# Inverter !



## TonyH (May 1, 2005)

Please can someone explain the principal of Inverters ! All I wanna do is look at TV so what type or size would i need and is the inverter connected to battery constantly ?

Tony.


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## 96088 (Aug 22, 2005)

TonyH said:


> Please can someone explain the principal of Inverters ! All I wanna do is look at TV so what type or size would i need and is the inverter connected to battery constantly ?
> 
> Tony.


Hi Tony...

Before the experts arrive and give you the 'full picture'

Check this link that was posted yesterday...

http://www.ccis.com/home/mnemeth/12volt/12volta.htm

It is american though and quotes 110ac as opposed to 230ac


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## 88966 (May 11, 2005)

Hi TonyH,

Nothing much wrong with that link.

However to answer your question as succinctly as I can without going into detail.
An inverter creates 240v AC from 12v DC.
The size of inverter depends on what you want to use it for - a good general purpose size that will handle things like, laptop or TV or phone charging, etc is a 300w. You can run a number of things as long as they don't total more than 300W

As the battery drain current for one of these can go as high as 25 amps (depending on load) it is best to keep it as close as possible to the battery. Inverters usually have a switch on them so it can be permanently connected to the battery, via a fuse of course.

If there is anything else don't be afraid to come back.


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## 96414 (Oct 1, 2005)

Hi Tony

A 100w or 150w would be best for a tv setup, this will be more than enough for any portable TV, these sizes do not have fans an so are quieter and more economical. They can be switched (some actually include an on/off switch.

Reference the 300w that BillD mentioned these can take around 50 Amps on surge (600w)


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## Scotjimland (May 23, 2005)

Hi Tony 

Bill has covered it very well, all I would add is that there are two types. 

1.Pure Sine Wave and 
2.Quasi Sine Wave.. 
I won't bore you with the techno talk.. 

The Quasi Sine is perfectly adequate for a TV but for more sensitive electronics a Pure Sine would be advisable.. 

The price difference reflects this.. a 600 watt pure sine will cost over £200 
A quasi sine wave about £100 or less 

As already said, ask if your unsure.. 

Jim


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## 88966 (May 11, 2005)

Hi Tony,

I tried to keep it simple and straight.

I maintain, as the price is also very little difference for the extra capacity, a 300w is a good general purpose size. If you want to run a TV and a digibox and/or a DVD player plus possible having your laptop on charge and maybe a mobile 'phone you cannot do that with a 100w or 150w. I don't know what book George has been reading to get a 50 amp surge from, I have never seen anything like it, on no load which they are when you switch on the load is negligible.

I have never used anything other than a cheapo inverter, for several years, with a laptop, etc and never had any problems.

I can only tell you what works for me.


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## 96414 (Oct 1, 2005)

Hi Bill, all

Nearly every invertor available gives double the rating available as surge, ergo a 300 watt invertor will generally be good for 600w for short bursts and therefore 600 watt divided by 12v = 50 Amps. If you look at any invertor specs you will see what I mean.

The reason's I suggested 100w are as follows

1. Nearly all invertors are most efficient at 50% of their normal rating.
2. The original poster asked about running a TV, an average Portable TV is 50 Watts so even with 100 watts there would be some spare capacity for running phone chargers, a TV and DVD or VCR player will both run from a small invertor with no problems.
3. the smaller invertors do not have or require a fan and therefore are even more efficient and importantly a lot quieter.

I have run a TV and DVD player many times from a 150w Invertor, also my Laptop and sat nav gear, the original poster only asked about TV, so a 100w will do that and more.

Here is a bit more info on invertors

http://www.sterling-power.com/htm/inv.htm


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## 88966 (May 11, 2005)

Hi TonyH, 

Have you got enough info. to be going on with, before this gets long-winded? 

George. 
I know what Tony asked but it is my experience that tells me that most people when they have an inverter suddenly find lots of other things that they want to plug in and it makes more sense to do them all at once. If they have started out too small they then have to buy again. Besides there is very little difference in the quiescent current at these small sizes. And if you read my answer to his question carefully you will note that I was giving an example. 

Check your figures again and you will find a TV, digibox and a decent laptop on charge will come to more than 50% of a 150w inverter (in fact probably more than 100%). As for fan noise, it is barely perceptible. 

It would be very bad practice indeed to run any inverter at double it's rated output. Surge current is usually limited to 150% of rated and it is only intended for instantaneous surges such as a microwave starting - not likely to be a factor at the level being talked about.


