Where to start? You can "get away with" a lot of things. Probably, there was a combination of enough resistance in the string of LEDs in series, combined with a low enough battery voltage & low discharge rate from the battery to keep anything from frying, at least in the short term. Let it run for awhile & you might have a problem. I know that probably doesn't mean much to you right now. Suffice to say that you got lucky. Nothing wrong with that at all. Sometimes, just playing around with stuff like that helps you get started, to see what works & what doesn't. Just be careful not to start any fires larger than what you can put out! The reason for the resistor(s) is to limit the current that flows through the LED(s). Current is what makes things go. Too much current can make them burn up, or maybe just keep your battery from staying charged as long as it should. Whether LEDs are connected in series or parallel isn't really what determines whether or not you need a current-limiting resistor; you need it. Series vs. parallel determines the VALUE of the resistor(s). To demonstrate, go to the LED calculator link I gave you earlier & play with that a little. Use the same values for voltage, voltage drop, & current for the same number of LEDs, in both series AND parallel configurations. See the different resistor values that you get. Probably the most important thing for you to understand at this side is Ohm's Law: E = I * R E = Electromotive Force; in other words, Volts. I = Current; measured in Amperes, also called Amps. R = Resistance, measured in Ohms So, Ohm's Law establishes the relationship between Volts, Amps, & Ohms. If you have a 6V power supply, & you want to limit current to 25 mA (milli-Amps, or 1000ths of 1 Amp; 0.025A), then what resistance do you need? From Ohm's Law we know that E = I * R. Our value for E is 6 (Volts). Our value for I is 0.025. We need to solve for R. 6V = 0.025A * R R = 6 / 0.025 R = 240, or 240 Ohms. Many times, a "ballpark value" is all you need. Also, it's often a good idea to "pad" it a little, for safety. It may help to think about electricity in terms of equivalents in a fluid system: Voltage is similar to Pressure (i.e. PSI). Current is similar to Flow Rate (i.e. GPM, GPH, etc.). Resistance is similar to Pipe Diameter. For a given pressure, changing the pipe diameter will affect the flow rate, etc. The relationship of pressure, pipe diameter, & flow rate is similar to Ohm's Law. Regarding the specifics or your setup: 3 3V LEDs: 3V refers to the maximum rating, in other words, what's the HIGHEST voltage that you should put on the LED? Battery: I have no idea what battery you used. There are a lot of different battery types, & if you'll tell me exactly what battery you used, I can tell you a little more about what's going on & why it worked the way it did. I'm guessing your battery is NOT a 12V SLA, & if you tell me what battery you DID use, I'll tell you why I made that guess. For 10 3V lights (LEDs?), whether to use series or parallel? I'd use parallel for ANY number when it comes to wiring up something for your ship. In series, as soon as there's 1 failure, the whole bunch go dark. Ever have that happen in a Xmas tree light string? It's hard to find the bad one, isn't it? Same thing here. There are other reasons, but that's probably enough. How to drop from 6V to 3V. I'm guessing that you have a 6V battery to go with your 3V LEDs. If it were me, I'd get a higher-rated LED. You could also use a voltage regulator (which works very much like your CO2 regulator, stepping a voltage down instead of a pressure). You could also add a resistor to the + side of the LED. What resistor? I'll let you figure that out! This post is getting long enough. Give it a try & I'll help you later if you need it. Hint: Use Ohm's Law. Hint #2: With a single resistor in a circuit, the supply voltage drops to 0V across the resistor. Where there are multiple resistors in series, the supply voltage drops to 0V across ALL of the resistors, but some lesser amount of voltage drops across EACH resistor INDIVIDUALLY. "I have no idea if the Ohm output of the battery is different than the voltage": No such thing as "Ohm output". Ohms are a measure of resistance, which is a force that opposes the flow of electrical current, kind of like friction in a mechanical system. A battery produces a voltage potential across its terminals. If (& ONLY if) the terminals are connected together, creating a circuit, then the battery will produce an electrical current that flows from the higher-potential terminal to the lower one. With no circuit, there is no current (infinite resistance). The simplest circuit would be just a piece of wire. With, for all practical purposes, no resistance at all, current will be nearly infinite (at least, up to the battery's ability to discharge). That's when you get big sparks, smoke, melted insulation, & other bad things. Chew on this for a little while, do some more experiments, & see what other questions you might have. Try to understand WHY things work the way they do, not just WHAT they do. If you can do that, you can make ANYTHING work. JM
I think I have been confused from using the diodes with the delta boards. I guess I was thinking the resistor dropped the voltage like the diodes do to drop the 6V to 5V. But what you are saying is that a 100ohm resister only lets through 100ohms, not dropping it by 100Ohms. If that is the case then it makes complete sense. I was using a 6v sla battery and based on what you said, 3 leds in series. Does the 100ohm resistor drop the voltage as well? I think I just about have it. Thanks
