

Here's a list of all of the materials:

  • 3x 18650 Lithium-Ion cells
  • 29.5mm heat-shrink tubing
  • 55mm heat-shrink tubing
  • 1mm heat-shrink tubing
  • Electrical Tape
  • JST type connector (or connector of your choice)
  • JST-XH 4 pin connector
  • Solder
  • 5mm Tin Wire

Here's all the tools I used:

  • Soldering Iron
  • Heat-gun
  • Hot-glue gun
  • Flux Pen

Obtaining 18650 Cells:

18650 cells are very commonly found within old laptop batteries. Laptop batteries that contain 18650 cells are commonly 19mm or thicker, and/or have circular ridges which correspond to the shape of the 18650 cells. You can Google the part number of your battery pack to figure out if it contains 18650 cells or not.

If you do not have an old laptop battery lying around, you can always buy 18650 cells online. Here's an eBay search link. Beware of fake cells! Here's another instructable which goes over fake 18650 cells. Basically, if there is no weight of the cell in the description, the seller is not genuine!

Step 2: Prepare the Lithium-Ion Cells

Before actually building the pack, you want to make sure that your cells are clean and well insulated. 18650 type cells have a negative outer jacket and a positive tip. It's important to insulate these cells from each other to avoid a short circuit.

The insulation on my cells was a little bit too thin for my liking, so I decided to insulate them even more. I cut some 29.5mm diameter heat-shrink tubing to the size of the cell, adding about a centimeter extra. I used a heat-gun to shrink the wrapping over each of the three cells.

Step 3: Join the Cells Together

Align the cells like in the picture above, with the center cell being backwards. This alignment is necessary to connect the cells together. To keep the cells together, I wrapped the cells several times with electrical tape, then I hot glued the cells together. At this point, I also marked where the positive and negative ends of the battery pack would be.

Step 4: Connect the Cells in Series

Once your cells are physically held together, it's time to form the electrical connections between them. Cut two, 20mm strips of 5mm tin wire. These two bits of wire are going to connect the cells in the diagram above. Use a flux pen to clean the two tips of each strip of wire, then use your soldering iron to tin the two bits of wire.

Do the same thing with all of the contacts of the cells (clean with flux, then tin). Then, using pair of needle-nosed pliers, solder the two wires according to the diagram above. These wires connect the cells in series, that is, plus to minus, and minus to plus. If you measure the difference in voltage from one end of the chain to the other, you should get somewhere near 11.1 volts.

Step 5: Solder the JST Connector

In order to connect the battery pack to different things, you need to solder a connector of some sort to the battery pack. Use a soldering iron to solder a connector according to the diagram above. If the leads of your connector are not long enough, you may need to extend them by soldering another piece of wire to the connector, then using some small heat-shrink tubing to protect the extension.

Step 6: Solder the 4-PIN JST-XH Balance Connector

Charging the battery pack through the JST connector is possible, but it is not recommended. Over time, the voltage in each cell deviates, which may cause a non-balance charger to overcharge a cell. A much better way to charge a battery pack is through a JST-XH connector. A four pin connector is required: one for each cell + a connection to ground. Solder the connector to the battery pack according to the diagram above.

Step 7: Add Tape and Shrink-wrap

I wrapped the leads of the connectors in electrical tape in order to secure them to the battery pack. I also cut some 55mm heat-shrink tubing and shrunk it over the battery pack. This is going to protect the battery pack from short-circuiting due to contact with other metallic objects. Add some velcro, and you are done!

Step 8: Charge the Battery Pack

In order to charge the battery pack, you will need to know the max charging current. If you got your cells from a laptop battery, you may be able to Google the datasheet for your cells. I found my datasheet from the manufacturer: Panasonic. My datasheet suggested a max charging current of 1925 mAh. If you cannot find the datasheet for your cells, a conservative charging rate is: capacity / 2, where capacity if the capacity of your cells.

There are two main types of chargers, "dumb" chargers, and "smart" chargers. Dumb chargers charge at a constant max current. You cannot change the max current on a dumb chargers. Smart chargers have an adjustable current limit. Whether you have a smart or a dumb charger, you must not charge your cells above the max charging current for your cells.

To charge your battery pack, just connect the balance lead to your charger, and if necessary, connect the main power connector as well. Set the voltage to 3 cell (11.1v), then set the max charging current (if available) and begin charging.

Step 9: Use the Battery Pack!

To use this battery pack, just plug in the JST connector to anything that needs power! I use this battery pack for my 250 size quadcopter, and FPV station. I do not know the C rating or internal resistance of the battery, but I can fly my quadcopter without them getting too hot. Use your battery pack at your own risk!