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## olley (May 1, 2005)

I bought a 300watt inverter about 3 years ago, plugs into the cigar lighter, used it to run desktop computer in motorhome, charge phones ect. never had a problem, when its only drawing small amount of power the fan dosn't run.

If you get one to small you will only end up buying a bigger one, I would suggest 300watt as Bill recommended.

If you going to wire it in permanently i would go bigger 1000watts or so. its something you can remove and take to your next van, and who knows what size you would want then. You might need one for a 42" widscreen telly perhaps.

Olley


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## TonyH (May 1, 2005)

*Inverters*

Hi Guys ,

Thank you all so much, appreciate all the info.

Tony.


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## 96414 (Oct 1, 2005)

Hi Bill

My figures are correct Bill I am answering the question that was asked, *All I wanna do is look at TV * He seemed pretty specific to me about his requirements and if thats all he wants buying bigger is a waste of money and battery power.

Nearly every invertor (decent anyway) as a surge capacity of double its rated output, its there for a reason and its not bad practice to use it, thats what its designed for.I personally have 4 different invertors from 150w, 300w 400w 1500 watt. I have set up invertors in 8 vans, for friends and relatives, and also sorted out the mains/invertor requirements of several people online. I have just unwrapped a new Nikkia from maplins Cheap (but good invertors) and their surges are as follows 150w as a surge of 450w, a 300w invertor as a surge of 1000w, because they use a slow blow fuse the 150w as a 20A fuse and the 300 watt as a 35A fuse.

For a TV 100w is more than enough, even if you wanted to add a DVD 100w OK, watching TV and Charging a phone no Problem, TV and freeview box still no problem, most laptops would run and charge from a 100w too, but if you want to use a laptop, I would recomend a 150W

Though microwaves are off topic here. Just to set the record straight as you have already mentioned them.
Say you have a 750 Watt Microwave it will use about 1050 Watts all the while, the reason is not start up current, 750 Watts is the cooking wattage (output) it takes roughly 50% more mains in to get that output.* I have measured several modern microwaves to be sure. *


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## 88966 (May 11, 2005)

Goodnight George.


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## 88966 (May 11, 2005)

Hi George, 

I am afraid I must not let such potentially dangerous and misleading information go unchallenged. 

To quote Maplin's website : 

"Care should be taken that the appliance that you wish to run from the invertor does not have a power rating greater than that of the invertor itself." 

The figures you quote (and recommend using the surge capacity of): 

" 150w as a surge of 450w, a 300w invertor as a surge of 1000w, because they use a slow blow fuse the 150w as a 20A fuse and the 300 watt as a 35A fuse." 

Taking your quoted 150w Inverter, its normal full load current will be approx.15 amps (using Maplins claimed 90% efficiency) a usable surge of 450w would require a fuse of at least 40 amps - I think not. You say it has a fuse of 20 amps - this will allow a surge of approx. 33% - more realistic. 

Now taking your quoted 300w inverter, its normal FL current will be about 30 amps - therefore with a fuse of 35 amps it is allowed a surge of about 20%. Not unreasonable. 

Most people are capable of reading the label that gives the power requirement of their equipment and can add together the likely max. load. I leave it their good sense to decide whether it is better to run using the surge capacity (as you appear to recommend in one place) or keep well with the rated capacity (as you recommend in another place). 

I don't know who these people are but I would recommend they check their setups very carefully: 

"Nearly every invertor (decent anyway) as a surge capacity of double its rated output, its there for a reason and its not bad practice to use it, thats what its designed for.I personally have 4 different invertors from 150w, 300w 400w 1500 watt. I have set up invertors in 8 vans, for friends and relatives, and also sorted out the mains/invertor requirements of several people." 

If people are in any doubt about anything involving 240 v electricity I advise talking to a knowledgeable friend or professional.


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## 96414 (Oct 1, 2005)

Hi Bill

*"Care should be taken that the appliance that you wish to run from the invertor does not have a power rating greater than that of the invertor itself." *

The specs inside the box state that is designed to have a surge capacity of 450w on a 150W invertor,so its not greater than the invertors rating its designed in.

To understand the fuse rating you need to know a little about fuses, the 20 Amp fuse is of a slow blow variety.

Surge capacity is there for starting any item that needs a surge of power to get going, not for the continued running of any appliance.

