Hey All..

I thought I would open up a Topic on Inverters for Dummies.. I'm not saying that I'm an expert but I thought I would open up a topic that everyone can put in their 2c's worth.. I can actually think of a few that will help steer people in the right direction..

I'm not going to talk about Batteries Other than the Different common Voltages that are out there 12v, 24v, 48v

I'm not going into the Good or Bad of different types, I'm just going to give you the basic's..

Ok inverter Basic's.. It's a device that converters 1 voltage source to another... the most basic form is an Inverter that convert's 12v dc to 240v~5% AC.

Types..

There are then 2 different form's of Conversion.. Cheapest --->  Modified Sine Wave.. They give a Wave shape that look's like

The Next type of inverter is what they call a Pure Sine Wave inverter..

The Sine wave is What we would see if we put test gear on our own Power point's..[ I Don't Recommend that you do this unless you know what your doing..]

The Sine wave inverter are a bit more expensive than the modified Sine wave inverters but cause less issue with the Gear that you want to hook up to the inverter.. It Like you are plugin the stuff into your own house power point's..

- So if you want to make sure you have a Better[Cleaner] Power source for your Setup a Pure Sine Wave inverter is Recommended..

Ok we have the 2 types of 240vAC inverters, the Next major issue is sizing what you need to have a happy family..

Sizing your inverter..

The biggest issue is that you have to ask your self the question.. What is the Biggest Load I expect to have on the inverter at any Single time..

- I'll throw up an example.. of a Aldi Coffee Machine..

in Standby mode the coffee machine has minimal load..

in operation.. 20 seconds of Preheating and then the Fill of whatever volume of Water.. say 30sec.. of 1000W +/1 100ws[Can't find the spec sheet]

--> The Aldi Coffee Machine has an Auto Shut down function set for 5min of ideal usage..

In this instance if all you were running was the Coffee Machine you need an inverter that can sustain a Load of 1100w of Power.. now due to the power loses involved in these devices it would be a safe beat to have an inverter of 1500-1600w's..

You ask Why I say 1600w's as the inverter size.. Well I would expect while you have the Coffee machine going you might have a TV going or a Radio or such item, it far better to have the EXTRA capacity on hand so that if you are Bush camping you Don't destroy your inverter, therefore leaving you short on not having any 240v power at All..

--> Now when you see inverters advertised in such Place as Ebay or anywhere else they will most probly give you an ad that says some thing Like..

1000W/2000W Pure Sine Wave 12v to 240v Power Inverter

Ok to unconfused the Rating's..

Whether the rating is in 1000w or 1000VA they are both the Same....

Now this Particular inverter will Put out[Handle] a Constant load of 1000w...[What they say] But Will be able to handle a Peak Load of 2000w's for a Short Time [5 maybe 10 SECONDS] they will only handle a Load Larger than 1000w for a fraction of 1 Minute..  You might say, my load is Only 1100w it should be able to handle that load... The short answer is NO.... Any load rated over the MAX Constant Load can and will cause an issue with the Inverter..

Specifications
Maximum Continuous Power: 1000W
Peak Power: 2000W
Maximum Efficiency: >80%
Input Voltage (DC): 12V
Output Voltage (AC): 240V
Output Wave Form: Pure Sine Wave
Socket Type: Australian Standard
Frequency: 50Hz
Weight: 2.7kg
Dimension: 31cm (L) x 13cm (W) x 7cm (H)

For the above mentioned inverter I have copied the Specifications of the inverter..

For this inverter in the worst case situation it is actually using .. 1250w of power from your battery system..

Now the Supply voltage of this inverter is 12v's, which is the most common voltage for Most RV's that are out there..

Another issue in sizing the inverter is... HOW many Amps does it draw...

In the situation of the Aldi Coffee Machine at Say 1000w's for 30sec[When the coffee is being made] the inverter is using 1250w of power for 30sec..

or 1250w/12v to give you a sum of 104A for 30sec's..

