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Picture of Make an inexpensive Lithium-Ion Battery Pack
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I started this project out of a desire to keep my phone working on long bike tours. I needed a lightweight, inexpensive battery to put on my touring bike. Unfortunately, the lithium battery I needed costs 200 dollars new. Add a charger and powersupply and that's another 100 dollars. Batteryspace is my favorite place to get anything battery related online. You can see a comparable battery here . Thanks to some good luck, I was able to cobble together an 8 amp hour battery for about 100 dollars. This project takes a lot of soldering. You don't have to be super skilled; just tin a bunch of wires, and soldering the PCB is pretty easy.

I use this one on my bike for a headlight, tail light, radio, and cell phone charger.
 
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Step 1: The PCB

Picture of The PCB
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If the batteries are the heart of the Li-ion battery, then the PCB is the brain. This is the one I used. It was 6.50 at Batteryspace. It was easy to solder wires on the PCB. It is designed to stop solder from spilling onto the rest of the board.

PCBs come indifferent varieties depending on number of cells, voltage, and capacity. Here is a list of all the PCBs you could use with 18650s on batteryspace.

Here are the specs for the one I used and I will explain what everything means...

Electric performance:

Overcharge protection voltage for single cell: 4.35V
Over discharge protection voltage for single cell: 2.40V
Over current detection protection: 4-6A
Supply current: Max 30uA
Short circuit protection
Protection circuitry resistance: <=50mohms

The PCB prevents overcharging because the delicate lithium ion chemistry of the battery can be damaged if charged with too high a voltage and the PCB will cut power to the cells if you did so. This should not be a problem if you charge with a smart balance charger. If you charge a cell with 4.2 volts, then the cell voltage will never rise above 4.2 volts, even if you charged the cell for weeks. You still don't want to charge a cell beyond the point at which it is charged. A smart charger will turn off once it has finished charging.

Many batteries can be discharged all the way to zero volts, this is not one of them. If the voltage of a lithium ion battery dropped to zero, or even below 2 volts, it would be damaged, and would never charge back up. Cell phones have this same protection. If you measured the voltage of a "dead" cell phone battery it would probably read 2.5 volts.

Over drain protection is necessary because this is a small PCB with tiny components and can only handle so much current. It shuts down to save itself when drawing between 4 and 6 amps.

Supply current is the current draw from the electronics on the PCB. It is practically nothing and will not drain your battery.

Short circuit protection means the PCB will turn off if it detected a short; if a wire became disconnected or if the wires crossed.

Protection circuitry resistance is the resistance caused by the PCB. All circuitry produces a little resistance. Again the drain is so little you will not notice it.

Step 2: Cells

Picture of Cells
The words batteries and cells are used interchangeably but the difference is that a cell is the most indivisible part of the battery which stores power and a battery can be made of many cells. This battery is made of 16 cells. The configuration is called 4S4P. That means 4 series and 4 parallel. 1S4P means the capacity is multiplied by four but the voltage remains the same. 4S1P means capacity remains the same but voltage is multiplied by four. 4S4P mean this is a battery 4 times the voltage and 4 times the capacity of a single cell. The newest 18650s are 2.6 amp hour. 4S1P is 16.8 volts and 2.6 amp hour. 4S2P is 16.8 volts and 5.2 amp hour. 4S4P is 16.8 volts 10.4 amp hour. Given that these are used batteries I will give it a more modest 8 amp hour rating. 18650s fall to 80% capacity after 200 cycles. You could test the exact capacity on yours if you had a watt meter.

The cells are a common format, and therefore widely available and cheap, called 18650s because they are 18mm by 65mm. They use 6800 18650s in the Tesla Roadster! My brother works at a university where he has access to an e-waste dumpster. Old laptops are often powered by these cells. Often you can look up the date of manufacture and capacity by looking up ID numbers on the cells. There is no way to tell how many cycles they have been through but the savings are so great over new ones that it is easy to ignore most lack-of-charge problems.

