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darrins

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Everything posted by darrins

  1. I considered using a timer. This is definitely a more economical and simpler approach. My appliance will dispense different kinds of powders with different characteristics, e.g. density, so I'll have to experiment with this to see if it is accurate enough. I appreciate the feedback. Darrin
  2. Thanks Ante. I ordered a couple of free sample MOC3041's from Fairchild. I found a schematic in the data sheet that has me a little confused. On page 5 of http://www.fairchildsemi.com/ds/MO/MOC3041-M.pdf, there is a circuit that shows 115V AC connected to the MOC3041. At pin 2, there is a symbol that looks like a plug. I believe this is a symbol to a 2 input NAND gate, but I'm not sure. ??? I want to make sure I know what I'm doing before I go messing with the AC. :o It seems like I could just put a relay betwen pins 1 and 2 to toggle this circuit. ??? Thanks again for you help. Darrin
  3. Just from experimenting with the heating element with 110V AC, my water tank gets too hot, too rapidly. The resistance of this heating element is VERY low, about 20 Ohm. From Ohm's law, this would be around 600 W (if my math is correct). So, I need even less power than 600W. I only got the triac with such a high voltage rating, because I read somewhere that it was wise to buy components with higher volt/amp ratings than you actually need. I will look into those triac drivers that you mentioned. One thing I'm concerned about is that the pins on the triac are very close together (about 2
  4. In a previous post, I asked about designing a controller to regulate the temperature of a small tank of water. Ante suggested using a triac to control power sent to the heating element. After some reading, I also agree that this is a good technique; however, I haven't been able to find any circuit examples on the web. My problem seems fairly simple. I have an aluminum tank with a flexible heating element wrapped around the outside surface of the tank. I would like to set a desired temperature using a potentiometer. I have a temperature sensor IC's that measures degrees Fahrenheit (10 mV per deg F). I put the IC in some copper tubing and sealed the end, making a temperature probe. This probe will be submerged in the water tank. I figure that a couple of comparator circuits could be used to compare the temperature from the probe with the desired setpoint and these comparator circuits could then control voltage to the gate terminal of the triac. Anyone know of an example that uses a simliar technique? The triac I have is NTE5629 rated at 400V and 4A. (Here's the datasheet http://www.nteinc.com/specs/5600to5699/pdf/nte5629.pdf). The triac came with a mica washer, which I assume goes between the metal part of the triac and the heat sink. Thanks in advance for any help. Darrin
  5. I'm working on an appliance that dispenses a powder from a hopper using a feed screw. I want to control the dispensed quantity by measuring the weight loss of the hopper. This change in weight will be on the order of 7 grams to 40 grams. I figure that this could be done by either: a) using a spring and measuring the deflection by a LVDT or b) using a strain gage load cell I'd prefer to use the load cell, but they are quite expensive. I have some literature on how to build a load cell, but I need to find out where I can buy inexpensive metal foil strain gages. Any suggestions? Thanks. Darrin
  6. Anyone know where I can buy cheap metal foil strain gauges? I'm trying to make a "poor man's" load cell. Thanks. Darrin
  7. I agree with audioguru. If you apply apply a huge force to a stationary object for a nanosecond, you probably won't move the object. To move a large object (do some work), you have to apply a considerable impulse. This is the area under the force vs time curve. Even though you have a large amplitude, you can't get any useful energy out of pulses that have too small a duration. cheers Darrin
  8. Any water heating experts here? I have a flexible heating element that is wrapped around an aluminum cylinder that contains water. It contains about 12 oz of water at room temperature. I want to heat the water to around 100 degrees Fahrenheit from an initial temperature of about 74 degrees Fahrenheit. I want to heat the water slowly, say during a 30 sec to 1 minute interval. My question is: How much voltage should I apply? From some quick and dirty calculations, I think this requires about 700 to 1000 watts of energy. I've tried hooking my heating element directly to an AC outlet and it gets HOT FAST! :o AND results in uneven heating. I'd also like to know if AC is more efficient when it comes to heating elements than DC. Something tells me that AC would be better, but I don't have anything to back that up. Also, I'd like to make a simple bang-bang controller that applies this voltage when the water temp falls below some value, say 95 deg and turns off this voltage when water temp rises above some value, say 105 deg. Can someone point me in the right direction? Thanks. Darrin
