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awright

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  1. One resource for information on systems installed in isolated areas with basic system data, but not detailed schematics, is Home Power Magazine. Lots of discussion and examples of system design and capacity calculation. They offer CDs of multiple years of back issues on each. I certainly do not speak for the publisher, but perhaps you can appeal for a free set of CDs. awright
  2. Have you looked at thedata sheet for the tlp741g? http://www.toshiba.com/taec/components2/Datasheet_Sync//209/4322.pdf It is a low-current (150ma), moderately high voltage (400v) SCR with a photo sensitive gate that can be triggered by light from the embedded LED with LED forward current up to 10 ma. A resistor of 27K to 33K should be installed from gate to cathode of the SCR to suppress self-triggering due to leakage from anode to gate. It can be applied like any SCR except that you trigger it with forward current though the LED rather than by a voltage applied to the gate. The LED t
  3. PWM is not the only way to soft start a DC motor but it is certainly the most efficient way in most cases. If you just want to soft start the motor and have no servo control requirements, I would think any basic PWM generating IC driven by a ramp and driving a single IGBT or MOSFET of sufficient current/voltage ratings would do the job. I haven't actually done this myself, so do not have design details to offer but I don't think a great deal of sophistication is required. If you want something that's been designed for you, look at this CANA-KIT <http://www.sparkfun.com/products/9668>,
  4. Sorry to make such an obvious suggestion, but have you asked the manufacturer of the power supply how his unit will handle your load and what precautions to take? Looks OK to me but then, it's not my $12K. awright
  5. While it is true that a neon sign transformer is current limited by design, do NOT assume that you can be casual about dealing with the high voltage. It only takes 10-20 ma through the heart to throw it into fibrulation with possibly lethal results and I believe that neon signs operate on higher currents than this. I presume you do not have a spec sheet on your transformer telling you what the current limit is. In any case, the nominal current for fibrulation is an average. You or your guests may be more sensitive. Be sure there is no possibility of human contact with the hot secondary
  6. Why is this question coming up again? Did you post the same question on a different forum? The answer is the same as before. There is nothing at all critical about the SCRs used in this circuit. Any voltage rating will do because you can't find an SCR with too low a voltage rating for a full wave rectified 17 volt supply. Look up the current ratings of the two specified SCRs and find replacements with at least those current ratings. Specifications for both SCRs are available on line. You can find satisfactory replacements for less than a dollar at digiKey, Mouser, and many surplus outle
  7. Using a commercial HV probe like the Fluke suggested by Ken is definitely the best way to go. However, such an accessory must be used with a DVM having the proper input resistance. This is automatically taken care of if you use the probe with most Fluke DVMs. It will definitely NOT work with any arbitrary 30 volt analog panel meter. The reason is that the probe contains a high impedance voltage divider consisting of an approximately 1000 Megohm series HIGH VOLTAGE resistor (one that resists flashover across the resistor) and a nominally 1 Megohm shunt resistor to ground. The actual values
  8. I wouldn't try to switch the secondary current. Switch the primary on and off, as is done in a soldering gun. You will pay dearly for a relay that will work in your secondary circuit. Also, you will be adding contact resistance to the secondary loop where it will affect performance. Remember that you have 12 volts supply in the car, but only a few tenths of a volt in your rig. The voltage drop across any contacts in the secondary loop would seriously affect performance. You are not going to see anything approaching 1 volt across the tip of a soldering gun. After writing a rambling specu
  9. Google "Watchdog Timers." TI, Maxim, Analog Devices, and many other chip makers make devices with various levels of complexity and sophistication to restart a system if voltage levels drop below some threshold or if the watchdog input senses an absence of normal system activity or if it receives a reset pulse. They come with preset or adjustable time delays of milliseconds to seconds. They put out a delayed logic "0" or "1" that can be used for whatever you desire. If you already have and are happy with a pulse from your system to command a reset you can use a TDR (Time Delay Relay) They
  10. Your machine will run fine on the original fuses but you will lose protection in the event of a failure that would have blown the recommended fuses. I strongly recommend installing the recommended fuses but if it will take some time to obtain them from the states, I would go ahead and use the original fuses temporarily. Utility line voltages are rarely exactly the nominal voltages stated by the utilities. The long-term average there is probably a few volts different from 230 volts and the instantaneous voltage will fluctuate with instantaneous loading on the line. If you can obtain a mete
  11. That's exactly what the new "Smart Meters" that the utilities are at this moment investing multi-millions installing do. They are queried periodically and respond with the electrical usage information. I do not know what technology they use for the link to the utility. I also do not know how often the meter "reports in," but I believe that it will be several times per hour. One of the guys installing "Smart Meters" here in the San Francisco Bay Area for PG&E told me he did not know anything about the technology, but that he thought a satellite link was involved. He did not know if t
  12. What makes you think that you must smooth out the ripple on the full-wave rectified waveform coming out of the rectifier bridge for welding? Why would a smooth DC voltage/current work better than the raw rectified wave? The heating value of the arc will not be significantly affected. Now, there IS good reason to provide an inductor on the output, but it is generally referred to as an arc stabilizer because it helps maintain the arc across the nulls of the rectified waveform. It also affects the handling characteristics of the arc, but not, I believe, because the DC is smoother (except that
  13. Are you still there and still interested, 89Panadol? Most likely your relay has a coil with too low a resistance. What type of relay is it and what is its coil resistance? How much current does the coil draw if connected directly from your 12 volt supply to ground? How does that compare with the maximum current rating of your darlington output stage transistors? What is the current capability of your 12 volt power supply? Is it capable of driving the relay coil directly? Measure the 12 volt supply while the device is trying to close the relay to be sure it stays at 12 volts. Your darli
  14. It would be more useful for you to tell us what you are trying to heat. It is straightforward to calculate the POWER dissipated in a given length of a given type of wire at a given voltage. Except for very standardized conditions and media, calculating the TEMPERATURE attained (In the wire? In the fluid medium? In the surrounding insulator?) is a very complex calculation involving surface areas and shapes, fluid flow, Reynold's numbers, thermal conductivities, etc. Consider a small space heater. The thermal POWER put into the room is fixed by the electrical characteristics of the heating
  15. stube40, what ever happened with your high power test load? awright
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