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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
 Posted - May 04 2005 : 11:32:51 PM
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Hey John,
Use this site to host any file type no bigger than 2MB. You'll have 100MB of free space and your account won't expire. Totaly free and easy to join.
www.thefilebucket.com
J.C.
Edited by - wasssup1990 on May 04 2005 11:54:18 PM |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - May 05 2005 : 12:20:44 AM
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Hi Johnny,
Thanks, but this site is only for chatting.On the other sites I attend we post projects, schematics and datasheets etc directly to the page all the time.
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hobby16
New Member
France
3 Posts |
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hobby16
New Member
France
3 Posts |
Posted - May 05 2005 : 04:20:51 AM
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Hi Audioguru,
If you don't buy an inverter for yourself but have the occasion to give some advice, here are tips I found for commercial products I bought for my yatching activities:
- Square signals are the cheapeast and work not bad. Beware, it may blow your old tv. But with new electronic devices which have plenty of filter and surge protector, the overvoltage due to the square signal does no harm. Expect to use it at best 60% of the specified power. More and you'll have trouble (blow the fuse, blow your inverter, blow your 220V device, in order of preference!).
- In most case, you can increase the frequency to 100 hz (open the case and turn the right trimmer). The transformer will make less noise and heat and your 220V device will see no difference (forget the 50 hz digital clocks!).
- Don't be fooled by the pseudo-sinus marketing term. It's just like square signal, with lower yield!
- Sinus inverter are more sophisticated with all the bell & whistle protections. I have bought one because it includes a battery low voltage protection and it interfers less with my VHF. But most time, I think they are not necessary: they are considerably pricier which is NOT justified imho. Maybe, one day the Chinese (or the Indonesian) will master the microcontroller design and prices will drop.
Back to your 500W inverter, I simply don't believe it. Maybe it will consume 500W at the 12V side but as to finding 500W at 220V, humm. Do your people know the yield of their beast, the dissipation at the transformer, resistors and transistors. If they don't, then 500W (650W ?) must be in their dream.
And again, I think that saying there is no cheap mosfet in Indonesia is misleading. They have plenty of cellular phones and PC power modules. And those have plenty of spare mosfet. The people you are generously helping are beginner electronicians with bad ideas or solutions.
(Edit...Remove notification)
Edited by - Aaron Cake on May 31 2005 10:20:48 AM |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - May 05 2005 : 08:51:54 AM
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Hi Hobby,
The Chinese inexpensive little inverters I can buy here have a processor and display all kinds of info (voltages, power output etc). They have a tiny fan for forced cooling. Some have a modified sine-wave output so that their stepped p-p and RMS output voltages equal a sine wave.
The 500W inverter that I helped design uses ten cheap 2N3055 transistors to produce 500W output with all transistors at their lowest guaranteed gain. With typical transistors its output power is considerably more.
My Indonesian pen-pal recently discovered that he can buy compact-flourescent lightbulbs very cheaply. Inside are nice expensive Mosfets and other valuable stuff. He is beginning to design inverters with those Mosfets.
Apparently, inverters and car batteries are a big business over there. Most towns don't have electricity but everyone has a colour TV and flourescent lights. The millions of inverters are powered by car batteries and some companies do nothing but charge them.
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hobby16
New Member
France
3 Posts |
Posted - May 06 2005 : 05:49:05 AM
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Hi Audioguru,
For your friend's information, some additional notes:
- Inverters are the future also elsewhere due to renewable energy. Here in France, wind and solar use must be increased even if electricity is predominantly nuclear.
- Mosfets (and in a lesser extend IGBT) price follow the same price curve of PC computers because they are hugely used in cars, cellular phones, hifi and other modern electronics.
- Beware between high voltage (main) and low voltage (<40V) Mosfets: low voltage offers very low On resistance and so low loss. Also, with a 4 milli ohm mostfet, good wiring is CRUCIAL. In an inverter , the use of high voltage Mosfets (with high RsdON) or IGBT is inappropriate. But you can always try with any Mosfet, the control stage remaining the same.
- My method of choice is for implementing a circuit is sourcing THEN design and NOT the other way round. But well, when you have Farnell or Radiospares, it helps!
