# Inverters . . . again



## Scattycat (Mar 29, 2011)

I've just bought a 600w inverter to run my Remoska.

Do you think I can run it off a standard 12v plug in the habitation area or will I have to run it direct off the battery?

Also, how many amps per hour would I be drawing off the batteries?

Any help much appreciated


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## SilverFox13 (Nov 20, 2007)

Hi
You will need direct connections to the battery. 600W / 12V = 50 amps ... a serious amount of current.

So use short good quality cables and keep your eye on the amount of charge you use.

Mal


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## rayrecrok (Nov 21, 2008)

Hi.

I would think it would have to be wired straight into your leisure battery with as short as possible thick wire, whether it needs a fuse others will advise... As far as the amperage it will take didn't you get any instructions with it?.. 

ray.


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## listerdiesel (Aug 3, 2012)

If you work on 90% for an average efficiency, plus take off a percent or two for cable and connector losses, the current draw would be 52amps, which as both Mal & Ray have said above, will require decent cabling straight to the battery.

16mm minimum cable size, 25mm would be better, plus a decent fuse in the circuit as well.

If it was me, I'd think about a pair of Anderson connectors, one on short tails on the battery, the other on the feed to the inverter.

There are some decent heavy fuse carriers on ebay, and I'd suggest either an 80A or 100A HRC fuse.

Peter

http://www.ebay.co.uk/itm/Mega-Fuse...al_Components_Supplies_ET&hash=item337e8f1af3


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## Scattycat (Mar 29, 2011)

rayrecrok said:


> Hi.
> 
> I would think it would have to be wired straight into your leisure battery with as short as possible thick wire, whether it needs a fuse others will advise... As far as the amperage it will take didn't you get any instructions with it?..
> 
> ray.


No, but working on 600w on 12v I presume that on full power it would be drawing around 50 amps, but if only pulling 480w for the Remoska it wold be around 40amps, but I wanted either conformation of my math or being put on the right track by those who know better, which is probably most contributors to this site :roll:


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## listerdiesel (Aug 3, 2012)

The other thing to remember is that your battery will not give the same rated capacity at high current discharge rates.

Example: 110ah battery rated at the 20hr rate would give 5.5amps for just about 20 hours, but would be pretty flat at the end of the 20 hours.

At 50Amps discharge rate, the available capacity drops down so you wouldn't get 110ah out of the battery, it would be 90ah or thereabouts.

I know most people using high discharge rates usually only run their equipment for short periods, but it is worth noting the effect of the higher rates, and also that you need to put the capacity back in again as soon as possible.

Peter


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## rayrecrok (Nov 21, 2008)

Hi.

When my 2000 watt inverter gets to a battery charge of just below 11 volts it trips out into safety mode, they don't work until your batteries are flat, only to the minimum voltage that will run it.

So how I see it one battery will only have so many amps to run it, two batteries will have twice the amperage to work etc etc. I have three leisure batteries to work with.

ray.


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## listerdiesel (Aug 3, 2012)

Ray et al:

Sorry if I was a bit confusing on the discharge figures, most if not all modern inverters will cut out when the volts get low as you say, but there will be more capacity left at high rates of discharge than at low rates.

Peter


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## WildThingsKev (Dec 29, 2009)

Is this really practical? 

I don't have a Remoska but isn't it an oven and will normally be on for over an hour, if so then even 200Ah of batteries will be seriously depleted just to cook one meal.

Kev


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## Pudsey_Bear (Sep 25, 2008)

I think a good lesson in cable sizes is a bout due, Peter quoted 16mm cable for the inverter, don't even think of going to Maplins and asking for that as they rate cable differently.

We could do with some sort of ready reckoner to assess what size cables we need to use for various equipment, and a way of knowing how that equates to the physical size.

Solar ready reckoner

Not sure if this one suits Motorhomes

Possibly this one

I'm no sparky (you guessed) so are any of the above useful to us, if so which and which would be the best way to use them.


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## rayrecrok (Nov 21, 2008)

WildThingsKev said:


> Is this really practical?
> 
> I don't have a Remoska but isn't it an oven and will normally be on for over an hour, if so then even 200Ah of batteries will be seriously depleted just to cook one meal.
> 
> Kev


Hi.

I too don't have Remoska what ever that is, but we do have a slow cooker we fill with something for a meal. we put it in the sink and plug it into the mains which can be fed by EHU or inverter via an isolator switch for whichever medium of power we are using.

The slow cooker is used when we are travelling as the engine and solar panel on the roof keeps on top of the leisure batteries as we drive along, and our dinner is ready at the end of the journey, so maybe the OP is doing something like that with his Remoska what ever it is. :lol: :lol: :lol:

ray.

