# low voltage lamp questions

#### ship

##### Senior Team Emeritus
What will happen if you run a 12V/30W lamp off a 6V/30w transformer?

What’s the maximum wattage of 12V lamp you can run off a 12V/100mA transformer?

What’s the maximum wattage of 12V lamp you can run off a 15V/100mA transformer?

If you have a 24V/20W transformer, how many 6V/20W lamps can you run in series off it?

If you have a low voltage swivel arm reading lamp fixture, where the power to the lamps goes thru the parallel swivel arms of the fixture, would your lamp dim if the paint were scratched and a grounded piece of metal touches that scratch?

Given two parallel pieces of 1/16" GAC wire rope mounted to two walls 20' away, and a 12V/100W transformer connected to the wire rope, what’s the maximum safe wattage of lamp you can hang and power up from the wire rope? Would assuming a 12v lamp, it get brighter the closer it got to the transformer? What would be the best lamp to use towards the end of the wire rope, 50W/6.6V EZP, a 90W/14.5V EPV, or a 42W/10.8V EPT? What would be a better improvement for this system, installing a different wire rope (which type) or installing a different transformer (what rating?) http://lightbulbsetc.com/ “Tightrope Cable Lighting Fixtures” would be a sample of this type of system.

##### Well-Known Member
> What will happen if you run a 12V/30W lamp off a
> 6V/30w transformer?

It will be dimmer?

> What’s the maximum wattage of 12V lamp you can run
> off a 12V/100mA transformer?

Well I plugged those numbers into Ohm's law and got 1.2 watts, but I might be going about that one the wrong way.

Yeah I picked the easy ones.

#### Diarmuid

##### Active Member
What’s the maximum wattage of 12V lamp you can run off a 15V/100mA transformer?

I think that it is still 1.2Watts, but i believe that it is not actually safe to run it off a 15V power supply, because the lamp is only rated to 12 v.

I'm not entirely sure, but i think thats the right answer.

#### Diarmuid

##### Active Member
Now that I think about it, if what I wrote above is true, then the answer to:
"If you have a 24V/20W transformer, how many 6V/20W lamps can you run in series off it?"

is also, none because they would blow. But that is only if what I wrote earlier is correct...

#### Mayhem

##### Senior Team Emeritus
Lamps are often run in series and like resistors, when in series you add up the voltage of each lamp. This is how we run 110V PAR lamps off of a 240V supply. It is also how ACLs are wired up.

##### Member
What will happen if you run a 12V/30W lamp off a 6V/30w transformer? I might be wrong, but I think it would appear at the same brightness but use more current.

What’s the maximum wattage of 12V lamp you can run off a 12V/100mA transformer? 1.2 watts.

What’s the maximum wattage of 12V lamp you can run off a 15V/100mA transformer? 1.5 watts, but the lamp might not like getting 15v when it is only rated for 12v.

If you have a 24V/20W transformer, how many 6V/20W lamps can you run in series off it? Four, but they would be dim (5 watt output). Then again, you could keep adding lights and they would get more dim every time.