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 12/120V inverter again
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gim
Apprentece

5 Posts

Posted - Nov 07 2008 :  04:27:12 AM  Show Profile  Reply with Quote
Audioguru, if I may ask you a question.

I have built an inverter, which works, as I have mentioned before. I have added to it a light sensitive switch, so that it turns on in daylight, and turns off in darkness. The switch consists of an LDR connected to a 555 timer IC, which does the switching, and in turn drives a MTP3055E MOSFET through a 47 ohm resistor.

The trouble is, sometimes, the circuit (I guess that is the MOSFET) oscillates at radio frequencies. It makes quite loud intereference on the audio of my TV.

Can you suggest a way to stop this HF oscillation? Would increasing the gate resistor of the MOSFET do it, and if so, what value should I use?
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Nov 07 2008 :  12:25:30 PM  Show Profile  Reply with Quote
A resistor in series with the gate of a Mosfet stops it from oscillating at VHF frequencies. It should be mounted directly at the gate pin, not connected by a wire. 4.7 ohms to 100 ohms should work fine.
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mleiss
New Member

2 Posts

Posted - Nov 11 2008 :  9:57:17 PM  Show Profile  Reply with Quote
If this doesn't work for you, try a RC snubber network between the drain to source of your MOSFET. You may have incurred a resonance or ringing between the leakage inductance of the transformer and the output capacitance of the MOSFET. Adding the RC snubber will help to reduce the ringing.

First, figure out what the frequency of the oscillation is, if you have a way. You can use this frequency to calculate the leakage inductance of your transformer with the following equation: L = 1/((2*pi*frequency)^2*Capacitance).

Select a capacitor that is about 3 to 4 times larger than the output capacitance of your chosen MOSFET. This should reduce the frequency of the resonance by a factor of 2. Then calculate your resistance based on the equation for characteristic impedance of a parallel resonant circuit as in the following equation: R = sqrt(L/C).

After the R-C circuit has been calculated, again place the resistor and capacitor in series between the drain and source of your MOSFET. Ensure you have a very good ground and minimize the lead length between the capacitor and ground. If the connections between all of these elements are not short, parasitic elements of a long wire can change this circuit and you will not dampen out the oscillations as you thought you would.

Hope this helps and good luck!
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fallo
New Member

1 Posts

Posted - Nov 19 2008 :  12:52:37 PM  Show Profile  Reply with Quote
Hi, Im currently working in building a photovoltaic system to power a complete room and at the end a complete house, do you have any idea of how much power would it need to generate. Im asking this cause obviously I need an inverter DC-AC, and I want to try building it my own, or would it be better if I buy it custom made? I appreciate your suggestions, thanks.

Fallo
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Nov 19 2008 :  2:25:53 PM  Show Profile  Reply with Quote
Simply add the amount of power you need for everything in the room. Then figure that not everything will be turned on at the same time. The result is the amount of power the inverter must supply.
Good inverters work well and are inexpensive. Solar panels are expensive. Windmills are less expensive.
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paul_ma7
New Member

3 Posts

Posted - Nov 22 2008 :  11:17:32 PM  Show Profile  Reply with Quote
i build the inverter but for some reason the current
is very low it will only handle about 2 amperes,
i'm thinking it might have something with the battery?
my batt is 12.7v and 7 amp, do i need to use a car battery?
also i'm not using the hep diodes, i'm using a regular silicon diode,
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paul_ma7
New Member

3 Posts

Posted - Nov 22 2008 :  11:29:30 PM  Show Profile  Reply with Quote
also i forgot to mention that i'm using a 150w transformer not the 300w transformer
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Nov 23 2008 :  11:08:03 AM  Show Profile  Reply with Quote
The inverter project DOES NOT WORK!
Read all about it in this thread.
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pebe
Nobel Prize Winner

United Kingdom
1078 Posts

Posted - Nov 23 2008 :  3:37:11 PM  Show Profile  Reply with Quote
I'm surprised Aaron has not removed this faulty circuit from the site.

Quite apart from the damaged components people have had to put up with, there's a potential personal accident from a blown up electroytic just waiting to happen!
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raaahuul
New Member

1 Posts

Posted - Nov 30 2008 :  1:06:48 PM  Show Profile  Reply with Quote
i want backup of inverter for 4 hours with 2 CFL(20 watt)& single fan what will b the battery's current rating?
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Nov 30 2008 :  2:58:48 PM  Show Profile  Reply with Quote
quote:
Originally posted by raaahuul

i want backup of inverter for 4 hours with 2 CFL(20 watt)& single fan what will b the battery's current rating?


The current rating of the battery is not its capacity. Its capacity is how long it can deliver a certain current and is measured in mAh (milli-amp hours).

Calculate the total output power required then add about 20% for running an inverter. then calculate how much current from the battery and compare it to the mAh of batteries.

Instead of wasting power with an inverter, use 12V CFL bulbs and a 12V fan.
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mansoorkkl
Apprentece

India
5 Posts

Posted - Mar 12 2009 :  12:58:02 PM  Show Profile  Reply with Quote
4000w inverter plz
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Amaar
Apprentece

Pakistan
6 Posts

Posted - Apr 05 2009 :  05:44:13 AM  Show Profile  Click to see Amaar's MSN Messenger address  Reply with Quote
[quote]Originally posted by audioguru

SupraGuy,
Sorry to hear your experience with this bad circuit.
For your applications, why not keep it supra-simple:
1) A CD4047 oscillator/divider/opposing-outputs chip as the oscillator-driver. It needs only 1 resistor and 1 capacitor. Its outputs are perfectly symmetrical, and are direct and inverting.
2) A pair of power MOSFETS with built-in zener protection diodes as the output transistors.
3) A regular 50Hz or 60Hz center-tapped transformer, or a smaller high-frequency one.

300W would be easy.
I would post a circuit but I don't need another power supply. Why don't you?


Hi sir, I tried to build a simple inverter using CD4047BE IC and two IRFZ44 MOSFETs but its not working on a proto board and the problem is that CD4047 is giving out continuous voltage
rather than pulses. I used DC link to provide 12V to the circuit.
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 05 2009 :  09:40:41 AM  Show Profile  Reply with Quote
Hi Amaar,
Post your schematic so we can see what is wrong with it.
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sympsyd
Apprentece

5 Posts

Posted - Apr 10 2009 :  10:10:47 PM  Show Profile  Reply with Quote
till now i have been using inverter circuit built up of thyristors. but upon seeing this particular inverter circuit, i found it very much interesting. so, can anyone here explain me the working mechanism of this particular invertor? i would be very much grateful.
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