Chinese capacity bragging

[bernardgreen]

At 30V it draws 0.072amp = 2.16W

Maybe a voltage limiting Zener diode starts conducting to shunt down the voltage applied to the LED driver module

 

[Harry Bloomfield]

I'm a bit confused now. Although it would explain the essentially identical currents you initially reported for different voltrages, I presume you can't have been using a constant-current source, since you would then not have been able to get the different voltages?

Kind Regards, John

I was testing it on a fancy voltage and current settable bench power supply, with the current set to wide open around 3amps.

 

[Harry Bloomfield]

Maybe a voltage limiting Zener diode starts conducting to shunt down the voltage applied to the LED driver module

Yes, that or as I suggested a earlier a linear regulator dissipating the current as heat. I didn't run it on 30v for long, it was cold in my workshop, too cold to hang around waiting to see if the lamp generated lots of waste heat. I just to confirm my suspicions that it was nowhere near the 5w I had ordered it as and see how much the light output varied with voltage, if at all.

 

[JohnW2]

I was testing it on a fancy voltage and current settable bench power supply, with the current set to wide open around 3amps.

Fair enough.

Kind Regards, John

 

[JohnW2]

Yes, that or as I suggested a earlier a linear regulator dissipating the current as heat. I didn't run it on 30v for long, it was cold in my workshop, too cold to hang around waiting to see if the lamp generated lots of waste heat. I just to confirm my suspicions that it was nowhere near the 5w I had ordered it as and see how much the light output varied with voltage, if at all.

If it were designed to produce roughly the same light output (hence current through the LED elements) at any input voltage between 10V and30V, then one assumes that there must be some 'constant current' electronics within the lamp - such that essentially the same current would be drawn regardless of the supply voltage within that range. If the LED elements were 'constantly driven', then that would obviously mean that increasing amounts of energy would have to be dissipated as heat somewhere as the voltage (hence total energy drawn from source) increased.

However, if the 'control' were primality by variation of pulse width of a pulsed supply to the LED elements, then things would be very different, and there then might not be much/any 'wasted energy' with higher supply voltages.

Kind Regards, John

 

[Harry Bloomfield]

If it were designed to produce roughly the same light output (hence current through the LED elements) at any input voltage between 10V and30V, then one assumes that there must be some 'constant current' electronics within the lamp - such that essentially the same current would be drawn regardless of the supply voltage within that range. If the LED elements were 'constantly driven', then that would obviously mean that increasing amounts of energy would have to be dissipated as heat somewhere as the voltage (hence total energy drawn from source) increased.

However, if the 'control' were primality by variation of pulse width of a pulsed supply to the LED elements, then things would be very different, and there then might not be much/any 'wasted energy' with higher supply voltages.

Exactly, which it didn't seem to do, so I made a presumption due to the increasing current with voltage, that it was wasting the extra current and voltage as heat - linear regulation, or as Bernard suggested perhaps a series zenor.

In which case - The lower voltage (12v), will be nearer the actual LED wattage. Obviously less than 1w and working at less than 50% overall efficiency at the 30v, due to wastage to heat.

 

[bernardgreen]

or as Bernard suggested perhaps a series zenor.

Shunt Zener

When the input exceeds the voltage of the Zener then the current through the resistor increases to drop more voltage

 

[JohnW2]

Exactly, which it didn't seem to do, so I made a presumption due to the increasing current with voltage, that it was wasting the extra current and voltage as heat - linear regulation, or as Bernard suggested perhaps a series zenor. .... In which case - The lower voltage (12v), will be nearer the actual LED wattage. Obviously less than 1w and working at less than 50% overall efficiency at the 30v, due to wastage to heat.

Shunt Zener .... When the input exceeds the voltage of the Zener then the current through the resistor increases to drop more voltage

All true as possibilities, but I suspect that, in an application like this, if there were a 'shunt zener' (i.e the usual arrangement for a zener-stabilised supply), I would suspect that it would probably only come into play if the supply voltage exceeded (or, perhaps, 'approached') the 'maximum permissible', since current through the zener 'during normal operation' would result in 'energy wastage' in the series resistor.

If I were designing such a lamp, I think I would try to do it such that, as input voltage increased above the minimum of the acceptable range, the LEDs would be increasingly 'over-driven' (current-wise) but with increasingly short pulses, such as the average current (both through LED elements and drawn from the supply) remained roughly the same at any voltage.

