Not afraid to be cheated!
Expert LED light lifetime knowing make it easy!
Article by: Rita Lee, Dirk Poloczek, Copyright 2017 by SLT-TECH®
Picture by Fluke
Most important part of any LED lighting product, as also for any other electronic product powered by AC-Line, is the Power Supply; and the main key for lifetime of this, is the Aluminum capacitor inside.
Overheating by ambient and/or working temperature, as well as, covering or wrong assembly of this component result in shortage of the lifetime or failure of the final product. So be careful whom you trust and which product you buy for your lighting design, or any other.
To make it easy to understand, we will give you a short explanation how to figure out how to find the right power supply and how to validate given numbers in data sheets.
First of all, a value of “MTBF” in data sheets, given by a big Asian brand in power supply business, is NOT lifetime, it means “Mean Time Between Failure”, but a number of more than 400kh (400.000h) is quite impressive, right?, NO, it’s not. In general, MTBF is the “working-time” between two failure states of a repairable system during operation; and it also means that the power supply at first have to get defect!
You are wrong to believe!, such power supplies with a weight of a heavy stone brick could not be repaired,because it’s electronic is complete covered in silicone and could only throw it away, WHAT A WASTE and surly not the right way to do green products.
So how to get on lifetime?
As we said, temperature is the key of lifetime in electronics, means, get as low with it as can be. What also means, it cost money!, not much but more as for such with low price, low quality and wrong construction or design.
Why wrong construction or design?
The physics teaches us, that in a closed room (housing) the whole temperature will reach the level of the hottest spot after a time. So, all components in a power supply will be heated up to the same temperature level as the hottest one, most of this is coming from the switching transformer, diodes and FET’s.
But why wrong?
Well, in power supplies there is always a pressure of costs and space. So many manufactures have to fight for placing components on a PCB (Printed Circuit Board) to get the product tiny, and forget the basics of physics.
Now back to lifetime of Aluminum capacitors.
There are many manufactures of this kind of components in the market, cheap, low quality, fake AND good ones.
Good Aluminum capacitor have an ambient working temperature up to 105℃ and a working lifetime of up to 12.000h, what means that this component will work for 12.000h at 105℃ by 100%.
Important for this lifetime are also other working conditions of this component, as maximum working voltage vs. maximum running voltage in the circuit and ripple current flow.
Each temperature reduction by 10 ℃ double the lifetime of the Aluminum capacitor!
If we now reduce the maximum ambient temperature in the power supply from 105℃ to only 75 ℃, we win 30 ℃ and can reach a lifetime in theory of 96.000h. But by this calculation we not pay attention on the maximum working voltage and the ripple current of the Aluminum capacitor, which also plays a big role in the lifetime.
Also we didn’t take attention of the ambient temperature around the power supply, means heating from the LED’s, which can reach up to 70 ℃ (in a Street Lamp) inside, ect., as in other LED product. Which causes also in lifetime shortage.
With respecting these condition this also reduce the lifetime with every 10 ℃ rise. So, if we have measured the maximum inside temperature in the power supply of 75 ℃ at 25 ℃ outside ambient temperature and we will have a rise of 10 ℃ to 35 ℃ outside, the lifetime of the Aluminum capacitor will be cut down to 48.000h only.
What did this tell us if the manufacture promise us 50.000h lifetime. Nothing, if such numbers are in a data sheet, without information about the working temperature inside the power supply.
By this short calculation we also not take attention of low lifetime Aluminum capacitor (5.000h – 8.000h) because of product costs, by market requests.
So far, so good.
To show you a sample of a cheap but well-known international BRAND product, “MADE IN POLAND”, we have done a test in our laboratory. The test was done by an outside ambient temperature of 28 ℃, power supply housing not closed in open area. Pictures was taken with FLUKE temperature infrared camera.
Result: the transformer have the highest temperature of 98.3 ℃ at 42W power
As final result and short lifetime calculation and the given information above, this product will never have a lifetime of 50.000h, as given as warranty from the BRAND manufacture.
As we know now from the physics and basics of lifetime calculation (10 ℃ basics), the product lifetime could reach only as maximum 24.000h, and nothing more.
For you reference we have done the same test under same condition’s with one of our products.
Result: the rectifier diode have the highest temperature of 75.5 ℃
As we know now from the physics and basics of lifetime calculation (10 ℃ basics), the power supply lifetime could reach as minimum 96.000h, but under final product conditions, we will give 65.000h lifetime.
BRAND or not, pictures tell the truth, the physics not lie and know-how leads to trust!
So, numbers in data sheets are nothing without evidence.