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Modifications to "the cube"
Well, I finally got around to making some necessary changes to the solenoid-actuated lead pot. Now it's fully functional and doesn't overheat. A single momentary push button fires the hold-in and pull-in coils, breaks the pull-in coil upon solenoid closure, and then breaks the hold-in when the button is released.
I've attached a schematic of the starter solenoid. The original solenoid is on top and my modified solenoid is on the bottom. The hold-in coil is solid, the pull-in is dashed. B is the battery positive terminal, M is the motor terminal, and S is the solenoid switch terminal. The "fix" looks pretty rough, so I'll spare you the pictures. I drilled a hole dead center in the solenoid cap and put a Chicago binding post through it to accept a dowel. I used a wood dowel (1/8") dropped through it and attached a metal post at 90° to make the electrical contact shown in the schematic. When the solenoid fires the copper disk pushes up on the dowel (wood to avoid conduction) and breaks the contact at M. The hold-in coil stays energized until the button is released.
Notice that I also ground down the motor terminal on the inside to avoid a dead short across the battery and motor terminals. That short across the solenoid is what allows current to flow to the starter motor and breaks the pull-in circuit when the solenoid is attached to a starter in a vehicle.
I also drilled out the restrictions in the street elbows. They were 1/4" and now are about 13/32" and are close to the ID of the 1/4NPT pipe. The lead really flows now, but thankfully not so fast that it splashes or causes problems.
I haven't added any burner under the pipe yet. It's just not worth the effort for me at this point. I only need to head the downspout once per casting session.
Next mod will be some heat shroud, akin to jmsj's thoughts (thanks!) and the addition of a chimney to vent the fumes and smoke during heating. I use used motor oil as my reducing agent ("flux") and it's gnarly!
[Thread hijack] BTW, starter problems are often simply the loss of electrical contact across the battery and motor terminals as they wear from use. If you hear click with no motor turning, simply pop apart your solenoid and inspect the terminals. Buy new posts, or add material by brazing. [/Thread hijack]