300W/12V Pool Light Draw

[Mystic Pools]

Folks, could not find any previous posts regarding this-I hope it's not a repetitive question.

Existing pool we renovated (35yrs old). (2) existing 300W/ 12V lights powered by (2) separate Intermatic 300W transformers. We installed new deck boxes, conduit and re-wired for both lights. Bonding is sound.

One light was not working so I started from the source. 110V power to transformers. 12V at transformer loads.
The deck boxes are approx. 50' and 75' from the transformers respectively. The furthest light is the one not working.

During testing I checked the power to the closest deck box without hooking up to the light that is working. I got 12V. The furthest deck box, to the light not working, I got the same. Ok, so I determined this light fixture or bulb is shot.

When I connected the closer light that is working, and tested, my voltage dropped almost in half. The Intermatic transformers give you (3) choices of output power 12,13 and 14V. I rewired for 13V and still had about 6.2-3V.

This light is working but is it on it's way out? What would cause the big draw? These are standard bulbs not LED's. The lights are not originals.

 

[iwire64]

I'm new to pools, but am doing one now. I'm told that I have to connect to the highest tap, i.e. 14v, or the lights will not work. I'm using LEDs. Not sure if the same holds true for standard bulbs.

Sent from my SM-G935P using Tapatalk

 

[Mystic Pools]

Yes, for LED's we have been using the 13 or 14V tap. If the voltage is low for LED's they will not last.

FYI: We have not used "standard" incandescent lights with the typical wet niche in more than 10 years for new installs. We have been using the nicheless LED's utilizing 2" or 1.5" PVC as the "niche" for these lights. No bonding or grounding, 12V, set 4"-9" below water level. Multiples to provide even lighting.
We can use a single 300W transformer for 13-14 20W LED's.

However, there are and have been replacement LED bulbs for the standard light fixtures.

 

[kwired]

Folks, could not find any previous posts regarding this-I hope it's not a repetitive question.

Existing pool we renovated (35yrs old). (2) existing 300W/ 12V lights powered by (2) separate Intermatic 300W transformers. We installed new deck boxes, conduit and re-wired for both lights. Bonding is sound.

One light was not working so I started from the source. 110V power to transformers. 12V at transformer loads.
The deck boxes are approx. 50' and 75' from the transformers respectively. The furthest light is the one not working.

During testing I checked the power to the closest deck box without hooking up to the light that is working. I got 12V. The furthest deck box, to the light not working, I got the same. Ok, so I determined this light fixture or bulb is shot.

When I connected the closer light that is working, and tested, my voltage dropped almost in half. The Intermatic transformers give you (3) choices of output power 12,13 and 14V. I rewired for 13V and still had about 6.2-3V.

This light is working but is it on it's way out? What would cause the big draw? These are standard bulbs not LED's. The lights are not originals.

What size are the conductors?

300 watts @ 12 volts is going to draw 25 amps. At only 12 volts you can't afford voltage drop, a one volt drop is 8%. Without running calculations I expect you may need at least 6 or even 4 AWG minimum conductor size to keep voltage drop at a reasonable level to get the most light you can out of a 300 watt lamp at the distances you mentioned.

 

[kwired]

What size are the conductors?

300 watts @ 12 volts is going to draw 25 amps. At only 12 volts you can't afford voltage drop, a one volt drop is 8%. Without running calculations I expect you may need at least 6 or even 4 AWG minimum conductor size to keep voltage drop at a reasonable level to get the most light you can out of a 300 watt lamp at the distances you mentioned.

OK my guess was way off, @ 75 feet you would need 2/0 copper conductor just to keep voltage drop around 3%.

 

[JFletcher]

Folks, could not find any previous posts regarding this-I hope it's not a repetitive question.

Existing pool we renovated (35yrs old). (2) existing 300W/ 12V lights powered by (2) separate Intermatic 300W transformers. We installed new deck boxes, conduit and re-wired for both lights. Bonding is sound.

