Salvaged batteries - 500mA/h 3.7V LiPO rechargeable

Hi,
young boys (age cca 14 yr.) make small powerbanks from e-cigarettes. An article in Czech (try a machine translator) is here.

VBR from Ivan

I think all of those relay contacts could be replaced with diodes if you used an ac supply for charging. Think along the lines of a diode/capacitor voltage multiplier. Each cell could have its own rectifier connected to a common ac supply via a pair of blocking capacitors so that although the cells are in series, they are in parallel as far as the charging circuit is concerned. If the capacitor values for 50Hz are impractical then a high frequency inverter could be used to provide a source of ac at a few 10's of kHz. DC power to the input side of the inverter could be regulated to provide 4.2V per cell as the output voltage will depend only on the transformer turns ratio and voltage drops of the rectifier diodes. By choosing suitable capacitor values the charging current will be limited by Xc.

If you have an even number of cells to charge half wave rectification could be used so that odd cells charge on one half cycle and even cells charge on the other, although if the balance is poor the transformer may saturate. 

I made a 6 channel continuity tester along these lines a few years back to monitor the state of 6 contacts that were connected in series but needed to be individually monitored, I used a CD4047 with a couple of MOSFETS to drive a ferrite transformer in push-pull, with 0.1uF blocking capacitors and 1n4148 rectifiers as the load was only a few LEDs. 

Regards,
John

Thank you very much for all the comments.
I am aware of the reason for the balancing circuit, but they all seem rather complicated. This is the problem if I am to balance many cells.
Also some of the circuits cannot be left in circuit because they use resistive networks that draw discharge current when the cells are not being charged.

I have done a lot more thinking about this and I have a few practical solutions in mind. My first thought is for the the 4-cell miniature (pocket) bench PSU for 0-12V.

The voltage regulator and current limiter is not a problem, and a commercial digital meter simplified the display problems.



Here is an idea for charging four series-coupled cells in such a way that each cell voltage cannot exceed 4.2V DC. This will give me 14-16V DC to feed the regulator. Naturally the regulator will need to be switched OFF when the PSU is not in use. That can be a switch on the voltage adjustment knob.

When there is no charger connected, all the cells are wired in series. There is a 1N4001 diode across each cell (not shown) as a crude attempt to help reduce reverse charging on discharge, but the regulator I am thinking about has a voltage shut-off at about 13.5V DC.

Operation:

• Plug in 5V to the DC IN Charge/GND terminals and the two US$2 relays energise
  
• RLA1A disconnects the regulator from the batteries
  
• RLA1B to to RLA1D, RLA2A and RLA2B switch all cells minus poles to ground, and all plus poles to the 4.2V supply (4.9V minus the 0.7V drop across the silicon diodes)
  
• If I can find a germanium diode that will handle 1A then I will put this in the charge supply so that a standard 5V USB charger can be used to charge the cells.
  
• It is the charger that limits the charging voltage, so it has to be a bit accurate, but I can always use my bench PSU as I do now
  
• In the event that one cell is REALLY low then the diodes prevent the other cells from dumping unlimited current into the low cell
  

PSU display - ready built (US$5) Volt / Ammeter


As regards the 90V problem, I can use five of these 3.7 LiPO batteries in the above circuit (using the two spare relay contacts) to give me 20VDC , and then a DC-DC converter get get 90V. I only need about 12mA @ 90 Volts.

So what do you guys think? Practical?

BR Harry - sm0vpo

PS - I am still occupied at weekends. This weekend I am going to London to visit the rain 

Hi, see another nice balancer.

VBR from Ivan

Hi Harry,
serial connected lithium cells always require a "balancer" both during charging and discharging, otherwise explosions and/or heavy fires may take place. See e.g. here or google for "lithium battery balancer circuit".
Your anode battery would require a lot of balancing circuits. This PSU might be suitable to charge it as a whole.

Just the first thoughts.

VBR from Ivan

Your charging scheme is simpler than mine, but without being able to easily post schematics, here goes:

TL431 anode to cell negative. TL431 cathode via a 1k resistor to cell positive. TL431 REF terminal to cell negative via a 10k resistor and to cell positive terminal via a 6.8k resistor. PNP transistor emitter to cell positive, base to the TL431 cathode/1k resistor junction, collector to cell negative. 


Charge cell using a constant current source. When cell voltage reaches 4.2V (16.8*(2.5/10)) the TL431 conducts, the PNP transistor is forward biased and shunts the charging current away from the cell. Several units could be stacked in series and charged from a higher voltage. Not sure what the current rating for the TL431 is but for low charging currents the PNP wraparound may not be necessary. 

May be worth putting a low value resistor in the PNP collector circuit to avoid a hard short across the cell if things go wrong.


