On Sun, 24 Sep 2017 18:33:27 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 18/09/2017 20:30, John Larkin wrote: >> On Fri, 15 Sep 2017 13:16:39 -0700, John Larkin >> <jjlarkin@highland_snip_technology.com> wrote: >> drops fast, to shut things down quick if a customer puts a hard >> voltage across one of our SSRs. The series resistor buys us enough >> time to do that. >> > >How fast will you switch off the fets? If too fast then any external >series inductance could overvolt the fets, or are you placing >transzorbs/movs across the SSR? > >piglet > >We can probably shut down the fets in under 500 us, given a big overload. We'll measure the voltage drop across the SSR, and PCB surface temp, and run a realtime simulation of resistor internal temperature, and limit that. Gate drive rise/fall times might be something like 100 us, maybe less. The fets that we will probably use are avalanche rated to about 80 mJ, so we'll tell our customers to provide external clamping above that. -- John Larkin Highland Technology, Inc lunatic fringe electronics
exploding wirewound resistors
Started by ●September 15, 2017
Reply by ●September 24, 20172017-09-24
Reply by ●September 25, 20172017-09-25
On Fri, 15 Sep 2017 13:16:39 -0700, John Larkin <jjlarkin@highland_snip_technology.com> wrote:> > >Lots of people make parts like this: > >https://www.digikey.com/product-detail/en/bourns-inc/PWR5322WR250JE/PWR5322WR250JETR-ND/2022962 > >The overload specs are almost always 5x rated power for 5 seconds, so >a 3 watt part can absorb 15 joules in that time. I wonder what happens >for shorter time overloads? Constant joules? > >Has anyone experimented with stressing this sort of small wirewound >resistor? > >I'll probably order some and blow them up. We'll be using low ohms, >0.2 maybe, so we'll need a lot of current. There's a car repair place >and a motorcycle shop on our block, so maybe I could buy or borrow a >battery. For pure fast joules, I could just discharge some big >electrolytics.This is weird: I'm banging a Vishay AC05W axial wirewound at 20 joules, 0.1 Hz. It has a green, sandy sort of coating. Every shot, I can see in my Mantis a brief red flash in the spiral pattern of the nichrome wire. But the surface temp only peaks around 100C. And if I switch off the illumination and look in the dark, nothing is visible. So it's not getting red hot, something weird is happening to the chemistry of the coating. Fluoresence? If I illuminate it with a UV flashlight, the effect is more visible. It smokes a bit for the first ten shots or so; I think it's burning off fingerprints. My weekend test died at some unknown point. The resistor is fine, but my cute little HP6212 power supply quit. I fatigued the line fuse with all that pulsing. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 25, 20172017-09-25
"John Larkin" <jjlarkin@highland_snip_technology.com> wrote in message news:1orisctm328t0lppij43o4v6j5hqqk4cos@4ax.com...> On Fri, 15 Sep 2017 13:16:39 -0700, John Larkin > <jjlarkin@highland_snip_technology.com> wrote: > >> >> >>Lots of people make parts like this: >> >>https://www.digikey.com/product-detail/en/bourns-inc/PWR5322WR250JE/PWR5322WR250JETR-ND/2022962 >> >>The overload specs are almost always 5x rated power for 5 seconds, so >>a 3 watt part can absorb 15 joules in that time. I wonder what happens >>for shorter time overloads? Constant joules? >> >>Has anyone experimented with stressing this sort of small wirewound >>resistor? >> >>I'll probably order some and blow them up. We'll be using low ohms, >>0.2 maybe, so we'll need a lot of current. There's a car repair place >>and a motorcycle shop on our block, so maybe I could buy or borrow a >>battery. For pure fast joules, I could just discharge some big >>electrolytics. > > This is weird: > > I'm banging a Vishay AC05W axial wirewound at 20 joules, 0.1 Hz. It > has a green, sandy sort of coating. Every shot, I can see in my Mantis > a brief red flash in the spiral pattern of the nichrome wire. But the > surface temp only peaks around 100C. And if I switch off the > illumination and look in the dark, nothing is visible. So it's not > getting red hot, something weird is happening to the chemistry of the > coating. Fluoresence? If I illuminate it with a UV flashlight, the > effect is more visible. > > It smokes a bit for the first ten shots or so; I think it's burning > off fingerprints. > > My weekend test died at some unknown point. The resistor is fine, but > my cute little HP6212 power supply quit. I fatigued the line fuse with > all that pulsing. > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com >Thermochromic? Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●September 25, 20172017-09-25
