Led driving lights - watts/amps query

[flylux]

Hi guys.
I bought two led driving lights off eBay for $400 new, 90w each, 10-30volt capable, 18x 5w leds. Installed them last night, with one 40amp relay and 6mm wire.

I suspected they weren't bright enough for the claimed 90watts so I started investigating.
Measured the current draw across the power to the relay and got 10.48 amps.

WATTS = VOLTS x AMPS

12.6v x 10.48amp = 132 watts
132watts / 2 = 66watts per light (not 90!)

So my question is, shouldn't I be reading 14.28amps if they are indeed 90 watts lights?

Amps = watts/volts
90w / 12.6v = 7.14amps
7.14 x 2 lights = 14.28amps

Have I been ripped off buying these lights?

Cheers
Brad.

[Mick.]

Yes if you are putting 12.6 volts into them you should be reading about 7.14 amps. Just remember though there are heaps of variants. You should be measuring the volts at the light not the relay so you know there is no voltage drop at all. The other thing is the quality of the gear your using. I have a cheap multi meter and I have 2 high end ones and the variation between the $50 one and the $1000 ones is chalk and cheese.

So to get exact readings it needs to be done at the light not the relay regardless of wire size there will be voltage drop and there is also the equipment your using could be giving you a wrong reading.

Also remember you bought off ebay which is probably your main issue here there is a lot of crap coming out of China and it's hard to know what your getting with these guys. lol

Cheers Mick

[flylux]

Thanks Mick.

[date]

You measured the current at 12.6 Volts. What about 30 V? You would probably get more current then, although not the full 30/12.6 times the current because the load would probably not be a purely resistive load. It would be interesting to see how much more light they put out at 30 Volts.

[oldmate]

Connect the light directly to the battery and measure the current, to eliminate a faulty relay or other wiring issue. 6mm wire is more than plenty.

If you can't get the full power that way I would be inclined to try and get a refund. 400 bucks sounds well and truly over priced for no name chinese lights. You could buy a set of light force lights for that kind of money.

Upping the voltage won't increase the light output. When they say 10-30 volt it simply means you can use it in a 12 or 24 volt electrical system. If you double the voltage you halve the current draw, but power remains the same.

[Lights]

What some manufactures claim their specifications are and what they REALLY are can be quite interesting...
Like lumen output. You can have two lightbars with identical specs yet one is brighter by 30%
Also, the majority of LED lights out there will work down to 9v in which case if you have 9v or 12.6v going in, it should have the same light output.