So you may have seen me yelling about power line harmonics… here’s what I was looking at earlier this morning. This is the power at a facility I was doing some work at earlier today. The same power has laid waste to two variable frequency drive units and an Omron 24v power supply used to run a Programmable Logic Controller (PLC).
I used the FFT mode on my Tektronix DPO 2012 oscilloscope to better detail what’s going on. The yellow trace is the waveform coming in (you can see it’s not a perfect sine wave). The red trace is a plot of the frequency vs. amplitude after a Fourier transform. This same kind of plot may already be familiar to you: it’s displayed on many audio players and stereo systems as a spectrum analyzer visualization.
If this were perfect clean 60 hz power, I would have only the tall peak at the left which is 60 hz, then it would roll off to the baseline. What I got, however, is this (and a realization I accidentally set my scope’s clock 12 hours off *before* DST kicked in…)
The FOUR other peaks are the harmonics. Initially I thought I was looking at a second, third, fourth, and fifth harmonic, which would put the last one at 300 hz– reading this again though, it’s scaled 500 hz/division so what I’m looking at is the odd order harmonics at up to 540 hz– a NINTH harmonic.
Now let’s look at that third harmonic, the most prominent. That one’s about 20dB down from the fundamental (the scale is 20dB per vertical division). That’s a voltage ratio of 0.1… so the third harmonic, if you were to isolate it, would be 12 volts at 180 hz. That just plain doesn’t belong!!!
A textbook square wave is the fundamental frequency plus all of its odd-order harmonics– 3, 5, 7, 9…. I suppose this makes sense, as if you smashed this AC waveform very very badly you would get a square wave.
Power line harmonics are an annoying effect of loads with a poor power factor. Want an example of a load with a poor power factor? You’re looking at it. The wall chargers for smartphones, power supplies for computers, and even LED, florescent, and compact florescent light bulbs are guilty due to the nature of their power supplies. Without getting too much into the theory I’ll say this: the way they work is that they draw power right at the peaks of the usual sine wave power. This is why the peaks in the above screenshot are getting smashed: that’s when EVERYTHING draws its juice.
Some *nicer* devices incorporate power factor correction circuitry to mitigate this. This usually takes the form of a low pass filter that acts on the amount of current drawn by the device, in an effort to keep it from just suddenly grabbing only the peak. Note that I say— “some”—
The harmonics tend to overstress everything by causing high currents to flow in wires, transformers, power supplies, etc– they are not only harsh to the equipment but they are a waste of energy.
And here, boy, do we ever have ’em.
The solution, ultimately, will probably be to have the local power company install a bank of capacitors for power factor correction on their poles.
Then, hopefully, the power will stop being quite so…….. hungry for electronic snacks……
Ahhh nostalgia —-
My first introduction to control logic design was designing and building pump control panels with my grandfather. If you happen to find a relay logic panel labeled “C&K Electric”, that was us.
This isn’t one of ours, but it’s pretty similar in design and construction. We really preferred Furnas relays though, and whoever ran the line entrance to this thing needs to be dipped in…. *bwahahahaha* THE PIT!!!
Here’s the basic operation: there are four float switches in the pit.
Switch 1: latch enable. Does nothing when switched on, but if a pump is latched on by its aux contact and it drops from low sewage level, it stops the pump(s). The alternator relay is also triggered at this point; it’s essentially a falling edge triggered gate. This changes up which pump will run next time so they take turns for wear leveling purposes.
Switch 2: start lead pump (as determined by alternator position). This will latch on until switch 1 opens.
Switch 3: Also start lag pump. This occurs when there’s too much flushin’ going on for one pump to handle it alone.
Switch 4: TURD ALERT!!! Condition BROWN! Sewage level is dangerously high; can occur due to pump failures, flooding, or a number of other very nasty things. While switch 4 is active, the red light comes on and an audible alarm sounds. This alarm can be silenced (will auto rearm as soon as the alarm condition clears).
On a side note– I recall the insides of those Diversified Electronics alternators being hilarious. It was like six tiny relays in a potted board and it invoked the obvious question of why not just use a spring loaded pawl mechanism like Furnas does?? Guardian Electric also made a version with a cam and ratchet; it was okay when new but the plastic cam was prone to degrading. Can’t win ’em all I guess.
A common mistake I see some people make when designing a solar energy system is that they will parallel the outputs of the solar panels without using a combiner box that has fuses or breakers.
