Has there been discussion about adding crowbar protection to old power supplies? I know hardware damage caused by the power supply might be rare, but I think it would be cool to have a crowbar board that would plug into the 4 pin drive connector. Fairly simple to design, too.
Got a pic of what you are talking about? You mean like a crowbar for pulling nails?
It is common for C64 power supplies to go high on their +5V output and destroy the computer. On the other hand, many PC supplies already have a crowbar circuit on +12V and Zener clamping on the other rails included. Before deciding to build your own crowbar circuit, I recommend you to check whether the supply of that machine already includes one.
Sphere478 wrote on 2022-09-27, 17:19:Got a pic of what you are talking about? You mean like a crowbar for pulling nails?
eesz34 is talking about https://en.wikipedia.org/wiki/Crowbar_(circuit), a circuit that creates an artificial short circuit in case of an overvoltage produced by that supply. This short circuit prevents damage to the computer caused by a broken power supply.
Ah, they have devices like these in the form of blue discs. They are used in lightening protection. They look like ceramic capacitors.
Sphere478 wrote on 2022-09-27, 19:00:Ah, they have devices like these in the form of blue discs. They are used in lightening protection. They look like ceramic capacitors.
They serve a similar purpose, overvoltage protection, but in a significantly different way.
These little blue discs are "metal-oxide varistors". Their purpose is to convert excessive energy that create a voltage spike into heat. They require that the current they draw causes the voltage to go down to a reasonable value. While the varistor dissipates the extra power added by lightning, the device can keep functioning. Whenever a varistor dissipates a significant energy spike, it ages. If exposed to a continous overvoltage driven strong enough, it will overheat and possibly catch fire.
Crowbar circuits on the other hand try to imitate a dead short as good as possible, driving the power supply either into short circuit protection or blowing a fuse, definitely disrupting operation. The advantage of creating a dead short is that the heat is created elsewhere, the crowbar itself (if dimensioned correctly) will not detoriate even when it activates, but the supply that is shorted might suffer from crowbar activation. You usually don't care about that supply, though, because the crowbar is supposed to activate only if the supply is already broken and outputs too much voltage.
One common use of varistors in many power supplies is between the legs of the 2 big capacitors on the primary. In addition to helping with voltage spikes, they can protect components from being destroyed if you do silly things like plugging a PSU with the switch on the "110V" position into a 220V wall outlet (I may or may not have done this in the past...). What happens in that case is that the varistors will fail short, which in turn creates a short in the primary, causing the fuse to blow. Not sure how effective this is in general, but in my case all I had to replace was the fuse and the two varistors, everything else survived just fine.
Sphere478 wrote on 2022-09-27, 17:19:Got a pic of what you are talking about? You mean like a crowbar for pulling nails?
NO! I'M WITH THE SCIENCE TEAM!
Garrett W wrote on 2022-09-27, 20:20:Sphere478 wrote on 2022-09-27, 17:19:Got a pic of what you are talking about? You mean like a crowbar for pulling nails?
NO! I'M WITH THE SCIENCE TEAM!
Sphere is just a regular Gordon Freeman !
Aint no problem a good crowbar cant solve.
TrashPanda wrote on 2022-09-27, 21:26:Garrett W wrote on 2022-09-27, 20:20:Sphere478 wrote on 2022-09-27, 17:19:Got a pic of what you are talking about? You mean like a crowbar for pulling nails?
NO! I'M WITH THE SCIENCE TEAM!
Sphere is just a regular Gordon Freeman !
Aint no problem a good crowbar cant solve.
I'm sure there are, otherwise what are sledgehammers for? Percussive repairs are the way to go 😀
See my graphics card database at www.gpuzoo.com
Constantly being worked on. Feel free to message me with any corrections or details of cards you would like me to research and add.
debs3759 wrote on 2022-09-27, 23:59:TrashPanda wrote on 2022-09-27, 21:26:Garrett W wrote on 2022-09-27, 20:20:NO! I'M WITH THE SCIENCE TEAM!
Sphere is just a regular Gordon Freeman !
Aint no problem a good crowbar cant solve.
I'm sure there are, otherwise what are sledgehammers for? Percussive repairs are the way to go 😀
...how about the good old Shifter ? should include that too for the trifecta of tools that work well for unintended uses.
TrashPanda wrote on 2022-09-28, 04:19:debs3759 wrote on 2022-09-27, 23:59:TrashPanda wrote on 2022-09-27, 21:26:Sphere is just a regular Gordon Freeman !
Aint no problem a good crowbar cant solve.
I'm sure there are, otherwise what are sledgehammers for? Percussive repairs are the way to go 😀
...how about the good old Shifter ? should include that too for the trifecta of tools that work well for unintended uses.
G62250-800x800-2449366689.jpg
Where is your god now?!?
