Light Bar Amp Draw

[stevemc181]

I borrowed a high quality clamp meter with DC function and checked the current draw at 12V DC . 9.0 amps, which equates to 108W in my world. I have fired off a message to the ebay seller requesting either an exchange unit or clarification on what is going on - will advise. Luckily i have not mounted it yet - looks reasonable quality though.

Yep, most of the ebay jobbies are woeful in their claimed wattage. Good Luck getting any satisfaction from the seller, hopefully they will give you a refund or a decent explanation. I'd check it out first and see if you are happy with the output. My 400 watt (claimed, 269 watt actual) bar, will singe the fleas off a roos gonads from a few hundred metres, so it's bright enough for me. Too bright actually if any road signs are around. This time around with the Patrol, I think I'll be going a set of Fyrlyt 9000 250watt halogens. The led bars are pretty harsh on the eyes over long distances.

[Ben-e-boy]

I borrowed a high quality clamp meter with DC function and checked the current draw at 12V DC . 9.0 amps, which equates to 108W in my world. I have fired off a message to the ebay seller requesting either an exchange unit or clarification on what is going on - will advise. Luckily i have not mounted it yet - looks reasonable quality though.

It has already been clarified on the first page. The specs are based on the highest input voltage. Given that my own calculation rated it at about 112W. I would say your readings are pretty much correct. Like I said, It's not a lie. But misleading

[PeeBee]

It has already been clarified on the first page. The specs are based on the highest input voltage. Given that my own calculation rated it at about 112W. I would say your readings are pretty much correct. Like I said, It's not a lie. But misleading

Ben=e=boy, the inference is noted except it is at odds with the statement below I believe. This is why i can't put the logic together.

"Do not get the idea that if you apply more voltage that the LEDs should give off more light. The amount of light an LED gives off is determined by current, not voltage. The current at each LED is maintained within a narrow range by a device known as an LED Driver."

What I am understanding is that Voltage only has a place within a performance band of the LED, but the current capacity of the controller is what delivers the 'shine'. So, in reality I am drawing a conclusion that the LED driver supplied for these 100 x 7w LEDS is rated at 9 amps total and in essence is too small to achieve the rated potential of the light bar combined output. The driver in effect should be closer to 58 amps. Does this make sense?

Simply saying the total capacity of the light bar is 100 x 7 and then driving it with a driver card too small is misleading and in effect fraudulent as there is no way the rated output would ever be achieved. May be a similar performance claim of some vehicles rated to run on 98 grade fuel, that exhibit acceleration and economy on that grade, but drop down to 91 grade and the performance is not delivered.

happy to hear your thoughts.

[Ben-e-boy]

The driver itself is designed to operate the LED at its peak efficiency. All the comments you have posted all regard the driver output. Those LED's probably run on 3.5V

You are measuring the total current and working out total wattage for that circuit. The lightbar itself has a resistance, that basically remains unchanged. All loads have some resistance. It's a dead short if it doesn't.

In a circuit where the resistive load remains constant, the wattage is proportional to voltage squared ( this is a basic fundamental of electricity ) i.e. if you double the voltage, multiply the wattage by 4, triple the voltage multiply wattage by 9.

So.......you lightbar consumes 108W @ 12Vdc. Given that the maximum working voltage of that lightbar is (as claimed) approx 30Vdc. You'll find that 30Vdc is 2.5 times greater than 12Vdc that 2.5 has to be squared. That equals 6.25.
Therfore 108W x 6.25=675W. Thats calculated at exactly 30Vdc. Use more decimal places and assume the test was conducted at between 30.5 and 30.6Vdc and you'll pretty much get bang on 700W

[PeeBee]

Well bugger me, that's beautifully explained, thanks, I get it. So, I have got what I paid for in essence?

[PeeBee]

If the bar will only ever draw 9 amps, and it's got pissy thin wires, why do they supply a 40 amp fuse? Is this part of the 'deception'? So to speak.

[Ben-e-boy]

Well bugger me, that's beautifully explained, thanks, I get it. So, I have got what I paid for in essence?

Yep, I would also piss that 40A fuse off too

[Ben-e-boy]

If the bar will only ever draw 9 amps, and it's got pissy thin wires, why do they supply a 40 amp fuse? Is this part of the 'deception'? So to speak.

They're idiots. Anyone who protects a circuit with a fuse that's higher than the current carrying capacity of the cable shouldnt be playing with electricity