  9. I like the Moderator's idea, but would this device accidentally get triggered by other noisy power tools? (obviosly the power to YOUR device would have to be ON). Just something to keep in mind. Here's a poor man's solution: Do you have to pull a trigger to operate the saw? If so, can you somehow use the same trigger for your vac? 8) Good luck. Darrin
  10. Here's a cool website that shows an animation of a 555 timer in astable mode. http://www.williamson-labs.com/480_555.htm To stop the timer, you can ground pin 4 (reset). Cheers. Darrin
  11. The 555 timer should be wired for astable mode for your application. I believe that there should be two timing resistors for astable mode and that pin 7 is wired at the junction of these two resistors. Here's a good website for a tutorial on 555 timers. http://www.uoguelph.ca/~antoon/gadgets/555/555.html I'm not sure about your replacing the 2N3053 with the TIP120 darlington. I'm sure someone more knowledgeable than myself can address that one. Good luck with your project. Darrin
  12. I just remembered that these temperature IC's have an upper range of about 300 deg Fahrenheit (about 150 deg C). This is probably good enough for your project, but just another thing to keep in mind. I think a typical automobile will overheat at about 240 deg F, but that's a water cooled engine. Is it possible that go-cart temperatures (I'm presuming air-cooled) will be much hotter? Good luck with your project. I'm a mechanical guy myself, so I'll be interested in your results. Darrin
  13. Have you considered using the LM34? It's already calibrated in degrees Fahrenheit. I'm from the states, so I prefer the English units. ;) It seems you could just use a simple comparator circuit. The following document has a lot of specs and some good application examples. See their example of the "Simple Fan Controller". I think it is similar to your needs. http://www.national.com/appinfo/tempsensors/files/temphb.pdf If you have to put the sensor in a hostile environment, you may want to put the IC inside a metal tube. I've noticed that the plastic package fits neatly into a piece of copper tubing (the kind you hook up to your refrigerator's ice maker). Copper is quite malleable, so you can just pinch the end with a pair of pliers to seal it. Copper is also an excellent thermal conductor, so you should get a nice response time. Good luck. Darrin
  14. I'm not sure exactly what you mean by "protective ground". When I built my other power supply, I used and old 3-pronged power cable from one of my old computers. It is my understanding that the middle prong is earth grounded when plugged into an electrical outlet. I wired this middle prong to the metal frame of my power suppply. Is this the right thing to do? On this 20-yr old power supply, theres a connection labeled "GND", so I'm assuming this is ground. I was planning to wire the middle prong of my power cable to this connector. Bad idea?
  15. I didn't notice any improvement with 47 uF. I tried a couple of large caps (1000 and 2200 uF) with varying results. Is the decoupling capacitor suppose to handle the sudden voltage requirement of the pump at startup? If so, shouldn't this capacitor be close to the supply leads of the pump? On another note, I bought a 20 yr old power supply from my local surplus shop for about $14. It has a few transformers and a couple of sets of rectifying diodes. It has 6 different output posts, so it appears that it will give me the decoupled power source that I'm looking for. Not the most elegant solution, but a solution nonetheless. Thanks again for your help. I'm a mechanical engineer, so I'm quite a novice at electronics. I've already flipped the circuit breaker in my garage a few times and smoked numerous IC's, but I'm learning. Haven't zapped myself yet (knock on wood).
  16. Thanks for the advice. I'll try it. The "dip" in voltage seems to be only a transient that lasts while the pump is starting up until it gets to its steady state running condition. I'm not sure what value of capacitor I should use. I suppose I'll just experiment until I get it working correctly. Thanks again. Darrin
  17. I am new to electronics, so I apologize for my ignorance. I working on a project that involves emptying a small tank of water using a solenoid valve. The valve is opened for a certain amount of time by using a 555 timer and a reed relay. When this timer goes low, the valve is closed, and another 555 timer turns on a 12V pump (again via reed relay). I have the 2nd timer set up so that it will run much longer than I actually need it to. When the water reaches a wire at the top of the tank (connected to pin 4 on 2nd 555 timer), I want the pump to cut off. The problem I'm having is that the pump draws a lot of current, which seems to drop my supply voltage, which triggers the first timer. This results in the valve just opening and closing (pump never comes on). From what I've read, I think I need some decoupling capacitors. I've tried this, but my circuit still behaves irradically. Any suggestions? Thanks in advance. Darrin
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