Inverter efficiency

[Lee72]

Hello all,

I just verified that my inverter (Powerbright 900W 24V, MSW) does not have the efficiency it claims in the spec ("Efficiency Approx. 90 %"). My measurements are around 75%.

Is this a "bad" unit or is the efficiency promise probably a lie?
Are pure sine wave inverters more efficient?
What would you recommend to buy for a 24V setup and 800-1000W with the focus on efficiency?

[Sunking]

Lee most inverter efficiency specs are obtained when operating at or near full power. Second thing is they are rated for pure resistive loads and not reactive loads. So if you are operating at say half power and reactive loads you will net achieve maximum efficiency.

This is a common mistake people make, they buy large inverters to power small loads then wonder why the battery dies so fast.

[Lee72]

My needs are 1000W surge power and 200W continuous power.

What inverter gets my efficiency closer to 90%

[Naptown]

Perhaps an outback inverter
Pure sine wave is better and will play better with electronics and motors.

[Sunking]

My needs are 1000W surge power and 200W continuous power.

That is not possible. Did you by chance mean 1000 watts continuous and 2000 surge?

Secondly is it just 1 thing you are powering or several? Might be better to have 2 or 3 smaller inverters.

[john p]

In many cases its better to have 2 inverters for effeciency
Example we use a 400w MSW inverter for whole house lighting and it opperates at about 250 to 300w most of the time and gives above 90% effeciency and draws very small self power, 270mw.
For desktop computer and projector TV and other occasional high power items we use a 1000w TSW inverter.This way its opperating at at least 500w and runs about 85% effeciency. Its self power use is about 1.5a . but its only turned on as needed.
Using a inverter that is high powered to provide power for low power use is very wasteful of your battery power.Self use can be significant
1.5a at 24 hrs = 36ahr
.27a at 24 hrs = 6.5 ahr
Big battery power saving on a small system.

[Lee72]

That is not possible. Did you by chance mean 1000 watts continuous and 2000 surge?

Secondly is it just 1 thing you are powering or several? Might be better to have 2 or 3 smaller inverters.

How do you know this is not possible? - I read these numbers on my watt meter.

I need that power to run the fridge. The plate on it read 110V 6.5A - no watts. That would be about 715W but with my current inverter (24V) in place I read about 1100W start surge power and about 200W when its running (using the Watts-up DC meter)

My current inverter gives 900W (1800W surge) but the efficiency is 75%.

[john p]

You cant just give inverter effeciency with just one figure. its totally dependant on load for the inverter size
ie
300w on a 1000 inverter mabe 70%

300w on a 400 inverter mabe 92%

MSW inverters tend to have higher effeciencies than TSW inverters also

[Lee72]

I am trying to optimize my solar system. I tried the 400W (800W surge) model from PowerBright but it shuts down when the fridge tries to start. Unfortunately there is no model in the middle.

I was hoping that pure sine inverters have a better efficiency but john p tells me that MSW have better efficiency. So I guess I am stuck with my current setup since my surge power is so far away from the cont. power.

I will put a load of 900W to the inverter tomorrow to see if it sticks to the promised 90% efficiency

[john p]

A fridge can only be made to start on a 400 w inverter if its been modified and from what im told the latest ones cant have the mod done to them for some reason.(im no fridge expert)
You are doing well to have it start on a 1000w many wont.
from my testing nearly all MSW inverters are more effecient than TSW inverters and use less self power(idle current)

[Sunking]

How do you know this is not possible? .

I misread your post, and thought you said you had an inverter rated at 2000 watts continuous and 1000 watt surge which is backwards.

[Mike90250]

You will have to decide on a tradeoff.

MSW inverter which runs at higher efficiency for a given load, but your fridge motor, will consume about 20% more power on a MSW and there goes your battery life. Motors also run hotter, which will have to be cooled by the fridge also (motors in in a sealed can with the coolant). So, a more expensive TSW inverter may give your better total efficiency, and normal compressor motor life.
Anyone have opinions on Exceltech or Samlex PSW inverters ?

[Lee72]

Is there a way to make cascading inverters?
Lets say between 0-300 W the small inverter and above the bigger inverter?

[Sunking]

There are inverters that can be cascaded already on the market, but none I know of in that small of a rating for battery inverters.

[Naptown]

There are inverters that can be cascaded already on the market, but none I know of in that small of a rating for battery inverters.

I only know of one, Fronius but only in grid tie I believe