I used a very similar crowbar circuit in my biggest power supply, it is very worthwhile insurance. It can also be worthwhile to put a few disc ceramics between the output terminals and the chassis, a lot of power supplies don't like common mode rf currents around them. 73 and well done on your videos.
I had a radio that would not work properly just made a buzzing nose. I then connected a second radio to the same power supply and got the same symptoms. It was at this point a realized the problem was with the power supply and not the radios. Yes I know this was not a very clever thing to do. My point is that power supply's can be dangerous, which means that this little device you have built is great idea and something every person with expensive equipment should give some thought to. Great video and very helpful as usual. I was fortunate that on this occasion my radios suffered no damage.
Great video. I built one of these into my home brew 10 amp power supply that I built for my VHF rig. It was many years ago and the choice of thyristors at that time was limited. So if an over voltage occurred it usually took out the thyristor as well!
I love SCR crowbars! I use them a lot in my projects, normally in conjunction with TVS diodes and PPTC fuses, right at the supply input stage. They already save my circuits from my own mistakes. However, I don't use any resistor between the Zener and resistor association, and the capacitor plus the SCR gate. The capacitor that I use, since it is normally 10nF, does not demand enough peak current to damage the Zener diode. Edit: I've seen that you added a 100Ω resistor because you were worried about the pulses. However, mind that the Zener below its region practically does not conduct, and as long as the pulses don't exceed the threshold voltage (that is, Vzener + Vgth), you will be fine. The SCR will need a certain amount of current, albeit tiny, to activate, and the Zener won't be able to supply even the minimum when it is blocking. I've used sensitive SCRs without that resistor and with a 10nF capacitor, and never had a false trigger, even considering long supply cables (and their annoying inductances) being connected right before that stage.
Hi Peter, Nice video. I thought your step by step explanation was great. Anyone should be able to build one from watching it. A very valuable circuit also. 73
As someone who is learning electronics on my own you are a great teacher. i learn a lot from your videos. Maybe you can do a video on how to and not to connect RF equipment up to test equipment like oscilloscopes, spectrum analyzers, frequency counters, and tone generators. Like how and when to use a RF tap and how to connect a radio up to all the test equipment at once. It would sure make me understand a lot more on how to test my radios so i do not damage my test gear i am slowly acquiring
Great addition to upgrade cheaper power supplies you made there Peter. Thats the reason I always use high end supplies. Last thing I want to do is blow up my radio or worse a customers radio. And I'm with you on switch mode supplies, very noisy. The only switch mode supply I have is a Wayne Kerr lab supply and it is very quiet but also very expensive. Mike
Thank you google for putting this video on my homepage. I've just built a linear MOS-FET regulator to allow for portable operation of a FT-892 from recycled 18650 cells. As good as it might be built, the extra safety of a cowbar is definitely a winner. All the parts for this circuit are already in my shack. However, if you have to buy everything new, you'll still be well below €10 for the circuit alone. Which is nothing compared to buying a new TRX that costs many €100. I'll definitely design it into my regulator. But i will definitely refrain from using a automobile blade type fuse. These things are absolute rubbish. ANL or AGU are much better for the job and aren't that much more expensive. Blade type fuses, which i found to be on most power connector cables for portable or mobile radios, have severe disadvantages in terms of contact resistance and reliability compared to ANL or AGU.
Peter another great video, and as is usually the case with your videos, very timely for me. I recently purchased a tech Special HP frequency counter (HP5385A) off of ebay and tracked the fault down to the crowbar circuit. As so often is the case, I learned a lot about this circuit during my troubleshooting and repair. I felt really smart and accomplished watching your video knowing where you were heading and why you doing what you did. Keep up the good work and take care my friend.
Very nice show and tell video Peter. Not sure how many times a radio comes in where the supply and failed and shot 24 volts to the rig. Most of the supplies I run have a crow bar circuit built in. But a lot of supplies on the market does not. This circuit is a sure way to save a lot of repair work. Big thumbs up my friend. 73 Buddy
Thank you Buddy. Yeah it is really a simple way to protect the radio gear and I have also seen to much power supplies with exactly this problem.. Tale care my friend 73
I have a 12v (13.8), 70 amp linear supply that has wheels on it! It has three transformers in it placed in a phased, parallel configuration which then feeds a monster bridge rectifier on a large heat-sink. The rectifiers appear to be Selenium but I can't be sure. That is followed by four 25,000mf capacitors which may be because of the Selenium rectifiers. It also has some in-rush current protection which is probably because of the 100,000mf capacitor bank. This feeds the regulator circuitry which contains several bipolar transistors on the back of the supply which is all heat sink. I would say that 3/4 of the weight is transformers, 1/4 is heat sinks and an insignificant portion is the electronics (that's why it's not listed in the weight). :) It's about 40 or so years old so your circuit is going inside.
Before i became a Ham radio operator, i dabbled in CB when i was young. I had a cheap voltmeter and liked to use it to examine voltages in everything. I discovered some radio guys were turning up the voltage in their power supplies as high as 16v thinking it would raise the power of their radios. So i did some reading about the relationship between voltage and current. I discovered that when you raise the voltage in an inexpensive power supply, the current drops. Aha ! Would that explain why their radios audio was clipping on peaks ? yes it did. I turned my power supply down to 12.8v insuring i would recieve the full current the radio was designed for. 13.8v in power supplies was meant to mimic an automobile alternators regulated voltage output, but it is not necessary your power supply voltage be that high.
