Da b0mb :)

This battery pack worries me, and I created it!

You are looking at a 4S(1P) Li-ion battery and charging electronics assembled out of parts from an hp/Compaq battery pack.

Five wires run from cells to the charger, which are used for charge balance. Since cells were already partially charged I had to be very careful not to short wires together. Next time I will solder first on the PCB side and then to the cells!

Charging at 1C (> 2 Amps) heats up cells. At one point the charging electronics was drawing 250mA into a couple of SMD transistors, which got pretty warm. I have no idea why that happened, because re-applying the power restored the charging process.

Once again charge was stopped at 4.0x V per cell, with a light unbalance. The bq2060 chip reports 80% charge, but that's probably computed from its past "experience" with other cells.

Next step will be to evaluate residual capacity, both of this 4S1P pack and the refurbished 4S2P. I don't have a costant current load so I will stick to a 12V car lamp and stop discharge at 3.2V/cell.

Packing it up

Once I found out the electronics inside battery packs is a balanced charger, all was left to do was to assemble a 4S2P pack out of the 24 Li-ion cells I got. Metallic strips that keep cells together can be easily soldered, which eases the construction of a sturdy energy reserve.

My "refurbished" pack.

I opened carefully the third pack so that I could reuse at least the lower part of the case, as a container for the 4S2P battery. Working with an open pack allows you to check voltages across single (group of) cells, so they can be characterised and, in case, replaced.

Fed with 18V, "the thing" drew 1.8A for a rather long while (hours). Then it stopped at 4.0V per cell without heating. The pack now measured 16V and the charger electronics reported 100% charge even after the night at rest.

Meanwhile I located the datasheet of these cells, and they seem to be Lithium-Cobalt batteries, a technology rated for 1C discharge current (ref. "battery university" website). I hoped for better, because they might not sustain the FT817 at 5W :-) Also, the datasheet calls for protection circuitry in case cells are paralleled together, while this high brand battery pack did not carry any!

Now I need a DC lamp to discharge the pack and test a full discharge-charge cycle, to get an estimate of the residual mAh capacity.

Electronics inside a laptop battery pack

Please meet the electronics inside a Li-ion laptop battery pack! There are two boards. Larger one has the smart charger IC (bq2060), five status LEDs, MOSFETs for charge control and other discrete components.

Smart charger circuitry.

The smaller connector board has 5 lines, out of which I could identify 4 and use 2: positive and negative battery pack leads, that are bidirectional (charge and discharge current flows there). Electronics on this board looks like a level converter for serial communication between the computer and the pack.

Connector board.

This setup works perfectly even without the small board, thus connecting directly to red/black thick wires between the two PCBs. I don't need the connector, nor the data communication feature: I want to recharge the pack and use its energy.

That's a fully featured charger! Sort of.

My venture in recycled Lithium battery packs has now brought my attention to the electronics hidden inside those expensive energy bricks.

A positive discovery was that if the battery pack circuitry is fed enough voltage (i.e. higher than pack fully charged V), cells get charged and balanced. Even without a computer attached. Cool! This means I have a balanced charger for 4s(2p) packs. At 14.8V they are too much for the FT-817 (even 16.8V at full charge!), but some uses would eventually come up.

Further inspection of the electronics led me to the datasheet of the charger heart chip: TI's bq2060. Reading the 59 pages datasheet here-and-there, it turns out that the chip is a smart charger that knows the whole history of its companion Li-xy cells. Not only it charges and balances the pack, but it keeps it in shape during storage and offers a lot of telemetry information like remaining energy and time, number of charge cycles, ... All this is achieved with a plethora of configuration parameters stored in an attached EEPROM.
It is possible to communicate with the chip and, if it is not locked, to review vital cell information (to make it look as new), but so far I have not found someone who shared the code for Arduino or in BASCOM-AVR or C. Not worth the effort writing my own, anyway.

Now what? While I wait for the 2s/3s charger to arrive I will try out this electronic "device" and recharge a DIY-assembled 4s2p Li-ion pack out of it. At least I will be able to evaluate the actual remaining capacity of what I've got (for free).

3v7 pocket heater

Everything was looking fine while trying to revive a single 3.7V Li-ion cell with my probably safe(*) method. Cell and voltage regulator were warm to touch, but it's also pretty cold in here these days (20°C in the room). When I disconnected the constant voltage source the measured voltage was 3.6V or so, showing a revived cell. My "procedure" calls for further checks of the open-circuit voltage,whenever I pass by the shack.

