Parallel batteries in DIY power bank modules

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rjng
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Parallel batteries in DIY power bank modules

Hello friends,

 

My name is Rafael, I'm new here.


I was looking for a power bank to buy, but I cannot find one that satisfied me, for a good price. So I've thought make one could be a nice idea. But many problems came in mind.

I'm not a technician, but I can understand something about electronic. So I searched many topics in many foruns, and electronic sites about batteries and chargers. The result is few answers and many doubts. 

 

If I want to make one cheaper charger, I will need a module board. There are many kind of DIY power bank modules selling in the internet. Look:
- http://s.aliexpress.com/eymUNvIZ
- http://s.aliexpress.com/UNvQnyUZ
- http://s.aliexpress.com/quaiiu6r

https://www.fasttech.com/products/1424/10004229/1703604-sc-0176b-1a-2a-diy-dual-usb-mobile-power-bank-pcb

https://www.fasttech.com/products/1424/10004229/1451602-sc-0184-diy-dual-usb-mobile-power-bank-pcb-module

https://www.fasttech.com/products/1424/10004229/1703603-sc-0230-1a-diy-single-usb-mobile-power-bank-pcb


My idea would be buy one module and use some 18650 batteries. Nice. Or not?

Well, I asked to sellers how many batteries can I use in each module. One told me 4, other told me there isn't a limit. What do you think? Many batteries will taken a long time to charge, but it's ok. But, will the module show the correct state of charging? Can the module deal with different charging state of each battery?

I extended my doubts to the problem of connecting batteries in parallel. When the module is off, the problem of one good battery charging a bad battery and it creates a great current could occour? Will I need to connect resistors among batteries? Would it occour even with protected batteries? (in principle, I want to use protected ones)

So I'm afraid to create a bomb instead of a power bank.


There are some ready to use DIY power banks selling too. Look:

- http://s.aliexpress.com/v2MNfmIZ

https://www.fasttech.com/products/0/10007172/1590401-single-usb-pcb-board-plastic-enclosure-for-power

The first problem I found in these products is my protected 18650 batteries don't fit the space for batteries. Protected batteries are bigger. But, my fear about parallel batteries wouldn't occour even with these power bank too? 

I don't know if the idea of making a good and safer power bank is practicable for me.

So, is there a good module in market that can deal with some batteries, even in parallel? Do you recommend this kind of DIY project? (I've saw some guys here making thein own power banks and it seems to be all right with them).


If I give up the idea, maybe the best option I found is TOMO V8-4. Although some guys had experienced not good results with it, Maybe it can be a nice choice ( $ 13.49 now in gearbest). And, complementing, you know Soshine E3 (almost the same as TOMO V8-4). In discussions and reviews here we could see it need some improvements. Do you know the new version E3S (http://www.soshine.com.cn/a674.aspx) ?? The LCD is different, and maybe there are software and hardware improvements, but I cannot find any review of it. 

Thanks guys! Sorry for being so long.


Rafael

Barkuti
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Hello!

Rafael, you can set up as many cells as you'd like in parallel; in such a case, unless you make something very wrong, they'll operate as a single battery with a capacity of the sum total of all of them, and an equivalent internal resistance equal to the inverse of the sum of the inverses of each battery internal/lead resistances (sort of the sum of all power delivery throughputs).

Just make sure you interconnect them properly so no cell steps out of the farmyard. Cells in parallel can't get imbalanced, they stay in balance by definition.

I've tried the first boards on both of your links from aliexpress and FastTech, they both seem to work great. FT's old-style LCD one reports both voltage and current output. Thumbs Up

 

Cheers Party

Please avoid fully quoting lenghty posts, namely with nested quotes. Trim quotes down to the essential. Helps with neatness and legibility. Thanks.

The human mind, and its programming, is at the forefront of a particular battle of The Light vs evil dark forces. Nearly every human being on this beautiful planet “Earth” has some sort of negative mind programming in its mind. And you better take care of your mind programming, or someone else will in this wicked world.

