inverter hookup

[iash101]

Hi im asking this on behalf of a elderly neighbour. he has a 2011 swift touring caravan ,running with 2 leisure batteries and a 120 w solar panel , He's looking to install something like a 3000 w inverter to power the kettle, fridge , tv and microwave ..
His question Is would it be possible to power his 240 v sockets with the inverter via the external 240v electric hook up ?? also is it possible to run both in tandem with the 12 v electrics for lighting etc
Any advice would be appreciated thanks

 

[Damian]

Without going into the technical reasons, the simple answer is NO, it is not a sensible idea.

 

[WoodlandsCamper]

His question Is would it be possible to power his 240 v sockets with the inverter via the external 240v electric hook up ??

Why not power the 240v sockets direct from the external 240v EHU? Why put an inverter in-line?

2 batteries and a 120w solar panel won't last long providing 3000w through an inverter. Less than an hour?

 

[iash101]

thanks guys ,that answered that lol.. the reason being he was hoping to save on pitching costs ie using not electric hook up pitches , he was looking to buy a 12v tv but someone mentioned an inverter instead ..
cheers guys

 

[Gozza]

12v TVs and kettles are certainly available, and although they will take a toll on the battery, it'll be less than powering an equivalent mains appliance through an inverter. This is because inverters are inefficient, even good ones. For every 100 watt-hours of usable "mains" electricity an inverter produces, it'll produce 100 watt-hours of heat which is just wasted, and take 200 watt-hours out of the battery. I've assumed the invertor is 50% efficient there, which is pretty good going, and the other parts of the system will have their own inefficiencies too - everything electrical wastes at least a little bit of power in heat generation - unless it's an electric heater of course, in which case the heat isn't wasted!

(before anyone says it, I know an inverter produces pseudo-mains, not real mains, but it's near enough).

If your mate wants to avoid mains hook-ups - I'd recommend he at least tries it because I think it's great, and would do it more often if Mrs Gozza could be surgically separated from her hairdrier, and Gozza Junior from about a hundred devices with names beginning with i- . Run what you can on gas (fridge, heating, water heating, cooking etc), but a 12v TV and have fun!

 

[ProfJohnL]

.................... This is because inverters are inefficient, even good ones. For every 100 watt-hours of usable "mains" electricity an inverter produces, it'll produce 100 watt-hours of heat which is just wasted, and take 200 watt-hours out of the battery. I've assumed the invertor is 50% efficient there, which is pretty good going,.......................

Hello Gozza,
I know inverters are not 100% efficient, but 50%????? I think a full sine wave inverter will be closer to 66.7% and pseudo (Three step) will be closer to 85% efficient. Despite these slight better figures I agree the concept of trying to run a full caravan on a 3K inverter from batteries is misguided.

 

[Gozza]

Your info may be more up to date than mine! Certainly both of my (quite old) inverters aren't much more than 50%, especially when getting close to the top of their capacity. Modern ones are probably better.

 

[iash101]

Thanks Gozza your advice is much appreciated .. If he was to go down the inverter route ,Do you know if he would be able to power up the 240 sockets in the van via the external the 240 electric hookup socket ?
Cheers

 

[Damian]

Just take a step back a moment.
Have you considered the size of the cabling required to supply a 3000w inverter.
At full power of 3Kw you would be pulling 250Amps and the cable would have to be massive !!!!
The batteries would be ruined in next to no time as they are NOT designed for heavy drain of this type, they are designed for prolonged low amp discharge.

 

[Gozza]

Thanks Gozza your advice is much appreciated .. If he was to go down the inverter route ,Do you know if he would be able to power up the 240 sockets in the van via the external the 240 electric hookup socket ?
Cheers

Well firstly, Damien's comment immediately above this one is absolutely right and is possibly the most important thing anyone has yet said in this thread.

Back to the question - yes he could, it would just be a case of getting the appropriate lead to go between the inverter output and the blue plug input. I wouldn't, because there would be too much temptation to try to run other mains things that are more than the inverter is powerful enough to run. But yes, as long as he can resist that temptation then in theory yes he could.

 

[Gozza]

At full power of 3Kw you would be pulling 250Amps and the cable would have to be massive !!!!

As an aside, can you even get 3kW inverters? I did a quick Google when this thread first came up and couldn't see any. I suppose they must make them for UPS's and things like that, but they wouldn't be designed for the great outdoors.

 

[ProfJohnL]

.......................
As an aside, can you even get 3kW inverters? I did a quick Google when this thread first came up and couldn't see any. I suppose they must make them for UPS's and things like that, but they wouldn't be designed for the great outdoors.

Yes you can get large inverters, but they become very expensive. For larger powers they tend to require 24, 36 or even 48V dc supplies. You can find then for canal and other marine applications, and they often include multistage chargers so they do act like a UPS.