There is not any potentaily dangerous or misleading information in *my* posts here.

Here are a few specs for Nikkai and other invertors

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=4578426144&category=36798

http://cgi.ebay.co.uk/1000Wpk-INVER...4585028821QQcategoryZ1294QQrdZ1QQcmdZViewItem

http://cgi.ebay.co.uk/1500-600w-INV...009850478QQcategoryZ76066QQrdZ1QQcmdZViewItem

Sterling

A high surge capacity is essential. In order to cut production costs, many manufacturers give little time to surge capacity. This is a false economy as it limits the ability of an inverter to start equipment such as drills, computers, and refrigeration compressors. It may therefore be necessary to purchase an inverter with two or even three times the output, simply to do the same job. *It is important for an inverter to be able to safely treble its rated output for a brief period to start some everyday equipment.* The cost of building the ability to deal with this surge start into an inverter is considerable and many manufacturers are reluctant to meet the expense which can increase the manufacturing cost by as much as 200%.

Victron p25 of this

http://www.victronenergy.com/upload/documents/Manual-ML-MultiPlusIni.pdf

Mobitronics (these are not so well endowed with surge)

http://www.onboardenergy.com/acatalog/Mobitronic_Sine_Wave_Inverters.html

Note all the Facts and evidence support my case, I do wish you would stop turning every post into a battle, especially when you get it so wrong every time.


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## 88966 (May 11, 2005)

George,

You say, 
"Note all the Facts and evidence support my case, I do wish you would stop turning every post into a battle, especially when you get it so wrong every time."

If you read back this thread you will recall that I offered some simple and sound advice to someone who obviously was looking for just that. It was you who came along with your arrogant and pedantic arguments.

I will leave it to other people to judge whether my advice based on an electrical engineering training and many years experience is the more sound or yours as a self proclaimed accountant.


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## 96414 (Oct 1, 2005)

Hi Bill

I also offered some simple to follow pointers, you then decided to dispute what I said and also to claim what I have said is dangerous.

That is why I linked to information to show that the information I presented is not misleading or dangerous and that in fact you are mistaken.

I also am qualified in electronics and engineering, but thats not really important here, anyone can read the links that I have provided and see clearly that *you* do not understand Surge ratings, you have no idea at all about fuse ratings and blow rates. And that your absurd claims that I have posted misleading or dangerous information are unfounded.

If you are qualified (I find it very hard to believe after all the basic mistakes that you make in this and other threads) then you are not very good at it at all.

Quote
*
Taking your quoted 150w Inverter, its normal full load current will be approx.15 amps (using Maplins claimed 90% efficiency) a usable surge of 450w would require a fuse of at least 40 amps - I think not. You say it has a fuse of 20 amps - this will allow a surge of approx. 33% - more realistic. *

Here is a link showing why you are mistaken on the fuse sizing, note the continuous and fusing ratings, unfortunately it does not quote the slow and fast blow ratings

http://www.vehicle-wiring-products.co.uk/VWPweb2000/fuse-2/fuse-2.html

If you are going to diasgree with me, at least show some evidence.


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## spykal (May 9, 2005)

temporary said:


> Here is a link showing why you are mistaken on the fuse sizing, note the continuous and fusing ratings, unfortunately it does not quote the slow and fast blow ratings
> 
> http://www.vehicle-wiring-products.co.uk/VWPweb2000/fuse-2/fuse-2.html
> 
> If you diasgree with me at least show some evidence


Hi George

I obviously don't understand fuses either...but I thought I did until I read this thread ...are you George, saying that it is Ok to use fuses above their rated capacity just because they do not actually blow until a much higher figure.

here is a link that I would like you to read ..I know you like evidence :lol: and it is for those of us more into horses mouth information (fuse manufacturer)

>>>>Fuse PDF<<<<

the manufacturers spec sheets seem to offer different advice

From the first page of the PDF:

_*Derating
In general it is recommended that fuses should be operated continuously at no more than 75% of rated current, in 25c ambient...etc

and further on

Slow blow fuses are more sensitive to heat and usually require a greater degree of derating*_

Give it a read George and comment please....I was taught as a rough guide to use a 20 amp fuse in a circuit which was never expected to exceed a 15 amp load, I do know that it is at higher figure than 20 amps that the blow will take place ....but I was also taught that if a fuse is taken to anywhere near its rating, degradation of that fuse will take place each time this happens and its rating will no longer be safe....and according to the PDF I have posted Slow Blow fuses need even more derating so maybe a slow blow 20 amp fuse should never be run at a load higher than say 12-15amps.