Viruses DON'T cause diseases, they rather are a consequence of them. Read the book “Béchamp or Pasteur” by Ethel Hume for more information.

rjng
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Hello Barkuti!

Thanks for your answer!

About the connection, I thought use this circuit:

(note I used comma instead of dot for decimals)

The switch in negative pole could avoid discharging when it’s turned off? Or it’s not necessary?

Additionally, can these kind of modules deal with batteries with different state of charging? Is there a problem in case I use batteries of different mAh, or brands, or state of charging? Do I need to balance the batteries before turn on the first time?

Thanks again Thumbs Up

Barkuti
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rjng wrote:
Hello Barkuti!

Thanks for your answer!

About the connection, I thought use this circuit:

(note I used comma instead of dot for decimals)

The switch in negative pole could avoid discharging when it's turned off? Or it's not necessary?

Additionally, can these kind of modules deal with batteries with different state of charging? Is there a problem in case I use batteries of different mAh, or brands, or state of charging? Do I need to balance the batteries before turn on the first time?

Thanks again :THUMBS-UP:

These modules usually have lower than 200μA of parasitic drain (quiescent current) so, even at this rate, no more than 5mA would be drained from the battery pack in a day, which is ≈150mA for a whole month. I wouldn't care for a switch.

Once you set any two batteries in parallel, a voltage differential balancing current starts to flow between them, equal to the voltage delta divided by the sum of the batteries and lead resistances. That is, the battery with the higher voltage “charges” its lower voltage sibling until the voltage differential becomes zero (batteries auto-balance themselves). This shouldn't be much of an issue if the initial voltages of each cells are close enough (so no ouch! in your fingers inrushes of current happen). In rookie words: just make sure the cell voltages are close enough prior to interconnecting them. Corollary: all cells' SoC equalize; as I said previously, they start to operate as a single battery to all effects.

Regarding differences in capacity, brands or even chemistries, I really doubt this could be an issue because of the low power delivery requirements for powerbanks. Just don't use worn out, Ultrafakeor other known PoS cells (plenty of cheap brand name units nowadays).

 

Cheers Party

Please avoid fully quoting lenghty posts, namely with nested quotes. Trim quotes down to the essential. Helps with neatness and legibility. Thanks.

The human mind, and its programming, is at the forefront of a particular battle of The Light vs evil dark forces. Nearly every human being on this beautiful planet “Earth” has some sort of negative mind programming in its mind. And you better take care of your mind programming, or someone else will in this wicked world.

Viruses DON'T cause diseases, they rather are a consequence of them. Read the book “Béchamp or Pasteur” by Ethel Hume for more information.

will34
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Barkuti wrote:
Regarding differences in capacity, brands or even chemistries, I really doubt this could be an issue because of the low power delivery requirements for powerbanks. Just don't use worn out, Ultrafake or other known PoS cells (plenty of cheap brand name units nowadays).

 

Powerbanks can draw 1 amp or even more from each cell in a 4P configuration under heavy loads, it is ALWAYS advised to use the same capacity, model and most importantly chemistry, because each can have different discharging curves and voltage recovery when not under load. 

Since there is no individual monitoring in a parallel setup the safest thing to do is to have matching batteries, this is Li-ion safety 101.

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will34 wrote:

Powerbanks can draw 1 amp or even more from each cell in a 4P configuration under heavy loads, it is ALWAYS advised to use the same capacity, model and most importantly chemistry, because each can have different discharging curves and voltage recovery when not under load. 

Since there is no individual monitoring in a parallel setup the safest thing to do is to have matching batteries, this is Li-ion safety 101.

While I am not going to deny the potential concerns regarding all of that battery mismatching stuff, and speaking here about chemistries of course, I bet you my kingdom two or more brand name batteries of different chemistries but at least comfortable enough power delivery margins would happily operate in parallel without issues. Properly connected, any voltage differential caused by faster discharging through the lower IR chemistries should be rapidly and continuously rebalanced because of the then inherent dV between the cells. I am not saying, in any way, that I support this but, because of the lack of actual testing data regarding these matters, this stuff could work well. Maybe not for n00bs/rookies, of course. 

