Landscape Light controller design feedback

Eight 10W lights is 80 W. That is 6.67 A. If you are running both sets at the same time, you are either overloading the power supply or the lights aren't taking their rated current.

If the power supply is a switch-mode one, it will have a current limit in it so fuses wouldn't protect anything. The danger with a short when you have a power supply like that is that the output voltage will reduce, and it could be the that a MOSFET doesn't turn on completely, and gets really hot. However, if they are pre-built MOSFET circuits then they may have protection against that.

Thanks for the feedback. Makes sense. The MOSFETS are the pre-built kind like DC 5V-36V 15A 400W Dual High-Power MOSFET Trigger Switch Drive Module 0-20KHz PWM. The power supplies are Switching Power Supply Light Transformer AC110V. 10A 12V Output over 2 leads. So I have 2 circuits built for 2 parts of the property each identical and with their own power supply and 2 banks of (what now seems enough light ) with 6 lights each so actually 120 W per controller or I think 10A max if the math is right. My main concern is over-loading in any way and how to mitigate. I suppose I could add a volt sensor maybe even an amp sensor and put some logic there.

Interesting though what you say about power limiting and MOSFETS I have observed on one of my other similar setups, a buzzing noise that kind of concerned me when in lower brightness mode. I thought it was about the Hz I have set in the application but am not sure.

Thanks for taking the time.

A drawing or schematic of how you actually have things connected together, along with links to the actual parts used, would be very helpful for us to give you the best feedback.

Also, the proper spelling is MOSFET, which stands for metal-oxide-semiconductor field-effect transistor

Thanks for the correction - yes a typo. I will try to depict in the attached. important added info is the two light banks have 6 lights each at 10W each and the 12 Gauge wires are min 150 feet in length. So I gather resistance is a factor.

6 x 10W lamps.
Each lamp is 0.83A at 12v
Total amperage between supply and first lamp will be 5A,
Amperage carried by the wire to each additional lamp will drop by 0.83A from the initial 5A.

12-gauge wire has resistance of 1.6 ohms per 1000 ft

Assume a bad case scenario where you have a 100ft run from supply to the first lamp. And 10ft to each of the next 5 lamps.

That means your voltage drop from wire resistance between supply and first lamp will be 200ft x 1.6 ohm/1000ft * 5A = 1.6 volts. Your first bulb will see 10.4v (actually slightly more because it likely won't draw 0.83A if it is not supplied with the full 12V.

Then, each additional lamp will see a step down of
20ft x 1.6ohm/1000ft * 4.17A = 0.13V

You can see the additional drop will be less and less because the wire to each successive lamp will have less current to carry.

The closer the first lamp is to the supply, the less drop you'll have at the first lamp but the sixth lamp at the end of the 150ft run will have the same voltage and brightness. To beat the wire resistance issue a bit, you can locate the supply in the middle of your 150ft strand (assuming you don't add more 12ga wire to get to the middle. You can use fatter wire to the first bulb(s) or run a second section of 140ft wire in parallel with the first and connect the first, third and fifth to that shorter wire. .

Good luck.

That is very helpful thanks - I wondered about ways to "boost" the power to mitigate voltage drops while still making the lights dimmable and reasonably consistent in brightness. Some sort of variable voltage buck converter-like device strategically placed. I placed 2 lights closest to the power module and then went all the way to the end (150 ft) and placed two more. At full bright you have to look hard to see a difference but as the brightness / voltage goes down you can see a gap in light level between them. It's not critical but interesting t explore solving this. I cannot bring the controller closer than about 30ft at 12 Guage but I could move to 10 Guage if that can help.

When I had a dozen 6W fence luminaires on a long extension of 16 gauge wire, I found it easier to power the 12V LEDs with 16V using an adjustable boost regulator. I just monitored the aluminum substrate temperature to be below finger burning temps of 55’C. They were significant brighter than anything else I’d seen with no visible glare. Power efficiency losses being cheaper than 8 gauge wire was my choice with a low cost adjustable booster.

But if your luminaire spacing is excessive for 12V then a better choice might have been 48V luminaires or more.

Makes sense - I have the "luxury" of 12 AWG and my longest run is about 150 feet from the power source. I prefer to have brightness control as different conditions warrant different brightness - i.e the light level as dawn progresses, wanting to be more discrete in lighting up the forest/lake (its a forest cabin on a lake) etc. It would appear from all the input I am not going to be able to get a consistent result with this design. It is however good enough for the cabin in the woods.