This works fine in the “yeah, the lights come on” sense, but if you should ever have a fault in one of the modules, you may very well experience a fire at the module that will spread to any other flammable materials nearby….. yes, that means your ROOF.
Note that while the solar panel’s encapsulant and backsheet self-extinguish and only exhibit a couple millimeters of flame spread, the sheet of paper I taped to it to simulate the flammable debris that *will* gather around your panels does not! 🙂
Flammable crap you will typically find around and on your panels includes oily soot from smoke/automobile exhaust, dried leaves, paper, bird nests… anything the wind or animals can bring in!
This is the Morningstar Sunsaver MPPT charge controller, capable of pumping 15 amps into a 12 or 24 volt battery system from an up to 75V input. It’s fairly simple, though the 6P6C jack can be used for Morningstar’s Modbus system or Remote Meter to add more control, programming, and monitoring capabilities. The unit is driven by a Microchip PIC18???* microcontroller.
A typical MPPT controller consists of a switching buck or buck-boost converter with the input connected to the solar panel array, and the output connected to the battery system. A microcontroller monitors the solar array voltage and current (and multiplies them to calculate the power) periodically, and adjusts the switching of the converter appropriately to keep the input side voltage at the solar array’s maximum power point, Vmp.
Inside the Morningstar Sunsaver MPPT, there is… a switching buck converter with a micro… etc. Here you go:
* The conformal coating stuck to the top of the chip made it difficult to read. Like the flavor of PIC matters? XD
No fans or other active cooling are needed. The inductor is thermally coupled to the back of the housing, which is a tall metal fin attached to the heatsink/base. The switching transistors are, undoubtedly, potted somewhere in there. The potted construction is also used on the SunSaver PWM controllers.
Simple, elegant, but here’s the big question: WHY does it cost $250?! Rest assured, I’m scouring the market for some *good* low cost MPPT controllers. This is just a very good and not quite as low cost controller!
Warning: Engineering porn ahead. All images are clickable to view in full resolution.
The Outback Power FM80 solar charge controller is a high performance MPPT controller which converts a solar array’s output (up to 150VDC, 64 amps) down to charge a 12, 24, 36, 48, or 60 volt DC battery string using a high efficiency switching buck converter and an extremely flexible microprocessor control system. It is field programmable from the front panel and can be linked to other system components using Outback’s communication buss and the MATE controllers for system logging and remote control.
I’ve been having fun with this AIMS Power PWRIC300012W while pretending to be productive here at the office for the last couple of days.
Franklin from IndoorGenerator sent this unit over for me to play with, and I’ve found it to be very good. The unit combines a 3000 watt modified sine wave power inverter, automatic transfer switch, and 30 amp smart charger all in one nice, compact, lightweight package.
Yesterday I beat the holy splunge out of it with various test loads including a portable air conditioner and large 1/3 horsepower AC motor, and ran it at 2.8KW output for the better part of an hour. It barely even got warm to the touch.
From my testing, I found that the inverter only has two weaknesses to it.
First, like any high frequency switching type inverter, it can sometimes run out of power and turn off suddenly while trying to start loads with a large inrush current. This includes large halogen/incandescent lights, large motors, and compressors. If you’re starting such a beast off a switching inverter, it should be the first thing to be turned on, and any other loads should be removed before attempting to restart the large motor/light.
Second, the transfer switch isn’t instantaneous. The power goes off for about a second during the transfer from battery to AC or AC to battery.
A very useful little LED meter is present on the end of the unit next to the outlets. By pressing the button next to it you can select whether to view the battery voltage, DC input amperage, or AC output wattage in Kw. While AC power is present and the unit is charging the batteries, the output Kw and DC amperage both show as zero. I would have liked to have a DC current measurement visible during charge like the Xantrex TR series provides, but I’m not gonna complain much about it.
When the inverter goes into overload, the LED display on the end shows “E01″. I also managed to get the inverter to glitch a couple of times – weird things happened like the battery voltage reading coming back as ” 0.4″, or the inverter shut down and showed “Err”. Both of these problems went away as soon as I replaced a 1 AWG battery cable in the test setup which was becoming stinky hot! Oops. Too much voltage drop!