Regards,
John

Hi Ivan and all,
As you are aware, I have been collecting these LiPo rechargeable cells from these disposable e-cigarettes for a number of months. Although I have not had much time on the bench, I have done some experiments and have some results that I should perhaps share.

1 - Capacity
The cells I have saved all seem to be quite high quality and I have measured their capacity quite accurately. Different brands of e-cig all have different cell capacity, varying from 400mA/h to 850mA/h.
Multiple charge cycles (more than 20) show no degradation in the measured capacity, in fact several of them have increased their capacity after a few discharge/charge cycles.

2 - The capacity is quite high in comparison with older technologies. The old FT-290 for example, had 10x C-cells of 600mA/h capacity, which took a lot of space in the rig. Four of the 550mA/h e-cig batteries have reduced the space to about 20% of the original size.

3 - The basic problems with these cells is:
a) a fully charged cell has a terminal voltage of 4.2V but this falls to 3.6V during the discharge cycle - a drop of about 14% before the discharge current begins to fall
b) serial coupled cells are dangerous as there needs to be some form of voltage limiting, both on charge and discharge. They usually explode during the charge cycle
c) charging a bank of these cells can be difficult unless you have some form of circuit that prevents over-charging of each individual cell.

Ideas on 3b and 3c above
I am building a 90V DC power bank (450mA/h cells) so it is not practical to have a single charger that monitors each individual cell. I have however, got a solution using just three components:

A 3.5V zener diode (3.4V are available) connected from the collector to the base of a BC547 will make a nice voltage limiter. If the voltage across the cell exceeds 4.1V then the BC547 begins to conduct and bypasses the charging current, allowing other cells in the chain to continue charging. This uses just two components.

I also added a diode across the cell so that a cell in a chain that becomes discharged, the diode will conduct and prevent the cell from from being revers-polarity charged. Unfortunately this is not perfect as it still allows the cell to go down to -0.7V. Ok, the cell will not explode, but it can damage the cell if this situation is prolonged.

Using these two techniques you can prevent the cells from exploding, and you can series charge a chain of them with a constant current source. The Zener/BC547 has a current limit of about 300mA, so the charger must charge at a limited and constant. If it is too high then some of the BC547s can pop. In addition, the "shunt current" circuit of this circuit is a little current sensitive: if the current is varied then the voltage at which the current-shunt kicks in will also vary a little.

Ideas on 3a above
Three LiPo cells have a nominal 3.7V * 3 = 11.1V. This is a little low for the FT-290 and other 12V equipment. Four cells can have a peak voltage of 4.2V * 4 = 16.8V, which may be too high for some equipment. 15V is often considered the absolute max for any instrument. The solution is to use four cells and a voltage regulator. The regulator can simply be three 1N4001 diodes in series to give a 2V drop down to 14.8V. This is the arrangement I am using in my FT-290. When all the cells are discharged, the terminal voltage is still 3.5V * 4 - 2V = 12.0V.

Capacity ideas and current
550mA/h is quite a respectable capacity for these cells and most projects. The cells can, however, start to get complicated if you connect them in parallel. You can double them to get 1100mA/h but in the event that one cell does die, then the other cell(s) will discharge into it. In the worst case this could result in smoke or yet another explosion.

My simple answer to this is an individual fuse for each cell. In the e-cig the current demand is only about 400mA or so the wires are very thin (cheapest for the job). The conductors are only about 0.1mm diameter. I have tried leaving a 1cm length of this jumper wire on the cells and when I short a cell the wire does indeed burn away and disconnects. I wonder if this is the original intention? Whatever, it works.

Other ideas
Now that I have found some solutions I have got some other ideas. When I play on the bench I really need a bench PSU that will supply 0-15V at 0-500mA. Most of the time I only need perhaps 20mA or so, occasionally up to 100mA. OpAmps and CMOS need very little, as do most of the smaller projects I build. My current bench PSY weighs about 5kg and I always have to plug it in.

For about US$4 you can get a digital V/A meter. This and four LiPo cells will fit in a really small (pocket-sized) project box. A simple series voltage regulator and you have an instant PSU. If you want to be really posh then you can have one with current limiting, which is the way I am going. This means that I can have a complete PSU in my shirt pocket, together with my credit-card digital multi-meter.

A problem for YOU
Ok, there are some ideas for you and ways you can re-use those e-cigaretter "vape" cigs and such. But you may like to give a thought to my 90V DC battery bank that I intend to use to power my old VIDOR Lady Margaret vintage valve radio.

I do not need a voltage regulator since they will work from 100V down to about 35V. 85V to 95V is easy with 22 of these cells. The problem is charging them.
Should I charge them with a custom 110V DC 300mA PSU? That would be a bigger project than the battery itself.
Should I use a coil with the bypass-diode to make an induction charger? That would be a challenge to uniform charging, and 22 coils.
Should I split the bank into several smaller chains, and charge them separately? It would mean more contacts on the replica 90V battery case.

