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 > Your search for posts made by 'LScamper' found 61 matches.

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RE: Exceptionally Good LED Power Tutorial

The reason for not using current limiting resistors to drive LEDs. Assume one 3.3V LED running off 12.5V at 20mA using a current limiting resistor. Voltage drop across the resistor, 12.5V – 3.3V = 9.2V. Resistor value, R=V/I, R= 9.2V/.02A, R = 460 Ohms. Power dissipated in LED, P=VI, P=3.3V*.02A, P=.066Watts. Power dissipated in resistor, P=VI, P=9.2V*.02A, P=.184Watts. Total power from power supply, P=VI, P=12.5V*.02A, P=.25 Watts. Efficiency = Pled/Pin, .066W/.25W, Efficiency = 26.4%! Not good. If voltage goes up to 14V then: Voltage drop across the resistor, 14V – 3.3V = 10.7V. Resistor value from last calculation, R = 460 Ohms. New current in LED and resistor, I=V/R, I=10.7V/460 Ohms, I=.023A. Power dissipated in LED, P=VI, P=3.3V*.023A, P=.076Watts. Power dissipated in resistor, P=VI, P=10.7V*.023A, P=.25Watts. Total power from power supply, P=VI, P=14V*.023A, P=.322 Watts. Efficiency = Pled/Pin, .076W/.322W, Efficiency = 23.6%! Not good. From this it can be seen that the LED current will go from .02A with a 12.5V source to .023A with a 14V source. A current increase of .003A or an increase of 15%. Not too bad. A current regulated power supply will hold the current to .02A and still have an efficiency of around 90%. Note it has to be a switching supply, a linear supply will be no more efficient. So what happens if you put several LEDs in series, lets say 3 LEDs. Total voltage across the 3 LED string, 3 * 3.3V = 9.9V. Voltage drop across the resistor, 12.5V – 9.9V = 2.6V. Resistor value, R=V/I, R= 2.6V/.02A, R = 130 Ohms. Power dissipated in LEDs, P=VI, P=9.9V*.02A, P=.198Watts. Power dissipated in resistor, P=VI, P=2.6V*.02A, P=.052Watts. Total power from power supply, P=VI, P=12.5V*.02A, P=.25 Watts. Efficiency = Pleds/Pin, .198W/.25W, Efficiency = 79.2%! Much better. If voltage goes up to 14V then: Voltage drop across the resistor, 14V – 9.9V = 4.1V. Resistor value from last calculation, R = 130 Ohms. New current in LEDs and resistor, I=V/R, I=4.1V/130 Ohms, I=.0315A. Power dissipated in LEDs, P=VI, P=9.9V*.0315A, P=.312Watts. Power dissipated in resistor, P=VI, P=4.1V*.0315A, P=.129Watts. Total power from power supply, P=VI, P=14V*.0315A, P=.441 Watts. Efficiency = Pled/Pin, .312W/.441W, Efficiency = 70.7%! Not as good as with 12.5V. From this it can be seen that the LED current will go from .02A with a 12.5V source to .0315A with a 14V source. A current increase of .0115A or an increase of 57.5%. Not very well regulated with using a resistor and may well destroy the LEDs A current regulated power supply will hold the current to .02A and still have an efficiency of around 90%. Note it has to be a switching supply, a linear supply will be no more efficient. If you look at a voltage from 10.5V, a dead battery to 14.8V when charging the current regulation with a resistor is really bad and most likely will cause a disaster. Hope I did not make a math error!
LScamper 03/26/14 04:09pm Tech Issues
RE: Not Balancing Three 12v Right

pianotuna wrote: “Balanced? *grin*” My post above was not meant as a joke, it was offered, free to use, as an alternative way to wire three batteries in a “balanced manner” as you like to say. I know that no two or three batteries are exactly the same but that is the assumption that is made every time someone on the forum talks about balanced manner. That is the assumption I will use here. As MEXICOWANDERER offered it is time to introduce Mr. Kirchhoff. His laws I became friends with almost 50 years ago. If someone takes the time to do the analysis it will be found that the star configuration and the parallel link configuration are electrically the same, no difference. The trick is to make the link from the + terminal of battery 1 to + terminal of battery 2 and the link from the – terminal of battery 2 to – terminal of battery 3 equal to on half the resistance of the other two links. This is done by putting two links in parallel. Do the analysis!
LScamper 03/19/14 10:04am Tech Issues
RE: Not Balancing Three 12v Right

