Hi Tom, many thanks for this and for allowing the use of your files to build the device. I was in the process of designing one myself until I saw your video. I’ve just ordered a few boards and will make a two or three for the shack. 73 Dave G0DDF
Great video. I will definitely be interested in purchasing the Mini Bar when it is available. I watched every video of your IC 7300 tutorial series when I bought mine. Thank you so much for helping all of us out.
Thanks a lot Tom. I've implemented crowbars in previous power solutions, but never felt that my own implementations were elegant. They were always very crude, just a fuse on the input and a zener diode capable of handling a lot more amperage than the installed fuse. I never considered using an SCR! I'll definitely be using your improved design should I ever feel that a crowbar is needed in future power solutions; thank you for making your board design and circuit schematic available. I prefer using XT60 connectors over powerpoles, so I'll have to make one myself.
What you didn’t mention is the mechanism of failure of the very cheap power supplies. It’s the output transistor that fails and the failure often causes a slow increase in supplied voltage. At total failure the output voltage is 24v (from memory, and I’m old, so check this number if it is important to you). I’m not a radio hobbyist but an astrophotographer. Our equipment is expensive. A lot of people use the inexpensive power supplies without understanding that failure delivers higher than intended voltage. Our equipment is usually tolerant to about 16v. I was burned in a remote placement of equipment on a mountain top in California when the cheap Pyramid power supply failed. The camera reported the high output (puzzlingly with a low voltage beep pattern). We shut down and replaced the power supply with a more expensive one built for ham radio use, and that power supply has a crowbar circuit. I was lucky, my equipment survived undamaged. Anyway the extremely cheap power supplies do commonly fail and they fail by supplying higher voltage to the load. (These cheap power supplies are listed as 12 volt but they supply 13.7 volts, presumably so they can charge a 12v battery.) The point is that cheap power supplies often fail and they can easily fry very expensive equipment. In my case the failed Pyramid power supply was tested after removal from the setup, it was delivering 17v. Looking back it was nuts to trust a $30,000 setup to the very cheapest power supply I could find. In my case it was ignorance, I just didn’t know. I do now and do all I can to spread the word to others.😂
Happened to me too on an old CB. Pyramids are ok until they screw up and ya get juiced my supply makes a recieve/transmit hum (but they all do..... just not like this) I prefer using a car battery clean and quiet
I designed and built a PSU / charger that has short circuit and overload protection using a high current DC relay. The relay drops and stays out whilst the short is present, removing the short, allows the PSU to slow start via 10 watt light bulb whilst the Capacitors are charging, then switches the relay for full output. Your circuit could be utilised to simulate the short, and instead of blowing the fuse, the relay would drop, cutting off the supply, until a reset button was pressed. Of course if the over voltage was still there, the crowbar would prevent the relay being engaged as there would be no voltage for it to energise it. David in the U.K. G1ZQC.
Years ago I built a home brew 30 amp supply for my radios. This was back when finding a transformer for such a project wasn't a big deal. I ran for years just on just the series pass transistors until one days I heard about a friend of mine that experienced a shorted series pass and blew his radio. Within a week I kluged together a crowbar circuit and placed in the output circuitry. And yeah I've got some of these cheap Chinese switchers that need protection added also.
I often use this circuit on every project I make. Depending on the current, I can use NYC222 thyristors to the MCR8 ones. I often try to use PPTC resettable fuses, for robustness, and I also couple a TVS diode for responsiveness to transients. To avoid false triggering, I use a 10nF capacitor in parallel with the 150 Ohm resistor that is pulled up by the Zener. These things are really robust!
Thanks, Tom! With so few components involved, it makes you wonder why the manufacturers don't build protection like this into their gear to begin with! Back in the '70s CB radios started coming out with built-in reverse polarity protection diodes across the 12-volt input. Normal operation, the diode did nothing; hook the rig up backwards and pow went the fuse. Many times the diode would become a dead short and require replacing, but it saved the rig. I even retrofitted a fair number of older units that didn't have the diode. Fuses and diodes were cheap, radios were not. As for overvoltage, I knew many people who would run a mobile CB on 15 volts to get more power, and had to try to fix some that got toasted by that or higher input. Take care, sir!
