Can I connect 2 x protected 18650 in series? I mean merge them(solder) similar like this one:
And once When I merge them could I saftey charge them with 8.4V charger like this:
http://www.ebay.com/itm/220800935948?ru=http%3A%2F%2Fwww.ebay.com%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D220800935948%26_rdc%3D1
I would add charging slot jack and charge them with this charger.
Is this safe?
I have a similar battery, but its 3.7v. Uses inbuilt charging and it came with 4.2 +/- .05 with 500ma charge current. Your battery has the inbuilt protection also, I dont think mine does.
Is there any particular reason that you need them like that rather than just charging one cell at a time on a standard charger? I definately wouldnt solder them together and if you do go with this, use 2 new matched cell’s.
Two protected cells in series would be safe. It may not be safe trying to solder them together though. Do they NEED to be soldered together? Why not use a neodymium magnet in between cells? Charging them with the linked charger would work.
I absolutely would never trust some random direct-from-china charger like that. Only use tested, known safe chargers that follow proper cc/cv li-ion charging or if not independently tested, at least from a major reliable brand. Never unbranded or unknown brands. Never from some random direct-from-china seller.
Dedicated 2*series 8.4v chargers are not really common or very popular. So locating a safe proper cc/cv 8.4v li-ion charger may take a bit of work. Instead what people often use is a “hobby charger” which provides many functions including series charging of multiple cells, 2*series and more. RC hobbyists (RC cars, aircraft, boats) occasionally use dedicated 8.4v chargers when they want something more compact than most hobby chargers. So an RC forum would be a good place to ask for recommendations for a safe dedicated 8.4v cc/cv charger.
How safe is it to charge cells in series without balancing them ??
I know I would not do it.
Cheers David
Series charging without balance leads is sometimes done. They mitigate some of the risk by using carefully matched cells, same internal resistance, same batch, same actual tested capacity (and of course brand new, same brand, chemistry) then permanently connecting them together. The idea is that they will always be charged and discharged together and should experience the same wear from use and storage environment, age together. And when done right it should have a protection circuit designed for 2*series packs which monitors voltage of both cells individually. Now, while the idea is that they both wear and age the same there can be problems. A defect in one cell, damage during use or despite appearing matched they just don’t age exactly the same and become unbalanced.
Guys mentioned charger is the best budget 8.4V charger you can get. It is absolutely safe for use. I use them to charge 2 x cell phone batteries in series. Chargers are all made in China like for example liito kala that died on me :)
I am trying to make permanent battery pack so individual charging each of them is out of a question.
So main intention can I connect 2 x protected high quality cells with their inbuilt PCB's and make one safe 8.4V series battery pack?
I got one confirmation answer that I can:
And then I did not completely understand this:
I mentioned that I want to permanently connect 2 x protected 18650 in series using only their PCB's. And now in your post I see that I got to have a protection circuit designed for 2 x series packs which monitors voltage of both cells individually.
So guys I don't know what is right here. Can I do it or not?
I know that this works with diy cell phone batteries without any issues with their stock pcb's. But cell phone bats are not capacity monsters like 18650's.
Thanks on answers :)
Can you do it? Yes.
Should you do it. No.
Sorry but very likely that charger will not be safe. There is more to being safe then just reaching 4.2 or 8.4. To start off, any AC powered device must use a proper safe design to ensure AC will stay isolated even when things go wrong like surges, component aging, physical drops and rough handling. The components use must be within their voltage, current, heat ranges and be certified to fail safely where required. I have just never seen a no-brand direct-from-china AC device that is actually manufactured to proper safety requirements. If no one is willing to even make up a brand to label a device with then they really do not want to be trackable, responsible in any way.
Certainly the number one reason people think it’s fine to buy a no-brand AC powered device direct-from-china from any random seller. “It’s all made in china, it’s all the same.”
It’s simply not true at all. Take a official canon li-ion camera battery AC charger. Yep, made in china. But in a very different factory, a world apart. With strict control of the components, traceable source of components, quality testing, accountability. Careful circuit design and component selection to meet safety requirements in all countries it will be sold in. And even non-safety requirements like FCC regulations on emitting interference to other devices nearby. Why the difference? Because major international companies are within reach of consequences. Fines, lawsuits, criminal charges even if they intentionally sold some of the blatantly dangerous products that many direct-from-china sellers do just to save costs.
And beyond the basic AC device safety issue, that ebay listing doesn’t even try to claim it’s a proper cc/cv li-ion charger. Not that you should believe it even if they did claim cc/cv, considering everything, the generic case, not even an attempt at branding, etc. Lets say the one you already have, surprisingly, is entirely safe, you sent it for teardown, inspection and testing. How do you know the next one you buy is the same inside? Everything about it is generic.
I don’t really mean to be harsh. Really I’m just tired of all the products that ignore safety just because the sellers and manufacturers are out of reach of any consequences.
If you want to do it anyway, you should only use batteries with quality seiko protection chips. Evva and keeppower are the lowest cost ones which provide this.
I don’t think you’ll find a 2*series protection circuit designed to fit on the end of 18650s stacked end to end that is for sale in low quantities. All the ones I’ve seen are meant for a side by side cell arrangement.
Why don’t you go with that battery pack itself?
http://eu.nkon.nl/eagletac-flashlights/r22-li-ion-batterypack.html
Mentioned charger is really good charger for what it does. I had crappy ones with tiny wires that died and this is really good.
Look this for example: https://www.fasttech.com/products/1331700
This is also good budget charger that is better in quality than all other budget chargers I tried even better than Wolf - Eyes single bay charger that is very similar to it. Also charging faster than any budget charger.
