Basic DIY questions?

[WouldBe]

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:

Mean Well HLG-150H-12A

Mean Well HLG-150H-12A AC-DC Single output LED driver Mix mode (CV+CC); Output 12Vdc at 12.5A; IP65; cable output; Dimming with Potmeter

www.meanwell-web.com

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.

Most transformers should be free floating. If you use diodes on the negative supplies as well then you'll get an extra 0.6v drop giving 1.2v drop in total which could affect the operation of the controller. Check what the controllers supply voltage range is.

 

[WouldBe]

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

Only via the transformer. There shouldn't be any direct connection.

 

[teuchter]

Most transformers should be free floating. If you use diodes on the negative supplies as well then you'll get an extra 0.6v drop giving 1.2v drop in total which could affect the operation of the controller. Check what the controllers supply voltage range is.

It just says 12-24v.

Might just have to try it and see.

What does "free floating" mean in this context?

 

[Magnus McGinty]

Centre tapped I think. Tbh I’m not entirely sure how it works.

 

[WouldBe]

It just says 12-24v.

Might just have to try it and see.

What does "free floating" mean in this context?

Isolated from the mains and earth.

 

[teuchter]

I am mildly curious as to how this particular arrangement came to be necessary, though

The explanation is sufficiently long winded that a higher level of curiosity than "mild" would be needed to justify typing it out.

I'm trying to remember what the term is, for decisions made in the past that set a certain path that then becomes more effort to deviate from, than to accept an arrangement that wouldn't make any sense if set up anew.

 

[WouldBe]

Centre tapped I think. Tbh I’m not entirely sure how it works.

Center tapped would give e.g. 12v-0-12v. So you could get 24v from the transformer or link the 2 12v outputs together to get twice the current. They should still be isolated from earth or neutral.

 

[teuchter]

Isolated from the mains and earth.

Does isolated mean unrelated to? As in, is it the case that there might be a difference in voltage between the "ground" within the 12v system and the "ground" of the mains system?

 

[StoneRoad]

The explanation is sufficiently long winded that a higher level of curiosity than "mild" would be needed to justify typing it out.

I'm trying to remember what the term is, for decisions made in the past that set a certain path that then becomes more effort to deviate from, than to accept an arrangement that wouldn't make any sense if set up anew.

inertia ...

 

[teuchter]

inertia ...

Certainly a weekend of trying to pull cables through multiple awkward gaps has confirmed the inertia in me, relating to rewiring things when it's not absolutely necessary.

 

[WouldBe]

Does isolated mean unrelated to? As in, is it the case that there might be a difference in voltage between the "ground" within the 12v system and the "ground" of the mains system?

Yes, there should be no direct connection between the 0v on the 12v side and either the earth or neutral on the mains side.

 

[teuchter]

Yes, there should be no direct connection between the 0v on the 12v side and either the earth or neutral on the mains side.

But should there be a difference in voltage?

 

[Magnus McGinty]

But should there be a difference in voltage?

Yes because you’ve said it’s stepped down from 240 to 12….

 

[teuchter]

Yes because you’ve said it’s stepped down from 240 to 12….

No, I mean should there be a voltage difference between the ground on the 12v side and the mains earth/neutral. Should that measure as zero, or is that not necessarily the case.

 

[Magnus McGinty]

This is a confusing question. Neutral will measure zero between earth on a fuseboard but that doesn’t mean there’s no voltage in the neutral. If you disconnect the neutral from the fuseboard it becomes live.

 

[Magnus McGinty]

It would probably be unwise to connect a 12v neutral directly to a 240v neutral, it has to be done through the transformer as per manufacturer’s instructions.

 

[teuchter]

It would probably be unwise to connect a 12v neutral directly to a 240v neutral, it has to be done through the transformer as per manufacturer’s instructions.

I'm not planning to do that. The reason behind my question I guess was wondering what actually happens if you connect the negative terminals of the two transformers (on the 12v side). If they are inevitably both at the same voltage relative to the outside world then there should be no voltage difference between them.

 

[Magnus McGinty]

I'm not planning to do that. The reason behind my question I guess was wondering what actually happens if you connect the negative terminals of the two transformers (on the 12v side). If they are inevitably both at the same voltage relative to the outside world then there should be no voltage difference between them.

If they’re both 12v transformers then there shouldn’t be a potential difference between them, I agree.

 

[WouldBe]

I'm not planning to do that. The reason behind my question I guess was wondering what actually happens if you connect the negative terminals of the two transformers (on the 12v side). If they are inevitably both at the same voltage relative to the outside world then there should be no voltage difference between them.

They may not be the same voltage relative to the outside world as they are floating. They will be the same voltage relative to each other when the negative supplies are linked.

 

[Magnus McGinty]

They may not be the same voltage relative to the outside world as they are floating. They will be the same voltage relative to each other when the negative supplies are linked.

It should work though with the scenario described of sometimes using both transformers together using diodes on the positive side though?

 

[WouldBe]

But should there be a difference in voltage?

You won't be able to measure a voltage difference because the 2 sides of the transformer are isolated.

 

[WouldBe]

It should work though with the scenario described of sometimes using both transformers together using diodes on the positive side though?

Yes it will work when linked.

If you had 2 9v batteries and put a volt meter between the +ve of one battery and the -ve of the other you would get a reading of 0v as the batteries aren't linked.

 

[Magnus McGinty]

Yes it will work when linked.

If you had 2 9v batteries and put a volt meter between the +ve of one battery and the -ve of the other you would get a reading of 0v as the batteries aren't linked.

There is a difference when connecting the live side of batteries in serial vs parallel though which must be the same with transformers. I assume that’s why you suggested diodes that control current?

 

[WouldBe]

There is a difference when connecting the live side of batteries in serial vs parallel though which must be the same with transformers. I assume that’s why you suggested diodes that control current?

The diodes don't control the current, they must be capable of handling the current of the controller which as it's only 20ma you would be alright using 1N4001 rectifier diodes.

 

[teuchter]

This all confirms how half-baked my understanding is, of what voltage actually is.

 

[Magnus McGinty]

This all confirms how half-baked my understanding is, of what voltage actually is.

Voltage drives current. Current is the one that can kill you.

 

[teuchter]

Voltage drives current. Current is the one that can kill you.

Yeah, that much I understand.

 

[existentialist]

I assumed the mains switches were double pole, but looking back at the schematic they’re not.

That's not relevant - the question is whether the PSU output is completely "floating" in relation to earth. As they're (presumably) identical, I think one could just common the negatives, but it's the sort of assumption that could in theory result in the magic smoke escaping.

 

[Magnus McGinty]

That's not relevant - the question is whether the PSU output is completely "floating" in relation to earth. As they're (presumably) identical, I think one could just common the negatives, but it's the sort of assumption that could in theory result in the magic smoke escaping.

Yeah I realised that as the conversation continued. Electronics not my forte tbh, which is mad as I love logic gates.

 

[iona]

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.

Thanks