Electrical question - amperage

[LightsinMaine]

Here's one for the electricians in the audience. I just plugged 45 sets of LED lights together that are listed as 0.04 amp per set. I should be running around 1.8 amps. But the reading on my kill-a-watt is saying 0.9 amps. Is it typical that LED lights may pull less than they are listed as or are these basically all mislabelled? I'm not planning on plugging anymore together because the boxes read to connect up to 45 sets (but says they are rated to 216 watts and according to Kill-a-watt I am only pulling 102 watts). Is this typical??

[Guest wbottomley]

Question. Are you blowing any fuses? If not, carry on.

[LightsinMaine]

Not at all William..... this is just the first year I've ever measured my usage with a meter is all. I've always just gone off the box and calculated how many sets and firgured out what I was using.... but seems as though I might be using significantly less now!!

[Guest wbottomley]

I did the math on one of my props using LED's. I came up with numbers relative to your's but after using a meter, it was much less. After that, I haven't worried about the load usage.

[edvas69]

This would be because of voltage drop to your LEDs, theres a difference between calculated load and actual load. If you are running mains voltage LED strings then the % of voltage drop shouldnt be much at all but with low voltage DC this can have a major effect very easily, Where you may actually be getting your voltage drop is from your mains supply (if these are mains supply LEDs). Depending on how far away you are from the mains supply distribution transformer will determine what voltage you are actually seeing at your house,

Also the resistors used on cheap christmas lights will have a high degree of variation in resistance which again effects the current drawn from a string and finally the load on the wire versus the load capacity of the wire used. The closer the load is to capacity of the wire the more voltage drop that will be experienced.

So if this voltage is lower then you will see less current drawn. The other thing it that the ratings are based on maximum calculated loads so generally you will see the measured load lower than the calculated load

So a few different things that can contribute to the true current draw.

But generally work to the specs and you will be fine.

[Troy_Connor]

If you really want to be precise, google "ohms law". As stated earlier every rating placed on a product is the maximum rating not the actual usage, since it will vary minutely between strings.

[LightsinMaine]

That's pretty much what I was wondering (and figured was true) that every rating was max rating. So that's all good news!! Who knew all these years I've been running lower on amperage than calculated from the boxes.

Edited October 11, 2012 by LightsinMaine

[Dave Batzdorf]

I also believe that the rated current is the nominal value, not necessarily what that particular string draws. Bottom line, if its below your calculated rate and is below your outlet rating, you should be fine. Always better safe than sorry. Don't want any melt downs due to overloads.

[plasmadrive]

Here's one for the electricians in the audience. I just plugged 45 sets of LED lights together that are listed as 0.04 amp per set. I should be running around 1.8 amps. But the reading on my kill-a-watt is saying 0.9 amps. Is it typical that LED lights may pull less than they are listed as or are these basically all mislabelled? I'm not planning on plugging anymore together because the boxes read to connect up to 45 sets (but says they are rated to 216 watts and according to Kill-a-watt I am only pulling 102 watts). Is this typical??

There may be yet one more explanation.... I don't have a Kill-a-watt unit so I am not sure how they are measuring.. but if you have half wave LEDs and the Kill-a-watt can't handle the non symetrical wave form accurately,... you might only see half of what you would think. Just a thought..

[R Weiland]

There may be yet one more explanation.... I don't have a Kill-a-watt unit so I am not sure how they are measuring.. but if you have half wave LEDs and the Kill-a-watt can't handle the non symetrical wave form accurately,... you might only see half of what you would think. Just a thought..

plasmadrive; I have a KILL A WATT model P4400 and it measures True RMS and from the P3 Website all the Kill A WATT models are true RMS measuring devices so the non-symetrical waveform is not an issue. My guess is it has more to do with the tolerances of the components used in the LED strings. The manufacturer had to select a value for the amperage and chose a nominal value based on componet tolerances.

[plasmadrive]

plasmadrive; I have a KILL A WATT model P4400 and it measures True RMS and from the P3 Website all the Kill A WATT models are true RMS measuring devices so the non-symetrical waveform is not an issue. My guess is it has more to do with the tolerances of the components used in the LED strings. The manufacturer had to select a value for the amperage and chose a nominal value based on componet tolerances.

I just looked up the K-A-W unit.. pretty cool for about $20.

I would wonder about the reading being 50% of the rating. I know tolerences can account for a lot.. but 50%?? I know this is nothing earth shattering.. but now I am just plain curious..

There are other things it could be..

Perhaps they make 220v strings as well and that rating carries over since it is higher and worst case, perhaps UL let it slide as a dual rating?

Could be the K-A-W unit is not accurate down that low?

edvas69 might be right and the voltage drop issue is the key. 45 strings in a row is after all quite a lot of very small wire. I wonder what the voltage is at the end of the last string.

Perhaps you are right and the value is arbitrary worst case or just plain component tolerances?

Now I am going to have to look at some of mine to see if they are the same... Or perhaps I can just leave it be and call it a wonder of the universe! (Hey, it's 5:30 in the morning.. coffee hasn't had time)