I think you are not quite grasping the whole picture. There are several fundamental properties in electronics to consider. So lets take a look at the basics... (all steady state for now, transients, logic, Impedance, ac, etc can be covered at a later date) as a side note, some folks use E for the electric potential, and some use V. Electric potential drop is sometimes shortened to voltage drop (which I tend to use, but I am using E to try to be consistent with john) Ohms (Greek letter Omega) are a unit of resistance (R) Volts (V) are a unit of electric potential (E) amps (A) are a unit of electric current Now lets look at some of the critical math. there are two, from which all other stuff springs or depends E=I*R. Now consider this. this is for the voltage DROP through some resistance at some current. I.E. If you have a known current flowing through a known resistance, the electric potential drop (in volts) between the two ends of that component will be I (current in Amps) X R (resistance in ohms) The second big one is P=I*E The Power, P, (in Watts) dissipated by a component is the current through the component multiplied by the electric potential drop across that component. these two equations can be rearranged to form all manner of useful ones. see the following link: http://xnet.rrc.mb.ca/rcharney/OHMS_Law.htm Now lets consider a diode: A diode is a device that has a forward voltage drop and a different reverse voltage drop (we will assume both are constant for now). Basically it is sort of like a check valve. The forward voltage drop will be small, while the reverse will be large. In the LED realm, the forward drop is typically between 1-6V with others available. LED's will also burn up if you heat them up to much, or in other words dissipate too much power. now take a look at the second equation: P=I*E. P=power.... if you have a current through an LED, and a voltage drop, E, then you have turned electrical potential energy into thermal (heat) energy. Produce too much and the LED dies. The LED datasheet will give you a maximum power dissipation, generally as a function of ambient temperature, as well as maximum sustained and transient currents. You need to set up your circuit so that you maintain the dissipated power below the max allowed for the led at all times (since we are in steady state). LED's also have rather poor tolerances on the voltage drop, meaning that even though the datasheet says say 3.0V, it may be +/- some tolerance value. this is why paralleling LED's can lead to trouble. If the LED's are not close enough to the same (or change over time) one LED will allow more current to flow through it than the others, and if that exceeds the LED's power dissipation limit, the LED WILL eventually die a premature death. That is where the resistor comes in. If you look at the tolerance band, select the minimum voltage drop for the LED (which might be 2.8 or 2.9V for a 3V nominal LED) and subtract that value from the maximum voltage your source (battery for example) can ever produce (about 6.5V for SLA batteries) you can then pick a resistor that prevents more than the max current from flowing through that leg of the circuit. You could series two or three LED's and then select the appropriate resistor but there is greater variation there (google tolerance stackup) and at least where I work, had bit some folks. The bulletproof way is to put one LED in series with one resistor. So, say you have your 6.5V SLA battery and want to light one LED... Say that LED has a power dissipation limit of 65mW (.065 Watts) and a nominal forward voltage of 3.0V with a tolerance of +/-.1V. Worst case would be a voltage drop of 2.9V on that LED. Now what is the max current that lED can safely handle? P=IV .065Watts = I X 2.9V solving , you get that I = .022 Watts/V = .022 Amps or 22 milliAmps so we need to limit this LED to less than 22 milliamps. I tend to add a bit of conservativism in and will round this down to at the most 20 milliamps just to give a bit more head room. Now go back to your battery: you start with 6.5V rise (6V nominal, 6.5V max) from the negative pole. now 2.9V are reduced through the diode, leaving 3.6 V left. That will allow a lot more than 20 mA to flow through the LED. we need to limit it. so we place a resistor in series with the LED. If that resistor is chosen so that it sees a 3.6V drop at 20mA of current, then this LED will not see more than 20mA of current, and we will have a working LED. So look at the first equation: V=I*R 3.6V = .020Amps X R or R=180 V/Amps = 180 Ohms so go buy a 180 Ohm resistor (or a bit larger if you want to be even more conservative) in this example. Your specifics will vary based on LED and voltage source you have
Sorry about all the ?... I'M still ADHD and it can take a while to sink in but I finally have it. Thanks Guys. I could never quite figure out how to choose the resister but now it all makes sense and I know how to calculate it. Thanks guys!
I don't know what a "delta board" is. Please explain. Yes, to a point. Pretty much everything has SOME resistance, including a diode. You will see a voltage drop across a diode in a circuit. You will also see a voltage drop across a resistor in a circuit. Ohms do not "get through". Ohms are units to measure resistance. Resistance is what opposes or restricts the flow of current through a circuit. Yes, there will be a drop in voltage across the resistor. Use Ohm's Law to figure out exactly what the voltage will be at the following points in the circuit: '+' side of the LED; between LED & resistor; between resistor & '-' terminal of the battery.
