Repairing and Adflo Speedglas battery ref 837621 with LI-ION 4.2V Cells

Lately I have been repairing multiple wireless devices whose NI-MH batteries have deteriorated ; usually get considerably cheaper make you the battery pack with a new charger is to buy it new; in this tutorial I will show how to build a battery of 4500 mAh 12.6V and 3 packs of 3 cell li-ion parallel each to replace a battery 10.8V and 4000 mAh NI-MH (9 batteries in series 1.2V) with just 32 € (charger not included).

Update: I uploaded how I repair them to youtube:

HD version

And slim version.

LITHIUM battery types depending on their composition

The Lithium-ION technology has improved a lot as  the advantages of having no memory effect and higher energy density per kilogram than any other current technology , we can add that  depending on the type of materials used , allows different power / energy densities; we can have instantaneous powers from 1C (2A / time to a cell 2000 mAh) of the LI-Cobalt portable typical 5C of manganese (LiNiMnCoO2) or 15C for the past employed in Automobiles (LiNiCoAlO2) or 30C with LiFePO4 .

In an apparatus for instant high demand as a drill we have to use the Lithium / Manganese (LiNiMnCoO2) or Lithium / Phosphate (LiFePo4) , with somewhat less energy density but more specific power; if we used the usual and economic with high charge density (LiCo) would degrade faster, but can serve if we packs of several in parallel to meet this increased instantaneous demand or limit the power protection circuits (which usually come already in most li-ion batteries sold loose).

Choosing the most appropriate battery configuration

We play with the number of batteries in series got the total voltage , and playing with the number of batteries in parallel to  each cell we get different total capacity and download speed recommended (C) . If we have 6 batteries in parallel in each cell 2A (2000 mAh) each, we 12A in total, giving us if 2C are each a load capacity / safe discharge of 24 Ah.

The famous "C" gives us the maximum download speed correctly and safely in relation to their ability ; if 1C and has 2400 mAh capacity, it says that we can get her 2400 mAh in 1 hour. If 15C outside, could deliver the 2.4A in just 4 "intense" minutes. The lithium / cobalt used in laptop computers have 1C. If we overcome the rate of discharge, sobrecalentaremos the battery and shorten its life (more the faster the download).

With lithium If we do not get a range of voltages with the apparatus in question can run(ranging from 4.2V to 3V discharged fully charged), we can always use the LiFePO4 (with a charger) with a range of 3.2V work charged (to 3.6V fully charged) and 2.5V download limit without significantly degrading.

Note: Total mAh gives us the total capacity of the battery pack in parallel; in this case if we each pack with 3 rechargeable li-ion 4.2V 1500 mAh each, get a pack of 4.2V and 4500 mAh capacity (which is equal to 4.5 amps); if you put three of these packs in series, sums voltages and get 12.6V and 4.5A capacity (assuming all packs are equal).

Repairing the battery

A 3.7 V is not empty, but 20%; 3V will be empty (recommended recharge sooner)

For repair I gained batteries "Trustfire" with a capacity of 1500 mAh with control circuit charge / discharge that prevents the battery charges and discharges above allowed values, and if there is a higher current at 3 amps (possible short), disconnect the battery.

There could be welded directly retaining its circuit board (PCB onwards) batteries, but I preferred to remove it and apply it directly to each pack of three , so that the capacity of each automatically and control is carried per pack of 4 from swinging , 2V which is what interests us.

These control circuits would not be worth if you require more than 2A instant , then have to use other types of batteries (which accept higher current charge / discharge) and different PCBs.

This model batteries feature a plastic and additional positive (as if the PCB is found to have added to their manufacture), so we can start coverage outer shield to be left original blue color and then, raising the plus button, let without PCB:

We proceed welded together by a positive side and negative each other on the other,with thin wire 1.5 mm2. is sufficient (12V 2A) ( here you can calculate the wire size according voltage, amps and longitude), and solder the PCB B- pack to the negative pole and the B + to the positive pole of the pack, leaving the PCB to a side up so that we do not reduce space as space is very limited battery 837,621.

We do the same with three packs , so to put them in series we can only weld the positive of a pack with the negative of the other , given that the two are in the bottom of the box with PCBs above (facing the positive and protecting electrical tape) and going up in the middle to drive aside, because we are also limited in height:

The packs soldiers in series: Positive negative the next PCB

You can see it's a pack of 3 in series with 3 in parallel (3S3P).

Nomenclature: You will see on websites that refer to batteries with formats like "3S6P Lipo" and the like; the S is P series and parallel). Example: 3S2P: 3 packs 2 cells in parallel interconnected in series.

Now we just have to put the packs in place being careful that the poles are well insulated with electrical tape so that there are no shorts .

Caution: A short circuit or overload a battery of this type is dangerous for the large capacity of stored energy per battery; if operated at a temperature above 60 ° C, could ignite . So be very careful when soldering, do not stay more than 30 seconds heating one of the poles to weld !

Only negative would weld the box (brown) to the lower PCB pack and positive (blue) to the positive upper pack and then isolate that there is no danger of short.

The battery repaired

Another example of 3 packs connected in series; one of each pack is different brand but same capacity.

We fix packs with silicone in the corners to avoid dislodging with the punches and fill the holes with plastic bubble for example to restrict its movements. 
We plugged and sealed with duct tape:

We can only get a 12V charger, and between 1 and 2 amps , I recommend either 13V to charge the batteries; thanks to its control circuitry is automatically disconnected after reaching the voltage limit load or discharge (4.2V-2.5V); one of 2A will take to charge 2 hours this pack of 4.5A.

Note: These batteries Speedglas old lead a bleeder resistor and voltage at the pole yellow cable that connects to the fan unit; in case of the low capacity ref. 7.2V 837 620 (6 1.2V batteries in series Ni-MH), carries a very small resistance of 1.5 Kohms SMD, if the value of 10.8V is 5 kohms .

Update 19/01/15: Now I use a more powerful, reliable and that charges equally the different blocks, cell controller chip for 3/4 to 5 Amps available on Aliexpress.

More information:

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Battery Basics