LED lights and power use... and the tools used to measure it.

I will put the obvious stuff first with wordy technical explanations after

First take a look at this video (second one) The part of interest is that he has 10 LED lamps, but they do not take 10 times as much power as one lamp... in fact they only take about double...

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Yes you got that right, one 9 watt lamp took 9 watts, but 10 9 watt LED lamps only took about 20 watts. What gives? Ok, try this at home: plug a LED lamp into an outlet and turn it on. Plug a hand drill (angle grinder, whatever) into the same outlet and turn it on. The LED (and some CFLs) gets brighter. (this may not work with all of them especially the dim-ables)

OK, what is happening? To understand this we need to understand how LED lamps work. In days gone by when LEDs were used mostly for power on indicators, the standard circuit was a simple dropping resister in series with the LED to drop the voltage to what the LED would handle. Because the LED is a diode and has a drop voltage, it acts as it's own voltage regulator and the resistor acts as a current regulator. Cheap and easy and a great way to start a child learning about voltage dividers and current through easy calculations. But! very wasteful. The dropping resistor was the main power grab at between 10 to 100 times the power draw of the LED itself. LED lamps do not work this way. LED lamps have a capacitor to act as a battery for the LED, this capacitor is kept charged by short little spikes of power at full voltage. This kind of power supply has become cheap and is even used to charge your cell phone these days. We have known for some time how to detect the AC zero crossing and time from there and this is how most dimmers work, they shorten the AC wave so that the incandescent lamp will get less power. This does not work with a switching power supply that just grabs a pulse of power near the beginning of the AC cycle. So an LEDs power saving is determined time rather than constant draw. The drill motor that is making power spikes every time the brushes make and break was making the lamp brighter because those spikes where high enough and at the right time to over charge the capacitor in the lamp.

So back the the joule ringer. The first thing to note is that the frequency is much higher than 60 Hz. The frequency is determined by the inductance of the coil and the capacitance of wire placement and whatever capacitance the load sends back up the line. I have an old inverter (12v dc to 120 ac) that works the same way, but has a capacitor that was chosen to work with the transformer to give close to 60 Hz. Modern inverters use switching technology instead to be lighter, smaller, and cheaper. (more efficient too) The frequency of the joule ringer sounds to me to be 10kHz or higher (digital sampling may take a frequency higher than 20kHz and fold it back down into audible range). Anyway, the power use of the LED lamps is being measured by knowing the peak AC voltage, multiplying by .703 for RMS voltage, then taking the peak current use and multiplying that by the same .703 for RMS current. Power is voltage times current. All of this is done inside the meter.... but it is not accurate. The the peak current draw is for a very short time and each lamp takes those peaks at different times depending on the charge state of the internal capacitor. So each lamp may be taking the same peak only occasionally... it seems to turn out only 10% of the time. The idea that this joule ringer saves energy because 10 lamps only takes twice the power as 1 lamp seems to be in error. The current needs to be measured with a true RMS meter... perhaps one of the old mechanical meter models.

This begs the question of how accurate the new "smart meters" are that the power companies are using. Though I am pretty sure they measure true RMS to make sure they can charge you for all the power used.

Anyway, the moral of the story is to understand the tools you use to measure things...

Edited above for right video, tried to directly embed youtube... didn't work

I think it's this one.

Excellent. Don't always trust your measuring devices - at least not blindly.

I am reminded of many "overunity" energy devices. I think blind confidence in meters has led to a lot of nonsense. We can't blame the meter, just the overzealous operator.

Len Ovens : You have now on the side of a great divide, while I would find it difficult to explain the way a 'joule thief' works to a layman, that appears to be simple
as compared to a joule ringer, I think most people over 30 years will have trouble with this, can you break it down so that we can find a common thread ? Big AL

allen lumley wrote:Len Ovens : You have now on the side of a great divide, while I would find it difficult to explain the way a 'joule thief' works to a layman, that appears to be simple
as compared to a joule ringer, I think most people over 30 years will have trouble with this, can you break it down so that we can find a common thread ? Big AL

I am not sure what a joule thief is, or if it is any different from the ringer. I will try, my background and training is in RF (Broadcast technologist as happens) and so this tank circuit was very obvious to me.

