What size Inverter

[Xenos]

I have an opportunity to select either a 2,000 watt or 3,000 watt pure sine 12 volt inverter as a prize in a competition.
I intend to connect it to a 300Ah LiFePO4 which will have 600 watts of solar panels.

It will be used infrequently.
On occasions for a 240 volt 340 watt washing machine.
An espresso machine every day and a 700 watt microwave in small bursts. Never all together.
The inverter will be connected directly to the battery and an AC power cord to the washing machine and the other appliance..

Is there any problem with using an inverter overrated for the washing machine and other appliances?
and really what would the benefit of taking up the 3,000 watt inverter?

 

[sunshine_eggo]

Inverters consume power just by being on and making AC power available. Cheaper units can use substantial power. Using an excessively large inverter can result in high idle consumption that may consume a substantial portion of your battery capacity.

Inverters maximum power efficiency is at about 30% of rated power. When an inverter says 93% efficient, its at the 30% rated mark. It's actually WAY worse as you reduce power from that point (using 1-5% of rated power can be as low as 60% efficient), and it tapers off gradually as you approach max rated power.

 

[Xenos]

Inverters consume power just by being on and making AC power available. Cheaper units can use substantial power. Using an excessively large inverter can result in high idle consumption that may consume a substantial portion of your battery capacity.

Inverters maximum power efficiency is at about 30% of rated power. When an inverter says 93% efficient, its at the 30% rated mark. It's actually WAY worse as you reduce power from that point (using 1-5% of rated power can be as low as 60% efficient), and it tapers off gradually as you approach max rated power.

The Inverters are Renogy and I only intended to turn it on when I was to use 240 volt appliance.
I did notice the static voltages of each are 1.3 amps.
I took that to mean the idle power consumed?

 

[sunshine_eggo]

"Static voltage" - voltage is not measured in Amps. Current is measured in Amps.

If these are 12V inverters, and 1.3A does indeed mean the idle current, then they burn about 16W, which is respectable.

 

[Xenos]

"Static voltage" - voltage is not measured in Amps. Current is measured in Amps.

If these are 12V inverters, and 1.3A does indeed mean the idle current, then they burn about 16W, which is respectable.

Total mistake. I should have typed.
Static Current: 1.3A

 

[Xenos]

"Static voltage" - voltage is not measured in Amps. Current is measured in Amps.

If these are 12V inverters, and 1.3A does indeed mean the idle current, then they burn about 16W, which is respectable.

Yep. Thanks for the reply. I may just go for the larger size. There's very few opportunities to do so for me and my very small but adequate off grid setup. If I can save a bit by not using a petrol generator for the washing machine I'll be so far in front. and truly more off grid.

 

[pollenface]

Is there any problem with using an inverter overrated for the washing machine and other appliances?
and really what would the benefit of taking up the 3,000 watt inverter?

There's not likely to be a disernable difference in standby consumption between 2000w and 3000w. Go big, unless you have space constraints

 

[Xenos]

Thank you for your reply pollenface.
The 3000 watt is a whopper in dimensions and I have no space constraints.
I plan to have it close and directly connected to the battery using an Isolation switch.

Which style of switch would be best suited to connect?
I believe the capacitors can store quite a charge.

 

[Mark48vMagnum]

I would look into a Midnite Solar DC Breaker in place of a switch. Remember if you will run 20 amps @ 120 vac with a 12vdc system you would be pulling 100 amps off your batteries.

 

[Vigo]

I agree that you should install some form of breaker. If you only turn the inverter on when you need it in theory a switch would be fine, but in practice an actual breaker will help protect you from the possibility of forgetting to turn it back off, and then having a big electrical failure in the inverter (or between breaker and inverter) lead to a fire. Ideally circuit protection devices like that should be installed as close to the battery as possible to limit the amount of 'unprotected' wiring that could short circuit and flow uncontrollably. Sounds like all your components will be close together so no big deal there.

Luckily for a 12v system such breakers are readily available and very cheap, although 'cheap safety equipment' may or may not be a path you choose to tread. I'll take cheap over none any day!!

 

[Xenos]

I ended up getting the 3000 watt inverter and it came with an on/off remote switch and two sets of short I think 4AWG cable which again I believe take about 150 Amps..They're attached to a 300Ah LifePO4 battery. Both sets were used. The cables came with their own lugs attached.
I only use one 240 volt kitchen appliance ( microwave, toaster, espresso machine and sandwich maker) at a time and thought I could do without the breaker.
The on/off remote is on the wall in the kitchen. It's so handy to close the inverter down.

Hopefully I've made the right decision

 

[Vigo]

12v systems are much cheaper and easier to fuse than higher voltage systems.

IF you decide to install one later, the cheapest ones are ~$15 on Amazon, at least. Such as: https://www.amazon.com/s?k=150a+dc+...sprefix=150a+dc+brea,aps,200&ref=nb_sb_noss_2

The only thing is it would require you to have one more wire/cable to add it to the circuit. One thing i've done that may or may not be kosher depending on who you ask, is just flatten out a small ~1/2" copper pipe and drill two holes in it to make it a 'bus bar' or 'rigid jumper'. I've even doubled up layers when i thought it necessary. Something like that could mount the breaker semi-rigidly just off the battery or just off the inverter and potentially be much simpler than cutting and crimping, or buying, another short cable.

 

[Mattb4]

Rather than using a short piece of smashed copper pipe you can order nickle plated copper bus bars from Amazon that are used to connect individual battery cells. Holes can be drilled larger or added just make sure you chamfer the edges after drilling They are rated for 360a. https://www.amazon.com/dp/B09TFJ4XHG?psc=1&ref=ppx_yo2ov_dt_b_product_details

 

[740GLE]

Cheap and high current are two and different things when talking breakers.

IMO I’d much rather have an ANL fuse vs some of those failure prone breakers, if you’re concerned with OCP.

Many of those cheap breakers have very high voltage drops when under heavy current draw.