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 12/120V inverter again
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Dino_25
New Member

2 Posts

Posted - May 20 2009 :  03:47:20 AM  Show Profile  Send Dino_25 a Yahoo! Message  Reply with Quote
I normally tinker around with simple RF receivers, low power TX, and audio-- inverters are fairly new to me. I thought I'd throw this piece of crap together to see what would happen. Well... It DID work... for about 30 seconds with a 75W bulb, then I found myself cleaning up electroylitic acid. I tried once more, but made various changes. I paralleled 2 more 3055's, added diodes in series with the transistor's bases with a couple of resistors to ground to turn the transistors off, and added some zener diodes in place of the 10 ohm resistors and diodes on the xfrmr. It helped a little. I ran a 75 watt bulb for a whole 1 min, 30 secs before it died. So I scrapped it.

Later, I read about an even simpler inverter circuit by Harry Lythall. Here's the link to the article http://web.telia.com/~u85920178/. I was skepticle, so I threw the thing together, powered it up, and heard the old familiar buzz. I conneted two 20watt flourescent bulbs and the thing worked. I left it on for about 30 minutes with no problems. The transistors actually didn't get that hot with no heatsink at all, but I connected a small fan to blow cool air on them just to be sure. I wouldn't dare try and connect my laptop to it though.

I CAN say, however, that the circuit on aaron's site works... for a few seconds, followed by explosions. Maybe there are ways to improve it (like audioguru suggested), but it would just be too much of a headache. For anyone who is looking for a permanent power back-up, just buy a cheap inverter off ebay or find a better designed circuit to work with. Or if you have a couple of uninteruptable power supplies (UPS), like I do, they work just fine. I have 2 small APC BK400 250W UPS's. I found them at a thrift store for $2.00 a piece!!! I use one to power a small 55 watt tv and playstation during outages.

I would go for audioguru's redesigned 500W inverter. It looks like a great circuit. And if anyone has difficulty find the CD4047 IC, jameco.com has them for about $0.29 a piece.

If it ain't broke, don't fix it!
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Dino_25
New Member

2 Posts

Posted - May 20 2009 :  03:50:47 AM  Show Profile  Send Dino_25 a Yahoo! Message  Reply with Quote
Sorry about the Jameco link... I must've screwed up. It should be easy enough to just enter www.jameco.com into your browser.

If it ain't broke, don't fix it!
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Alberto
Apprentece

23 Posts

Posted - Jun 29 2009 :  8:27:14 PM  Show Profile  Reply with Quote
I guess I joined too late. I´ve been reading this topic and replies from the start and the more I read the more I get confused. That´s just because Me ( and anybody who joins late ) doesn´t know WHICH schematic ALL of you are rfering to. So, why can´t everybody attach their schematic when you post, either a questio or an answer. Thanks.
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Alberto
Apprentece

23 Posts

Posted - Jun 29 2009 :  9:07:59 PM  Show Profile  Reply with Quote
Sorry, everybody. I guess I posted when I shouldn´t. I started reading this thread from the BEGINNING.
Although I did SMILE and LAUGH sometimes, I´m getting more confused. I try to solve my problems by myself before, read all threads and posts and then ask my SPECIFIC questions. But it seems that a lot of us could go crazy if we´re not sure about WHICH schematic we are discussing: The original, rvised, corrected, functional, etc.
I strongly advise that whenever you post refer to THE schematic you´re talking about. I hoe this helps EVERYBODY!
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jun 30 2009 :  8:31:49 PM  Show Profile  Reply with Quote
This thread is about the inverter circuit that has the polarity of its capacitors backwards so they blow up.
It also has the max allowed emitter-base voltage of the transistors exceeded so they also blow up the capacitors even if their polarity is correct.
The base current of the transistors is much too low so that they need driver transistors.
The circuit is a joke.
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Alberto
Apprentece

23 Posts

Posted - Jul 01 2009 :  5:36:59 PM  Show Profile  Reply with Quote
Excuse me audioguru. I´m going through this thread from the beginning ( 2004 ) and the forum mentions too many schematics. Anyway, have you ever discussed this one. If so could you direct to where it began. If not, how about your opinion and any suggestions. Thanks.

Download Attachment: New Drawing.PNG
147.62 KB
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jul 02 2009 :  09:24:58 AM  Show Profile  Reply with Quote
Hi Alberto,
The circuit you found was "corrected by MP" but he made many errors:
1)It doesn't have enough output transistors for 500W output. Each 2N3055 output transistor has an absolute max allowed current of 15A but performs poorly above 10A. But with a 500W load each output transistor must pass 25A.
2) Its 2n3055 transistors must be matched.
3) There are no protection diodes to arrest voltage spikes.
4) The resistor R2 in the CD4047 oscillator is only 1k ohms but Texas Instruments says it should be a minimum of 10k.
5) The timing capacitor in the CD4047 oscillator is way too high at 4.7uF and a low tolerance capacitor cannot be found with such a high value.
6) It doesn't have a fuse to stop a fire.
7) It uses two LM324 quad opamps instead of just a single LM358 dual opamp.
8) Its output is a square-wave without voltage regulation.
9) It does not shut down when the battery voltage gets low.

