Converting dc to single phase ac

Thread Starter

sunnsa

Joined Sep 10, 2022
15
Hello. I have some LED lights which run on single phase ac supply. I would like to be able to power them using batteries as well. The total wattage of the lights is around 12W. Can you tell me how I can do so? Will I be able to get an inverter for such a small rating?
 

LowQCab

Joined Nov 6, 2012
2,506
The Voltage-Conversions will make this project use ~20 to ~30% more Battery Power,
than would normally be expected for the amount of Light that it will put out,
and it's a lot of extra-effort and expense.
I would just start with some lower-Voltage LEDs.
.
.
.
 

Ian0

Joined Aug 7, 2020
6,294
Don't - LED lights often have capacitive dropper power supplies, which means they don't like modified sinewave inverters. A small inverter circuit would probably be modified-sine-wave and it will give large pulse currents which will either damage it or the LED lights.
You would need a proper sinewave inverter, and that won't be worth the cost.

Maybe the LED lights have built-in switched-mode supplies. You'll have to take them apart to find out for sure and then they are useless, but if you do, and you find a flyback converter than runs on 90V-250V AC, then you can also run them off 120V-320V DC, and making a 120V DC supply might just be cost-effective, especially if you want to run really long cables to them.

@LowQCab is correct. Just get some 12V DC LED lamps. If you subsequently want to run them on AC, get a cheap 12V 12W power supply.
 

Thread Starter

sunnsa

Joined Sep 10, 2022
15
The Voltage-Conversions will make this project use ~20 to ~30% more Battery Power,
than would normally be expected for the amount of Light that it will put out,
and it's a lot of extra-effort and expense.
I would just start with some lower-Voltage LEDs.
.
.
.
Thank you @LowQCab for your advice
 

Thread Starter

sunnsa

Joined Sep 10, 2022
15
Don't - LED lights often have capacitive dropper power supplies, which means they don't like modified sinewave inverters. A small inverter circuit would probably be modified-sine-wave and it will give large pulse currents which will either damage it or the LED lights.
You would need a proper sinewave inverter, and that won't be worth the cost.

Maybe the LED lights have built-in switched-mode supplies. You'll have to take them apart to find out for sure and then they are useless, but if you do, and you find a flyback converter than runs on 90V-250V AC, then you can also run them off 120V-320V DC, and making a 120V DC supply might just be cost-effective, especially if you want to run really long cables to them.

@LowQCab is correct. Just get some 12V DC LED lamps. If you subsequently want to run them on AC, get a cheap 12V 12W power supply.
Thank you@Ian0 for your advice. The LEDs have a driver which drives them at constant current of 350mA.
 

DickCappels

Joined Aug 21, 2008
9,317
It appears that your real challenge is to either produce 350 ma DC or find a way to power the constant current power supply.

If you can power the 350 ma current source from batteries that might save a

We already know that the constant current supply was designed to take an AC input. The odds are that the AC input is changed to DC before going to the constant current circuit. What is the DC voltage at that point?

Incidentally, do you know how much voltage your string takes?
 
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Thread Starter

sunnsa

Joined Sep 10, 2022
15
It appears that your real challenge is to either produce 350 ma DC or find a way to power the constant current power supply.
We already know that the constant current supply was designed to take an AC input. The odds are that the AC input is changed to DC before going to the constant current circuit. What is the DC voltage at that point?
Thank you @DickCappels for your reply - I don't have the value of the DC voltage, but I'm assuming its 12V.
 

Thread Starter

sunnsa

Joined Sep 10, 2022
15
Hello. I have some LED lights which run on single phase ac supply. I would like to be able to power them using batteries as well. The total wattage of the lights is around 12W. Can you tell me how I can do so? Will I be able to get an inverter for such a small rating?
Edit : I want to power them using batteries for 8-9 hours.
 