This is were I get not 100% sure But I'll try..  for the one cup of Coffee the inverter will draw off [ 104A X [30/3600] to give you a figure of 0.86 Ah of Power[ there are 3600sec in 1hr]..

So for a single cup of Coffee you will draw 0.86Ah from your battery..

Now the other side of the scale is if you bought yourself a Better Quality inverter.. and you also had a 24v battery system.. Just by having a 24v system you drop the amount of power that you draw from the system by 50% because you have twice the voltage, therefore half the Amp's...

1250w/25v = 52A..    [52A x [30/3600] = 0.43Ah..  for for a 100Ah battery if you took it to a max of 50% State of Charge == 116 cups of Coffee..

One very important issue between the Big major difference between a 12v and a 24v Inverter.. The MAX expected Load in  Amp's[A's] between the 2 is the amount .. A 12v system draws 2x the Amp's therefore the size of the cable that you need to have are Larger than those that you need for a 24v system..

Most Inverter will come with a set of cable that the manufacture recommend for the Inverter.. They will be a set length and set size.. Some inverter will come with 2 or even 4 sets of cable depending on the Size of the inverter.. The reason that they give you the cable is So that you have to mount the inverter within a Set distance from the batteries..    IF you mount the Inverter Further from the Batteries than the cable are, you will need to ask/find-out what size cables you need to run so that the inverter runs correctly.. [there are a few factor like Load, and Cable loses[Voltage drop] that come into play]

>> One issue with the cable size.. The Higher the Source Voltage[24v over 12v] you the Smaller the Supply cables become [ dependent on Load and Distance ]

Addition to Cable selection.. A Website I found with a Calculator..

Cable sizing

Re: the Cable Length Runs you need to Account for the Distance x2  there and Back.. to get an accurate valve.. Also My own Personal rule of thumb Only allow for a voltage drop of LESS than 2%, it means that you will be running a heavier cable, But I feels its better to be Safe than sorry..

 -- Think of this.. If you are running AGM batteries and you have to high a voltage drop the equipment might be expecting to see 12v and it might only be getting 11.5v

J

RE the Fuses.. the Fuses are Rated to Protect the Cable..

Ok so we have discussed -

The Type of the inverter : Modified or Pure sine wave[Which I recommend]

The Size of the inverter : I recommend at least 20-30% above what your expected MAX Load..

One issue that crops up.. What can I plug into the inverter...

-- Their are different class of Electrical gear out there.. Most common forms are Class 1 and Class 2..

Class 1 gear is distinguished by have an EARTH Pin.. [3 pin Plug]

Class 2 gear is only the other stuff with 2 pins.. Phone chargers, Laptop chargers etc..

The recommendation is that you only Plug in 1, yes I said 1 Class 1 piece of equipment into the inverter at a single time..

You can Plug as many Class 2 items into the  inverter as you Want... [ I DO NOT recommend that you use Double adapters or Power boards Plugged into Power Boards like a Daisy Chain.... Not a Good Practice..

With the changes of the types of system that are now beginning to show up in the RV Market where Inverters are being hard wired into the RV's and connected to Power Switchboards with Circuit Protection, you still have to Look into the what you are operating.. For example a Standard GPO is Rated for 10A's of power.. That is 2400w's of Power...  If the Cabling has been configured to Australian Standards it Should be heavy enough to handle the number of Power Point's in the circuit with their expected load..

Now unless you have a huge inverter[3000w constant plus] I would not expect the inverter to be able to handle the expected power demand's.. Must also remember the higher the demand the Larger/More the Batteries you need..

There are a few of the newer models of Inverter that give you the Ability of having the power come from a different Power source.. External to the batteries.. They have a system of sensing if they are plugged into the External Power[Grid connected or Generator]  -- > [Be-careful some of these Inverter are extremely sensitive to the Power from generator's[ sine wave type]

These Inverter can have a Battery Charger inbuilt into the inverter which comes in handy as it give you the ability to charge your batteries..  One draw back is that if you Blow something in the inverter, You will have no 240v unless you have a spare inverter..

