DIY powerbank

no boost/step down board required but you cant mix capacities in with lithium batteries, 4.2v is max charging voltage and min drain is down to 3.2v.

if you have 2x2000mah and 3x4000mah you're gonna damage the charging circuit and be limited to the 2000mah of the 4000 of the other 3

>>996970
yeah that's what I thought, is there any board I could replace the original charging circuit to avail of all batteries?>>996970

You could, but at that point, you might as well spend the $10-20 on a 15000mAh power bank that's built specifically for the task and ready to go.

>>997007
yeah that's true

>>997007
Let's say that I'm trying to make a sort of power bank but I need it to be 12 volts. Is there a decent diagram for a circuit out there?

>>996969
i just can feel the smell of your house burning, anon

>>997075
so can I anon, so can i

File: image.jpg (79KB, 1200x1200px) Image search: [Google]

79KB, 1200x1200px

op here,

would this circuit work??
the charging circuit has an LED indicator for charging progress so I'd know when one is done and flick to charge the next and so on, and the same with using the USB output, when one battery is dead, flip to the next. I could try find a guitar 5 way switch or just make my own with 2 3 way switches. any ideas??

File: dip switch.png (2MB, 1677x920px) Image search: [Google]

2MB, 1677x920px

>>997481

What you are looking for is called a Dip Switch.

Not being an asshole by posting google- genuinely trying to help.

>>997481
This could work, but there is a questionmark above practicality. It'll just be bulky, and making a powerbank where you can just exchange the cells would probably be more useful.

>>997031
The circuitry needed to charge and monitor multiple cells gets quite complicated. There are powerbanks out there that have multiple cells and a built in buck/boost-converter so they can deliver 5V and 12V.

>>997494
thanks anon I'll definitely look for one of these

>>997481
Seems overly complicated. You might as well just make the cells removable in a single cell power bank that has the benefit of being 80% smaller, and charge the cells individually.

>>997481
you can put as many batteries in parallel as you want (4.2v will be max voltage) they'll just take longer to charge, if you have 3x2000mah you have around 6000mah total cap @ 4.2~3.7v

>>997603
just to add to this you'll need balance the discharge/charging, so discharge them to 3.2v or till your battery charger says they're flat then do that with each cell separately then you can put them in all in parallel and charge them at once, once they're balanced with that processes you can keep them in parallel setup

>>997603
Batteries don't work that way in parallel. Even a small difference causes more current to drain from the higher battery, and batteries to cross discharge. Even a tenth of a volt difference divided by the like thousandth of an ohm resistance ends up being 100 watts going from one battery to another. Even if the batteries only had .1 ohm resistance, that's one watt just being lost in the battery when it's doing nothing. That shit will blow up.

>>997031
"12V" is doable, but when you put 3x3.7 in series you only get 11.1V. You could go for 4x3.7 e.g. 14.8V. That might actually work well, because at that voltage, there's more than a 2V drop for a linear regulator to work in. You could also do a buck converter, but that'd be a lot more complicated and possibly less efficient. Similarly you have to do nx4.1V for charging in series.

>>997631
in my experience batteries don't fantastically blow up. I hooked a bunch of same capacity batteries in parallel, they didn't blow up, then attempted to charge them all to max best i can.

I didn't have the equipment to check the voltage/charge of each of one and to me these batteries were disposable so i hooked it up and and it worked. then discharged and charged them a few times just to make sure they were fine.

>>997631
But yeah listen to this guy he knows what's up.

>>997631
lemme guess you work at Ivanpah?

