I looked over some different publications to write this blog entry, and narrowing the field down took some time. For those wondering what some useful bookshelf references might be, I have a general list of a few that are easy to find still, online, used book stores, etc. New, some are offered through Lindsay books, others are available elsewhere.
Some of the better books for reference that apply here outside of manufacturers selector guides. application notes, and data sheet, are are:
Numerous books by Forest Mims III,
ARRL Annual handbook,
Impoverished Radio Experimenter
(I will also give mention to the folks of the Crystal Set society at http://www.midnightscience.com )
Some other useful books are some in the the series of “Evil Genius” books published by McGraw Hill. It is this latter group I will start with first.
Evil Genius Series:
Mainly written for an audience of 4th grade through middle school grades, some of the books have merit for some projects that could be scaled up or slightly modified to achieve a desired circuit on large scale. All are aimed at the middle school grades of perhaps 4th through 12th in the US public School system organization, and the projects are pretty basic small scale items to get the reader used to some of the concepts, principles and methods, some projects build on a basic circuit, others move on to different circuits. They are designed to be “hands on” learning tools, and tend to be written in a manner suitable for children. Some adults may not care for the book’s tone, some adults may find it monotonous to offensive even. Which is why I warn you now of what to expect before you invest in these books as they are not the cheapest books around.
Electronic Circuits for the Evil Genius is a self paced book that uses the breadboard system that I discussed on the other blog, and it is a pretty good introductory book on electronics in general. The descriptions are basic and aimed at a reading level of perhaps a 4th grader, and the reason is pretty simple- the author is a retired school teacher. Not a crime, but former teachers tend to lead to rather simplistic examples and explanations, some can be good, some can be bad. However with that said, it would be a good first book for someone just starting out learning about electroincs as long as they are aware ahead of time the audience it is written for.
The book is in it’s second edition, which is usually a good sign of usefulness. It does also have unit questions in the event one wishes to use the book as a textbook either for a classroom or individual study.
While some of the circuits are not entirely useful to the areas discussed on the alternative energy blog, the principles and theory do apply.
One title in the series, “Solar Energy Projects for the Evil Genius” has only a couple useful projects potentially as they are designed to be “hands on” learning tools for teaching the basic concepts of some alternative energy systems to kids. Some of the circuits can be useful for a full fledged system, but they are outnumbered by those that are nothing more than demonstrations of how to make a Copper Oxide photocell of low conversion efficiency and similar. The book however is not one I would suggest for anyone out of high school.
The ARRL Handbook:
The ARRL Handbook is aimed at the radio ameteur, with the first few chapters dedicated to electronics theory. Rather fast paced and may not be adequate for many as they use very few examples compared to post graduate texts. While the book could be used as a textbook, it does fall a little short in that it is assumed the reader has some basic electronics knowledge already and can absorb their approach to the material. (I had the opportunity to listen to an educational consultant in the 1980’s, Gary Wong, who pointed out in his presentation that there were some 20+ different learning styles, so if one book does not make sense to you, find another book until you do. The ARRL handbook is good for reference, and good for some who are good at filling in details themselves.
Impoverished Radio Experimenter series:
It is a good reference, aimed at getting the reader used to electronic theory, with a focus on tube radio designs, it is not for everyone, and not directly applicable to alternative energy systems, but it starts small, is well ilustrated, and well written and concepts are adequately described. There are 6 books in the series, and also a good reference. The fact it is more focused on vacuum tubes/thermionic valves limits it’s direct applicability, but at the same time, when one considers how FETs work, (they work along similar principles as vacuum tubes/thermionic valves,) the oscillator theory is directly applicable, as well as the information on turns ratio and it’s influence on circuit impedance, etc.
The Entire set can be ordered from Lindsay publishing, and they have many other good books as well. http://www.lindsaybks.com
Various electronics texbooks:
Most are well written, and most are decent, they are aimed at senior high school level students and many post secondary students. Many also have unit questions, which can help cement ideas and theory as well. There are some specialized texts that are used post secondary as well that have their own focus and have potential uses for alternative energy systems, such as those dealing with Industrial Electronics, Op Amps, motion control, Power management and a few others.
I just happen to have numerous texts like these, when I come across them at yard sales they invariably seem to be in the “free” box. If people only knew. Not they have intrinsic value, but they have informational value.
