chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- Retired electrician
There is a debate at the shop as to wether a 100watt pool lamp on a 300watt pool transformer will affect lamp life. Any one heard of this?
300w tranny, 100w lamp
- Thread starter chris kennedy
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
I don't know much about pool lights but why does someone think that a transformer capable of delivering 300 watts to a load would in any way affect a 100 watt load? I'm trying to see the logic involved because I don't see how it would matter. 
mcclary's electrical
Senior Member
- Location
- VA
SWAP those numbers and you've got a problem,,,,,but you're fine the way you presented it. Actually, IMO, to be safe, a transformer should always be capable of delivering more watts than are being used. That way you know you're not maxxing it out.
cadpoint
Senior Member
- Location
- Durham, NC
- Occupation
- Electrician - but not by NC Law.
Gee, if you just do the rough math it's 100/300, if you add 125% for continuous duty thats still only
42% used of the total available power.
This is of course does not include any consideration of properties of lamp or ballast or transformer.
Which flag are you running with Chris
It'll be hard to take sides tonight !!! Go ACC :roll:
42% used of the total available power.
This is of course does not include any consideration of properties of lamp or ballast or transformer.
Which flag are you running with Chris
It'll be hard to take sides tonight !!! Go ACC :roll:
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
The only thing I could see, is if a smaller transformer closer to its maximum output was used, would have more voltage drop, thus longer lamp life due lower operating voltage at the lamp.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Heard of the debate, yes. It's like believing that a 300w amplifier will automatically destroy 100w speakers.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Transformers for low voltage lighting approximate constant voltage sources. Lamps for conventional low voltage lighting expect a voltage regulated supply. Operating 100W of such lighting with such a transformer rated for a maximum of 300W is just fine. You can add more lights in parallel and increase the load if desired.
But this is _not_ a general case; this is a _nearly_ universal specific case.
For example, certain types of lighting don't work with voltage regulated supplies, but rather work with _current_ regulated supplies. Arc lights are one example; more relevant today are LED lighting systems. If you have an electronic power supply designed to supply regulated current to LEDs, with a rated output of 700mA, and you connect a 100mA LED to it, then the LED will fail, and quite quickly. Such power supplies can be made using current regulating transformer designs, rather than switching designs. I bet some ballast transformers act in this fashion.
In designing LED lighting circuits, one of the approaches that I've considered is an electronic power supply designed to regulate the output _power_, by charging an inductor up to a specified current level, and then discharging that inductor completely at a fixed frequency. Such a power supply would deliver voltage and current that changed with the load characteristics...but would always deliver the same amount of power. Design such to deliver 300W, but connect a load rated to 100W to it, and the load will fail quickly.
-Jon
But this is _not_ a general case; this is a _nearly_ universal specific case.
For example, certain types of lighting don't work with voltage regulated supplies, but rather work with _current_ regulated supplies. Arc lights are one example; more relevant today are LED lighting systems. If you have an electronic power supply designed to supply regulated current to LEDs, with a rated output of 700mA, and you connect a 100mA LED to it, then the LED will fail, and quite quickly. Such power supplies can be made using current regulating transformer designs, rather than switching designs. I bet some ballast transformers act in this fashion.
In designing LED lighting circuits, one of the approaches that I've considered is an electronic power supply designed to regulate the output _power_, by charging an inductor up to a specified current level, and then discharging that inductor completely at a fixed frequency. Such a power supply would deliver voltage and current that changed with the load characteristics...but would always deliver the same amount of power. Design such to deliver 300W, but connect a load rated to 100W to it, and the load will fail quickly.
-Jon
DownRiverGUy
Member
- Location
- Canton, MI
Is someone confusing generator charteristics with a transformer ??? :-?
A transformer will output whatever voltage the winding ratio are designed for.
Doesn't matter if there is no load it will show the correct voltage across the windings.
As mentioned before. So long as you don't overload the transformer and start melting the poor thing you should be fine.
Now there ARE issue regarding loading a generator part way (depeding on the manufactures specifications).
-Chris
A transformer will output whatever voltage the winding ratio are designed for.
Doesn't matter if there is no load it will show the correct voltage across the windings.
As mentioned before. So long as you don't overload the transformer and start melting the poor thing you should be fine.
Now there ARE issue regarding loading a generator part way (depeding on the manufactures specifications).
-Chris
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
There are losses in transformers too, ever wonder why a fully loaded transformer puts out more heat than a lightly loaded one? These losses also reduce the voltage output. With small transformers like the one Chris Kennedy is talking about, the wire used in the windings is small, as with any wire voltage drop is related to load and resistance. Depending on the manufactures choice of wire size, output voltage, this can be several volts lost.
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