(Edit...Remove notification)
Edited by - Aaron Cake on May 31 2005 10:19:34 AM |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - May 25 2005 : 09:25:22 AM
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Hi Francisco,
This project doesn't work:
1) The caps explode because they were backwards and because their ripple-current rating is exceeded. Each cap is charged to about 24V, one-at-a-time. Then they have the transistor's collector end driven to ground, but therefore the other end tries to drive the other transistor's base to negative 24V.
All silicon transistors have an absolute max reverse-biased voltage rating for their base-emitter junction of only about 5V to 7V. Therefore the transistor's base-emitter junction is avalanching and causing an extremely high current in the cap and a huge waste of power. Over and over again by the oscillation.
Lots of power in a small cap equals a nice explosion!
2) Adding a protection diode in series with the base of each transistor will prevent the above problem. Then each transistor will need a resistor to ground at its base to turn it off.
3) You are correct that to produce 300W, the current from the 12V battery and conducted by each transistor is 25A, so TIP35C 25A transistors can be used.
But the inverter will have losses which reduce its output to about 210W.
The circuit's 180 ohm base resistors can provide a base current of about 61mA.
The datasheet for the TIP35C shows it conducting poorly with a max 4V loss with 5A of base current! The 2N3055 is much worse.
You can't simply use more-powerful transistors without increasing their input power.
4) You can use extremely low value base resistors and enormous caps to keep the oscillator's frequency down, to fix the above problem. But the resistors will cause a huge power loss. Therefore you need driver transistors or Mosfets.
So you see, it ain't easy to fix this poor design.
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - May 27 2005 : 05:32:24 AM
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Hi Francisco,
I can't read the snakes and ladders of your TEXT schematic. This inverter should work fine and produce about 20W if its capacitors have the correct polarity and the supply is a 6V battery. Then the transistors won't avalanche breakdown.
Your ideas:
1) Without the 10 ohms resistors and diodes, the 2N3055 transistors will blow-up if a load is turned off with the inverter still running.
2) The reversed diodes you connected from each base to ground still cause a huge current in the timing capacitors when they are discharged into them. Also, the capacitors cannot swing to negative 24V then discharge slowly into the 180 ohm resistors for the timing period.
3) When paralleling transistors, each should have an emitter resistor to help equalise the different base-emitter voltage of them. They provide more output even though their drive is halved because their current gain nearly doubles with the lower collector current. Adding a paralleled transistor to the other side will increase the output even more. All transistors should each have an emitter resistor of about 0.1 ohms.
4) You won't need huge 330V capacitors if their discharging current is reduced by adding diodes in series with the base of each transistor. Then you can easily calculate the inverter's frequency since the discharge is only an RC network.
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - May 28 2005 : 02:46:13 AM
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Hi Francisco,
1) All inductors produce a very high voltage when their current is stopped, like a car's ignition spark coil. Although the primary winding is electrically insulated from its secondary, the high voltage spike is inductively coupled from the secondary to the transistors in its primary. The resistors and diodes cause an enormous loss so perhaps zener diodes would be better like most power Mosfets have.
Your low current is reducing the voltage spike.
2) The center-tapped primary winding is a transformer all by itself. Since the center-tap is connected to +12V, when one end is driven to ground then the other end swings to +24V. So the caps charge to +24V.
3) When you parallel transistors, each one needs its own emitter resistor to ground. Because each transistor will have a slightly different base-emitter turn-on voltage and the one with the lowest voltage will take most of the current, which causes it to heat and reduce its turn-on voltage even lower while the higher voltage turn-on transistor does nearly nothing. Some manufacturers match transistor so they are about the same. You don't have a big box full of transistors to pick and match them so you should use 0.1 ohm emitter resistors to raise the turn-on voltage enough so that your transistors perform nearly the same.
4) Add a diode in series with the base of each transistor with its cathode to the base and a new 1k resistor to ground to turn-off the transistor. The anode of the diode connects to the cap and 180 ohm resistor. Then when the other transistor drives the junction of the cap and the 180 ohm resistor to about -24V, the diode will be reverse-biased and protect the base-emitter of the transistor from avalanche breakdown and allow the cap to discharge into the 180 ohm resistor for its timing period.