Forest Mims III numerous references published by Radio Shack:
Most are pretty good for quick reference, although some of the IC’s are now obsolete, they are quite useful. While much of the information is collected from various data sheets, mostly National Semiconductor, there are also some circuits that are adaptations and different from those data sheets. Having them does save some time in researching as the books compile numerous IC’s into one book. Minimal text for the most part when in the “meat” of the book. He does write some preliminary information at the front, which I for one tend to skip, which may be the reason I suggest his writing is aimed at perhaps a high school student as the writing is aimed much higher than those of the “Evil Genius” series; a level as I percieve it to be. You are free to disagree with me on that point, but his various books are useful nonetheless.
Most of his books are written at a level of the upper grades of high school or post secondary education, he did write one that was aimed at about a 4th grade level, and that was his book on environmental circuits. The image is of just 2 of larger format books, but there are numerous smaller books that do duplicate some of what is in these 2 books, but also covers some additional circuits and concepts.
And Lastly, but perhaps most important are the Data sheets, Application Notes and “Suggested designs” from the manufacturers themselves. Sometimes sample circuits are presented in the Data sheets, otherwise look to Application Notes. Some of the Application notes are even compiled into a book in such a way that the book could be used as a textbook. One such book is a set of application noted compiled in the late 1970s into one book published for what was then “Siliconix” which proved to be an excellent primer for Feild Effect Transistors or FETs. They discussed characteristics, differences between some of the types, such as a simple MOSFET or JFET (Junction FET.) That company traded hands faster than a dollar bill at a poker game. The last company that most recently purchased those holdings was Avago. I queried with no response so the best I can do is take a picture of the book, I believe for awhile it bore the designation of “AN-1.”
2 other useful shortcut items are these two templates:
Some additional various notes are useful to mention here.
Line Frequency- or Mains power Frequency: The North American standard for mains power is a split 240 system dor home wiring. In other words, the power at your wall outlets in the US is typically going to be a nominal 120 Volts AC, however that has been incresing in many areas to a nominal 125 VAC. with a line frequency of 60 Hertz/Cycles per second.
In most of Europe the power mains standard is 250VAC at the wall outlets and a line frequency of 50 Hertz/Cycles per second.
A few notes on these diferences are in order. Timing circuits in most digital alarm clocks are relying on that line frequency to keep time. They amount to little more than calibrated counters of line frequency. Converting these to run on DC is not practical without a time base reference. Synchronous clocks (those with a motor to drive the gear train) is dedicated to the region it was made for. They will however operate on other line frequencies, but they will run faster or slower depending on where they are “from” and where they end up. In other words, a european clock runing on a step-up transformer to get it’s 250 volt supply, will run faster on the US 60 hertz standard. On the order of 20 percent faster- which is the ratio of line frequencies. This is an important consideration when you consider in numerous places around the globe, you will have a mix of equipment.
In power generation considerations, the 60 hertz electric motors will operate on 50 Hz, but will also run slower and slightly hotter as well. 50 hertz motors will operate on 60 hertz standards only running slightly faster. The only exceptions to this are the “universal motors” that operate with brushes- many of these can operate on DC as well, and if the potential/voltage supplied is the same in each case, the motor runs nominally at the same speed in each case.
With power generators in emergency relief situations for example, If medical equipment that is crucial is needing power, depending on what the item is, and what it has internally for circuitry should be operated on the Euro standard line frequency when possible. Those that require that 50 Hz timing constant should have highest priority for europower generators. If equipment has an internal transformer and it’s own timing reference that is not the power line input, these can be run on the North American standard 60 hz sources. They may run a little warmer than they would on europower, but in most cases this is not an issue to otherwise normal operation.
The same is true for most US equipment, including some medical, they can operate on 50 Hz euro power, reduced to 120VAC via reducing transformer with the considerations for timing differences mentioned above.
If there are any doubts and the equipment is capable of battery operation with rechargeable batteries: operate the equipment on batteries and charge the batteries from the line source with equipment otherwise off , rotated with charged batteries or unit disconnected from batteries.
Computers use switch mode power supplies and Many these days are made to operate on either US or Euro standard with no change to a switch position, or adjustment. The label inside the case on the power supply itself will tell you for certain. Many of these can be used as low voltage sources for nominal 12 volts, 5 volts and 3.3 volts within limits printed on most of the power supplies. Grounding one wire, the “sense wire” will turn on the power supply. Be aware there is no isolation from the 120 or 250 volt source, however with due cautions considered, this provides yet another option for power other than that generated from the mains power or battery Buss.