On Tuesday, 26 September 2017 00:00:39 UTC+1, Tim Williams wrote:> "John Larkin" <jjlarkin@highland_snip_technology.com> wrote in message > news:1orisctm328t0lppij43o4v6j5hqqk4cos@4ax.com... > > On Fri, 15 Sep 2017 13:16:39 -0700, John Larkin > > <jjlarkin@highland_snip_technology.com> wrote: > > > >> > >> > >>Lots of people make parts like this: > >> > >>https://www.digikey.com/product-detail/en/bourns-inc/PWR5322WR250JE/PWR5322WR250JETR-ND/2022962 > >> > >>The overload specs are almost always 5x rated power for 5 seconds, so > >>a 3 watt part can absorb 15 joules in that time. I wonder what happens > >>for shorter time overloads? Constant joules? > >> > >>Has anyone experimented with stressing this sort of small wirewound > >>resistor? > >> > >>I'll probably order some and blow them up. We'll be using low ohms, > >>0.2 maybe, so we'll need a lot of current. There's a car repair place > >>and a motorcycle shop on our block, so maybe I could buy or borrow a > >>battery. For pure fast joules, I could just discharge some big > >>electrolytics. > > > > This is weird: > > > > I'm banging a Vishay AC05W axial wirewound at 20 joules, 0.1 Hz. It > > has a green, sandy sort of coating. Every shot, I can see in my Mantis > > a brief red flash in the spiral pattern of the nichrome wire. But the > > surface temp only peaks around 100C. And if I switch off the > > illumination and look in the dark, nothing is visible. So it's not > > getting red hot, something weird is happening to the chemistry of the > > coating. Fluoresence? If I illuminate it with a UV flashlight, the > > effect is more visible. > > > > It smokes a bit for the first ten shots or so; I think it's burning > > off fingerprints. > > > > My weekend test died at some unknown point. The resistor is fine, but > > my cute little HP6212 power supply quit. I fatigued the line fuse with > > all that pulsing. > > > > Thermochromic?I've got some of that. I bet it would make a very cheap IR camera if you add a really large plastic fresnel lens. NT
Reply by ●September 26, 20172017-09-26
On Monday, September 25, 2017 at 5:17:37 PM UTC-4, John Larkin wrote:> On Fri, 15 Sep 2017 13:16:39 -0700, John Larkin > <jjlarkin@highland_snip_technology.com> wrote: > > > > > > >Lots of people make parts like this: > > > >https://www.digikey.com/product-detail/en/bourns-inc/PWR5322WR250JE/PWR5322WR250JETR-ND/2022962 > > > >The overload specs are almost always 5x rated power for 5 seconds, so > >a 3 watt part can absorb 15 joules in that time. I wonder what happens > >for shorter time overloads? Constant joules? > > > >Has anyone experimented with stressing this sort of small wirewound > >resistor? > > > >I'll probably order some and blow them up. We'll be using low ohms, > >0.2 maybe, so we'll need a lot of current. There's a car repair place > >and a motorcycle shop on our block, so maybe I could buy or borrow a > >battery. For pure fast joules, I could just discharge some big > >electrolytics. > > This is weird: > > I'm banging a Vishay AC05W axial wirewound at 20 joules, 0.1 Hz. It > has a green, sandy sort of coating. Every shot, I can see in my Mantis > a brief red flash in the spiral pattern of the nichrome wire. But the > surface temp only peaks around 100C. And if I switch off the > illumination and look in the dark, nothing is visible. So it's not > getting red hot, something weird is happening to the chemistry of the > coating. Fluoresence? If I illuminate it with a UV flashlight, the > effect is more visible.Do you have any idea about how much wire is in the thing? And have you tried to guesstimate how much the wire temperature will rise. George H.> > It smokes a bit for the first ten shots or so; I think it's burning > off fingerprints. > > My weekend test died at some unknown point. The resistor is fine, but > my cute little HP6212 power supply quit. I fatigued the line fuse with > all that pulsing. > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●September 26, 20172017-09-26
George Herold <gherold@teachspin.com> wrote:> Do you have any idea about how much wire is in the thing? > And have you tried to guesstimate how much the wire temperature > will rise.> George H.Superbly important questions. Then we get to the problem of trimming the resistance. Seems similar to evaporation of the tungsten filament in a light bulb. Will fail. The main problem is trying to pack too much power in too small a space. This is doomed to failure. Already his main fuse blew to shock loads. Basic designs used to last for hundreds of years. You can see them in museums in working condition. This is not one of those examples.
