two seprate circuits, one switch?

If we call switches #1, #2 & #3 S1, S2, S3.... Then how about: S3 turns both on (overriding S1 & S2) and... If S3 is off, S1 & S2 determine the state (ie, S1 on & S2 off means each load is on & off respectively. That is easy with plain toggle switches, 2 diodes, & 2 relays. If that is not the operation you want, then explain the change(s) you want.

guys, theres no mystery here, the loads are lights. current draw is irrelivant at this point. I just want to learn how to control two seprate circuits in this manner. I havnt even got to the confusing stuff yet lets not jump the gun LOL IAAI, thanks for taking the time to draw me a picture! I wish it was that easy. oldspark, heck yeah! I think that is what Im after, Im ready! with a common 12vdc source (for now) and *lights* ;-)

Lights? What do you think I am - confused? This is toooo EEEEASY! Ooops - re-edited with correct switch labels. And note that S3 will power S1's & S2's upstream sources, but 2 more diodes will prevent that too.

LOL! But it's unfair twisting 2-12's "current draw is irrelevant at this point" to being a high current draw. Novices may try to implement 4 relays to boost current rating and then wonder why contacts fuse or relays smoke! If needing that for say 1000A, I'd be looking at an SCR! (Or at least have SCR-quenching across each contact!!) Hey 2-12 - we have a "Red Rooster" ad down under here that has a soon-to-be classic line "Some people just don't get it!". It has interesting relevance (Hint: It wasn't set in Australia)

oldspark, thats it right there! very simplistic.. even I can manage that. now, would it matter if S1 & S3 source was seperate 12vdc than S2 but still common ground? (two seperate and isolated batteries) if so what would change? and whats SCR? KP, thats nice to know but Im not understanding how paralleling relays increases current capibility.. is that why the "just dont get it" comment OS? is KP's diagram failure prone or is it just me ;-) Im not trying to operate two seperate winches or anything that loaded.

SCR = Silicon Controlled Rectifier

Hi Two, It won't matter if the voltages are from different sources provided you add the extra diodes as shown in the updated dwg below (Version-1). As mentioned before, they each switch powering the other switches. (Current can only flow out of the K = Cathode end, not into it.) Hence different battery/source voltage levels won't have any effect. (That's assuming a common earth/ground as you stated, and that each source has enough voltage to energise the relay(s).) If mixing different voltages - say 5V, 12V, 24V etc - then you would use ground switching on hot relays. But that's probably not required here. ("Open-Collector" outputs refer.) FYI - I've done a similar design where a vehicle has its standard electrics, but a second alternator and two batteries have been added. Except for common chassis/ground, they are independent (although the orig alternator can charge the 2nd & 3rd batteries if the 2nd alternator isn't charging.) And forget about SCRs, triacs etc. (Unless you are switching several thousand Amps DC lol!, or maybe AC.) As to the importance of the current being switched, maybe it's because I break solution down into respective parts, but I agree with...

two12 (paraphrased) wrote: ..there's no mystery here.... current draw is irrelevant at this point...

(I can hear T'ilk saying "Indeed!".) In this case, the load does not impact the "front end" design. (The FE is whatever it has to be - in this case a logic circuit.)    If the load is too big for the circuit (switches), you power the load via relays. It's the same with anything. If the load is bigger than what a CPU etc can handle, you buffer it with whatever it takes - FETS & transistors to relays to contactors etc. The load current might effect the final implementation. If they were LEDs, we'd probably just use a hex inverter chip, 3 push buttons & a few Rs & Cs. If they were AC or DC lamps, then maybe be used Triacs or SCRs, or contactors for sodium lamps etc. Is there something that I am missing? How would (say) my design change if the output were a few giga-Amps other than that the switches would power relays powering other relays etc until the desired amplification/fanout is achieved)?