# Inverter guidance please



## EuropeanCampers (Mar 28, 2008)

Im new to this inverter stuff so would appreciate a little advice.

I have two inverters now, a 150w and a 500w, both can be wired to "12 sockets" or straight to e battery.

My questions are:

1) Say Im running an appliance, a laptop for example that uses 75 watts. Would both inverters use the same battery power to run this as they draw the required watts? Or does the larger one draw more therefore using more battery, making the smaller one better for this specific exmaple?

2) Is it ok to plug either the 150w or the 500w through 12v sockets? Or should the larger one only be wired direct to the battery whereas the smaller one is fine in 12v sockets or both only on the battery?

Thanks.


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## johng1974 (Jan 17, 2007)

hi Geh

on the second question I would say both should be run from the battery, as near as possbile, using thick wire

pulling 150W through a 12V socket is , a lot....

hope that helps a bit 
John

but my maths could be suspect...

edit....

I hold my hand up , I am wrong... I just can't remember how..


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## AberdeenAngus (Jul 26, 2008)

They should both use the same power. The value 150W and 500W are maximum power outputs.

You need to check the power rating of the sockets.
In my van, for example, I have 12v sockates rated at 6 Amps.
12 x 6 = 78 Watts
So I would have to run even the small invertor straight off the battery.

150w at 12v is about 13 Amps. Heavy duty 12v sockets may be up to this.

500w at 12volts is 40 Amps. This requires seriously heavy cable and I doubt this would normally be fitted to your van.


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## pippin (Nov 15, 2007)

Just to answer part of your query, with some basic electrical theory.

Assuming that you are using each inverter to its maximum capacity - to be on the safe side - the currents taken at 12V are as follows.

150W @ 12V = 12.5A
500W @ 12v = 42A

Adding a bit for inverter inefficiency gives 15A & 50A respectively.

That is quite a bit of current for the one and heck of a lot of current for the other!

If you are using 75W then that is only some 6.25A but then add a bit for inverter inefficiency and you are sucking nearly 8A. Both inverters should be about the same.

So, your 12V socket would just about be safe if that is all you are consuming.

BUT and it is a big BUT - you might just plug in something a bit bigger than your laptop - after all you have a regular mains socket on the end of the inverter just inviting you to plug in the hairdrier or curling tongues or whatever.

Your 12V socket and its wiring would not like a constant 15A for long and as for 42A that would spell a blown fuse at best and a disastrous fire at worst.

I would be going direct to the battery via substantial wiring and a suitable fuse.

Usual caveats apply regarding any electrical work.
If you don't know what you are doing then don't do it! 
Just covering my back in this litigeous (?) world!
E&OE


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## DC4JC (Sep 19, 2007)

I'd like to ask another question around an inverter as I'm considering one.

Where do you typically install them? Is it close to the battery box and then you run the cable of what ever you intend to plug in into that area?

Or do you have them somewhere inside your MH?

Sorry if its a thick question

Thanks

Dave


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## 108717 (Dec 12, 2007)

I see you're running a Hymer B534. Bear in mind that when stationary, if you use the cab lighter socket it will drain your starter battery not the leisure unless I'm mistaken. 

I can vouch for it on our 1988 B544 because despite being outside the house on EHU an old GPS reciever managed to kill my starter battery over time. 

I have now fitted a (covered and fused) 12volt socket in the cupboard for use when not moving.

J


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## CliveMott (Mar 10, 2008)

Yep, Mount the inverter in a well ventilated place close to the battery you intend to use. Keep the DC wires short and direct and don,t forget the fuse. If necessary install a mains extension lead to put the "mains" where you want it.
Alternatively you could have your inverter installed so that it powers your existing sockets automatically.

http://www.motts.dsl.pipex.com/INVERTER.htm
C.


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## spykal (May 9, 2005)

DC4JC said:


> I'd like to ask another question around an inverter as I'm considering one.
> 
> Where do you typically install them? Is it close to the battery box and then you run the cable of what ever you intend to plug in into that area?
> 
> ...


Hi

The shorter you can make the 12volt side of the wiring the better.

Having said that it is best if you can reach the inverter from where you will be using it's output as it will need to be switched off when you are not using it, so inside the van but close to the battery ... they usually have an isolating switch built into them.

mike


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## DC4JC (Sep 19, 2007)

Thanks Clive and Mike.

Dave


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## b6x (Feb 26, 2007)

When you say "don't forget the fuse", is that just an inline fuse on the red DC cable? If so, how do you know which size to make it? As one post above says, it can be anything from 15A to 50A for these inverters?


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## spykal (May 9, 2005)

Hi

All the inverters I have have seen have a fitted inline fuse holder in the supply cable that comes with the inverter. The fitted fuse will be sized to protect the inverter at its maximum output.

You can of course work out the size that a fuse needs to be to protect a circuit...Ohms Law is you friend here ...it will calculate an unknown value if you have some known values...read up on it via google or do what most do and use an Online calculator <<  like the one on the end of that link :wink:

Mike


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## teensvan (May 9, 2005)

Hi.

It is also best to fit an in line isolator that can be turned on and off inside the van. Get the battery isolator type about £5-6. Also get the correct size of cable lug.

steve & ann. ----------- teensvan


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## EuropeanCampers (Mar 28, 2008)

Thanks for the responses.

Sounds to me like the best combination is the 150w plugged in to a 12v socket in the rear to power small consumption items. (laptop, phone charger and so on)

Then hard wire the 500w near to the battery for the times when more grunt is required (hairdryers and the like).