I am about to build my string. I got some resistor thought they are large (but the smallest 180ma they had). I want to put a strobe light on one end of the ship. Is there a resistor that will do this? Anyone know an easy way?
Well made a light string to test the idea. It doesnt work. They lit for an instant and I assume died forever. I bought 280ma resistors (there werent any small ones) and tried to follow the diagram that was posted on this thread. Does the direction matter on the resistors? I think they might be wrong as its obvious the 6v is too much. My understanding is that the resistor would limit power to 280ma but does that reduce the voltage as well? Does anyone have anyone have any ideas where I went wrong? I connected one end straight to my 6v gel cell. Thanks
280 mA current sounds a bit high... in fact it sounds about 10 times too high for most LED's I deal with on a daily basis. do you have a link to the datasheet on those LED's you were using? If they came on and then died, you most likely burned them out. You may want to limit them to 20mA-30mA depending on the LED specifications
Please don't "think"; take a few extra seconds & check to be sure. Not to pick on you, Joker, but that's a real problem with technical issues in forums like this. Somebody posts what they "think is right", & somebody else who doesn't know better takes that as being "right" & runs with it. The fact is that the long lead in a standard LED package is the anode (+) lead, so you were right. Without actually checking your facts, though, you had a 50/50 chance of being wrong, & giving somebody wrong information. It only takes a few seconds to look up the answer to something like this. Please, everybody, take those few more seconds. Further confusing somebody who's already confused doesn't help matters. JM
There is no such thing as a "280 ma resistor". As long as you insist on using incorrect terms, it's going to be very difficult (if not impossible) for people to help you. Resistors are rated in 2 ways: - Resistance, expressed in ohms or some fraction/multiplier thereof. This often includes 1000-ohms (kilo-ohms, k-ohms, or just "k"; 10^3), 1,000,000-ohms (mega-ohms, M-ohms, or just "M"), thousandths of an ohm (i.e. 1/1000 ohm; milli-ohms; m-ohms; 10^-3). Resistance is how much something "resists" the flow of current through itself. Everything has some resistance (except "superconductors", but don't even think about stuff like that). - Power, expressed in watts (usually 1/4 watt, 1/2 watt, 1/8 watt, or 1 watt). The power rating of a resistor refers to how much power you can run through it before it melts down. No. Resistors are not polarity-sensitive. I have no earthly idea, since you're using terms inappropriately. Well, that's (connecting one straight to a battery, without any current-limiting) liable to fry most LEDs. Honestly, getting light out of a LED is about the most simple, basic electronic circuit there is. If you're having trouble getting that right, then maybe you shouldn't be messing around with electronics at all. OTOH, if you can make it work, you'll find all sorts of uses for it, including figuring out whether or not other things are working. Actually, the simplest, most basic circuit would be a battery & a resistor. Start there. Figure out the voltage drop across some random resistor, then measure it & see if you were right. Figure out the current through the circuit, then measure it & see if you were right. Did you smell or see any smoke? If so, ask yourself why (the answer will have something to do with current, which is expressed in amps). Repeat for several different values of resistors. Get comfortable with the ideas of resistance, current, & power. To make your LED string, back up a few steps. Start with a(n) LED(s) that is(are) rated for the voltage you're going to be using. Then, with your comfortable knowledge of the relationships among voltage, current, resistance, and power, figure out the appropriate resistor(s) for the LED(s) you have chosen. JM
i have some LEDs on my ship and thay do work http://www.rcnavalcombat.com/FileManager/Storage/633420756235781250.png i dont remember what resistors i used but colored stripes around it. 2 are orange, then one brown
2 orange, one brown, assuming left to right reading, would be 330 ohms http://www.dannyg.com/examples/res2/resistor.htm
What do you think? See: http://physics.nist.gov/cuu/Units/prefixes.html http://dbhs.wvusd.k12.ca.us/webdocs/Metric/Metric-Prefixes.html JM
Well when I went to the store I got 280ohm resistors from the bin. When I looked up the bands it said 2.8k so I am confused. Either they put the wrong resistors in the bin or 2.8k and 280ohms are the same. If I had grabbed resistors from the 2.8k bin and not the 280ohm bin then it would make more sense. As I am not an electronics engineer I just wasnt sure about any abbreviations or naming shortcuts for these things. I just did a search online and found that there are 1/4w 1/8w and 1/10w 280ohm resistors. I am not sure if I missread anyones earlier posts but I didnt see where I take that into account in the calculations. I think in the end just a 280ohm or 240ohm result was giving. How would I determine which wattage I need beyond the 240 or 280ohms that was calculated? Thanks