 

Cheers Party

Please avoid fully quoting lenghty posts, namely with nested quotes. Trim quotes down to the essential. Helps with neatness and legibility. Thanks.

The human mind, and its programming, is at the forefront of a particular battle of The Light vs evil dark forces. Nearly every human being on this beautiful planet “Earth” has some sort of negative mind programming in its mind. And you better take care of your mind programming, or someone else will in this wicked world.

Viruses DON'T cause diseases, they rather are a consequence of them. Read the book “Béchamp or Pasteur” by Ethel Hume for more information.

rjng
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Hello guys!

I read some about this issue, and I will use Li-ion batteries, with good batteries. I have 2 UltraFire 4200 mAh (fake, of course, usin in a simple DIY power bank) and 2 protected Sanyo 2600 mAh from DX.com (don’t fit my DIY power bank). I intend to use this 2 Sanyo and more from Sanyo or other good brand.

Maybe now I’m just afraid about the case of the batteries are in different state of charging. I don’t know exactly how much charge they are. With a voltimeter, how many volts difference is acceptable to connect them in parallel?

I’ve seen a suggestion of balance circuit, as below:

In case I dont know exactly the state of charging of batteries, is necessary a circuit like above? Is it enough? Or it’s exaggeration?

And, do you know a holder for 18650 protected batteries (mine about 69.5 or 70mm)? I’ve read many topics in other forum looking for one, but I didnt see a good suggestion. I’ve found some in AliExpress. One seller told me it fits protected 18650, and another, with a similar (or the same?) product, told me it don’t fit.
Told me it fits link
Told me doesnt fit link
Dont told me anything link
And here, a similar product and a little datasheet at the end. Although the leght of my protected batteries is about 70mm, and the lenght of this holder is 77.7mm, I dont know if the 70mm batteries fit the shell.
One other point is the quality of contacts, some guys told there are a lot of bad contact products in market.

So, do you have a suggestion about holder for protected 18650 batteries?

And do you have favorites modules (the are a lot in the market) to make you own power bank?

Thanks!

Rafael

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Welcome to the forum Rjng. Smile I’m with Barkuti, not really concerned about the imbalance of cells connected in parallel in a 1S situation. I agree with will34, that it is best practice to use similar cells in similar condition. But, I don’t think it is battery safey 101 in a 1S situation. Now, in a 2S, 3S, 4S, etc situation, I agree that is it a safety 101 because you don’t want one or more bad cells bringing down one of the parallel banks of cells that are in series with other parallel banks. A cell or cells that is not in good shape and is self discharging can drain a bank of parallel cells and create a very dangerous situation when that parallel bank becomes drained and the other banks that are in series reverse charges the said drained bank. You have not mentioned using cells in series. So that situation does not apply in your situation.

Really been enjoying watching the Olympics hosted by your country.

EDIT: All the above, assumes your are using healthy cells from a decent manufacturer.

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rjng wrote:
…In case I dont know exactly the state of charging of batteries, is necessary a circuit like above? Is it enough? Or it's exaggeration?

One other point is the quality of contacts, some guys told there are a lot of bad contact products in market.

So, do you have a suggestion about holder for protected 18650 batteries?

And do you have favorites modules (the are a lot in the market) to make you own power bank?

Thanks!

Rafael

rjng, man, just full charge all of the batteries to be teamed; that's it. Smile

Oh! Get a multimeter, there are some good inexpensive models (Uni-T, etc).

The first FastTech link in the opening post shows a really cool module I tried. Solid performance and the LCD reports battery voltage plus current output. Uses two independent current sensing resistor arrays, one for each port. I bridged them in parallel to slightly increase the efficiency/diminish voltage drop without issues. Handy.  A bit expensive, though.

 

Cheers Party

Please avoid fully quoting lenghty posts, namely with nested quotes. Trim quotes down to the essential. Helps with neatness and legibility. Thanks.

The human mind, and its programming, is at the forefront of a particular battle of The Light vs evil dark forces. Nearly every human being on this beautiful planet “Earth” has some sort of negative mind programming in its mind. And you better take care of your mind programming, or someone else will in this wicked world.