Some extra functions of the inverters..

- Power saver Mode...  unless the Power is over a certain Load the inverter will not turn on.. it basically goes to sleep[No Power Draw].. Which can be Good as an inverter in standby mode will have a Small Trickle draw while it's doing NOTHING.. So unless you physically turn the inverter of it will draw a small charge off the batteries.. Typically about 1A maybe even more..

~~~~~~~~~~~~~

I'm not sure if I've missed anything.. If I have just ask and if I don't get back to you I bet some of the Other will..

Juergen

-- Edited by SnowT on Monday 14th of July 2014 02:28:18 AM

-- Edited by SnowT on Monday 14th of July 2014 02:58:35 AM

-- Edited by SnowT on Monday 14th of July 2014 04:10:36 PM

Added in Cabling Size chart..

-- Edited by SnowT on Monday 14th of July 2014 04:30:18 PM

Added VA Description..

-- Edited by SnowT on Monday 14th of July 2014 07:42:50 PM

HI Snow

A good post  which I am sure many will find interesting

But recheck your [quote}" You can Plug as many Class items into the inverter as you Want" [end quote],you left out the 2

Yes, some gear will require at least  NEAR pure sine wave

Some will run  on not so pure sine wave but may overheat OR simply malfunction

The correct terminolgy is:

[a]Square wave

modified SQUARE wave [sine waves do not need to be modified]

A modified Square wave can vary greatly in its wave form depending on how many steps there are in the wave form .

They can also lack any real smoothing,so have sharp rise rates in each step  this can be detremental to some gear .

[c]A "pure" Sine wave inverter has many, many, steps with smoothing of those steps  to reduce the flat sections

Rating

The next thing to consider is the inverter rating

It will have two ratings

[a]The continious rating  is that load IT can handle indefinately, without overheating.

That cannot always be considered as a simple WATTS loading ,as the actual Amps loading is the heating factor 

Inductive loads[ motors are a typical example, but Switch mode devices also have PF]  will draw more  current than the Watts rating of the motor/device   would indicate due a condition called "power Factor"

Pf can vary from around 0.5<,1.0

At 0.5PF  the actual current for a 100W device will be double the calculated current using the simple Watts/volts  rule

[bThe short term overload or surge rating 

This is the load that the inverter can handle for a specified time with out damage, with low thermal mass devices such as inverters it is usually only for a few second.

This is for such purpose as Motor Starting where the motor should be up to speed within a few seconds

[c]  within those limits there are small degrees of overload that can be tolerated for SHORT periods, exceed  those limit s& the inverter should trip out to protect itself

The load rating of a device /appliance includes it losses

If It is rated @100W that is the load it will put on the source[ inverter]

If the inverter is rated@ 100W Continious,It should be able to run that 100W load without over heating ,however ambient temp can come into the picture so it is best to have a margin of safety in the inverter rating for those situations.

Inverter Efficiency

Depending on quality Inverters have a load efficiency usually ranging from  80% to 90%

That simply means they have internal losses  when under  load of  of 10 < 20% of that load

If the load is 100W they will draw 110 <120W from the source

If the voltage ,[under load  of 100W] at the inverter terminals is 12.6V , they will draw is 8.73 A<9.52A

If the  voltage at the inverter terminals is 11.6V, they will draw 9.48A<10.34A

PeterQ

hako wrote:

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Can something be added re 12V cable sizing from battery to inverter plus fuse size required to operate with please.
I bought a 2000/4000W unit which required starter motor thickness cables plus a 200amp fuse otherwise it overheated the cables.

---

 I see if I can re-find the information that I used for my system..

Re - the Fuse Size..  All the Fuse is for is to Protect the Cable... At least that was what I was taught at trade school..

I see if I can find the information..

And yes Peter I'm Glad you added to the Topic..

Juergen

SnowT wrote:

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SNIP 

Re - the Fuse Size..  All the Fuse is for is to Protect the Cable... At least that was what I was taught at trade school..

 

I see if I can find the information..

And yes Peter I'm Glad you added to the Topic..

 

Juergen

 