Mike

P.S. to tony....do what I did and wait until Maplin do a special on either the 150 or the 300W invertor ....I bought the 300W one when they were priced at just £20 and it is just fine.... the fan only comes on fully with a big load so it is totally silent when used with my canon printer that I carry to print photographs and A4 OS maps of the local area.


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## 89122 (May 14, 2005)

We are not going to go through all this again are we ?


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## spykal (May 9, 2005)

a helpful post eddie? I suppose so, well meaning anyway :lol: But you see today I don't have better things to do so I thought I would go in for a bit of S. I. P. and also I do like things to be neat and tidy and this thread is a mess.

mike


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## 88790 (May 9, 2005)

Very simple, I use a 150watt inverter to power my Sharp 15" LCD tv and DEC freeview box. There power consumption is well within the 150 watt limit and gives me no trouble.

John 8)


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## DJP (May 9, 2005)

*My 2p's worth*

As the post started all I wanted to do was run 15" LCD TV and maybe sat system OR DVD from an inverter. 
I bought a 300w inverter which worked fine for an hour JUST running TV. No lights NOTHING else, then TV switches off, showing signs of a flat battery. But lights work ok. Start engine tv works fine. Switch engine off tv goes off after 5 minutes. 
So I THINK inverter is not man enough (not be a electronics wiz) and go and buy a 600w fan cooled. It was WORSE 10 minutes and TV goes off. 
Have 2 x 110 amp leisure batteries checked OK, charging system checked OK 
I then decided to connect inverter DIRECT to battery and NOT via cig accessory plug into tv point as I had done previously. WORKED PERFECTLY.

So had cig socket checked out. It was a simple case of the additional cig socket installed by dealer had been wired using to low a amperage of cable creating a higher resistance? (At least thats what they said) They rewired with a higher rated cable and it's now working fine.

So, if you are using an inverter which is NOT connected directly to you leisure battery, take advice on the correct amperage of cable to be used. 
I am sure one of the "qualified" posters previously on this thread will be along and tell us how to calculate current drawn x resistance x cable length x inverter size = how thick it should be and maybe even what color to use and whether the connectors should be gold or not. 
Gets me coat and leaves


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## spykal (May 9, 2005)

Hi DJP

I had the same sort of experience recently with the cigar lighter socket in the cab...the one I use to power the laptop while on the move. It had always been just fine but then The Laptop kept complaining of low voltage whenever I stopped the engine (it beeps annoyingly). It turned out that the spade type of connection onto the back of the cigar lighter had become "high resistance" (a bad connection in english) and the only time it was giving enough " umph" to the laptop was when the engine was running and the voltage was a little higher.....It took longer to find the fault than fix it...all it needed was a good wiggling to clean it up...been fine ever since. 

Used into a cigar lighter socket I think that inverters can draw currents which are pushing the cigar socket to its limit....but it does make them easy to use so i'll stick with it I think.

Mike

P.S. No qualifications to speak of but lots of experience some of which I refuse to share on the grounds that it may incriminate me :lol: :lol:


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## 96414 (Oct 1, 2005)

Hi Mike

Quote

*are you George, saying that it is Ok to use fuses above their rated capacity just because they do not actually blow until a much higher figure. *

Yes I am saying that, because in practice Invertors that are OK to Surge to way above the rating of the fuse work, because for short periods it is OK. And on Invertors it works does it not? Are you going to claim that all the invertor designers have got it wrong? (nearly all some overate by a big margin too)

Sterling Use a 300 Amp fuse when the max surge is 238 Amps, but you have to remember fuses are there to protect cables, the invertor as its own protection.

Nikkia use a 20A fuse when the max surge is 37.5 on the 150 W invertor and on the 300W invertor with a 1000w surge they use a 35A fuse when the surge suggests 83.3 Amp fuse.

OK this may go against what you are taught *BUT* it works

Mike I notice you have a Nikkai have you left the fuse that came with it in place? or have you changed it to how you were taught? I would Imagne you have trusted the designers to have known what they were doing.

Invertors will generally shut themselves down if you use the surge for to long, I have never known an invertor fuse to blow, I have seen many overloaded and shut themselves down. The fuses we are discussing here are to protect the cable, most have thermal or overload shut down to protect the invertor.