Viruses DON'T cause diseases, they rather are a consequence of them. Read the book “Béchamp or Pasteur” by Ethel Hume for more information.

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I have the tomo v8 and 4 protect Panasonic ncr18650b do fit in it. Its a tight fit but that fit and can be taken in and out. I’ve had multiple brands and different mah batteries in it together never a issue. It can be used as a charger for other batteries if needed. Its not a bad charger my wife uses it daily with two small kids not easy to stay near a wall charger. Probably get around 4 or so charges on full charge. Probably more with a smaller phone. I’ve had 2200mah batteries with 3400mah batteries of different charge states never had a problem. It charges each battery slot independent of each other as a lithium charger should. This sounds like it maybe the best solution to your problem. Protected batteries aren’t needed though. It only discharges down to around 3.0-3.1 volts. I was scared of lithium batteries when I first started now only use unprotected. I’ve pulled the protection off on all my other Panasonic batteries. But since those arnt on flashlight duty anymore I’ve just left them alone. Get the charger and buy 4 new batteries with it and be done or get a diy one with 4 new batteries and be done. Your really over thinking it. New chemistries don’t go boom only the first gen ICR batteries. Only exception is like if you threw it in a fire. But these new cells vent and not boom. You don’t hear of computers and phones burning up any more. There are safe guards in place in the batteries and products now. The manufactures test these batteries and try to blow them up under extreme conditions. Your little powerbank isn’t going to be a pipe bomb. You can order a decent manufactered one for about $25-30 if you take it apart you’ll see it not any different then the ones you put together yourself. Only difference will be the chip/firmware the company uses pretty much. Its good to have respect for lithium but don’t overthink it bud. The tomo has protections built in and is easy to take the batteries in and out. You don’t seem comfortable with the other options out there. Get the tomo with 4 Panasonic batteries 3400 unprotected or protected on gearbest and be done with it. Unprotected version is cheaper buy a few dollars. $25 and your powerbwnk is done with high capacity batteries and can charge two devices at once 1 amp and 2 amp port

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rjng
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Hello guys!

I think I lost my fears with this discussion, thank you! Now I believe I can do this without blowing up my body Big Smile

I have one USB volt/amperemeter, and one chinese standard multimeter that has been enough for me for general use. Soon will arrive one new USB volt/amperemet with mAh meter.

Ok, maybe I will buy one TOMO. However, where is the fun of buying one ready to use? I will make my own, of course!! Cool

As soon as I have them in hand, I show you the results.

Guys, thank you a lot!
Let’s keep in talking.

Rafael

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Please avoid fully quoting lenghty posts, namely with nested quotes. Trim quotes down to the essential. Helps with neatness and legibility. Thanks.

The human mind, and its programming, is at the forefront of a particular battle of The Light vs evil dark forces. Nearly every human being on this beautiful planet “Earth” has some sort of negative mind programming in its mind. And you better take care of your mind programming, or someone else will in this wicked world.

Viruses DON'T cause diseases, they rather are a consequence of them. Read the book “Béchamp or Pasteur” by Ethel Hume for more information.

Speed4goal
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rjng wrote:
Hello guys!

I think I lost my fears with this discussion, thank you! Now I believe I can do this without blowing up my body Big Smile

I have one USB volt/amperemeter, and one chinese standard multimeter that has been enough for me for general use. Soon will arrive one new USB volt/amperemet with mAh meter.

Ok, maybe I will buy one TOMO. However, where is the fun of buying one ready to use? I will make my own, of course!! Cool

As soon as I have them in hand, I show you the results.

Guys, thank you a lot!
Let’s keep in talking.

Rafael

There you go, glad to hear it. I got the tomo because its easy to swap batteries out if/when needed some power banks once closed its real hard to get them apart again About once s year I’ll swap them out. Or if traveling I’ll use it to charge batteries out of my flashlights. A power bank definitely comes in handy. Eventually might purchase a second one. I didn’t know they made a new version like you pointed out need to research it and see if the efficiency has increased.

