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DynamoBen
04-29-2008, 04:08 PM
A while ago there was a discussion here about how to double the quantity of dimmer outputs. Since Christmas lighting is low wattage but high channel count having the ability to increase the number of dimmable channels without additional electronics would be a huge win.

In a previous life I worked for a company that made dimmers and splitters that could take a single dimmed channel and split it into two. It did this by "dimming" the top half and bottom half of the sine way independently. Between the dimmer output and the fixture was a splitter that sent each half of the sine to a different fixture (there were diodes in the splitter). The only down fall to this method of doubling your dimmer count is you had to use 77V lamps instead of 115V (splitting halves the voltage). However for us this would mean we would either need to cut the string in half or rewire it.

Datasheet with conceptual description of how dimmer doubling works (page 2):
http://www.diversifiedlighting.com/pdf/ETC_DIMMER_DOUBLING_FEB-08.pdf

djulien
12-13-2008, 05:30 PM
The only down fall to this method of doubling your dimmer count is you had to use 77V lamps instead of 115V (splitting halves the voltage). However for us this would mean we would either need to cut the string in half or rewire it.

Could you clarify the voltages for me? I thought that a half wave 120V would still use the same peek voltage (170V or so), just in one direction only, so you would still need 50 x 2.5V bulbs. I understand that half wave would only be half as bright because the bulbs are lit only during half the wave. Are you saying use fewer or lower voltage bulbs because the average voltage is lower? I thought I still need to account for peek voltages.

(I just found this topic via a link from the charlieplexing thread - sorry for the late reply.)

don

DynamoBen
12-13-2008, 07:02 PM
AC power voltages are measured peak to peak. So the voltage from the positive peak to the negative peak. If you use 120V the positive side is ~65V and the negative ~65V. So in this setup you would need AC lamps that where over 60V, if you use 120V lamps they will run at 1/2 intensity.

NogginBoink
12-15-2008, 06:05 PM
How bright is a string of mini's at half voltage? If they're reasonably bright the output may be acceptable for many of us and require no rewiring at all.

P. Short
12-15-2008, 06:34 PM
It's not 1/2 voltage, it's 1/2 power (voltage is 70%). How about just cutting a 50-count string down to 35-ct.

djulien
12-19-2008, 02:29 AM
AC power voltages are measured peak to peak. So the voltage from the positive peak to the negative peak. If you use 120V the positive side is ~65V and the negative ~65V. So in this setup you would need AC lamps that where over 60V, if you use 120V lamps they will run at 1/2 intensity.

Sorry, I'm still a little confused. I'm using rectified AC on some of my SSRs (running the 120 VAC through a diode bridge before giving it to the SSRs), and the minilights seem as bright as with regular AC. The total voltage across them is half what it would be with regular AC, and the resistance is the same, so the current would also be half. Then their power consumption should be half and they should be ~ half as bright.

OTOH, could I just use 25 bulbs in series because the voltage swing is only ~ 65V, and I should get the same brightness as 50 bulbs in series with regular 120 VAC?

don

djulien
12-19-2008, 04:26 AM
The total voltage across them is half what it would be with regular AC, and the resistance is the same, so the current would also be half.

d'oh, I think I've finally got it. The voltage (differential across the string of bulbs) is *not* half - it's still 120V. It's just that the polarity is always the same, correct? That means same current, same power, same brightness, and I can't use substrings at that voltage.

don

DynamoBen
12-19-2008, 12:40 PM
Sorry, I'm still a little confused. I'm using rectified AC on some of my SSRs (running the 120 VAC through a diode bridge before giving it to the SSRs), and the minilights seem as bright as with regular AC.

Please keep in mind that the doubling method described here only works on AC loads (not rectified DC loads). This method maintains the voltage on each side but dims via phase-angle dimming the top and the bottom of the sine wave separately.

djulien
12-19-2008, 03:00 PM
How bright is a string of mini's at half voltage? If they're reasonably bright the output may be acceptable for many of us and require no rewiring at all.

There's a noticeable difference. If they have completely dark surroundings, they are okay. But if there is ambient light or they are near full-power lights, they look dim.

don

alwysrit2
12-19-2008, 06:57 PM
This is interesting, but I don't see this as a huge savings in any direction. Can you help me understand what the savings would be?
-Don