Another note is in order too- most of the inexpensive lightweight generators operate with a mechanical governor to run them at 1800 RPM. These can be adjusted to operate at 1500 RPM to achieve Euro power rating by reducing the spring tension on the governor, which can be achieved by stretching a coil or two of the spring or adding to the length of the spring. Most generators will have a second spring to hold tension between governor arm and the throttle shaft- this should be left alone, although adding tension here will not hurt it, it will not affect engine speed directly, as it is there to keep the connections tight by eliminating any play in the linkages. That second spring is there to reduce “hunting” or speed variation due to clearances in linkages that will occur if it is removed.
If yours demonstrates opposite behavior to the above adjustment, just do the opposite of the above steps. I am basing these modifications upon setups that have the spring as the mechanical link from the throttle plate lever arm to the manual speed contol mechanism many generators have, and most power equipment, many of which I have serviced.
Euro generators that are generally made by the same companies, or at least along similar basic designs of the US generator manufacturers and there are some exceptions, but those that have mechanical governors can be sped up by tightening spring tension on the main governor spring by shortening the spring overall, or removing a coil or two to bring the generator to 1800 RPM for the reasons cited above.
Mechanical engine governors are usually in one of two places, either in the crankcase from a gear driven speed governor in mesh with the camshaft, or under the flywheel shroud where it is driven by air from the flywheel. This latter method is usually reserved for smaller engines as it is not as precise. From the governor, a lever arm is moved, which is attached via mechanical and spring linkage to the throttle plate to regulate speed.
If no tachometer or stroboscope is available, use a piano. The lowest note is 27Hz, 8 white keys up is 54Hz, each suceeding octave is twice the frequency of the one before. You can either rely on the noise through an AM radio to try adjust speed based on the generator output, or the noise of the spark plug if you gap the connection to the electrode slightly, or use a non-resistance type of spark plug. You would be up on the musical scale a ways to match engine speed, and either method does take a little bit of learning, plus you do need some musicality to recognize when you are on speed, close, or not close. If you are tone deaf- find a tachometer.
There are some generators, usually larger and industrial types where the speed is controlled electronically. These you have to locate the manuals for them and adjust the timing control circuits to the desired engine speed- which will vary in many cases due to the number of poles on the armature. Some are also 400Hertz for military and aircraft applications. These can be used for lighting with incandescent lamps or those lamps that can use a 400 hz imput frequency. Most often a 400 hz transformer applied across 60 hz or 50 hz will act as a dead short.
Some additional notes on the use of automotive alternators as a 120 volt source- if you try this, know that due to the mechanical advantage issues, you will need a higher (horse)power/wattage engine to keep one of these turning a constant speed under load. You will also need to apply adequate power to the rotating armature to achieve the 120 volts output. On average the automotive alternator is 2:1 for a turns ratio when in actual operation (this means you may need to apply 60 or more volts to the rotating armature to achieve 120 VAC. You can also rewind the alternator to achieve higher output voltage at lower output current as well. Then there is the matter of heat- adding supplemental cooling to that alternator is a requirement.
This Prestolite is rated at 155 Amps at 12 volts. At 24 volts, the current output is 77.5. The integral regulator brush holder fits in the cavity. You see polarity markings as the alternator that allow it be used in several ways in application. Factory fitted, it can be operated at 12 volts. It can also be operated at 24 volts with a factory regulator. However if you fabricate your own brush holder from Phenolic or other stable heat resistant nonconductive material, you can apply whatever voltage you choose to that rotating armature to achieve whatever output voltage you desire. An adjustable regulator of sufficient current carrying ability can be utilized here to achieve higher voltages or custom voltages other than factory designed regulators. This is where the actual regulator location when this is in typical application service. If you make your own brush holder, it must be non-conductive while also being heat resistant. A block of Phenolic material would work well here.
The alternator in general can be spun in either direction and it will generate power. The direction of that rotation should match that of the external centrifugal fan. Automotive generators on the other hand must be spun in the direction they were originally designed for. Here too, the external fan MUST be rotating the correct direction for cooling purposes.
The smaller alternator is a Chrysler “Square back” 100 Amp alternator. A very simple and efficient design. One brush is grounded, either to the housing directly, or through a wiring harness connection to the vehicle body. The other brush goes to a simple regulator. If you use a heavy duty variable resistor, you can apply constant power to the alternator’s rotating armature and get an output that will be suitable for welding or charging batteries at a constant rate you choose rather than at full charge rate if a regulator were used when loaded with a completely exhausted battery.
