failsafe led wiring

I would like to run a bright white LED that stays on all the time with a back up bright white LED and a red LED ( to indicate the first LED has stopped working) that would turn on the moment the primary Led fails. This circuit will run on a 12V supply ( not AC to DC converter). Can this circuit be built using relays or would it be better to use electronics? Is there a wiring schematic for this type of circuit or is this type of circuit even possible. R

Note for fail safe led wiring 1990 Chevy Silverado 350 4x4 fleet side

You'd need electronics - probably a current sensing circuit depending on your design.

I'd suggest it's combined with a low voltage cutout to disconnect or disable the red LED if the battery voltage gets too low (assuming cranking or battery life is a concern).


Another application for the PICAXE 08M2 perhaps? (That's a programmable 8 pin device - very low standby current (14nA?) and had counters, analog to digital converters, etc.

Tks. for reply, answer and insight. Will look into PICAXE and see where that road takes me.

There may be novel circuits that do the same. I can imagine certain parallel resistor & LED combinations where one LED illuminates given the other's failure provided it's an open circuit failure, but you'd have to search for that.


I'm tempted to ask why, or what for? Many years ago a certain telco was about to release a spec requiring a LED (or lamp) to indicate an ok battery bank (that's ok) and a LED to indicate when not ok - eg, if flat. I simply asked "And how do you intend powering that LED?". It seems I saved them lots of embarrassment.
The solution for such alarms (failures) is extendible alarms - ie, the NO contacts of a normally energised SPDT relay connect some remote or separately powered OK LED; the NC contacts are used to connect a similar NOT OK LED or alarm.

Sorry for not replying sooner. This project is for a timer (a distributor of sorts) that runs a 12V motor ( better put, a type of motor that runs from 12Vs). I am using a veritable resistor to control the RPM and I have the timing, dwell and duration sorted out. But I am having some trouble with the electronics. Simply...I do not know enough. I know how to assemble the LDR (OPR12 break beam) circuit and the primary constant on white LED. Switching from the primary LED to the secondary (backup) white LED and red (primary circuit fail warning light) circuit seems to be a bit more complex. It seems the more I read the more confused I become as to what the best circuit for reliability and simplicity is, and, how to put it all together. It should be easy enough to build but the theory behind it is over my head and this 4x4 is just about out of warranty. If all this works I will send you a pic of it, though it will still be awhile before it is up and running. Tks. for your reply.

Ah - that's very different to a LED failure indicator.
You don't want to monitor the LED, you want to monitor the circuit...


Chances are that something (12V) turn on your ok LED.
Simply attach that lead to the 'not ok' LED which is oriented in the same direction (as the ok LED) but connects to the opposite power rail.

EG - if wire supplied +12V to anode of grounded ok LED, connect not-ok LED cathode to wire & anode to +12V (but make sure it has whatever series required resistance - but that can be part of the wire).

The above does assume that the wire can both source and sink (supply or ground) current as does f.ex output pin#3 of a 555 timer, otherwise a bit extra is required.


Thanks for describing your system etc. IMO solutions are so much easier (and cheaper!) when the system and desire is specified rather than a specific narrow requirement.

[ It reminds me of two famous 'quality' projects (TQM, ISO9000 intent, etc) for the same thing. The first took months and tens of $thousands to install a system to weigh boxes on a conveyor belt. The second was implemented within hours or days with a hardware cost of under $100. Both met ISO9000 & TQM standards and no customer thereafter ever received the delivery of an empty box. IMO the %49 electric fan solution was by far the superior. ]

TKS for info. Makes perfect scene now that you have explained it in layman's terms. As always... sensibility from theory,but it seems the more I learn the less I know. Again TKS and be well.

Hence imagine how much I DON'T know!!
LOL - like others, I found that the more I knew, the more I knew I didn't know.
Oddly enough I stopped wanting to know more because it became too difficult dealing with others. Initially that was limited to business & employment, but later socially as well.

But losing sight of the issue is not uncommon. If most do it for ordinary everyday issues, why not for new technical issues?

And if this is an academic project... No - I'll keep my fingers tied (if not my mouth shut..)


Thanks for (eventually) stating the raw/basic intent - it made all the difference.
(It is funny isn't it... nearly using a uPC (PIC) to do something that already exists...? Reminds me of voltage sensing battery isolators as well as several multi-$million projects.)

