DIY low voltage transformer

Thread Starter

stryped

Joined Sep 17, 2023
47
I am thinking of building my own hard scape landscaping lighting. Particularly to mount on landscape retaining wall type blocks. Have thought of using square tubing and cutting open the bottom to mount some 12 v dc bulbs, (maybe an G4 type single bulb for each fixture) and installing a plexiglass lens. How could I go about building a low voltage transformer that could be mounted in a box outside and be heavy duty enough to last for many years so as to not make any repairs for a long time.
 

BobTPH

Joined Jun 5, 2013
9,149
Get an old discarded microwave oven.

Make sure it has been unplugged for one month.

Open it up and take out the large transformer.

Remove the high voltage secondary,

Wind a few turn of 14 ga wire where the secondary was.

Wire a power cord to the primary.

Plug it in.

Measure the voltage on your new secondary and adjust turns to get 12V.

A you tube video would be helpful to learn how to do this.
 

Tonyr1084

Joined Sep 24, 2015
7,956
Instead of using 12V G4 base (probably halogen) use LED's. I lit up my driveway with THESE. They come in different colors. I used white. Could have used blue but I didn't want the near by Air Force Base trying to land an F35 on my 100 foot driveway. It wouldn't end well.

Since you are building your own transformer you can use multiple taps to get different voltages. At 12 volts mine are plenty bright. They've been working for a couple years now. And off of a small power supply (2A) with 7 LED lamps on circuit. They are controlled by a photo cell and relay assembly. THAT didn't last very long, the plastic bubble deteriorated in the direct sunlight. Replaced the plastic top with an old LED house lamp. Took the dome off of a dead LED lamp and sealed it to the electronics package. That was last year. Will have to see how it holds up under the direct sunlight and intense heat of Northern Utah.
 

Externet

Joined Nov 29, 2005
2,234
Why removing the high voltage winding of a microwave oven transformer ? Connect that high voltage secondary as primary to 120VAC and measure what you get at the other winding first. If convenient voltage, then half,-full rectify/filter.
 

MisterBill2

Joined Jan 23, 2018
18,984
Why removing the high voltage winding of a microwave oven transformer ? Connect that high voltage secondary as primary to 120VAC and measure what you get at the other winding first. If convenient voltage, then half,-full rectify/filter.
That is a very interesting concept indeed! One possible issue could be with hose transformers that intentionally have one end of the high voltage secondary tied to the transformer frame. I just came across one of those in the transformer of a junk-brand oven. Easy to detect measuring, and difficult to correct. But certainly worth taking a look to see if reversing can be used.
One will still need to remove the magnetic shunt, though.
I have been wondering about changing the transformer to step up from 12 volts from an automotive electrical system. Just driving a transistor to switch it on and off, or maybe a push-pull scheme for more efficiency.
 

MaxHeadRoom

Joined Jul 18, 2013
28,768
As per post #2, I would saw through and remove the HV windings, taking care to not damage the primary,
Wind on 10 turns as per post#2 and establish the turns/volt, then wind on what you require with a suitable gauge wire.
I have customized Many transformers over the years for various projects.
One of the first was most challenging for a tube tester that covered all filament eventualities. !
 

Thread Starter

stryped

Joined Sep 17, 2023
47
Instead of using 12V G4 base (probably halogen) use LED's. I lit up my driveway with THESE. They come in different colors. I used white. Could have used blue but I didn't want the near by Air Force Base trying to land an F35 on my 100 foot driveway. It wouldn't end well.

Since you are building your own transformer you can use multiple taps to get different voltages. At 12 volts mine are plenty bright. They've been working for a couple years now. And off of a small power supply (2A) with 7 LED lamps on circuit. They are controlled by a photo cell and relay assembly. THAT didn't last very long, the plastic bubble deteriorated in the direct sunlight. Replaced the plastic top with an old LED house lamp. Took the dome off of a dead LED lamp and sealed it to the electronics package. That was last year. Will have to see how it holds up under the direct sunlight and intense heat of Northern Utah.
How/where did you mount those lights?
The reason I thought of using bulbs is the bulbs are replaceable. If I use a led strip or something without a bulb then basically the light is non repairable if the light goes out.
 

Thread Starter

stryped

Joined Sep 17, 2023
47
I have no microwave transformers. Is there something else I can buy or use to make a transfor capable of sending steady 12 volts for 200 feet or more. Without buying a 300 dollar landscape low voltage transformer?
 

MaxHeadRoom

Joined Jul 18, 2013
28,768
I have no microwave transformers. Is there something else I can buy or use to make a transfor capable of sending steady 12 volts for 200 feet or more. Without buying a 300 dollar landscape low voltage transformer?
You have to come up with a required power rating, V/A , for the transformer first.
Depending on the demand and rating, HD has a selection.
 

