I bought these lights from Evemodel and they say "must connect (supplied) resistor in series before you will use them on 12V or 16V". As can see there are 10 lamps with 2 LEDs each and, using their included resistors, my question is IF I DOUBLE THE VOLTAGE (am using a 24v dc pulse modulator for 'old' switch machines as well) WOULD CONNECTING TWO IN SERIES (onto only 1 resistor) compensate adequately for the higher voltage involved? Am 'testing' as I type and, with nothing burning out as of yet, I have one lamp conx to 20v track transformer's accessory AC and two others, conx in series, to the 24v DC modulator and . . . The DC ones are definitely BRIGHTER? ! CHEERS TO ALL & THANKS! (ps: for the old swiches I run the modulator at 'bout 70% but can also dim the lights down to 5% before they turn off. lol "night lighting"? ALSO have had success at track powering an Atlas SnapRelay to test polarity, via a momentary switch machine, where mainline meets reverse loop, adjusting "RYG signal LEDs" as appropriate but . . sigh . . it's not "automatic" 'ave to push the button to see.)
Sure. They're diodes. They don't mind if electricity moves backwards half the time. They can put a stop to it. But when it's trying to go backwards, they can't use the stuff. So though the electric is cycling faster than the eye can see, the things are still only actively glowing half the time. Yes, connecting pairs in series halve the voltage. Yes, I'd use one resistor per pair.
Ah Ha! Thanks "acp"! An hour later all is still burning fine! One more 'dumb q': what's the easiest method found to connect up all of these resisters without excessive soldering? Am thinking two Terminal Blocks, mounted in parallel with resistors in between, then common grounding (via attachable 'tab strip') to negative side? (all pos being tied directly). Am looking at these. (lol for $13.99) Are there fancy yet inexpensive multiple of 4 inline connectors (that "cando" same with just one mount)?
Connecting two like LEDs in series doubles the voltage drop; however, you cannot assume that with double the voltage drop you can double the supply voltage without changing the resistor. No, if you double the voltage, two LEDs in series will not compensate for the higher voltage, in fact, to operate the LEDs at the same current you would also have to double the resistors (also in series, or a single resistor with double the value). In your case you're not actually doubling the voltage (according to the link the maximum voltage with the included resistors is 18V, so a 33% increase from maximum), so you may be ok, but the only way to know for sure is to know the voltage drop of the LEDs and the resistor value (or measure the current draw). For example: Let's say the LED voltage drop is 4V (white LEDs are typically 3.5 - 4V), then 820 Ohms is the lowest 10% resistor that keeps the current under 20ma at 18v and it gives a current of 17ma: (18 - 4) / 820 = .017. 24V with two LEDs gives (24 - 4 - 4) / 820 = 0.0195, or 19.5ma, still under the 20ma limit listed. Alternatively, if the LEDs have a 3.5 volt drop, 18V and 820 ohms gives (18 - 3.5) / 820 = 0.0177, or 17.7ma, and 24V and two LEDs gives (24 - 3.5 - 3.5) / 820 = 0.0207, or 20.7ma, slightly above the 20ma limit. Also note that if the resistors are 5% or 1% they can get closer to the maximum current at 18V meaning you're more likely to go over at 24V Realize that running a 20ma LED at 20.7ma is not going to instantly kill it, or likely even kill it quickly, but it will shorten its life. Of course, there's also the possibility that the included resistors run the LED well below 20ma as safety margin, in which case two LEDs with one resistor at 24V may be just fine. Again, the only way to know for sure is to know the voltage drop and resistor value.
Actually, LEDs do mind if electricity moves backward half the time. They are not designed to withstand high reverse voltages and powering them from AC can (in some cases drastically) shorten their lives.
If you can find the datasheet for the LEDs you are using, it will specify maximum reverse voltage. Remember, when no/little current is flowing through the resistor, it is dropping no/little voltage across itself, so the LED itself sees the entire voltage (when voltage is reversed.)