Thanks for sharing. Just had a conversation about these circuits on EEVBlog forum. Nice to see your in action. Definitely good to have that second fuse.
I guess im randomly asking but does any of you know a trick to get back into an instagram account? I was dumb forgot the password. I would love any assistance you can offer me!
@Lukas Gerald thanks for your reply. I found the site on google and Im in the hacking process now. I see it takes a while so I will get back to you later with my results.
in addition to this problem, seems that 31Vcc as input for a transistor produce a lot of dissipation if we have 13.5Vcc as output..more than 200watt, a little varistor it could be a 2nd idea. Good explanation !! :)
Crowbar protection used to be an integral part of almost every linear power supply. But sometimes not. If you have power supply without this protection, it is wise to add some. But this power supply can damage your equiptment in another way (and crowbar does not help at all). The problem is, that GNDs of almost everything is connected together. And when you accidentaly hit the transistor case with your +12V banana plug when the PSU is running, it could lead to a great disaster. It should have at least some protective cover, but in fact, I don't like theese PSUs. It's much better to do the regulation in negative side of the power supply. Then the collector of the TO-3 transistor is on the GND youtput, so you do not have to isolate it from the heatsing and the PSU's case, which is good from the thermal point of view, you also do not have to care about things accidentaly touching that transistor, because its collector, heatsink, PSU's case is on the GND potencial. Regulating at the positive side is much easier, you do not have to build supplementary PSU to power the regulator (using PNP transistors would also eliminate this, but high current PNP transistors was not easy to buy for a good price), but on the other hand, it complicates mechanical design, especially when 20 and more amps are needed.
Thyristor current flows through anode, to gate, which causes forward bias on zener, which conducts, and causes current to now flow through the anode/cathode of the thyristor, to cause a direct short, blowing the fuse.
Conduction voltage and current of the thyristor will indicate level of conduction for the gate, which is the switch for the pN juntion of the thyristor reverse bias of the gate, it will conduct, turning on the path through the thyristor, to ground, pulling excessive current to blow the fuse.
Of course, great video. I plan to use a car battery in parallel with the PS. In this way I can ensure both consumption and protection, besides a protection circuit. I have heard about crowbar circuits that didn't work, maybe the thyristor failed..
Peter, I use the exact same circuit (though my thyristor is 300a), it is cheap insurance against destroying a radio. My power supply has soft start so in the event of the thyristor triggering it simply shuts down. It is sad that few manufacturers fit crowbar protection.
It would be interesting to see how fast this circuit is. There will be a measurable delay in the time it takes for the zener to break down and the switching speed of the thyristor will have a time constant as well. I'm curious to know what these delays add up to and if the circuit is fast enough to prevent damage to sensitive semiconductors in whatever is connected to the supply.
Good video. I would prefer to see the Thyristor trigger at 15V though. Is the Thyristor mounted directly against the metal project box case or is there an insulator between it?
Hi Peter - I just found this video which is very helpful. I have an older Kenwood PS-30 supply I got to power an older Kenwood TS-570D I got at a flea market. The supply does not have protection and I would like to use your circuit. But in the specifications for the supply, it states the open circuit voltage can be as high as 20V. I assume your circuit can clamp almost instantaneously. My question is if I insert the circuit and turn on the supply, wouldn't it clamp before the transceiver load stabilizes the voltage? Actually my question is more general in that many supplies when turned on have a period of time before the voltage is regulated. Wouldn't that effect the operation of your circuit? Or am I wrong about the moment supplies turn on?
I made a mistake on the specs. The PS-30 is 16V max at no load. The TS-570D is 13.8 +/- 15%, so the max high would be 15.87V. I guess I am okay to use your circuit. But my question becomes what behavior should expect from most power supplies shortly after you energize them. I looked for spikes on my PS-30 with a scope and didn't see any.
A very good video on the tyristor crowbar. Well, since you have a German power supply, you must be Deutsch. My power supply weighs over 20 lbs. since it has such a large transformer in it. It's a linear power supply. MFJ 4035MV which is 30 watts continuous and 35 watts surge. Now days they are making power supplies with over voltage and over current protection. Ich spreche ein bischen Deutsch. Ich bin einer Swizer. W Rusty Lane K9POW in eastern Tennessee
The newer switching power supplies are much better now days, even the internal supplies in newer radios are switching. I have both but choose to use the switching supply because it has all the over voltage/current sensors included.
it might be that the resistance of the secondary winding of transformer is such that at full load, you've got a couple of volts left across the power pass transistors (product cost tradeoff)
I would just like to add my personal opinion: The crowbar protection is better to realize it and insert it inside the container; Also verifying that a fuse with a capacity proportionate to the capacity of the thyistor is really present inside! because if the inside of the power supply is not inspected, it could happen that the fuse is only assumed and not really foreseen by the manufacturer of the power supply!
Yes Peter I totally agree with the rest of the comments. This is a great video very well explained. You do make some great videos my friend and this one is no exception. Thanks Peter 73's my friend
A more elegant solution would be to connect the thyristor across the fuse before the regulator while supplying the gate voltage from the output of the regulator. When the crowbar trips all power is removed from the regulator preventing possible fires. Having a crowbar on the outside of the PSU is dangerous.
