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  Reply # 948888 10-Dec-2013 18:36
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Fred99: 13.8V DC 20A switchmode benchtop PSU, for $119.00

http://www.jaycar.co.nz/productView.asp?ID=MP3078&form=CAT2&SUBCATID=999#3

D
o anything you like with the 13.8V out - it's not subject to any electrical reg.
Much less mucking around than trying to adapt a computer PSU.


Unfortunately you can pretty much legally do a lot on the output of that. Like use crappy passive baluns for cctv and not fuse it so when someone chops off your outside camera and shorts it you have no over current protection and the whole cable cooks up to have crispy insulation. Same for landscape lights installed by idiots with no appropriate over current protection.




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  Reply # 948889 10-Dec-2013 18:50
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gregmcc:
Fred99: IMO, there's a much more serious issue here - from the original post:
"With an isolating transformer there is no way you can get an electric shock (this is why they were created)"


Been quite honest here, this is the kind of thing that someone who thinks they know what they are doing, but doesn't says.

A little knowledge is a dangerious thing, this is why the electrical industry is heavily regulated.





can someone clarify how one get get shock from isolating transformers? I have seen personally people using drilling machines 230V IN THE RAIN because they were supplied from an isolating transformer. They are used on construction sites in certain difficult conditions, for a reason. Or maybe they have no idea either? If the insulation between the two windings is OK then there is no danger. I agree this was an "instant" idea, I am sure there is a reason why is not used for this application. But I have been through situations where a different idea was not accepted purely because "it was never done". It happened to me. No engineering argument, no downside to the solution proposed, but "it was never done". No worries, I will not attempt such thing but I was hoping I can also understand why it was never done.

To agree that I need an electrician to cut the 12V cables coming out of a PSU and connect to the garden lights, this I cannot easily do. Same as the idea that people with grid connected solar panels, should pay tax on the "income" created by generating power into the grid.

No wonder houses are so expensive...  






mobo Intel DH55PJ, RAM: 4GB RAM, Nova-T 500 HD + Avermedia Trinity tuner card, Geforce 520 video, 120GB SSD Sandisk + 640 WD + 1000SG, Win7 Home Prem 64-bit, Media Portal 1.15.0; BTC 9019URF Cordless Keyboard, Panasonic 55" (HDMI cable), HTPC Case Silverstone Grandia GD05B.


 
 
 
 


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  Reply # 948919 10-Dec-2013 20:03
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richms:
Fred99: 13.8V DC 20A switchmode benchtop PSU, for $119.00

http://www.jaycar.co.nz/productView.asp?ID=MP3078&form=CAT2&SUBCATID=999#3

D
o anything you like with the 13.8V out - it's not subject to any electrical reg.
Much less mucking around than trying to adapt a computer PSU.


Unfortunately you can pretty much legally do a lot on the output of that. Like use crappy passive baluns for cctv and not fuse it so when someone chops off your outside camera and shorts it you have no over current protection and the whole cable cooks up to have crispy insulation. Same for landscape lights installed by idiots with no appropriate over current protection.


10 minutes on google will have you sorted for cable sizes for 20A DC load, the unit is fused, but of course you can't always save people from themselves.  I'm jolly glad I'm still "allowed" to change the brake pads on my car, possess whisky, and cook for my family.

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  Reply # 948931 10-Dec-2013 20:16
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aucklander:
gregmcc:
Fred99: IMO, there's a much more serious issue here - from the original post:
"With an isolating transformer there is no way you can get an electric shock (this is why they were created)"


Been quite honest here, this is the kind of thing that someone who thinks they know what they are doing, but doesn't says.

A little knowledge is a dangerious thing, this is why the electrical industry is heavily regulated.





can someone clarify how one get get shock from isolating transformers? I have seen personally people using drilling machines 230V IN THE RAIN because they were supplied from an isolating transformer. They are used on construction sites in certain difficult conditions, for a reason. Or maybe they have no idea either? If the insulation between the two windings is OK then there is no danger. I agree this was an "instant" idea, I am sure there is a reason why is not used for this application. But I have been through situations where a different idea was not accepted purely because "it was never done". It happened to me. No engineering argument, no downside to the solution proposed, but "it was never done". No worries, I will not attempt such thing but I was hoping I can also understand why it was never done.