One light was not working so I started from the source. 110V power to transformers. 12V at transformer loads.
The deck boxes are approx. 50' and 75' from the transformers respectively. The furthest light is the one not working.

During testing I checked the power to the closest deck box without hooking up to the light that is working. I got 12V. The furthest deck box, to the light not working, I got the same. Ok, so I determined this light fixture or bulb is shot.

When I connected the closer light that is working, and tested, my voltage dropped almost in half. The Intermatic transformers give you (3) choices of output power 12,13 and 14V. I rewired for 13V and still had about 6.2-3V.

This light is working but is it on it's way out? What would cause the big draw? These are standard bulbs not LED's. The lights are not originals.

300W bulbs draws 25A on a 12V system.

If the wire distance is 50' one way, the voltage drop is going to be nearly a third (33%) with 12ga wiring:

http://www.calculator.net/voltage-drop-calculator.html

Using input values of copper, 12ga, 12V, DC, single, 50', and 25A

Any extra distance of wire drastically affects the voltage drop with such a large draw on small wiring. Since you are reporting about a 55% VD, I'm guessing the wire distance is maybe 75' to your light 50' away 'as the crow flies'.

eta: as kwired noted, you'd need ridiculously large wire to keep VD at recommended (3-5%) values. Are the xfmrs supposed to be much closer to the lights than 50 or 75 (or more) feet away?

 

[JFletcher]

I see kwired also beat me to the punch on the other calculations. |

I noted this on the Intermatic 300W xfmr installation instructions:

• The transformer should be mounted at least 1 foot above the deck level with the field wiring
compartment down.

Which makes me think the xfmr is supposed to be mounted much closer to the pool than 50+ feet away.

The instructions here:

https://a89b8e4143ca50438f09-7c1706.../intermatic-px300-instructions.pdf?1442933156

Show a 30' max for #12 wire at a 300W output with 14V output selected. For wire distance over 80', you'd need #6.

You really need #10 for a 25A load, and istm that, if possible, locating the xfmr closer to the pool would be the best option.

 

[Mystic Pools]

OK thanks for responses.

#12 wire to the closest light and #10 to the further light. The transformers are mounted in a room behind the pool house with the pool equipment.

I think I can overcome the wire size change and swap the incandescent bulbs for LED's. Besides my conduit is 1" and the larger conductors won't all fit.

Or, set the transformers adjacent to the deck boxes. Or, change the lights all together to 110V and eliminate the transformers.

One light is not working and I'm not crazy about replacing bulbs. I'd rather change out the entire fixture. Once the seal is broken it opens a can of worms after years of being in a corrosive condition of chlorine and other chemical fluctuations to seal it properly.

 

[kwired]

OK thanks for responses.

#12 wire to the closest light and #10 to the further light. The transformers are mounted in a room behind the pool house with the pool equipment.

I think I can overcome the wire size change and swap the incandescent bulbs for LED's. Besides my conduit is 1" and the larger conductors won't all fit.

Or, set the transformers adjacent to the deck boxes. Or, change the lights all together to 110V and eliminate the transformers.

One light is not working and I'm not crazy about replacing bulbs. I'd rather change out the entire fixture. Once the seal is broken it opens a can of worms after years of being in a corrosive condition of chlorine and other chemical fluctuations to seal it properly.

For 50 feet run I'm coming up with about 4.9 volts dropped on 12 AWG (that is about 41% of 12) or 3.1 volts dropped on 10 AWG (which is about 26% of 12).

stepping up voltage if you can to say 14 volts will help some, still won't get the same light level you would with rated 12 volts at the lamp. The good news is the lamp life should be extended by a fair amount over what it would be at 12 volts.

 

[Mystic Pools]

Thanks for all the responses. This was an existing set up and I guess it never really worked properly.
I have no idea how well the pool is lit or was ever lit at night. I work during the day so I don't see the lights in action at night.

The homeowners are new last year and the lights worked then, but they have nothing to compare the light output to as they are first time pool owners. So no red flags from them regarding illumination issues.

I'll probably switch over to new LED lights. Guessing existing lights are 15+yrs old.