Telescope Reviews: Crow Haven Observatory - a small nested ROR design

Here's what Paul has to say--

DC Power:

First, I offer the considerations that must be made to provide reliable, clean, DC power. Next I'll cover how we were able to accomplish this.

The two biggest enemies of electronics are heat and humidity and the system needs to be designed to minimize both.

Humidity - Promotes corrosion which can increase resistance at connections ultimately leading to system failure. We address this problem by installing a dehumidifier.

Heat - DC power is much less efficient in transmission than AC power. There are some things we can do to minimize the amount of power we turn into heat.
-- Use heavy wire. For example 10 gauge wire will only efficiently carry 40a at 12V DC for approx. 10 ft. without a large voltage drop.
-- Minimize DC wire run lengths.
-- Use large enough connectors. The key number is the current rating, not voltage.
--Isolate DC wires from AC wires as much as possible -- do not run them in parallel less than 18" apart. The AC will couple across to the DC wires and may cause interference problems.
-- Use multistrand wires. Electrons travel with less resistance along the surface of a conductor. Multistrand wire increase the surface area of the conductor over single-wire conductors.
-- Run DC power supply at 30 - 50% of max. rated output.
-- Maximize cooling airflow around and through the power supply.
-- Crimp or soldered connectors, there's a place for both. Soldered connectors are a personal favorite. Use rosin flux, tin the wires, clean up after soldering with isopropyl alcohol. Use minimal solder -- the old saying "The bigger the glob, the better the job" just isn't true. Crimped connectors use a conductive grease inside each pin before crimping to prevent corrosion.

What We Did:

Requirements: 12V DC, 40a regulated DC power supply.
This seems like a lot of power -- 500W. It's roughly twice what we would need with our current set-up. As time goes on we tend to add more stuff and I wanted to allow for future growth.
It was relatively simple to find a 12V DC, 40a power supply on the internet. However, none of them offered any detailed technical data. In addition, the few reviews we could find were not at all complimentary.
Maya asked for some assistance and rsbfoto/Rainer responded by recommending Micropower Direct. They offer a wide variety of custom DC power supplies. In addition they provided all the technical data up front, including MTBF (mean time between failures), noise limits, etc. I ordered model MPA 500RE-12T.
After a 5 week wait, the power supply arrived. Total cost was $255 US including shipping.

I then constructed a plenum box with an additional fan (12V DC, 3" diameter, 33 CFM, vanaxial type). Both ends are screened to keep out the critters. This will be installed under the wooden floor at the base of the pier.

It was suggested by Scott K that we utilize a RigRunner DC power distribution panel (model 4010s) by West Mountain Radio. In addition to providing 9 fused DC outlets it monitors the input voltge, has both audible and visual warnings, and offers an automatic switching option. This will be mounted on the side of the pier near the top.

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