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

[tvtech]

Crowbar...110A Thy......as in the Video.

That smoothing Cap alone will blow it and the Fuse to smithereens if it connected anywhere but at the Output of the supply....and then it is probably too late anyway...

That begs the question: Did the original designer ever really Crowbar this PSU on purpose to see if the protection really works.....

I doubt it. Waaay to much energy there for one "little" Thyristor to handle even only once. And it's borderline anyway...no matter where it get's put.

Maybe a case of...design of the PSU was superb, enough cooling and all components working well within Spec....so the Crowbar circuitry never needed to prove it can work anyway....

Interesting

Regards,
tvtech

 

[Billy Bowling]

Hi,

What are you going to use for the INPUT source for this thing?
Is it to be powered by 120vac or something else?

For that you need either a big transformer or build a good quality (buck) switching regulator.

120V into a 100A Peter Nahl transformer ( Very heavy, 40LBS) that has a 3 stage output. 13.?V, 14.?V and 17.?V. I think I am asking to many questions at once! I have the 120V to transformer to Bridge Rectifier to Regulator board pritty much figured out! Above in the first comment are some of the problems and questions I have. Any info is good info if its the right info! THX

 

[Billy Bowling]

Crowbar...110A Thy......as in the Video.

That smoothing Cap alone will blow it and the Fuse to smithereens if it connected anywhere but at the Output of the supply....and then it is probably too late anyway...

That begs the question: Did the original designer ever really Crowbar this PSU on purpose to see if the protection really works.....

I doubt it. Waaay to much energy there for one "little" Thyristor to handle even only once. And it's borderline anyway...no matter where it get's put.

Maybe a case of...design of the PSU was superb, enough cooling and all components working well within Spec....so the Crowbar circuitry never needed to prove it can work anyway....

Interesting

Regards,
tvtech

This power supply will never see 100A even in its life! 60 to 70 tops and that will be a pep 70A at that. As far as the unit in the video it works perfectly and he has built several others. Getting info on how to build is a different story. He will give up none! As far as cooling, I have 4 6" Be Cool fans that will be mounter internally 2 directly over the 2N2772's and 2 over the 6 2879 amplifier also mounted internally. The driver or drivers are mounted to there own heat sink with a 3.5" dedicated fan ! The hole chassi is 3/8s aluminum as well. Cooling is not going to be a problem!

 

[Billy Bowling]

Well, it seems you have are making some circuit that you have in mind, so why don´t you post a schematic of what you are going to connect where. Seriously, if you know what wire to connect to which component, then you have to be able to do the same on a piece of paper.
Also some specs of what you hope to build or what someone else has already built would be really helpful.

If you could tell me how to find a down load or maybe a app that can to help me draw out a schematic I would greatly appreciate that! I cant seam to find a good down load off the net that works properly. I can draw it out on paper . As far as specs I am looking for 100A @15V max at 60HZ. I have everything written down at the shop and I will post it when I get back.

 

[kubeek]

For example LTspice is free and you should be able to do almost any schematic with the stock symbols, plus as a bonus it also allows you to simulate the circuit.
Other then that, why not simply draw it by hand and upload a scan or a photo of what you have in mind?

 

[Billy Bowling]

Yes Jim, Billy is completely confused about what a crowbar circuit is - it's called that because it essentially 'throws a crowbar' across the power supply terminals, causing the fuse to blow.

You wouldn't normally place the crowbar across the output of the supply though, the monitor circuit monitors the output, the crowbar thyristor would be across the output of the bridge rectifier (input to the regulator) to avoid damaging the regulator circuit.

Balancing the load equally across the multiple transistors is achieved simply by suitable emitter resistors balancing them out.

I understand what the crow bar does and how it works. What I dont understand is how to properly install it ! I have everything I need for it buy no experience on how to put the thing together. That is why I am here. What I say may not be technical to your terms but I am trying here.

 

[Billy Bowling]

For example LTspice is free and you should be able to do almost any schematic with the stock symbols, plus as a bonus it also allows you to simulate the circuit.
Other then that, why not simply draw it by hand and upload a scan or a photo of what you have in mind?

I can draw it by hand but I would like to check into this site you mentioned. As far as the design I am basing it off the one in the video above. If you watched the video, that is what I am going for!

 

[Mikebits]

Dang dude, that's a big HF amp. Why not go for something more like a 100W amp?

 

[Billy Bowling]

Dang dude, that's a big HF amp. Why not go for something more like a 100W amp?

