Out of curiosity, Anyone out there know how load detection circuits work in a dimmer pack? Like the leprecon vx series, where it has a light that tells you if there's a load connected or not I think I have an idea of how they work probably, but haven't been able to find out for sure in my searchings of the Internet.
Load detection circuits
- Thread starterbshock84
- Start date
Well, I'm not sure how the VX does it, but I can tell you how it was done on L86 dimmers.
L86 put a neon lamp across the power cube output and neutral. Since most power cubes of the time would have a small amount of leakage current and full voltage when control was at zero, the neon would light up if there was no load. Once a load was on the circuit, the neon would stay out because the load would draw the leakage current and the circuit voltage would drop to zero.
The fun part was that when a dimmer was driven above zero, and a load did exist, the neon would glow again. Even more fun was that later model power cubes did not have enough leakage current to drive a neon at no load and no control.
Ok, so try to use that as a viable troubleshooting tool....tricky.
The VX may do it differently, but I'm sure some sort of power must be sent down the line for viable load detection.
David
L86 put a neon lamp across the power cube output and neutral. Since most power cubes of the time would have a small amount of leakage current and full voltage when control was at zero, the neon would light up if there was no load. Once a load was on the circuit, the neon would stay out because the load would draw the leakage current and the circuit voltage would drop to zero.
The fun part was that when a dimmer was driven above zero, and a load did exist, the neon would glow again. Even more fun was that later model power cubes did not have enough leakage current to drive a neon at no load and no control.
Ok, so try to use that as a viable troubleshooting tool....tricky.
The VX may do it differently, but I'm sure some sort of power must be sent down the line for viable load detection.
David
Here's the schematic. http://www.leprecon.com/productfiles/301105EVXpowermodule_.pdf
Only works when not in test mode and dimmer is at less than 90% control. Perhaps it is using lamp return voltage in the off time of the dimmer to determine a load. A little tricky but fairly certain to work on most loads. JD might have a better answer.
David
Only works when not in test mode and dimmer is at less than 90% control. Perhaps it is using lamp return voltage in the off time of the dimmer to determine a load. A little tricky but fairly certain to work on most loads. JD might have a better answer.
David
JD
Well-Known Member
The linked diagram uses two opt-isolators. One that fires the SCR's and one that provides a comparison. If the output circuit conducts at a time when U2 is not conducting, then D5 the "error" light lights. Bleed-through on the firing circuit (unloaded) will light D6, the output indicator.
Back in the 80's, I added my own output detector circuits to my dimmers, but it was a little simpler. Diode, zener, LED and resistor across the filter choke. If there was any flow through the choke (meaning a load was attached) then the LED would light. Even at idle set, enough waveform appeared across the choke that the LED would light if a load was attached. (There was enough noise at all settings to light the LED.) The zener and resistor limited current and voltage flow through the LED.
Note, this was my own modification, and as such technically removed the UL rating on the unit. (Hey, it was the 80's!) The circuit was so simple that I would be surprised if no one duplicated it in the last 30 years.
Back in the 80's, I added my own output detector circuits to my dimmers, but it was a little simpler. Diode, zener, LED and resistor across the filter choke. If there was any flow through the choke (meaning a load was attached) then the LED would light. Even at idle set, enough waveform appeared across the choke that the LED would light if a load was attached. (There was enough noise at all settings to light the LED.) The zener and resistor limited current and voltage flow through the LED.
Note, this was my own modification, and as such technically removed the UL rating on the unit. (Hey, it was the 80's!) The circuit was so simple that I would be surprised if no one duplicated it in the last 30 years.
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