So here's how to build a recycled 18650 battery pack! If you liked this instructable, check out my electric longboard!

Comments

author
fiktin101 made it!(author)2015-07-15

Made my own. it's for a different application but used your tutorial. thanks very much!

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author
comsa42 made it!(author)2015-07-16

Awsome! :)

author
Hassan+Omari made it!(author)2015-07-14

thank you, always wondered what's inside those batteries, geat instructable (y)

author
comsa42 made it!(author)2015-07-14

Awesome! Thank you!

author
C-R-E-8 made it!(author)2015-07-14

Is that a custom drone?

author
comsa42 made it!(author)2015-07-14

Yes it is! I'm making a video/instructable on it now!

author
DodgeD1 made it!(author)2017-02-22

Cheers for the info and pics! all ready to go, just needs tidying up =]

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author
smohammad1 made it!(author)2017-01-12

Do I need any additional protection circuit for that? I want to charge them ith IMAX B3 PRO

author
the_phantom_boy made it!(author)2016-09-25

Is it possible to use a single 18650 battery, in a JJRC H31, instead of that tiny li-po 3.7v 400mAh battery?

or... an old smartphone battery, since it is lighter than 18650 cells?

author
PatrickN39 made it!(author)2016-08-12

Very nice tutorial, well explained and nice diagrams for the connectors!

author
MecreeL made it!(author)2016-06-26

I'd like to know if it's possible to connect two 18650 packs which i bought from http://www.dnkpower.com/battery-solution/lithium-ion-battery-pack/ in series to double the voltage?

can anyone help me

author
cliffyd made it!(author)2016-06-25

just made these. bought a new in the box vehicle monitor that attaches to the roof. its 13" and powered it from 4 laptop batteries.

author
balamurugans1 made it!(author)2016-05-16

Can we charge it using the normal lipo battery charger

author
18650+battery made it!(author)2016-03-14

Never charge recycled cells unattended. The grooves in the negative terminals are quite deep and that will absolutely affect the electrochemical reactions taking place in the electrolyte foils towards that end of the cell.

The capacity difference between cells is another point of stress. As the cells in series or parallel will start working as one unit, extra energy may be pulled from a cell that is lower than others.

If you want to be safer, you should capacity test the cells and marry those that are the most similar.

I personally would never recommend recycling, except in the maker spirit of DIY.

That is, they are really not exceptionally safe and should be managed accordingly, especially during charging they need observation.

author
nemeen made it!(author)2015-08-02

can you give me circuit diagram for 4 cell battery pack please its urgent

author
akolev made it!(author)2016-02-16

Doesn't matter how many cells there are. Every cell is connected between two adjacent pins starting from positive on first cell.

author
Joseph+W.H made it!(author)2016-02-14

question: Can CR2032 lithium batteries be recharged?

author
JackB64 made it!(author)2016-02-15

no

author
manuel+bernal made it!(author)2016-02-15

PVC coated battery

author
manuel+bernal made it!(author)2016-02-15

PVC coated battery

author
manuel+bernal made it!(author)2016-02-15

I made my own packages whit this PVC coating, for my ESP8266 project. The result is very tough and neat. You only have to dip the battery and wait around one hour to have it dry

author
FredRoyal made it!(author)2016-02-14

One safety comment. If you only had red wire to extend the plug wiring you should have extended the Pos (+) lead an not the Neg (-) lead. Never should you change color of any power lead.

author
ohoilett made it!(author)2016-02-14

Any safety tips on re-purposing the batteries from a laptop?

author
Philippe+MiguelW made it!(author)2015-07-15

whats the average weight of one of those battery packs

author
comsa42 made it!(author)2015-07-16

~140 grams.

author
Philippe+MiguelW made it!(author)2015-07-21

ok thanks

author
Kinnishian made it!(author)2015-07-20

I like remaking laptop batteries for other things! Like small USB chargers, low power flashlights, and the like!

Quadcopter is a baddddddd application though :p. Most laptop cells can barely muster 1-2C, let alone the 10-40C you subject them to with quadcopters. Better have a lot in parallel and it would be aweeesomme if you could measure their internal resistance first to make sure you don't have an especially low-C laptop cell.

Other people have and will end up mentioning the same.

author
maniacse made it!(author)2015-07-19

Just to point it out: do not mess charging current and capacity. Obviously, you know more then me about those, so make this ibble perfect, not just average. Also, I remember something about charging with 1/10 of capacity, but maybe it is for LiPol baterries. Also another point: your charger looks like smart one, do you have also balanced LiIon charge mode? I am not sure, if LiPol charging mode characteristic fits with LiIon batteries.

author
osterac made it!(author)2015-07-19

First, not all laptop batteries are li-po (lithium polymer).
Some are li-ion (aka lilo) lithium ion batteries. Li-po batteries are
3.7 volts per cell and lilo batteries are 3.6 volts per cell (older
laptops have lilo, newer sometimes have li-po). Fully charged a li-po
will be 4.2 volts and a lilo will be 4.1 volts. They will NOT use the
same setting on your charger. If you try to charge a lilo as a lipo, you
will overcharge it and risk a fire - the kind of fire that can't be put
out.

