EBL Gold Pro AA NiMH 2800mAh rechargeable

EBL Gold Pro AA NiMH 2800mAh rechargeable low self discharge battery (90% after 3 years) , weighs 28.90g, costs about $1.87 per cell, or 1500mAh per dollar, which relatively inexpensive compared with other brands (Amazon Basic 1290mAh per dollar, Energizer 890 mAh per dollar, Eneloop 460mAh per dollar, POWEROWL 1320mAh per dollar).

Multiple users have showed that the actual capacity of EBL 2800mAh battery is only about 2400mAh.  The discharge rates for their tests are probably high to keep the testing time short.  Here we measure the capacity by discharging it at a low rate with an 80-Ohm resistor load.  We record the voltages over time and calculate the current and integrate to get the capacity.  At the average discharge rate of about 15mA, we expect it to take 7-8 days.  First it is charged from 1.28V for about 2hrs at 0.3A to 1.440V, which drops to 1.365V after about 1 day and 1.350 after 2days without load.  Then the measurements are taken with load.  It is fully discharged in about 150hrs and the capacity is 2338mAh.  More appropriately, the capacity is 2865mWh.  (Or 2388mAh if divided by the nominal 1.2V.)  In any case, it is only about 85% of stated capacity, consistent with other user reports.  Using the measured capacity, the cost is 1250mAh per dollar, on par with the Amazon Basic.  The big brand name batteries are rather overpriced (perhaps they are better in the number of charge cycles or internal resistance).

Fail Safe

Recently a 15-year old gas water heater stopped working; the pilot could be lit and would not stay on.  It can found on the internet a diagram of the gas water heater controller.  It becomes clear that the thermocouple is the issue.  Commonly, we use thermocouples as temperature measuring devices, but here it is actually a fail-safe device, which seems ingenious.    The thermocouple is an electricity generating device.  The thermocouple is in contact with the flame of the pilot and generates electricity (rated for 30mV) for a solenoid coil to open a gas valve.  So in case the flame is out, the gas value is automatically closed.  When we light the pilot, we push down a switch to bypass the solenoid to get gas flow and once the pilot flame is lit and the thermocouple is heated sufficiently to open the valve we can release the switch.  

The whole thermocouple assembly costs less than $10.  It can be appreciated the simplistic yet robust and rugged solution.  It is self powered and the very thing energizes it is controlled by it.  When the thermocouple fails, it closes the valve to keep the system in a safe state.  It is amazing that it has lasted for 15 years bathing in the flame constantly.  The life time is longer than the average life of water heaters.  Ultimately, oxidation probably claimed its life.  It is relatively easy and inexpensive to replace.

Wireless Remote Control Switch

Wireless remote control switch modules can be purchased for a few US dollars (around $7 for one pair).  They come with coil antennas.  They controls 4-channel output with Learning Code 1527, and can be programmed (using button presses) to operate in the momentary, toggle and latched mode.  The Learning Code 1527 has 20-bit identifiers(for over 1 million possibilities) and followed by 4-bit button code (for 16 states).    Most of the inexpensive modules have no marking on the ICs, so there is little information about the circuitry.

We can capture the RF wave using a oscilloscope with a loop antenna.

It appears the modulation is OOK.  Every burst is about 30ms.  It continuously transmits as long as the button is pressed.  It can be observed that the last few bits change depending on which key is pressed.  It appears that the bits are decoded according to the pulse duration or PWM encoded.  The bit 0 is a short duration of 0.3ms, and the bit 1 is about 0.9ms.   The total bit time is 1.2ms.  I counted total of 25 bits instead of expected 24 bits. Possibly the first bit is for synchronization only.

Something is also interesting about the 20-bit identifier code.  I was able to turn on and off using a key FOB from a different vendor and the code pattern is clearly different, but the receiver decodes it nevertheless, so it may not actually enforce the code or only subset of the code, or there is a master code.

Carbon Composition Resistors

I got a box of carbon composition resistors which are perhaps 40 or 50 years old.  They are things of past, having been replaced by carbon film and metal film.  They are probably made by Allen-Bradley, which were the main supplier of discrete resistors.  They have the distinct dark brown base color with 4 to 5 color rings (some have a visible 5th ring for temp coeff, yellow for 25 ppm/C, most are probably 100ppm/C which is brown same as the background), and are of straight cylindrical shape with sharp ends.  (The carbon film resistors have light brown base color and have end-cap bulge then tapered shape at the end).  The most common ones have 1/4W power rating, with body length 0.25", diameter 0.090",  lead length 1.5", diameter 0.024".   The 1/2W has body length of 0.385", diameter 0.140", and 0.032" lead diameter; and 1/8W body length 0.150", diameter 0.062" and lead diameter 0.015".

One thing I noticed is that how badly they are out of tolerance.  There are 5% resistors as indicated by the gold color ring.  But a lot of them are more than +5% of the nominal values.   All resistances are larger than the nominal value.  Aging or environment conditions (such as moisture) might have a large influence, which causes at least +5% resistance value shift.  But carbon composition resistors, which are not film construction, are more robust and have good surge performance, low inductance, and good high frequency capability.