Reply by ●September 26, 20172017-09-26
On Tuesday, September 26, 2017 at 10:02:30 AM UTC-4, Steve Wilson wrote:> George Herold <gherold@teachspin.com> wrote: > > > Do you have any idea about how much wire is in the thing? > > And have you tried to guesstimate how much the wire temperature > > will rise. > > > George H. > > Superbly important questions. > > Then we get to the problem of trimming the resistance. Seems similar to > evaporation of the tungsten filament in a light bulb. Will fail. > > The main problem is trying to pack too much power in too small a space. This > is doomed to failure. Already his main fuse blew to shock loads. > > Basic designs used to last for hundreds of years. You can see them in museums > in working condition. > > This is not one of those examples.Steve, you seem a little negative. What's up? I find it an interesting problem. I'd be happy to help JL if I could, but chances are he knows more than me. Can you solder to nichrome? ... (fabricating your own resistors would be spendy.) George H.
Reply by ●September 26, 20172017-09-26
Steve Wilson <no@spam.com> wrote:> George Herold <gherold@teachspin.com> wrote:>> Do you have any idea about how much wire is in the thing? >> And have you tried to guesstimate how much the wire temperature will >> rise.>> George H.> Superbly important questions.> Then we get to the problem of trimming the resistance. Seems similar to > evaporation of the tungsten filament in a light bulb. Will fail.> The main problem is trying to pack too much power in too small a space. > This is doomed to failure. Already his main fuse blew to shock loads.> Basic designs used to last for hundreds of years. You can see them in > museums in working condition.> This is not one of those examples.Why not use constant current loads using MOSFETs or bipolar. Spread the power over a longer time and reduce the peak values. MOSFETs are rated for this kind of work. They have good thermal conduction to heatsinks. Dumping the load into a resistor seems like applying power to a device that is not designed for the application. First task is to find a device that is designed for this work. Then design the rest of the control circuitry.
Reply by ●September 26, 20172017-09-26
George Herold <gherold@teachspin.com> wrote:> Steve, you seem a little negative. What's up?Headaches from mold spores. I have been fighting this problem for 20 years. Constant day and night. Cannot sleep. Headach pills have no effect. No solution so far. Kind of gives you a shitty outlook on life. I thought I was doing a bit better. You are very sensitive. Thanks. I wish I could sleep.
Reply by ●September 26, 20172017-09-26
On Tuesday, September 26, 2017 at 10:49:14 AM UTC-4, Steve Wilson wrote:> George Herold <gherold@teachspin.com> wrote: > > > Steve, you seem a little negative. What's up? > > Headaches from mold spores. I have been fighting this problem for 20 years. > Constant day and night. Cannot sleep. Headach pills have no effect. No > solution so far. Kind of gives you a shitty outlook on life. I thought I was > doing a bit better. You are very sensitive. Thanks. > > I wish I could sleep.Sounds like you need to move to a dry climate. Maybe Arizona, hang out with Jim. GH