Sine Versus modified Sine:
This is just the output waveform of the inverter. Most motors will run on modified sine, but will run hotter. The reason being that the sine wave is just a 2 dimensional representation of a three dimensional event. If you thiink in those terms, you see there is less actual energy in the waveform of the modified sine wave. The modified sine wave is in essence comparable to an Amplitude Modulated signal. If you compare a 1/60th of a second wave form, the sine wave is continuous and the modified sine wave is made up of a number of chunks that the peaks approximately resemble that of a regular sine wave. If you consider power to be the area under the sine wave, there is less area under the modified sine. I know engineers and HAM radio enthusiasts are cringing at that description, but it is fundamentally true. The reason is there many facets of that wave, heat, magnetism, current flow, potentially light, And there is a lag to some of those as well when applied in a circuit.
If you think of the waveform as an envelope of energy with an aspect of power being the component beneath that waveform; if you rotate the waveform around the time axis, you can see a little better representation of the differences between the power differences of a modified sine wave and a true sine wave.
Motors are inductive devices. Shunt wound motors used in autombile starter motors are a perfect example for description. With a fully charged battery, they spin at a given speed determined by how it was wound and how many poles are present in the stationary field windings. If the voltage is reduced, the current draw increase. it is as simple as that. With a modified sine wave, the magnetic field is building and collapsing at the rate of the modified sine’s smaller component. If you had a motor fail on a modified sine wave, it was largely due to this aspect as the Pulse width modulation signal was slow enough for the magnetic field to completely collapse in that motor. Smaller motors are susceptable to this because they have less iron, and less magnetic flux to collapse.
A partial solution for modified sine users is to include a heavy inductor of adequate current carrying capacity in series with that motor.
It is with no irony that a Class D audio amplifier can theoretically be pressed into service as an inverter with only minor modifications. At the audio input- you apply your 50 or 60 hertz signal. On the output, you install a step up transformer. A microwave oven transformer can be used in a pinch, but is not the best option. you would apply your amplifier output to the 120 volt windings of the microwave transformer. Depending on the transformer, your output will be approximately 150 volts modified AC or about 200 volts modified AC. Since these transformers have a 6000 volt isolation rating on the varnish, the transformer is safe to operate up to 85 degrees C, although the cooler they run the better. The power output of the amplifier as an amplifier will be rated higher than it will be as an inverter due to the matter of “peak” ratings where an amp is not always running. safe estimates are 50 percent to 60 percent of rated output if you can apply an adequate input signal voltage to get the finals to “swing” from “rail to rail.” All that means is the output waveform if it were a sine wave, would have the peaks of each half cycle of the wave be almost at the limits of the Positive and Negative buss mesured at the transformer input windings.
This is one future project on my list to fully test out. I have a few amplifiers to test this theory out on, and if you have read the literature on Class D amplifiers, and are familiar with how inverters work, there is no significant reason for this not to work. Obviously the loading on the output transistors is an unkown until tried and measurements taken, but it is more likely that the output current will be lower due to a higher impedance from the transformer windings than indirectly calculated, and the influence of the external load resistance also plays a factor in this as well. It is about the turns ratio and the load resistance/reactance. The fact too that the block diagram of the circuit is nearly identical to that of an AM transmitter should make people curious as well, instead of the transmitters tuned tank circuit, you have the PWM circuit operating at what really is a radio frequency in normal operation. Just remove the low pass filters used for audio, add an antenna…. An interesting nexus point in technologies to say the least.
Back to the amplifier as inverter, or home brewed inverter even. A 60 hz signal for the input could be taken off from a fueled generator operating something else (a small wire wrapped a number of times around a single wire of the generator output,) or from a signal generator ot a simple timing circuit. The output modified wave will resemble the input wave, so a sine wave input would be ideal. A triangular wave is tollerable, and a square wave on the input is acceptable within reason. as long as the waveforms are regular and symetric. If there is a concern on the output, use a heavy inductor adequate for the current on the order of a 2.5 Millihenry choke such as some Uniteruptable Power Supplies for computers utilize, or the heavy set of windings of a microwave oven transformer. Keep the other set of widings from shorting out, or just carefully remove them. Your output voltage will be significantly lower, and much of this has to do with the way inductors store energy magnetically and release it. This inductor will get hot, so give it plenty of air for cooling.
Images of actual waveforms will eventually get uploaded, please be patient.