I like the idea of wiring the 500w inveter into the mains socket circuit so that it can take stright over for all sockets when not on hookup. Problem is I wouldnt have a clue where to start and Im guessing having it done would be expensive!


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## DABurleigh (May 9, 2005)

Yes, I have a similar arrangement.

As to powering the mains sockets, there is a lot on MHF about the various ways of doing this, varying in price, convenience, and even safety, or perhaps I should say foolproof protection.

Dave


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## Penquin (Oct 15, 2007)

But remember that if you are running it off the 12v socket in the *back,* that socket will be draining the leisure battery at the quoted rate e.g.12.5 amps;

1. will the cable to that socket take that current? 
2. how long is that cable run from the battery?

- there will be voltage drop if the run is not very short and if the voltage drops the required current goes up (from Ohm's Law), inverters can seriously drain batteries fast and batteries don't like being drained!


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## EuropeanCampers (Mar 28, 2008)

Penquin said:


> But remember that if you are running it off the 12v socket in the *back,* that socket will be draining the leisure battery at the quoted rate e.g.12.5 amps;
> 
> 1. will the cable to that socket take that current?
> 2. how long is that cable run from the battery?
> ...


Thats a good point. But even though its a 150w unit, Ive no intention of running it at full tilt. Laptop, phone charger, ipod charger and so on, highest of which would be laptop and thats probably only running 40w or so continuous. If my calc is correct, thats only about 5 amps which I presume any rear 12v socket should comfortbaly cope with.

Unless Ive misunderstood and someone disagrees, I reckon up to about 80w useage (just shy of 10amps) should be ok with the 12v leisure sockets??


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## EuropeanCampers (Mar 28, 2008)

I've decided to go for the 150w through the 12v socke and hard wire the 500w direct to the battery. Can anyone advise what size of cable I need for this and where best to get it from?

Thanks


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## Bagshanty (Jul 24, 2005)

I run my laptop off a 150W inverter, plugged into a 12 v auto socket. My built in meter shows 5 amps max, often less (depends on state of laptop battery charge). Neither the connector nor the inverter get particularly warm - the only thing that does is the 240V to 19 V transformer. (How much easier if the laptop ran off 12 V!)

I wouldn't DREAM of running appliances that require a lot of grunt off my batteries. If you need all that then you're better off with EHU or a holiday cottage!


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## EuropeanCampers (Mar 28, 2008)

Well Im sorted.

Got the 150w plugged into 12v socket in overhead cupboard.

HArd wired thr 500w to the battery and mounted it neatly rear side of cab area. Then I got thinking, what the hell am I ever going to plug in that needs 500w? I sat there and thought about appliances that you can plug in and they are either small enough for the 150w or need a 1500w plus (hairdryers etc).

So, what needs between 150w and 500w? Have I just fitted a pointless supply!!!!


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## johng1974 (Jan 17, 2007)

:lol: 

a collection of things is all i can come up with,.,

in my case, a pc, ps2, lcd, skybox all running at once...

500w is not quite enough for anything juicy, and a bit too much for small stuff ....

I have ran a jigsaw from about that wattage before, but quite why you'd be using a jigsaw and not doing one is beyond me 8)


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## DABurleigh (May 9, 2005)

"So, what needs between 150w and 500w? Have I just fitted a pointless supply!!!!"

I'm not sure quite what it is about motorhomers, but I do find it a regular occurence that they are extremely keen to talk about fitting "best" solutions when only subsequently it emerges they never had the foggiest idea of what the requirement was they were trying to satisfy. I tend to conclude they have more money to burn than me! 

Perhaps the 500W inverter came into your possession and you simply wanted to make it available for good use. In any case, it's never too late to start thinking about your requirement. You might then consider selling it and buying a bigger one!

When I said earlier in the thread "I have a similar arrangement" that is true. But it is 150W modified sine-wave and a 1.6kW pure sine-wave combination.

Dave


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## EuropeanCampers (Mar 28, 2008)

DABurleigh said:


> "So, what needs between 150w and 500w? Have I just fitted a pointless supply!!!!"
> 
> I'm not sure quite what it is about motorhomers, but I do find it a regular occurence that they are extremely keen to talk about fitting "best" solutions when only subsequently it emerges they never had the foggiest idea of what the requirement was they were trying to satisfy. I tend to conclude they have more money to burn than me!
> 
> ...


Exactly right Dave. I was given the 500w by a good kind friend and member of this very forum so I thought it should be fitted!! It's doing no harm, presume there's no drain with it switched off, and may come in useful at some point, I just cannot for the life of me think what for!

The little 150w will get plenty of use Im sure.


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## Proff (Jul 22, 2005)

The 500w fitted by GEOH was used to power my aircon last year on continental jaunt...
never had a problem 
My aircon unit is a 450w italian split unit, fits on window ledge and cables are flat to enable window to be closed for security.
we have now gone to a 1000w invertor unit for TV Freeview DVD 700 w kettle etc..

Hope you had a good time on Angelsey Geoh


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## Moonlight (Aug 12, 2006)

*IMPORTANT SAFETY NOTE*

*IMPORTANT SAFETY NOTE*

_*This MAINS WIRING is potentially lethal if not done correctly. *_

So why keep referring people to - 

http://www.motts.dsl.pipex.com/INVERTER.htm

And then right at the very end put -

*Several details are omitted from this description and if you are qualified to do this work you will not need to ask*


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