(edit) Had a look at one on amazon, I was too curious. :wink:


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## Pudsey_Bear (Sep 25, 2008)

rayrecrok said:


> the engine and solar panel on the roof keeps on top of the leisure batteries as we drive along,
> 
> ray.
> 
> (edit) Had a look at one on amazon, I was too curious. :wink:


I didn't know it did that, I thought it was either one or the other, but never both.


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## listerdiesel (Aug 3, 2012)

Kev_n_Liz said:


> rayrecrok said:
> 
> 
> > the engine and solar panel on the roof keeps on top of the leisure batteries as we drive along,
> ...


No reason why not, if the solar panels are in circuit, they will charge if the voltage is below the set point for the controller.

Peter


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## listerdiesel (Aug 3, 2012)

Kev_n_Liz said:


> I think a good lesson in cable sizes is a bout due, Peter quoted 16mm cable for the inverter, don't even think of going to Maplins and asking for that as they rate cable differently.


Commercially, cable cross-sectional areas are quoted in square millimetres, or in Wire Gauge sizes (SWG AWG etc)

At the level of Motorhoming:

18awg is 1sq mm
16 awg is 1.5sq mm
14awg is 2.5sq mm

As far as current handling goes, I work on:

6A max for 1mm
10A max for 1.5mm
20A max for 2.5mm
30A max for 4mm
40A max for 6mm

All are for single cables. All should be fused at those values and no more. The fuse should be rated so that a fault in the circuit will not allow the cable to overheat before the fuse blows.

Once you get outside of the smaller sizes, you start to get into supply issues, as Maplins and the like don't carry big stuff, and your local electrical wholesaler may not want to break into a 100m reeel to sell you a couple of metres of 10mm.

We keep up to 170sq mm cable, which is pretty serious stuff, but our main usage is for cabling up to 50sq mm, and we hold stocks of those sizes.

We'd be happy to help out for small quantities if anyone gets stuck, but it would have to be done properly with a VAT invoice etc etc.

Peter


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## airstream (Jan 7, 2009)

*voltage drop*

Hi,
reasonable explanation and chart at att. link

http://www.rpc.com.au/pdf/efn133.pdf

Voltage drop is just as important as the theoretical amp carrying capacity of the cable

Ray


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## Pudsey_Bear (Sep 25, 2008)

Thanks Peter, but this is where I and I assume others get lost with possible disastrous results.

I hope you can fathom my following questions.

"At the level of Motorhoming: "

(18awg is 1sq mm) does that = 6 amp below?
(16 awg is 1.5sq mm) does that = 10 amp below?
(14awg is 2.5sq mm ) does that = 20 amp below?

As far as current handling goes, I work on:

6A max for 1mm
10A max for 1.5mm
20A max for 2.5mm
30A max for 4mm
40A max for 6mm

All are for single cables. All should be fused at those values and no more. The fuse should be rated so that a fault in the circuit will not allow the cable to overheat before the fuse blows.

Going back up to the AWG
Does 12awg is 3.0sq mm
Does 10awg is 3.5sq mm
Does 8awg is 4.0sq mm.

As for fuses, I assumed the that as a fuses main job was to protect from fire, it should be of lower amps then the cable will tolerate, so a 40amp cable should have a 35amp fuse, and a 6amp cable should have 5amp fuse.

And if I'm correct in that a fuse is to protect the cable why do some domestic appliances have a 3amp fuse when the cable will stand more, or is that to protect the appliance cable.

I'm getting lost so I'll stop there.


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## rayrecrok (Nov 21, 2008)

Kev_n_Liz said:


> Thanks Peter, but this is where I and I assume others get lost with possible disastrous results.
> 
> I hope you can fathom my following questions.
> 
> ...


Hi.

The simplest way I can get my head round the wireing needed for an inverter in the sizes we are talking abut is, the same size as the ones you have on your battery to start the engine..

ray.


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## tulsehillboys (Jul 22, 2010)

Don't use an inverter to run a remoska - get a big heavy frying pan with a lid and pop it on the gas. 
The strain on your batteries (just providing heat) will dramatically reduce their life and unnecessary when you have a perfectly good heat source (hob). 
Inverters are great for occasional use but not for anything that needs to be connected for a long period. 
The remoska is great if on hook up and saves on gas!


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## CliveMott (Mar 10, 2008)

Are you sure you really want to do this?