16v should be the trip point. Most txcr;s work with better IMD specs at 15.5v, especially Elecraft. 13.8V is not the best operating voltage expecially allowing for TX volt drop. All my txcrs run at 15.6v with no issue, usually ~14.8v during TX. Makes for a much cleaner signal.
Many thanks for all your video work. Would a BTW69 with a voltage rating of 600v or 1200v be a suitable substitute as I'm struggling to find the 800v version? All other specs. being the same of course.
Very good logic. But still the whole thing depends on a fuse which might not be fast enough to protect radio electronics. I have seen 100$ transistors that burn faster to save 0.1$ fuses. :-) That being said, I recently discovered your channel and you have very informative videos. Also I admire your workbench equipment, especially the mini VNA.
Well the fuse is not the critical component which needs to do the fast switching therefore this little crow bar will protect your radio for sure. Thanks for watching 73
Bora, at the instant the thyristor fires the positive rail (and your radio) will be shorted to near 0V. This happens within about a microsecond, long before the fuse gets around to blowing a fraction of a second later.
I have mine drive a relay that locks open with a led also have a switch so I can see the voltage at the output an the relay stays open so no power can get to radio there is also this one in it that will blow a fuse
Very nice explanation but my concern is that the thyristor/fuse combination might be slower to react than components in the radio. So the radio may be damaged before the crowbar fully operates. Is it possible to measure the time for activation?
I am wondering this as well. The thyristor will have a speed at which it switches, plus there is the delay as the zener breaks down and a delay as the fuse opens. These would all add up, and likely be longer than it takes for a semiconductor junction in the radio to experience damage.
Thank you , for such a professional, theory and by the way. To those who suggested to put a relay, it's quite good but not safety, as long as any sudden high rise voltage bounce up above 13.8(v) which in turn risck the output. And that is why a fuse burn out for safty.
I must get around to doing this on my 40A supply. Do they have larger thyristors? I found BTA100A-800B. But thinking I can use the 69 because the fuse should blow fast enough to protect the btw69 thyristor even on a 40A supply.
An ounce of prevention. I think I used a triac on the last crowbar I made. The thyristor is about the same thing. Triac or thyristor into a diac, and you have what? Maybe $12 invested in protecting $1000-$14,000. I have a thyratron running a protection circuit in one of my old boat anchors. If only I had a dollar for every man named Peter with a German accent I have worked with. I think we had 5 at one company. We also had a Hans too. 73 KI7AQJ
interested in building some of these but i know little about electronics. the components listed you have given values for but when i look to buy them they have voltages on them, wattage and what type of capacitor or resistor you used. apart from that good video
Great video. invaluable little circuit. I have a question regarding the zener diode. i know you said 13V but is current rating of that zenner inportant? and what value did you use? thank you in advance. ivan vk5rs
sorry power rating not current .... my bad ... for exmple .... 1N5243B is 13V but 500mW max power. would that be sufficient for this circuit? thanks once again
well, to handle that current you're using a power thyristor. but instead of that, if you uses a power transistor even the same type that uses the source power, in the case that the transistor of the source power will sorted, you can change the damaged power transistor with the protection transistor. in this way you will have a change to make a call with your radio without overvoltage protection. using the little thyristor used in the first part of the video to trigger and lock the circuit.
Hi Fede, well yes as long you have only 1 power transistor but what if you have may be 5 power transistors in parallel than your approach becomes a bit complicated.. 73
Peter, If you were building a Crowbar circuit for say a 25-30 Amp supply, would it not be a good idea to lay down a thick layer of solder along the tracks feeding power to the radio? Surely the copper tracks on the Vero board would not be of sufficient thickness to carry 25-30 Amps of current?
A switching PSU don’t work like a linear one. If the transistor in a switching PSU is failing the output voltage will drop. But you shouldn’t use switching PSU for radio equipment because of the ripple it produce. But yes you can use this for any PSU. Only the zener and resistors must match the output voltage.
What does the voltage rating on the thyristor need to be - do they work like other things which are actually wattage based . Like a switch will be rated at 220 volts at 3 amps or 110 volts at 6 amps which would make it like 600 watt rated?
With the straight path from the fuse to the output which is the path of least resistance - what actually causes it to take the path of the protection circuit?
I always use the dedicated over voltage IC from Motorolla the MC3423 and a Thyristor..... I've a video of a homemade supply on TH-cam with this IC ... Gw0wvl....... great video and thank you.
Is the proto board really needed? With terminals, a chassis fuse holder and terminal tags there are few enough components just to use point to point wiring.
hi Peter! is there any chance to do something similar (I mean an overvoltage protection) for variable power supplies: for example that DF-1730SB you are using in the video? if one of the pass regulating transistors fails (going short circuit) you get the whole voltage on the output and "fry" the equipment you are powering!!!
LOL thank you Digger for reminding me and I agree I have noticed it. May be that I always think I was not able to get the message over. I need to improve it. Damn my videos will only last 5 minutes then. 73
Is it possible to get a high voltage spike due to the small delay in the Thyristor circuit, especially with a capacitor on the gate? Maybe this could be measured by putting a scope on the output?
But if there is a short delay before the thyristor triggers, won't there be a short period of high voltage just before it is grounded? Maybe the spike will be filtered by capacitors in the rig.
