HOW TO BUILD A 100A VAIRABLE VOLTED 0 TO 15V POWER SUPPLY USING CROWBAR?

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Hi Nigel and others

Problem is one of those classics again..

The OP has some Electronic knowledge.....but just not enough. There is basic understanding from the OP...but now once again it is extremely hard to try and help the OP without all of us ending up discussing "Crowbar Circuitry" and the merits thereof..where the OP did not really understand what a "Crowbar" circuit doe's??. So now we sit here debating the in's and out's of where the Crowbar should be and why.....

You see where I am coming from?. The OP thought that was a good way to protect the pass Transistors from individually working too hard...where we all know (regulars here at ETO)...a Crowbared Circuit is to prevent Overvoltage....not to work regularly. A once off protection circuit....

You see I am battling here too. The OP had it wrong from the word go....

I will try and explain it easier to the OP here (please excuse the bold lettering):

Hi Billy

What a Crowbar Circuit essentially does is to make an electronically induced short circuit on your Power Supply. A dead short that gets activated when for some or other reason the output Voltage rises above the set point...in other words it is there to protect the load (output) from damage above the set Voltage.

Whilst the electronically induced short is taking place....very, very quickly...a fuse supplying power will be blown open. Cutting off power. Until the fault that caused that the problem is fixed. The link is broken.

A once off protection system. Not for regular use.

I cannot explain it better than that.

Regards,
tvtech
 
Mikebits said:
To get a 1000W RF at 100A your final PA will need to be around 80% efficient. This is tough to achieve even by a seasoned designer.
Click to expand...
It is 1000 W pep which is only about 650 to 725 Average. I dont use a PEP Watt meter, I use a Bird 54 Trueline meter! With this same amplifier tested on my 200A bench power supply @ 18V it is doing 1150 plus Average @ 16V right at 950 average and at 13.8 its doing 750 plus! All these readings were gotten on the 10 meter band 28.502.50 mhz and achieved with a Standing Wave Ratio of less than 1.1 to 1 as read by my MFJ989D and my SARK100 Antenna Analyzer!
 
This does not have to be a crowbar set up! I have the SCR but it does not have to be used. SCR 1913 pictured
 

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Billy....

I think the original PSU design was brilliant.....just your confused Crowbar understanding worries me.
You asked for advise here...and we are generally accurate. Not a bunch of chancers.

Personally, as much as you wan't to build this, I think you are going to battle....

And you are dealing with massive energy.....not for the faint hearted..even practised pro's would think twice...

I wish you luck

All the best,
tvtech
 
I admit I did no
t fully understand. I thought it (SCR) did more than 1 specific thing! I had the 2 SCR1913's and thought it would be nice to include one in the power supply. I have a 110 and a 75! Now that that has been said, I sure thought this was going to go differently! I was thinking I would say what I had and what I wanted to do and then people would say" you can or cannot do this or that then I would get info on how to do so" Not the case thus far! I have learned what a SCR does and a Variable voltage wont work with it. I am learning! Lets forget about the variable voltage! I need this thing to power a amplifier ans a couple other smaller devices! Amp Freq counter some LEDS and thats about it! 80A max. Maybe I send some pics of where I am now and you guys tell me if I am going at this the right way or not?? I am at a stand still here and need some help badly.
 
I understand that this is something that could potentially kill me or someone else it they got into this thing opened. I understand that 180000uf is not nothing to screw around with. This is not my first power supply tho! I have built smaller ones! I However I have never built one using 1 2N3772 driver driving 12 nor have I ever built one with a SCR Crowbar. You guys I would like to think are pros here! I am here for your help! If the SCR is not needed then I wont use it! I am goingto build it tho.I have to much invested not to. I am in the process of making a schematic for you guys to see and tell me maybe where I am going wrong! I started it last nite but lost it because I forgot to save it! Ill try again this evening.THX
 
I like a separate current shunt so that it can be integrated into the current protection/limit. You definitely want a variable current limit/protection for the supply, especially if using it for light loads.
 
moffy said:
I like a separate current shunt so that it can be integrated into the current protection/limit. You definitely want a variable current limit/protection for the supply, especially if using it for light loads.
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The only lights/light load will be the lights/LEDS that show power on/off and on/off for the other components. There will only be 8 or 10 lights total. I have a 8 digit freq counter intergraded along with a parted out Bird 43 Watt meter with PEP, Average, 2X and 5X kit and antenna selector. The only thing that requires power is the lights, 8 digit counter and 9 to 12V connection for the pep/2x/5x kit on the bird meter. Basically all the power is going to be dedicated to the amplifier. There will be several 6" fans inside, 4 I think plus 2 or 3 smaller 2.5 to 3.5" fans as well. I think 3.8A is the total max amps all this stuff including the fans together will pull. The amplifier needs a max of 70A but I have tested it and never seen it draw more than 54 A @ 15V and I am sure it may raise slightly ar 13.8 so I am saying 80A will be the max this unit will ever hit.
 
Billy Bowling said:
You guys think there would be any way I could get some info on some of the questions I had in the first comment? THX
Click to expand...

Do you mean in your very first post?.

The 'equaliser' resistors are simply fed from each of the individual 12 emitters, and their other ends all joint together to create the final output.

One 2N3772 drive should be fine, VERY crudely each output device provides 10A, so assuming they need a base current of 1A the driver needs to be able to supply 10A as well, and needs 1A base current itself - which comes from the TIP31 (told you it was CRUDE!!)
 
Take a look at this and see what you think:
There may be a couple of things you need to add like inrush current limiting.
 

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An interesting circuit.
I am nor sure that I like the so called "Overvolt Protection".
And what on earth is going on with that voltmeter circuit?

Where did you find that circuit, it looks like it is cribbed from an RSGB publicaton?

JimB
 
ronv said:
Take a look at this and see what you think:
There may be a couple of things you need to add like inrush current limiting.
Click to expand...
It has inrush current limiting, R1/SW2/RLa. You'll have to hold SW2 until RLa latches. Could you please supply the text that goes along with the circuit? There are obviously some subtleties going on e.g. DS1/R9.
 
I never got to the site itself as I got a virus warning. You can get there (I think) by googling high current power supplies and looking thru the pictures. I think the diode indicates over current.
Yes, interesting voltmeter circuit. I was just looking around for an example of parallel transistors trying to help with the first post.
 
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ronv said:
Take a look at this and see what you think:
There may be a couple of things you need to add like inrush current limiting.
Click to expand...
ronv said:
Take a look at this and see what you think:
There may be a couple of things you need to add like inrush current limiting.
Click to expand...
Outstanding RonV this is nice to have. I have seen some that look like thin online but nine with the Inrush Current Limiting! Thx RonV
 
Guys I am going to to my best to build a schematic tonight for ya! I hope if I can do this properly maybe you guys can tell me where I am going wrong! There are some circuits I dont know where they go so I may have to leave some connections out. Maybe someone can pick it up and finish it for me. This is the hole reason I started this post was to find out how to connect some of these components. I am a welder and a Diesel mechanic so unlike some of you guys I am not around circuits like this every day. Any information will be greatly appreciated. Thanks Bill
 
Nigel Goodwin said:
Not really, it's only low voltage so not a danger - it's no different to playing with a smallish battery.
Click to expand...

LOL...Remember he is building this from scratch.....if the Cap happens to be charged and things are not connected correctly....bang.

Goodbye circuitry. Never discourage caution.....
 
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