There are 18650s all over the net which claim capacities all the way up to 4.2 amp hour and they are half the price of the ones on batteryspace. The highest capacity 18650s on batteryspace is 2.6 amp hour. I called a tech guy and asked him about these 4.2 amp hour Ultrafire 18650s. He said he never heard of Ultrafire and that 2.6 amp hour cells have been the industry standard for years. I haven't tried the Ultrafire batteries and I am not sure if they would work for this project. You can read more about them on Candlepower Forums .

New cells are 7.25 dollars each new on batteryspace here so I saved 116 dollars by finding used ones. If you can't find old batteries for free you can sometimes find used 18650s on ebay.

Step 3: Battery Holders

Picture of Battery Holders
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If you bought a pack off of batteryspace it would be wrapped in shrink wrap and the cells would be spot welded together. This makes them a little smaller and lighter than my battery but they are unserviceable. Professional pack builders use spot welding machines.  Here is video of one in action. Here is home made spot welder. You could also try tab welding. Here is a video.  This is easier and cheaper than spot welding but not as easy or as safe as battery holders.

Battery holders are a much better option because you can remove cells easily if they die. This is very likely since we are using used batteries. You can get battery holders here . You will need 4 of them. Play around with the shipping options. There are around 10 different ways to ship and I don't remember which is the cheapest.

Solder the contacts in the back together so all the positives are connected to the other positives and do the same with the negatives. In the end you will have two wires coming out, one pos and one neg. There are 4 cells in this holder but it will act as one cell once it is connected to the PCB. This batteries in this holder will be in a 1S4P configuration.

You could use any number of cells provided you have a number divisible by 4. If you had 8 four-cell battery holders and 32 cells you could make a 4S8P pack. If you only had 4 cells you could make a 4S1P pack.

Step 4: Project Box

Picture of Project Box
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I happened to have a little file bin just the right size for the guts of the battery. You can use anything. I recommend something to keep the batteries still so they don't shake apart. There are 32 places where the batteries are held there by nothing but springs. The wires could shake out of the terminal blocks as well. Screw them in tightly. This is just a small price to pay for serviceability.

I used some nuts and bolts to connect the terminal blocks to the project box. Use any size that will fit through the terminal blocks.

Put thin plastic or some sort of insulation between the layers of batteries. The battery holders are covered with pointy metal objects which could cause a short.

Step 5: Wiring the PCB and Balance Leads

Picture of Wiring the PCB and Balance Leads
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The best way I have found for wiring everything together is to use European Style terminal Blocks. As I put the pack together for the first time I wired it together in all kids of upside down and backwards ways before getting it right. Having screw type terminals greatly facilitated my trial and error assembly.

You cannot electrocute yourself with 16.8 volts but you could get a burn. You could damage your cells or PCB as well. Take necessary precautions.

This is technically a 14.4 volt battery. It ranges in voltage between 9.6 and 16.8 volts depending on its state of charge. 14.4 volts is in the middle, its nominal voltage. Follow this guide and everything should turn out fine. Once you are done there will still be no power coming out of P+ and P-. We will fix that in step 7.

To be more clear I don't mean individual 18650 cells here. I mean 4 18650s in a battery holder. That is a single cell as far as the PCB is concerned.

Cell 1 + goes to B+
Cell 1 - goes to B1-
Cell 2 + goes to B1-
Cell 2 - goes to B2-
Cell 3 + goes to B2-
Cell 3 - goes to B3-
Cell 4 + goes to B3-
Cell 4 - goes to B-
wires to main power are connected to P+ and P-

To charge the battery you find some 4S JXT type plugs. You can get them here . Put the red wire in at the same place where Cell 1 pos and B pos from the PCB are wired into the terminal block. Wire the rest of the black wires in order to the rest of the cells.  

This site is where I got the wiring diagram and shows different ways of wiring of batteries with balance leads.

