How to use LED strips from a now obsolete 44 inch with 4 PCB's with mounted LEDs

westbranch

I removed 2 - 2 Fluorescent 4' tube units in the kitchen and replaced them with 44 inch LEDs. One of the units LED Driver faiiled and I find it has been placed with a new model... I want to use the 1000Lm strips at the cabin, ...

Is it possible to run them with a DC - DC converter as I have 24 volt system and the driver was a 10V unit?

Are there any other pieces I might need to make this project work.

thanks

BB.

I am not quite sure of your plans.

a) To use a DC converter to run a 24 Volt (AC or DC?) input LED driver?

b) Or to use a DC to DC converter to drive 10 VDC directly to the LED strip lighting?

"b" can be a problem. "bare" LEDs need a current limiting device (resistor, current mode power supply, etc.) to limit current flow through the LEDs (aka an "LED ballast"). If you just feed them with 10 VDC (or whatever), the LED strip current will not be stable over time and temperature and can self destruct from too much current/heat.

-Bill

jonr

A DC-DC converter with current control can be connected to your strip of LEDs. Start with it set at very low current (like .1A). I don't know what voltage and current output you will need from this DC-DC converter. Perhaps 70V and <.3A, but it could be quite different - it depends on how the individual LEDs are wired. 10V at < 2A is possible but unlikely.

mcgivor

Measure the current drawn at 10V, take the maximum battery voltage at night, when the light would probably be needed, subtract the required voltage from the actual battery voltage , then divide by the current, this will give a figure, this is the nessersary resistor value needed to drop the actual voltage to the required voltage value in series, the resistor needs to be able to handle the wattage, so a resistor of equal or more than the light requires, needs to be used,

Example: Battery voltage 25V, required voltage 10V, difference 15 V, current required 150mA, 15/ 0.150=100, so a resistor of 100 ohms is required, led's cam be over driven at the axpense of life expectancy, so it's best to operate at lower voltages, by choosing a resistor of a slightly higher value, to ensure a higher voltage drop..... clear as mud, no doubt, but it actually quite simple

jonr

Say this is a 20W LED strip. While resistors can work at low power, they will produce 30W of wasted heat if you use them to take voltage from 25V to 10V.

mcgivor

True, it's not efficient when the reduction is greater than the need .

Tecnodave

I have several Chinese LED troffer fixtures that had a failed led driver. The original driver is not available so contractor threw out 4 nearly new 2 X 4 foot troffer LED fixtures rated at 27-46 volts at 1400 milliamperes. I purchased DC-DC boost converters on Amazon that were rated approately for the job.. Rated 8-46 volts in and 12-56 volt out at 6.0 amps. I set the volts max at 46 volts and amps max at 1400 ma. Walla...I have very good lighting....flush mount led troffers for $12.00 each running from my 24 volt battery set....no inverter

david

Tecnodave

WB,

LED fixtures are like floursents in that they both cannot control their current. Ballasts in floursents and LED drivers do the same thing....they limit the current preventing thermal runaway. That is the limiting factor with LED's , the hotter they get the more current they will draw and they get hotter and draw more current....thermal runaway...then failure. Just control the maximum current and don't worry to much about the voltage, let it stabilize where it will.

david

Tecnodave

Ok

my assumptions as these were replacement units for floursents that they would be 110 vac led drivers. They would not use 10 volt or 12 volt led groups but all the led's will be in one series string unlike low voltage led where 3 5050 led and 3-10 k dropping resistor would be used in each string for a 12 volt led fixture.

david

westbranch

wow, lots to look into..

Thanks all , especially Dave for all the details.

Not at home, up in the mountains so do not have the unit hereto add more specs.

Headed back tonight, more then.