Thanks Juergen - I thought it was to protect the appliance?....anyway, I found that when I used thinner cable and a 100amp fuse, both cable and fuse were hot  so I doubled the sizes of both and then they stayed cool till the inverter died. This was with a 2000W PSW inverter.  

Regards 

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Mike C wrote:

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Confused... mine is a Victron 3000 VA inverter Charger so how many watts is that?

cheers

Mike

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HI Mike

Unfortunately there are two ways of rating Inverters & generators  that nan be in watts /kWatts  or Va/kVA

To Find the watts rating the specs should indicate at what Power factor PF the kVA rating applies

It is usually around 0.6PF ,that would give a WATTS rating of 1800Watts

kVA 3000  x by PF 0.60 = 1800W

PeterQ

Countrytech wrote:

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A question on where is the best place to mount the inverter. Ideally close to the battery is advised, but there are suggestions that it is not advisable with regard to battery emissions, in a confined space. How to determine a 'closed space'. Is the front boot of a van, with 2 sealed lead acid batteries, a suitable place? Is an enclosure within the van, containing a SLA battery, but having some air circulation ok? Is under the bed, with inverter and batteries a safe place? I have seen all these situations, but would like to know which is the recommended mounting place.

Thanks

John

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 Hi John

Any electronics do not like Acid fumes

Flooded wet cell batterries near an inverter is a definate NO NO .

So called seal batterries do still have vents to release gas pressure, if required.

The other slight risk is an explosion due to hydrogen gas emmisions from the battery.

Best that the inverter be well shielded   from the battery comprment. so no possabity of fumes/gases  getting to the inverter

The requirement to be as closes as PRACTICAL to the battery is due the voltage loss in the 12V connecting cables

That loss can be compensated for with HEAVIER cables  , the actual conductor size will depend on distance [cable length] & MAX current to be drawn .If  

PeterQ

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hako wrote:

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Can something be added re 12V cable sizing from battery to inverter plus fuse size required to operate with please.
I bought a 2000/4000W unit which required starter motor thickness cables plus a 200amp fuse otherwise it overheated the cables.

---

---

HI Hako

The Actual cable size [Coppper cross sectional area] depends on length of cable & MAX current the cable will be requires to carry

Cables that are too small for the current can l give two problems:

[1]They may overheat

[2]THe voltage lost in the cables will do two things ;

[a]The inverter attempts to draw even more current to supply it's load with a degrre of snow balling .

The more it draws to more the voltage drops until something happens

Either the Supply fuse blows or the inverter shuts down on UNDER voltage to protect itself from burn out

The voltage X by current is energy lost in the form of wasteful  cable heating.

 

The supply fuse should be at the source to protect the cables

  It's rating should be NO MORE than the cables continiuos rating, corrected for ambient temp, or lack of free air cooling.

It can have a lower rating to match that of the inverter ,as ADDITIONAL protection, but they do have their own  internal fuse protection 

That only applies if the inverter is the only load on THAT circuit.

 

That 4000W inverter could draw a peak current of 380/400A[If due to voltage drop in the cables the actual voltage at it's input wasdown to10.6>10V  

 PeterQ  

I

Just found the spec sheet for the Victron Quattro Unit I have

Cont output power @25c (VA) 3000
Cont output power @25c (W) 2500
Cont output power @40c (W) 2200
Peak Power (W) 6000

So assume the PF must be around 0.833

Why don't they simply stick with one unit of measure... or is it that 3KVA sounds more powerful than 2500 Watts?

Cheers

A slightly more educated (but still confused) Mike

Mike C wrote:

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Just found the spec sheet for the Victron Quattro Unit I have

Cont output power @25c (VA) 3000
Cont output power @25c (W) 2500
Cont output power @40c (W) 2200
Peak Power (W) 6000

So assume the PF must be around 0.833

Why don't they simply stick with one unit of measure... or is it that 3KVA sounds more powerful than 2500 Watts?

Cheers

A slightly more educated (but still confused) Mike

