Calling all 'crats, techno, electro, intellectual, regarding inverters

[Becky]

Calling all \'crats, techno, electro, intellectual, regarding inverters

We have just bought an inverter, not pure sine wave, the cheaper square wave type.

Now what concerns me is the wiring in to the boat's 240v circuit. Obviously to work, it needs a significant 12v supply (it is 1500w), but can we hard-wire it into the main circuit? Will there be any 'leak-back' (can't think of another way to describe it) of current from for example shore power? Or will it not matter at all.

So to turn it on, all one would do is switch on the power from the batteries.

Or, should we also have a switch to isolate it from the remaining 240v circuit, which would also need turning when when we need to use it?

The 'book of words' that came with it doesn't make this clear. It has a 3 pin mains plug on the front, and a switch beside it. But it is big (and ugly) and I want it mounted in a ventilated locker out of site.

I hope I have made my query clear.

So, come on you knowing peeps, what should we do? /forums/images/graemlins/confused.gif

 

[capt_courageous]

Re: Calling all \'crats, techno, electro, intellectual, regarding inverters

Becky
Do you really mean 1500 watts or is it 150 watts. If it is 1500 watts you are in serious danger of burning out a lot of cables and perhaps your boat. The current ( amps ) will be horrendous, something like 4 times the maximum any wiring in your house will take. Check it!

 

[pvb]

One solution...

One solution would be to use a changeover switch (something similar to pic below) so that you can keep the shorepower and inverter circuits separate and choose which one to power your onboard AC circuit from.

And please don't be alarmed by the Capt Courageous comments - he obviously isn't well up on electricity!

 

[Salty John]

Re: Calling all \'crats, techno, electro, intellectual, regarding inverters

Your 1500watt inverter must not be allowed to feed your 240v system at the same time as any other source of 240ac, such as shore power or generator. Some have an automatic transfer switch that switches the inverter off if another source of 240ac is on line. Others require that you have a manual switch to select the source of 240ac.

 

[BlueSkyNick]

Re: Calling all \'crats, techno, electro, intellectual, regarding inverters

[ QUOTE ]
Becky
The current ( amps ) will be horrendous, something like 4 times the maximum any wiring in your house will take. Check it!

[/ QUOTE ]


i don't know what you are on about here - 1500 watts is a perfectly normal load in a domestic system, eg kettle, heater, microwave, plenty of other examples.

Just had a quick look in PBO - there are boat invertors available up to 5000 watts. 1000W is middle of the range.

 

[Norman_E]

Re: One solution...

Capt. Courageous has a point. Without allowing for any losses if the inverter is 1500 watt output, then at 12 volts input the current drain is 125 amps, which requires some pretty serious cables.

 

[BlueSkyNick]

Re: One solution...

Fair comment - having re-read Capt-C's post, along with yours, I now understand the point he is making.

i would have thought the invertor specification or instructions would stipulate what cable is required on the input.

 

[Norman_E]

Re: Calling all \'crats, techno, electro, intellectual, regarding inverters

No problems on the 230 volt side, it is the 12 volt input cables that need to be massive. The ones on my boat (for a 1200 watt inverter) are as big as the main battery connection cables. Big inverters will quickly flatten a battery. Even without any losses due to inefficiency a 1500 watt inverter will draw more current than most yacht engine alternators can replace. My own boat has an upgraded 120 amp alternator to cope with the 1200 watt inverter driving the fridge.

 

[Becky]

Re: Calling all \'crats, techno, electro, intellectual, regarding inver

I think some of you have missed the point.

I know it isn't easy to explain, even HWMBO didn't get my meaning, andf he asked me to post it.

So, here goes again.

It is 1500 watts, capable of 1800 watts for 10 mins and 2kw for 10 secs. See I have read the book. I realise that the 12v cables are big; the instructions tell us so.

BUT, if we wire the thing into the main circuit (240v) permamently, BUT only switch it on when we HAVEN'T got shore or gen power on, then will that matter?

In other words, will electricity go back into the 240 wiring in the inverter and harm it when it isn't on?

OR should we have a switch in the 240v wiring from the inverter to the 240v boat corcuit as well as the switch in the 12v supply.