Step 6: Balance Charging

Picture of Balance Charging
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There are two ways to charge a battery like this. You can either apply 4.2 volts to individual cells or you can apply 16.8 volts to the whole battery. While the latter is more simple, in this case the former is better because we are using used cells. When new packs are made, they all use new batteries of the same amp hour capacity. This way they can be charged hundreds of times without going out of balance. However, balancing will extend the service life of any pack. With our pack, the batteries are in various states of wear and amp hour capacity, therefore balancing is a must. A balanced battery is one in which all the cells remain the same voltage.

Let me explain how packs can become unbalanced and why that is really bad. Batteries will inevitably wear our at slightly different rates. Say the voltage of each cell in your pack is 4.2 volts after charging when new.

Cell 1 is 4.2
Cell 2 is 4.2
Cell 3 is 4.2
Cell 4 is 4.2
Whole battery is 16.8 volts

Now say one of the batteries has started to wear out. They manifest their wear by sometimes refusing to charge all the way to 4.2 volts. Now cell 4 only charges to 3.8 volts. The charger doesn't know this but still charges to 16.8 volts and the other cells are charged higher to compensate.

Cell 1 is 4.3
Cell 2 is 4.3
Cell 3 is 4.3
Cell 4 is 3.8
Whole battery is 16.8 volts

You can see how one bad cell could destroy the good ones because the others are overcharged. Balance chargers never charge cells above 4.2 volts and they can tell you if one cell refuses to charge completely. My charger has four lights and shows blue for fully charged and red for not there yet. They make a volt meter here that is perfect for monitoring the health of cells.

Balance chargers are more common in hobby batteries.  People use lithium polymer (LIPO for short) batteries to power model helicopters, airplanes, boats, etc.  LIPOs are cheaper and tougher, better for surviving crashes.  They require more balancing then lithium ion.  Some have C rates of 50!  That means a 5 amp hour battery could supply 250 amps and completely discharge in only a few minutes!  The chemistries are almost the same so the chargers are interchangeable.  I suggest looking through Hobbyking so you know what all is out there.  They have an especially dizzying array of chargers.

Step 7: Activate the PCB

Picture of Activate the PCB
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When I first wired everything together I was worried to find that even though I had everything wired correctly and the batteries were charged, the PCB was not working. I got it to work finally when I applied 16.8 volts to the P+ and P- terminals on the PCB. That's because this PCB was designed to be charged serially, with 16.8 volts. I didn't want to do that for reasons I've already described. You have to trick the PCB into thinking it is being charged through P+ and P-. I used a variable power supply to jump the PCB. I touched the wires to the PCB for just a second and this activated the PCB.

I discovered I had to do the same thing if a wire came loose and the PCB lost connectivity to one of the cells. This is a fail safe in the PCB. It turns off so there are no shorts. The PCB assumes you must have reconnected the wire if you are attempting to charge the battery. Lastly, you have to jump the PCB if the battery goes dead from running out of juice. If you never let the battery run completely dry and the batteries do not become disconnected then you don't have to jump it at all (aside from the first time).

Step 8: Charger and C Rating

Picture of Charger and C Rating
You hear a lot about C ratings when you start building battery packs. C means capacity and it represents whatever your battery capacity happens to be. If I have an 8 amp hour battery and I charge it at 8 amps, then it is charging at 1C and would finish charging in one hour. If I charged it at 2 amps, the rate of my Hextronics charger, then it would be charging at one quarter C, and would charge in 4 hours. If I drain the battery at 8 amps it will last for an hour; that is a drain of 1C.

Battery capacity is also measured in watt hours. To get watt hours you use a formula (Watts= Volts x Amps) to multiply capacity (8 amp hours) with voltage (14.4) to get 115 watt hours. It will run something using 1 watt for 115 hours or any other equal ratio. Of course that is its theoretical run time. Actual time will be less. Calculating remaining battery capacity based on current drain is complex and inexact. If you want to learn more read through Battery University .