-- Edited by Mike C on Monday 14th of July 2014 09:07:04 PM

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 Hi Mike

I thnik some do fall for the kVA rating being bigger & better

In the past All Ac power generating sources were rated in kVA.Even power houses were quoted as xxxx mKVA,  Now virtualy all use mW

But it has been the general practise for quite a while to use the more understandable Watts method

PeterQ

Mike C wrote:

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I could make a fortune by putting 2KVA stickers on 200W inverters just have to add PF 0.1 in the small print :)

---

PeterQ

Thanks to all of you Fellas for educating a genuine electrical/electronic dummie especially SnowT for getting it started

Thanks

Friar

Hi Guys

Thanks for that. These bloody inverters have been a thorn in my side for ages. The prospect of cables CSA has raised its ugly head, when I was installing in industrial and domestic installs, we used maximum demand as in AS3000 as the guide to cable cross section. It was related to length of cable run, maximum expected current, etc.

As far as DC is concerned thats a new can of worms, we have a 2500W (not VA, it says) inverter two 12mm sq cables on both pos and neg terminals, cable length is about 400mm, expectation from me is not too much volt drop at max current.

This is the big deal for DC applications as the higher the wattage device the more current it draws thus heating the cable and causing more ohm's law volt drop (not nice) V = IxR. Imagine 200 watts on 12 volts a lot of amps.

Anyway, thanks to all for the enlightenment.

Safe travels

Mike C wrote:

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I could make a fortune by putting 2KVA stickers on 200W inverters just have to add PF 0.1 in the small print :)

---

Hi Mike

[1] The cause of overheating in any electrical device  is excess current [Amps x Ohms{Watts} heat generated in the components

[2]A little futher SIMPLE explanation 

[a]AxAxR=Watts

AxV=Watts

[c]AxVx PF =Watts

[3]AS you can see in each of the above Amp  is a factor

Now PF is the result of the current lagging the voltage due to inductance

That simply means that a PF of 1.0 the current a voltage peak together on each half cycle[10A at 240V =2400W]

All the curren tis being supplied at full voltage

But with a PF of say 0.5, the Current peak is delayed until after the voltage peaks [ by 50% in each cycle] 10A At 120V=1200W

With a PF of 0.1 = 10A x24V =240W

Taking the last case you can see that the power is actual =1A x nominal  240v =240W

That apparent  extra 9A that would be flowing is referred to as WATTLESS current,   since it does not have a voltage component, it has no energy

But look again at [1][a]that Current still has to obey that law , the souce winding have resistance  lets say that is 2 Ohm thn Ax AxR =10x10 x2 =200W

Tthe losses as heat in the  SOURCE windings is the same no matter watt the PF of the load. 

Be aware it is the inductive load  that has the PF generating effect

How is that for confusion

PeterQ

hako wrote:

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Here's something to ponder: what happens when when you have loose or corroded terminals....how will that effect the fuse and cable. I know from experience both will get very hot despite not being overloaded. How can one ensure the connecvtion matches the cable/fuse?
Regards

---

 Hi

What actual happens will depend on the resistance in that connection

If 10A is flowing & the connection has 0.5 Ohms resistance ,then the heat generated in that very localised area would 50W

This would apply even if the cable rating was far in excess of 10A the cable size only effect is possible conduction of some of the heat away from the actual faulty connection & THAT usually means damaged insulation, even further encreasing the risks [possibly of short circuits]

50 Watts of very localised heat can get very hot, just consder a 50W soldering iron or even a 50W light bulb[although a lot of that 50W isused generating light]

Fuses' circuit breakers cannot detect localised heating , that heat ,to them is just the same as the load [solderig iron]

The localised heat will oxidize the connection ,encreasing the resistance, which will / may reduce the current a little, but actually  the effect will snowball ,getting hotter & hotte ,rPossibly resulting in a major fire 

.There realy is no protection against overheating connections causing fire, except assembling/  maintaing ALL connection with  a Clean contact to contact face & TIGHT.

THe best way to mimimise the problems are:

[1] use connections that are rated no less than the cable rating 