They're still putting out 230V.  If there was a fault (or just water) then without an isolating transformer the appliance may short to earth and blow a fuse (or it might very easily short to earth through you - which is very bad).  The isolating transformer removes the risk of it shorting to earth through you, but it doesn't eliminate the possibility of you becoming "live" if there's a fault, unaware that this has happened, then the problem is that if you touch something connected to the other lead from the isolating transformer, then you get 230V straight across the chest - potentially worse than from one hand through your shoes to earth.  RCDs tend to be used instead of isolating transformers these days.  But they can fail too.  Treat them (isolating transformers and RCDs) like having a parachute on a plane - you still don't want the plane to crash.

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  Reply # 949008 10-Dec-2013 22:12
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gregmcc:
fastmikey:
gregmcc: The computer as a whole box is an appliance and 1 (c) would apply, but the PSU as an internal component of that appliance would not, the PSU is desgined to be mounted and contained with a PC case, it is not desgined for use as a stand alone unit, as it is desgined as a component that operates at low voltage >50VAC to <1000VAC then any work done on a component that operates at low voltage is perscribed electrical work


Oh, I'm not disagreeing there, but computer shops assembling PCs are exempted under 1 (c). Just don't want to see any SME business owners unduly freaking out 


And I would disagree there, 1 (C) is reffering to appliances, such as your jug or toaster or fully assembled PC, as soon as the cover comes off the PC then you are now preforming a servicing or assembling task, when the PSU is removed (or installed), remembering that clause 2 goes on to describe exacty what is not perscribed work and assembling a PC PSU in to a case or using it in another manor does not fall in to the defination of none perscribed work.

You just can't pick out 1 clause of the regs and say look that clause seems to fit what I think so it must be so, a full and complete understanding of all the regulations is required, and when a particular reg quite clearly defines what is not perscribed work as in clause 2



I'm sorry, but I can't see how that can be right. A PSU is a sealed unit, with a LV feed on one side, and ULV on the other. If they were to crack the PSU and play around inside of it that would be completely wrong, but at no point assembling a computer are you ever exposed to more then ULV. You suggesting that mounting a PSU in a case being servicing/assembling, is akin to saying that if I mount a power board to the wall I can't do it. And by that token, if you were to only assemble PCs that had the PSU already mounted to the case, it'd be a moot point...

At any rate, we're grossly off topic here, so I think I'll leave it at that 

[Edit - I realised my first draft of wording was a bit... aggressive. ]

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  Reply # 949017 10-Dec-2013 22:31
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aucklander:
gregmcc:
Fred99: IMO, there's a much more serious issue here - from the original post:
"With an isolating transformer there is no way you can get an electric shock (this is why they were created)"


Been quite honest here, this is the kind of thing that someone who thinks they know what they are doing, but doesn't says.

A little knowledge is a dangerious thing, this is why the electrical industry is heavily regulated.





can someone clarify how one get get shock from isolating transformers? I have seen personally people using drilling machines 230V IN THE RAIN because they were supplied from an isolating transformer. They are used on construction sites in certain difficult conditions, for a reason. Or maybe they have no idea either? If the insulation between the two windings is OK then there is no danger. I agree this was an "instant" idea, I am sure there is a reason why is not used for this application. But I have been through situations where a different idea was not accepted purely because "it was never done". It happened to me. No engineering argument, no downside to the solution proposed, but "it was never done". No worries, I will not attempt such thing but I was hoping I can also understand why it was never done.

To agree that I need an electrician to cut the 12V cables coming out of a PSU and connect to the garden lights, this I cannot easily do. Same as the idea that people with grid connected solar panels, should pay tax on the "income" created by generating power into the grid.

No wonder houses are so expensive...  




You can get a shock if you become the connection between phase and neutral on the secondary side. The only thing an isolating transformer does, is isolate the supply from earth.
Our Power supply system is a MEN (Multiple Earthed Neutral) which means the Neutral is tied to Earth at your switchboard and the transformer and a whole lot of other places too. While it makes things safer in some ways, it also makes thing dangerous in others because you are almost always earthed, you can easily become a conductor if you come in contact with a live part. An isolating transformer simply removes the path between Neutral and earth, making electric shock much less likely.




Location: Dunedin

 

 


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  Reply # 949018 10-Dec-2013 22:32
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One thing people seem to be missing here is that a PSU is a switchmode power supply and not an isolating transformer. Therefore the output is not isolated from earth.

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  Reply # 949019 10-Dec-2013 22:36
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Greg, you are full of crap!

I am sick of reading your scaremongering here. You do give some sound advice at times, but most of the time you're just making stuff up.
The only thing you are achieving, is making these people wary of professional opinion, and causing them to question everything you say.

