12v AC garden lighting circuit- ? convert to 12v DC

Thread Starter


Joined May 23, 2020
I can't understand why an admittedly old garden lighting circuit wont run on 12v DC, when it was previously running on 12v AC.
On checking, the output voltage is switching from 0.0v to 5V every few seconds, instead of a steady 12v
Could there be some type of rectifier in circuit...or another reason?
The lights are old filament type lights, but are to be replaced once the circuit problem is understood.

Strangely, a completely separate circuit with the same type of garden lights does work on the 12v DC
(Picture shows the 12V DC power supply/old power supply).
Thanks, Tinkerer



Joined Dec 31, 2017
How many lights are on the circuit?
Sounds like the power supply is over loaded.
Those garden lights could be 10 to 20 watts each.

Thread Starter


Joined May 23, 2020
good question...there are two that work, and one that was broken but still showed power, although this was only 8v rather than 12v when tested...thinking because it was at the end of the long cable?
Maybe if I disconnected these lights and retested the Voltage?

Jon Chandler

Joined Jun 12, 2008
The DC power supply is most likely a switch mode power supply. Most switch mode power supplies have a strong self-preservation instinct, and when overloaded will cut the voltage. The 0v —> 5v cycling is the power supply starting up, sensing the overload as the voltage increases and shutting down.

Replacing the incandescent bulbs with LEDs should cure the problem.


Joined Aug 1, 2013
Are the lights LED, incandescent, or other?

Also, are you checking the output with a meter or a scope? A whole lot of strange things can show up as 5 V on a digital meter.



Joined Sep 24, 2015
Measuring AC with the meter set to DC will give you all kinds of weird readings and they will be constantly changing.
Measuring DC with the meter set to AC will give you almost no reading. Set to AC it expects to see a cycle of some sorts. You won't get an accurate reading with DC on the AC setting.


Joined Jul 18, 2013
I switched over to these, and have not regretted it, seem to last forever. Amazon
12V LED Bulb E26 7W AC/DC 12Volt Low Voltage Lights 6000K Daylight White 60Watt Equivalent-6 Pack


Joined Sep 24, 2015
I can't understand why an admittedly old garden lighting circuit wont run on 12v DC
From this one statement I'm thinking more along the lines of something like this. No particular reason other than this is what came to my mind. Swapping out the 12V incandescent lamps for LED lamps seems like a reasonable swap. As to why it doesn't work on 12V DC I don't know. If someone changed the lamps to LED and powered it from a DC source then there's a chance it may be a polarity issue. I'm just not sure the TS had taken the measurements correctly. (see post #6)
Notice "Interior", as opposed to the TS statement of garden lighting.


Joined Sep 24, 2015
Amazon Canada.
Also, and I suspect Max already knows this, but everything from the question mark on is used for tracking. Using just
Amazon.ca/Voltage-Equivalent-12volt-Battery-Interior-Lighting/dp/B07MCGH7N4/ref=sr_1_1_sspa (everything from ? on deleted)
in the address bar brings you to the same page without giving Amazon the ability to track this link back to you. Of course, if your account is open then it will still track you. But I always remove everything from the question mark on back. The links almost always work. Tried that with YouTube and that's the only place I've found that the question mark and address beyond that is necessary.