I like the technology in the circuit but wouldn't it be possible instead to use an appropriately dimensioned, normally closed relay that is driven by a resister divider so that it opens (and interrupts the current to the radio) when the voltage goes above a certain level? The relay could require, for example, a 5v input with a series connected resistor dimensioned to the current consumption of the relay so that ty he relay opened when energized above, for example, 14v. The resistor could even be variable (a pot) to allow adjusting of the overvoltage set point. Or did I miss something?
Nice project Peter. I've been intending to make one of these for some time now. Just a thought.... Why not put a high current reversed biased "stupid" diode across the output to protect against reverse polarity connection? I know the radio will probably have one anyway but better safe than sorry! 73 Malcolm
+TRXBench Yeah thats right, but it could be possible that there is a voltage on the outside of the case. And of people with no or less experience. Its always a preference for me to insulate everything. But as you said its not always dissapating 20A, and on for a short time.
Hi Charlie, well very simple as you can see it on the schematic. A z-diode 13V 0,5W, resitor 740ohm and 33ohm, a cap of 100nf and a power thyristor BTW69-800. That's it. Hope it helps 73
I don’t trust myself to build so I will try to buy… I enjoy your explanations of ham radio projects. Well done. ✅ 💙
I used a very similar crowbar circuit in my biggest power supply, it is very worthwhile insurance. It can also be worthwhile to put a few disc ceramics between the output terminals and the chassis, a lot of power supplies don't like common mode rf currents around them. 73 and well done on your videos.
Glad that you like it thanks for watching 73
I had a radio that would not work properly just made a buzzing nose. I then connected a second radio to the same power supply and got the same symptoms. It was at this point a realized the problem was with the power supply and not the radios. Yes I know this was not a very clever thing to do. My point is that power supply's can be dangerous, which means that this little device you have built is great idea and something every person with expensive equipment should give some thought to. Great video and very helpful as usual. I was fortunate that on this occasion my radios suffered no damage.
This crow bars are so simple and cheap it is a shame that they are not installed in general to all psu's.. Thanks for watching 73
Great video. I built one of these into my home brew 10 amp power supply that I built for my VHF rig. It was many years ago and the choice of thyristors at that time was limited. So if an over voltage occurred it usually took out the thyristor as well!
better the thyristor than the radio :-) Thanks for watching
Great video of the classic "crowbar" protection circuit, enjoyed your very thoughtful review, testing and the project box.
I love SCR crowbars! I use them a lot in my projects, normally in conjunction with TVS diodes and PPTC fuses, right at the supply input stage. They already save my circuits from my own mistakes.
However, I don't use any resistor between the Zener and resistor association, and the capacitor plus the SCR gate. The capacitor that I use, since it is normally 10nF, does not demand enough peak current to damage the Zener diode.
Edit: I've seen that you added a 100Ω resistor because you were worried about the pulses. However, mind that the Zener below its region practically does not conduct, and as long as the pulses don't exceed the threshold voltage (that is, Vzener + Vgth), you will be fine. The SCR will need a certain amount of current, albeit tiny, to activate, and the Zener won't be able to supply even the minimum when it is blocking. I've used sensitive SCRs without that resistor and with a 10nF capacitor, and never had a false trigger, even considering long supply cables (and their annoying inductances) being connected right before that stage.
Hi Peter, Nice video. I thought your step by step explanation was great. Anyone should be able to build one from watching it. A very valuable circuit also. 73
Hi Larry, thank you very much, I'm glad that you like it! 73
As someone who is learning electronics on my own you are a great teacher. i learn a lot from your videos. Maybe you can do a video on how to and not to connect RF equipment up to test equipment like oscilloscopes, spectrum analyzers, frequency counters, and tone generators. Like how and when to use a RF tap and how to connect a radio up to all the test equipment at once. It would sure make me understand a lot more on how to test my radios so i do not damage my test gear i am slowly acquiring
Thank you! Well a video you are asking for is already on my list but it will take a while... Thanks for watching. 73
Nice little circuit Peter!
Yes works perfect.. Thanks for watching Paul! 73
Hi. Your a genius.
Glenn, Suffolk county L.I N.Y.
Great addition to upgrade cheaper power supplies you made there Peter. Thats the reason I always use high end supplies. Last thing I want to do is blow up my radio or worse a customers radio. And I'm with you on switch mode supplies, very noisy. The only switch mode supply I have is a Wayne Kerr lab supply and it is very quiet but also very expensive.
Mike
Thank you Mike! Yes it totally agree with your statement. My lab psu is also a switching one but that's it...Take care 73
Thank you google for putting this video on my homepage. I've just built a linear MOS-FET regulator to allow for portable operation of a FT-892 from recycled 18650 cells. As good as it might be built, the extra safety of a cowbar is definitely a winner. All the parts for this circuit are already in my shack. However, if you have to buy everything new, you'll still be well below €10 for the circuit alone. Which is nothing compared to buying a new TRX that costs many €100. I'll definitely design it into my regulator. But i will definitely refrain from using a automobile blade type fuse. These things are absolute rubbish. ANL or AGU are much better for the job and aren't that much more expensive. Blade type fuses, which i found to be on most power connector cables for portable or mobile radios, have severe disadvantages in terms of contact resistance and reliability compared to ANL or AGU.
