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 12/120V inverter again
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n/a
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2 Posts

Posted - Oct 12 2004 :  09:56:00 AM  Show Profile  Reply with Quote
audioguru,

Thanx for the reply. Just wanted to make sure 5% variation doesn't make a difference. You know here in India we get 230v at home.
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n/a
DELETED (Inactive)

9 Posts

Posted - Oct 12 2004 :  10:20:18 AM  Show Profile  Reply with Quote
Uhhhhh, me thinks the paint on cars is several mils thick. About the same as the varnish on magnet wire. Anyhow, it as safe as anyone being in their own home. If you think this should be illegal, maybe you should tell the power company the same thing. One can be electrocuted the same as your mentioning, in ones bathroom, or in the kitchen, same difference. I hope your not one who sues others if they fart?

Matter of fact, there's more here on the internet, much more dangerous than this. Amateur RF amplifiers use plate supplies anywhere from 2500 Vdc to 10,000 Vdc, all can be found all over net. Those will kill you dead Fred! Another fact, in the right situation, and if your health couldn't take it, a simple shock from 12 Vdc could kill you. Enough current at 12 Vdc will do it, especially if you have a weak heart or a pace maker.

Oh how the frivolus law suits abound! About like a parent too afraid to let their little boy have a BB gun. Saying what we're discussing is dangerous is nothing more than twaddle in todays age.

Will





quote:

My goodness, just doing a quick search for some inverter designs and I come across this... firstly a multivibrator running a transformer and then pushpull designs... Firstly, inefficient. Secondly, deadly! Where is your isolation?! Should there be a fault with your equipment or your transformer, you have high voltage AC on your 12V side. Anyone who touches your car's chassis will be electrocuted. Far out. Posting things like this should be illegal. You're letting novices try these prototypes and run the risk of getting them, and even yourself, killed. A good inverter has opto-isolation/feedback. You need this feedback to control the PWM incase of variations in the voltage. If anyone is attempting to build these, do not use them for permanent fixtures, and be very careful.





-=Will Matney=-

(Edit...Remove email notification due to bad address...)

Edited by - Aaron Cake on Nov 25 2005 09:15:08 AM
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n/a
DELETED (Inactive)

9 Posts

Posted - Oct 12 2004 :  10:39:49 AM  Show Profile  Reply with Quote
Audio,

That is similar to a circuit I once used except I didn't use any IC's in the project. Really, I used a small version of a multivibrator similar to this, running a set of drivers first, then the final switching bipolars. I used 2N3772's though, to increase the current capacity to about 7 amperes each. I went back and looked through some power supply books I have here, one in particular about invertors. They mentioned a 5 ampere maximum current through the 2N3055's (safety margin). The 2N3772, is used in most high current power supplies like Astron, and Pyramids 50 amp supply. They have 8 of these which would bring their rating about 7 amperes a piece (56 amperes). The spec sheets should about all have a voltage to current graph which shows the current, power, and collector voltage. Generally most are rated for the designated current at 5 Vdc. After that, it drops off as the voltage rises. Without looking, I'm not sure what the graph would show for a 2N3055 running at 12 Vdc. Anyhow, that is a good design for an invertor that can be built cheaply.

Will Matney




quote:

BTW, Will,
The 500W inverter project that I fixed was reported to deliver 720W. So its output transistors must have had an emitter current of almost 15A.Since its driver transistos were connected in a darlinton arrangement, they probably had a collector current that exceeded that of the output transistors, and all currents went into the transformer. I would never push transistors so hard, therefore rated the circuit at only 500W.
The link to that schematic is posted again here:
http://www.electronics-lab.com/forum/attachments/500Watts_Inverter.gif





-=Will Matney=-

(Edit...Remove email notification due to bad address...)

Edited by - Aaron Cake on Nov 25 2005 09:15:28 AM
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Oct 12 2004 :  1:47:19 PM  Show Profile  Reply with Quote
Thanks, Will.

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n/a
DELETED (Inactive)

2 Posts

Posted - Nov 02 2004 :  3:19:54 PM  Show Profile  Reply with Quote
quote:

You are talking about using opto-feedback and PWM. Are you rich?


