How to convert 120V AC to 1.5V DC lighting?

[JimG]

I have 150 individual outdoor solar lights (line a 700' long driveway) that are single bulb 5mm LEDs that each run on 1.5V AA battery.
Because of trees, shade, and therefore sporadic lighting on the driveway, I would like to (not really LIKE to...but need to) wire them and run them off a (landscape?) transformer of some type. I have not been able to find one that handles more than 3w so far (like for dollhouses). Any suggestions?
Also...do I need to run the lights in serial or parallel connection? I can split the lighting runs into 3 runs of approx 50 lights each if that will help.
Thank you so much for your help.
Jim

 

[Resqueline]

That is actually a tricky project, due to the distances & numbers involved.
One has to determine how many can be connected in series and/or in parallell, and where to connect.
Do they use white LED's? How many individual cells does each solar panel comprise & what's their area?
3W can only run 30 white LED's. Could it be feasible to relocate the solar panels?

 

[JimG]

Thanks for the reply. They are white LED's and they are bollard (sp?) lights...each light has it's own little solar panel with dusk-to-dawn sensor. There is also a small 1/2" x 1.5" circuit board in each...don't know what all is on the board, but I hope to possibly just use the + & - wires to the new power if it is possible.

 

[Resqueline]

Ok. White LED's require 3-4V & 20-25mA to operate. The board converts the battery's 1.2V to this. It also takes care of charging and switching on/off.
So, there are several options to hook power into the system. It can go where the solar panel goes, it can go instead of or in addition to the batteries, or it can go directly to the LED.
There are several advantages, risks, & disadvantages with each option.

 

[JimG]

I tried to attach a picture, but couldn't.
As for power options, I would like to bypass the batteries somehow, as using and replacing 150 rechargeable batteries can get expensive. As far as the light sensors, it would probably make more sense to just install one at the transformer to turn them all on/off at the same time.
What are the advantages, disadvantages and risks then for my possible options?
Does anyone make a 120v to 3-4v transformer?
Do you know of any (preferably outdoor) transformers that will handle all these and what amperage and wattage would I need? Again, I can split the runs into 3 50-light runs.
Lastly (I hope), do I need to run them in serial or parallel connection to keep them all the same brightness?
Again, Thanks so much for your help. I really appreciate it.

 

[Resqueline]

Ok. Parallelling 50 LED's directly results in a current of 1A, making voltage drop in the wiring a concern. They would need one resistor each so they could be run from 6V for instance, making brightness equal. A higher drive voltage makes the circuit less sensitive to voltage drop, but also wastes more power.
Connecting 50 LED's directly in series results in a voltage requirement of 175V DC, making isolation safety a concern. I don't know about any ready-made power supplies handling this.
Connecting 50 lamps in series at the battery results in a voltage requirement of "only" 60V DC, but I don't know how the inverter in them would respond to that.
I believe 24V AC is a common lighting transformer type, but I'm not up to date on the market today.
Are the 3 runs in a row or in a Y, and where's the power? Do you have any particular kind of wire in mind?

 

[JimG]

Thanks for the reply. I could easily do the runs in a Y with all the power at the center. I remeasured for the lights and would have 3 runs of 300' each.
So far most of the landscape transformers I have found online are multi-tap ones that have the ability to do 12, 13, 14, 15, 17, 20, 22v....and others just do 24v. But, do I need the 12v - 24v to be AC or DC?
I have read somewhere that DC does not do well over long distances...that AC does better, but yet read somewhere that I should use DC for the LED's....true? false? comments?
I have no idea on the kind of wire to use yet, or what kind of voltage drop I would have with 300-400' runs.

 

[Resqueline]

Multi-tap would be ideal to fine-tune the voltage and hence the current & light intensity. A Y would also be ideal.
AC for long distance has high-tension lines in mind, where cheap & easily applied transformers step up the voltage & down the current - making for less losses in the wires. Long-distance submarine cables however use high-voltage DC due to their higher capacitance which would lead to a high AC current in itself. This requires the use of more complex & costly AC-DC & DC-AC inverter stations at either end.
LED's require DC so if only AC output transformers are available you'll have to add a rectifier & a capacitor yourself to get DC (which will be 1.4 times higher than the AC).
How about using multi-pair telecom cables? Knowing the gage we can calculate the losses, but I think it would be negligible at 30V & 50-60mA.
If the lamps can be series-connected at the battery connections it would be ideal to split the 50-lamp-runs in two, making for a manageable 30-36V supply.
Parallell connection would require the use of a heavy mains- or speaker cable.