But of course there are better ones like liito kala enginer(which was review by HKJ and by me personal before HKJ, but that was crappy review :) ). But that same liito kala died on me. It was good while it lasted but it died.
You got me I will not connect 2x protected 18650 in series cause obviously this is not safe.
Reason why I asked because I tough that it would be simple as putting magnet or solder between them, add male/ female connectors on it and plug and play:) and I have 50 pcs protected LG cells.
But if it is not safe I don't want to even try.
Recommend me charger for http://eu.nkon.nl/eagletac-flashlights/r22-li-ion-batterypack.html please :)
Good: it dies when some part fails — assuming you got it with a warranty worth having
Bad: some part fails and the charger fails in a way that continues to operate but out of spec, no telling what happens or when.
Can you find us a good unbiased review of the DSS brand charger you’re so enthusiastic about recommending? I looked and could not find anything.
They’re widely sold. They look like a wall wart to me. If there’s smart charging circuitry inside that little plastic thing, someone ought to crack it open and check it out.
Warranty? :) It is online ordered item from China. Yes it has factory warranty. But:
Would you return 20$ worth charger back to China for replacing and then pay back shipping of another one? That would cost around 30$ :)
Main theme was not charger. I did mentioned charger I use at home, and it is really good charger for charging my 8.4V battery packs. I trust it. But my main question is like a mystery for BLF.
Can I connect 2 x protected 18650 in series? Is it Safe?
I got 2 split answers from 2 knowledgeable members(you can, and you'd better not) and that is enough for me that I don't do any diy assembling of potential battery pack cause no one is sure about this.
You got one answer, but it has several parts that sum up what people here have learned.
What Halo wrote above is wise advice. Consider it.
When someone keeps telling you X is wonderful with no evidence — don’t trust, verify.
Yes,
I agree. This are not things to play with if one is uncertain what he's doing.
YES, what Halo said is correct and for the safest and most ideal situation, his advice is sound. 
If you are satisfied with the charger’s performance and are willing to accept that the overall lifetime of your battery may be reduced, why not use it? I would.
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WRT series cells: if you have two cells A and B with cell A having a little higher internal resistance (or slightly less capacity) than cell B, then, even if they are charged to exactly the same voltage initially, cell A will ‘die’ faster than cell B. With both cells in series, if you drain the battery fully, it is likely that the protection circuit of cell A would trip fist. This would mean that cell A is more empty than Cell B and when recharging in series, cell B will be fully recharged first while cell A is not fully charged. It is possible that over time, when recharging, the protection circuit of cell B would ‘trip’ to prevent overcharging of that cell. In time, the general trend would evolve to: cell A is always drained below 3V and cell B is always charged above 4.20V. Both cells will have reduced lifetimes compared to properly charged cells and the battery (two cells in series) will not have its full capacity.
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Are your cells out of balance? How fast will they get out of sync? How much capacity will be lost? How many cycles will you have before needing to change the battery? I can’t answer these questions however, if you don’t mind possibly having less capacity over time and possibly having a reduced battery life, then go for it. (I would. :bigsmile: )
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Given what I’ve said, I once gave a friend a bike light using an 8.4V charger that charged up to 8.56V. I attached balancing leads and a detachable LiPO alarm to the pack and told the guy to unplug the charger when it says 8.4V when he needs maximum runtime… If he does not unplug the charger, then the battery will wear down faster than if properly charged. His loss. It’s not going to explode or catch fire, it’s just going to suck in a few years. He has had the light for a couple years now and it still works and lasted through over 8 hrs of dark when we rode a 73 miler a month ago.
So you want to persuade me to sin? 
I have very equal and brand(LG) protected cells. Mentioned charger has build PCB and stops charging at 8.4V, mentioned batteries have their own PCB's.
I think we should start again with this picture and ask ourselves how Eagtac manage to do this? Is this battery build out of 2x protected cells or it is build with 2x unprotected cells with their own unique pcb's that monitors charge and discharge of each cell? To my eyes it looks like 2x protected cells in series(maybe connected with bigger magnet at the middle?). If I am wrong how that pcb for unprotected cells should look?
This is 2x18650 unprotected in series but with added special PCB that monitors it:
Or this type pcb:
Packs that are made in side by side side has bigger pcbs. I don't see that fitted in Egtac cell.
So building of packs of already protected 18650 should be as easy as adding magnet and wrapp the cell?
This sounds to easy for me. And I am still not sure I want to try that. Probably special PCB's for 2 x 18650 in series is must. So how and where Eagletac added them in their 2x18650 pack?
“Ask ourselves” because — why?
When you could
Seems to me asking “ourselves” is an invitation to what they call recreational typing.
Man we are on forum. On BLF forum... We discuss here... And why should I buy if someone knows how to make this.
You apparently like myself have no clue about this.
Edit:
I learned how to de dome from Tom E
I learned how to make FET driver from Djozz
I learned basic DMM measurements from HKJ
I learned some soldering techniques by following threads and post of many members here
So why we could not learn how to make this from Mr. X that knows how to do it?
To put it simpler - no matter how good the charger is, the equation seen from the pack can be:
4.2 + 4.2 = 8.4
4.3 + 4.1 = 8.4
5.0 + 3.4 = 8.4
In absence of balancing, all of the above will be acceptable by the charger. It will charge until it gets that 8.4.
Without protective circuit, my answer is it’s not safe. But in presence of individual protective circuit, it can be safe, yes, but be prepared to unpack and rebalance them every once in a while. Once unbalanced, the pack will get tripped often, and you get diminished capacity.