If so then the amps quoted are correct. The cable sizes suggested by listerdiesel are correct. 
BUT
I would NOT connect it to the leisure battery at all. I would use a heavy duty relay or CONTACTOR to connect the inverter to the starter battery ONLY when the engine was running and the alternator charging.
i.e. a duplicate of the Split Charging circuit using some beefy components, fuses, contactor and wiring.

Contactor from Albright Engineers would be my first choice.

http://www.albrightinternational.com/lang/en/index.html

http://www.motts.org/SPLIT CHARGING SYSTEM.htm

C.


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## Pudsey_Bear (Sep 25, 2008)

rayrecrok said:


> Hi.
> 
> The simplest way I can get my head round the wireing needed for an inverter in the sizes we are talking abut is, the same size as the ones you have on your battery to start the engine..
> 
> ray.


I'm meaning more the wiring sizes in general Ray, it's almost like a gentlemans club, if you don't know the password you can't get in.

I have a few reels of multicore singles in the garage, and the labels fell off ages ago, so I only have the physical OD to go from, and that varies by the smallest amount they go from around 3.6mm up to 4.2mm if memory serves. 2.5 T&E has it written all along the cable, why doesn't all wiring have it's spec on it.


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## listerdiesel (Aug 3, 2012)

Kev:

You can measure a strand, work out the individual cross-sectional area, multiply by the number of strands and that will give you the cable size.

The general wire/strand sizes for what I quoted are:

16/0.032 = 0.5sq mm

32/0.2 = 1.0sq mm

32/0.235mm = 1.5mm

52/0.235 - 2.5mm

4awg is 25sq mm
6awg is 16sq mm
8awg is 10sq mm
10awg is 6sq mm
12awg is 4sq mm
14awg is 2.5q mm
16awg is 1.5sq mm
18awg is 1sq mm

My current ratings are lower than commercially used, as I have no idea of what ventilation is available or whether the cables are in conduit or bundles.

Fuses have to take into account the impedance of the circuit, such that if the impedance is high, the fuse will still blow, rather than the cable catching fire, so 6A or less for 1mm and so on.

For small lighting circuits, I'd fuse at 3A or 2.5A for 1mm cabling, that will cover up to 30W of load.

Peter


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## steven2002 (Sep 12, 2012)

listerdiesel said:


> Kev:
> 
> You can measure a strand, work out the individual cross-sectional area, multiply by the number of strands and that will give you the cable size.
> 
> ...


excellent peter..i have stood with a roll of 6mm2 and 4mm2 cable and could never work out where the sizes came from..thanks..


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## Pudsey_Bear (Sep 25, 2008)

Thanks Peter, I don't understand it yet though :roll: :roll:

At first reading "work out the individual cross-sectional area" is going to be my stumbling block, I always went missing when it was maths, I was in class physically, but away with the birds as far as listening was concerned.

I'll have to look at it later when I'm a bit more awake and see if it goes in.


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## listerdiesel (Aug 3, 2012)

If you can measure a single strand of the bundle of copper wires in a cable, you will have the diameter.

Let's assume you have 16 strands of 0.2mm diameter wire.

pi X (R X R) gives you 3.142 X 0.01 = 0.13142 sq mm per strand.

Multiply that by 16 strands = 0.5040sq mm or 0.5sq mm.

32 strands is obviously double that.

We had to take our son up to the 24=hour Doctor in Kettering last evening, and in the kerfuffle I made a mistake in the figures above:

I typed: 16/0.032 = 0.5sq mm but it should have been 0.2mm, not 0.032, sorry for the error. 

Peter


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## Pudsey_Bear (Sep 25, 2008)

listerdiesel said:


> If you can measure a single strand of the bundle of copper wires in a cable, you will have the diameter.
> 
> Let's assume you have 16 strands of 0.2mm diameter wire.
> 
> ...


Sorry Peter, I'm at my thickest with maths and Pi is food to me.

I can measure the individual strands as I have a digital vernier, only a cheapo one but should suffice here.

*pi X (R X R)* not a clue what that means, then I'm OK with the rest except *3.142 X 0.01* I don't see where the x 0.01 comes from.

I wish I was clever like you lot.


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## listerdiesel (Aug 3, 2012)

Formula for the area of a circle is Pi X (R squared) or pi X (R X R)

R is 0.1mm (half of the 0.2mm diameter) and if you square it, you get 0.01mm.

0.01mm X 3.142 = 0.0315sq mm for ONE strand

0.0315sq mm X 16 = 0.5040 sq mm

Peter


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## Pudsey_Bear (Sep 25, 2008)

listerdiesel said:


> Formula for the area of a circle is Pi X (R squared) or pi X (R X R)
> 
> R is 0.1mm (half of the 0.2mm diameter) and if you square it, you get 0.01mm.
> 
> ...