I wouldn’t mind getting a big diy one with 7-8 batteries like I’ve seen online. That maybe my next project. A 20000mah power bank

2/9 Fox Co (2009-2015) Semper Fi 0311/0331 Rifleman/Machine Gunner
Blf has changed a lot since I've been here. Lots of snow flakes and easily offended over nothing. When the forum use to be great and people joked around and could take a joke. It's a forum it's not that serious. Let's make BLF great again!

rjng
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I have one simple power bank (this) and it’s very hard to open after closed. As you said, it discourages to buy one DIY power bank like this. The sum of a module (maybe the same), a battery holder and a shell exceeds some DIY power banks already with module and shell. But it’s not cool they are almost not re-openable.

Talking about nice power banks, have you ever seen some power banks with car starter function? They are very expensive, I don’t know if works (some comments say it works). Just as curiosity. Look here.
One day, who knows…

Barkuti
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rjng wrote:

Talking about nice power banks, have you ever seen some power banks with car starter function? They are very expensive, I don't know if works (some comments say it works). Just as curiosity. "Look here.":http://pt.aliexpress.com/af/car-power-bank.html?ltype=wholesale&d=y&orig...
One day, who knows...

Of course I have never seen and/or tinkered with any of those units but, seriously, all of that stuff seems to be another cheap chinese joke to me…

¿1'2Kg of weight? Well, that means, at the very most, just 21×18650 cells could be inside of it (3S7P arrangement). Now, if these cells were to be top of the line VTC5As or VTC6s, we would be speaking of 10'8V nominal, 18'2/21Ah peak capacity and about 210A of continuous discharge, with higher peak value yet with subsequent larger output voltage drop.

To my knowledge, that would only guarantee starting relatively small engines by itself. 

Now, who's gonna believe that stuff is equipped with battery guts already more expensive than the whole shebang? 

69800mAh… LOL!

 

Cheers Party

Please avoid fully quoting lenghty posts, namely with nested quotes. Trim quotes down to the essential. Helps with neatness and legibility. Thanks.

The human mind, and its programming, is at the forefront of a particular battle of The Light vs evil dark forces. Nearly every human being on this beautiful planet “Earth” has some sort of negative mind programming in its mind. And you better take care of your mind programming, or someone else will in this wicked world.

Viruses DON'T cause diseases, they rather are a consequence of them. Read the book “Béchamp or Pasteur” by Ethel Hume for more information.

Speed4goal
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Barkuti wrote:

rjng wrote:

Talking about nice power banks, have you ever seen some power banks with car starter function? They are very expensive, I don’t know if works (some comments say it works). Just as curiosity. Look here. />One day, who knows…

Of course I have never seen and/or tinkered with any of those units but, seriously, all of that stuff seems to be another cheap chinese joke to me…


¿1’2Kg of weight? Well, that means, at the very most, just 21×18650 cells could be inside of it (3S7P arrangement). Now, if these cells were to be top of the line VTC5As or VTC6s, we would be speaking of 10’8V nominal, 18’2/21Ah peak capacity and about 210A of continuous discharge, with higher peak value yet with subsequent larger output voltage drop.


To my knowledge, that would only guarantee starting relatively small engines by itself. 


Now, who’s gonna believe that stuff is equipped with battery guts already more expensive than the whole shebang? 


69800mAh… LOL!


 


Cheers Party

Its not a Chinese joke they really do work. Go on YouTube type in portable lithium jump starter. You’ll see a handful of different brands with demonstrations. They completely disconnect the battery and jump off multiple vehicles.
The days of the large jump boxes are over. One of the larger units is 50,000 mah. You do know a car battery will start your vehichle even down to a 1/3 charge. You don’t need close to the full 600-700 cold cranking amps they are rated at
10 quality cells could easily produce a short burst of 200amps

2/9 Fox Co (2009-2015) Semper Fi 0311/0331 Rifleman/Machine Gunner
Blf has changed a lot since I've been here. Lots of snow flakes and easily offended over nothing. When the forum use to be great and people joked around and could take a joke. It's a forum it's not that serious. Let's make BLF great again!