I repaired a few AM CB radios that had been reversed connected, they blew the fuse, then bypassed the fuse and still reverse connected it. Smoke smoke smoke....
@@G1ZQCArtwork "Been there, smelled that!" 🙂 I can sympathize, way too many cases of ever-increasing amperage rating on fuses; 2 amp replaced with 10 or 20. 🙄
They would power it in reverse, blow the fuse, put a bigger one in or short it altogether, reverse connect it again and blow the diode open. I often had to replace the PA transistor, and if the radio was switched on at the time, the Audio chip would fry too. Kept me in business. Aerials too, just tag it on the Car, no grounding so the SWR would be sky high, first transmission, POP goes the PA..@@bobblum5973
Nice little circuit, I remember a few of the power supplies for some of the raadio gear I worked on in the service and they were pretty slick but not nearly are streamlined as yours. When you get it into production I will be looking to purchase one I think. Thanks for sharing Vic de KE8JWE
This is a good idea for mobile applications in the event your vehicle electrical system loses the connection to the battery or something goes wrong with the alternator’s voltage regulator.
Excellent design! I plan to build 3 or 4 to incorporate in to the power supplies I have. Sure it's old fashioned, so is the wheel. I'm going to use an old fashioned axial lead zeners and 3AG fuses. I will not be using Chinese ATC no-blow fuses. That was an eye opening YT.
Tom, I just completed the build of your mini-crowbar. I ordered the boards from JLCPCB and components from Digikey. Completed my first SMD project with a aluminum block heated to 165C with a solder iron.Worked like a charm and once completed I proceeded to test it with a variable power supply and load. The 5,10,15 amp fuse does not blow but the crowbar shorts at 15.8 and switches the power supply off. I guess PS has its own short circuit protection. What determines what size fuse to use? The load or the input specs. Many Thanks
Hi. Glad you were able to do everything from the documentation I provided. It is both the input source and the load that determine the fuse size. Obviously, the fuse has to be large enough to carry the current your load will draw. It must also be small enough that the power supply can source enough current to blow the fuse. I've been recommending that the supply should be able to source roughly twice the fuse rating to insure that it blows quickly. About your supply switching off-- If you watched the entire Mini-Bar introduction video, you saw that my MFJ power supply had similar behavior. Most modern, switching power supplies have short-circuit detection and will go offline before the fuse can blow if the crowbar trips. Keep in mind, however, that the crowbar circuit is in place to protect against something going bad in the power supply. If a power supply failure causes the crowbar to trip, the short-circuit detection in the supply may have failed as well.
I'm familiar with crowbars and have even recommended them in some situations (thinking about one in particular where an industrial process came to a complete halt because several boards full of CMOS were blown thanks to a bad power supply). And at first I thought that perhaps it would be good to add one to my setup. But thinking on it a bit, I don't see a failure mode for the switching power supply that I'm using that's going to over-volt the output. If something in there fails, the supply will just quit working. Oh, and I'd add at least 10nF of capacitance across that gate resistor for some noise immunity.
Hi Roy. The MiniBar is now at Rev-C and it does include capacitance across that gate resistor. Thanks! On switching supplies- You are correct that failure modes in the power transistors (shorts/opens) will result in no output. However, there are failures in the regulation circuitry that can cause the output to go to too high of a voltage. Most high quality supplies have internal crowbars or other circuitry to prevent this, but not many of the super cheap ones.
Tom yes a crowbar is a good idea for protecting yourself. I will use it for my portable operations too. Why if you have your power supply on or battery and a long cable when you plug it in you will get a nasty transient that can be a large voltage. That will look like overvoltage.
When you connect any load to a live voltage source there is almost always some amount of arcing that occurs at the connection point. Connectors are not perfect at the microscopic level. So the voltage connects and disconnects a few times during the connection process. This all happens in microseconds. As the voltage goes from full voltage back to 0, stray inductance in the circuit can produce voltage spikes. They are very short, but they are there. I have added filtering to the MiniBar to prevent false trips from this.
Note that a fully charged lithium polymer battery has a voltage in excess of 16V and should not be used with amateur gear (or telescopes in my case). LiFePO4 seemed fine.