I suggest you go read the regs yourself, and while you're at it, pick up a copy of "the little boy who cried wolf"




Location: Dunedin

 

 


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  Reply # 949021 10-Dec-2013 22:40
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You will get a much safer and more robust system if you use a proper powersupply, and I don't think they're too expensive either.




Location: Dunedin

 

 


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  Reply # 949074 11-Dec-2013 01:25
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larknz: One thing people seem to be missing here is that a PSU is a switchmode power supply and not an isolating transformer. Therefore the output is not isolated from earth.





Every single computer power supply I have seen is isolated. If they were not then swapping the phase and neutral connections would make the output live. If you open up a broken one you will see a transformer in the middle of the circuit board. This provides the isolation. Look at the solder side of the board and you will see a line down the middle with no tracks on it and the transformer bridging both sides. This is the division between the primary side and the secondary side.

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  Reply # 949080 11-Dec-2013 05:35
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andrewNZ: Greg, you are full of crap!

I am sick of reading your scaremongering here. You do give some sound advice at times, but most of the time you're just making stuff up.
The only thing you are achieving, is making these people wary of professional opinion, and causing them to question everything you say.

I suggest you go read the regs yourself, and while you're at it, pick up a copy of "the little boy who cried wolf"


I do have a copy of the regs, the full and most recent version, and making personal coments is just away of attacking someone you know is right without admitting you are wrong.







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  Reply # 949121 11-Dec-2013 08:44
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I suggest that Peter Reader is programmed to respond to any text referring to electrical and plumbing regulations with an appropriate response.
If electrical regulations are so problematic (WRT what the unqualified may or may not do), then the plumbers, gasfitters and drainlayers regulations take obscure, convoluted, and complex to another level.

My brief glimpse of the electrical regs linked to above, defining prescribed electrical work leads me to believe that it's probably illegal to hook up speaker wires to your home hifi system - even worse if it's "fixed wiring" in your walls. RMS voltage going to your speakers will exceed extra-low voltage and will be "low voltage" (unless it's a very small stereo) to be treated the same as 230V - unless there's an exception to allow for this, buried somewhere in the regs.

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  Reply # 949137 11-Dec-2013 09:30
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Aredwood:
larknz: One thing people seem to be missing here is that a PSU is a switchmode power supply and not an isolating transformer. Therefore the output is not isolated from earth.





Every single computer power supply I have seen is isolated. If they were not then swapping the phase and neutral connections would make the output live. If you open up a broken one you will see a transformer in the middle of the circuit board. This provides the isolation. Look at the solder side of the board and you will see a line down the middle with no tracks on it and the transformer bridging both sides. This is the division between the primary side and the secondary side.


Every single one I have seen has the 0v line connected to the chassis ground so they are not isolated as is needed to prevent a fault to ground.




Richard rich.ms

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  Reply # 949190 11-Dec-2013 10:16
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Fred99: I suggest that Peter Reader is programmed to respond to any text referring to electrical and plumbing regulations with an appropriate response.
If electrical regulations are so problematic (WRT what the unqualified may or may not do), then the plumbers, gasfitters and drainlayers regulations take obscure, convoluted, and complex to another level.

My brief glimpse of the electrical regs linked to above, defining prescribed electrical work leads me to believe that it's probably illegal to hook up speaker wires to your home hifi system - even worse if it's "fixed wiring" in your walls. RMS voltage going to your speakers will exceed extra-low voltage and will be "low voltage" (unless it's a very small stereo) to be treated the same as 230V - unless there's an exception to allow for this, buried somewhere in the regs.



This is where common sense should kick in, having a look around I can't see any specific exclusion for speaker wiring, but common sense says generally it's classed as ELV

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  Reply # 949240 11-Dec-2013 11:44
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Going back to the original OP, using a PC PSU, the 12v start would be too sudden - for halogen you need a slower start to minimise thermal shock of the filament. I have seen circuits that kick in the 5v rail for a pre-warm, and switch to the 12v rail after a second or two.

Conversely, I have picked up a couple of 105VA dimmable halogen slowstart switchmode PSU's for $14.00-odd + gst from one of the major electrical suppliers. No point messing around with switching rails, and using a 6" cube PSU when something the size of a deck of playing cards will do. No IEC power socket through, these are expected to be part of the fixed wiring.




My thoughts are no longer my own and is probably representative of our media-controlled government


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