Thanks for all your responses & detailed explanations. To err on the 'safe side' I've decided to go with the 24v (off house batt solar power ) but, in running the modulator only at approx 70% and to make the wiring easier, will connect 3 in series instead as I see little to no 'less brilliant' effect. I DO know if one goes ALL will go out but with the LED leads being long enough to easily connect lamps in groups of three (using multiple small parallel terminal strips) LAST QUESTION IS -> does it really matter if resistor is on the "+" or "-" side as I see "polarity" is not an issue as long as all are consistent? Resisters are very small, can barely determine color code (am "color blind") and, wire leads looking to be same lenght (rather than "+ side" being supposedly "longer"), should they NOT WORK AT ALL if indeed hooked WackBards?
Resistors don't have polarity, no. But whether they will work as well here in a circuit as there depends on the circuit.
Ultimate Plan: mount two parallel 12-position" " terminal blocks (small resisters in-between) close to SnapRelay ground (inside "church" rather than underneath?) with smaller 3-position "+" plus "-" blocks which are strategically connected, using light 26g wire, to various lamps located 'round the board?
Sorry! Am reverse engineering/thinking out loud . . Use a fusebox holder with individual taps to hold & connect all LED resisters to 24v ground? For the price the included not used/unneeded fuses (24 total) would make it a deal?
The fuses are required, to connect the stud to each of individual screw terminals. The LEDs make me wonder if using it in the reverse polarity for your layout (with common tied to ground) would be damaging. While fuses are not directional, the led circuits generally are, and may be damaged by using it for ground connections. The fuse panel puts the fuses on the source (+V) side of the load, not on the sink (ground) side. This approach protects the load and all of the wiring for it, from fuse box, to the load, to ground.
TB, am confused (& WHY posting such basic things?) Are you saying LED resisters generally serial connect on the "+" side rather than to "negative ground"? The plan (above) was to replace the fuses with resisters, tie ALL to ground "-" then use the taps to individual lamp(s) then to '+". I suppose could do the reverse, to "+" instead, it's just my technique at soldering and/or stripping/connecting 26awg in general is NOT great! (ps: I DO switch the SnapRelays via "reversible 16v track power" (where mainline(s) & reverse-loop meet) but the LEDs are connected/accessory powered same as the switch turnouts.)
TB, upon 2nd read (& night's sleep) I "get" what your a'sayin' the built-in indicator LEDs may not work correctly and/or cause a problem (lol & I wish whole thing was smaller). On a related note: anyone ever use Scale Telephone Power Poles to run actual power lines (as opposed to under layout)? Or 'Heat Shrink Butt Wire Connectors'? Been using 26awg "wrapping wire" for LED power but this stuff, and especially the LED wire, is tough to strip/connect.
I use printed circuit board (PCB) to make ties when building turnouts but also use it all the time for things like what you are doing. Above I tool a small piece of PCB and filed two gaps into it. I bridged the gaps with 1K resistors but they could be any value that works for the light intensity one wants. The common ground for the project connects to the center section of the PCB. The resistors bridge the gaps and connect to the outer pads. The circuit controls 3 LED's. The two to the left indicate which battery is being used or charged so only one is on at a time and their black cathode wire can to to the pad for the left resistor. The LED to the right is an On/Off indicator for the throttle. The black cathode wire for it goes to the solder pad the other resistor connects to. The red LED anode wires go through switches to the 3 volt output from the ESP32 that is being used in the throttle. I use the PCB all the time for things like this. It is very cheap. You can use it in many ways. Takes up less room than terminal strips. I find it about as quick to solder the wires on or off (if needed) as dealing with the screws on a terminal strip. You also don't have to mess with putting spade connectors on the wires like you do (should) using a terminal strip. The seller I buy from is on vacation until the end of the month ( CopperPCB ) but ( HERE ) is an example of another seller with similar pricing. A lot of PCB with free shipping for $10. I get the double sided .030" for my turnouts but if you use it for something like this and are using more than one screw to hold it down make an isolation cut on the bottom side somewhere between the two or more screws. In your application you could make the PCB somewhat like I did above with a common ground down the middle with isolated pads on each side for the resistors to bridge. The resistors could be different values if need for different light intensities. You could have individual on/off switches or use only one to control all the LED's that are connected. Or the PCB could be cut into isolated pads in a different configuration. Sumner
Yeah, on 2nd read, I was a little difficult to follow. I didn't recognize your idea for installing (leaded) current limiting resistors in lieu of the fuses. That might work, but the fuse sockets are expecting wide, thick blades (built for MUCH MORE CURRENT), not thin, round resistor leads. I would be worried about how reliable the electrical contact would be. Experimentation is warranted. Sometimes you can double over a length of stripped wire or component lead, and twist the wire together with itself, perhaps multiple times (doubling & twisting), to get enough thickness to reliably engage the contacts. That still seems a little iffy to me. Actually stringing wires on telephone poles, used for signals and controls (like 1:1 scale used to do) might work for larger scales. But this leaves the wires exposed to damage and shorting (they'll need to be too fine to be insulated) and dust accumulation (and subsequent damage from removing the dust.) Fine thread (as in sewing) would hang/sag far more realistically than wire, especially insulated wire. I would not recommend running, let alone using the conductivity of, actual wires on scale telephone poles.