I agree it would be nice, but I didn't want to put a 20+ amp diode on the board. That would increase the size considerably and add losses. The Anderson PowerPole polarity arrangement is universal enough now that reverse polarity should be a very rare problem.
Hi. There’s been some interest in this. I’m looking at offering it at least as a partial kit. Maybe surface mount parts completed and through hole parts as a kit. Some people are also interested in something other than Power Poles. So a kit would solve that as well. I’ll be getting some new information out shortly.
Thanks for this Tom. I have tried to upload the gerber files to both PCBway and JLCPCB, which I have used before without issue. But these gerber files you have supplied are missing a BOM that both services are asking for . Have you left these out so we don't run off and sell our own board of your design or is there some other reason. I have created a couple small TTH project using JPLPCB and it was easy as pi. Perhaps a video for procedure to upload and refine your gerber file list to JLCPCB and proper BOM upload for them would be helpful. Thank you so much. 73
I didn’t thank you for your post, so thank you. I do have a question. In your presentation you say you have a fuse in your circuit, but later you seemingly have it tripping and resetting. Is it a fuse? I know just enough electronics to get by so please be tolerant of my ignorance. Isn’t a fuse a consumable, a one time item that must be replaced once blown? Is your circuit more akin to a circuit breaker, that survives the high voltage event and lives on?
It was the MFJ power supply that was continually resetting due to the short and therefore not blowing the fuse. The power supply had inbuilt short circuit protection. The Mini Bar circuit still prevented the voltage exceeding the safe value.
Hi. @brianm9962 is correct. I may not have explained that as clearly as I could have. In the 2nd test, with the MFJ power supply, it is the overcurrent protection in the power supply that is shutting off the power. When I raised the voltage high enough to trip the crowbar, the overcurrent protection in the power supply turned off the voltage fast enough that it didn’t blow the fuse in my circuit. As soon as the voltage goes away, the crowbar circuit resets - not the fuse, but the short circuit from the SCR. Then when the voltage comes back and gets high enough again, the crowbar circuit re-trips. Each time, the power supply shuts off it’s output fast enough to keep the fuse in my circuit from blowing. I hope this helps explain it better. 73, Tom
Talking just home built stuff here... If you're using a buck /boost circuit with a higher voltage series battery, maybe a crowbar might be warranted? If like a couple minibars on hand if they're reasonable! /Dave kd0ndc
I used a P channel FET a Zener a transistor and some resistors to make a series overvoltage latching switch. A single push button will toggle it on or off. Why blow the fuse if you don't need to.
For SSB, CW and most typical digital mode operations a 25 amp fuse should be fine. The duty cycle is low enough that your average draw will be well below the 23 amps.
2:00 I think I'd rather trust an ex-Server PS, for example made by HP and probably cost a small fortune when new, than any MFJ (Makes F'n Junk) product. Furthermore, the HP ex-Server PS I use has a built-in crowbar circuit. But yes, using a cheaply-made PS is asking for trouble. MFJ products are too often cheaply made.
Great device and project! Thanks for selling these and for making the schematics available for DIY as well!
Hi Tom, many thanks for this and for allowing the use of your files to build the device. I was in the process of designing one myself until I saw your video. I’ve just ordered a few boards and will make a two or three for the shack. 73 Dave G0DDF
Fantastic!
Great video. I will definitely be interested in purchasing the Mini Bar when it is available. I watched every video of your IC 7300 tutorial series when I bought mine. Thank you so much for helping all of us out.
Great presentation! Thanks for your effort in producing this video. The device is "cheap insurance" if the over-voltage demon strikes!
Thanks a lot Tom. I've implemented crowbars in previous power solutions, but never felt that my own implementations were elegant. They were always very crude, just a fuse on the input and a zener diode capable of handling a lot more amperage than the installed fuse. I never considered using an SCR! I'll definitely be using your improved design should I ever feel that a crowbar is needed in future power solutions; thank you for making your board design and circuit schematic available. I prefer using XT60 connectors over powerpoles, so I'll have to make one myself.
