25 June 2013

Li-X charger, first impressions

The Li-ion/poly charger finally arrived from China. At less than 10USD shipped I expected it to get the job done and nothing more.

In 10 minutes I threw together a 3S 2200 mAh pack and started charging. Cells were highly unbalanced and had been restored from the deep sleep state with a constant voltage about one month ago. They measured something like 3.2 and 3.6V unloaded.

The "Mystery B3AC" charger reports a worrying "do not leave charging unattended". It should charge a 3S pack at 1A and 2S pack at 1.5A.

I was listening to 2m SSB when I first plugged the battery pack and a strong QRM appeared. Uh! Oh! The charger is absolutely NOT RF-friendly! (No, I haven't checked if the noise was coming through the antenna or the PSU) I looked every now and then what was happening in the shack, without monitoring the actual DC current flow. The charger temperature was high, it was smelling too. I couldn't almost keep my hand on it.

Nevertheless, about two hours after charging, first LED turned green, shortly followed by other two. Temperature returned normal.

Next step will be to power the FT817 with this 11.1V (nominal) pack while studying the charger circuit.

So far .. no fire.

19 June 2013

2m ES opening - antenna

Yesterday I didn't use a high-end antenna for my sporadic-E QSOs, not even an antenna in a good position!

When propagation helps, a big antenna is not needed. Of course I could not hear everything that was on the band, but I worked what I could hear.

Given the typical figure-8 dipole radiation pattern, I wonder if I should have installed it vertical. Original polarization is lost when the ionoshpere reflects our signals, so for ES DX-ing you don't need to match with the correspondant. "Same polarization" is true for (almost) line-of-sight contacts and, probably, tropo.

18 June 2013

2m ES opening

I was home this time! A strong sporadic E opening reached 144 MHZ today. I could hear DX traffic on the rubber duckie antenna, indoor.

How to participate, since I have no antenna?! Laying in the shack was the dipole of my homebrew VHF yagi. I quickly hanged it outside on the HF antenna fishing rod support, fired up the IC706 at 20W RF and worked two stations at 1600 and 1200 km distance (SSB).

In DX terms that counts for two squares and two DXCC entities. Probably only one of them is a new-one for me (but do I really care?).

15 June 2013

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.

12 June 2013

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.

06 June 2013

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.

03 June 2013

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).