Assembling a DPS3005 combined with a offline SMPS module in case.

Assembling a DPS3005 combined with a offline SMPS module in case.
Posted by David_ on 06 Oct, 2017 18:11
Hello.

I have recently received all the parts of a soon to be adjustable power supply based on a DPS3005 unit from ebay, I got a DPS3005, a custom metal enclosure and a offline 36V @ 5A SMPS module(which fits perfectly in the DSP3005 custom case).
Here are links the the exact products I have:
DPS3005
Enclosure
SMPS

I still don't understand how to actually attach a picture and then use the "Insert image" option to insert it into a post but I will attach pictures, the first is showing all of the components that I might come to use(in the picture there are a mains EMI-filter that I first thought to use but I will probably not bother with it because why would it be effective for a converter who's frequency I don't even know...)

The SMPS unit fits perfectly in the case as can be seen in the second
picture, so what I will do is to put the SMPS into the box and connects it's output to what was supposed to be the input to the box which also drives the fan somehow(I got a little circuit board in the enclosure but no directions what so ever, and there are more places on the PCB to connect everything to than one, I have emailed the seller who never returned a answer) and rework the back plate to fit one of those 3-pin mains connectors used on ATX PC power supplies, and then somewhere on the case fit a new 250V @ 6,5A switch which will be the main on/off switch feeding the SMPS.

This will make the finished enclosure into a power supply that can be connected directly to the mains and output 0-32V @ 5A, which would be great.

However I am a little uneasy about what to do about the SMPS mains side, and the PE-GND.

The SMPS unit have those mains voltage X/Y capacitors on the input, which needs to be connected to PE-ground, but then I should also connect the enclosure itself to PE-ground right?

The problem is that it is not conductive, I don't know anything about metals and surface treatments but it does not conduct so I thought to take a tool and sand away the non-conducting surface and then somehow ensure a connection to PE-ground.

I don't really like that solution, but does anybody have any other idea?

#1 Reply
Posted by Phoenix on 07 Oct, 2017 02:45
Anodizing creates/thickens the oxide layer on the aluminium surface - which as you've discovered is non-conductive. Pretty much your only option is to sand or brass wheel the anodizing off where you need electrical connection and then drill a hole and use a circular lug.

For safety the metal housing must be, in its entirety, earthed. The earth pin from your mains connector must go directly to the housing with some kind of reliable/shake proof connection. Each part of the housing will need it's own earth strap or the mating surfaces sufficiently sanded to create a reliable contact surface.

For EMI the mounting hole of the AC-DC converter should be connected to the chassis earth too. This is often achieved through the metal stand-off, but in your case you may need another earth strap for it.

#2 Reply
Posted by rdl on 09 Oct, 2017 05:50
The listing for the "Aluminium Housing" says it's made from cold rolled steel.

Quote
2. The shell is made of cold-roll steel sheets. Please be careful in case that it is scratched by sharp objects or damaged by direct sunlight and humid environment.

It only makes a difference in that Aluminum oxidizes quickly, so make the connection as soon as possible after removing the non-conductive coating. Also, use a star (or toothed) washer that bites into the underlying metal to make a good electrical connection.