Tecnodave

WB,

if you can get the nameplate rating of the led driver I can pick out a Chinese DC boost or buck converter approiate for this application.... I have several in use

24-28 volt buck converter providing 20 volt DC for charging Lenovo notebook from solar

10-16 volt boost converter providing 20 volt DC ....................Lenovo .......automobile....etc.

and I few others in use.....I find these on Amazon. Just can't stop tinkering

Dvd

Tecnodave

WB,

This is what I use for this. I have several in use:

https://www.amazon.com/gp/product/B019W4C5IE/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

4 of them now driving the 2 X 4 foot troffers and a couple more driving 60 watt led floods that were 120 AC powered Not al all hard to do..need voltmeter, ammeter, dummy load to set basic parameters, volt limit, amp limit

Don't remember price right now......maybe $12 or so

david

Tecnodave

WB,

One more charging my Lenovo Idea pad notebook computer from 12 volt DC source, provides 20 volts at 4 amps .

it will do more current, I'm limiting to protect computer.

david

Tricksailing

LEDs don't need a series resistor if you use the correct voltage or put the correct number of LEDs in series to accommodate your voltage supply. You could probably get away with putting the two strips in series for your 24 v supply. It is a bit hotter than the 2 x 10v (20v) supplied by your original system but probably not critical. If you wanted to adjust with a series resistor, you can use a modified version of the resistor calculation described by mgivor with a much reduced power loss / heat generation due to the resistor since the second series light means a much smaller resistor. You may also check if you get enough light from 3 lamps in series as this would put the voltage ~ 20% below the optimum for the lamps. Just depends how much light you want in your cabin. Since LEDs are non-linear I/V devices the light output could drop significantly.

Typically LED lights have individual LEDs in a series/parallel mix to get the correct voltage per LED and sufficient light level. An effective way of adjusting to different voltages is to modify the LED circuitry, most importantly to get the correct number of LEDs in series. A typical white LED requires a 3.3v supply and no series resistor. Just arrange 4 (8 or 9) in series to run from a 12v (24v) supply. You can usually do this by modifying the circuit board the LEDs are mounted on. Safe operating currents for LEDS are usually between 10 and 30 ma, with the lower value recommended. Note also that battery supply voltages are often higher than the standard quoted, depending on charge status.

You may be able to check out the supply voltage for the individual LEDs by identifying the LEDs or figuring the voltage from the cicuitry. Another way is go put a 1k resistor in series with a single LED and 12v battery and measure the voltage across just the the LED. The resistor limits the current to ~ battery voltage / 1000. The 12v - 1kohm combination sets up a ~ 10ma current which is typical for LEDs. Otherwise you should select the appropriate resistor to provide a 10 ma current with your battery voltage. Typically LEDs run between ~1.8 (red) and 3.3 (blue, white) and require 10 ma to power them. This page has some examples of LED voltage/current curves - http://lednique.com/current-voltage-relationships/iv-curves/.

BB.

No. LEDs do need a ballast (current limiting thing). Whether it is a resistor, or a switch mode current based regulator--Ballast(s) are needed. You (almost) never connect an LED to a regulated voltage source... Only to a current regulated source.

You will see installations that do not have a resistive ballast--A series capacitor (of correct size and rating) is common in 120 VAC AC Christmas lights to limit current.

And these days, there are a huge range of LEDs out there now... From ~3-6 volts, from mWatt to 1 to 10 to 100 Watt LEDs (the larger ones tend to be arrays of LEDs). It is not a good idea to use rules of thumbs around (white) LED designs. There are way too many options out there to generalize.

LEDs are just diodes whose IV transition curve is very sharp, and the transition point on the curve is very temperature dependent.

On page 24, you can see a while LED that goes from 0.1 amps to 1.6 amps from ~3.2 volts to 3.85 volts

http://educypedia.karadimov.info/library/DS51.pdf

LEDs are one device that cannot be mounted in parallels (unless they are on the same heat sink). As the temperature rises, the current allowed rises, and the die temperature rises more, which causes the current to rise more... Thermal runaway situation, and the "one hot LED" will draw all the current intended to be shared among multiple paralleled LEDs until it overheats and fails.

In general, if you have multiple LEDs, you would place them in series with a ballast of some sort.

In your link, you can see there is (virtually) zero current flow until the LED (diode) goes into conduction, then within a few tenths of a volt further increase, the current increase dramatically (very non-linear, vs the resistor IV curve above).