The JST connector you are using worries me. With this kind of electrical current, a JST connector and what looks like 20 gauge wire really isn't sufficient. Most store-bought battery packs are going to be using XT60 connectors and 14 gauge wire. You could get away with 16 gauge.

For the people getting low voltage alarms, it could be (I'm guessing here) that your wiring isn't sufficient to carry the required current, or that the cells that you're using aren't capable of providing the current your aircraft needs. In that case you would would need a battery with a higher "C" (discharge) rating. Not sure how you could figure that out for a laptop cell.

Be careful using high gauge wiring in high current applications - it can get hot an catch fire. I have seen a wire glow white hot and burn it's insulation off when hooked up to a 2200 mah 11.1 volt battery.

author
comsa42 made it!(author)2015-07-19

I agree with your first point. There is an important difference between li-po and li-ion batteries; such batteries must be charged appropriately. However, not all li-ion batteries are 3.6 volt, and not all li-po batteries are 3.7 volt nominal. It's just a matter of reading the datasheet for the cells you have and charging appropriately.

The JST connector I use has the same diameter wire as the rest as my quadcopter. I've flown it more than 50 times now, and I have never had the battery or wires getting hot. So the wire gauge is okay, and the C rating is okay too. If the battery did not have a high enough C rating, the internal resistance of the battery would cause the battery to heat up, decreasing run-time and capacity.

author
MMelfe made it!(author)2015-07-19

Can i this type of batterie with arduino without problems?

author
comsa42 made it!(author)2015-07-19

You must plug this battery into the VIN port, not the VCC of an Arduino in order to use this battery pack.

author
alirezam1 made it!(author)2015-07-19

خیلی خوب و عالی و از تمام متخصصین تشکر میکنم

author
andrew_h made it!(author)2015-07-19

I'm not convinced this is a good alternative to LiPo to be recommending. I have 18650's and use them for low to moderate current devices but if you're only getting about 6 min run time of 2700mah cells, you are discharging them at WELL over the rated spec for even these panasonic cellls (some of the best you can get). For someone recycling old cells from a laptop battery that might have many cycles on them, discharging them that fast could be disastrous but if nothing else, will damage the cells quickly. 18650 max discharge rate should be about 2C (some cells such as the panasonic can be ok up to about 3C).

That being said, I like your attention to detail and quality of instructable.

author
Riconec made it!(author)2015-07-19

I think that you will have troubles with your batteries very soon. Discharge current 2C (from datasheet) means than you can have 2*2.7A = 5.4A current, but on quadrocopter it might be times higher. In this case voltage and capacity will dropout very soon, flight time will be decreasing every charge cycle.

author
billbillt made it!(author)2015-07-19

SMART!!..

author
BarryWite made it!(author)2015-07-14

agree with upstairs!perfect!

author
comsa42 made it!(author)2015-07-16

Upstairs, lol! But thank you!

author
schobet made it!(author)2015-07-15

Nice Instructable! I have some old laptop batteries and that exact 250 quad frame. I look forward to your video on the quad because I need to finish mine and get it flying.

author
comsa42 made it!(author)2015-07-16

Awsome! I'll post my video soon!

author
DmitryU made it!(author)2015-07-15

Good instruction!

What about weight (compared to standart LiPO pack) and flight time?

author
comsa42 made it!(author)2015-07-16

Weight is 143 grams (a little bit heavier than my 2.2aH battery which is 120g) and flight time is about 4-7 minuites depending on flying style.

author
rsmith79 made it!(author)2015-07-16

Have you got a cell monitor or voltage alarm on the quad?

I'm flying a dji330 frame with 30a plush ESCs and when I punch it, my 3s 2200mah 25C packs cant supply enough current, the voltage dips and it alarms (and logs an error in the FC)

I've got tonnes of 18650 cells around but at the moment, only use them for torches and portable usb chargers...

aiming for FPV pretty soon so ground station /headset battery pack sounds like a good idea.


author
comsa42 made it!(author)2015-07-16

Yes, but I do not use it. It is too annoying. Regardless of what battery I use, the alarm still goes off even if the battery is fully charged. My 12amp Afro ESC's limit the current if the voltage gets too low, so the quad just begins to descend if the battery dies. For a FPV platform these 18650 cells are even better. Good luck!

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