User avatar
piglet
Posts: 909
Joined: Sat Aug 27, 2011 1:16 pm

When you need more power - how to be safe?

Fri Mar 13, 2015 1:56 pm

This is a general question about how to be safe with power supplies when you start trying to do things which need more power.

The specific application I have in mind is that I'd like to run a 5m length of 5v WS2812B RGB LED strip - at 74 RGB's a meter it needs a reasonable power supply: 18watt/meter, 90watt for 5m.

Pretty much all the supplies I can find with enough grunt to power this look like this - random example image shown below.

The question I have is "How do you mount or enclose something like this to ensure it's safe?" The 240v connections seem to be exposed, or occasionally covered with a flip-down piece of plastic.

This form factor of PSU seems to be the norm for anything over 5A/25W. I can see how you might use something like this in an installation which is itself enclosed - e.g. signage. I'm surely not the only person flummoxed on how to safely use such a thing around the house.



Image

User avatar
RaTTuS
Posts: 10461
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK

Re: When you need more power - how to be safe?

Fri Mar 13, 2015 2:23 pm

Posting to subscribe ;-p
I'm also interested in the answer to this....
I have a few [quite a few] PSU units of similar design....

I also have a 12V supply running round part of my house using 2.5mm twin and earth which has to be separated from normal mains .... [but that is another matter ]
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

toxibunny
Posts: 1382
Joined: Thu Aug 18, 2011 9:21 pm

Re: When you need more power - how to be safe?

Fri Mar 13, 2015 2:26 pm

Me too! I'm especially worried because my entire house is made of wood.
note: I may or may not know what I'm talking about...

hampi
Posts: 223
Joined: Fri May 31, 2013 11:29 am
Contact: Website

Re: When you need more power - how to be safe?

Fri Mar 13, 2015 7:15 pm

The ARRL Handbook for radio amateurs, Practical Design and Projects and there chapter on Safety. The RSGB might have a similar book.

The power supply module is normally put into a separate closed metallic enclosure. This enclosure is connected to safety ground via the mains cable. Depending on your national legislation you may be able to do this yourself or may have to ask professional help in building the power supply box.

User avatar
piglet
Posts: 909
Joined: Sat Aug 27, 2011 1:16 pm

Re: When you need more power - how to be safe?

Fri Mar 13, 2015 8:00 pm

Hmmm - these PSUs are being advertised all over the place to the general public. It seems odd that there don't appear to be any readily-available enclosures. I spent an hour searching at lunchtime and all I could find was other people asking a similar question.

User avatar
morphy_richards
Posts: 1603
Joined: Mon Mar 05, 2012 3:26 pm
Location: Epping Forest
Contact: Website

Re: When you need more power - how to be safe?

Fri Mar 13, 2015 8:31 pm

Could anything like this be useful? :?

User avatar
SteveDee
Posts: 343
Joined: Thu Dec 29, 2011 2:18 pm
Location: Sunny Southern England
Contact: Website

Re: When you need more power - how to be safe?

Fri Mar 13, 2015 9:40 pm

piglet wrote:..."How do you mount or enclose something like this to ensure it's safe?" The 240v connections seem to be exposed, or occasionally covered with a flip-down piece of plastic....

...I'm surely not the only person flummoxed on how to safely use such a thing around the house.
This is an instrument power supply, which has to be designed into a system. It is not a component to be used around the house.

Any plastic tags over the mains terminals are simply there as an additional safety measure for anyone working on the equipment when "live" and exposed. But normally neither these contacts, or the power supply case itself would be accessible to a user.

I'm not sure why you would expect there to be information on how to safely install this component into a system, anymore than you would for other high voltage components that are available, such as 240V relays or mains transformers.

Looking at the example illustrated, the whole thing needs to go into an enclosure, as you wouldn't want a child to poke metal objects through the grill or come into direct contact with the wires or terminals at mains potential.

Since the power supply case has lots of holes, the components inside probably need plenty of air-flow. So if put inside a totally sealed enclosure, the enclosure needs to be of an adequate size and may need to be metal to conduct the heat away (this info may be deduced from the specification). Note that fitting a fan inside a closed box will only help cool the component if the box is large enough to conduct the heat away from its surface fast enough.

The cable connecting the supply to the mains needs to have a current rating higher than the power supply input current rating. The fuse used in the mains plug must have a rating lower than the mains cable rating. The mains fuse is there to protect the cable, not the power supply (i.e. it is important that the mains fuse blows before the insulation on the mains cable starts to melt).

The cable must be adequately clamped inside the enclosure so that if pulled, the terminating wires are not strained (i.e. adequate strain relief).

If the enclose in conductive (metal) it must be connected to earth.

This is not an exhaustive list. It is just to warn you that you can't just hang a few wires onto a chassis power supply and leave it laying around your house.

I hope this helps.

User avatar
Tage
Posts: 287
Joined: Fri May 24, 2013 2:29 am
Location: St Thomas, Ontario Canada

Re: When you need more power - how to be safe?

Sat Mar 14, 2015 1:10 am

When using a power supply like this I buy a plastic enclosure that is big enough for the power supply, and make holes and mount a cooling fan if the power supply does not already have one. In any case, you need to add holes in the plastic box so that cooling air can move through. you cannot just put the power supply in an enclosure with no air flow, it would overheat. The holes must be small enough that if a kid sticks his finger into the holes he cannot access mains voltage.

Some of these power supplies will have a 12V output for a cooling fan, and will turn on the fan as needed.