Kind Regards, John

 

[bernardgreen]

the LEDs would be increasingly 'over-driven' (current-wise) but with increasingly short pulses, such as the average current (both through LED elements and drawn from the supply) remained roughly the same at any voltage.

High current pulses cause damage to the LED element by forcing atoms out of one semiconductor layer and into another layer thus over time demolishing the structure of the LED element.

Generally the more efficient the element is the thinner the semiconductor layers are and the easier it is to force atoms permanently into other layers.

Early indicator LED elements could be pulsed ar 10 times rated current with a ON -OFF ratio that kept the average current about 70% of rated average current
This pulsed driving resulted in the elements appearing to be several times brighter than when run as constant rated current. The semiconductor layers in these elements were ( compared to modern illumination elements ) very thick and thus very resistant to damage by the high current pulses.

Modern high efficiency LED elements used for illumination purposes do not have the same resistance to damage from over current pulsing.

 

[JohnW2]

High current pulses cause damage to the LED element by forcing atoms out of one semiconductor layer and into another layer thus over time demolishing the structure of the LED element.

Maybe, but we know that it's a technique commonly used in LED 'lamps'.

In any event, I wasn't suggesting that the LED current with the lowest supply voltage would necessarily be anything like as high as the 'rated maximum' of the elements. If it were considerably less than that maximum then, although the current pulses would be greater (but of shorter duration) with higher supply voltages, they would not necessarily be markedly (or at all) above the 'rated maximum' for the elements.

Kind Regards, John

 

[Harry Bloomfield]

A complaint to the seller, first had them offer that I keep the lamp (not worth it to return) and they refund me 10% of the cost. I replied with it has no use or value to me at 1/8 the wattage I ordered, they have since increased their offer to 30% which I have likewise refused with an offer to take my complaint to ebay/paypal. Obviously Chinese - it's what the do.

 

[Jackrae]

Talking of Chinese bragging, I once bought, from fleabay, a high capacity USB battery pack, somewhere in the order of 20,000mAh (20Ah). It seemed quite substantial but failed to live up to its capacity rating. When I opened it up for inspection I found that at least 90% of its weight consisted of a thick steel plate !

 

[Harry Bloomfield]

Talking of Chinese bragging, I once bought, from fleabay, a high capacity USB battery pack, somewhere in the order of 20,000mAh (20Ah). It seemed quite substantial but failed to live up to its capacity rating. When I opened it up for inspection I found that at least 90% of its weight consisted of a thick steel plate !

It's what they do, steel is cheaper than batteries, but the quote impossible figures for most of them. I really didn't expect it for LED lamps.

 

[JohnW2]

Talking of Chinese bragging, I once bought, from fleabay, a high capacity USB battery pack, somewhere in the order of 20,000mAh (20Ah). It seemed quite substantial but failed to live up to its capacity rating. When I opened it up for inspection I found that at least 90% of its weight consisted of a thick steel plate !

A while ago, I brought your to your attention some of the crazy 'USB Power Banks' being offered on eBay., This one ("5,000,000 mAh") is by no means the 'record holder', but I can't be bothered to look for 'higher capacity' examples ...

Kind Regards, John

 

[Harry Bloomfield]

In their latest email, they want me to post it back to them, at my expense. I have written back to say I will happily post it back, but only if they pay for postage or arrange it's collection.

As this was dragging on and the lamp was needed to light a Christmas tree, I took a look in Home Bargains - maybe in the hope of being able to get an MR11 12v 16w capsule QH lamp. All it would lack is the reflector and had in mind to see if I could somehow botch that by removing the reflector from the old lamp. HB had some MR16 ac 5w LED lamps on display, at £1.29, equivalent to 50w - so I grabbed one. Original was a MR11 GU4, 12v 16w QH lamp. MR 16 has the same pins, but wider/taller reflector. I managed to adapt it to fit, by adjusting the lamp socket position.

Tree was OK with the original 16w QH lamp, but could have done with being brighter. The supposed to be 5w LED, provided only enough light to become visible at night, with lights dimmed, the 10w QH borrowed lamp was best of the bunch, but could not compete with daylight. The 5w LED just sourced from HB, is very visible even in daylight.

It's a fibre optic tree - fed from a 12v ac transformer. A bunch of optical fibre at the base, which lead up and fan out along the branches. Between the lamp and the bunch of fibres, is a rotating filter, either B&W, or random colours, with the filter driven round by a synchronous 12v ac motor.