Does that make my query clear?
/forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif

 

[Rowana]

Re: Calling all \'crats, techno, electro, intellectual, regarding inverters

I agree.

See here - http://www.sterling-power.com/htm/downloads.htm

Scroll down to 600W inverter and open the pdf file.

You will see that max load at 12volt is 70, yes SEVENTY amps.

You'll need an effing big battery for 1500W


Same web site shows 1800w inverter with a 180amp full load draw at 12v

 

[Rowana]

Re: Calling all \'crats, techno, electro, intellectual, regarding inver

Yes it will matter. If it does not have an auto-switch over as in UPS systems, then you will need a switch.

Just as a matter of interest, what size batteries do you have?

What load are you going to put on it?

 

[capt_courageous]

Re: One solution...

Yeh
Like a degree that would burn your brain out. Plus forty years experience of serious electricity and RF. I suggest you look up a thing called Ohms Law. It is common knowledge among intelligent 12 year olds.

 

[Guest]

Simple answer is what you want - simle answer here ...

Becky - you struggle like a lot of others when you want a simple answer ..... /forums/images/graemlins/tongue.gif

Yes you should put a switch or relay to cut the inverters link to 240V circuit when using shorepower or other source eg Generator. To leave it connected could be dangerous.
And I would use a dual pole switch so it cuts +ve and -ve leads ...
Yes you should put a switch between inverter and 12v - as the amps the machine pulls if anything should go faulty could cause a disaster ... and if you need to cut power to it - then a Dual pole switch is best.

Does that answer your post ??

(Oh and by the way - the inverter will kill your batterys real quick !! So I hope you have good recharge capability .... !!)

 

[Sixpence]

Re: Calling all \'crats, techno, electro, intellectual, regarding inver

Becky
Use a manual changeover switch as pictued above , it's the accepted way to stop either your inverter trying to feed the mains , or the mains trying to feed your inverter . Both ways are not good for your boat . The changeover switch will isolate the supply you're not using , and connect the boat to the one you are using



Ah , beaten to it

 

[pvb]

You\'re digging a bigger hole...

For marine use, a 1500w inverter isn't huge - many leisure boats have much bigger inverters. Of course they need hefty cables for the DC supply, and Becky has confirmed that she understands this. With your apparent qualifications, I'm just surprised that you chose to scare her rather than answer her question.

 

[Talbot]

Re: Calling all \'crats, techno, electro, intellectual, regarding inverters

Becky,

My vote is also to have a changeover switch that allows one or the other only. I would also make sure there was a serious fuse between inverter and batteries.

 

[Richard10002]

Re: One solution...

[ QUOTE ]

[/ QUOTE ]

This is what I've got, although it has 1 0 2 as the selections.

200Ah battery and a 1700W, (max 2500W) invertor... seems to work fine.

 

[rwoofer]

Re: Calling all \'crats, techno, electro, intellectual, regarding inverters

Becky, We had ours done last year with the changeover switch above. We got marine maintenance in Haslar to do it. Even though ours is only 600W is still needed some very big cables!!

 

[andy01842]

Re: Calling all \'crats, techno, electro, intellectual, regarding inverters

If one was to feed 240v mains into the output of an inverter i think you could kiss the inverter good bye, and the boat. I would not like to try it. If you use a switch to change from inverter to mains it must be a brake before make switch, ie isolate the inverter b4 conecting the shore power mains.

 

[Becky]

Re: Calling all \'crats, techno, electro, intellectual, regarding inver

''Just as a matter of interest, what size batteries do you have?''

We have 4x 110 amp hour batteries, a 90 amp alternator and an Adverc on the engine.
The inverter is needed to run the watermaker 240v motor while the engine is running; this summer when we have wanted to make some product water we have had to run the generator as well as the main engine (when there has been no wind). Which is wasteful to my little mind. The watermaker motor is something like 750 watts, (and takes 2.5 amps when running), but it is the start-up current that we are covering with the bigger inverter.

Incidentally, I went into Marine Superstore on Saturday and collared one to the serving guys. I told him that this thing (the inverter) had been on their shelves for AGES (pure guess, but he checked & I was right), and I would take it off their hands for a reasonable discount. Which they gave me after a bit of grumbling; I suggested and got £50 off for just asking. Should have suggested more!