You will need a way to plug it into something eventually. I used RCA plugs from radio shack. The gauge of the wire and quality of the contacts are more than enough for the 1.5 amps max I draw from my pack. You may want something more substantial for higher draw.

You generally don't want to charge above 1C. If you did the battery could wear prematurely or catch on fire.  Also, the maximum continuous current draw possible from this battery is 12 amps. I calculate that from the ratings of a single 18650 which is 1.5C.  1.5 multiplied by 8 amp hours is 12 amps.  Of course the batteries could handle this but not the wires. I used small wires in mine because I don't draw very much current from it. For higher drain use bigger wires. Look up a table of wire gauges and current capacity to pick the right wires. Use the smallest wires possible which can still handle the current. Also use threaded wire because it's easier to work with.

This charger is "smart" because it monitors the voltage of the battery as it charges. It would not charge if it detected dead cells (below 2 volts) or if the voltage was already above 4.2 volts.

Step 9: Balance the Pack

Picture of Balance the Pack
To be clear I am not talking about balance charging. This is something else. You will inevitable have one cell which has higher capacity than all the other cells. They will drop in voltage at different rates. One cell will drop below 2.4 volts before the others, then the whole battery will shut down. Once dead, if there is a large difference in voltage between lowest voltage and highest voltage cell, you should take two cells from the highest voltage cell and swap them with two cells of the lowest voltage cell. That way the weakest link will not be so weak and your battery will last longer.

Even better would be to replace the lowest voltage batteries with different ones if available.

Step 10: Safety

Picture of Safety
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If your battery shorts, it will most likely heat up and smell like fried electronics. That's what happened to mine a few days ago. It was an easy fix actually. I needed to more insulation between the stacks of batteries

However, worst case scenario, it could catch on fire when you are not at home and burn your house down. That doesn't mean this is a terribly dangerous project, you just have to be careful. Many projects on this site could end in fires. Only take on this project if you have a good idea of what you are doing and understand the risks.

A simple precaution is to break the battery in while it is in a bucket of sand or on a bit of concrete at least 8 feet from anything combustible. By breaking in I mean charge it and discharge it a few times to make sure it works with no problems.

So there you have it. Once you make one battery you will have the confidence to make packs in any configuration you need.
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ShanL12 days ago
I also have a 18650 battery project, but spent much less for a 4S4P
darter221 month ago

I have a friend that works for a cable company. They use back up battery packs in telephone modems and he had a bunch that were taken out of service and he gave them to me. They all had 2 or 4 18650 batteries in them. I ended up with 24 of them for free. Some were light blue and some of the better ones were purple.

CosminA12 months ago
Thanks, these are the most detailed instructions ever about li-ion battery packs.
DennisJ43 months ago

I love this project. I am a total novice when it comes to electronics but it is very interesting. I am trying to build a light weight battery to run my telescope. It will run on the 11.1 volt configuration. I have 21 good cells, so I was going to place them in a S3P7 configuration. My question to you is, can you recommend a PCB for that configuration? I the one you have is only for a P4? I do not understand that part of the build. Thank you so much for posting such a cool idea.

dimvasilk3 months ago

Very informational instructable! I'm planning on using it to make a battery pack for a quadcopter. Originally, I was planning to use Panasonic NCR18650B's for it, but then I found these on eBay. What do you think - can I use these? I'm going for ~ 2 C discharge rate. Thanks!

MarcC84 months ago

is it really usefull to have a pcb + hobby charger?

DJEnD6 months ago

Hi there, stumbled upon your tutorial whilst searching for how to DIY a battery pack.

Here's my issue, I don't come from an electronics background so pardon me if this sounds a bit simple.

From what I gathered on your 2nd page and what I have in mind, I'm actually planning to make a single pack of 6 18650s, 7.4v, into a camera battery casing which is meant exactly for that, but I'm using higher capacity cells because the originals are quite low cap.

