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henryv · 21-08-2020, 10:22

We have an 800 watt 110 volt microwave on board. We also have a 2000 watt Xantrex inverter. When we use the microwave the inverter panel indicates a power draw of 150 amps which at twelve volts would be about 1800 watts. I can't believe the inverter efficiency should be that low so what is happening? The inverter is 20 years old so possibly newer units are more efficient?

Any ideas?

Henry

henryv · 22-08-2020, 08:36

Quote:

Originally Posted by henryv

We have an 800 watt 110 volt microwave on board. We also have a 2000 watt Xantrex inverter. When we use the microwave the inverter panel indicates a power draw of 150 amps which at twelve volts would be about 1800 watts. I can't believe the inverter efficiency should be that low so what is happening? The inverter is 20 years old so possibly newer units are more efficient?

Any ideas?

Henry

I think I have figured out part of the answer. It seems the 800 watts is the microwave rating only. The power used to create the 800 watts is 1300 watts so the power discrepancy is much less.

smac999 · 22-08-2020, 12:19

they should be around 90%. those numbers seemed way off.

motion30 · 22-08-2020, 14:00

My almost new 700 watt microwave drawers 97 amps Tru the inverter. Just for comparison

**a64pilot** · 22-08-2020, 14:39

A 20 yr old Xantrex woud be a rare thing.
I think on average a good inverter will give about high 80’s in efficiency, some will be rated higher and I believe they are most efficient when making rated power, but most of us use them at about half power and I believe they are less efficient there.

Inverter efficiency isn’t as important for short time loads like a Microwave, but if you wanted to run a 110V fridge, inverter efficiency can be more significant.
In other words yes, a new “better” inverter will be more efficient, but it may not cut down power usage that much unless your using the microwave to actually cook meals and having it on for long times. But 60 sec here and there to heat something up, I’d stay with what I have.

kchace · 23-08-2020, 13:17

Also consider that at high amps, you won’t be getting 12 volts to the inverter - it will be somewhat less, so more amps are required to create the “wattage” needed out the other end.

Ken

Nicholson58 · 23-08-2020, 14:22

Quote:

Originally Posted by smac999

they should be around 90%. those numbers seemed way off.

I agree. Efficiency of modern inverters is high. Typically the loss is expressed as a percentage of the full scale capacity. Loss may be around 1 to 5% of the inverter full rating for a very good inverter. Obviously, running a monster inverter to charge a cell phone results in parasitic losses greater than charging the phone. We have a 300 watt extreme high efficiency inverter for small devices and a 24-volt high efficiency 4-port USB Charger.

mako · 23-08-2020, 15:16

What is the rating of your “extreme” high efficiency unit?

henryv · 23-08-2020, 16:16

Quote:

Originally Posted by motion30

My almost new 700 watt microwave drawers 97 amps Tru the inverter. Just for comparison

I would be happy with your numbers. I will put a meter on the AC line to the microwave to see if that is where the problem lies. If the amp draw on the micro is OK then I need to look at the inverter.

Nicholson58 · 23-08-2020, 19:16

Quote:

Originally Posted by makobuilders

What is the rating of your “extreme” high efficiency unit?

Samlex 300. Not as efficient as I remembered. About 89%. Sorry about that.

https://www.samlexamerica.com/docume...-1119_Hrez.pdf

Pizzazz · 23-08-2020, 19:54

Inverter efficiency is high. My 25 year old Heart Interface is specifies as 86% full load efficiency, 93% peak. Most of the time the efficiency is above 90% for small loads. The original poster likely has some other device drawing power at the same time, water heater, space heater, TV, etc. My 800W microwave draws 850W through the inverter charger.

**StuM** · 23-08-2020, 22:13

Quote:

Originally Posted by Pizzazz

My 800W microwave draws 850W through the inverter charger.

What make/model is that.

Unless it uses something instead of a magnetron to generate the microwaves, you should donate it to science to find out how it achieves unheard of efficiency. (A magnetron is generally about 65% efficient).

Chotu · 23-08-2020, 23:46

I'm seeing around 80-something percent efficiency for inverters these days. Not as good as I would have hoped either. Stunning, really.

henryv · 26-08-2020, 11:46

I checked the microwave operating current today. It was drawing 13 amps at 110 volts so that is 1430 watts. The inverter was drawing 150 amps at 11.5 volts which is 1725 watts. This works out to an inverter efficiency of 83 percent.

My battery bank is six 6 volt golf cart batteries. They were reading 13 volts before I ran the inverter and went back to 13 after.

The 1430 watts input seems high for a 700 watt microwave. I looked at another brand at a local store and it indicated an input of 1050 watts. At the 1050 input I would expect the inverter draw should be about 110 amps. Still higher than I would like to see but better.

It appears my inverter is operating properly but I need to find a more efficient microwave. Reducing the power draw should also reduce the voltage drop which should also lower the amps a little.