Irving

Joined Jan 30, 2016
3,133
Typically those 12 - 18W AC-powered 350mA CC potted supplies output ~36v - 48v to drive 2 or 3 parallel strings of 8 - 12 X 3v White LED at 120mA a string. I have several ceiling and bulkhead lights and they are all remarkably similar internally.

To power from batteries for 8 -10 hours you'd need a 10 or 11 cell stack of 5Ah capacity, that's 2 or 3 good quality 18650 cells in parallel; so 20 - 30 cells in total (IE 10S2P to 11S3P configurations depending which Lithium technology you choose). Alternatively 4 X 12v 7 or 10Ah lead-acid batteries would do the job but would require a much longer recharge time.

In either case you'd need an appropriate (automatic?) charging solution and a simple constant current circuit between batteries and LEDs.

You could get away with a smaller number of higher capacity batteries by using a boost converter to give 36+ volts from say a 12 or 24v input.
 
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Thread Starter

sunnsa

Joined Sep 10, 2022
15
Typically those 12 - 18W AC-powered 350mA CC potted supplies output ~36v to drive 3 parallel strings of 12 X 3v White LED at 120mA a string. I have several ceiling and bulkhead lights and they are all remarkably similar internally.

To power from batteries for 8 -10 hours you'd need a 10 or 11 cell stack of 5Ah capacity, that's 2 or 3 good quality 18650 cells in parallel; so 20 - 30 cells in total (IE 10S2P to 11S3P configurations depending which Lithium technology you choose). Alternatively 4 X 12v 7 or 10Ah lead-acid batteries would do the job but would require a much longer recharge time.

In either case you'd need an appropriate (automatic?) charging solution and a simple constant current circuit between batteries and LEDs.

You could get away with a smaller number of higher capacity batteries by using a boost converter to give 36+ volts from say a 12 or 24v input.
Thank you @Irving for your reply - could you kindly let me know how to connect the batteries to the existing single phase leads? I think as you mentioned, I require a 10Ah battery, but I didn't fully understand why we require 4 such batteries. Why can't we do with just one?
 

Irving

Joined Jan 30, 2016
3,133
Thank you @Irving for your reply - could you kindly let me know how to connect the batteries to the existing single phase leads? I think as you mentioned, I require a 10Ah battery, but I didn't fully understand why we require 4 such batteries. Why can't we do with just one?
You can't connect to the AC input, you have to replace the AC supply with a DC equivalent eg batteries, maybe a boost converter and a constant current driver.

You need enough volts to drive the current through the LEDs. If there are 8 LEDs in series that needs around 28v for typical white LEDs before they will turn on (8 * 3 to 4v per LED), more for a 12 LED string.
 

MrAl

Joined Jun 17, 2014
9,546
Hello. I have some LED lights which run on single phase ac supply. I would like to be able to power them using batteries as well. The total wattage of the lights is around 12W. Can you tell me how I can do so? Will I be able to get an inverter for such a small rating?
HI,

You might need a special kind of converter called a synthesized sine wave converter. This is not something someone with not too much experience in electronics can build unless maybe they have a complete schematic. Even then there could be problems that come up which make it very difficult to get up and running. I actually worked in this industry for several years in the past and designed these converters and i can say they are the most complicated type you can build and that comes with special problems that have to be addressed.
So if you find a schematic for one on the web then you MAY be able to build one, but it's really not worth the effort and losses that come with the conversion process.

The heart of the design is an H bridge that creates a pulsing pattern that looks like a sine wave when filtered a little. You can get away without using a transformer that is one benefit but you may still need some filtering. Even filtering is not that simple because you are dealing with 120vac so you need an inductor and capacitor output filter.

In the end you will find it would even be simpler to just buy a whole new system that worked on DC voltage rather than try to convert this system into DC. I know that's not what you wanted, but you will save yourself countless hours of problems and headaches.

If you are a diehard do it yourself'er, you may want to try this, but be prepared to chuck the whole thing in the garbage and go out and buy something ready made anyway.

If you are still not convinced, i can list some of the problems that come up with these kinds of converters. I seriously doubt you will want to deal with any of these.
 