Thanks for watching and comment. All the best and 73
Peter another great video, and as is usually the case with your videos, very timely for me. I recently purchased a tech Special HP frequency counter (HP5385A) off of ebay and tracked the fault down to the crowbar circuit. As so often is the case, I learned a lot about this circuit during my troubleshooting and repair. I felt really smart and accomplished watching your video knowing where you were heading and why you doing what you did. Keep up the good work and take care my friend.
Hi Michael, I'm always glad if my videos are helpful! Thanks for the kind feed-back! 73
Very nice show and tell video Peter. Not sure how many times a radio comes in where the supply and failed and shot 24 volts to the rig. Most of the supplies I run have a crow bar circuit built in. But a lot of supplies on the market does not. This circuit is a sure way to save a lot of repair work. Big thumbs up my friend. 73 Buddy
Thank you Buddy. Yeah it is really a simple way to protect the radio gear and I have also seen to much power supplies with exactly this problem.. Tale care my friend 73
Cool little circuit, this is my next project to protect my Icom....Thank you Merry Christmas
Hi James, thanks for feed-back. Yes that is a nice little circuit so have fun with the project. Merry Christmas 73
Nice job Peter. Thanks. Always a good idea to protect our equipment.
That is true Robert! Thanks for watching 73
I have a 12v (13.8), 70 amp linear supply that has wheels on it! It has three transformers in it placed in a phased, parallel configuration which then feeds a monster bridge rectifier on a large heat-sink. The rectifiers appear to be Selenium but I can't be sure. That is followed by four 25,000mf capacitors which may be because of the Selenium rectifiers. It also has some in-rush current protection which is probably because of the 100,000mf capacitor bank. This feeds the regulator circuitry which contains several bipolar transistors on the back of the supply which is all heat sink. I would say that 3/4 of the weight is transformers, 1/4 is heat sinks and an insignificant portion is the electronics (that's why it's not listed in the weight). :) It's about 40 or so years old so your circuit is going inside.
Before i became a Ham radio operator, i dabbled in CB when i was young. I had a cheap voltmeter and liked to use it to examine voltages in everything. I discovered some radio guys were turning up the voltage in their power supplies as high as 16v thinking it would raise the power of their radios. So i did some reading about the relationship between voltage and current. I discovered that when you raise the voltage in an inexpensive power supply, the current drops. Aha ! Would that explain why their radios audio was clipping on peaks ? yes it did. I turned my power supply down to 12.8v insuring i would recieve the full current the radio was designed for. 13.8v in power supplies was meant to mimic an automobile alternators regulated voltage output, but it is not necessary your power supply voltage be that high.
Thanks for sharing. Just had a conversation about these circuits on EEVBlog forum. Nice to see your in action. Definitely good to have that second fuse.
Ah okay, so just in time hi hi 73
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I was dumb forgot the password. I would love any assistance you can offer me!
@Damien Arlo Instablaster ;)
@Lukas Gerald thanks for your reply. I found the site on google and Im in the hacking process now.
I see it takes a while so I will get back to you later with my results.
@Lukas Gerald it did the trick and I actually got access to my account again. Im so happy!
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in addition to this problem, seems that 31Vcc as input for a transistor produce a lot of dissipation if we have 13.5Vcc as output..more than 200watt, a little varistor it could be a 2nd idea. Good explanation !! :)
I use that with a second circuit to latch a relay as well has saved one radio up to now as a PSU did pop
Crowbar protection used to be an integral part of almost every linear power supply. But sometimes not. If you have power supply without this protection, it is wise to add some. But this power supply can damage your equiptment in another way (and crowbar does not help at all). The problem is, that GNDs of almost everything is connected together. And when you accidentaly hit the transistor case with your +12V banana plug when the PSU is running, it could lead to a great disaster. It should have at least some protective cover, but in fact, I don't like theese PSUs. It's much better to do the regulation in negative side of the power supply. Then the collector of the TO-3 transistor is on the GND youtput, so you do not have to isolate it from the heatsing and the PSU's case, which is good from the thermal point of view, you also do not have to care about things accidentaly touching that transistor, because its collector, heatsink, PSU's case is on the GND potencial. Regulating at the positive side is much easier, you do not have to build supplementary PSU to power the regulator (using PNP transistors would also eliminate this, but high current PNP transistors was not easy to buy for a good price), but on the other hand, it complicates mechanical design, especially when 20 and more amps are needed.
There are different types of regulators would suggest parallel regulator for better safer
Another great lesson about Crowbar. Thanks Peter.
Thank you Pasquale! Hope you are came safely home from your week end trip :^) 73
Thyristor current flows through anode, to gate, which causes forward bias on zener, which conducts, and causes current to now flow through the anode/cathode of the thyristor, to cause a direct short, blowing the fuse.
Peter well thought of little safety circuit as you say you never know when a power transistor can fail and 30 volts would blow the radio :)
Conduction voltage and current of the thyristor will indicate level of conduction for the gate, which is the switch for the pN juntion of the thyristor reverse bias of the gate, it will conduct, turning on the path through the thyristor, to ground, pulling excessive current to blow the fuse.
Thank you for your video and the time you have taken to explain this topic.
Thanks for watching 73
Of course, great video. I plan to use a car battery in parallel with the PS. In this way I can ensure both consumption and protection, besides a protection circuit. I have heard about crowbar circuits that didn't work, maybe the thyristor failed..
