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JoeGadget's

Technical Page - 4th Edition

This edition of the page is the analysis of the power supply. The power supply is a motor/generator (alternator) with a step up transformer. It must be studied to know exactly what is coming out of it when it gets used to power the transmitter. This study is one of the boring parts of research and development but it must be done. The power supply is fairly powerful and very dangerous. You cannot just turn it on and start playing around with it or you may get seriously hurt. You may also burn it up because you did not know it was being overloaded. The study is also important because there are other uses for the power supply and a detailed knowledge is needed to design new projects and test plans. For those of you who are not serious engineers you will probably wish to skip this edition of the page. It's going to be a dry one.

There are two interesting features to this edition though. A tachometer has been added to the motor. It is made from an automobile speedometer. The real fun part of the testing is the Jacobs Ladder that was added at the end. A Jacobs Ladder is merely a pair of straight wires which have an electric arc between them. The arc starts at the bottom and climbs to the top. It used to be seen in every science fiction movie before space travel and aliens stole the show. A study of it revealed some interesting things about capacitance and capacitive loads.

Another reason that the power supply has to be studied in such fine detail is because its design (and the rest of the entire project) has been literally made up out of thin air. I had no idea if it would work at all when I started. Its components are not carefully chosen and matched together. They are a collection of what was available on the junk heap. If it had not worked I would have had to study these fine details to find out what did not fit together right or what had to be replaced with something else. Fortunately, it worked even better than I thought it would and it was able to go even one step further to power the Jacobs Ladder. That did not even occur to me until I finished the testing.

So... let's get on with the testing. Because of the designs origin it has to be examined in every tiny detail starting with static measurements which are done before anything is activated at all. Some of these statistics are useful, some are just trivia that gets gathered along the way. You don't really know in advance which is which. Some of this data will only be useful for future experiments. It all has to be done carefully or it will be useless for whatever it gets used for.

There are also two new pieces of support equipment for the alternator that have not yet been tried. They were difficult to construct and have gathered a lot of dust while waiting to be tested.

A third piece of equipment has been created for the tests. It is a tachometer for the motor. The load of and on the alternator will be shown by how much the motor slows down. The alternator itself is like a transformer with one additional feature. The faster it spins the higher its voltage output is. When it slows down because of a load its voltage drops because of the speed decrease as well as because of the load increase. It would have been nice to measure the alternator speed directly. Its RPM is to high for the modified speedometer to measure directly. Speed reduction pulleys or gears would be to complex and expensive. Because of this compromise there is slippage of the pulley belt. That will greatly affect the accuracy of the measurements. The information it provides will still be useful but it must be handled in ways that take these errors into account.

Testing the Power Supply

Finally, with all preparations made, it is time to begin testing the power supply. This testing will go forward one tiny step at a time to gather as much information as possible. The first test is to measure the motor all by itself. The pulley belt is removed and only the motor with it large fan like pulley are plugged in. The second test is to add the pulley belt and measure the motor again. The third test is to remove the toothpick that has been holding back the brushes of the alternator. The motor is then measured with the additional load caused by that too.

Mechanical Load Tests

From this it can be seen that the load of the pulley belt is 38 Watts. The additional load of the brushes adds another 8 Watts. There are no connections to the alternator at this time. This is pure mechanical loading. It can be seen that the motor has caused an electrical load on the supply lines as its burden increased. The RPM readings are somewhat speculative. It could be seen that they dropped a tiny bit when the toothpick was pulled out, but the scale does not actually read that fine.

With the alternator brushes in contact to the rotor the resistance of the rotor circuit can now be measured. The measurement is difficult because it is a low resistance. The test clips and the rotor position have to be jiggled around to get the lowest reading possible. It measures 5.2 Ohms. After all tests were completed this measurement was taken again. It was the same.