Reloadron

Joined Jan 15, 2015
7,546
I have no microwave transformers. Is there something else I can buy or use to make a transfor capable of sending steady 12 volts for 200 feet or more. Without buying a 300 dollar landscape low voltage transformer?
Steady 12 volts is no problem the problem is knowing how much power (measured in watts) you need and allowing about a 20% overhead. When looking at landscaping transformers you will notice phrases like "50 watt, 60 watt, 100 watt, 200 watt and larger and cost is tied back to the wattage or power requirement. Next does your lighting require AC or DC current? Most are generally AC. Once you know what you need things become easy. So do you know how much power you want / need?

Ron
 

Tonyr1084

Joined Sep 24, 2015
7,956
How/where did you mount those lights?
The reason I thought of using bulbs is the bulbs are replaceable. If I use a led strip or something without a bulb then basically the light is non repairable if the light goes out.
First I bored a 3/4" hold deep enough to fit the whole lamp into. Then I bored the rest of the way through the 4x4 fence post exiting on the far side. Then I ran some sprinkler control wire along the fence and simply butt spliced the wires together and on to the next post. The splices are tucked up under the fence rail. It hardly sees any moisture. Yes, someone's going to say it will deteriorate. But so far more than 2 years it's been doing just fine. Probably 3 to 4 years; just don't remember for sure. And if/when they deteriorate they're cheap and easy enough to replace.
IMG_4235.jpeg IMG_4236.jpeg IMG_4237.jpeg

This is the photo sensor with the LED bulb cover over it. It's holding up fairly well so far. Time will tell.

IMG_4238.jpeg
 

Thread Starter

stryped

Joined Sep 17, 2023
47
Steady 12 volts is no problem the problem is knowing how much power (measured in watts) you need and allowing about a 20% overhead. When looking at landscaping transformers you will notice phrases like "50 watt, 60 watt, 100 watt, 200 watt and larger and cost is tied back to the wattage or power requirement. Next does your lighting require AC or DC current? Most are generally AC. Once you know what you need things become easy. So do you know how much power you want / need?

Ron
DC current, probably a total of 100 watts.
 

Tonyr1084

Joined Sep 24, 2015
7,956
Make sure it has been unplugged for one month.
Good safety advice. But a bit overkill.

You can unplug it and within an hour the cap should be drained. To make sure it's drained, grab a nail, hold it with insulated pliers and short out the cap leads. No need to put a project on hold for 4.3 weeks. (365 ÷ 12 ÷ 7 = 4.345238, the average number of weeks in a month.) Using this method I've not found a charged cap even within 20 minutes. BUT! Should the bleeder resistor fail open - the cap will hold a lethal charge for considerable time. That's why I recommend shorting the leads.

Better yet - I'd recommend not messing with that thing at all. One mistake and it can be your last.
 

MisterBill2

Joined Jan 23, 2018
18,984
How/where did you mount those lights?
The reason I thought of using bulbs is the bulbs are replaceable. If I use a led strip or something without a bulb then basically the light is non repairable if the light goes out.
Unless you abuse them badly, LEDs last a very long time, and consider that their normal failure is declining to 50% of the original light output. so they would be still lighting after 30,000 hours. And while it takes some effort to replace them it certainly is possible.
 

Reloadron

Joined Jan 15, 2015
7,546
DC current, probably a total of 100 watts.
OK if you want / need DC 100 watts at 12 volts is about 8.3 amps. I can buy a 12 volt 10.0 amp DC supply for about $21.00 USD which is more cost effective than rolling (building) my own. Just use suitable underground direct burial cable. Next most supplies custom made for this include dusk to dawn On/Off control or other On/Off features. So you decide what you need/want. List the features you want and choose a supply based on that.

Eon
 

Thread Starter

stryped

Joined Sep 17, 2023
47
OK if you want / need DC 100 watts at 12 volts is about 8.3 amps. I can buy a 12 volt 10.0 amp DC supply for about $21.00 USD which is more cost effective than rolling (building) my own. Just use suitable underground direct burial cable. Next most supplies custom made for this include dusk to dawn On/Off control or other On/Off features. So you decide what you need/want. List the features you want and choose a supply based on that.

Eon
I have seen those, but how far will they supply that 12 volts before that voltage drops? (If I have a long fence row to cover?
 

BobTPH

Joined Jun 5, 2013
9,149
I have seen those, but how far will they supply that 12 volts before that voltage drops? (If I have a long fence row to cover?
Distance is not the problem, it is resistance of the wire. Until you tell us how many amps you need, and over what distance, we cannot tell you what gauge wire to use.
 
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