Both are fairly simple to design, and I dunno about other countries, but in Austalia, electronics parts are cheap, especially if you have staff discount at a retail electronics store. ;-)

For north america/canada: http://www.jaycarelectronics.com/
For Australia: http://www.jaycar.com.au/
For wholesale: http://www.electusdistribution.com.au/

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n/a
DELETED (Inactive)

1 Posts

Posted - Nov 10 2004 :  11:05:44 AM  Show Profile  Reply with Quote
i think it's easier to use a UPS. not only they are more safer you can get one for free, if its batteries are dumped, and a new one starts at 20E(350W) and 45E(800W). ;)

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Techoduro
New Member

1 Posts

Posted - Nov 12 2004 :  6:16:48 PM  Show Profile  Reply with Quote
No big deal, Aaron´s design ???, a simple oscilator seems to me more like a challenge to make it work as inverter than a serious project, since elementary in circuits told us you could not use it that way but as a driver to other circuit to reach the goal. I don´t think you would use a fork to have soup, all you have to do is using a spoon.
By the way thanks for all the information provided by some of you, which is being very usefull to me.


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maloy
Apprentece

6 Posts

Posted - Dec 12 2004 :  5:55:15 PM  Show Profile  Reply with Quote
hi guys , I complitly solved all problems in this schematic , I improved it a little bit and now I have good 100wats 240v inverter I spent 2 months of time and good amount of money so I have it running at least. My inverter was completed one year ago ,no problems sinse that time.all I can say schematic is partially wrong ant can be build even cheaper than stated.

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 12 2004 :  10:11:45 PM  Show Profile  Reply with Quote
Hi Maloy,
It is wonderful that you solved all the problems with this inverter, improved it, corrected its schematic error and made it even cheaper.
Aren't you going to tell us how?

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Aaron Cake
Administrator

Canada
6702 Posts

Posted - Dec 16 2004 :  10:30:55 AM  Show Profile  Visit Aaron Cake's Homepage  Send Aaron Cake an ICQ Message  Send Aaron Cake a Yahoo! Message  Reply with Quote
This was emailed to me by someone who doesn't want to register, yet has some suggestions with regards to this circuit:


----

I do not want to join the forum, however, I think I can toss a tidbit that way if you want to post it to the forum:

The basic free –running flip-flop part of the concept is fine. Someone mentioned an IGBT, which is used specifically in instances like this one (on/off… strictly square wave). Some IGBT’s also contain the back-emf surge protection.

My suggestion is to remove the power robbing R1, R2, D1, and D2. Use a smaller, cheaper NPN transistor in place of the 2N3055’s. Break the collector connections to the transformer and connect them to the base of a couple IGBT’s. Connect the collectors of the IGBT’s to the transformer and the emitter to ground (if you use emitter resistors on all the IGBT’s, you can parallel transistors to “UP” the current rating). IGBT’s come in very high current ratings because they are either “on” or “off” devices.

Since the IGBT’s carry the power and the NPNs are not directly connected to the transformer, you won’t have the “exploding capacitor” syndrome. Forget about both NPN’s trying to turn on at the same time and locking up. Send that one to “Myth Busters” for de-bunking. Some AC clocks can run on square wave. When you get the inverter running, use a clock to time the frequency and tweak the resistor/capacitor combination so the clock moves one revolution per minute.

It might not take any IGBT bias tweaking to get it to run properly, or it might take some IGBT bias tweaking (base resistors). Just remember, an IGBT is not a linear device. The base cannot take a ramp type of input. Use a square wave such as the flip-flop provides. It will not require as big a heat sink as an NPN, nor does it require much base current since it is a voltage device. The 2N3055 takes one heck of a drive current… therefore, your circuit was prone to problems.

Another point, each transistor is only driven during one-half of the cycle. A transistor run like that can supply twice as much current (half as often). Its heat dissipation is averaged.

Sincerely,

Been There

I just realized that in the description below, you will also need resistors going from the NPN collector to positive power supply when you disconnect it from the transformer. Try a resistance between 240 and 10,000 ohms. Try 4,700 ohms to start with.

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 16 2004 :  11:26:36 AM  Show Profile  Reply with Quote
I agree that the inverter will be able to provide its rated output if "insulated gate" devices were used as its transformer driver such as IGBTs, or even power Mosfets.
However a problem with the transistor multivibrator was overlooked: a transistor's base-emitter junction has an reverse-biased absolute maximum voltage rating of only 6V or 7V. The capacitors in the multivibrator will attempt to drive the bases down to -11V, since the multivibrator has a supply voltage of 12V. Therefore the reverse-biased base-emitter junctions will breakdown in a zener fashion, causing a short duration high current to flow in the capacitors and transistors.
The solution is to add diodes in series with the emitters to ground, as discussed previously.