The discharge time of a capacitor into a resistor in parallel is RC where R is in ohms, C is in Farads and the time is in seconds. R times C is called one time constant and the voltage at a discharge time of RC equals 37% of the cap's fully charged voltage. The discharge is exponential so the amount of time that the cap discharges to the voltage to turn-on the transistor must be calculated. Making it more complicated is the fact that the cap isn't discharging into a parallel resistor. The resistor is connected to +24V. It is too late now for me to figure it out. I would just try it and measure the frequency.
Use electrolytic caps, not tantalum because the cap will be charged to about 1V in reverse for a moment.
When you have the inverter producing more power this way, you can try reducing the value of the 180 ohm base resistors (and increasing the value of the caps to keep the same frequency) for more base drive to the transistors. You will reach a point where the increase in power simply heats those resistors.
Edited by - audioguru on May 28 2005 02:56:20 AM |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Jun 02 2005 : 09:37:18 AM
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quote:
3) Added diodes (for the two sides only), between the cap and the 180 ohms resistor that goes to the base of the transistor.
The transistors on each side should be in parallel with their bases connected together, then there is only two sides.
The caps won't charge and discharge properly with diodes between the cap and the resistor. The diodes should be in series with the bases of the transistors to protect them from avalanche breakdown. Then the bases need an additinal 1k resistor to ground to turn them off.
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engineer66
New Member
Jordan
1 Posts |
Posted - Jul 23 2005 : 06:17:37 AM
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quote:
Aaron or YS -- could you please tell me what the next higher power transistor than that of the 2N3055 is? Amperage and voltage. This is to use in this crazy 12V-120V inverter. Thank you...Tim.
fadi |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Jul 23 2005 : 07:34:12 AM
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Tim,
Higher power transistors won't make much difference in this simple circuit.
First, the circuit needs to be fixed so that its capacitors are not backwards and so that the base-emitter of the transistors don't breakdown. Then the 2N3055 transistors will conduct about 6.3A and the project will make about 63W at 118V, when the battery is 13.8V.
Second, the base current for the transistors needs to be increased so that paralleld output transistors can provide more power.
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jecjec
New Member
3 Posts |
Posted - Aug 03 2005 : 6:27:11 PM
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Hi Audioguru,
May i seek ur advise regarding my newly purchased 500watts power inveter. My question is , can i use my 3/4 Hp. electric motor on it and what size of battery would u recomend for me to use.My second question is, will it be possible to connect my inverter into my old model jeep that has original alternator ? some auto-technician said that my original alternator is only 25ampere and it impossible for my inverter to produce the amount current to run my electric motor.Im seeking second opinion,pls.need ur advise,many thanks in advance.
Jessie
p.s. my inverter is modifide syne
wave
Edited by - jecjec on Aug 03 2005 6:33:26 PM |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Aug 03 2005 : 11:28:52 PM
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Hi Jecjec,
The electrical power used by your motor depends entirely on how much mechanical work it is doing. I have my 1/2hp furnace fan running at its limit of 10A, therfore if your 3/4hp motor is fully loaded then it would use 1800W and your inverter is much too small. A 3/4hp motor might draw 18,000W when it starts. If your 500W inverter is trying to power it then you can kiss the inverter good-bye.
Many inverters operate at their max rated power for only a short time. If yours is rated to supply 500W continuously at 120V, then it will draw 43.5A from a 13.8V car battery. The Jeep's little alternator will probably overheat trying to power it and also charge the battery. Get a more powerful alternator.
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Aug 03 2005 : 11:31:53 PM
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Hi Jecjec,
The electrical power used by your motor depends entirely on how much mechanical work it is doing. I have my 1/2hp furnace fan running at its limit of 10A, therfore if your 3/4hp motor is fully loaded then it would use 1800W and your inverter is much too small. A 3/4hp motor might draw 18,000W when it starts. If your 500W inverter is trying to power it then you can kiss the inverter good-bye.
Many inverters operate at their max rated power for only a short time. If yours is rated to supply 500W continuously at 120V, then it will draw 43.5A from a 13.8V car battery. The Jeep's little alternator will probably overheat trying to power it and also charge the battery. Get a more powerful alternator.
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12/120V inverter again
