Niche light question

[tj__r]

I have old 12VAC niche fixtures where I'd like to screw in some 12V LED bulbs. Here's the trouble: I used a multimeter to measure voltage at screw in socket. It's 13VAC. But when I screw in the bulb I get no light. I shined up the socket with some fine sandpaper so I don't think corrosion is the problem. I also tried just holding a 12VAC little landscape bulb with pins on the two conductors of the socket. No light there either. Both bulbs lit fine using the wires at the junction box, so I know I have power to there.

Looks like there are some electronics in the base of the fixture potted in clear plastic. Is it possible those have gone bad, such that I'm not getting enough current? What do those electronics do?

 

[nuttyp]

As far as I know none of those 12VAC niche fixtures (Pentair, etc) have any electronics in them. Mine surely does not. Sounds to me like you have a murphys law of contact problems. When I have issues like that (and it happens a lot) I take an old lamp cord, plug intact but other end cut off, screw into your fixture one of those adapters typically used around Christmas to adapt the standard E26 socket and plug the cut-off lamp cord into it - then you can bring the cord out with stripped ends for more convenient testing. Another possibility, although it's rare, some landscape systems are 12V DC, or you maybe broke the landscape bulb taking it out (murphy again). If you have another source of 12VAC you can bench test the new bulb. A bench AC variac is a nice tool for that. And if your new bulb is a fancy RGB remote controllable bulb, some of those require a few power cycles to change modes. It's also typical that the unloaded transformer will show 13VAC until it gets a load, maybe still 13 with a low LED load. Most transformers also have a few taps for slightly higher voltages, just in case the bulb needs something lower, but I doubt that's the problem. Best guess is the new bulb is no good. All I can think of at the moment, but I'm guessing your niche and transformer are fine.

 

[tj__r]

Thanks - I think the new LED bulb is fine. I opened the junction box above the pool deck and touched the 2 wires there to the tip and shell of the bulb, got light. So the transformer and bulb are definitely good. It's possible that you're right about the current situation, that the socket is too corroded to pass enough current and I'm only seeing 12 to 13 VAC with no load. If I can figure out how to post a picture, I could take one of the socket etc. There's what appears to be a nichrome wire coil that comes out of the back plus another device.

 

[nuttyp]

In another thread @rhythm posted this attached picture, perhaps yours looks similar? I don't know what the little coily wires are for - perhaps to discharge possible bulb static or help cool the bulb? Mine does not have those, maybe someone can ID their purpose. Also don't know what the purpose of that tube is that extends out of the potting area at the top. Did some web searching about the coils, nothing found by me :-( The other thread is Light fixture leaking? - questions

 

[tj__r]

Yeah, thanks. That's exactly how mine is set up.

 

[nuttyp]

I ran across Pentair documentation that calls the little "wire loop" (aka "coil spring") sometimes a grounding loop or a leakage current collector - depending on the fixture and documentation - in their higher wattage 120 VAC light fixtures, picture attached. Gosh I didn't even know you could still buy and install 120V pool lights. Perhaps in some jurisdictions, and perhaps it's the only way to get to 500 watts without impossibly heavy conductors to handle the current if it were 12VAC. But I don't think I would want 120V anywhere near my pool whether or not it was all GFCI protected and whether or not it had "leakage collectors".

Perhaps it's a bit of a digression, but I ran across a lot of discussion, mostly in Canadian forums, about proposals to require leakage current collectors at the water inlet & outlet of every piece of powered pool equipment. Yikes! Passions were emerging among commentary, not sure where it all went. But if you love TFP for everything pool related (and I do and have for many years), if you're looking for "everything electrical", I find Mike Holt's forum and resources similarly invaluable. Electrical Training Solutions |Mike Holt Enterprises and the forums at Information by Electrical Professionals for Electrical Professionals

 

[tj__r]

Hmm, thanks much! I wonder if mine was originally a 120V housing that was rewired later to use 12V bulbs. That would be pretty simple since both bulb voltages use E26 sockets (that seems like a bad idea as it's easy enough to screw the 12V bulb into an ordinary socket and burn it out immediately.) Also there's that little "tail" directly above the "i" in Figure 2 that's not explained. In any event, shining up the brass in the socket with a tiny Dremel wire brush will be my next move. Maybe there's just too much corrosion for adequate current to flow.