24.11.2020 MW PSU containment.

 *

Tuesday 24th. A grey, overcast day with a hint of rain in the air. The proper rain!

The "posh" IP44 plastic box. Which I had ordered two weeks ago. Proved to be a few millimetres short for the new PSU. I would have had to modify the box far too much to take the PSU. 

So I looked elsewhere and immediately found a transparent, snap-on lid, sandwich box which fitted the PSU perfectly. 

The opaque, white lid is a better material to make a hole for the 40mm cooling fan. Which would go inside without interfering with the PSU's perforated cage. 

I found a piece of 5mm scrap aluminium plate. Which was the perfect fit to go under the PSU base plate as a heat sink. While neatly holding the PSU clear of the plastic box base. This will provide a wide channel to hide the necessary cables neatly out of sight.

I'm now juggling with different ideas to maintain waterproofing of the PSU in unexpected rain. Any holes I make for ventilation might let rainwater into the box. The cables can enter at the bottom of the box base. When the box is mounted on the steep slope of the pyramidal pier. Perhaps these holes will provide a rain-sheltered exit for the airflow from the fan?

How best to shelter the fan hole from unexpected showers?  Logically it should be in the base and "underneath" when on the sloping surface. Then any moisture will not enter. Thought that would required stand-off feet on the bottom of the box to allow air to enter the fan. An "eyebrow" shield would divert moisture away from the fan.

The lid can only be peeled off the base by lifting a tab on one corner. Trying to pull the lid [or base] straight off the other half is almost impossible. Which strongly suggests the lid should be outwards when the box is mounted. Which is a bit of a shame. Because it would be nice to see the PSU through the clear base. 

Perhaps the lid can be mounted on the pier on rubber feet or spacers. With the PSU screwed to the lid of the box over the heat sink plate. The clear box base can then attached, as a lid, to provide full
protection.

While leaving the lid's corner tab accessible and still flexible enough, to allow a finger nail to press downwards. For when removal of the clear cover is required. While still maintaining the security of the clear box to avoid shock from probing fingers or tools. Or contact with the bare mains terminals. The clear lid will also allow the fan to be monitored for rotation without physical contact.

The images show the result of a couple of hour's practice after talking it to death on my blog. The fan hole was 38mm and cut with a hole saw. 

I used stainless steel Nyloc nuts on the fixing screws to ensure the fan won't vibrate loose. I still need to make cable holes and exit holes for the exhaust air pushed out by the fan.

The last image shows the smart little 6-way fuse box. Though I'm not sure I will fix it onto the PSU enclosure. Perhaps on a plate carrying both items. That will make it easy to hang both of them from the pier via a screw through a simple keyhole.

I'd like some rubber feet to provide enough stand-off to allow free air flow through the base holes. I have the "sandwich box" lying on its side for now. It badly needs the drive electronics resited. They are sitting on the L-branch of the desk as a temporary support for the laptop. Neither arrangement is ideal. 

The AWR drive boxes are physically restrained together and apart by all the cables. The whole set-up gets in the way of the telescope when I do a meridian flip too soon after lunch. With the camera barely scraping the bare desk top I have to "steer" it around the laptop and drives on the paddle. Or there would be a collision. 

*