Installing an inverter

[Tikitin]

The specifications of the inverter I am thinking of installing are as follows:
Input 12 V AC
Output 220-240 V DC
Modified sine wave
600 W continuous
1200 W max out

What size of the fuse should there be between the battery and the inverter?
What size (square millimeters) should the cable between the battery and the inverter be?

 

[Scott Danforth]

The inverter instructions will have this info. However you may want to look at what you typed.

For what you typed, you would be looking for a step- up transformer and diode pack. AC to DC

Inverters are for going from DC to AC

 

[matt167]

Inverters usually have their own ATC or ATM fuses inside or on the outside. You can wire them direct to battery providing that is true, otherwise you need to fuse them identically to what they are fused for.

FWIW I ran 10 gauge for a 400W inverter. 1200w is a lot of current. you better over size it.

 

[Tikitin]

The inverter instructions will have this info. However you may want to look at what you typed.

For what you typed, you would be looking for a step- up transformer and diode pack. AC to DC

Inverters are for going from DC to AC

Oops!

 

[Tikitin]

FWIW I ran 10 gauge for a 400W inverter. 1200w is a lot of current. you better over size it.

1200W is a lot of current! That's why I was wondering about it. A smaller one would be enough for me, but this is one that I'd get free. Now I just need to to find out what 10 gauge means in square millimeters (by now you probably realize that I am from (continental) Europe! Sometimes I sure wish you guys would go for SI-system!

 

[mike_i]

1200 watts is a power rating not current. What are you powering with the inverter? Inverters convert DC to AC power.

 

[Tikitin]

1200 watts is a power rating not current. What are you powering with the inverter? Inverters convert DC to AC power.

Right, 1200 watts is a power rating, but it means there's going to be a lot of current. Actually I do not need that much power, I just have an inverter of that size available. AC/DC written wrong way around was a typo.
I was calculating that 1200 W means that on the AC-side (220 V) there is a current of approximately 5,5 A. On the DC-side (12 V) the current would be 100 A. Am I correct? What I am looking for, is the formula to calculate the thickness of copper wire which could handle that sort of current.
Like I said, I really do not need that much power, but the wiring should anyway be in proportion to the inverter. Just in case someone decides to use an electric lawn mower on the boat.

 

[dingbat]

I was calculating that 1200 W means that on the AC-side (220 V) there is a current of approximately 5,5 A. On the DC-side (12 V) the current would be 100 A. Am I correct? What I am looking for, is the formula to calculate the thickness of copper wire which could handle that sort of current.

Wire sizing is load over round trip circuit length distance from source.
Wire sizing calculator

Circuit Wizard - Blue Sea Systems

circuitwizard.bluesea.com

 

[mike_i]

To determine the cable size you need to measure the distance from the inverter to the battery bank and double that number.

I just noticed dingbat already suggested the same as I did. Also just in case you didn't know not everything likes to be powered by a modified sine wave inverter.

 

[KD4UPL]

If it's free then that's one thing; otherwise I wouldn't install a modified sine wave inverter. They are kind of like black and white TVs; you could use one but why? 1,200 watts output will be drawing around 100 amps on the 12 volt input. You would want a bare minimum of 35 mm2 wire for that. If you're running more than a few feet to the battery I would step up to something like 70 mm2 wire. You will want a fuse or breaker very near the battery where the wire connects. I would fuse it at 150 amps minimum.

 

[Tikitin]

Wire sizing is load over round trip circuit length distance from source.
Wire sizing calculator

Circuit Wizard - Blue Sea Systems

circuitwizard.bluesea.com

Thanks! This is what I needed.
And the conversion table from AWG to mm2:

Wire Size and Amp Ratings - Applied Industrial Controls

The tables below are intended to be a general guide for wire size and amp...

www.aic-controls.com

(just in case another European reads this!)

 

[Tikitin]

If it's free then that's one thing; otherwise I wouldn't install a modified sine wave inverter. They are kind of like black and white TVs; you could use one but why? 1,200 watts output will be drawing around 100 amps on the 12 volt input. You would want a bare minimum of 35 mm2 wire for that. If you're running more than a few feet to the battery I would step up to something like 70 mm2 wire. You will want a fuse or breaker very near the battery where the wire connects. I would fuse it at 150 amps minimum.

I think I'll go for a less powerful inverter!
(And I just realized I have turned from *recruit* to a *cadet*! Cool.

 

[Tikitin]

not everything likes to be powered by a modified sine wave inverter.

The most important thing I'll be using the inverter for, is my laptop (a lot less power is needed!). Do you think a modified sine wave inverter does the job? To make matters worse, my laptop is a Mac, which presumably is very picky in all possible ways. But that's probably something I should inquire on a Mac forum!

 

[matt167]

If your operating equipment with chargers/ power adapters it will be fine. The chargers don't like the power, and you will actually be able to hear coil whine if you put your ear up to a plugged in adapter, but it sends clean power out and it does work.. Your Mac charges with USB-C and there are 12v car chargers for that. Your wall charger is 87W, but down to 60W will still charge it. Going to DC-DC is better than going DC-AC-DC

 

[KD4UPL]

Do NOT charge your Mac laptop from modified sine wave power. Apple products are one of the most sensitive and are often damaged by MSW. One of my former employees found this out the hard way. He plugged his Mac into a MSW inverter after I warned him not too and he ended up having to buy a new computer.