Thirty minutes after removing the charging current ... voltage across the cell was 0V and it was warm! Obviously it was self-discharging fast, producing heat. I moved the battery outside on a flameproof surface and let it exhaust the charge before hitting (gently!) the battery recycle bin.

(*) Feeding the cell with 4.0x Volts for 15-30 minutes while monitoring the current consumption to be (well) below 1 Ampere. This procedure should not (further) damage the cell and/or risk to set it on fire. YMMV.

Anatomy of a laptop battery pack

Three packs at different stages of dismantling

After successfully reviving 7 out of 8 Li-ion cells (3.7V, 2200 mAh), while waiting for the balanced charger to arrive from China, I started working on pack #2.

In this post I will show how these three packs look like. Inside a pack there are 8 cells, in parallel 2-by-2 (marked in violet). Hidden on one side there are a lot of electronics and taped between two cells a thermocouple.

Zooming in pack internals.

In pack #2 at reachable joints I could measure some 3.6V, so perhaps these cells do not need a restoring current. Disassembling is next.

Cells from pack #1 still hold the partial charge and I am optimistic they can be turned into a set of working battery packs.... when the balanced charger will arrive.

First experiences with Li-ion cells

I have been curious for a while about Lithium based rechargable batteries, and how I could get to play with them without investing too much money. Yesterday I was given three identical exhausted HP laptop batteries, marked to be 14.4V 4400 mAh, Li-ion. Not having a way to try a recharge, a disassemble was strictly necessary.

Those batteries even have 5 LEDs that show the charge level, and of course they were reported as dead. Once open I was presented a series of two elements in parallel, 4 each: 4s2p, and a lot of electronics. 

Meanwhile I had read something about these batteries at batteryuniversity dot com and I learned that:

• to protect cells from overdischarge, then internal circuitry disables the cell, resulting in 0V across the poles; the cell can be reactivated with a charge current
• Li-ion cells can be recharged with a constant voltage not higher than 4.20V, with a high current, even equal to C [cell's capacity], for the right amount of time

Each of my eight cells, left uncharged for an indefinite amount of time, measured 0V. So far so good. I threw together a 4.04V 2A voltage source and, while monitoring current (DVM in the picture) and voltage (analog voltmeter, not in the picture), I started charging each cell one-by-one for 30-45 minutes: in my opinion this is a safe time that does not pose the risk of (literally) blowing the cell. YMMV.

First cell went fine. After the initial 1.5A spike, it charged at 400 mA (and decreasing, 310mA on the DVM at picture time). After 45 minutes it had reached 3.8V and held it for hours with a slight decrease to 3.7V. Looks good.

Second cell was a surprise, since it initially behaved as the first but then went short circuit! Since it was unattended, I found a pretty warm regulator and cell when I checked in 10 minutes. Current was 3.5A. Maybe this cell was the faulty one in this battery pack?

Lesson learned: add a (resettable) fuse in line so that cells can be left unattended and, if they go short circuit, nothing blows or melts.

Third cell was better too. I will continue with the 45 minutes cycle to see if I can revive these cells. Having 3x8 = 24 potential Li-ion cells for free is interesting, but most important I can learn something new.

23cm biquad and coax

After a long a careful theoretical planning, I moved the 23cm RX-only biquad antenna in a more permanent location, not obstructing the view out of the balcony.
Since the antenna is now closer to the coax entrance into the shack, I could shorten the cable: what a better chance to take a couple of measurements?

After fixing the antenna in place I fired up SDRsharp and tuned the local 23cm beacon. Its carrier was peaking -40dB (relative). Then I cut at least 4 metres off the coax cable (unknown 75 ohm), re-soldered the TV-plug at the shack end and measured again: carrier now peaks at -35 dB (relative). That's about 5 dB S/N improvement.

Lacking proper instrumentation I cannot certify the gain is due just to the shorter coax, or to any other factor like: impedance match (remember my antenna R+jX was never measured), better coax-to-connector(s) junction, ... In any case apparently now I have 5 more dB of RX "power" for the next 23 cm event.

I am still after a simple method to remotely turn my antenna over a 90° range (max). I have few ideas but they are mechanically too complex for my time and tools.