As the inverter begins to get near maximum power output, the peak to peak voltage begins to fall a bit. The unit compensates by shortening the 0-volt pauses on each cycle to maintain 120Vrms through manipulation of the duty cycle. Lights will not change brightness, but some AC induction motors may become weak as the wave approaches being a 120V peak to peak square wave. I noticed this only after applying around 2.7KW of load. The Daewoo portable air conditioner I was running did not show any problems with this, but a large industrial fan (of doom) began to slow down a little.
The charger is rated at 30 amps output. I clocked it at 33-34. It is, interestingly, built on its own board inside the top of the unit. This is a lot different than the charge system in the Xantrex Freedom series units I’m used to refurbishing, on which the same (massive) transformer and transistors are used to convert and regulate the current for charging. The internal 3-stage charger works fine on flooded cell batteries, but the absorption voltage got too high for a gel battery. I measured 14.82VDC. This may be in range for AGM batteries, however — check your battery manufacturer’s recommendations!
Today, I popped the top off and started looking around inside.
The build quality is very nice. It appears that the lower board is in charge of converting 12VDC to 170VDC. The board at upper right contains the AC transfer circuitry, a current sense transformer, and an H-bridge to chop the 170VDC into modified sine wave. The board at upper left is the charger.
The charger board has a jumper (JP1) located on it. Removing JP1 and turning on the charger activates equalize mode (about 15.3VDC). The small green LED located near JP1 comes on when the charger is in absorption or equalize mode. Unfortunately, significant disassembly of the unit is needed to access JP1, and activating any function of the unit while it’s open like this will expose lethal voltages to the user… so let’s just say that until a switch is brought out to the end panel of the unit, this feature is not Ready For Prime Time. AIMS didn’t even know the jumper was there! I only figured this out as I tried toggling the jumper to see if it was there to reduce the voltages for use with gel batteries.
The cooling fans at the end of the unit run whenever the charger is active, and otherwise… very rarely. It barely gets warm at all while in invert. All of the transistors that have any significant amount of current across them are heatsinked to the extruded, finned alumimum chassis. This is a design borrowed from high power car audio amplifiers, which have to put up with being wedged in all sorts of weird ways into hot car trunks with little air circulation.
My final verdict: If you’re looking for a good low-cost, lightweight modified sine wave inverter/charger, this is probably just what you’re looking for. If you’re running any large motor loads, however, be prepared to go over and reset the inverter when they fail to start.
If the cost and weight aren’t that much of an issue, I’d step up the Xantrex Freedom or Xantrex TR series; they cope with starting large motor loads by just throwing everything they’ve got at it, current limited only by the inductance of the transformer. The motor makes hilarious sounds and the inverter output voltage dips during the ordeal, but it’ll start the motor, whereas a lightweight switchmode inverter like this will just go “Noooo! OVERLOAD! Now you get to come over here and reset me! HA HA!” Plus, the Freedom and TR have a much stronger charger.
Or, “Now presenting, the all new for 2011 International Rectifier PwndFET Transistors”
I suspect this happens when someone reverses the battery leads on a Xantrex Freedom series inverter. The IRF1010E HEXFETs are blown to bits! On the power board for a 1000 or 1500 watt unit (they both appear to be the exact same board), there are ten on each side.
The symptoms are usually an inverter which goes through the right motions of going into charge and invert, but no output is seen. Sometimes, the unit even makes the right sort of sound as if it were going into charge/invert. Inspection of the FET board will reveal… this.
The other devices on the board appear unaffected. Coming soon: an experiment to see what happens when the IRF1010E’s are replaced! Does this lead to a perfectly working board… or just an object which remains a paperweight? Stay tuned…
The designer of the IndoorGenerator power units just dropped by here at Sun a few minutes ago. Their products are really interesting, especially for those of us down here in the Hurricane Belt.
Their product is, in a sense, like a giant UPS. Sealed maintenance-free lead-acid batteries are paired to a power inverter/charger unit in a nice cabinet. It’s also possible to get a unit from them which features a solar charge controller, and an outdoor rack to pair a couple of nice big solar panels to the system for off-grid operation!
Now, you see where I said “nice cabinet”? I mean it. Go look at their page for the PowerCubes – they look like a piece of fine furniture. You could use one as a nice end table or coffee table.
They also make some less aesthetically fancy but very functional UPS systems for commercial and office use. He was talking about using Outback Power inverter/charger units inside some of his systems, and those would be awesome for such use – they produce very clean power and transfer back and forth perfectly.