Testing my pool light?

gtm · Oct 29, 2008

My pool light hasn't worked since before I took over the pool, which is sad because I really liked it. I miss it. It's been dead so long.

I opened the box the light is fed from and there's no juice there. Disconnected the wires on the light side of the transformer and no juice there either. There is, however, juice on the house side of the transformer. So I know that the transformer is bad.

The input to the transformer is a 120V, 15 A circuit and it's a 12V DC circuit going out. I'd like to check the light before I bother with this, since I don't want to replace the transformer if it won't make a difference. The light is not trivial to change, but hopefully I won't have to ask about that if I'm lucky and it's only the transformer. Unlike my (unlucky) Tampa Bay Rays an hour or so ago ...

Does anyone have an idea of what sort of amperage a pool light would draw? I'm trying to figure out what sort of battery I might be able to test it with? That is, do I need a car battery, something bigger, a pink bunny, or just a couple of lantern batteries?

Thanks, Gary

Ke · Oct 29, 2008

Just use a multimeter to test for continuity of the light, if the light is burnt out, you will get an open circuit, otherwise you bulb is most likely OK.

spishex · Oct 30, 2008

Do you know how many watts the bulb is? Should probably be 100-300, so that would give you an amperage range of 8.3-25 on 12v. However, your bulb is probably 12v AC so the car battery won't do the trick.

gtm · Oct 30, 2008

Ke said:
Just use a multimeter to test for continuity of the light, if the light is burnt out, you will get an open circuit, otherwise you bulb is most likely OK.

Thanks Ke. That's a great idea, but have you heard the one about the big dummy who went to his Dad's (450 miles away) this summer to do some repairs on the wiring in his shed and forget his multimeter? Rumor is he'll get it back at Thanksgiving. Of course, this assumes that his Dad won't lose it by then. He loses lots of things, including dummy's younger brother in the woods once when we they were kids. In his defense, however, Dad claims that he didn't "lose" him, he "left" him. Probably true.

Thanks again!

gtm · Oct 30, 2008

spishex said:
Do you know how many watts the bulb is? Should probably be 100-300, so that would give you an amperage range of 8.3-25 on 12v. However, your bulb is probably 12v AC so the car battery won't do the trick.

Thanks! You caught me in a bad mistake. You're absolutely right that it's 12V AC.

No reason that you would've read my "Introduce yourself" post from a few months ago, but one of the main characters in it was the one-man pool service business guy I used to use. My wife still refers to him as "He Who Shall Not Be Named". Anyway, he told me (before I let him go) that the output of the transformer was 12V DC and I never questioned it. Which was really dumb since this was also the guy who told me that the reason the pool was perpetually green was that the raccoons around here are clever enough to get into a completely screen enclosed pool deck, sneak past my dog, and poop in the pool without ever being glimpsed. Or actually leaving any undissolved poop in the pool. And I believed him about the electrical transformer. Go figure.

Anyway, after I saw your message I took the transformer to a very good electrical supply place we have here and they confirmed that it was a simple step down transformer. No AC-DC rectifier in there. Thanks again for the catch.

BTW, just FYI, they said, as you did, that the bulb was most likely 100-300 W, but also said that the amperage on these was computed based on the supply side voltage; i.e., a 300W bulb would draw 300W/120V = 2.5 amps. That makes sense, I think, since this bulb as well as the deck ceiling fan and light fixture are both on the same 15 amp breaker in the subpanel on the deck and there weren't any problems with that setup.

Thanks again for catching the AC-DC thing. I went ahead and bought the transformer. If that doesn't fix the problem I'll do as Ke suggested and check the continuity of the bulb. After Thanksgiving, of course.

Cheers, Gary

spishex · Oct 31, 2008

BTW, just FYI, they said, as you did, that the bulb was most likely 100-300 W, but also said that the amperage on these was computed based on the supply side voltage; i.e., a 300W bulb would draw 300W/120V = 2.5 amps. That makes sense, I think, since this bulb as well as the deck ceiling fan and light fixture are both on the same 15 amp breaker in the subpanel on the deck and there weren't any problems with that setup.

Yeah, that's right if you're running it from 120v with the transformer instead of trying to use a 12v source. Glad it worked out for you!

gtm · Nov 1, 2008

spishex said:
Yeah, that's right if you're running it from 120v with the transformer instead of trying to use a 12v source. Glad it worked out for you!

Thanks Tim. Between your input getting me on the right reading track and the very helpful guy at City Electric I think I understand it all now. I've done a fair bit of home electrical in the past, but this is my first time dealing with transformers. Thanks again for the help with it.

Also, to Ke, I (temporarily) liberated a multimeter from a friend at work's lab and followed your advice. The bulb checks out fine.