Anyway, from your explanation, it seems that I'm looking at a 2S3P configuration am I right? If I am, the problem now is the soldering. I need help wiring them to each other. Could you hit me up at ho.zhenjie@gmail.com? Appreciate it tons!

QuyenC6 months ago

Dear experts,

Look like you can solve the problem that I am facing now.

I have about 20 x 5mw lasers and I need to design a system to drive it. At the moment I have 8 x 3.7V batteries (18650) connected in series and I found that even if I don't turn them on for a few days all the batteries became flat. Maybe because some of them are faulty and used up all the power?

The system that I am going to design include a Microchip PIC16F876A which needs 5V to drive it. So should I connect 2S4P (2 in series & 4 in parallel) and use a voltage regulator to regulate it to 5V? I want to monitor it and charge them when required. Is this a good way to connect them? My concern is if one of them faulty then the whole thing will upset? How to avoid this? What is the best practice? I heard you guys mentioned about charging/discharging protection device - will this help? What sort of charger should I use because I am going to use this one from ebay to charge it:

http://www.ebay.com/itm/5A-DC-to-DC-CC-CV-Lithium-...

If you have any suggestion please let me know.

Many thanks in advance

blorbyblorb7 months ago

Just so you're aware, for less than $30 you can head on down to any battery shop and pick up an 8AH SLA that'll run all your equipment just as long, and doesn't require expensive or complicated equipment.

First and foremost thanks for the article. I was wondering if it is necessary to use a PCM/PCB if you are buying tabbed batteries (built in protection circuits). Also, I'm thinking of charging straight from my PCM with a voltage regulated line from solar - thoughts? Again thank you so much!!!

caimartin1 year ago

hello i need help i'm starting out making portable chargers and speaker systems powered by recycled li-ion batteries and this helped alot but couldn't i charge 2 li-ion batteries in parallel if it is being powered by a 5v charger

assaad1 year ago

hello .. amazing project , well built

but i have some question here

the pcb has an over charge protection beside other functions . yet you used a charger to charge the batteries with ballance . im a little confused here !!

can the pcb be used to charge the batteries instead the charger ?

because when reading the specs of the pcb it says ( charge and discharge terminal on p+/p-)

plz do correct if i missed any thing .

(sry . old post but i need some answers .. thanks any way)

You got it right. The PCB is a protection board which does all of the balancing on its own. Connect any power supply under 20 volts and it should work just fine. Buying a balanced charger defeats the whole purpose of trying to save money.

john52471 year ago

Any 18650 above 2600mA hour is probably unprotected. Some of the space is used for the protection circuit in the cell and prevents fires from faulty chargers. The Chinese batteries with no built in protection use the space for more chemistry, but I would be suspicious of anything more than 4000mA Hour.

The protection board in this 'ible provides full protection for single cells connected correctly to it's pads. You can then use a laptop power supply to drive the board. If you only need 15 volts at 3Amp / hour just use 4 Chinese cells.

If you need to parallel the cells they should have individual protection (and cost twice as much and have a maximum 2.6A/h capacity.) To get your 15 volts at 3 A/h you will need 8 cells wired in parallel pairs to the protection board in this 'ible.

If you charge and discharge your battery pack through the circuit board you can not go above the current ratings for the board without damaging it.

tldr? 4 cheap hi capacity chinese cells on the board in the 'ible will not catch fire

if using 8 or 12 cells they should be protected cells. The board can't protect them all, because it can't monitor separate cells - only paralleled sets of 2/3/4 cells

Protected cells don't really need this board, but would still benefit from a smart (expensive) charger. The more you pay the less chance of Li-ion fires.