>>996969
>>997075
>>998954
http://www.candlepowerforums.com/vb/showthread.php?280909-Ultrafire-18650-3000mA-exploded

>>997494
i will have to advise against these
5v*500mA = 2.5w = 3v*800ma
5v* 2A = 10w = 3v * 3.3A
just make sure the switches can handle the current

>>996969
i have successfully wired in parallel in this scenario, however the batteries have to be matched sets.
> bought at the same time
> used at the same time
> charged at the same time

File: 0305161843.jpg (3MB, 4160x2340px) Image search: [Google]

3MB, 4160x2340px

I'm hijacking your thread to tell of one of my greatest diy moments. About 2 months ago I was in the middle of a cross country bicycle trip. I had two cheap chinese 10,000 mah power banks to charge my phone. due to the heavy vibrations of riding a bike the charging port on one board broke of and the discharging port of the other broke off. I had a rest day to see if I could fix it, so I gave it a shot. I was able to do exactly what you are suggesting connecting all the batteries in parallel and using one board for charging and one for discharging. I was actually able to solder everything together using a wrench that I heated over a camp stove. I then thoroughly wrapped the whole thing in electrical tape and bam I had a working 20,000 mah battery bank. So long story short its fairly easy just hook as many batteries as you want in parallel to a single board. Pic related.

>>997631
If you've taken apart as many battery banks as I have you'd know that the all use pretty much the same board and chip set. The only difference is the amount of batteries present. so assuming there is a difference in the batteries and that the circuit is diode protected the cross discharging should Reach an equilibrium and act to evenly charge the batteries. You are correct in that because of the variations in resistance some of the batteries will not fully charge.

You should be able to parallel many 18650s as you want, so long as they are the same chemistry. Be careful because not all 18650s have the same chemistry.

The easiest way to get what you want is to buy one of these:

http://s.aliexpress.com/qiieMNFj

The /diy/ way to get what you want is to buy this and make your own housing:

http://s.aliexpress.com/UfeUjaYJ

File: Laterne groß (8).jpg (3MB, 3264x2448px) Image search: [Google]

3MB, 3264x2448px

>>997631
Nonsense.
Paralleling cells of identical chemistry is no problem at all. The only thing that counts is the voltage specifications. If the batteries you choose have a max voltage of 4.2V and a min voltage of like 3V, all is ok.
As practically all 18650 LiIon cells are built like that, there is no problem at all with connecting different ages, capacities, or brands together. Just make sure the voltages are not more than 0.1V different at the time of connection to avoid equalizing currents. So charge them to max individually, then connect.
It will work just fine on your initial power bank's electronics as well. It will last longer and need longer to recharge.
More professional would be this one, which I have and like.
https://www.fasttech.com/products/1424/10004461/1341300

Pic related is a pack I built from various cells I salvaged from old laptop packs. Not a problem in the last years, so obviously "muh exploding cells" is garbage.

File: ANIMvasicomunicanti.gif (53KB, 220x176px) Image search: [Google]

53KB, 220x176px

When cells are connected in parallel, they basically work like a row of buckets which are connected with tubes to each other, and the tubes are connected at the bottom of the buckets. Over time, the water level in all buckets will be equal.
https://en.wikipedia.org/wiki/Communicating_vessels

As power banks only charge and discharge with small currents, the internal resistance (differences) of the cells do not matter much. So all cells will be fully charged, as it is not possible to have charge differences in LiIon cells which are used in parallel.

>>1000122

Were you not worried about it rupturing on you?

>>1000211
>Not a problem in the last years, so obviously "muh exploding cells" is garbage.

You've been relatively lucky.

The risk with paralleling up large numbers of random old cells is that if one begins to short out, you have a HUGE amount of potential energy in the parallel cells, which could result in the faulty cell drawing enough current for a long enough time to heat it up and cause a hazardous situation.

You're probably going to dismiss this, but as someone who's been there and done that, I'll tell you that you learn really quickly once you stumble upon your first shorted cell.

>>1000211
If even one of those cells start to fail it could overheat and cause some pretty nasty behavior and take the rest of them with it.

Then what you have is at best a firebomb, at worst it will simply blow up.

>I recently purchased a power bank for €10/$11 and when I opened it, it's a simple circuit using and recharging a 18650 4000mAh 3.7v battery.

>4000mAh

Oh you stupid shit.

That thing is 2500 if you're lucky, but its probably closer to 2000 or less.