Housing a Power Supply

Question

This is an extension to the question "Safely housing a power supply" asked by Harry Braviner.

I plan to use a very similar power suppy as the main compnent:

In my case the need is to power a 24v 130w motor to drive a clockmaker / watchmaker 8mm lathe. A speed controller will be separate and not contained within the power unit housing. The lathe will be mounted on a stand which is about 4" deep and has a central slide out drawer, but that will leave an underside compartment ether side of the central area, which might be large enough to house the power supply subject to the answers I receive. Alternatively I'll build the supply as an external power brick with a fly lead that plugs into a socket on the lathe cabinet. A controller for the motor speed will be mounted on (or beneath) the lathe stand.

My questions are:

1. The answer to the original question recommended a metal junction box. Could a rigid plastic box be a safe alternative if the heat from the power supply is fairly low (or is it best to play safe and use a metal box)?
2. Is a ventilation fan likely to be needed, or can that be determined only by experiment?
3. If the power block is kept exernal (like a laptop) wth a fly lead to a socket on the lathe base, what style plug and socket would be appropriate to use that can take the likely current?

many thanks in aniciption,

Answer 1

These power supplies are not safe to leave exposed due to mains wires connections, they are meant to be inside an equipment enclosure, but they do need quite a bit of airflow. So a small enclosure with no air circulation won't cut it.

If you can put it in your lathe stand, that would be practical, since that would make the whole device self-contained, easier to move or store without a power brick attached. But if it fits inside a small compartment it will need a fan, and if this jeweller's lathe is used to cut metal, it will also need an air filter to prevent metal shavings from ending up inside the power supply. Make sure the airflow goes inside the power supply, not around it.

If the motor is brushed and uses a simple PWM controller, it should be possible to control the fan from the same controller.

You could also use a power supply that doesn't need a housing.

Although these have rather short wires, so you still need to put the wire nuts somewhere. You could also use a readymade brick rather than build one:

This will most likely be cheaper than a separate enclosure for your power supply.

Answer 2

My questions are:

1. The answer to the original question recommended a metal junction box. Could a rigid plastic box be a safe alternative if the heat from the power supply is fairly low (or is it best to play safe and use a metal box)?

Plastic is a thermal insulator and raises hotspot temp and lowers MTBF but could be done with a fan which eventually needs vacuuming for dust and may cause noise if against a vent. Plastic also accumulates static which might cause static discharges. Conclusion: cheap choice but hotter

2. Is a ventilation fan likely to be needed, or can that be determined only by experiment?

This depends on the efficiency and power utilization. A 300W fanless design might not but costs more, while 150W on a 180W unit will need cooling by excellent fanless design e.g. Meanwell, TDK Lambda (only) with thermal conduction or with a thermal-controlled fan. I would estimate if you only use <50% of max power, a fan is not needed. Accumulated hot time just accelerates wear on capacitors and other hot parts.

3. If the power block is kept external (like a laptop) with a fly lead to a socket on the lathe base, what style plug and socket would be appropriate to use that can take the likely current?

Depends on the likely current 5A 7A 10?

Perhaps the best consumer connector are the extra ones inside PC towers for HDD connections coined as "MOLEX" connectors, just a brand once famous for this style. Then use 2 pins for each +24 and 0V. It is keyed and easily inserted in line with wired pigtails. Depending on the cable length, use stranded AWG 16 for a nominal choice.

Never use a coaxial barrel Plug/Jack. They will eventually oxidize and melt.

So ultimately every choice depends on your priorities for open-frame with lid, enclosed, enclosed with fan, enclosed without fan.

e.g.

• lower cost but check efficiency 85% (more heat) vs 96~98% rating = Open frame in a low dust environment, hard-wired.
• reliable? only suppliers with a good reputation and MTBF spec vs temp
• appearance? depends on how crafty you are but observe cooling, moisture, dust control and other requirements

I once disqualified PowerOne after they moved production to Mexico and if the isolated DC output was earth grounded , it failed power line transient tests in a dozen different ways due to common-mode E-stress imposed by transformer capacitance on primary parts (which took them months to fix) They only did production testing 100% of all units with DC output floating.
So I used my second source Lambda instead.

Here's one https://www.digikey.ca/en/products/detail/tdk-lambda-americas-inc/LS200-24/2336564 $86 but only 85% efficient @ 200W