The next test is to see if the car battery and the regulator can power the rotor. The car battery is an old one with a high internal resistance. It took a 6 amp charger an entire day to 'top off' the battery charge to the point that it was only drawing about 1 amp from the charger. The battery voltage before the next test series was 11.9 volts. The voltage after the tests was 11.6 volts. The voltage during the tests is shown in the table. The meter on the regulator showed 0 for all test entries except the last one (12 volt setting). On that setting it showed 25 mA. The battery was failing under the load and the regulator power supply had begun to help. These test were made while the alternator was stationary.

Rotor Load on Regulator

On the 6.0 setting I noticed that the power transistor was getting quite hot. It has no collector load resistor and so it must dissipate the resistive heat difference by itself with no additional heat sink. Through the remainder of the tests it had to be checked frequently. Once in a while the tests were stopped for a few minutes to let it cool down. It is a 2N3055 rated at 100 Watts. Overall it did pretty good.

The alternator is a standard Delco-Remy found in most automobiles. The voltage may be measured across any two of the three terminals from the stator. It is a Wye configuration. That means that each of the three stator windings is connected to a common ground. The alternator is rated at about 2.5 to 3 Horse Power. That is equivalent to 1520 to 2280 Watts. 1 HP = 760 Watts. That is input Horse Power. The efficiency is somewhere in the ballpark of 60 % +/- 10%. The output power for continuous operation should be 912 to 1368 Watts. A power pulse may be 10 to 100 times that much.

The other most common version of alternators is the 5 HP version. Its statistics are 3800 watts input power, and 2280 watts output power. It has a Delta configuration. That means that its three windings are wired in a triangle with no common ground. If you want maximum amperage use it as is. If you want maximum voltage you'll need to clip the winding between whichever two stator terminals you decide to use.

The maximum voltage that you can get out of either of these will be at least 600 volts and probably not more than 1000 volts before internal arcing occurs. They will function as a motor or as a generator. They may be used to bring power in from a windmill or water wheel at a high voltage. That allows the use of smaller cheaper power lines from the power source to the delivery point. At the delivery point the motor unit may then drive an inductive motor as a generator. That will allow the electricity to be automatically in phase when it gets put into the power lines.

An inductive motors true idle speed is 1800 RPM. Its maximum load speed is 1725 RPM. Its maximum generation speed is 1875 RPM. These are maximums for efficiency. They may be exceeded but the trade off is that you get lower power in or out of it. That is the reason the tachometer was added to the power supply. Future experiments will use it as a power plant instead of a power supply. The alternator will drive the motor (as a generator) instead of the way it is used here

The next series of tests are to see what is the maximum open circuit voltage that the alternator can produce at each setting of rotor excitation. DC motors and generators have a property about them called magnetization. This means that the rotor remains slightly magnetized even after the power to it has been removed. It is very important to not forget this feature! When the ignition coils are connected to the alternator later on they will deliver 480 Vac even when the rotor excitation is turned off. The power level can be as much as 2 Watts. That means if you are adjusting a Jacobs Ladder and you've made the mistake of thinking that it was safely off you could get electrocuted or shocked. The shock could cause you to land on the pulley belt when you fall back.

The measurements for the next series of tests are of the motor amperage & RPM and of the alternators input & output voltage. A new setting is now added for the magnetization effect. It is abbreviated as 0-mag in the settings column. The stator output voltage returned to 2.5 Vac between each of the settings tested. The initial motor amperage with no load was 5.7 amps. Between the test settings of 3.0 and 4.5 that no load amperage went up to 6.0 amps. This is attributed to fluxuating line voltage which has been recorded at a peak of 120 Vac and at a minimum of 117 Vac. The variation is due to other electrical loads (such as the refrigerator) and the long length of the electrical lines to the test site. It is made worse by the voltage drop across the two watt meters in series at the test site.

Stator Output Voltage for No Load

These tests show that the alternator is functioning as a magnetic brake even though it has no load. The last setting was a greater load than the motor could drive and it began to stall out rapidly. The wattage calculations used an arbitrary value of 117 Vac. The last entries were probably of a lower voltage due to the overloading. The amperage of the last entry was a starting point for a rapidly increasing amperage load of the motor. The motor is 3/4 Horse Power. It is only intended to deliver 570 watts of power maximum.