I fixed it and it is used in 3rd-world countries. It would be much better if a Mosfet circuit replaced the 2N3055 transistors but Mosfets are rare in 3rd-world countries. It would also be better if gates were added to make it have a "modified sine-wave" output waveform. We discussed the gates, shutdown when the battery gets low and even discussed voltage regulation in this and other threads.
Here is my fixed version of the 500W inverter:

Download Attachment: 500W inverter final.PNG
86.17 KB

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albertok
New Member

3 Posts

Posted - Jul 07 2009 :  11:05:14 AM  Show Profile  Reply with Quote
quote:
Originally posted by audioguru

3000W is way too much for an inverter. If you use only 12V then its battery current will be 300A!
You would need to have a large room full of batteries to power it for a short time. Then it will take 1 week the charge the batteries.
Its wiring must be huge and it would need 48 output transistors and many driver transistors.
Its transformer would cost a fortune.




Why do you keep saying that it's not possible to make an 12V 3000W inverter? And that you would need a room full of batteries?? It simply is not true and you know it.

A well built 12V 300W inverter consumes about 300A at full load give or take. Well, that said I think you would agree with me that it's not impossible nor dangerous to take 55 Amps out of a small vehicle 55Ah battery, right? Neither is it any more danger involved in taking off 300Amps from a 300Ah battery, (given you know what you're dealing with), it CAN KILL YOU, but not because the battery is programmed to explode like you try to scare people with. So you probably should stack up with a couple of heavy duty 230Ah batteries.

3000W inverters have been around for a long time running on 12V, but given the high amperage you're dealing with it's more than twice as dangerous as a 3000W 24V inverter.
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albertok
New Member

3 Posts

Posted - Jul 07 2009 :  11:11:34 AM  Show Profile  Reply with Quote
Furtermore it's worth to say about heavy cables and large inverters that for any 12V invertes from a few hundred watts and up, it is absolutely nessesary to keep cable lenghts to a minimum. Unless you have a wery deep wallet :)
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jul 07 2009 :  3:09:10 PM  Show Profile  Reply with Quote
A battery rated at 300Ah is tested with a 30A current, not 300A.
Cold Cranking Amps are tested for a very short duration.
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albertok
New Member

3 Posts

Posted - Jul 07 2009 :  4:14:22 PM  Show Profile  Reply with Quote
I'm not talking about CCA, I'm talking bout if there is a chance for a battery to blow up when you draw from it Amps in the range of its rated Ah capacity. It will not. I have never had any of my approx. 55Ah car batteries that's been fitted to my car blow up even when I draw up to 200 Amps. 30 Amps run just by turning the key, another 75 - 150 when I crank it. Comes close to 200. When that's said I'm also aware of it's intended purpose, and the fact that you'd drain it extremely fast. But for testing purposes it's close to ideal because you get quick response from the battery when you test your low voltage cut-off, and voltage regulator. You just turn off your charger and voltages drop fairly quick.

Also something I forgot to mention earlier is the main reason many people buy 3000W inverters in the first place. Some just want to be able to run 1000W power-tools for a few seconds at a time now and then, some want the convenience of haveing a microwave owen in their trailer, boat or cabin. Most do not intend using its full rated power for an extended period of time.

Edited by - albertok on Jul 07 2009 4:23:22 PM
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antish
New Member

Ethiopia
1 Posts

Posted - Aug 20 2009 :  2:48:23 PM  Show Profile  Reply with Quote
i have a problem in 12/24vdc input to 220/230vac output with 4000w and above.please help me to do that
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superchad
New Member

3 Posts

Posted - Oct 30 2009 :  4:32:06 PM  Show Profile  Reply with Quote
hi i saw this simple inverter when googling schematics for and inverter, i saw that it might have problems, well i need to know what would best for me, i need to make an inverter that is about 75 Watts to 100 Watts (for using a laptop in a car) i want it to be as simple and cheap as possible. thanks in advance.
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Oct 31 2009 :  12:16:01 PM  Show Profile  Reply with Quote
This week, Canadian Tire store is selling a Name-brand 150W inverter for $19.99.
It would cost about $60.00 to make one.

They also have an 800W one on sale for $59.99.
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superchad
New Member

3 Posts

Posted - Oct 31 2009 :  5:19:14 PM  Show Profile  Reply with Quote
i estimated the originaly circuit aaron posted at around $20 to $30 to make (for the parts) i want to make one someday so id like to have the link to schematic for one.
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