Let me have a few ideas from you. How would YOU tackle the problem?

Very best regards from harry - sm0vpo

sm0vpo wrote:Here in Sweden they have banned totally all cigarettes that are flavoured, such as menthol cigs. The reasoning is that nice flavours make them attractive to young people.

Hi Harry,
AFAIK flavoured cigarettes are banned in the whole EU. Slim ones are banned as well.

I have tried "creamy tobacco" (tastes like chocolate), red grape, mango peach and pineapple (Just waiting for the rhubarb and garlic ).

You are probably a gourmet!

But these things are made in China so one does not know exactly what is in them.

It may be better to stay uninformed. But it should be still less dangerous than those hundreds of toxins and cancerogens in tobacco tar and smoke.

I think that I may put together a little something to show how these cells can be used.

A nice idea! Do not forget some clues how to charge these cells without danger of explosion, please.

VBR from Ivan

Hi Ruud,
Thank you for the links. They were very interesting, so it seems that these cells are widely known. As soon as any environmentalists wake up then these will probably be banned.

Here in Sweden they have banned totally all cigarettes that are flavoured, such as menthol cigs. The reasoning is that nice flavours make them attractive to young people.

Now these e-cigarettes come in all manner of flavours. I have tried "creamy tobacco" (tastes like chocolate), red grape, mango peach and pineapple (Just waiting for the rhubarb and garlic ).
I am willing to bet that the Swedish authorities will ban everything that has a flavour. But these things are made in China so one does not know exactly what is in them. Glycerine, water and nicotine is common, but the flavours?

I think that I may put together a little something to show how these cells can be used. I know that they can easily pull an ampere so the possibilities are endless. Standard LiPO cells have that little protection chip that limits the current, but these things have nothing whatsoever. That may make them dangerous. If you know what you are doing then they should be safe enough with the correct  precautions.

I have one cell that is used to run my micro-helicopters and that has been cycled about 8 or 9 times.

I also saw a YouTube video where a guy used these cells to make a micro power-bank.

Thank you for sharing the links. Very best regards - Harry - sm0vpo

Youtuber 'Bigclive' has made several videos about the reuse of these batteries. Here is one.
And a second one .

Hi Ivan, I totally agree.

In today's world we have to be very careful, but there are many holes in the system. I think that the only true solution is to have users pay a returnable deposit on purchase. Otherwise the nearest trash-can will be too easy for people who are too lazy, or don't give a hoot about the environment.

The batteries themselves seem to be working well. I have cycled one battery about 5 times with no noticeable degradation in capacity. After charging, the 4.2V is maintained so there appears to be little self-discharge.

I have 100s of uses for these cells, for example:

- Power my FT290 - the original batteries were six X 600mA/h NiCad C-cells (works on low power)
- Power my X1M radio - there is space inside for three of these cells
- LED "extra lamp" for cars = 45 Watts, but only take 175mA - 3 hours on three of these cells
- LED Pocket lamp using the 12V kitchen lamps - 100mA
- LASER pointer for entertaining cats. Button cells only work for a few minutes
- Repaired my noise-cancelling headphones
- One cell will also drive my micro R/C helicopter (4-CH)

But the best use of all is to send them to the recycling depot where they belong - IMHO.

BR Harry

Hi Harry,
you made an interesting discovery. I, as a non-smoker, never have dealt with e-cigarettes and their construction. After a short search, I found tons of single use ones, priced from 99 CZK (approx. 4 euros). It is probable that they use the same type of battery. The question is how many cycles such battery withstands.

These batteries should be collected and recycled in any case, as the resources of lithium seem to be rather limited.

VBR from Ivan

Hi all,
Here is a rather interesting topic. Since Maj-Lis passed I have had a year where my cigarette intake rose. Of course, the usual chesty coughs and such.

Last week I found that there are available small disposable e-Cigarettes from the local garage. They cost about SEK69 (£5.50)[US$6.50].
By "Disposable" they mean about 700 puffs and throw away. They do not give any tar or carbon-monoxide, which are the elements that do the worst damage.

These units have a small plastic cylinder containing "the stuff", but they also have an LED, a sensitive air-pressure switch, and a 500mA/h rechargeable LiPO battery. The battery is used to feed about 1-Ampere to the heater element, so they are more "meaty" than you bog-standard LiPO batteries in a silver plastic bag. Such a battery costs about SEK110 each, here in Sweden.

The batteries easily power my 4-channel helicopters, and three of them will run power FT-290R on low power. In addition to this I have not had a cigarette since Wednesday the 22nd of March.

This is all very good for me, but I cannot help but wonder about the sustainability of throwing away rechargeable LiPO batteries after just one use. Mine will get put to good use but the average user is not likely to recycle these things.

Best regards from Harry - sm0vpo