Peter, I use the exact same circuit (though my thyristor is 300a), it is cheap insurance against destroying a radio. My power supply has soft start so in the event of the thyristor triggering it simply shuts down. It is sad that few manufacturers fit crowbar protection.
Yeah a crow bar is so simple to fit in I agree it is sad...Thanks for watching 73
You can also use a circuit breaker with manual reset.
Circuit breakers trip on over-current situations, not over-voltage.
It would be interesting to see how fast this circuit is. There will be a measurable delay in the time it takes for the zener to break down and the switching speed of the thyristor will have a time constant as well.
I'm curious to know what these delays add up to and if the circuit is fast enough to prevent damage to sensitive semiconductors in whatever is connected to the supply.
Also the sender diode and 470 ohm resistor will draw current from the supply, reducing the voltage applied to the radio.
Enjoyed watching that and will be building the circuit into my supply. Thankyou.
Thanks for feed back
As usual, peter, very interesting, instructive and of practical use. Thanks. Giorgio
Thank you Giorgio! 73
Good video. I would prefer to see the Thyristor trigger at 15V though. Is the Thyristor mounted directly against the metal project box case or is there an insulator between it?
Great Video Peter! Thank you 73's de K8KEM. David from Cleveland, Ohio
Glad that you like it David! Thanks for watching 73
Hi Peter - I just found this video which is very helpful. I have an older Kenwood PS-30 supply I got to power an older Kenwood TS-570D I got at a flea market. The supply does not have protection and I would like to use your circuit. But in the specifications for the supply, it states the open circuit voltage can be as high as 20V. I assume your circuit can clamp almost instantaneously. My question is if I insert the circuit and turn on the supply, wouldn't it clamp before the transceiver load stabilizes the voltage? Actually my question is more general in that many supplies when turned on have a period of time before the voltage is regulated. Wouldn't that effect the operation of your circuit? Or am I wrong about the moment supplies turn on?
I made a mistake on the specs. The PS-30 is 16V max at no load. The TS-570D is 13.8 +/- 15%, so the max high would be 15.87V. I guess I am okay to use your circuit. But my question becomes what behavior should expect from most power supplies shortly after you energize them. I looked for spikes on my PS-30 with a scope and didn't see any.
A very good video on the tyristor crowbar. Well, since you have a German power supply, you must be Deutsch. My power supply weighs over 20 lbs. since it has such a large transformer in it. It's a linear power supply. MFJ 4035MV which is 30 watts continuous and 35 watts surge. Now days they are making power supplies with over voltage and over current protection. Ich spreche ein bischen Deutsch. Ich bin einer Swizer. W Rusty Lane K9POW in eastern Tennessee
Like the SCR crowbar protection on the Astron PSUs
Always good Solid advice , concerning these tpyes of issues, and trouble shooting it with fantastic solutions that are good electronic wisdom!!👍
Thanks
The newer switching power supplies are much better now days, even the internal supplies in newer radios are switching.
I have both but choose to use the switching supply because it has all the over voltage/current sensors included.
Yes I agree newer psu's are Fine 73
Hi Peter, getting ready to build this but noticed we haven't had any new vids in a while. Hope your doing well.
I must say they really went a bit overboard with around 17V drop on these power transistors in this PSU design.
transformer cost???
it might be that the resistance of the secondary winding of transformer is such that at full load, you've got a couple of volts left across the power pass transistors (product cost tradeoff)
You are also protected by your barking dog! (lol). greetings from the Netherlands.🐶
lol absolutely :-)
I would just like to add my personal opinion: The crowbar protection is better to realize it and insert it inside the container; Also verifying that a fuse with a capacity proportionate to the capacity of the thyistor is really present inside! because if the inside of the power supply is not inspected, it could happen that the fuse is only assumed and not really foreseen by the manufacturer of the power supply!
Yes Peter I totally agree with the rest of the comments. This is a great video very well explained. You do make some great videos my friend and this one is no exception. Thanks Peter 73's my friend
Hi Gary, thank you very much appreciated! 73 friend
A more elegant solution would be to connect the thyristor across the fuse before the regulator while supplying the gate voltage from the output of the regulator. When the crowbar trips all power is removed from the regulator preventing possible fires. Having a crowbar on the outside of the PSU is dangerous.
It is incomprehensible that this circuit is not immediately built into the power supply units.
I wonder if the base station radios have over-voltage protection built into their circuits?
I was waiting untill he mentioned "...the painting wiz ze fallen Madonna wiz ze big boobies."
Why not use a zener diode? They use zener in laptops to prevent high voltage damage for example.
18 VAC input to the bridge is plenty once some decent caps are in use . this 25 vac and up is mad
16v should be the trip point. Most txcr;s work with better IMD specs at 15.5v, especially Elecraft. 13.8V is not the best operating voltage expecially allowing for TX volt drop. All my txcrs run at 15.6v with no issue, usually ~14.8v during TX. Makes for a much cleaner signal.
Many thanks for all your video work. Would a BTW69 with a voltage rating of 600v or 1200v be a suitable substitute as I'm struggling to find the 800v version? All other specs. being the same of course.
sure
Very good logic. But still the whole thing depends on a fuse which might not be fast enough to protect radio electronics. I have seen 100$ transistors that burn faster to save 0.1$ fuses. :-) That being said, I recently discovered your channel and you have very informative videos. Also I admire your workbench equipment, especially the mini VNA.
