I’ve previously wanted to know how much do cheap led strips last: turned out they don’t even pay for themselves over incandescent bulbs.
Here is the third incarnation of the experiment, after the second one failed and sat in a box for a couple of years. My motivation for fixing this was very low, as it already showed what I was interested in. As I received a few requests to resume the experiments from interested people and began to be interested in newer types of LED like the WS2812, here it is.
The logger has got some new updates to measure everything possible and benefits from a Wi-Fi connection.
LED logger V 3
In short: 16 LED channels are measured, one is kept for control of the sensor. For each LED the power supply and current are measured. The temperature of the aluminium plate is measured as well. In total there are 16 light channels, 15 current channels***, 4 voltage channels and one temperature channel.
Power supply: The strips I am using are 12V operated, but there are some WS2812B LEDs powered from a 5V DC/DC converter, along with the electronics. The power supply is loaded to about 30%. Both supplies are monitored, and 2 more channels are available for the future.
Current: The current of each LED channel is measured along with the light intensity. The current measuring sensor along with the switching transistors are made to have a very low burden voltage, in the order of mV, using a 10mW shunt and a 40mΩ RdsON transistor. The voltage across the shunt is amplified with a MCP6V31 low offset amplifier.
Temperature: there is now a one wire temperature sensor. Even though there are a few more LED strips added and power dissipation is 2-3 larger, the temperature rise is only about 10C over ambient.
Sensor degradation: in order to verify that the sensor is still reporting correctly I have installed a strip that will only be lit for a short time at each measurement to check that the sensor has not changed. By measuring a strip identical to the first I have found that the sensor produces identical results, so there appear to be no degradation over the experiment.
***I designed the circuit to switch off the negative supply. It turns out that this is a bad idea for the WS2812 LEDs, as the first one breaks very soon after. So the current for the WS LEDs is not measured.
The current data is available here (or click the picture below), check under for description of each strip. I have decided not to plot the variation over time for now (it’s stored) and only show the running time and intensity of each led, reported as percentage of initial intensity as well. The temperature and supplies are monitored along with the current for each LED. As with the previous experiment there are fluctuations in the readings, but they seem to average out nicely over time.
Meet the candidates
The control strip is identical to the strip used in the first experiment, except that is has not been used. It turns out that it produces the exact same readout as the first strip, meaning that the sensor has not been degraded over the 1400 hours of initial test. The control strip and the original strip are the best aligned to the sensor.
Strip 1 is the strip used in the first and the second led logger. It starts with about 5500 hour usage.
Strip 2 is made by Optoflash, it’s similar to the others except that the light is cold white. It’s a bit more expensive, comes from TME and there are no details about lifetime in the datasheet, but at least there is some sort of datasheet. It starts with 4500 hour usage.
Strip 3 is an Ikea ledberg strip. It’s rated at 20.000 hours, but without any info as to how this time is measured. It starts with 4500 hour usage.
Strip 4 is actually a waterproof module from a local shop that I paid about 1 EUR for. I don’t know anything more. It starts with 4500 hour usage.
Strip 5 is another waterproof strip. It starts with 0 hour usage.
Strip 6 is a much brighter PLC LED chip strip. It starts with 0 hour usage.
Strip 7 is similar with Strip 6, but encased in gel. It is also the most expensive one, bought from a more reputable online shop. Added on 28.03.2015.
Strip 16 is three WS2812B LEDs, which used to be 4 until I realized there is no easy way to measure the current on the WS2812 without breaking it. It starts with 0 hour usage.
Strips 7 to 14 will be determined and added later.
There is now a brand new, factory made PCB, schematic and layout available of course. Quite a lot of changes have happened: I switched the micro to a bigger XMEGA, added more channels, more voltage channels and current monitoring. Plus, now it is wirelessly connecting to the internet with the help of an ESP8266.
I have switched from the public data loggers and installed emoncms, the open source energy monitoring software on my website’s server. This has quite a few extra features and I have a sort of guarantee that once I get it working there will be no disruption due to domain changes, API changes etc. Plus, I own my data.
The software of the logger is quite a big mess, it is put together from many places which makes it far from optimal, but it does the job. Available on github.
Schematic is below. It’s grown a bit now, but there is nothing special about it.
Everything is built around the same box used in the previous projects, except that now the wire mess has grown significantly due to more channels and extra features. I move the controller on the inside to avoid disrupting the wires and stupid questions from visitors.
The ESP module sits on the outside, although it worked from the inside in the brief tests that I have performed. Still, I don’t want to risk any issues so outside it stays.
The temperature sensor is placed on the outside of the aluminium plate, in the centre where I expect the temperature rise to be maximum. It is placed in thermal contact with the plate and then some isolating foam and a few layers of tape disconnect it from ambient influences.
Interested in replicating the experiment and sharing your results? I will be happy to offer some PCBs for free (you pay the postage), but I will not have time to offer support. PCBs will be limited to 1 per person, I only have a few available. Still all information to replicate the experiment is here.