I already have 100w amplifier. I built a 300w but I used a power supply already built and a amp already built and just put them together in a housing. Anyone can do that so I decided to build one from scratch. 1KW is perfectly legal for 10 to 160 meter use. This amp can take about 150 to 200w of drive tho so it may do a bit more, If I can get 16 or 17V of output from the power supply. I think I am just going to go for 14 or 15 tho.

 

[moffy]

Your emitter resistors should be between 0.025 to 0.05 ohms, assuming 10A max for each 2N3772, gives a max voltage drop 0f 0.25v to 0.5v. Probably go with the 0.05/5W. What do you others think?

 

[Billy Bowling]

Your emitter resistors should be between 0.025 to 0.05 ohms, assuming 10A max for each 2N3772, gives a max voltage drop 0f 0.25v to 0.5v. Probably go with the 0.05/5W. What do you others think?

You are correct. I am using**broken link removed**

 

[moffy]

Nice. I like to overate my resistors power by 100% also. Keeps them from burning fingers or the board. How are you monitoring the total output current? Perhaps a 50 to 100mV current shunt?

 

[Billy Bowling]

I have not made it that far as of yet! That is why I am here. I was wondering if I had to have one for my digital read out. I know know I am going to need one! I found a**broken link removed**on Ebay for $8.50 plus tax. If I were smart I would of looked into these before buying the ones I did. You can buy the digital meter with the shunt cheaper than a shunt alone. I can still use the ones I already bought. Mite just go ahead and box those up for the future and go ahead and but the meter/100A shunt kit!
And yes as a recomendation from a friend years ago I have learned to take that extra step when buying components that take a load! If it wont hurt always go bigger! Bigger dont mean better but the life span can be stretched a bit if it is not under its max load all the time!

 

[Billy Bowling]

I have not made it that far as of yet! That is why I am here. I was wondering if I had to have one for my digital read out. I know know I am going to need one! I found a**broken link removed**on Ebay for $8.50 plus tax. If I were smart I would of looked into these before buying the ones I did. You can buy the digital meter with the shunt cheaper than a shunt alone. I can still use the ones I already bought. Mite just go ahead and box those up for the future and go ahead and but the meter/100A shunt kit!
And yes as a recomendation from a friend years ago I have learned to take that extra step when buying components that take a load! If it wont hurt always go bigger! Bigger dont mean better but the life span can be stretched a bit if it is not under its max load all the time!

The ones I have say they will take 99.9A but by no means are they heavy duty. There just a .56" digital meter. Here it is so you can see for your self. I didnt realize they were so cheep made but for less than 5 bucks I thought Hell yeah when I seen them. **broken link removed**

 

[Billy Bowling]

The ones I have say they will take 99.9A but by no means are they heavy duty. There just a .56" digital meter. Here it is so you can see for your self. I didnt realize they were so cheep made but for less than 5 bucks I thought Hell yeah when I seen them. **broken link removed**View attachment 86919

I like this one **broken link removed** but there are many to choose from. Like to find a place that sold ones for AC and DC that matched tho. Ill do some searching I guess.

 

[Mikebits]

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.

 

[KeepItSimpleStupid]

The Chinese combo meters like to put the shunt in the ground lead.

 

[Nigel Goodwin]

Yes and no.
If the crowbar is at the output of the rectifier, it will be directly across the smoothing capacitor and potentially the peak current in the crowbar condition will be higher, possibly leading to damage to the crowbar device (usually a thyristor).

Even on the output of the supply you've still got a potential high current when it shorts out, it's far better before the regulator - simply add a low value high wattage resistor in series with the thyristor, or a suitably large thyristor

Notice the one mentioned above is rated at 110A, presumably for that reason - so it's surge capabilities will be a great deal higher than that, but a 0.1 ohm resistor in series wouldn't do any harm, this also applies if you place it on the output as well.

Another reason for NOT doing it on the output is speed, it's likely to blow the fuse far faster on the input side than the output.

 

[KeepItSimpleStupid]

FWIW: Crowbar: This usually describes a SCR type circuit that quickly shorts the output of a power supply due to an over voltage condition

 

[Nigel Goodwin]

We're all happily talking about crowbar circuits, but what about the fuse and fuseholder?, surely they are going to be pretty expensive?.

Also, as the OP strangely seems to be wanting a variable supply?, a crowbar is less usual (as it tends to be one fixed voltage, due to the crude and reliable design).