Academic, for me it is, fly in ointment for others would be more concise. Straight up...over-unity (remember..the fly in the ointment). I know, I know, you do not have to say anything. However, it has plagued me for years thinking about it and the more I though about it the more I though they were going about it the wrong way, hence being so vague (sorry). It seems you saw through it. People laughing at me makes little difference, I can only imagine what they said about that idiot with the telescope. Since I already started down this road of futility I want to take it as far as I can even if it does not bear any fruit (at least I tried). I have the motor parts constructed and it does turn very freely when pulsed by hand (hence LED timer) and the amp meter says it consumes 1.56V from a 12V power supply. It should (should being key word here) produce 2amps at 800rpm if ( once again key word here) my coils (250T of 0.90mm enamel) are correct. I do not think of this as over-unity project as eventually I want it to produce a true sine wave mains. I could care less if this is considered over-unity or not as my goal is to be self sufficient. Every time a tree moves the power goes out. Its not that I'm too busy to reply, apparently you need power to run a computer..Who knew?.   I believe the consumed amps to Hp produced is only a small part of the equation ( reason for very very simple LED timer in the 1500 rpm range.) So, since the chickens have got out let it be know-en I have never undertaken electronics and apologize for the deception in the quest for answers. The target of 1500 rpm is "not" for recharging the battery but more for future use. Thank-you for directing me in the right direction, now, off to this silly little town to see if I can find an LDR, Photo-diode, CAD cell or "something" I can use as I'm tired of scavenging electronics and parts from the dump. Just so you have some understanding... nearest city going West..10 hours...East..16 hours, just don't forget to pick up milk! Once again Thank-you, Thank-you, Thank-you. Be well.

What are you using to drive the generator?

Presumably you are talking about a permanent magnet generator or typical rotor controlled generator in which case its output will be (pure) sinewave. However its load may change that shape.

If you are saying your motor/generator consumes 1.56A @ 12V (and 800RPM?) it probably won't produce more than 1.5A @ 800RPM.
And if 1.5A @ 12V (18W) output at 800RPM it'll be a max of 1.5A @ 22.5V (33.75W) output at 1500RPM. (The voltage versus current can be jiggled by various means, but not the max power.)


If by unity you mean efficiency (as opposed to power factor), you will never get above unity efficiency without tapping into some external energy source. For example, the up-to 300% efficiency of a heat pump (ie - reverse-cycle air conditioner used for heating) is thanks to the atmosphere acting as a heat source, but as a closed system it is - as always - equal to or less than 100% efficient. It's like how keeping a fridge door open to cool a house will heat the house even more - unless you place its condensor outside.

You won't gain energy or power by driving a generator from an electric motor. If putting a fan (wind generator) on a car roof to generate electricity, you'd use less fuel by tapping into the alternator.
We cannot create energy or power, merely convert it. EG - fusion to solar radiation to photosynthesis to generate trees & oxygen; nuclear, fossil, solar or trees etc to heat to electricity; etc.
Even super-conduction makes merely 100%/unity efficiency possible.

Even "free" energy by running a cart with alternator down a hill will cost more energy to get it back up the hill. It's fine if it's you or an animal or water or wind or solar etc that gets the cart back up the hill, but a definite loss if using it's own generated electricity to do it.


To paraphrase again - to go above unity means tapping into another source. Hence generator windings would have to be able to use solar radiation; or electronic tunnelling from where ever; or singularities or wormholes - probably to other universes; etc.


I hope the above makes sense, and I hope I understand what you are trying to do.
You will not get greater than unity in a closed system.
Even if you manage a (closed) unity system, you'll probably get a Nobel Prize.

You understand completely. As I am limited as to what I can do physically this gives me something to think about and build in doors. Not looking for any prizes, unity or over unity. As for wormholes I'll leave them in the garden. I honestly do not know How I started this project but the more answers I could not find the more intrigued I became. Now I am here, flying a kite with no wind. Never though this would be a field I would be interested in until I tried to understand something. Until now I've being living a life of blissful ignorance. I have figured out how to make a multiple voltage step down from 12V to needed supply (buying them is of no learning value at all) and how to build a IR photo-transistor break-beam sensor. It's as you said before , I'm fishing in a dry creek (and I know it) but I have come this far and do not intend to stop until I have learned Something. Maybe after all is said and done I can make a auto water filler circuit for the coffee maker. What could be more useful and useless at the same time other than knowing that you yourself took the time to learn something, understand it and then make it function as intended. My project, what better way to start understanding loss and gain with a bit of physics throw-en in just to mess things up. Its a challenge to learn, that's all. Now to make up these parts and move on to the next solution. I must say it has been a long time since I have met some one who actually belongs with Tesla and not a "wanna-be" that just speaks over head lingo. Be well.

Indeed, Tesla was great - IMO greater than those that worked with Patents that happened to be married to a brilliant wife, and not to mention modern short-sighted physicists in their own time. Not that I'm anywhere near Tesla's ability...

But cool. I was worried you were one that thought they could crack perpetual motion or energy gain using conventional means.

I got into electronics etc as a means of solving problems. Usually the solution came first, then the education or detail. IMO that was an advantage because no one told me the stuff I built was impossible - until after I had built them, but by them it was too late for them (tho some say it was too early for me...).


Best wishes.
May you enjoy the trip.