Chinese capacity bragging

[Harry Bloomfield]

The Chinese, as we all should know, brag wildly about their rechargeable battery's aH capacity. They also brag about lamp output watts.

I put the Christmas tree up 10 days ago, then not long afterwards, its 12v 16w MR11 GU11 QH lamp blew. I managed to borrow a 10w version, left over from converting the caravan to LED a while ago, it worked, though a bit under bright.

Ordered a 5w 10v to 30v MR11 GU11 ac/dc LED spot, which should have been a bit brighter than the 16w original, in fact it was much dimmer than the 10w, so I emailed the seller - not cheap these lamps. Seller replied to my complaint suggesting it was nearer 0.5w than 5w LED, with a request for the usual photo of the problem - what, or perhaps watt?

My usual reply to that silly request is - I do not possess a digital camera, despite having several.

Out of curiosity, I have just carried out a few tests of the lamp on my work bench...

At 12v it draws 0.070amp = 0.84w

At 20v it draws 0.042amp =0.85w

At 30v it draws 0.072amp =0.86w

Far below the 5watt lamp it was sold as. No doubt the seller will send me a replacement, which will be identical and I will reject that too and eventually demand a full refund.

Were it not for the fact that the 2w LED's are dc, which I replaced the 10w QH lamps with and which I found were much brighter than the 10w jobs - I would borrow one of those.

 

[JohnW2]

At 12v it draws 0.070amp = 0.84w
At 20v it draws 0.042amp =0.85w
At 30v it draws 0.072amp =0.86w

I don't understand your arithmetic - can you perhaps explain/clarify?

Kind Regards, John

 

[Harry Bloomfield]

I don't understand your arithmetic - can you perhaps explain/clarify?

Kind Regards, John

John, really?

 

[SFK]

At 12v it draws 0.070amp = 0.84w
At 20v it draws 0.042amp =0.85w
At 30v it draws 0.072amp =0.86w

30V x 72mA is = 2.2W
With your numbvers the LED bulb is acting in a (interesting for me) non-linear manner. :>

 

[JohnW2]

John, really?

Yes, really You wrote:

At 12v it draws 0.070amp = 0.84w
At 20v it draws 0.042amp =0.85w
At 30v it draws 0.072amp =0.86w

Per the arithmetic I understand ...
0.070A at 12V = 0.84W
0.042A at 20V = 0.84W
0.072A at 30V = 2.16W

You 12V figure is correct, your 20V one nearly correct, but as for your 30V one .... !

Am I missing something?

Kind Regards, John

 

[Harry Bloomfield]

30V x 72mA = 2.2W
And bulb is acting in a non-linear manner. :>

I would not expect the current to act in a linear manner, especially to an ac/dc wide voltage range lamp. The light output is fairly consistent, thought all the way from 10 to 30v.

 

[Harry Bloomfield]

You 12V figure is correct, your 20V one nearly correct, but as for your 30V one .... !

Am I missing something?

Yes, that I need a new calculator for Christmas

 

[SFK]

I would not expect the current to act in a linear manner

My point of concern was that I also saw the typo as I was not expecting a U shaped curve for the current with increasing voltage. 70mA >> 42mA >> 72mA

I was expecting
70mA >> 42mA >> 34mA

At 30V it draws 0.034Amp =0.86W

 

[Harry Bloomfield]

My point of concern was that I also saw the typo as I was not expecting a U shaped curve for the current with increasing voltage. 70mA >> 42mA >> 72mA

I was expecting
70mA >> 42mA >> 34mA

At 30V it draws 0.034Amp =0.86W

I wasn't, because the weird constant current driver will make a lot of difference to the input curve.

 

[SFK]

So which is it?:

At 30V it draws 0.072amp = 0.86w
or
At 30V it draws 0.034amp = 0.86w
or
At 30V it draws 0.072amp = 2.16W

 

[Harry Bloomfield]

So which is it?:

At 30v it draws 0.072amp =0.86w
or
At 30v it draws 0.034amp =0.86w
or
At 30v it draws 0.072amp =2.16W

The latter.. and possibly using a series regulator, judging by the increase in consumption, without an increase in light output.

 

[SFK]

Thanks - needed closure on that :>

 

[Harry Bloomfield]

Thanks - needed closure on that :>

You can sleep tonight

 

[JohnW2]

I wasn't, because the weird constant current driver will make a lot of difference to the input curve.

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

 

[ericmark]

10 to 30 volt LED lamps are common for boats, https://bedazzledledlighting.co.uk/ but in the main DC, they are designed for battery use.

Did you supply AC to a DC lamp?