What you didn’t mention is the mechanism of failure of the very cheap power supplies. It’s the output transistor that fails and the failure often causes a slow increase in supplied voltage. At total failure the output voltage is 24v (from memory, and I’m old, so check this number if it is important to you). I’m not a radio hobbyist but an astrophotographer. Our equipment is expensive. A lot of people use the inexpensive power supplies without understanding that failure delivers higher than intended voltage. Our equipment is usually tolerant to about 16v. I was burned in a remote placement of equipment on a mountain top in California when the cheap Pyramid power supply failed. The camera reported the high output (puzzlingly with a low voltage beep pattern). We shut down and replaced the power supply with a more expensive one built for ham radio use, and that power supply has a crowbar circuit. I was lucky, my equipment survived undamaged. Anyway the extremely cheap power supplies do commonly fail and they fail by supplying higher voltage to the load. (These cheap power supplies are listed as 12 volt but they supply 13.7 volts, presumably so they can charge a 12v battery.) The point is that cheap power supplies often fail and they can easily fry very expensive equipment. In my case the failed Pyramid power supply was tested after removal from the setup, it was delivering 17v. Looking back it was nuts to trust a $30,000 setup to the very cheapest power supply I could find. In my case it was ignorance, I just didn’t know. I do now and do all I can to spread the word to others.😂
Happened to me too on an old CB. Pyramids are ok until they screw up and ya get juiced my supply makes a recieve/transmit hum (but they all do..... just not like this) I prefer using a car battery clean and quiet
I designed and built a PSU / charger that has short circuit and overload protection using a high current DC relay. The relay drops and stays out whilst the short is present, removing the short, allows the PSU to slow start via 10 watt light bulb whilst the Capacitors are charging, then switches the relay for full output.
Your circuit could be utilised to simulate the short, and instead of blowing the fuse, the relay would drop, cutting off the supply, until a reset button was pressed.
Of course if the over voltage was still there, the crowbar would prevent the relay being engaged as there would be no voltage for it to energise it.
David in the U.K. G1ZQC.
Thanks for the video and the info. I ordered one of your circuit kits : )
Thanks!
Crowbar circuits are cool. Some older regulated linear power supplies will go into fault mode and then sit there and cook themselves to death.
Great video Tom! Love the concept! 73
Excellent Documentary Tom 💯👍
Years ago I built a home brew 30 amp supply for my radios. This was back when finding a transformer for such a project wasn't a big deal. I ran for years just on just the series pass transistors until one days I heard about a friend of mine that experienced a shorted series pass and blew his radio. Within a week I kluged together a crowbar circuit and placed in the output circuitry. And yeah I've got some of these cheap Chinese switchers that need protection added also.
I often use this circuit on every project I make. Depending on the current, I can use NYC222 thyristors to the MCR8 ones. I often try to use PPTC resettable fuses, for robustness, and I also couple a TVS diode for responsiveness to transients. To avoid false triggering, I use a 10nF capacitor in parallel with the 150 Ohm resistor that is pulled up by the Zener. These things are really robust!
Thanks, Tom!
With so few components involved, it makes you wonder why the manufacturers don't build protection like this into their gear to begin with!
Back in the '70s CB radios started coming out with built-in reverse polarity protection diodes across the 12-volt input. Normal operation, the diode did nothing; hook the rig up backwards and pow went the fuse. Many times the diode would become a dead short and require replacing, but it saved the rig. I even retrofitted a fair number of older units that didn't have the diode. Fuses and diodes were cheap, radios were not. As for overvoltage, I knew many people who would run a mobile CB on 15 volts to get more power, and had to try to fix some that got toasted by that or higher input.
Take care, sir!
I repaired a few AM CB radios that had been reversed connected, they blew the fuse, then bypassed the fuse and still reverse connected it. Smoke smoke smoke....
@@G1ZQCArtwork
"Been there, smelled that!" 🙂
I can sympathize, way too many cases of ever-increasing amperage rating on fuses; 2 amp replaced with 10 or 20. 🙄
They would power it in reverse, blow the fuse, put a bigger one in or short it altogether, reverse connect it again and blow the diode open.
I often had to replace the PA transistor, and if the radio was switched on at the time, the Audio chip would fry too.
Kept me in business.