Thread Starter

sunnsa

Joined Sep 10, 2022
15
You can't connect to the AC input, you have to replace the AC supply with a DC equivalent eg batteries, maybe a boost converter and a constant current driver.

You need enough volts to drive the current through the LEDs. If there are 8 LEDs in series that needs around 28v for typical white LEDs before they will turn on (8 * 3 to 4v per LED), more for a 12 LED string.
Thank you @Irving - however, the wattage of the entire light fixture is 12W, and I thought there will be a 12V input to the LED, so the current drawn will be 1A. For 8 hours of usage, I will require one 8Ah battery. Am I correct? And from the batteries, is it possible to connect two wires to a small dc-ac converter, at the other end of which I feed my LED wires? Kindly advise.
 

Thread Starter

sunnsa

Joined Sep 10, 2022
15
HI,

You might need a special kind of converter called a synthesized sine wave converter. This is not something someone with not too much experience in electronics can build unless maybe they have a complete schematic. Even then there could be problems that come up which make it very difficult to get up and running. I actually worked in this industry for several years in the past and designed these converters and i can say they are the most complicated type you can build and that comes with special problems that have to be addressed.
So if you find a schematic for one on the web then you MAY be able to build one, but it's really not worth the effort and losses that come with the conversion process.

The heart of the design is an H bridge that creates a pulsing pattern that looks like a sine wave when filtered a little. You can get away without using a transformer that is one benefit but you may still need some filtering. Even filtering is not that simple because you are dealing with 120vac so you need an inductor and capacitor output filter.

In the end you will find it would even be simpler to just buy a whole new system that worked on DC voltage rather than try to convert this system into DC. I know that's not what you wanted, but you will save yourself countless hours of problems and headaches.

If you are a diehard do it yourself'er, you may want to try this, but be prepared to chuck the whole thing in the garbage and go out and buy something ready made anyway.

If you are still not convinced, i can list some of the problems that come up with these kinds of converters. I seriously doubt you will want to deal with any of these.
@MrAI Thank you for the idea - it sounds interesting, but as you said, I think it is very expensive and time consuming
 

Ian0

Joined Aug 7, 2020
6,294
If your LED lamps have switched-mode supplies, then they will more-than-likely work off DC of a suitable voltage. Making a high DC voltage is a lot easier than making a sinewave.

Your choice of battery is technically correct, but if you are thinking of using lead-acid, then you will only get a 100% discharge a small number of times before ruining that battery. If this is a battery backup that is meant to operate once in a great while when there is a power cut, then that is OK, but if it is a regular occurrence, then aim for no more than 50% depth of discharge, and use 16Ah.
 

Thread Starter

sunnsa

Joined Sep 10, 2022
15
If your LED lamps have switched-mode supplies, then they will more-than-likely work off DC of a suitable voltage. Making a high DC voltage is a lot easier than making a sinewave.
@Ian0 These lights have a single phase ac supply, and a constant current driver to feed 350mA CC.
 

Thread Starter

sunnsa

Joined Sep 10, 2022
15
If your LED lamps have switched-mode supplies, then they will more-than-likely work off DC of a suitable voltage. Making a high DC voltage is a lot easier than making a sinewave.

Your choice of battery is technically correct, but if you are thinking of using lead-acid, then you will only get a 100% discharge a small number of times before ruining that battery. If this is a battery backup that is meant to operate once in a great while when there is a power cut, then that is OK, but if it is a regular occurrence, then aim for no more than 50% depth of discharge, and use 16Ah.
It is meant to work like a battery backup
 

Ian0

Joined Aug 7, 2020
6,294
@Ian0 - 300V DC - okay, so I'll need more than 12 12V, lead acid batteries to proceed!
Or a boost coverter.
I recently did a 7kW emergency lighting system with 216V DC (18 x 12V 100AH batteries) using LED lamps with electronic ballasts. It switches from 230V AC to 216V DC when the mains fails.
 
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