First one has to understand why. Why is this person interested in this joule ringer? The reason is because of the way a lead acid battery behaves and so the way that current power inverters are constructed. A power inverter takes a DC battery voltage in and puts out 110 volts AC (or 220 volt in some countries). However, for protection of the batteries they are built with constraints to make sure they don't "break" the battery as these are expensive. So they shut off long before the battery is fully discharged. This person on the other hand is not using batteries as his power source but rather capacitors which are quite happy to keep supplying power till they are fully flat. They also have a much more linear discharge path than a battery. That is, a battery in it's whole useful cycle will remain at more than 10 volts (for a "12 volt" battery) and will be at 15 volts fully charged, drop quite quickly to around 13 volts while discharging the slowly from there to 10 volts or so of useful power, then the drop speeds up again till it is fully discharged at 0 volts (and quite probably damaged). Sort of "s" shaped. For all practical purposes, a capacitor discharges in a straight line, dropping evenly from charged level to 0 volts. Most of todays inverters would work with capacitors, but not make the best use of them. So the joule ringer is an inverter for the purpose of providing a voltage suitable for AC devices (some of them... maybe not very many) from these voltages.

It is based on the very first kind of inverters built. (I have a home made one from years ago) It is a low voltage oscillator and a transformer to jump the voltage up to a useful level. The primary side of the transformer is used as one of the elements of the oscillator and normally a capacitor is chosen to set the frequency close to 60 Hz (or 50 Hz elsewhere). In this case the capacitor has been eliminated and the stray capacitance of the wiring and load determine the resonant frequency. Stray capacitance is normally something an engineer tries to avoid but in this case, it serves a purpose. Any two wires in close proximity are a capacitor, but their capacitance is normally measured in nanofarads (1x10-9 or 1/1000000000) that is very small. So the operating frequency rather than being 60Hz is somewhere around 10000 Hz (which you can hear on his video) so we have to name "ringer". Note that LED and CFL lamps both have internal capacitors as well this is why in some of his videos he is quite excited that he can run incandescent lamps which have very little self capacitance.

The circuit is so simple it is almost hard to explain, the most basic class "C" amplifier/oscillator and a step up transformer all in one.

This circuit could very well have use in off grid systems (smaller ones because there is a limit to what can be powered) for lighting and maybe other kinds of things too. I was only pointing out that in spite of appearances, power out is still less than power in. Physics still works. Where I could see this working is for emergency lighting, batteries too low for the inverters to run, everything shutdown... but this could run a few LED lamps for a long time while doing repairs or waiting for sun.

By the way, I have not tried it, but the same kind of measurements may happen with 10 LED lamps plugged into normal household AC. That is, 10 LED lamps may appear to take less than 10 times one lamp worth of power.

I am wondering about the power consumption as well. The watt meter somehow does not play well with the high frequency pattern of the load. Here is some math how we can solve the problem -- it only involves measuring time till the capacitors are fully discharged. The amount of charge in a capacitor can be calculated using this formula:

J = 1/2 * C * V^2 (J = Joules, C = Farad, V = volts)

example: Cap with 12V and 8000uF --> 0.5 * 8000x10^-6 * 12^2 = 0.676 Joules

To translate joules to watt --> W = J/s

So you have to calc the energy J for your setup and count the seconds to discharge them.
Then you divide J by the secs and you have the watts!

Markus Loeffler wrote:I am wondering about the power consumption as well. The watt meter somehow does not play well with the high frequency pattern of the load. Here is some math how we can solve the problem -- it only involves measuring time till the capacitors are fully discharged. The amount of charge in a capacitor can be calculated using this formula:

J = 1/2 * C * V^2 (J = Joules, C = Farad, V = volts)

example: Cap with 12V and 8000uF --> 0.5 * 8000x10^-6 * 12^2 = 0.676 Joules

To translate joules to watt --> W = J/s

So you have to calc the energy J for your setup and count the seconds to discharge them.
Then you divide J by the secs and you have the watts!

Yes that would work as well. I have gotten lazy I guess, it has been years since I have used some of this math

My main point though, was to know what your instruments measure and if it looks too good to be true... it is.