There is more than one way to skin a cat for those that want to exactly balance the current in three batteries in parallel. The standard way is to use a star configuration with equal length links to each battery. This will exactly balance the current in the three batteries. There are other ways to balance three batteries also. Assume three matched batteries. Assume all interconnect links are the same length and gauge cable. Batteries are connected as usual: Load at opposite ends, + lead from + terminal of battery 1, - lead from – terminal of battery 3. Link 1 from + terminal of battery 1 to + terminal of battery 2. Link 2 from – terminal of battery 1 to – terminal of battery 2. Link 3 from + terminal of battery 2 to + terminal of battery 3. Link 4 from – terminal of battery 2 to – terminal of battery 3. Now to make it balance: Put another link from + terminal of battery 1 to + terminal of battery 2, making it two links in parallel from + terminal of battery 1 to + terminal of battery 2. Put another link from – terminal of battery 2 to – terminal of battery 3, making it two links in parallel from - terminal of battery 2 to – terminal of battery 3. Adding these two links will make the current in the three batteries exactly match and may be easier than making up a star configuration. There are other ways to do this by using different lengths of cable between the batteries but this is the easy way.
LScamper 03/17/14 02:40pm Tech Issues
RE: RV Plan 'N' Go 2013

It is junk, forget it! Maybe in a year or two they may get it to be usable.
LScamper 02/22/14 09:18am Technology Corner
RE: More Griping About Missing Standards LED lamps and lumens

GordonThree thanks. I guess that as long as all the LEDs are on a common heat sink so they are at the same temperature the forward voltage will track OK.
LScamper 02/21/14 10:16am Tech Issues
RE: More Griping About Missing Standards LED lamps and lumens

GordonThree wrote: "However, you could run six or nine leds, in parallel strips of three." LEDs need a current source as you have said. This controller is a current source. The LEDs need to be in series so all LEDs see the same current. If they are in parallel they would have to be matched exactly to share current, this won't happen. A parallel string is not a good idea in my opinion.
LScamper 02/21/14 09:06am Tech Issues
RE: Rechargeable Batteries

eneloop specs: clicky
LScamper 02/18/14 10:00am Technology Corner
RE: Frank's autotransformer question.

pianotuna wrote: "This will regulate both high and low incoming line voltage. I emailed Sola. The 60 va unit, which would be wonderful for a 30 amp RV, is about $411.00 plus shipping." Did you really mean 60 VA? That would be OK for a 60W bulb. I think you need the 5000 VA unit, at 222 lbs that would be a bit heavy to carry plus expensive.
LScamper 02/18/14 09:48am Tech Issues
RE: Rechargeable Batteries

clicky
LScamper 02/17/14 09:58am Technology Corner
RE: 80VDC 10A fuse?

KD4UPL wrote: "When the fuse blows there will no longer be a short. The panel will return to Voc. If the gap left in the blown fuse isn't large enough the Voc may arc the gap." In air at atmospheric pressure it is impossible for an arc to start at less than 327V.
LScamper 02/09/14 11:03pm Tech Issues
RE: 80VDC 10A fuse?

No need for a fuse as it will never blow. (Salvo X2) "Fuses are to protect the wire--not to protect devices so that is why I'd use a 30 amp fuse with #10 wire." X2. Small point to remember, the fuse should be located at the source. In this case at the panel to protect the wiring just as a fuse should be located at the battery if it is to protect the wiring.
LScamper 02/09/14 09:50am Tech Issues
RE: Helping

"If you can't fix it with a hammer, it's an electrical problem." ? I always fix old TVs with a hammer. Works most of the time.
LScamper 02/05/14 09:33am Tech Issues
RE: Big Project LED's

"do you have a engineering link, wiki's are NOT always correct" http://www.learnabout-electronics.org/ac_theory/ac_waves02.php http://arcarc.xmission.com/PDF_Electronics/Alternating%20Current%20-%20Part%202.pdf
LScamper 01/28/14 11:20am Tech Issues
RE: Big Project LED's