The alternator output voltage is directly proportional to the RPM. Because the RPM was going down as the magnetic loading increased, the true value of the output voltage could have been higher if the motor could have held a constant speed.

Now that we have some idea of what goes into the power supply let's see what we can get out of it. A collection of electric irons and hot plates was gathered and measured to use for test loads. The next series of tests will be to hang these loads on the alternator output and see what effect they have. The measurements will be of the amperage and voltage delivered to the loads along with the resulting RPM of the motor. The amperage and wattage of the motor can be constructed later from the RPM data. There is only one AC ammeter to use for testing. The alternative method presented in the section on measurements will have to be studied and analyzed before it can be considered reliable. It is not ready to use at this time.

Stator Output Power

The previous series of tests used all available loads until the motor stalled when the 6.0 setting was attempted. The next series is to explore how much loading can be used on the 6.0 setting.

The last entry gave some data because the stall was slow instead of the usual rapid overload. The next series is for the 7.5 setting.

The RPM of the motor with no load stayed at 1745 Rpm until the just before the last entry of the previous test. It only returned to 1740 Rpm and stayed there for the following tests. The next attempted test would have been for the 9.0 setting. The motor stalled with no load. The line voltage during the stall dropped to 112.5 Vac. The amperage started at 15 A, rose to 20 A and then proceeded to rise faster as the stall continued. The corresponding power consumption of the motor is 1687 W rising to 2250 W and then increasing. The stator voltage of 0-mag excitation was 2.6 Vac before and after the preceding three sets of tests. The motor amperage also remained the same at 5.9 A.

It may be noticed that the motor was able to produce 42.5 Vac for the stator tests with no load but could not do so in the above tests. This may be attributed to temperature. The stator tests with no load were done on a cool day. Several days later it was a much warmer day (almost hot) for the stator output power tests and for the following tests as well. Notice the voltage differences for the entries with no load. They should be the same.

Having determined that 10.4 Ohms is about the maximum load that the power supply can deal with at its maximum deliverable voltage of 37 Vac the above tests are now repeated for all the lower settings using the load of 10.4 Ohms. This will be the upper limit when the data is graphed.. The open circuit voltages are measured again in the process. These tests continued on the same day as the previous ones.

Stator Output Power using Constant Loads

The step up transformers that the power supply will use have a series and a parallel setting. The coils measure 1.2 Ohms each. The parallel setting measures 0.8 Ohms which is below the total of all available loads (1.2 Ohms). The series setting measures 2.35 Ohms. Loads are selected to produce a resistance of 2.3 Ohms and the test is repeated one more time.

The last test of the series stalled out to fast to get a voltage reading. The power could not be computed because of it.

The next series of tests would have been the testing of the high voltage transformer output. However since I did not have the data from the tests done so far I could not plan it out ahead of time. The results are few and unreliable. Different equipment and testing methods will be required to do it properly. The VOM can only read up to 1 kV. Only three readings were within that range. With the coil set to the series configuration the 0-mag voltage was 220 Vac. The output at the 1.5 setting was 420 Vac. With the coil set to the parallel configuration the 0-mag voltage was 480 Vac. The output for the 1.5 setting was off the scale.

An attempt to measure the voltage using a spark gap was tried. The breakdown voltage of air is 10 kV per 1/4". For the parallel configuration a spark was made at the 4.5 setting across a gap of 1/4". It did not arc across a ½" gap (20 kV). At the 6.0 setting an arc was made across a ½" gap but not across a 5/8" gap (25 kV).

At the 12.0 setting the series configuration arced across a 1/4" gap and the parallel configuration arced across a 5/8" gap. These are very unreliable measurements because the power supply is in the middle of stalling out as the magnetic field builds up. The actual voltage delivered by the alternator is in transition and beyond guessing at.