[2]Ensure cables & all connection contact faces are clean bright metal  

[3]Ensure they are fully tightened  ,

oops I see Snow just beat me 

PeterQ

Hi

Informative posts all.

However there is one thing that has not been said about inverters. Safety !! They put out 240volts just like the mains and can kill you just like the mains power. HOWEVER the mains have an earth connection and possibly an earth leakage shut off to protect you in case of a fault in the appliances or the like. A stand alone inverter (or a generator too), do not have these protections. If you get an appliance fault then it could be live and no fault would be noticeable!! Being inside a metal frame or metal case would mean that you could get a circuit if you touch it. Care is always good but more so with these situations. Water spilt or rain is to be avoided also.

Take care Jaahn

Bravehearts wrote:

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Hi to all, please forgive me as I am still a little confused. My van is 18months old and I have two 80W Solar panels, two brand new 120amp hour heavy duty batteries (I replaced the single marine type battery supplied with the van) and a 600W pure sine wave inverter connected to the batteries via fused (50amp) cables. The inverter and panels were supplied by Jaycar and fitted by a recognised Solar Company in Gin Gin, Qld. I also have a 2KVA Honda generator. My issue is when we are in a area where we are not allowed to run the generator (e.g Seaforth Council Parl near Mackay) and

[1]I want to run the washing machine (which is a top loader small capacity fitted in the ensuite)

[2] what is the correct method of operation. I have been told the inverter could be hard wired into the 240v power system via a registered sparky,

[3]or altenativley I could have a cable made up to plug into the inverter and then a plug fitted to the other end to plug into the van which would then make the entire system 240v.

However I believe such a cable is not legal, although I have seen them used.

[4] Another suggestion was to purchase an Amphibian Cable which is legal and simple plug that into the inverter and then into the van power inlet point

[5] I have contacted four companies who advertise themselves as RV/Caravan Solar specialists and I am still in the dark as I cannot get a definitive answer from anyone. I would greatly appreaciate any advice on this.

---

Hi

[1]It will be case of trying the washing machine on that inverter & see if it will handle it OK

It may be best to alaways start it with no load in the machine whenever possible Doing that will reduce the START up load on the inverter

[2]Yes, it can be hardwired in by a registered sparky, who understands the requirements of the Standard AS 3001[Many have no experience with THAT standard]

It will envolve change over switching to ensure the RCD/Safety switch is fully functional

[3] Anyone who makes up such a lead should be shot,  such leads are potentially DEADLY & are forbidden!

!Do not even THINK of such an arrangement 

[4]THat would have little advantage as the RCD/ safety switch will still not be operational

[5]Not surprised

Now the best /safest way apart from [2] Is to simply plug the washing machine  drectly into the Inverter[you may use a short extension lead if necessary]

One safety recommendation should always be considered when using"Portable inverters "[not permanently wired in as in {@] above

IS :

Do not connect more than ONE class 1 appliance [have a 3pin plug] at any time

BUTyou may connect more than one if they only have a 2pin plug 

Hope that helps

PeterQ

it

Jaahn wrote:

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Hi

Informative posts all.

However there is one thing that has not been said about inverters. Safety !! They put out 240volts just like the mains and can kill you just like the mains power. HOWEVER the mains have an earth connection and possibly an earth leakage shut off to protect you in case of a fault in the appliances or the like. A stand alone inverter (or a generator too), do not have these protections. If you get an appliance fault then it could be live and no fault would be noticeable!! Being inside a metal frame or metal case would mean that you could get a circuit if you touch it. Care is always good but more so with these situations. Water spilt or rain is to be avoided also.

Take care Jaahn

 

   

 

 

 

-- Edited by Jaahn on Friday 18th of July 2014 09:34:55 AM

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Hi Jaahn

YES , a timely warning & it does not just apply to inverters

IT also applies to portable generators

See  my last post

PeterQ

Peter