Fluorescent bulb wattage vs ballast ?

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ritelec

ritelec

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Jersey
Hi.
I need to replace one 2 bulb ballast for 2 T8 4 foot bulbs.

Supply house doesn’t have 27w bulbs or ballasts.

Counterman with 40 years experience gave me 32w bulbs and 32w ballast for that fixture and says I can replace the existing 27w bulbs in other fixtures that have 27w ballasts with new 32w bulbs to match the fixture I’m changing the ballast on.

Can I do this? Is it safe and “approved”

To note. I haven’t opened the fixture yet.

The existing fixtures look like they were retrofitted. Might it be possible that there are no such thing as 27w ballasts and someone used 27w bulbs instead of 32w to save energy ??
 
I read previous forms, seems like you can just modify the old fixture if the bulbs state that in instruction, since they were listed with said instructions.
Or an I wrong hope not or I got to fix a lot of fixtures
 
Location makes a difference. I wanted to replace the 50 or so high bays in our shop with LED.
70' ceilings and Houston area temps shut down that idea.
I cant find one rated above 130f.


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220112-1920- EST

You folks need to understand the basic theory about things with which you work.

A fluorescent bulb is a gaseous discharge device. This means there is a cathode voltage drop, an anode voltage drop, and gas discharge voltage drop. The gas discharge drop may fall into a negative resistance over part of its V-I curve. Thus, a fluorescent bulb is not like a linear resistance. You have to look at a fluorescent bulb more like a constant voltage drop device. Meaning voltage drop may remain semi constant or drop as current increases. Thus, it can not be driven by a constant voltage source. It must be driven from a constant current source, or at least an approximation to one.

The ballast is a device, usually an inductor, that somewhat limits current.

If you change bulbs, but do not change the ballast you may destroy the bulb.

An LED is almost as bad as a fluorescent, but it does not go into a negative resistance mode.

.
 
Shaneyj said:
Location makes a difference. I wanted to replace the 50 or so high bays in our shop with LED.
70' ceilings and Houston area temps shut down that idea.
I cant find one rated above 130f.


Sent from my SM-G965U using Tapatalk
Click to expand...
Old magnetic ballasts for fluorescents tolerate(d) high ambient temperatures far better than electronic for either FL or LED.
 
AC\DC said:
Why not led? And avoid ballast!
Click to expand...
Changing out that fixture I would have to change another in that one office room so they would match. Rest of office and rooms are fluorescent. I will keep that in mind for future replacements. Thanks.
 
ritelec said:
Changing out that fixture I would have to change another in that one office room so they would match. Rest of office and rooms are fluorescent. I will keep that in mind for future replacements. Thanks.
Click to expand...
You don't have to change the fixture to change to LED. That's one of the strong selling points. Say a customer has a ceiling mounted fluorescent in their kitchen and it needs repairing/replacing. Replacing it would, in most cases, not cover the footprint exactly of the old fixture. They then would have to paint their ceiling. Another reason being time, especially in commercial/industrial. Just rewire the socket ends, bypassing the ballast, installing LED tubes. This can all be done by the time you disconnect the old fixture.
 
Little Bill said:
You don't have to change the fixture to change to LED. That's one of the strong selling points. Say a customer has a ceiling mounted fluorescent in their kitchen and it needs repairing/replacing. Replacing it would, in most cases, not cover the footprint exactly of the old fixture. They then would have to paint their ceiling. Another reason being time, especially in commercial/industrial. Just rewire the socket ends, bypassing the ballast, installing LED tubes. This can all be done by the time you disconnect the old fixture.
Click to expand...
Yes, I meant rewiring and installing the led bulbs not swapping the fixture. Thanks for the clarification. 👍
 
ritelec said:
Hi.
I need to replace one 2 bulb ballast for 2 T8 4 foot bulbs.

Supply house doesn’t have 27w bulbs or ballasts.

Counterman with 40 years experience gave me 32w bulbs and 32w ballast for that fixture and says I can replace the existing 27w bulbs in other fixtures that have 27w ballasts with new 32w bulbs to match the fixture I’m changing the ballast on.

Can I do this? Is it safe and “approved”

To note. I haven’t opened the fixture yet.

The existing fixtures look like they were retrofitted. Might it be possible that there are no such thing as 27w ballasts and someone used 27w bulbs instead of 32w to save energy ??
Click to expand...
Would be cheaper to remove the ballast and change over to LED lamps that get power directly from the 120 or 277 volt line. Usually have to replace sockets. Converted 1 luminare in my home and like it. My inspector always tell us that bulbs go into the ground and lamps go into luminares. I'm thinking about installing an in line fuse for every flurescent luminare that I convert with say a 0.75 or 1 amp fuse normal. ( not time delay ) If the lamp holder that has the line voltage breaks and contacts short out would clear the short faster and keep rest of circuit energised.
 
gar said:
220112-1920- EST

You folks need to understand the basic theory about things with which you work.

A fluorescent bulb is a gaseous discharge device. This means there is a cathode voltage drop, an anode voltage drop, and gas discharge voltage drop. The gas discharge drop may fall into a negative resistance over part of its V-I curve. Thus, a fluorescent bulb is not like a linear resistance. You have to look at a fluorescent bulb more like a constant voltage drop device. Meaning voltage drop may remain semi constant or drop as current increases. Thus, it can not be driven by a constant voltage source. It must be driven from a constant current source, or at least an approximation to one.

The ballast is a device, usually an inductor, that somewhat limits current.

If you change bulbs, but do not change the ballast you may destroy the bulb.

An LED is almost as bad as a fluorescent, but it does not go into a negative resistance mode.

.
Click to expand...
It may not be negative resitance, but LEDs do have thermal runaway as a possiblity.
 
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