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Old 05-20-2019, 10:56 PM   #1
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1000w vs 120w inverter

I asked this elsewhere but got no response. Perhaps this is the better forum for this question. Iím sure the question reveals my ignorance of things electrical.

I have the standard 1000w inverter in my Airstream and though I rarely use it, I might want to use the TV when boon docking. The TV has only a 20 watt draw ( no 12v power brick). Just wondering if a 12v-car adapter type plug 120w sine inverter is more efficient than the 1000w inverter, or is the draw is the same (20w)so it wouldn't matter.
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Old 05-20-2019, 11:32 PM   #2
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1000w vs 120w inverter

Car type inverters are not usually pure sine wave type. They put out a badly shaped voltage that can mess up electronics. Iíd stay with the 1000 watt pure sine inverter that came with the Airstream.

Your built-in inverter will only suck on the batteries hard enough to power what you have plugged in plus a bit for powering the inverter electronics.

The cheap inverter is not as efficient either. It wastes more power, typically and will get quite hot when running. They are only designed for short usage times.
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Old 05-21-2019, 12:12 AM   #3
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The car inverter I was looking at was actually a pure sine inverter * https://www.amazon.com/dp/B00IXOWPQM...v_ov_lig_dp_it) but you answered my question - there really wouldnít be a difference in efficiency between the two inverters. At first glance I was wondering if the 1000w inverter was overkill for a 20w TV - but since it only draws enough to power what I have plugged in - it doesnít make much difference.
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Old 05-21-2019, 05:33 AM   #4
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All inverters have an efficiency loss measured/stated in percent. Often, not always, the larger inverters have lower efficiency rating. This means the larger inverter May use more power from the battery to run your tv than the smaller inverter.

Also, inverters have a background parasitic load when it is on and the bigger the inverter, generally, the larger the parasitic draw. Eg, a friendís airstreamís 3000W inverter has a 4A-ish background. My Morningstar hardwired 300W inverter has a background of less than 0.5A. Not such a big deal if you always turn off the inverter when not in use. But then Iíve *never* fallen asleep after/during watching tv and forgotten to turn it off.

So yes, depending on the specific inverters in question, a larger inverter may well cost you more battery capacity than a smaller one. YMMV
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Old 05-21-2019, 07:22 AM   #5
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Now a careful reading of the specifications of both inverters is in order to decide....
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Old 05-21-2019, 09:16 AM   #6
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Hi

Inverter efficiency at full load to near full load can be anywhere from 60% (yikes !!!) to well over 90%. There is no "magic rule" that tells you what the number will be. At very low loads the efficiency is going to be awful. They pull power at zero load so .... do the math. ( = it can be 1% efficient at a low load).

It is not uncommon for a "large" inverter to pull 10 to 12W just sitting there. With a 20W load, that inverter isn't getting past 66% and probably isn't getting past 50%.

The same math likely applies to power conversion in the TV. There's no reason to make it efficient. It might pull 20W and 60 VA. Guess which one matters to the inverter?

Lots of variables !!!!!

Best answer - get a TV that runs on 12V

Bob
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Old 05-21-2019, 09:32 AM   #7
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My TV draws 36 watts and rather then having the 1000 w inverter on I took out the Wineguard amplifier and replaced it with a Wineguard amp and cig lighter. Bought on Amazon for about $20. I use a 75w car inverter that works perfect and saves energy. It took less than 30 minutes.
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Old 05-21-2019, 09:39 AM   #8
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My stock AS inverter (WFCO WF-5110 HP) runs its cooling fan even when when we are not using power. So best not to forget to turn it off when not in use.
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Old 05-21-2019, 09:51 AM   #9
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The simple answer is the 1000 or 120 is the maximum 120 volt AC power each particular inverter will supply.

If the appliance plugged into the inverter does not draw the maximum, the inverter will draw only enough 12 volt DC to answer the 120 volt AC demand, not the maximum.

