| Electronics > Projects, Designs, and Technical Stuff |
| Need some help building a circuit involving switchs and relays |
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| Shaydzmi:
This is the big led that I promised to give you a photo of it: |
| Renate:
This is a cute little circuit that feeds the 24 VAC to the light bulbs. It's "hard" (low resistance) in the sense that the triac is on most of the time. It's "soft" because the rest of the time it's just a 470 ohm resistor. A 50 mA bulb will cause a 12 V drop when the triac is off. (Ok, the triac is off only in the low voltage part of the AC cycle so it doesn't generate that much, maybe a volt or two.) The thermistor will reduce the current if too many bulbs are on. There's no reason that a dozen bulbs can't be on at the same time. The triac also can be a dimmer for all the bulbs, it's just a question of the voltage of the two zener diodes. Edit: Graphic corrected, added sensing, added 24V supply |
| Shaydzmi:
Where are the in and the out? And where are the 3 big resistors? |
| Renate:
I corrected and updated the drawing above. As I said, the two stacked power resistors are bypassed with a solder blob. The 24VDC supply is riding on top of the 24VAC (which is a bit unusual to see). They have to do that so that they can measure the sense. The "floating ground" is the minus side of the 24VDC supply. |
| Shaydzmi:
Hi, I tried to de- bypass the two resistors, the bulbs almost would not even glow. The zeners D2 and D3 have this: 1N5225 (if they have the same value). The thermistor gets hot even if one bulb is on. Does this information help? |
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