-Bill

Tecnodave

I use a lot of the COB LED boards from China, these have no regulator, three 5050 smt led's in series with a resistor to control maximum current. There are allways in multiple of threes. I.e. 18 led..24 led..36 led 48 led. These have no buck converter to control the voltage only the dropping resistor. This is less efficient but makes no EMI/RFI . The much better method is to use a buck or boost converter that will allow only so much current to flow. When I turn on the 50 watt troffer arrays the voltage is at about 42 volts but when the current ramps up to the 1400 ma. max rating of the array the voltage drops very dramatically to 25-30 volts as the led's warm up their resistance drops dramatically. The cheaper COB LED arrays start to burn out in 6 months, better ones last a few years, far less than the led's life. This is due to the poor control provided by the resistors. The regulated led array' s last years. It's the "ballast" that fails. One of my freind's is the repair electrician for a chain of eateries and pulls these troffers out with a failed LED driver, the LED driver is not available so with little experimenting I have awesome bright LED troffers for a few bucks each.

Common user 12 volt led's have a built in resistor and do not need an external resistor. If you connect a non-protected led to a non controlled power source you will get a quick flash of light one time, it will be bright!

Tecnodave

WB,

For what I'm doing I needed a boost converter, the one pictured above works very well. For your application you need a buck converter. I buy bags of ten LM-2596 buck converters on Amazon for about $10.00/lot. They will handle 3 amps each and would work perfect with those 10 volt chip boards that you have.

Interchangable wording ..........LED Driver<=>Ballast..........same thing the word ballast is more common to floursents lamps which exhibit the same behavior , the hotter they get the more current they draw and get hotter and draw more current...... term to describe this....thermal runaway This behavior is also common to street lites be it mercury vapor, sodium, and metallic halide. They must have ballasts as well

mike95490

LED's NEED a method to limit current, or they will overheat and fry themselves. Cheap flashlights rely on the internal resistance of the batteries to limit current.

Once you get to larger devices, say for a car, that run off a beefy 12V battery, you can certainly use resistors, but resisters are simply heaters and you are throwing away power as wasted heat. LED Current Drivers (they are not voltage, but current) deliver the proper current) are generally the efficient way to power LED's

LED's must have enough voltage to "turn on" and different doping provides different colors and the doping and fabrication set the voltage needed to start conduction

Tecnodave

The buck converters and boost converters that I use are cv/cc that is to say they have adjustable voltage and current settings. The current setting is the important setting. As the LED's get hotter the required voltage will drop, the current should be clamped by the cc function of the buck or boost converter

jonr

I've successfully used LEDs with no current limiting. But I recommend against it.

Estragon

@Tecnodave - have you ever had (or heard about) a fail in a way that a (lm2596 based) buck converter exposes higher input voltage to the lower voltage device on output?

I'm not overly concerned about one toasting a pi zero or arduino type of thing, but I'm thinking about using for higher value devices also.

jonr

It's a common failure mode (mosfet shorts). TVS diodes and very fast fuses are helpful.

BB.

Our supplies for high value electronics had a crow bar circuit.

An independent voltage checking circuit that places a dead short on an over voltage error.

Dead shorts are pretty easy. Remember p=v×I.... zero volts x 100 amps = zero watts.

Bill

Tecnodave

@Estragon,

Yes, I do not trust the cheap ones with anything valuable I have burned a few of them. $1.00 ea. For the cheap LM2596.. they do not tolerate too much wattage at all. I use them for led but for my passive infrared sensors, I use better ones to buck the 24 volts down to 12 volts and run common 12 infrared sensors to a "ice cube" relay to switch the 24 volt lights. I have bought about a dozen or so types from Amazon and weed out the best and use them. Decent ones with full current limiting at about 100 watts or so are about 10-12$ ea. The one pictured above is in use here maybe 10 or so of them doing various duties. Charging my notebook from 12 volts, pictured one is boost converter, I think it's rated several hundred watts but I use at 80 watts maximum.

Tecnodave

BB,

Fridays job was a crowbar job, I'll be back there later today and take a picture of that one.

Tecnodave

@Estragon

Samlex America makes some very good DC to DC converters both buck and boost I use the SDC-30 20-32 volt in to 13.7 vdc output. These are very clean, low EMI , made in holland. This one is non isolated I have another that is fully isolated, I'm not sure how they accomplish that, the inputs and outputs are not in common at all. The IDC360 it is 20-32 volts in and 12.5 volts out ..very clean output, very good for sensitive communications, I'm a radio buff so this is what I use for 12 volt radios, etc. it was expensive, forgot how much maybe $300, the SDC-30 was about 120 at azamon. Their literature states that on fail the output voltage cannot rise to dangerous levels. I had a Pyle DC to DC converter which was junk compared to the Samlex units, passed that one to someone.