Well the fuse is not the critical component which needs to do the fast switching therefore this little crow bar will protect your radio for sure. Thanks for watching 73
Bora, at the instant the thyristor fires the positive rail (and your radio) will be shorted to near 0V. This happens within about a microsecond, long before the fuse gets around to blowing a fraction of a second later.
I have mine drive a relay that locks open with a led also have a switch so I can see the voltage at the output an the relay stays open so no power can get to radio there is also this one in it that will blow a fuse
Thank you. My Pyramid 20amp 13.8v sent 24.9V to my President Lincoln' . Killed it!
I'd make that 100R resistor 1k0 thus making 100us time-constant filter while still providing very fast acting over-voltage protection
Hello peter Great video Please tell me Where can I buy this little metal box for my projects ?
best regards
Harry
Peter,
Nice circuit design. Guess we need to make sure the power supply has a built in crowbar circuit. :-)
Thank you Donald, yes it is crucial you we need to have an eye on it.. 73
Very nice explanation but my concern is that the thyristor/fuse combination might be slower to react than components in the radio. So the radio may be damaged before the crowbar fully operates. Is it possible to measure the time for activation?
I'm sure a single shot capture with an oscilloscope you could measure this
I am wondering this as well. The thyristor will have a speed at which it switches, plus there is the delay as the zener breaks down and a delay as the fuse opens. These would all add up, and likely be longer than it takes for a semiconductor junction in the radio to experience damage.
Great video and a great idea, I'm going to build one for my power supplies.. Thanks
Good luck with the project Joe! 73
Thank you , for such a professional, theory and by the way. To those who suggested to put a relay, it's quite good but not safety, as long as any sudden high rise voltage bounce up above 13.8(v) which in turn risck the output. And that is why a fuse burn out for safty.
Very good video and solution. In your opinion is the Switching Power Supply more secure?
Hi, well a smps has some protection circuits so it might be more secure but even so you never know how bad i can go.. Thanks for watching 73
I must get around to doing this on my 40A supply. Do they have larger thyristors? I found BTA100A-800B. But thinking I can use the 69 because the fuse should blow fast enough to protect the btw69 thyristor even on a 40A supply.
An ounce of prevention. I think I used a triac on the last crowbar I made. The thyristor is about the same thing. Triac or thyristor into a diac, and you have what? Maybe $12 invested in protecting $1000-$14,000. I have a thyratron running a protection circuit in one of my old boat anchors. If only I had a dollar for every man named Peter with a German accent I have worked with. I think we had 5 at one company. We also had a Hans too. 73 KI7AQJ
LOL, yeah too may Peter's and Hans on this planet :-)... Thanks for feed-back Seth! All the best and 73
Seth B: a little note:
Hans is in fact a Dutch name,
while Heinz is the German version!!
Nobody knows this!!
A bit wordy but well explained. Thanks for sharing
interested in building some of these but i know little about electronics. the components listed you have given values for but when i look to buy them they have voltages on them, wattage and what type of capacitor or resistor you used. apart from that good video
What is the Rating for the Cap. Ty great video
Hi Jack, 100nF as shown in the video.. 73
Great video. invaluable little circuit. I have a question regarding the zener diode. i know you said 13V but is current rating of that zenner inportant? and what value did you use? thank you in advance. ivan vk5rs
sorry power rating not current .... my bad ... for exmple .... 1N5243B is 13V but 500mW max power. would that be sufficient for this circuit? thanks once again
Thanks Peter , what amp fuse are you useing
well, to handle that current you're using a power thyristor. but instead of that, if you uses a power transistor even the same type that uses the source power, in the case that the transistor of the source power will sorted, you can change the damaged power transistor with the protection transistor. in this way you will have a change to make a call with your radio without overvoltage protection. using the little thyristor used in the first part of the video to trigger and lock the circuit.
Hi Fede, well yes as long you have only 1 power transistor but what if you have may be 5 power transistors in parallel than your approach becomes a bit complicated.. 73
great great and great tip ... tanks so much ... one more time teaching us about helpfull tips ... (sorry my english) all the best
Thank you Neto! No worry my English is even worse than yours. Take care 73
Fuse after the zener for faster action.
What amp. ( fuse ) did you use's and what (watt zener - dio ) did you use . Thank You ( w4btt )
Fantastic explantion, and fantastic idea !! tks
Thank you 73
I have same type of power supply 7amp
And it has short circuit protection writes on it ? Is it ok?
Great video, Peter!!! Thank you so much as always! 73 de N0BPS
Thank you Brian! 73
Peter, If you were building a Crowbar circuit for say a 25-30 Amp supply, would it not be a good idea to lay down a thick layer of solder along the tracks feeding power to the radio? Surely the copper tracks on the Vero board would not be of sufficient thickness to carry 25-30 Amps of current?
John yes you need a strong power bus but make sure that the fuse which needs to break is rated right. 73
Great video....will this work in any switching power supply too ?
A switching PSU don’t work like a linear one. If the transistor in a switching PSU is failing the output voltage will drop. But you shouldn’t use switching PSU for radio equipment because of the ripple it produce.
But yes you can use this for any PSU. Only the zener and resistors must match the output voltage.
