Dimming Ballast

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adavey

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Does anybody have a rough estimate how much extra a 2 lamp 32watt t8 fixture would cost w/ a "FLOURESCENT DIMMING BALLAST" ???????
 
Rewire is right on, 70 to 90 bucks for the ballasts. Don't forget to add an additional 100 to 125 bucks for the fluorescent dimmer switch as well.
 
Jljohnson said:
Rewire is right on, 70 to 90 bucks for the ballasts. Don't forget to add an additional 100 to 125 bucks for the fluorescent dimmer switch as well.
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I've had to change the tombstones in the past also.
 
Hi, never had to install a dimmable ballast. Chris, are you deriving the two hots by saying one constant feed and the switch leg? qcroanoke, why would the tombstones need to be replaced?
 
mark32 said:
Hi, never had to install a dimmable ballast. Chris, are you deriving the two hots by saying one constant feed and the switch leg? qcroanoke, why would the tombstones need to be replaced?
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I think it had something to do with the type dimming ballast we used. It was quite a few years ago too! Can't really remember exactly why but I still have some of the tombstones we took out of the fixtures, I mean luminaires! LOL
 
The Lutron Hi-Lume ballast requires the extra wire that is always hot and they claim to be able to dim down to something like 1%. The Mark X ballast does not require the extra wire and can dim to approximately 10%. Now if you can tell the difference between a 1% & 10% dimming level on a fluorescent tube you are better than me without having them side by side.

-Ed
 
ed downey said:
The Lutron Hi-Lume ballast requires the extra wire that is always hot and they claim to be able to dim down to something like 1%. The Mark X ballast does not require the extra wire and can dim to approximately 10%. Now if you can tell the difference between a 1% & 10% dimming level on a fluorescent tube you are better than me without having them side by side.

-Ed
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Ratings on dimmable fluorescent ballasts are based on percentage of lumen output. There is a big difference between a 1% ballast and a 10% ballast if you are planning to "dim it up" from off, or dim it all the way out in a nice smooth fade.

Dimming ballasts come in the 3 basic variations. 2 wire ballast (like the Mark X) wire like a normal incandescent fixture wired to a dimmer, 3 wire ballasts (like the Hi-Lume) require a constant circuit and dimmed circuit with a common neutral as described above. Usually works best if the 2 "circuits" are from the same actual breaker. 4 wire ballasts use a constant circuit and a 0-10v dimming signal.

Make sure you match the ballast type to the dimmer type. Been doing this for over 10 years and still managed to have a conflict on a current job.:mad:
 
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090327-2018 EST

Filament type fluorescent lamps need the filaments heated to emit reasonable quantities of electrons. Once started the normal current at full brightness is enough to keep the filaments hot without external excitation.

If you want to dim the lamp to a low level, then external heating by a filament transformer is required. This is why there needs to be a full excitation hot wire to the ballast. However, this should only be powered when the lamp is to be operated.

Open up a Lutron SF-10P dimmer and you will see this full excitation wire, red, comes from the output side of the on-off switch. Yellow is the phase shifted variable output. This dimmer requires a neutral and appears to be able to start at the minimum dimming position. The maximum brightness position turns the Triac on at about 45 deg, and minimum is about 142 deg. With 120 V input and a 75 W incandescent lamp load this corresponds to RMS voltages of 116 V and 24 V across the lamp.

In my opinion this dimmer is way overpriced for what is inside and the labor to make it. Assuming any reasonable market for this the UL and development costs should not be a big factor either.

.
 
the lamp sockets look like tombstones hence the term. t8 and t12 sockets are the same design and every thing. shunted referrs to a socket where the fixed pin holders are connected together, which requires only one point of connection to the socket. a single wire socket, which is a normal fixture.
 
I have replaced T-12 ballasts and tubes with T-8's, and have never had to replace the sockets. I just connect each pair of wires to each single ballast wire.

However, since T-8's have both pins tied together, the filament becomes nothing more than an electrode, so how does the filament get heated for dimming?
 
090328-0759 EST

Larry:

I do not have an answer to your question. Maybe a Google search on the specific components you used might indicated how these function.

Here is a reference that is useful on the general concept of dimming fluorescent lamps and includes some quantitative data on lamp voltage drop.
http://www.irf.com/technical-info/whitepaper/howtodesignadimmingfluorescentelectronicballast.pdf

Mentioned is that below typically 20% brightness the lamp requires more than self heating of the filaments. For a 35W/T5 the voltage drop is 310 V at full brightness and 425 V at 5% brightness. Equivalent resistance of the lamp at 100% brightness is 1400 ohms and at 5% it is 129,000 ohms.

These values imply that operation is in a glow discharge region rather than an arc discharge. See Chapter XV page 463 ("Criterion for Distinction between an Arc and a Glow Discharge.") and Chapter XVI of "Fundamentals of Engineering Electronics", William G. Dow, John Wiley & Sons, 1952.

It is interesting that for a brightness ratio of 100/5= 20 that the power ratio is 35/0.7 = 50. I also wonder why at 100% brightness the calculated power from 310 V and 1400 ohms calculates to 68.6 W and the lamp power is listed at 35 W. At 5% brightness the values listed are 425 V and 129,000 ohms with a calculated power of 1.4 W and a listed power of 0.7 W. The ratio of 68.6/1.4 = 49 and that is close to 50.

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gar said:
090328-0759 EST

Here is a reference that is useful on the general concept of dimming fluorescent lamps and includes some quantitative data on lamp voltage drop.
http://www.irf.com/technical-info/whitepaper/howtodesignadimmingfluorescentelectronicballast.pdf

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That was an interesting read Gar,

I found Figs 9 and 10 interesting. It appears as though the frequency of the output is only shifted a small amount of Approx. 50Khz - 54Khz to go from 100% to 5% dimming - if I read those plots correctly?
 
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