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Old 27-09-2019, 14:03   #1
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Inverter efficiency

I can deduce from my Link 2000 panel that my old Xantrex Freedom 1000 inverter draws about 1.6amps just being on. Question I have is whether that is all of the inefficiency, or is there also a general percentage lost when converting from DC to AC? In this specific case, I'm trying to get a rough estimate of what additional efficiency loss I'd have when drawing a continuous 6 amps off my inverter (for a specific electronic device)? Doesnt have to been customized for my specific inverter, just curious if theres a general % rule of thumb??
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Old 27-09-2019, 14:14   #2
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Re: Inverter efficiency

Most are around 80% efficient in conversion based on amp draw. Obviously wire size and the efficacy of all connections can result in further loss.
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Old 27-09-2019, 16:53   #3
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Re: Inverter efficiency

There are three things here at play, when thinking of losses in the use of inverters:

1. When an inverter is switched on and providing power to the main voltage, but no power is used, then often such power usage (sometimes referred to as resting current) is a few amps (as measured that battery is supplying). Generally this resting current is getting larger as the capacity of the inverter increases. Such power use can add up quite a bit over 24 hours.

2. Many inverters have a sleep mode, to reduce such resting current. In fact the main power is disconnected, and as soon as something is plugged in, then power is restored. They need at least 5 to 15 watts appliance connected to the mains to switch the power on, ie a small phone charger at times might not be able to switch the power on. Such level of minimum power can be adjusted on some inverters.
Resting current can be that way reduced to 200 mAmp to 1 Amp. Still over 24 hours quite a drain on the house batteries.

3. Lastly there is the efficiency factor, as previously mentioned often around 80%, although the spec of some inverters offer 93-95% efficiency. That means, if a main appliance is using 200 watts, then with an efficiency of 80%, the batteries has to supply 100-80=20% more power to provide that 200 watts. So the battery is supplying 200+40=240 Watts. For a 12 volt battery that is an extra 40 watts, 40:12=3.3 amps.
Note that loss of efficiency is generally not linear with power use.

One can measure measure those losses and efficiency easily, with an amp meter in series with the battery supply of the inverter and using a incandescent globe (remember those?) connected to the inverter. Comparing that to the power used by the globe.
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Old 27-09-2019, 17:02   #4
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Inverter efficiency

A properly sized inverter can be up to 95% efficient.
However running my Magnum MS 2812 to watch TV isnít efficient at all, it draws 20W just sitting there, powering nothing.
So I bought a small very good about 150W inverter just for the TV, and use the big boy for the toaster, blender, vacuum cleaner etc.

So my point is I guess that if a high quality, properly sized inverter is used. Itís very efficient, but maybe you donít want to use a 5,000W one to charge your tooth brush.
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Old 27-09-2019, 17:07   #5
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Re: Inverter efficiency

These sorts of devices have a parasitic loss, the penalty for being on. This is a function of the size of the machine. They also have a conversion efficiency. It follows that itís not a great idea to run a large inverter to charge a laptop or phone. It is for this reason that in addition to our 3.5 kw inverter we have an especially efficient 300 watt full sine inverter for the small loads. The Samlex is around 97-98% efficient as I remember and the parasitic loss is proportionately less as well.

We also installed a DC-DC USB charging station. No more wall warts and conversion efficiency is improved.
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Old 28-09-2019, 06:39   #6
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Re: Inverter efficiency

IMO if energy efficiency is actually important to you, inverters are to be avoided as much as possible.

For load devices that are truly required, install a right-sized one that gets turned on and off with the load, and I do mean off completely, no parasitic standby mode.
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Old 28-09-2019, 07:21   #7
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Re: Inverter efficiency

I can give you one simple real world example of inverter use vs straight 12 volts.

I like a fan on at night so I bought a 120 volt 60 Hz fan since I already had a 400 watt inverter onboard to charge my laptop, handheld VHF/GPS, and to run my drill if needed etc. (this back in 2012)

My voltage in the am would be around 11.8 - 11.9 volts after having the fan on sometimes from 4 pm on. (plus depth finder and lights intermittently)

At the beginning of this year, I bought a 12 volt fan and wired it in directly to an existing switch. Now in the am I have 12.1 - 12.2 volts

My battery bank is two 12 volt batteries in parallel of maybe 90 ah each. No fridge etc. Charge is all solar maybe 115 watts - 155 watts depending on which panels I have deployed
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Old 28-09-2019, 08:05   #8
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Re: Inverter efficiency

We have 5 fans on our boat. Three different sizes, and all of them are computer type 12 volt. They were sized for ample air delivery without needing lots of amps.
There are two in the V berth, two in the saloon and one on a hinge in the galley which can be swung out to use to blow the fumes from the stove top out the companionway hatch.

Their small size works well on our smallish interior.


We only need one inverter, a 1,500 watt sine wave for the coffee grinder, occasional tools and Janet's hair dryer.


I split all of our duplex outlets so one side is inverter output and the other is for shore power.
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Old 28-09-2019, 12:04   #9
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Re: Inverter efficiency

How efficient the item is is at least as important.
I too like a fan when itís hot and I have the little Carafamo fans throughout the boat, but when itís hot they are after all little bitty fans.
So so was running I believe a 10Ē 110V fan.
Then I bumped into this one, itís native 24V so I got a 12 to 24 converter to run it, and it honestly uses about 1/4 the power of a regular fan. Iím not sure why itís so efficient, but it really is, Iíve measured its draw.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 28-09-2019, 12:59   #10
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Re: Inverter efficiency

Their efficiency is usually not static.

I ran across this, if feels about right based on my experience.

https://www.e-education.psu.edu/eme812/node/738
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