Aerials too, just tag it on the Car, no grounding so the SWR would be sky high, first transmission, POP goes the PA..@@bobblum5973
Thank you Tom !!!
Great video. This is something new to me but am always looking for items to protect the radios. I am looking forward to the production of the crowbar.
Wow, really good stuff Tom 👍
Thanks Ape!
Nice little circuit, I remember a few of the power supplies for some of the raadio gear I worked on in the service and they were pretty slick but not nearly are streamlined as yours. When you get it into production I will be looking to purchase one I think. Thanks for sharing Vic de KE8JWE
This is a good idea for mobile applications in the event your vehicle electrical system loses the connection to the battery or something goes wrong with the alternator’s voltage regulator.
Excellent design! I plan to build 3 or 4 to incorporate in to the power supplies I have. Sure it's old fashioned, so is the wheel. I'm going to use an old fashioned axial lead zeners and 3AG fuses. I will not be using Chinese ATC no-blow fuses. That was an eye opening YT.
Tom, I just completed the build of your mini-crowbar. I ordered the boards from JLCPCB and components from Digikey. Completed my first SMD project with a aluminum block heated to 165C with a solder iron.Worked like a charm and once completed I proceeded to test it with a variable power supply and load. The 5,10,15 amp fuse does not blow but the crowbar shorts at 15.8 and switches the power supply off. I guess PS has its own short circuit protection.
What determines what size fuse to use? The load or the input specs.
Many Thanks
Hi. Glad you were able to do everything from the documentation I provided.
It is both the input source and the load that determine the fuse size. Obviously, the fuse has to be large enough to carry the current your load will draw. It must also be small enough that the power supply can source enough current to blow the fuse. I've been recommending that the supply should be able to source roughly twice the fuse rating to insure that it blows quickly.
About your supply switching off-- If you watched the entire Mini-Bar introduction video, you saw that my MFJ power supply had similar behavior. Most modern, switching power supplies have short-circuit detection and will go offline before the fuse can blow if the crowbar trips. Keep in mind, however, that the crowbar circuit is in place to protect against something going bad in the power supply. If a power supply failure causes the crowbar to trip, the short-circuit detection in the supply may have failed as well.
I'm familiar with crowbars and have even recommended them in some situations (thinking about one in particular where an industrial process came to a complete halt because several boards full of CMOS were blown thanks to a bad power supply). And at first I thought that perhaps it would be good to add one to my setup. But thinking on it a bit, I don't see a failure mode for the switching power supply that I'm using that's going to over-volt the output. If something in there fails, the supply will just quit working. Oh, and I'd add at least 10nF of capacitance across that gate resistor for some noise immunity.
Hi Roy. The MiniBar is now at Rev-C and it does include capacitance across that gate resistor. Thanks! On switching supplies- You are correct that failure modes in the power transistors (shorts/opens) will result in no output. However, there are failures in the regulation circuitry that can cause the output to go to too high of a voltage. Most high quality supplies have internal crowbars or other circuitry to prevent this, but not many of the super cheap ones.
Thanks Tom I have astron 35 m and kenwood PS 33 I think I am good for know, very interesting info.
Thanks Tom! Great video.
2 XBOX power supply you will have a good 28 Amps. Great video
Can you have option for a kit ?
Tom yes a crowbar is a good idea for protecting yourself. I will use it for my portable operations too. Why if you have your power supply on or battery and a long cable when you plug it in you will get a nasty transient that can be a large voltage. That will look like overvoltage.
When you connect any load to a live voltage source there is almost always some amount of arcing that occurs at the connection point. Connectors are not perfect at the microscopic level. So the voltage connects and disconnects a few times during the connection process. This all happens in microseconds. As the voltage goes from full voltage back to 0, stray inductance in the circuit can produce voltage spikes. They are very short, but they are there. I have added filtering to the MiniBar to prevent false trips from this.
@@HamRadioA2Z That looks to be a good idea to protect your radio. I wanted to ask if you tried reverse voltage test as well. Ps I did order one.
Thanks for your order! On reverse voltage: No, unfortunately the MiniBar won’t protect you against that.
