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Old 06-03-2019, 11:55 PM   #1
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100W 120V LED vs 100W 12V LED Electrical Question

Iím exploring electrical setups for my future RV. Letís say I have a 3000W inverter and a 100 amp-hour battery. Of two led lights, a 100W 120V and a 100W 12V, which would drain the battery faster?

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Mike
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Old 06-04-2019, 12:44 AM   #2
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The 100W 120V LED would drain the batteries faster, because you would have to power it from an inverter, which would not be 100% efficient so there would be significant losses.


That being said, are you sure that you have your numbers correct? I have never come across a 100W LED for any voltage. A 10W LED is a big one.


Joel
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Old 06-04-2019, 02:32 AM   #3
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The 100 Watt, 120 volt LED will draw .8 amps.
Creating 120 volts from 12 volts, thru an inverter is a 10 to 1 conversion, so it will draw 8 amps at 12 volts. Add the 10% to 20% losses thru the inverting prosses ( no inverter is 100% effecent ), and your looking at another about 1.5 amps. Next you need to add the 1/2 to 4 amps the inverter draws just being on. Depends on the inverter.

8 amps for the LED + 1.5 for inefecency + 2 amps inverter draw = 11.5 amps.
11.5 amps for 1 hour is 11.5 AH, so your battery will light the light for 8.6 hours before its dead.


The 100 Watt, 12 volt LED will draw 8 amps. Leave it on for 1 hour and it will draw 8 AH.
You battery will light the LED for 12 hours before your battery will be dead.
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Old 06-04-2019, 03:55 AM   #4
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I have to say....it is so comforting that we have so many people here that can break down complex scenarios for those of us that are “complexed challenged”.


Yes am truly grateful for those that do, and hope I will be able to understand the info they share.

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Old 06-04-2019, 05:17 AM   #5
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TwinBoat is right on the money, but I think the whole question is probably academic. Most coaches have all the accomodation lighting on the 12 volt side. It would be a serious customization to feed them with 120 volts anyway.

Either way, LEDs are low voltage, DC devices so keeping them on the low voltage DC side is the best solution anyway.
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Old 06-04-2019, 08:35 AM   #6
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LEDs are low voltage DC devices that run about 3.6v each. Don't try that directly, it would be too easy to fry it.
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Old 06-04-2019, 11:21 AM   #7
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Quote:
Originally Posted by twinboat View Post
The 100 Watt, 120 volt LED will draw .8 amps

8 amps for the LED + 1.5 for inefecency + 2 amps inverter draw = 11.5 amps.
11.5 amps for 1 hour is 11.5 AH, so your battery will light the light for 8.6 hours before its dead.
Don’t you mean 0.833 amps + 1.5 + 2 = 4.3?

Where can I find the numbers for the inverter? Would I have to contact the manufacturer?

Also, would a 4000 watt inverter use more power than a 2000 watt inverter?
Thanks,
Mike
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Old 06-04-2019, 11:24 AM   #8
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Joel, I was looking at outdoor floodlights, not individual leds.
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Old 06-04-2019, 11:38 AM   #9
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Donít you mean 0.833 amps + 1.5 + 2 = 4.3?

Where can I find the numbers for the inverter? Would I have to contact the manufacturer?

Also, would a 4000 watt inverter use more power than a 2000 watt inverter?
Thanks,
Mike
The idle current should be listed in the specs. May be listed as amps or watts.
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Old 06-04-2019, 11:45 AM   #10
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Quote:
Originally Posted by Sailmike View Post
Donít you mean 0.833 amps + 1.5 + 2 = 4.3?

Where can I find the numbers for the inverter? Would I have to contact the manufacturer?

Also, would a 4000 watt inverter use more power than a 2000 watt inverter?
Thanks,
Mike
Inverter efficiency is a moving target. However, the bigger the inverter the higher the idle current. If you only need 300 watts, a smaller inverter will waste less than a bigger one. Low load on a big inverter probably has pretty high losses in efficiency as well.

Two small ones is better than one great big one.
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Old 06-04-2019, 12:04 PM   #11
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Does the idle current include both inefficiency and inverter draw? Or do I just have to assume 1.5 amps lost?
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Old 06-04-2019, 12:10 PM   #12
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Most coaches have all the accomodation lighting on the 12 volt side. It would be a serious customization to feed them with 120 volts anyway.

We have 2 plug in 120V table lamps in our fifth wheel that we added.
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Old 06-04-2019, 12:28 PM   #13
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Idle current is with no load. Efficiency is another thing and I think it gets better as the load increases on a given design.
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Old 06-04-2019, 12:54 PM   #14
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Looking at a few inverter specifications, I didn’t see any listing for idle current for any of them. What do I look for?
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