Sphere478 wrote on 2022-09-28, 05:05:https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSMT8s2n-mQEVFblr-8KzERgA5sLaSB0DUehQ&usqp=CAU […]
TrashPanda wrote on 2022-09-28, 04:19:debs3759 wrote on 2022-09-27, 23:59:I'm sure there are, otherwise what are sledgehammers for? Percussive repairs are the way to go 😀
...how about the good old Shifter ? should include that too for the trifecta of tools that work well for unintended uses.
G62250-800x800-2449366689.jpg
Where is your god now?!?
Oh shit .. Sphere really is Gordon Freeman!
Crowbar Shifter.
TrashPanda wrote on 2022-09-28, 04:19:debs3759 wrote on 2022-09-27, 23:59:TrashPanda wrote on 2022-09-27, 21:26:Sphere is just a regular Gordon Freeman !
Aint no problem a good crowbar cant solve.
I'm sure there are, otherwise what are sledgehammers for? Percussive repairs are the way to go 😀
...how about the good old Shifter ? should include that too for the trifecta of tools that work well for unintended uses.
G62250-800x800-2449366689.jpg
Well, a pipe wrench was the only tool I used to build my raised beds, and this is just as good to have in a toolkit 😀
See my graphics card database at www.gpuzoo.com
Constantly being worked on. Feel free to message me with any corrections or details of cards you would like me to research and add.
I've discovered that some cheap power supplies will run with the +5V rail shorted at a 4-pin drive power connector until the insulation melts off the wires (even if they had 18AWG wire). A crowbar circuit would have to be internal to the power supply because of that.
lti wrote on 2022-10-01, 16:09:I've discovered that some cheap power supplies will run with the +5V rail shorted at a 4-pin drive power connector until the insulation melts off the wires (even if they had 18AWG wire). A crowbar circuit would have to be internal to the power supply because of that.
I had an Enermax that 465VE that did that on the 3.3V rail when it accidentally got shorted on a SATA power connector. Power supply still seemed to work, but I was not going to trust it even if I could confirm it just needed a new SATA power cable . I had previously shorted one newer Antec and one older Enermax and OCP kicked in quickly on those (can't recall which rail).
Crowbar is very oldest way but sometimes destructive results in smoked parts and burnt copper tracks. Modern designers had to design in protection triggers into their interface chipsets that is exposed to the external ports that breaks the circuit instantly or kick the power supply into protected mode that needs to be reset via unplugged for few minutes. Yet still there is diodes and zeners on the signal tracks and lack of resistors used as sacrificial cows. And not inserting capacitors into the signal lines if can be used.
But too many chips made out of design teams did not have protection built in meant we had to charge lot of money to repair devices. Good examples: Apple's tristar IC, PI3USB and M92T36 plus burnt filter array and (In Switch) so on. And I never trust destroyed PC motherboards (notebook mainly), due to shorted USB-C connector due to bent pins touching another pins used as charging port input. I no longer repair these as there is long lead on hard to get parts and they keep coming back failed everywhere else even the replaced parts were fine.
Good case due to using zener without much considerations to give way gracefully is big problem, one of these cases is I had a shorted USB-C used also as charging port fry open circuit a buried track due to zener diode array doing good job but this failed and blew the IC too.
In a way crowbar circuit is derided loudly.
Cheers,
Great Northern aka Canada.
TheMobRules wrote on 2022-09-27, 20:13:One common use of varistors in many power supplies is between the legs of the 2 big capacitors on the primary. In addition to helping with voltage spikes, they can protect components from being destroyed if you do silly things like plugging a PSU with the switch on the "110V" position into a 220V wall outlet (I may or may not have done this in the past...). What happens in that case is that the varistors will fail short, which in turn creates a short in the primary, causing the fuse to blow. Not sure how effective this is in general, but in my case all I had to replace was the fuse and the two varistors, everything else survived just fine.
In this (old) PSU design the two primary electrolytics are a series circuit for 240V mode. The voltage behind the bridge rectifier is about 300V DC, the nominal voltage of each capacitor is 200V DC in most cases.
Since the circuit is "floating" without a fixed connection to ground, there´s a serious risk of overvolting (one of) the electrolytics when they don´t age concurrantly.
Different insulation resistances could make one capacitor work at - let´s say - 250V so it would explode.
To prevent this situation the varistors keep the circuit balanced so every cap works at 150V.
When the PSU is set for 110V and plugged into 240V the varistors "try to protect" both caps, but they cannot take the high current and melt/ short.
Some PSUs have fixed resistors for this task. (They cause a permanent power consumption of ca. 1W.) The resistors also make sure the electrolytics get discharged when the PSU is unplugged.
Electrical surges (spikes) should be neutralized by the capacitors at the mains connector, behind the filter coils and at the bridge rectifier.
At this time there were also large inductors for PFC in many PSUs that can cause heavy voltage spikes also when the unit is turned on/off. I guess this was another reason for having VDRs at the electrolytics. PSUs with a PFC choke often have both VDRs AND fixed resistors.