Cheap Chinese high A/h cells or reclaimed / secondhand cells need a protection board or smart balancing chargers to avoid fires.

monideth2 years ago
Hi,

Sorry, to dig up an old thread, but I was interested in this project and was also questioning/converned whether the PCB can be connected to more the battery cells in parallel and series.

I found this PCB on eBay:

http://www.ebay.com/itm/4S-Li-ion-Lithium-Battery-Input-Ouput-Protection-Board-PCB-14-4V-14-8V-16-8V-5A-/221179238980?ssPageName=ADME:X:RTQ:US:1123

which has been designed for 4S battery packs. However, it does state:

"Could also work for 4S2P (8 cells) , 4S3P (12 cells), 4S4P (16 cells) etc."

I enquired about this to the seller and they responded back that it can be done and helpfully provided this diagram of how it can be wired (for 4S3P):

http://postimg.org/image/ray6gs0yv/

However, I am still concerned by the fact the each individual in each 3P pack cannot be protected.

I found this very useful page about parallel charging battery packs:

https://sites.google.com/site/tjinguytech/charging-how-tos/parallel-charging

You can also use do  parallel balance charging (with appropriate parallel balance adapters). So I'm wondering whether this may be a better (but more expensive) method/option - i.e. you have separate 3S (or more) battery packs, each one having its own PCB. You would then parallel balance charge all the indivial 3S packs.
Li-Ion PCB - 4S3P.png
lawsonrw2 years ago
If I want to make my own battery pack what consideration do I need to make for the wires? As the voltage and amperage increase do I need to use ever larger wires? If I just use the same large wire t/o the build won't the increased resistance keep any of the cells from contributing power?

In short, if I want to build a battery that can power a 72 volt motor, what gauge wire should I use when wiring up my parallel/series pack?
as i said befor here you need 4 pcb's to keep all batterys balanced
Noblenutria (author)  dasimpson19813 years ago
You only need one PCB. And you balance the pack with the balance leads and charger.
one battery holder with 4 in parallel one battery could be dead and other will charge higher like they would in series i have tried it and this happens

i had 2s4p and found that they was one bettery not charging right when i stripped the pack the others were higher then they should of been the dead one wasent charging to 4.2 but maxed at 4v the other were at 4.4 after the unit was broken down
same for "protected" batteries?
as far as I know yes cos the power applied keeps the battery reset I could be wrong
this is what i am trying to explain this only happens if it is 4s1p
agoldsmith12 years ago
This PCB has a balance function and is rated at a higher max amperage: http://www.batteryspace.com/Protection-Circuit-Module-PCM-with-Equilibrium-Function-and-Fuel-Gauge-for.aspx

it's bigger but it seems worthwhile if you're going to be charging a laptop, which can draw more than 5 amps.
agoldsmith12 years ago
based on the PCB, wouldn't the amperage be cut above 5 amps? Or is the pcb amp rating for charging the battery?

how do you set up the charger to use one lead per cell? I only see one lead for four cells?
i think i just found 18650 at 5000mah (5amph) will know more when money comes to get them
Be careful here.

I HAVE found some 4200mAh rated 18650 cells, but they were Ni-MH(like here http://www.all-battery.com/browseproducts/One--4-3-AF-%2818650-Size%29-4200-mAh-high-capacity-NiMH-battery.html).

Those are completely different animals from Li-Ion 18650s.


You COULD use them for the same style project, but you'd need a different charger/charging setup.

Not to mention, they are still 1.2 volt.
So to get equal capacity...
for every two 18650 Li-Ion cells(we'll use an "average" 2600mAh@3.7v) you would need 3 18650 Ni-MH cells.
2x2600mAh@3.7v = 5200mAh@3.7v
3x4200mAh@1.2v = 4200mAh@3.6v