 

[Dustydog]

I bought my caravan where everything you need to enjoy a happy healthy holiday can be run on gas 12v where mains electricity is unavailable.
Your " friend" needs to calculate the cost of the Inverter and all ancillaries against the cost of nightly EHU. He may be shocked!

 

[colin-yorkshire]

hi all,
the OP asked the question can a inverter be used instead of EHU, in theory yes it can. and Gossa's reply is correct.
however in practice it is very difficult to do, and moreover even more difficult to do right so Damian's answer is also correct.
the real question is why would one wish to do it!! with all the hassle it takes to make the system bullit proof, most of the caravan systems will run quite happy on either gas or 12v a large battery and solar panel would suit better [which the owner has already] so why the need for 230v off grid when the cost of EHU is so small. if it is to save money this would be a false economy as it would take so long to recover the cost of buying the inverter and wiring in.
actually there is very little in the way of dedicated 230v equipment one needs most can either be run off the12v system or even battery power. for instance, a gas kettle will use less energy than say a electric one via a inverter, a 12v one would use even less but would take longer to boil [if this is important]
even her ladyships hair drier is no problem just send her over to the toilet block and use their power "usually for free"
most chargers have a 12v equivelent also.

to give the OP some idea however when I rebuilt the motor home I devised a system to do exactly what he intends.
it was fully integrated into the charge circuit, and comprised of.
a standard EHU,
a charger
2 [1kw inverters],
1 small power cell
2 high capacity batteries plus the normal vehicle one
a bank of switch gear
several [7] relays
and about a mile of wire.
it took 2months to devise the system and another to fit it, to be honest I only did it because I was told it was not possible at the time :woohoo: also extra weight was not an issue in the m/home it would be in a caravan.
although the system worked well it was bulky and in the 10years we used it the number of times we went off grid using the inverters could be countered on one hand.

 

[Gozza]

even her ladyships hair drier is no problem just send her over to the toilet block and use their power "usually for free"

The sites we stay on that don't have mains, don't have toilet blocks either! One of them doesn't even have a tap...

it took 2months to devise the system and another to fit it, to be honest I only did it because I was told it was not possible at the time

Now that's my kind of project! "We do not choose to do these things because they are easy, but because they are hard" ! :lol:

 

[colin-yorkshire]

even her ladyships hair drier is no problem just send her over to the toilet block and use their power "usually for free"

The sites we stay on that don't have mains, don't have toilet blocks either! One of them doesn't even have a tap...

Yeah we have stayed on a couple of those "" think they are called Lay-bys"" hmy: hmy: hmy:

 

[Gafferbill]

.......I often stay on sites with only a tap and a toilet emptying point and I use inverters in the way the OP suggests to produce mains power.
However you have to remember they do not produce electrical power.....they just convert it for use in an appliance.
It is pointless having a 3 kilowatt inverter unless you have a means of producing 3 kilowatts in the first place.
Such an inverter would need a massive battery bank to be of any use if you don't.

I use a small 150 watt modified sine wave inverter that gets it's 12 volt power from the caravan leisure battery to power a mains TV and Sky box and any small mains charger such as for a tablet or phone.
Don't use an inverter to charge an electric toothbrush.......in my experience it will destroy the charger.

I also use a 600watt pure sine wave inverter which can be temporarily connected to the tow car battery to provide mains power to the caravan via the normal EHU socket using a suitable connecting lead.
The 12 volt leads from the battery to the inverter have to be short meaning the inverter has to be next to the battery. The mains wire from the inverter to the caravan can be of any suitable length.
This set up is used to charge the caravan battery via the on board smart charger or to power a 500 watt hair drier. It will also power the fridge but I never make use of this.
The tow car battery is monitored and never allowed to fall below 12 volts to make sure there is power left to start the engine.

So long as the tow car engine is run on trips out from the camp site fairly regularly to recharge the battery and gas is used for cooking, heating, hot water and the fridge, then I can survive without EHU indefinitely winter or summer.

 

[Gozza]

It's just occurred to me to wonder if the o.p. has considered a generator? A decent one with high capacity is beyond my price range...thats why I've got a small cheap rubbish one...but compared to the cost of a big inverter, plus a battery bank and associated cabling capable of driving it, it's got to be worth looking at?

 

[bertieboy1]

Damien - moderator,
Further to Damien's response,the current drawn at 12 volts would be much higher,With a 3000W output and taking the prof's efficiency into account (66,7 %), The input wattage would be 3000/.667 = 4497 watts.Divide this by 12 volts and the current is 374,75 amps.This of course assumes the inverter is working at it's rated output (3000W)
At lower outputs the efficiency will be lower as will the 12 volt current.
When referring to a 100,200, 3000 W inverter this should always refer to the output rating.