The mains cable must be mounted so that if you pull on the cable it cannot come loose. and if you pull really hard and it comes loose, the last wire to break will be the protective earth wire in the cable. this is usually done in the way that you cut off the Neutral and Live wires so they are much shorter than the Protective earth wire.

Tage

piglet wrote:This is a general question about how to be safe with power supplies when you start trying to do things which need more power.

The specific application I have in mind is that I'd like to run a 5m length of 5v WS2812B RGB LED strip - at 74 RGB's a meter it needs a reasonable power supply: 18watt/meter, 90watt for 5m.

Pretty much all the supplies I can find with enough grunt to power this look like this - random example image shown below.

The question I have is "How do you mount or enclose something like this to ensure it's safe?" The 240v connections seem to be exposed, or occasionally covered with a flip-down piece of plastic.

This form factor of PSU seems to be the norm for anything over 5A/25W. I can see how you might use something like this in an installation which is itself enclosed - e.g. signage. I'm surely not the only person flummoxed on how to safely use such a thing around the house.



Image

User avatar
RaTTuS
Posts: 10461
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK

Re: When you need more power - how to be safe?

Tue Mar 17, 2015 4:06 pm

as an additional to this ,,,,,
can anybody recommend a 12V distribution panel [fused with blade fuses idealy] so I can use one of this but split it into 12+ output channels [IYSWIM]
so I can run
lights , CCTV , NVR , IR lights , other 12V stuff, all from a nice unit giving easy screwed in connectors
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

stevend
Posts: 213
Joined: Fri Oct 11, 2013 12:28 pm

Re: When you need more power - how to be safe?

Tue Mar 17, 2015 9:37 pm

RaTTuS wrote:as an additional to this ,,,,,
can anybody recommend a 12V distribution panel [fused with blade fuses idealy] so I can use one of this but split it into 12+ output channels [IYSWIM]
so I can run
lights , CCTV , NVR , IR lights , other 12V stuff, all from a nice unit giving easy screwed in connectors
Have a look at marine and caravan parts suppliers
If you just want a bank of fuses, car spares shops.

hampi
Posts: 223
Joined: Fri May 31, 2013 11:29 am
Contact: Website

Re: When you need more power - how to be safe?

Tue Mar 17, 2015 9:42 pm

RaTTuS wrote:can anybody recommend a 12V distribution panel [fused with blade fuses idealy] so I can use one of this but split it into 12+ output channels...
Something like this?

http://www.g0hwc.com/anderson-powerpole.html

User avatar
RaTTuS
Posts: 10461
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK

Re: When you need more power - how to be safe?

Wed Mar 18, 2015 2:07 pm

yeah the Anderson power pole stuff looks interesting .... umm
I suppose I'm really looking for
http://www.ebay.co.uk/itm/18-WAY-10A-CC ... 1397601252 sort of thing
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

User avatar
BAStumm
Posts: 134
Joined: Fri Aug 23, 2013 3:37 pm
Location: Loon Lake, WA USA
Contact: Website

Re: When you need more power - how to be safe?

Wed Mar 18, 2015 8:05 pm

First, for LED you want a constant current driver or power supply. I think what you are looking for is IP68 rated enclosure. Perhaps something like this:

http://www.aimtec.com/amepr60-12500az-6 ... wer-supply

User avatar
RaTTuS
Posts: 10461
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK

Re: When you need more power - how to be safe?

Thu Mar 19, 2015 8:54 am

no not using for LED's
what I'm using it for [in this case] is a CCTV / NVR system , [well mostly] , I have a 12V Ethernet switch , 12V 720p Cameras [supplied over PoE and or 2.5mm mains cable no worries about voltage drop], additional IR lights NVR , external Hard disks , small monitor etc...
I use fused lines for the garden runs [mostly protected but have had foxes chew though cables before now] so have a need for many terminals not one output.

I currently have a couple of car blade fuse box thingies in use but am always looking for other methods.

neater is better

;)
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

DaveSemm
Posts: 160
Joined: Thu Jun 21, 2012 1:16 pm

Re: When you need more power - how to be safe?

Thu Mar 19, 2015 10:47 am

I am wiring up my house so I can control everything with my Pi's. I found this very useful: a cabinet for the power supply, and a distribution board with fuses, in case a wire shorts.
Power supply box 1.jpg
Power supply box 1.jpg (55.38 KiB) Viewed 2548 times
I got it at a CCTV place.

User avatar
RaTTuS
Posts: 10461
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK

Re: When you need more power - how to be safe?

Thu Mar 19, 2015 11:38 am

where did you get the distribution board from ?
that is what I'm after [though blade fuses would be better for me]
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

DaveSemm
Posts: 160
Joined: Thu Jun 21, 2012 1:16 pm

Re: When you need more power - how to be safe?

Thu Mar 19, 2015 11:53 am

RaTTuS wrote:where did you get the distribution board from ?
that is what I'm after [though blade fuses would be better for me]
I'm in South Africa, so the shop won't help you. But it is a place that sells home security equipment, e.g. CCTV. They use these to distribute power to CCTV cameras, etc. There is space for the Pi and the drivers. It has jumpers to disconnect each output - I just took off the jumpers and connected the pins to my driver board, so it is all very neat.

hampi
Posts: 223
Joined: Fri May 31, 2013 11:29 am
Contact: Website

Re: When you need more power - how to be safe?

Thu Mar 19, 2015 9:22 pm

For indoor use a recycled PC case should work as a safe and economic enclosure for the power supply module, Raspberry Pi and other things - just an idea.

Return to “Automation, sensing and robotics”