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

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Billy Bowling

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OK I am fairly new to electronics and then again, not so much! I have worked on CB radios and Ham radios plus HF amplifiers on and off my home life. I Have decided to build my own power supply. Not sure how to draw you a diagram but I can tell you what it consists of at the end of my problem question!
I am building a 100A variable(0V to 15+V) power supply I have 3 total TO3 heat sinks with a total of 13 2N3772's. 1 driving the 12( I had them so I used them!) Would like to know how to wire this up (Base drive line)??(Equalizer Resistor assembly)??( Collector Wiring)??, 1 driving 12? (CROWBAR)?? Also wondering if it would be better for a 2 driving 12 configuration.
I am using a
1)Peter W. Dahl Co 100A 3 stage 13.8V/14.2V/17.6V!
2) 180000uf 63V Filter cap!
3) Stock from Astron, Dual 100V/1000A Rectifiers!
4) 8 or so current limiting resistors 0.5ohm/5W!
5) Stock from Astron Regulator board with LMR723 with pre driver and variable!
6) Some type of RF Bypassing for AC input? Not sure maybe some info on this subject!
7) Some type of RF Bypassing for DC out? Not sure maybe some info on this subject!
8) Digital Current meter with or without Shunt??? Will I need a Shunt? Not sure maybe some info on this subject!
9)Crow Bar 1913, 110A SCR
10) All Digital meters for AC and DC including digital temp gauges for inturnals,( Because I have them)!
Any info will greatly appreciated! THX Bill
 
Looking to build a variable volt 100A power supply with crowbar circuit! Just wanting any info or ideas you guys may have on this design. Also wondering if I can get someone to draw me a schematic if I give them the parts I am using and maybe tell me if I am leaving something out. This is a great form. So glad I found it. Any info will be great even if it is to say I am a dumb ass. That is better than no feed back what so ever. THX
 
Yup, your leaving something out.

100 A at 5000 kV or something smaller? 1 V maybe? Fixed or variable? Welder? Plasma cutter?
 
Billy,

Welcome to the forum.
Please don't start separate threads relating to the the same topic, all that does is create confusion and minimises the chance of a good solution to your problem.
With that in mind I have merged your two threads.

JimB


PS
KISS and Crut, the clue to the voltage is in the title of the thread.
 
KeepItSimpleStupid said:
Yup, your leaving something out.

100 A at 5000 kV or something smaller? 1 V maybe? Fixed or variable? Welder? Plasma cutter?
Click to expand...
This is going to be used to power a HF linear amplifier! The amp has 6 2879 transistors! It will also be used as a bench powersupply for anything I may be performing work on at the time!
 
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.
 
CROWBAR circuit assures that all 12 2n3772's get exactly the same voltage and amperage! This way not just 1 2n3772 takes all the power at once.
Click to expand...
I am using 1 2n3772 driving 12 2n3772. To assure that all 12 get the same power at all times. The Crowbar circuit is ideal for this application.
Click to expand...

No.
I think that you misunderstand the operation of a "crowbar" circuit.

A crowbar circuit is a protection circuit which puts a short circuit across the output of the power supply if it detects an output voltage higher than some preset value.
Example: the unregulated supply voltage before the pass transistors may be (say) 20volts, if one of the pass transistors were to go short circuit that 20 volts would be connected directly to the load.
If the load cannot handle more than (say) 15 volts, then the load will be damaged.
However, if we have a crowbar which is set to trip at 14.5 volts, as the output voltage rises due to the faulty transistor, the crowbar will connect a very low resistance across the output of the power supply and so limiting the voltage rise.
There may of course be secondary complications due to shorting the output of the (faulty) power supply, but that is maybe a lot cheaper to fix than the expensive bit of kit being powered by the power supply.

JimB
 
A Crowbar circuit is normally used for Overvoltage Protection sensing at the output of a PSU where a Thyristor is then triggered and puts a short across the works and blows a fuse stopping damage to the load.....once it triggers no more power until the fuse or fault has been sorted...

Something wrong with your understanding of the thing you are building Billy...

Regards,
tvtech
 
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 must learn to think and type quicker...both at the same time

Cheers Guys,
tvtech
 
Billy Bowling said:
I would like to think you guys are the experts! What other info would you need?
Click to expand...
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.
 
^^^^Original PSU here:
[/QUOTE]

Looks nice and well built. All the Specs are there too. Please watch to the end of the Video.
 
Last edited:

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).

If the crowbar is at the output of the power supply, if the overvolt fault is caused by a faulty pass transistor, then things cannot get much worse anyway.
If the overvolt is caused by a transient error in the control circuit, then the current limit circuit can protect the pass transistors by turning them off.
In each of these two cases, there is a little resistance between the smoothing capacitor and the crowbar device to limit the peak current.

Where the crowbar device is connected is probably down to preferential engineering on the part of the guy designing the power supply.

JimB
 
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