A 30 amp RV plug does not "force" 30 amps into ones tailer, it allows the trailer to draw any amount it needs up to the 30 amp limit. The breaker will then trip to keep from melting the wires and plug.

Buying a 120 watt inverter will not make your batteries last longer than they would using the 1000 watt inverter you already have.


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JD



Regards,

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Old 05-21-2019, 10:20 AM   #10
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Quote:
Originally Posted by rmkrum View Post
Car type inverters are not usually pure sine wave type. They put out a badly shaped voltage that can mess up electronics. Iíd stay with the 1000 watt pure sine inverter that came with the Airstream.

Your built-in inverter will only suck on the batteries hard enough to power what you have plugged in plus a bit for powering the inverter electronics.

The cheap inverter is not as efficient either. It wastes more power, typically and will get quite hot when running. They are only designed for short usage times.
I concur
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Old 05-22-2019, 05:22 AM   #11
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Hi

Inverter outfits come up with a wide range of terms to describe the output of their devices that include the term sine wave but do not indeed mean pure sine wave out. In some cases, the only way to figure out what's what is to put an oscilloscope on the output and *see* what it is.

Worse, some put out different waveforms at different power levels. I have an inverter that can (if you enable it) do that or not. Most inverters are not very programable. Being able to tell it "don't do that" is unusual.

Even *with* what looks like a pure sine wave, you can still have issues. Some inverters put out a lot of RF trash. Try to listen to AM radio when one is on ... not so much. There are cases of it extending up into the TV broadcast bands.

So yes, lots and lots of variables ....

Bob
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Old 05-22-2019, 08:31 AM   #12
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I think what he is trying to avoid is the same as myself. There is a fan that runs with the 1000w inverter which you can hear but also does draw an amount of power. I don’t know how much but do know that when watching the TV it can be annoying.
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Old 05-22-2019, 09:46 AM   #13
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Quote:
Originally Posted by jdalrymple View Post
The simple answer is the 1000 or 120 is the maximum 120 volt AC power each particular inverter will supply.

If the appliance plugged into the inverter does not draw the maximum, the inverter will draw only enough 12 volt DC to answer the 120 volt AC demand, not the maximum.

A 30 amp RV plug does not "force" 30 amps into ones tailer, it allows the trailer to draw any amount it needs up to the 30 amp limit. The breaker will then trip to keep from melting the wires and plug.

Buying a 120 watt inverter will not make your batteries last longer than they would using the 1000 watt inverter you already have.


Regards,

JD



Regards,

JD
Sorry, JD, but not correct. Typically power supplies, including inverters, are designed (and specified) to provide maximum efficiency at full load. There is very little incentive for the designer of a high power inverter to reduce the inverter draw at low output. As previously stated, a 20 watt idling draw in a 1000 watt inverter is only a 2% hit to efficiency at full load while it is a 13% hit for a 150 watt inverter. The designer of the 150 watt inverter is going to work to reduce the idle draw of the 150 watt inverter because it hurts his efficiency while the designer of the 1000 watt inverter likely will not. Reducing the draw to even 10 watts will save nearly an amp hour for each hour the inverter is operating.

Been there, designed that.

Al
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Old 05-23-2019, 09:26 AM   #14
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Quote:
Originally Posted by Al and Missy View Post
Sorry, JD, but not correct. Typically power supplies, including inverters, are designed (and specified) to provide maximum efficiency at full load. There is very little incentive for the designer of a high power inverter to reduce the inverter draw at low output. As previously stated, a 20 watt idling draw in a 1000 watt inverter is only a 2% hit to efficiency at full load while it is a 13% hit for a 150 watt inverter. The designer of the 150 watt inverter is going to work to reduce the idle draw of the 150 watt inverter because it hurts his efficiency while the designer of the 1000 watt inverter likely will not. Reducing the draw to even 10 watts will save nearly an amp hour for each hour the inverter is operating.

Been there, designed that.

Al


This is starting to sound like a discussion of hitches or tow vehicles.



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