Nah sorry, I need to go lie down and try again later, no clue about Pi, I might have to google Pi for dummys.

I think i need to find a local brain and just give them the wire and tell me, as said print it on the wire. simples.


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## listerdiesel (Aug 3, 2012)

Pi is a constant, usually expressed as 3.142 but is in fact 22 divided by 7 which gives 3.1429 on my calculator.

Peter


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## Scattycat (Mar 29, 2011)

rayrecrok said:


> WildThingsKev said:
> 
> 
> > Is this really practical?
> ...


Up until now we have done the same with a slow cooker but having used the Remoska at home and in the van when on mains hook-up I thought I'd give it a try via an inverter when off hook-up, so I bought a bigger inverter to cover it, but may be I've made an error.  Oh well such is life, it's not the first time and probably won't be the last :roll: Ya live and learn as they say


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## listerdiesel (Aug 3, 2012)

After discussions on here about slow cookers, we bought a large Russell-Hobbs unit from Argos, 6.5L capacity.

It's not in the catalogue, only on their ebay shop.

Works well and very pleased with it, but too big for the trailer!

Peter


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## rayrecrok (Nov 21, 2008)

Hi.

They have it easy now with calculators and buttons.. When I was at school all we had for pi was 22/7 as a fraction and a pencil to work it out.. :lol: :lol: :lol: 

ray.


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## listerdiesel (Aug 3, 2012)

rayrecrok said:


> Hi.
> 
> They have it easy now with calculators and buttons.. When I was at school all we had for pi was 22/7 as a fraction and a pencil to work it out.. :lol: :lol: :lol:
> 
> ray.


Yes indeed, AND we had to learn all of the Times Tables as well, but Kev is within that age group....

Peter


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## Pudsey_Bear (Sep 25, 2008)

listerdiesel said:


> rayrecrok said:
> 
> 
> > Hi.
> ...


I can remember the tune but not the words, told ya, crap at maths.


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## listerdiesel (Aug 3, 2012)

Kev_n_Liz said:


> I can remember the tune but not the words, told ya, crap at maths.


Don't feel too bad about it, there's lots of things I'm useless at, woodwork being one of them.

If they did welding rods for wood panels I'd be fine (to quote my good friend Martin Perman)

Otherwise, I did get Tech Drawing and Metalwork O-Levels, failed at Maths but took it again at night school after we had the kids, did English Lang and Maths, got a B and C respectively.

As I do all of the mechanical drawing and CAD work for our company, I have to have all that stuff up top, plus a load of other stuff that is completely useless in a normal motorhome construction environment, like PCD circles and calculations and working with 0.1" pitch for components on printed circuit boards.

Drawing the trailer out took a few months, and we went to quite a few revisions, here is one of the 14 drawings:










Peter


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## Pudsey_Bear (Sep 25, 2008)

I wish I'd listened to what my Grandad used to say.

As for maths my Dad :evil: :evil: was a Meteorologist in the Navy WW1 (it's bad when we started numbering them) and was brilliant at maths, as were my brother and sister, he meted out a clout round the ear every time I got something wrong which did nothing for me, so I hate maths and always will, good memories not.

Truant was my favourite game at school, but I did enjoy English, and woodwork, metal work, left school as a apprentice tool room fitter, day 1 great I got to play with some big brushes, day 2 I got to use the shovel, day three I told them where they could put them. Day 4 I was an apprentice Sawyer, day 5 the guy teaching me got distracted and lost his little finger, that left him with 2 and a thumb on one hand, I didn't stay to count the other hand.

I suppose it could be said that these days I'd be classed as having learning difficulties and I suppose there are those who genuinely have, as for me I was just bored senseless, I've learned more about how to do things in the last 5 years of MH ownership and having to figure out stuff for the self build than I ever learned at school or in my earlier life, these days I can spend an hour or more watching youtube on how to do some aspect of the job with different approaches to doing the same thin with different tools, and I could do that all day every day, but not maths.


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## CliveMott (Mar 10, 2008)

In those terms 16 sq mm is between twice and three times as much copper as cooker cable, and this depends on what diversity factor was applied to the cooker!!

Defo a Gentlemans Club though!!

C.


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## listerdiesel (Aug 3, 2012)

I think we have 10mm T&E on our cooker, and 16mm T&E on the shower. Longish runs so upped a size on the shower.

Less than 10mm on a modern cooker or hob and oven is pushing it a bit.

Peter


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