EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Jordanaudio on June 14, 2024, 01:21:09 am
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I must admit that I don't know enough about electronics yet, but everyone started with no knowledge, so be kind. I've built a dim bulb tester. For safety, I have it plugged into a variac and that is plugged into an old BK Precision TR-110 isopack with a 3-amp slow blow fuse.
I, perhaps, was a bit ambitious on my design, as I wanted a bulb bypass switch and LED indicators. The yellow indicator lights when I turn the master switch on to the box. It's a lighted switch but the LED is hard to see so I added the yellow indicator. The green indicator lights when I switch it to limit through the bulb circuit. The red indicator lights when I switch to short the bulb circuit. The LED indicators are 120V AC.
It took me several hours of trial and error to get things wired to the point they are now and, as long as have both bulbs screwed in, the circuit is complete and the indicators light as well. I cannot figure out how to make this work so that I can use a single bulb, instead of 2 bulbs if I wanted an even greater current limit.
It seems like it should be incredibly simple and I feel very stupid that I can't figure this circuit out. But every different combination I've tried has resulted in either the indicators not lighting properly, or the current limit bulbs lighting up when they shouldn't.
I have included photos of my build and a schematic (which I believe I've drawn correctly according to how it's wired). Any advice is appreciated. Thank you for your knowledge and guidance.
- edit, uploaded corrected schematic to include the ground wire
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put a switch across 1 lamp,when its open the lamp is in circuit,when its closed its bypassed.
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Low wattage 120V ES base incandescent bulbs are still reasonably available from specialist suppliers, so there is absolutely no need for two 'dim' bulbs in series (which doesn't work well anyway). The preferable arrangement would be two E26 and one E17 or E12 socket, all in parallel. Maybe have both E17 and E12 sockets, depending on your existing stock of low wattage bulbs. Current limit selection is by screwing in a appropriate bulb or parallel combination of bulbs when you need more current than you can get through a single 100W bulb.
If you want the red indicator to go out when the green is on and visa versa, vou need a DPDT for the dim bulb bypass switch. Use one pole for bypass and the other to choose between the red and green indicators.
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Use a multimeter to check if all connections are correct. You should make sure there are no short circuits. Verify that the LED indicators light up correctly according to the switch positions.
Bulb Sockets. Each bulb socket should be wired correctly and the bulbs should make good contact.
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Your circuit shows a dead short across the L N after the main switch. Obviously a drawing error, otherwise it wouldn't work at all.
As mentioned, put the bulbs in parallel, not series, to increase the wattage.