12 volt to 240 volt invertor

[mhutsby]

Hi can anyone help me with the circuit diagram & components to build a 12 volt to 240 volt invertor that i may simply plug into a car cigarette lighter.

Many thanks Mark

 

[andrew2022]

**broken link removed**

NOTE: i tried this last night, and the capacitor exploded, so be warnedyou may need to change a few things

 

[Nigel Goodwin]

**broken link removed**

NOTE: i tried this last night, and the capacitor exploded, so be warnedyou may need to change a few things

You could try putting the capacitors the right way round for a start :lol:

But it's a pretty poor design anyway!, I would also add diodes from the base of the transistors to the emitters to prevent the transistors failing (cathode to base, anode to emitter).

 

[andrew2022]

i did put the caps the right way round... it still blew for some reason... and what would you say was a better inverter schematic?

 

[Nigel Goodwin]

i did put the caps the right way round... it still blew for some reason... and what would you say was a better inverter schematic?

If you put them the way shown in the diagram, that's the wrong way.

There are a number of inverter circuits on the net, mostly much more complicated than this one - for good reason. This one is really an example of how NOT to do it 8)

 

[andrew2022]

If you put them the way shown in the diagram, that's the wrong way.

am confused. from lookin at the diagram i thought they were in the right way?

 

[Nigel Goodwin]

If you put them the way shown in the diagram, that's the wrong way.

am confused. from lookin at the diagram i thought they were in the right way?

The positive side of the capacitors are shown connected to the base's of the transistors, which can't go higher than 0.7V positive. The negative end of the capacitors are connected to the collector's, which will reach 12V positive when the transistors turn off (ignoring any effects from the transformer).

So as shown the capacitors are reverse polarised by around 11.3V, result - BOOM!! - well, at least a quiet hiss!.

Also, without any catching diodes, even with the capacitors the correct way, it's likely to blow the transistors - as one transistor turns on it drives the base of the other around 11V negative, much too high for a 2N3055.

 

[andrew2022]

ill have a look for a better inverter... prob safer aswell

 

[J0HN1]

Hi mhutsby, Hi andrew,

This inverter circuit has cropped up a good few times.
Every time i see it, i cringe.

I consider it to be a poor circuit,
however, i have not constructed it.

Although i have constructed other low power inverters
most of which have worked adequately.

Here is a link to the thread on this forum where i first
saw this particular circuit:

https://www.electro-tech-online.com/threads/ip-core.2695/

I too thought the capacitors were the wrong way round,
but this is not the opinion of others who have examined
this circuit.

One point which was made clear is that the high ripple
current demanded of the capacitors in this configuration
means they have to be tantalum types. (or equiv)
Cheaper electrolytics will not stand the heavy demand
and will fail.

That earlier thread has many useful comments from other
constructors too.

One basic point is to check that the two 12volt windings
are correctly oriented.

Normally i don't reply to a post where the original poster
has only posted once.
There are too many that never post again.

Little home made inverter units are a favourite of mine,
i've made quite a few.
I favour the bridge type circuit with four Tr's or Ft's
which i originally started using because it has a single
winding as primary.

Best of luck finding a nice simple inverter Andrew,
Regards, John

 

[sronggot]

Rectifier Circuit

any one have rectifier circuit with thyristor ?

I need it for my hobbies

 

[Nigel Goodwin]

Hi mhutsby, Hi andrew,

This inverter circuit has cropped up a good few times.
Every time i see it, i cringe.

Same here 8)

I too thought the capacitors were the wrong way round,
but this is not the opinion of others who have examined
this circuit.

I wouldn't have really thought it's a subject for debate?, the circuit is a simple astable multivibrator, it's very simple to understand how it works (or at least how it's supposed to work). I suppose it could be interesting to build it and measure what's happening? - possibly the back EMF from the transformer could alter things - but I'm highly dubious about it

 

[J0HN1]

Hi Nigel,

Please have a look through that earlier thread about
the same circuit, and the thoughts of others who have
looked at it.
That earlier thread has a colourful diagram with all the
component values included.
This poster did not mention that he was using 3055's
but you are correct, those are the ones that this is
supposed to use.

https://www.electro-tech-online.com/threads/ip-core.2695/

I would be very interested in your comments on what
others have said about it.

Regards, John

 

[Nigel Goodwin]

Hi Nigel,

Please have a look through that earlier thread about
the same circuit, and the thoughts of others who have
looked at it.
That earlier thread has a colourful diagram with all the
component values included.
This poster did not mention that he was using 3055's
but you are correct, those are the ones that this is
supposed to use.

https://www.electro-tech-online.com/threads/ip-core.2695/

I would be very interested in your comments on what
others have said about it.

There was only one person who suggested the capacitors were the correct way round, 'Andrew Partridge', although 'john1' (is that you as well?) agreed afterwards - but the similar circuit the link was posted for (by john1) specified non-polarised tantalums, and no polarity was marked on that circuit.

As I see it, the positive side of the capacitors should go to the collectors, otherwise they are reverse polarised by 11.3V or so, and (as has happened) the capacitors will vent.

As also mentioned, I agree that the diodes and resistors are to absorb the back emf from the transformer - probably the only part of the circuit which isn't completely horrible :lol:

 

[J0HN1]

Hi Nigel,

yes you are right, this earlier circuit and description from
Tony Van Roon clearly stipulates non polarised tantalum caps

**broken link removed**

Regards, John

yes that is me too, i was away at another machine, and got
no cookie. I couldn't remember my password, so i just registered
again. Later realised i could have asked for my password !

 

[Nigel Goodwin]

yes that is me too, i was away at another machine, and got
no cookie. I couldn't remember my password, so i just registered
again. Later realised i could have asked for my password !

It wouldn't actually send you your old password, but would generate a new random one for you - not even the administrator can find out what your existing password is.

 

[john1]

found it now.

 

[andrew2022]

to make the inverter more powerful can 2 3055 transistors be connected in parallel

 

[Nigel Goodwin]

to make the inverter more powerful can 2 3055 transistors be connected in parallel

You can parallel bipolar transistors, as long as you fit seperate resistors in the emitter lead of each one, to ensure the current is divided evenly - generally you would use very low values, depending on the current handling required.

In this case though, the circuit would be even less likely to work!.

 

[andrew2022]

to make the inverter more powerful can 2 3055 transistors be connected in parallel

You can parallel bipolar transistors, as long as you fit seperate resistors in the emitter lead of each one, to ensure the current is divided evenly - generally you would use very low values, depending on the current handling required.

In this case though, the circuit would be even less likely to work!.

not a good thing... plan B is to get an old UPS... ideally i need an inverter what can handle 900W min

 

[Nigel Goodwin]

not a good thing... plan B is to get an old UPS... ideally i need an inverter what can handle 900W min

Maplin sell a 600W inverter for £80, which sounds pretty reasonable, but bear in mind 600W is 50A at 12V, assuming 100% efficiency!. They do either 12V or 24V versions, which would obviously half the current at 24V.

So a 900W 12V inverter would require upwards of 75A.

Do you have a specific use in mind?.