Electrical Question - Pool light

[Reel]

I have a pool light problem that I can't figure out. The light does not turn on. The bulb is a 12V 300W pool bulb from the pool store. It worked last night but then died out shortly after it turned on. The previous nights since Sunday it worked the whole timer cycle.

Checking for continuity with the multimeter by checking the base contacts, it has continuity. Checking the socket, the voltage measures 14.3V AC which I realize is higher than 12V but I would think it would still light up.

I have checked the circuit breaker box and timer and transformer and all appear to be connected properly. The output of the transformer matches that at the socket - 14.3V. The input to the transformer is 120V.

I am stumped. Can anyone suggest some additional things to try or identify the problem?

Thanks in advance.

 

[edro]

Is it just that one socket?
Have you tried another known good bulb in the same socket?

14vac is fine to run the bulb, so that's not your issue.
Transformers always output higher than necessary to account for voltage drop and loading drop.

Is the bulb making good contact with the socket and socket pin?
Try bending the socket center pin up a little.

 

[Reel]

I have only that one socket. I am going to try picking up a new bulb tomorrow but this will be my third bulb in a year and they are $25 a piece so it is pretty annoying. I checked the center pin and bent it up a bit when I had it open earlier and that didn't help any.

 

[edro]

Try connecting it straight to the transformer to eliminate other issues. (timer, socket, etc.)

 

[Fritzo]

Just take that light out, and then put a regular table lamp in it's place. They work great underwater.

 

[ussfletcher]

Just take that light out, and then put a regular table lamp in it's place. They work great underwater.

I'm not sure what to make of this comment.

 

[Modelworks]

Have you checked the voltage on the wires of the socket with the lamp connected ? Measuring voltage without a load can be problematic because a meter will not tell you how much current is there, it can read 14V but only have 1ma of current , plug in the bulb and that 14v drops to 0v.

 

[Fritzo]

I'm not sure what to make of this comment.

:twisted:

 

[feralkid]

Did you touch the bulb with bare fingers when installing it?

 

[Reel]

Have you checked the voltage on the wires of the socket with the lamp connected ? Measuring voltage without a load can be problematic because a meter will not tell you how much current is there, it can read 14V but only have 1ma of current , plug in the bulb and that 14v drops to 0v.

Good idea. I will try that.

 

[Reel]

Did you touch the bulb with bare fingers when installing it?

Yes. It is incandescent not halogen though.

 

[Analog]

I don't understand - you say you checked continuity on the bulb's filament and it is okay, yet you want to replace the bulb? Sounds like a high impedance / poor connection somewhere in the circuit, not the bulb. Modelworks' idea is likely the cause.

 

[Reel]

Have you checked the voltage on the wires of the socket with the lamp connected ? Measuring voltage without a load can be problematic because a meter will not tell you how much current is there, it can read 14V but only have 1ma of current , plug in the bulb and that 14v drops to 0v.

Measured with it off at 0V. When I flipped the switch, it went to 14.3V. This was measured at the connection point between the transformer and the conduit that runs to the pool socket. The bulb is in the socket right now.

 

[LTC8K6]

300W at 12V = 25 amps. That's gotta be a hefty transformer and some hefty wiring.

 

[Squisher]

Is the bulb making good contact with the socket and socket pin?
Try bending the socket center pin up a little.

This

 

[LTC8K6]

This

Yeah, if the center contact isn't making good contact, it will get hot and probably bend, disconnecting the bulb.

 

[Rubycon]

300W at 12V = 25 amps. That's gotta be a hefty transformer and some hefty wiring.

Yes! OP do you have part numbers for the bulb? You sure it's not 30 watts?

ANY kind of corrosion or bad contact is going to cause lots of heat. Incandescent bulbs will measure very low on a DMM. Cold tungsten is like a dead short. This is why light bulbs make effective high frequency driver protectors in loudspeakers.

 

[Reel]

Yes! OP do you have part numbers for the bulb? You sure it's not 30 watts?

ANY kind of corrosion or bad contact is going to cause lots of heat. Incandescent bulbs will measure very low on a DMM. Cold tungsten is like a dead short. This is why light bulbs make effective high frequency driver protectors in loudspeakers.

http://www.aquasuperstore.com/products/Replacement-Pool-Light-Bulb-300W-Flood-R-40---12V~1590.html

This is likely not the exact manufacturer bulb I have but it is the same wattage/voltage as mine was from the local pinch a penny store. There was a decent amount of corrosion on the base of the bulb that I tried to take off by scraping it. I imagine there is a similar scene on the socket threads.

 

[Rubycon]

Oh wow a reflector bulb! Yes this is a medium base just like a regular 120V bulb. I wonder how many folks screw them into a household socket. Older RV lamps used those too but much lower (< 60W) sizes...

The best way to optimize your socket and bulb contacts is treat them with Caig DeoxIT - http://caig.com/.

Also if you are measuring transformer volts with a DMM, remember that your meter is a high impedance device and while you may have >12V at the terminals the voltage may sag way down when presented with a 300W load! Try a smaller load such as a 12V automobile lamp out of your car's dome light, for example.

 

[Reel]

http://www.1000bulbs.com/product/3355/ELEC-T40004RT3.html

This is the panel I have. At the bottom are spec sheets and a manual in PDF. It appears the panel is bundled with the transformer.

 

[ussfletcher]

Try a smaller load such as a 12V automobile lamp out of your car's dome light, for example.

Wouldn't it be bad to put a 12v DC car lamp into a 12v AC socket?

 

[ussfletcher]

Whoops double post

 

[Rubycon]

Wouldn't it be bad to put a 12v DC car lamp into a 12v AC socket?

No, an incandescent lamp does not "care" if AC or DC is present at its terminals. This would be used to see if the transformer can put out more than a tickler current.

 

[ussfletcher]

Ah, I didn't know that.. but it certainly makes sense now.

 

[Reel]

Updated: I got a new bulb and still nothing. The bulbs appear to both be functional so I suspect my old bulb is fine. I am at a loss as to why the socket is not lighting up a bulb since there is voltage getting through to the socket. I don't know if the fixture is bad or something electrically is off. I will have to figure it out over time. The fixture is about $300 to replace the whole thing so next investigation will be into all the wiring by the transformer.