Magnetic Circuit Breaker box

[nevetslab]

The Hammon Diecast Aluminum Box finally came in, so I was able to cobble together a simple 2A & 5A Magnetic Circuit Breaker box, with a toggle switch to select which breaker is used for those times when you'll probably blow fuses on a project. I still have to put the Light Bulb Limiter box together, having been using a Variac & Power Analyzer and periodic collection of fuses when problems arise. I have 20A, 15A & 10A Airpax Curve 64 Rocker-style Magnetic Circuit Breakers like I used at BGW Systems for the higher current loads, and a power cable set up to swap whichever one is needed. I did have a different cable for the 5A Airpax, different format (toggle), and didn't have quck-disconnect terminals.

After I found/ordered a moderately inexpensive Carling 2A Magnetic Breaker and it arrived, I finally put this simple box together.



The Hammond Box is a 1590V 4.7" x 4.7" x 3.7" diecast box, wall thickness of 0.092", so punching thru that with my Whitney XX Punch with a 3/8" punch/die installed, it took all of my might to punch thru it. Really needed a torque amplifier on the handles (12" length of fitted pipe to get more drive torque. Cutting the rectangular hole was a matter of scribing the outline of the opening and then fitting a 0.125" punch/die and sitting there forever punching fractions of a hole to for a straight line of holes, doing my best not to go over the scribe line. Shaped it square with a nice carbide mill file.

Nice that the molded plastic cord grips have come down to being afforable...Home Depot caries those for around $2.39 ea, if memory serves. The Yellow Arrow-Hart Nema 5-15R Outlet was under $5, and the Hubble Nema 5-15P plug came out of my inventory....I'd pick those up on ebay at affordable prices anytime I'd find them. 18AWG SJT power cable, cotton fiber fill.

The toggle switch came out of a Fender Amp's Ground Reverse Switch...Carling 6A/125V, which selects which breaker is in use. The Carling 2A Push-to-Reset Magnetic Breaker wouldn't have been my first choice, but it was all I could find at the time I was looking. I tend to like breakers that can function as a power switch, which this one doesn't. RED Button stays in unless tripped.

A quickly drawn up schematic:

Magnetic Circuit Breaker Box.pdf

I joined the Neutral wires together with an in-line crimp splice, and connected both Ground wires to a grounded #8-32 chassis screw, first fixed with a Keps Nut, then the ground lugs of the two wires under a second Keps Nut, so the box is properly grounded.

[Greg Robinson]

Steven, thought I might share my LBL to give you some ideas. I use halogen bulbs, which are actually better for this service than standard incandescents, as they run hotter in operation, so have a sharper PTC knee. Also handy that halogen are still available for sale here in Australia for "special applications" (though disappearing). I've been using the same batch of 77W bulbs for years now.
Each bulb has its own switch to turn it on in parallel with the others, there's a master "on" switch, and a "bypass" switch. I took these photos years ago before I'd labelled it.
There's a "Kill A Watt" style meter, which I modified so it will display correctly at all times. Out of the box it is self-powered by the same port as the voltage measurement input, it was quite simple to open up and split the capacitive dropper supply from the meter input and add an extra terminal that's fed directly from the "on" switch rather than after the bulbs, else it would turn off below about 200VAC (from memory).
It shows voltage, current, wattage, VA, PF, and can count kWh (though I never use that feature).
There's enough ventilation holes/gaps in the 2U 19" rack chassis I used to easily see if bulbs are glowing, though also easy to tell watching the meter.
People always ask if it gets too hot being enclosed, but no, if the bulbs are glowing bright you've got a problem in the DUT, so you should turn it off.
This has served me well servicing even monster multi-killowatt PA amps. About the only time I use my Variac is when validating designs will work correctly over the full tolerance range of the mains supply here, else this is much more useful.

Hope you find it helpful.

[nevetslab]

Steven, thought I might share my LBL to give you some ideas. I use halogen bulbs, which are actually better for this service than standard incandescents, as they run hotter in operation, so have a sharper PTC knee. Also handy that halogen are still available for sale here in Australia for "special applications" (though disappearing). I've been using the same batch of 77W bulbs for years now.
Each bulb has its own switch to turn it on in parallel with the others, there's a master "on" switch, and a "bypass" switch. I took these photos years ago before I'd labelled it.
There's a "Kill A Watt" style meter, which I modified so it will display correctly at all times. Out of the box it is self-powered by the same port as the voltage measurement input, it was quite simple to open up and split the capacitive dropper supply from the meter input and add an extra terminal that's fed directly from the "on" switch rather than after the bulbs, else it would turn off below about 200VAC (from memory).
It shows voltage, current, wattage, VA, PF, and can count kWh (though I never use that feature).
There's enough ventilation holes/gaps in the 2U 19" rack chassis I used to easily see if bulbs are glowing, though also easy to tell watching the meter.
People always ask if it gets too hot being enclosed, but no, if the bulbs are glowing bright you've got a problem in the DUT, so you should turn it off.
This has served me well servicing even monster multi-killowatt PA amps. About the only time I use my Variac is when validating designs will work correctly over the full tolerance range of the mains supply here, else this is much more useful.

Hope you find it helpful.

Very nice piece of engineering work! I'm definitely impressed! Thanks for sharing that for all of us to see.

[GoldtoneWorkshop]

Wow! That bulb limiter is drool worthy!!!