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I want to use 5 step down converters (220 VAC -> 5V DC) inside an enclosure inside an enclosure (double isolation).

The step down converters are similar to these. There will be 5 of them, where one is connected to an RS485 transceiver (MAX1485CPA), and the other 4 have each an optocoupler (6N137) and RS485 transceiver (MAX1485CPA).

The inner enclosure is completely closed, plastic, and just big enough to contain them with about 1 cm / 0.4" space between each converter.

In the outer enclosure (also plastic) will only be XLR (DMX) connectors and max. 10 small LED lights.

Also I will use a fuse (1A?) for safety.

Questions:

  • Will heat be an issue? If so, should I make 'holes' in both enclosures for air flow?
  • As you can see I cannot screw the devices in an enclosure (no holes), so I want to glue them (upside down with the yellow flat area glued for a maximum and a flat glue area). Besides that, I'm intending to use wooden popsicle sticks to 'physically' make sure they never can touch each other (by glueing them somehow between the converters. Is there a problem or better solution (without having to buy new converters)?

enter image description here

Update

After a discussion it is best to use a switching supply with enclosure already around it (being an amateur):

5V 3W mini power supply module Hi-Link HLK-PM01

enter image description here

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    \$\begingroup\$ Please add a link to a datasheet or spec sheet for the adapter. It is not at all clear from just the picture what the characteristics of this adapter are and whether it is a high heat producer or not. \$\endgroup\$ – Michael Karas Aug 27 '18 at 9:58
  • \$\begingroup\$ @MichaelKaras I did for the 2nd (updated) supply. \$\endgroup\$ – Michel Keijzers Aug 27 '18 at 12:14
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Small transformers are very inefficient, it's just the way that the parameters of iron and copper turn out.

You will have much smaller heat problems if you use a single power supply of 5x the current output.

Sometimes it's worth paralleling smaller devices, and sometimes it isn't. This is definitely a case where one bigger is better than many smaller.

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  • \$\begingroup\$ However, I want isolated power distribution (for a DMX-512 splitter). So a single power supply will not help (unless I put 5 of them inside), but than I need much more space. \$\endgroup\$ – Michel Keijzers Aug 27 '18 at 10:51
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Any enclosure that has power being dissipated inside of it will create a situation where the temperature will increase. The more that you cram into a smaller space the worse the problem can become. You should evaluate just how much heat each of the modules creates when in the proposed enclosure before you commit to a final design/build. It could be that you may even have to add a fan to force air through both enclosures to keep things cool. Remember that excess heat is the enemy of electronics.

The flat yellow surface is just some tape wrapped around the transformer core. It is probably not the best gluing surface and the tape could easily come loose. I would suggest that after attaching your input and output wires that plopping each adapter into a good pool of hot melt glue may be a better mounting scheme. Just make sure that the hot melt glue adheres to the inside of your enclosure before committing to use it.

I have to ask why you think it is necessary to have five separate power adapters in one enclosure when the load on each one is so small. Maybe you could explain that with a schematic.

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  • \$\begingroup\$ Thanks for the answer, I hope I don't need a fan, that would mean I need to by another (big) enclosure. Thanks for the tip about glueing the adapters. I need five power adapters to make an isolated DMX-512 splitter as explained in question electronics.stackexchange.com/questions/391264/… \$\endgroup\$ – Michel Keijzers Aug 27 '18 at 10:46
  • \$\begingroup\$ @SamGibson ... If I did it was a mistake, sorry, I didn't mean to edit the answer. Thanks for the comment, so I could move the removed part as comment below. \$\endgroup\$ – Michel Keijzers Aug 27 '18 at 11:45
  • \$\begingroup\$ Schematic (sort of): DMX Splitter Instead of the double inductor to 4 outputs, I want to use 4 separate converters (since I'm an amateur so don't want to make my own AC/DC converters). Also, I want 4 instead of 3 outputs, and with one input, I need in total 5 converters. \$\endgroup\$ – Michel Keijzers Aug 27 '18 at 11:47
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Based on your previous question, this looks like an X-Y problem. You can actually get your task (powering isolated DMX lines) done with a single mains-powered AC-DC converter and 5 isolated DC-DC converters - they exist and they aren't that expensive, and it certainly will be safer in terms of operating voltages. I can't give a model suggestion, but even eBay gives plenty of suitable listings.

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  • \$\begingroup\$ That's an interesting solution too, I found something like B0505S-1W aliexpress.com/item/… ... is that what you mean? \$\endgroup\$ – Michel Keijzers Aug 27 '18 at 13:04
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    \$\begingroup\$ Something like that would work great, it seems, and the price is very OK. Here's the datasheet. So, given that the only reason you need separate AC-DC power supplies is the isolation requirement, these DC-DCs can do it better, you can test it easily if you unsure (with any USB port), and in unlikely case they don't work for you, the cost is, like, $5? \$\endgroup\$ – Арсений Пичугин Aug 27 '18 at 13:11
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    \$\begingroup\$ Nice! I might get some too, then. I suggest you get a couple of spares, actually - I always do that with cheap Chinese modules because 1) sometimes it turns out you need these same modules for something else 2) sometimes you might want to build more of the same thing 3) sometimes one of the modules is defective from the factory, and even though you certainly can get a refund, it will delay your project. \$\endgroup\$ – Арсений Пичугин Aug 27 '18 at 13:29
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    \$\begingroup\$ That's something I've heard about, too (someone complained about having 7V on the output). If so, given your low current requirements, you can either use a 78L05 regulator (or some other LDO), or even a simple "low-value resistor + 5V zener" circuit to drop the voltage down to something your ICs can handle. radio-electronics.com/info/power-management/… The Zener circuit is something I'd use in a pinch, as it's good for low current requirements and I don't have lots of 5V regulators lying around, unlike 5V1 zeners. \$\endgroup\$ – Арсений Пичугин Aug 28 '18 at 11:48
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    \$\begingroup\$ Found this calculator: 320volt.com/en/zener-power-supply-calculator with 8, 6, 5 and 30 inputs, it gives a 25ohm/0.5W resistor and 5V1 Zener requirement. Depending on which parts you have access to, it's either this or a 78L05, your call =) \$\endgroup\$ – Арсений Пичугин Aug 28 '18 at 12:03
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Will heat be an issue? If so, should I make 'holes' in both enclosures for air flow?

Yes, you either need to ventilate or derate enough that they do not dissipate much energy.

Is there a problem or better solution (without having to buy new converters)?

Gluing PCB's is bit of an amateur solution. Potting is more common if that's what you need.
Buy better converters, or put each in their own enclosure. Remember that mains is a fire hazard.

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  • \$\begingroup\$ Using 5 enclosures is also not really what I want (it would make the device quite big). But glueing is also amateur (which I am by the way regarding electronics). I will search what potting means, thanks for the tips. \$\endgroup\$ – Michel Keijzers Aug 27 '18 at 10:50
  • \$\begingroup\$ Potting seems like a quite professional/expensive solution for my 'hobby' project though. \$\endgroup\$ – Michel Keijzers Aug 28 '18 at 13:28

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