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maloy
Apprentece

6 Posts

Posted - Dec 17 2004 :  12:08:18 AM  Show Profile  Reply with Quote
Hi guys, today I'll try to explain how to do it working.First of all : I am not an electronic engineer but a mechanic so I vill explain everything from mechanical point of view. At the beginning , when I started to build inverter I tried to follow instractions and finished with exploded capacitors . After several attempts and losing my money again and again I started to think that there something wrong. Thus surcuit itself is not bad or wrong , what was wrong? From technical point of view the transistors are not synchronized and practically we have some sort of backwave that mean that circuit conduct current back through capacitors to transistors, so simply there is no longer direct current but some sort of alternative current ,thus my solution is cheapest bipolar capacitors, in my case:47uf 50v electrolite caps,they work great never getting hot. Next point : do not use expensive power transistors , they are good but if you get them overloaded the next thing they could be used for is to be thrown away thus they are not so durable. What can I say about their cheap brothers (2sd850 , 2n3055) you can overload them for a short time without problems bbut do not forget about appropriate colling . the schematic is not so powerful as stated but said that could be designed for greater output . In the state the schematic presented it can produce no more than 35-40w at 120v and not capable to initiate transformers ratios designed for 240v, the usage of more powerful transistors can solve that problem but they simply getting overloaded, why? because physical thickness of conductor is not thick enough; we drain huge amounts of current through curcuit and if you remember that to rotae dc motor rated at 1hp at full load we need condactor wire no less than 3mm in diameter , so what the thickness of the transistors legs? Solution is use as many as you can instale , connect them in paralel (I use 4 of 2n 3055 2on each side) so they act as one big super transistor and their combained thickness is powerfull enough to connect any load you like. Transistors mast be connected to each other with reasonably thick wire . The rest of curcuit could be connected ordinary as you like, my transformer is was taken from video recorder power supply,its dimensions;5x5x6cm. This transformer has been rewind , I used wire from microwave transformer for centertaped winding I used thick wire and for output winding the thin wire.So if you did not anderstand something just ask me and I'll try to enplane everything, other way the system should work without any major adjustment.

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 17 2004 :  03:27:27 AM  Show Profile  Reply with Quote
Hi Maloy,
1) Did you connect your cheap capacitors backwards like in the original project?
2) You are using 4 transistors that are rated at 115W each, to get only 100W output?
3) Where did you find 2N3055 transistors with such a high current gain that they conduct 9A with hardly any base current?

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maloy
Apprentece

6 Posts

Posted - Dec 17 2004 :  05:37:13 AM  Show Profile  Reply with Quote
, Hi again,Audioguru, as I mentioned before I am not a electronic engineer and I do not know all the terms what you mean under backward connection? yes I connected capasitors as stated in original project , they are bipolar ones that the key because as current passes transistors there is no longer direct current and polirpolarized capascapacitors simply will explode so your can experiment for ages without success.
Yes I use 4 transistors 2two at each side those couples are connected in parallel and two transistors at each side act as one big transistor , the advantige is increase of condactivity therefore you can drain bigger amounts of current.
Yes I use 4 transistors to get 100w , as I said before it is tricky to get this inverter work I don't think that many of you who decided to build this project ended with any success at all but with blown up capacitors , I read this forum many times I saw how people were straggle, there were many opinions but no result , so I decided to share what I get working.That correct 4 four transistors for 100w
I found that schematic is not poverfull enough with two transistors, you can use two expensive and powerful ones but they are too sencitive to owerloading, but price the same for four cheap and durable as for 2 expensive and sensible . Some times it is impossible to excite any transformer if you will use schematic at presented state, so if you would like to keep simplicity of this schematic just try what I already done and use.

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 17 2004 :  09:24:00 AM  Show Profile  Reply with Quote
Hi Maloy,
It is wonderful that you managed to make this project work. I understand that you used non-polar electrolytic capacitors, which may be big enough to withstand the current surge when the input of the transistors breakdown.

How did you measure its output power? Most meters don't measure its square-wave accurately. A better way would be to measure its battery current, and subtract a percentage for its inefficiency (heating).

In Canada, we can buy a 100W inverter with a digital display for only 20 or 30 bucks! They have a small fan in one end and the fine print says 100W for 5 minutes max. or 75W continuously.Bigger, more powerful inverters cost a little more. They probably all use Mosfets.

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