Landscape Lighting Question

[The Rodent]

Full disclosure, I know very little about anything electrical.


Back in the day, before LED bulbs became popular I installed some landscape lights. 1200W transformer with 20 halogen lights at 20W each (400W total load). Works great. Yes I know the transformer is way too big.


Now as the bulbs burn out, I started to replace them with equivalent 3W LED's. Eventually this will be a total load of only 60W on that 1200W transformer.


I've been told that I won't realize any electricity cost savings until I downsize the transformer. That does not sound logical to me. Also, I've been told that the 1200W transformer will not likely function with the small 60W load.


Should I replace all the bulbs with LED and get a 150W transformer?

 

[retire-early]

The transformer is to step-down the 120VAC to a lower voltage generally 12VAC for outdoor lighting.

The 1200W is the maximum that the transformer can provide.
Here is an explanation. https://homeguides.sfgate.com/size-transformer-landscape-lights-34303.html

There is no point in replacing the transformer.
The power usage is determined by the bulbs.

Replace the halogen bulbs with LED ones.

 

[latexman]

Replace the bulbs as they burn out with LEDs. Do not replace the transformer until a real problem materializes.

 

[The Rodent]

Thant's good news. Thank you.

 

[Out-to-Lunch]

Agree with the above. There will be a very small parasitic loss in the transformer, which could be reduced a bit by using a smaller transformer, but the benefit would be minimal.

 

[ncbill]

Is it a transformer or switching power supply?

The latter are what have been used for years because they're more efficient.

If the latter there's no need to replace it.

 

[The Rodent]

Is it a transformer or switching power supply?

The latter are what have been used for years because they're more efficient.

If the latter there's no need to replace it.

It's definitely a transformer (Vista Pro CT8-1200)

 

[ERD50]

Is it a transformer or switching power supply?

The latter are what have been used for years because they're more efficient.

If the latter there's no need to replace it.

No, that's not correct - it's just the opposite (in general).

Transformers are very efficient.

https://www.electronicsforu.com/technology-trends/learn-electronics/step-down-transformer-working

Advantages of Step-Down Transformers

Step-down transformers are very efficient and can give the desired output with an efficiency of up to 99 per cent.
We can get the desired output voltage easily without loss of much power.

Switching power supplies will have some overhead, and that will generally be a % of their max rating. So a 1200 W switcher will have draw more idle current than a 120 W switcher.

I think you are thinking of linear voltage regulators versus switching voltage regulators. In that case, yes, a switcher is generally more efficient than linear.

But those lighting circuits usually just use an efficient transformer.

-ERD50

 

[CaliKid]

I'd wait until the transformer goes out. I can't imagine you'll save enough in electricity to justify the cost for quite some time.

 

[Souschef]

If memory serves, the open circuit magnetizing current in a transformer ia about 10% of full load. However, it is mostly reactive and is not that many watts.

 

[TriumphTR3fan]

We had a temporary low voltage installation before landscape LED’s became common when we built our house 14 years ago. It’s still in place. We switched to LED’s several years later. Although you have excess capacity as you switch your halogen bulbs to LED’s you still have line resistance. Some of your excess capacity is consumed by that. You won’t save much by changing your transformer & the line resistance could become a factor. The good news is that you can add lights & not worry about overloading the system. We’ve added lights that highlight part of the house & indirectly light the path around the house.

 

[travelover]

I've switched all my landscaping lights to LED and the power use is almost insignificant now. As far as the wires consuming power, the power used by the wires is still current squared times resistance. Since current is so low, wire loss is also minimal. And, the wiring is fat since it was originally wired for a lot of halogen bulbs.

 

[ERD50]

The following [struck out] is not correct. Although the line resistance is constant (and probably not a big factor even with the original bulbs), it is even less of a factor as the current draw of the LEDs is far less:

... Although you have excess capacity as you switch your halogen bulbs to LED’s you still have line resistance. [-]Some of your excess capacity is consumed by that. ... the line resistance could become a factor. ..[/-].

This part is correct:

... The good news is that you can add lights & not worry about overloading the system.

travelover has it right:

I've switched all my landscaping lights to LED and the power use is almost insignificant now. As far as the wires consuming power, the power used by the wires is still current squared times resistance. Since current is so low, wire loss is also minimal. And, the wiring is fat since it was originally wired for a lot of halogen bulbs.

-ERD50

 

[Telly]

A transformer's output voltage is usually specified at a specific load current. Reduce the load current, the output voltage will increase, and vice-versa. A 1200 watt (probably 1200VA) transformer with only a ~60 watt load on it is running very lightly loaded at only ~5% load, so would expect the actual output voltage to be quite a bit above (percentage-wise) the rated output voltage. I cannot say if this will shorten the life of your LED bulbs or not.

IIRC, some of those landscape lighting transformers may have the output multiple tapped, so you could move the load over to a lower-voltage tap to correct for the very light load. Some transformers may instead have a switch like a HI - LO output voltage, that you could switch to LO.

An easy way to check on this concept, is to totally disconnect the load from the transformer's output, and then measure the output voltage It will come down as a load is applied, but a load of only ~5% ain't much!

 

[qwerty3656]

I'm sure I'm missing something, but you can get simple solar powered landscaping lights that work great. I bought the ones in the link. There are all kinds of options like it

https://www.amazon.com/gp/product/B074PPWTPD/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[ERD50]

A transformer's output voltage is usually specified at a specific load current. Reduce the load current, the output voltage will increase, and vice-versa. A 1200 watt (probably 1200VA) transformer with only a ~60 watt load on it is running very lightly loaded at only ~5% load, so would expect the actual output voltage to be quite a bit above (percentage-wise) the rated output voltage. I cannot say if this will shorten the life of your LED bulbs or not.

IIRC, some of those landscape lighting transformers may have the output multiple tapped, so you could move the load over to a lower-voltage tap to correct for the very light load. Some transformers may instead have a switch like a HI - LO output voltage, that you could switch to LO.

An easy way to check on this concept, is to totally disconnect the load from the transformer's output, and then measure the output voltage It will come down as a load is applied, but a load of only ~5% ain't much!

That's a good point. It looks like the 12V outdoor LED replacements have active driver circuits in them (not just a passive series resistor), so they *should* be tolerant of a ltitle higher voltage with almost no added power dissipation. But some may use just a resistor, I don't know. I'd bet this is discussed on the web somewhere - model numbers of the original bulbs and replacement LEDs might help.

I'm sure I'm missing something, but you can get simple solar powered landscaping lights that work great. I bought the ones in the link. There are all kinds of options like it

https://www.amazon.com/gp/product/B074PPWTPD/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

But if the wiring is already in place, I'd go with that. No concerns about shading, no batteries to replace, and no problem if you get a few overcast days.

-ERD50