True true will let know how works. The 24 included fuses make the $18 investment worthwhile so . . WHATEVER! The alternative is a standard yellow 3 position Atlas "+-" on/off switch with the resistors inline between that & small terminal blocks? Am using very fine 26guage "wrapping wire" but sigh, it's blue not black, figure could run the 'pos' via poles and the "neg" underneath? Still waiting on shipments (from China?) hide/decorate the whole mess within (best price found) a Power Station?
You might look at Woodland Scenics' power systems for products and ideas too: street and interior building lighting, etc. Great stuff, but pricey (also pre-assembled and painted). Wirewrap wire, with the insulation, is fairly rigid for it's size, and will need to be formed carefully for natural draping between poles, buildings, etc. Worked with WW wire plenty in my career (originally for WW circuit card assemblies, and later as the choice for prototype PCB modifications. It's good stuff, but get yourself a suitable, high quality wire stripper. Incidentally, the curve formed when wire/rope of uniform density & diameter hangs between poles is called a Catenary. Mathematically, the curve is described by the hyperbolic cosine function. But this description neglects stiffness and stretch in the wire. Nevertheless, it is very close to the actual curve. So now you have a use for that "HYP" key on your scientific calculator/app!
Hmmm... I just realized the "uniform density" requirement may apply radially within the wire, not just longitudinally along the wire, so an insulated wire may not hang according to that curve very well. But I bet it's close enough for my eye.
Been there done that already and, peering at the current wiring mess under the board already, perhaps black thread for 'looks only' and a change of plan again as a central resistor box (sans the fuses) would only compound the spaghetti wire situation so may opt, 'ave already ordered, a good deal ($1 apiece) on under table, local to lamp(s), "3-position terminal blocks" instead? On first 2 terminals jump the resistor on one side to opposing '-' lamp & common ground with the third being either "-+" feed to next lamp in series and/or to jumped common "+" power too. Will tie intermediate lamps together using simple twisted wire under "heat shrink connectors" making "which wire goes where" much more distinguishable for sure! OMG WOW LOL Climbing under "wooden board" still looks much easier than climbing in there!
Fuse box (with fuses) arrived today and accepts resisters, with a 'lil wiggling, just fine and works as planned but another, related question: would a fuse, say smallest avail 5amp should do, on the "- ground" side between the 48v deep cycle batts and the switch/LED power supply (an % adjustable pulse modulator) offer any overload and/or short protection at all? Tiny gauge heat shrink connectors arrived as well: the idea is to slip bare wire thru, strip and twist two connecting ends together then, after folding down flat, slide the clear tube back over and blow-heat until "sealed". If I drill holes to hold lamps in place it appears the heat shrinks may be small enough to pre-connect "above-board" and then, 1-by-1, slip thru with lengths needed already being "pre-measured"? Terminal blocks & RYG signals yet to arrive will 'prolly wind up doing a combo of "all-the-above"?