Trade offs are, safer to use/charge, but more weight, more space, less capacity, and good luke finding cheap/free Ni-MH.
http://www.ebay.co.uk/itm/ws/eBayISAPI.dll?ViewItem&item=270821277749&clk_rvr_id=275620926262&item=270821277749&lgeo=1&vectorid=229508

were the ones i was looking at to me it says 10x 18650 at 5000mah but it could also be 10 18650 5000mah total.
just depends id wording is right
Noblenutria (author)  dasimpson19812 years ago
I don't trust several brands of 18650s like trustfire and Ultrafire. They are poor quality batteries and they overestimate their capacity. There is no way a single 18650 could be 5 amp hours. A good quality cell could be no more than 3 amp hours. The cells on batteryspace are expensive but I am sure they are legit.
you are very right they turned out to be 1100mah
agoldsmith12 years ago
I found some trustfire batteries for $10 per 2 pack.

With all the components for the summer project, my setup totals $200 plus unknown shipping for some things.

If the batteries are found in laptop batteries, why not buy some of the mass-produced laptop batteries, take them apart, and save a few bucks over buying new individual cells?

for example, buying 3 dell 11.1 volt, 4400 mah laptop batteries would cost $52 and gives 2 extra cells in case of a dead cell.
link: http://www.amazon.com/Dell-Inspiron-1545-Laptop-Battery/dp/B002MG6OO6/ref=sr_1_4?s=pc&ie=UTF8&qid=1366750261&sr=1-4&keywords=dell+laptop+battery


Individually, the best price/quality I could find was trustfire @ $5/cell with unknown shipping cost, which adds up to $80 plus shipping.
bobcool092 years ago
To activate the PCB you can also put together 11 AA batteries in series, and if they are new the voltage will be higher than the expected 16.5v, mine was around 17.6, but it still works. If you are worried about that just use the batteries a little bit (or short them, if you wanted). This method doesn't require you to have a variable DC power supply, which is nice
bobcool092 years ago
Would the board you use still work if I only connected 2 sets of four? Because I only need 5v and (please correct me if I'm wrong) if I have 4 of them then it would give out about 16.8v, and if I only had 2 of them it would only give 8.4v. Also, hoe would I connect a RCA cord to a USB/Micro USB?

Thank you!
bobcool092 years ago
http://www.digikey.com/product-detail/en/BK-18650-PC8/BK-18650-PC8-ND/2330515 That is a link to the battery holder he is using, the link that he uses doesn't exist anymore.
Looking forward to trying this out and using it to power a Raspberry Pi! (You should look them up, it's a nice little computer the size of an Altoids Tin)
matroska2 years ago
I might be wrong, but I believe that when arranging li-ion cells it is preferable to have them balanced when charging, as usually cells do not have exactly the same capacity.

However considering you are using used cells, I guess you could overlook this detail for the profit of simplicity.
seems everyone here is an expert,could you please help me?
I am using lifepo4 7 cells in series 2 in parallel,i dont know what kind of PCM I shoud use,my machine need 100A to boost first,then after started,the current only need around 30-50A.

Please help to choose one good PCM from BesTech Power.
owendaniel2 years ago
Top work!

I found that RCA plugs are a bit dangerous as the two poles are exposed as the batteries have a lot of punch if short circuited!
Hey i got total six 18650s from an old laptop battery...
They were connected in 3S2P, which i want to refix as 2 X 3S1P connections, as it provides a good 12v supply 4 my circuits.
It Would Be if You could please tell the necessary mods in your circuit for that....

Thnx A Lot
=V=
why 16.8volt you could just make a 7.2 volt battery pack use an 7805 to bring to 5 volts and give your self even more amp hours
Noblenutria (author)  dasimpson19813 years ago
What is a 7805?
l7805cv is a 5v regulator brings the 7.2-12v down to 5 volts but needs a heatsing for voltages higher then 7.2 or if it going to be under heavy load.
what i use with my diy mobile charger 2 18650 in series for 7.2 volt then reduced to 5 volt by the 7805 ok losses of heat but if you look at that compared to a dc -dc converter that can use 1.5amp the little loss in heat is worth it
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