Ideas for powering post-mounted light from low-voltage AC landscape lighting?

[Nathan Schrenk]

I have a post on the corner of a fence in my front yard where I want to mount a light. I have a fixture that looks something like this: http://www.homedepot.com/p/Hampton-Bay-3-Light-Black-Outdoor-Lamp-HB7029-05/205202509

The fixture is designed to be powered by 120V AC, but I'm wondering if I can retrofit it to be powered by low-voltage (12V AC) supply that powers my existing landscape lighting. If I can reuse the power line for the landscape lighting, which is already run directly to the base of the post where I want to mount the light, it will allow me to avoid running a 120V AC line all the way from the side of my house down to the sidewalk.

I spent a long time looking for a post-mounted fixture that looked like a normal yard post light and was designed to be powered off of low-voltage supply, but I came up empty. So then my thought was to buy a fixture that had the look I wanted, and replace the electrical components inside. Now I'm looking for advice on how to do that.

I know the basics of powering LEDs from a DC supply and how to create a circuit with the appropriate resistor(s), but I'm fumbling around in the semi-dark about the best approach to do this with 12V AC.

I could buy a 12V AC to 12V DC converter module like this one (https://www.superbrightleds.com/moreinfo/battery-and-cps-compact-power-supplies/12v-ac-to-dc-converter-module/1725/) , and then build a normal DC circuit inside the fixture. I'm pretty sure I can then just hide this converter inside the post.

Is there a better approach?

Nathan

[Nathan Schrenk]

Hmm, I just ran across another option:

--
You received this message because you are subscribed to the Google Groups "Arch Reactor" group.
To unsubscribe from this group and stop receiving emails from it, send an email to arch-reactor+unsubscribe@googlegroups.com.
To post to this group, send email to arch-r...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/arch-reactor/CAK%2Bxjc_4883Lu%3DiCsCqQ5_tzBjsAUx1hr0KPOF388Vc8KtDHtQ%40mail.gmail.com.
For more options, visit https://groups.google.com/d/optout.

[Nathan Schrenk]

Oops, hit send too soon.

I just ran across another option: http://a.co/evgMH7l

It seems like I could just wire the 12V AC supply directly to these LED bulbs?

[Chris Weiss]

bridge rectifier.  you can make a full wave rectifier from 4 diodes, but you can use a large filter cap and one diode if you don't mind a minor 60Hz pulse.

those bulbs likely have one built in.  

[Jim S]

You can avoid the diodes by putting two strings of a few LEDs each back to back and in series with a resistor (or something more elaborate to limit current).  One string conducts on one half cycle and the other on the other half cycle.  But if you don't want to design and make everything there are 12 VAC bulbs as you have found.  I would go with LED to get the most brightness for the current you have available.  And if you replace your other landscape lights with LED bulbs that will also make more current available.  Converters have losses and you probably have limited power to begin with - just something to keep in mind.

[Ben West]

LED's definitely can be powered off half of the 60hz cycle via half-wave rectifiers, and many of the 120VAC LED-based replacement bulbs sold may do exactly that.  Although, sporadic Googling suggests that stepping the 120VAC down to 24VAC is common.  My thought is the the ~0.7V you lose to diode bias voltage on a 12VAC source might produce a more noticeable 60Hz flicker than on a 24VAC source.  Unless it's an LED fixture intended for 12VAC, that is.

Besides that, there are simple (i.e. capacitor and diode-based) circuit topologies for doubling AC voltage, e.g. 12VAC -> 24VAC.
https://en.wikipedia.org/wiki/Voltage_multiplier

--

You received this message because you are subscribed to the Google Groups "Arch Reactor" group.
To unsubscribe from this group and stop receiving emails from it, send an email to arch-reactor+unsubscribe@googlegroups.com.
To post to this group, send email to arch-r...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/arch-reactor/a1269e1d-aff5-4fd1-bff5-a0270a46b13e%40googlegroups.com.

For more options, visit https://groups.google.com/d/optout.

--

Ben West

m...@benwest.name

[Jim S]

You could use a 115 to 12 VAC transformer in reverse to step up the voltage back to 115VAC and run a standard LED bulb provided the 12VAC system has enough current capacity to supply the power.  A 60W equivalent LED bulb is about 9 - 10 W IIRC so probably around 1A from 12VAC with transformer losses.

[Jim S]

You could also convert the supply from 12VAC to 12VDC and then use an LED RV bulb that fits a standard screw fixture but runs from 12VDC.  The other bulbs on the circuit would not need to be changed.

[Nathan Schrenk]

Thanks for the ideas, everyone.

The option I'm going to try is to order LED bulbs that will run off of 12VAC, retrofit the fixture to fit those bulbs, and then directly connect the 12VAC supply to the fixture's supply wires. 

--

You received this message because you are subscribed to the Google Groups "Arch Reactor" group.
To unsubscribe from this group and stop receiving emails from it, send an email to arch-reactor+unsubscribe@googlegroups.com.
To post to this group, send email to arch-r...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/arch-reactor/62fce06c-ae02-4a29-bba1-e6819dd67cdc%40googlegroups.com.