Personally if I was protecting a circuit that I had set up I would use a fuse nearer to your suggestion ie a 20 amp to rptect a 15 Amp cont load.

When using an invertor I use the fuse reccomended by the designer and If I ever hardwire an invertor in it always as the correct fuse wired into the circiut ie if they use a 35 Amp Blde thats what I use.


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## 96414 (Oct 1, 2005)

Hi DJP

Thats a very good point, in reality its best never to run an invertor via a socket that the motorhome manufacturer as fitted, I have never yet seen one with a decent thick cable.

The Nikkai 300w as a 35 Amp fuse when connected direct to the battery, but they include a 15A fuse for use with cigar lighter plugs, but this would be for the original vehicle cigar lighter, rather than the light duty accesory sockets in the rear. Distance and voltage drop is a major issue here too.

In all the motorhomes that I have fitted these in, I always hardwire the invertor as close as possible to the Battery and have never had a problem. Keep the leads as short as possible, shorten the supplied leads if you can every little helps. If you want to change and improve the situation shorter and thicker cable than supplied and you cannot go wrong.


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## spykal (May 9, 2005)

temporary said:


> Mike I notice you have a Nikkai have you left the fuse that came with it in place? or have you changed it to how you were taught?


Hi George

to be honest I have not even looked inside the cigar plug to see what rating the fuse is, in there :lol:

Another thing about it is that most of the stuff we run from our invertors is everyday stuff so if it packs up because the fuse has got tired ..so what.. the fuse finally gives up the ghost so what...no problem..... fit another fuse.

But if you are a motorhomer just reading all of this please don't listen to any of the crap on here especially if you are running an important piece of equipment on an invertor ..play safe have it installed and maintained by someone you can legally sue if it lets you down :lol: :lol: 
Mike


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## olley (May 1, 2005)

In the 80t's my brother and I built a couple of square wave inverters, about 600watts output, one thing we noticed was on overload the output voltage dropped, quite significantly, meaning that it drew less current.

Do the modern ones have voltage compensation circuits built in?

olley


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## 96414 (Oct 1, 2005)

Hi Olley

Its all switch mode now so the output is pretty good settles very quickly, even with something like a Fridge compressor or a Microwave cutting in. Having measured bith via an invertor and both via normal mains the both drop then recover with big loads. Of course if you did that with only one battery it will sonn pull the terminal voltage down and the battery low will cut in...

Hi Mike 

In the cigar lighter plug you have a glass encapsulated rapid blow 15Amp fuse, two other things are protecting this line, one voltage drop and the generally poor connection.


Generally things dont get fubar'd by Invertors, the one thing that does is rechargeable toothbrushs that use inductive chargers. So if its an inductive charger..... Most of the other stuff just doesnt work right if its going to have a problem, but doesnt come to any harm.

I tested everything you could think off with invertors, faxes, phones, Computers (laptops, desktops, PC and Aplle Macs), printers, TV's Large small and flatscreens and monitors all flavours, DVD, Video, Toasters, Kettles, ovens, Microwaves, Playstations, hairdryers, Zip drives, boilers, heaters, Sky and Sky Plus, freeview boxes, Fridges full size mains and Dometic 3 way. Huge G&H mains awning.

Everything I have tried as worked ok and without a problem, I have heard that certain TV/DVD combo's dont like quasi sine wave, but every one that I have checked so far have worked no problem.

The list of things that require pure sine wave is pretty short, toothbrush chargers, washing machines (its the thyristor control) thats the only 2 definates that I know of.

Edited to add the fuse size


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## olley (May 1, 2005)

Thanks for the info george, we built them because of the power cuts that we where all suffering at the time.

Interesting how things have changed in the last 30 years we used an oscillater, divider network, three sets of triacs and torodial transformers, do you know how they do it now?

Olley


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## 96414 (Oct 1, 2005)

Olley

I did have a drawing somewhere of a switch mode power supply (and whats that got to do with the price of cheese? I hear you cry) I'll try and dig it out

I cant remember the last time I did any big electronics building project.


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## olley (May 1, 2005)

Thanks george that would interesting to see.

Olley


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## 88790 (May 9, 2005)

Thanks for the info. George. I don't use an electric tooth brush in the Clubman and you have just given me the perfect reason to ditch the 'Washing Machine' project!

John 8)


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