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Basic DIY questions?

Electrics.

I have a lighting controller thing that runs off 12v. The lighting it controls is powered via two transformers each of which outputs 12v.

I want the controller to be active when either of those transformers is switched on. I can't just connect it directly to the +12v of both transformers because then I'll connect the two lighting circuits together.

However, I think I can do this if I use two diodes. Is that right or is it not as simple as that? But if it is, I just find a diode that's rated for 12v & whatever current the controller draws?
 
Yes effectively a kind of OR gate.

Two diodes seems like an easy solution but I'm not sure if something weird happens when the thing is connected to both transformers at the same time?

Had considered relays but not sure exactly how that would work. I want the controller to get its power from one of the two transformers rather than from a third source.
 
Yes effectively a kind of OR gate.

Two diodes seems like an easy solution but I'm not sure if something weird happens when the thing is connected to both transformers at the same time?

Had considered relays but not sure exactly how that would work. I want the controller to get its power from one of the two transformers rather than from a third source.

Are both circuits ever on together or is it just one or the other?
 
Electrics.

I have a lighting controller thing that runs off 12v. The lighting it controls is powered via two transformers each of which outputs 12v.

I want the controller to be active when either of those transformers is switched on. I can't just connect it directly to the +12v of both transformers because then I'll connect the two lighting circuits together.

However, I think I can do this if I use two diodes. Is that right or is it not as simple as that? But if it is, I just find a diode that's rated for 12v & whatever current the controller draws?
Yep, two diodes will - in effect - create the OR gate you mention. You'll get a 0.6V drop across each diode, which probably won't be significant.

You will need to know the maximum current load, but, as an example, a 1N4001 diode is rated to 1A at 50V, but don't make the mistake of assuming that the lower voltage means you can use a higher current (ie, it's not a 50W device)

The somewhat rarer 6A05 (6A) or 10A05 (10A) will handle higher currents. All are available at sub-fiver prices.
 
Yep, two diodes will - in effect - create the OR gate you mention. You'll get a 0.6V drop across each diode, which probably won't be significant.

You will need to know the maximum current load, but, as an example, a 1N4001 diode is rated to 1A at 50V, but don't make the mistake of assuming that the lower voltage means you can use a higher current (ie, it's not a 50W device)

The somewhat rarer 6A05 (6A) or 10A05 (10A) will handle higher currents. All are available at sub-fiver prices.
Yes but doesn’t having multiple transformers increase voltage or current depending on whether they’re in series or parallel? Would a third diode solve that at the point where they join?
 
Yes but doesn’t having multiple transformers increase voltage or current depending on whether they’re in series or parallel? Would a third diode solve that at the point where they join?
Not really. On the assumption that what Teuchter is trying to do is to supply power to the controller from either (or both) of the transformers, the whole purpose of the diodes is to completely isolate the transformers from each other.

There are other considerations - eg., depending on what the lighting controller is, it may not work effectively if it's being powered up just before being given a command - but the two-diode solution will do the practical job of being an OR gate, powering the controller only when one or both of the input supplies is active.

And it's a simple and cheap enough solution that it's got to be worth a try - it certainly won't damage anything.
 
Actually I need to connect the controller V- to V- on both the PSUs, right? Not just one like I have drawn.
Yes, otherwise it would only work with one of the transformers. I can’t actually see what the controller is actually doing there other than being fed from two transformers.
 
Yes, otherwise it would only work with one of the transformers. I can’t actually see what the controller is actually doing there other than being fed from two transformers.
It's a DMX controller, so it sends control data via a completely separate data line. My diagram is simplified; the box that says "lights" is actually a DMX decoder connected to various lights.

If I was starting from scratch I'd do this differently. However it's ended up as it has, for historical reasons.
 
Electrics.

I have a lighting controller thing that runs off 12v. The lighting it controls is powered via two transformers each of which outputs 12v.

I want the controller to be active when either of those transformers is switched on. I can't just connect it directly to the +12v of both transformers because then I'll connect the two lighting circuits together.

However, I think I can do this if I use two diodes. Is that right or is it not as simple as that? But if it is, I just find a diode that's rated for 12v & whatever current the controller draws?
Yes. Use 2 diodes connected to each transformer and joined together the feed the controller. You'll need diodes that will handle the current not the voltage.
 
Yes. Use 2 diodes connected to each transformer and joined together the feed the controller. You'll need diodes that will handle the current not the voltage.
This. I hadn't thought about the issue of commoning the negative lines. Chances are, it'll be fine, but without knowing the full spec on the power supplies, we can't know if the outputs are completely free-floating with respect to earth, so doubling the diodes to isolate both sides makes sense.
 
While yous are all here can anyone point me to some kind of beginners guide to electricity for proper idiots? Website/book/whatever.

Specifically electric fencing that's the main issue atm but it would be good to have a basic understanding of how this shit works generally.
 
This. I hadn't thought about the issue of commoning the negative lines. Chances are, it'll be fine, but without knowing the full spec on the power supplies, we can't know if the outputs are completely free-floating with respect to earth, so doubling the diodes to isolate both sides makes sense.
The transformers should be free floating wrt earth.

Yes the 2 negative lines will need joining together.
 
While yous are all here can anyone point me to some kind of beginners guide to electricity for proper idiots? Website/book/whatever.

Specifically electric fencing that's the main issue atm but it would be good to have a basic understanding of how this shit works generally.
Basically it uses a big battery, the voltage is stepped up and fed in pulses down the fence. When the animals (or you) touch the fence you create a circuit between the fence and ground and get zapped at the next pulse.
 
This. I hadn't thought about the issue of commoning the negative lines. Chances are, it'll be fine, but without knowing the full spec on the power supplies, we can't know if the outputs are completely free-floating with respect to earth, so doubling the diodes to isolate both sides makes sense.

The transformers should be free floating wrt earth.

Yes the 2 negative lines will need joining together.

I've bought some diodes on ebay. Minimum quantity was 10 so I will be able to put them on the positive and negative sides if necessary (ie 4 altogether).

These are the transformers:


But if the question of whether I need diodes on the negative lines is related to the specifics of the transformers, then I'd prefer to have a fail-safe arrangement; that is, if I replace one of those PSUs with a different model in the future it'll still work.

The data sheet for the controller says it only wants 20mA by the way, so hardly anything.
 
I assumed the mains switches were double pole, but looking back at the schematic they’re not.
If you saw the whole of my wiring diagram, for the mains side of things, your eyebrows might be raised.

But the mains switches, they are effectively the light switches, they are single pole, in each case they are fed by a live wire, then there is a switched live to the PSU, which is then connected directly back to neutral.

I suppose the negative line, on the 12V side of things, is somehow connected back to the neutral on the 240V side?
 
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