Note that a fully charged lithium polymer battery has a voltage in excess of 16V and should not be used with amateur gear (or telescopes in my case). LiFePO4 seemed fine.
NIce job! an addition to this would be to add reverse voltage portection. not likely to happen but the one time it does could save a radio. K6DCH
I agree it would be nice, but I didn't want to put a 20+ amp diode on the board. That would increase the size considerably and add losses. The Anderson PowerPole polarity arrangement is universal enough now that reverse polarity should be a very rare problem.
Hi Tom, Any chance you will be offering this with an option of a kit?
Hi. There’s been some interest in this. I’m looking at offering it at least as a partial kit. Maybe surface mount parts completed and through hole parts as a kit. Some people are also interested in something other than Power Poles. So a kit would solve that as well. I’ll be getting some new information out shortly.
Just had an issue on my motorcycle where the regulator failed and was pushing 17v to the battery. Luckily for me i had my radio unplugged.
Thanks for this Tom. I have tried to upload the gerber files to both PCBway and JLCPCB, which I have used before without issue. But these gerber files you have supplied are missing a BOM that both services are asking for . Have you left these out so we don't run off and sell our own board of your design or is there some other reason.
I have created a couple small TTH project using JPLPCB and it was easy as pi. Perhaps a video for procedure to upload and refine your gerber file list to JLCPCB and proper BOM upload for them would be helpful. Thank you so much. 73
Hi Clive. Sorry about that. I did use PCBway, but I created the BOM separately in a spreadsheet as I am not having them populate everything.
Thanks Tom. I decided to do the same. Thanks very much for the gerbers.
I didn’t thank you for your post, so thank you. I do have a question. In your presentation you say you have a fuse in your circuit, but later you seemingly have it tripping and resetting. Is it a fuse? I know just enough electronics to get by so please be tolerant of my ignorance. Isn’t a fuse a consumable, a one time item that must be replaced once blown? Is your circuit more akin to a circuit breaker, that survives the high voltage event and lives on?
It was the MFJ power supply that was continually resetting due to the short and therefore not blowing the fuse. The power supply had inbuilt short circuit protection. The Mini Bar circuit still prevented the voltage exceeding the safe value.
Hi. @brianm9962 is correct. I may not have explained that as clearly as I could have. In the 2nd test, with the MFJ power supply, it is the overcurrent protection in the power supply that is shutting off the power. When I raised the voltage high enough to trip the crowbar, the overcurrent protection in the power supply turned off the voltage fast enough that it didn’t blow the fuse in my circuit. As soon as the voltage goes away, the crowbar circuit resets - not the fuse, but the short circuit from the SCR. Then when the voltage comes back and gets high enough again, the crowbar circuit re-trips. Each time, the power supply shuts off it’s output fast enough to keep the fuse in my circuit from blowing. I hope this helps explain it better. 73, Tom
It’s perfect. Thanks.
@@HamRadioA2Z
Talking just home built stuff here... If you're using a buck /boost circuit with a higher voltage series battery, maybe a crowbar might be warranted? If like a couple minibars on hand if they're reasonable! /Dave kd0ndc
I used a P channel FET a Zener a transistor and some resistors to make a series overvoltage latching switch. A single push button will toggle it on or off. Why blow the fuse if you don't need to.
For a FT891 the max current draw is about 23 amps at 100w.
What fuse should be used in a Minibar? 4S7EF
For SSB, CW and most typical digital mode operations a 25 amp fuse should be fine. The duty cycle is low enough that your average draw will be well below the 23 amps.
@@HamRadioA2Z Thank you. I will buy a mini bar after I get approved to import the FT891. 4S7EF
2:00 I think I'd rather trust an ex-Server PS, for example made by HP and probably cost a small fortune when new, than any MFJ (Makes F'n Junk) product. Furthermore, the HP ex-Server PS I use has a built-in crowbar circuit. But yes, using a cheaply-made PS is asking for trouble. MFJ products are too often cheaply made.
I woukd like to make a purchase once you get a price together.
Power supply juiced....
I applied crowbar ......
Now i have dented radio and the hum is gone but the radio dont work anymore 😁
Tom, I would be interested in buying a few of them when you get them into production. Jim - W5SWV