# Wiring in an inverter, some questions.



## Glandwr (Jun 12, 2006)

Hi I’m thinking of swapping my quasi sine 300 watt inverter with a 600 watt pure sine and would like some guidance/reassurance. It’s secondhand so unfortunately no manual.

It’s a Waeco continuous output 600W, surge 1000W, input current 70Amp.

Current wiring to inverter looks much to flimsy. I was thinking of upgrading to 10mm2 cable overkill or not? Short run one mtr tops. 

Inline fuse would that be 70amp?

Would you recommend an isolator as well? 

There is an earth connector on the metal case. Recommendations as to what I should do with that please.

Thank you Dick


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## airstream (Jan 7, 2009)

*Cable size - volt drop*

Hi, 
You cant go to large on your cable size 
I would use 16 mm on a 70amp load up to a max of 3 mtr cable length ie 1.5 mts per cable

If you assume a nom voltage under load of 12.25 volts @70amp the volt drop using 16mm cable will be approx 0.22volts just keeping you above 12v

This is at max output and will knacker a small ie 110 a/h battery in no time but when will you using 600watts?

Batteries will need to be in good order and a/h rating for the expected loading (70 amps is a high load)

In my van I use a 1000 watt pure sine with a 245 a/h Trojan deep cycle battery and only use it on a heavy load ie 600watt hairdryer with the engine running

Deep cycle batteries are designed for low amperage loads of say a max of 10% to 20% of the a/h rating for extended periods between charges

We use starter batteries for short duration high amperage loads ie engine starting, bow thrusters on boats etc

Fuses - inverter should have internal fuse - fuses in cable runs are to protect the cable so anything above the load max and the cable rating will be fine, I always fuse the cable to near the cable rating as the larger value fuse has a lower volt drop

Good Luck Ray


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## Glandwr (Jun 12, 2006)

Thanks Ray. Batteries are 3X110 ah. I can see it used a full throttle infrequently. The voltage drop? Can I measure this without load or not? That is check at battery then at terminal or will I have to be drawing a load?

Dick


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## Goldwinger (May 10, 2005)

Hi I am thinking of fitting the same size inverter should the fuse size be a 70 amp we are looking to charge an electric bike battery only using the original cable size.


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## airstream (Jan 7, 2009)

*not easy*

Hi, 
Its not easy to "calculate" the actual volt drop as there are many variables that can affect a simple calculation

The only real life solution is to go with the theory ie ohms law and add a bit

Volt drop is the loss resulting from pushing amps through a resistance, so yes, to measure the actual loss (volt drop) you need to measure the voltage at the load terminals

Also as the battery voltage lowers the amps used will increase

Also you need to ensure the cables connecting your three batteries together are at least the same size as your proposed inverter cables and that your batteries are connected so that the load is not taken disproportionately from one battery you need to have them connected so the pos is from battery 1 and the neg from batt 3 this will help ensure that all three batteries share the load and the charging at the same level

Ray


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## airstream (Jan 7, 2009)

*MENT TO*

Hi 
In case I did not make it clear 16mm cable is the absolute minimum I would use for your proposed inverter

On my boat I used 95mm cable on my 3000 va inverter!

Ray


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## Glandwr (Jun 12, 2006)

Many thanks again Ray. I have realised it was a stupid question about the load no load reading after thought. :roll: 

The Earth connection does puzzle me though. It’s obviously a design after thought, a simple bolt through the metal casing with a securing nut and washers and tightening nut. There is an earth symbol next to it. I suspect that it could be a UK modification. The model number does have an obviously added /UK at the end and a UK plug socket (3pin). 

My guess I’ll find continuity between that and the earth pin socket. Trouble is multimeter is not working at the moment. As I can’t imagine using anything but two wired double insulated things in it I think I’ll ignore it, unless advised agin.

Dick


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