What does the voltage rating on the thyristor need to be - do they work like other things which are actually wattage based . Like a switch will be rated at 220 volts at 3 amps or 110 volts at 6 amps which would make it like 600 watt rated?
With the straight path from the fuse to the output which is the path of least resistance - what actually causes it to take the path of the protection circuit?
Great idea Peter thanks for video
Thanks Dennis. 73
An excellent project, to protect expensive equipment with a small investment. thank you, 73 de 9A6GEZ
Thanks for watching Jura 73
Hello Peter, thank you for this video. 73 from Brazil. PY1XW. I am learn speak english.
Hi Claudio, glad that you like it! Thanks for watching 73
Great video & clear explain.
I always use the dedicated over voltage IC from Motorolla the MC3423 and a Thyristor..... I've a video of a homemade supply on TH-cam with this IC ... Gw0wvl....... great video and thank you.
Hi Marc, of course there are many ways to protect your stuff and the MC3423 is a good one... Thanks for feed-back All the best 73
Is the proto board really needed? With terminals, a chassis fuse holder and terminal tags there are few enough components just to use point to point wiring.
No you can build circuits like this according your own preferences. Thanks for watching 73
hi Peter!
is there any chance to do something similar (I mean an overvoltage protection) for variable power supplies: for example that DF-1730SB you are using in the video? if one of the pass regulating transistors fails (going short circuit) you get the whole voltage on the output and "fry" the equipment you are powering!!!
Hi Claudio, not as easy as this project but it is possible and you can buy psu's with over voltage protection. Thanks for watching 73
thanks Peter, but I wanted something to add to my cheep Chinese Power Supply!!! hahaha
I will look around and see if I can find something suitable.
I really enjoy your videos BUT you state something and then you state it again and then you state it again... Drives me crazy LOL! Still thanks!
LOL thank you Digger for reminding me and I agree I have noticed it. May be that I always think I was not able to get the message over. I need to improve it. Damn my videos will only last 5 minutes then. 73
"Repetita iuvant" :) :) ;) ;)
***** Repetita iuvant? It's a video - you can repeat it as many times as you wish ;)
There is much harder to do a short video than a long one though :) we just need to watch these long ones on 10x speed :D
***** I find they are worth the annoyance though ;) I learn a lot and patience too lol.
crowbar is cool. I hate switch modes! Love linear.
Hi Victor, correct! Crowbar is cool :-) 73
Do older Astron Linear supplies have this protection ?
I don't know sorry
How do you know if the power supply already has this type of protection built into it??
you should find it in the manual..
Is it possible to get a high voltage spike due to the small delay in the Thyristor circuit, especially with a capacitor on the gate? Maybe this could be measured by putting a scope on the output?
Hi, well even if it will be grounded..so no problem. Thanks for watching and comment. 73
But if there is a short delay before the thyristor triggers, won't there be a short period of high voltage just before it is grounded? Maybe the spike will be filtered by capacitors in the rig.
will this work in any dc supply?24vdc 32 vdc supply?
Yes it will but you have to adapt the z-diode that's it 73
thanks trx
Damn good idea Sir! Thanks for sharing!
Thank you and thanks for watching 73
I like the technology in the circuit but wouldn't it be possible instead to use an appropriately dimensioned, normally closed relay that is driven by a resister divider so that it opens (and interrupts the current to the radio) when the voltage goes above a certain level?
The relay could require, for example, a 5v input with a series connected resistor dimensioned to the current consumption of the relay so that ty he relay opened when energized above, for example, 14v.
The resistor could even be variable (a pot) to allow adjusting of the overvoltage set point.
Or did I miss something?
Yes theoretically it is possible but a relay is much to slow. Until the relay is switching off the radio is already damaged.. Thanks for watching 73
Gut erklärt und gemacht. Vielen dank aus Irland. 73 Adrian
Thank you Adrian! Do you really speak German?? 73
TRX Bench Ja wirklich! Aber heutzutag mein Deutsch ist sehr rostig. Ich hab' zwischen 94 und 95 in LU am Rhein gewohnt. 73 Adrian
Oh wow meinen 100% Respekt! Ich weiß wie schwierig es ist deutsch zu lernen! Alles Gute und 73 Adrian
Nice project Peter. I've been intending to make one of these for some time now. Just a thought.... Why not put a high current reversed biased "stupid" diode across the output to protect against reverse polarity connection? I know the radio will probably have one anyway but better safe than sorry!
73
Malcolm
Hi Malcolm, what ever helps to make it more safe can't be wrong. Thanks for watching. 73
Great video 👍 thanks!
Is there no thermal paste/pad placed between the box and the thyristor? Or did I missed it?
Hi Jordy, no not so much important as the component is not always in use... 73
+TRXBench Yeah thats right, but it could be possible that there is a voltage on the outside of the case. And of people with no or less experience.
Its always a preference for me to insulate everything. But as you said its not always dissapating 20A, and on for a short time.
+Jordy Tax less experience people can be shocked, or feel some of the voltage.
what part list to make that voltage droper ?
Hi Charlie, well very simple as you can see it on the schematic. A z-diode 13V 0,5W, resitor 740ohm and 33ohm, a cap of 100nf and a power thyristor BTW69-800. That's it. Hope it helps 73
TRX Bench Hi, neat solution but is the 740ohm resistor a typo did you mean 470ohm as per your diagram?
73 Dave G7HJX