MEX heat sink http://www.allelectronics.com/make-a-store/item/HS-176/17.25-ALUMINUM-HEATSINK/1.html should be about .3 degree C / Watt in free air. So say max temp is going to be 65 degree C and ambient is 25 Degree that would be a 40 degree rise. So LED power could be 40/.3 = about 130W LED dissipation with that heat sink, more with fans. Not sure what the max temp rating of the LEDs are but this gives you an idea of what to expect. Also the LEDs will only conduct when the voltage is over their forward voltage drop rating. 33V x 4 = 132V. At that point they will draw a very high current spike. It will last long enough to smoke them. "Hoping the watts area under curve would be small enough for the devices to take it." It is the peak current that will kill the LEDs, not the average power. The peak current will last long enough during the peak of a half cycle that the LEDs think it is almost continuous power.
LScamper 01/25/14 05:03pm Tech Issues
RE: Big Project LED's

Gdetrailer wrote: "Half Wave rectification without filter caps will result in HALF the voltage at 89V in theory but in practice generally you can count on about half of the AC RMS or about 60V-70V. Assuming those LEDS are designed from 32V to 36 V or 96V-108V for three in series which should be well high enough." Not correct but not going into it. The LEDs will see the peak voltage of about 180V. At that time the current will be at maximum, well over what it is at 127V. The LEDs are sensitive to peak current and will smoke. Also, dissipating 400W will need a huge heat sink with fans on it. Or maybe water cooling.
LScamper 01/25/14 11:31am Tech Issues
RE: Big Project LED's

MEX wrote: "(4) 33 volt 100 watt LED's wired in series, with a 25 amp 800 PIV stud mounted rectifier for 127 vac operation. Dang I wish this would work, it would save me a lot of money. Or then it might make the prettiest smoke signal" Don't forget that the peak voltage is 1.4 times the RMS voltage. 127 x 1.4 = 178V! It will make a pretty smoke signal.
LScamper 01/25/14 10:09am Tech Issues
RE: Pure Sine Wave Inverter

I used a 1000W MSW inverter for years on several TVs, DVR, computer, and on my VIP211k sat receiver. It worked fine! Just bought a Samsung 32" TV. When I plugged it into my MSW there was a pretty loud buzz coming from inside the TV. It worked OK but I thought that the buzz was a sign of problems down the road. Better safe than sorry so I bought a 300W Go Power PSW inverter and it works fine, no more buzz! The buzz may be from an inductor in the switching power supply saturating because of the low peak voltage of the MSW inverter. Just guessing on that.
LScamper 01/16/14 06:40pm Technology Corner
RE: HELP AC Outlets blowing devices!

An open neutral between service panel bus bar and utility transformer would smoke things in the house as well as the RV. Problem should be between service panel bus bar and RV distribution panel. Start by loading as mex said but start at the house connector before plugging in the RV. Then work to the RV.
LScamper 01/06/14 09:56am Tech Issues
RE: HELP AC Outlets blowing devices!

MEXICOWANDERER has the best 100% sure way to find an open or high resistance nuetral. Do not plug in anything to the 50A plug until the problem is found. You will just destroy more equipment.
LScamper 01/05/14 09:46am Tech Issues
RE: Multi-meter recommendations, please!

Sorry for the overload! "I know a few people who have private museums of vintage test equipment" You must be talking about me. EICO Model 950B AC bridge, EICO Model 324 RF signal generator, EICO Model 425 5" Push Pull Oscilloscope, EICO Model 232 VTVM, battery eliminator with volt, current and a variac to set it and several other EICO items. Most bought by saving lunch money in 7th > 12th grade, late 50s early 60s. Still have the instruction manuals and the construction manual for them! Also have RCA Senior VoltOhmyst, Simpson Model 377, Triplett Model 666-R, and Triplett Model 310. A few other old meters laying around too. Have several Fluke meters some that I have used from the early 70s. Oh and one TEK RM 45 to heat the house! OK, back to this thread. If he is a true engineer he will appreciate quality equipment. You can'nt get better than Fluke! If he would like an oscilloscope, for about $400.00 on Amazon you can get a Rigol DS1102E 100MHz Digital Oscilloscope. It is a very good scope for little money for a scope. I have had one for about 3 years and really like it.
LScamper 12/21/13 07:05pm Technology Corner
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