Rewiring a ballast. Help needed.

My bit of experience with a few of these is not only that mentioned above, but also lower light output than with a good ballast. A spikier lamp current give reduced efficiency because the low pressure mercury arc is less efficient at higher instantaneous current. But in addition to this, it appears to me that these cheap undersize "shop light" ballasts do not even give full power to the lamp(s).

One more thing about those cheap "shop light" ballasts: At least some of these are less tolerant of heat than good ballasts, and that is why many cheap "shop lights" come with chains to hand them on - the ballast may overheat if the fixture is mounted flush against a beam. (Not sure the latter is good practice even with a good ballast, but I sure have the impression that the cheap ballasts in cheap fixtures that mostly go into basements, etc. tend to be fussier about heat and maybe anything else.)

What I like to do with cheap fixtures: Replace the ballast with an electronic one for T8 lamps, trashpicked from a dumpster by a hospital that has a new or recently renovated section being renovated (or renovated again) - and check that the ballast takes 120V rather than 277V. Get T8 lamps.

- Don Klipstein ( snipped-for-privacy@misty.com)

quoting:

the

Replying to my own post here...

I just checked the price of the 8' tubes:

60w $2.71 75w $4.71

So figure that you'll need two 4' tubes to make an 8' section, if this were around here, it would not be a large enough savings to make the switch. But, just for the energy savings alone, it would still be worthwile to go to T8.

But, if you don't care about the energy savings, then I would just keep the

8' tubes, replace the dead ballasts, and relamp the dead tubes with 75w ones for the the highest possible light output.

Rest of my OP still applies:

how

ballast,

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light

Mine appear to use a triac as the ballast resistor.

N

A triac can't be a resistor. It has two only states: on and off. The triac is probably used as a switch to start the lamp.

--
Vic Roberts
http://www.RobertsResearchInc.com
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fluorescent

(The

the

$30,

how

If you're gonna bother to go through the effort and expense to replace all those lamps, I strongly suggest you look into F32T8 trichromatic phosphor lamps using electronic ballasts. The initial cost is higher, but they've made the old T12 stuff obsolete. A 32W T8 trichromatic tube such as the F32T8/830 or 850 is brighter than a 34W T12, and with the electronic ballast you get no perceptible flicker. For a store, the greatly improved color rendering of the trichromatic stuff (CRI >80 for the 800 series stuff) has a lot of benefits, the reduced energy consumption and increased sales will pay for the conversion. Additionally you have a wide choice of color temperatures from 2700K (warm incandescent color) to 6500K (icy daylight) with 3000K and 4100K being popular middle ground. Personally I like 5000K as it's a nice pure clean white without being icey but it's a matter of personal preference.

Obviously they use some sort of driver circuit to control current to the lamp via the triac. I would have assumed you knew that - from your own website.

N

Spot relamping is not a good idea in a retail business (or most places really), discharge lamps suffer lumen depreciation as they age and should be replaced on a time schedule. Otherwise they get dimmer and dimmer while still consuming full power and if you spot relamp them you get bright spots and dim spots and overall it just looks shabby. A better approach which is more cost effective in the longrun is to run the lamps a specified number of hours and then replace them all at once, though it's hard to get people over the "incandescent mentality" of running any lamp completely into the ground. As others have said, the cost of the electricity over the life dwarfs the cost of the lamps and lost sales due to the store looking like a cave will cost more than a set of new lamps. Look around and once you start noticing this it'll drive you nuts, gets even more fun in places using metal halide lighting as not only do the depreciate more substantially but they tend to suffer color shift as they age. I've been in places with old mercury lights that were so dimmed from age that I practically needed a flashlight to find my way around.

Are you claiming that your "ballast" has no inductor or no capacitor? That the only device connected between the lamp and the power line is a triac?

The problem with a triac is that once it is on it will not turn off until the current drops to zero. Triacs can be used to dim incandescent lamps by cutting off the early part of the 50 or 60 Hz power line cycle. However, the resulting on time, while a fraction of the a normal half-cycle, is far too long for a fluorescent lamp, which can run away in far less than 1 msec in less the current is controlled.

There are circuits where a secondary triac is used to dump reverse current through the main triac and therefore force it to turn off. I have never seen these used for a lamp ballast, and I'm not sure they can switch fast enough to keep the lamp from running away. It would also require two triacs which is inconsistent with your message.

Are you sure it is a triac? The lamp current can be controlled by quickly switching a BJT or FET, but that mode creates a lot of EMI.

--
Vic Roberts
http://www.RobertsResearchInc.com
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be

spots

of

Yep. In the factory I used to do them all at once. I also washed all reflectors with soap and water. Saves dragging the scaffold out over and over again.

N

All I know is that the entire ballast is the size of a pack of cigarettes - I see no cap or choke of any size.

N

The inductor and capacitor used in 2-lamp T12 shoplight-type L-C ballasts can easily fit into a package the size of a pack of cigarettes.

--
Vic Roberts
http://www.RobertsResearchInc.com
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quoting:

Is this happen to be a "lights of America" shoplite BTW? Those things pretty much have what Vic had described (capacitor and small inductor) in series with the lamps. There is also a triac or triac-like switching device in these LOA ballasts that rapidly switches the preheating of the lamp electodes, and LOA marketed this as "instant start".

IIRC, these are a single 40 W 4' lamp.

N

That is right. There should be one series L-C ballast per lamp.

--
Vic Roberts
http://www.RobertsResearchInc.com
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cigarettes -

pretty

Sounds like a very cheap HF electronic ballast.

The ballast is not electronic - it is just a L and C. The starter is electronic, but this is inactive once the lamp starts.

--
Vic Roberts
http://www.RobertsResearchInc.com
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Sounds also like a device that should have been built into the lamp itself since its life is probably closer to the lamp life than to the life of the usual commercial ballast. Wonder why we've not seen that for linear lamps especially for residential applications.

Terry McGowan