On Tue, 26 Sep 2017 07:37:09 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>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.No, nichrome has to be welded. I was thinking about actually measuring the wire peak temperature and its decay time constant. I'd have to make my own resistor, using copper instead of nichrome, and use the copper tempco to measure its temperature after a big pulse. But that's too much work, so we'll just blow up resistors to ballpark their thermal dynamics. There are papers and stuff online about thermal modeling of wirewound resistors, but they are mostly a lot of equations and few numbers. I had to upgrade my test gear: https://www.dropbox.com/s/oz62u59ourty079/Z420_C1.JPG?raw=1 There are now three 22mF 80 volt caps (210 joules) and an IXYS mosfet (IXFH-FT400N075T2) rated for 1000 watts dissipation and 1000 amps peak current. This experiment is slow: occasional setup and days-long experiments. Meanwhile the product PCB layout is in progress. -- John Larkin Highland Technology, Inc lunatic fringe electronics
exploding wirewound resistors
Started by ●September 15, 2017
Reply by ●September 26, 20172017-09-26
Reply by ●September 26, 20172017-09-26
George Herold <gherold@teachspin.com> wrote:> 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.> GHYou are very knowledgeable about mold. It will grow on anything, including silicon shower sealants and ordinary concrete. They look for the sulfur and bury the hyphae throughout the concrete until it disintegrates. Boulder, Colorado, was a very nice place. Dry, good building codes to eliminate basement humidity and kill mold. I am very sorry I ever left. The only problem was the buildings tended to tilt a couple of degrees due to the gravity well from the nearby Flagstaff mountains. You can barely notice. I can live with that. Moving is not a good option. No matter where I go there will be mold. I have to conquer the problem at the source. Conventional filters, including HEPA, do not work. They suck in the stray lint particles which cling to the input. The mold loves these particles as a food source. Within 3 days, the filter is now a generator of mold spores. Conventional elecrostatic cleaners do not work. The spores float past the collection electrodes as it they were not there. I have invented a new type of electrostatic air cleaners. Most ionic generators require high voltage to ionize the air. The voltage is applied to a thin electrode that must be thick enough to support cleaning. The conductor radius determines the applied voltage that is needed. This determines the minimum spacing you can use between elcrodes. It also generates ozone, which is harmful. Instead, I use the aluminum foil from party balloons. The metal thickness is around 40 nm, which creates an extremely sharp radius. The electrode separates the need for strength which is needed for cleaning, and the need for sharp radius which is needed for ionization. This means you can reduce the electrode voltage and reduce the electrode spacing without problems with arcover. Eventually, I will solve these problems. I have a lot of new ideas for products for industry. But it is a race against time. I am old, and growing older faster. I don't have the strength I used to have. I need to find someone younger and stronger who can absorb what I have learned though the years, and apply it to a new company. I have made millions in the past, and I'm sure I can do it again. But I'm starting to recognize my weaknesses, and I have to figure a way around them. This has never happened before.
Reply by ●September 26, 20172017-09-26
On Tue, 26 Sep 2017 14:41:46 GMT, Steve Wilson <no@spam.com> wrote:>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.I'm quantifying when the resistor will fail. Isn't that good to know?> >> 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.A slo-blo fuse fixed the HP supply.> >> 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.I'm designing an SSR; the customer supplies the current. My job is to set the specifications, and do my best to protect the SSR if the customer exceeds those specs, specifically applies a hard voltage across the SSR contacts. A 5-watt wirewound resistor can absorb ballpark 100x as many joules as a DPAK mosfet, and mosfets have better SOARs than bipolars.> >Dumping the load into a resistor seems like applying power to a device that >is not designed for the application.But power resistors are exactly designed to have power dumped into them. But most are poorly characterized for joules-vs-time, so I'm blowing some up to see their limits. Looks like, with the right resistor, I can have a safety factor at least 4:1. We were just noting that we're grossly overkilling this product from a design standpoint, but it's fun. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●September 26, 20172017-09-26
On Tuesday, September 26, 2017 at 11:45:14 AM UTC-4, John Larkin wrote:> On Tue, 26 Sep 2017 07:37:09 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >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. > > No, nichrome has to be welded.I was just wondering if one of the stainless steel fluxes would work. I've tinned SS and then soldered that to some other hunk of copper. I was thinking about actually measuring> the wire peak temperature and its decay time constant. I'd have to > make my own resistor, using copper instead of nichrome, and use the > copper tempco to measure its temperature after a big pulse. But that's > too much work, so we'll just blow up resistors to ballpark their > thermal dynamics. There are papers and stuff online about thermal > modeling of wirewound resistors, but they are mostly a lot of > equations and few numbers. > > I had to upgrade my test gear: > > https://www.dropbox.com/s/oz62u59ourty079/Z420_C1.JPG?raw=1 > > There are now three 22mF 80 volt caps (210 joules) and an IXYS mosfet > (IXFH-FT400N075T2) rated for 1000 watts dissipation and 1000 amps peak > current.> > This experiment is slow: occasional setup and days-long experiments. > Meanwhile the product PCB layout is in progress.I don't know how many resistors you'll need, but I wonder if it's worthwhile talking to some pulse power resistor person/company? There is most likely all sorts of weird stuff going on. It sucks to use some part in a way that the manufacturer didn't intend, and then have them change the process. (I've had that happen with optical components.) George H.> > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●September 26, 20172017-09-26
John Larkin wrote...>WW is a bad idea, you want a bulk-style resistor. Like Ohmite's OZ and OY series, they are even rated to handle 14 to 20kV for a short while! -- Thanks, - Win
Reply by ●September 26, 20172017-09-26
On 26 Sep 2017 12:15:04 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:>John Larkin wrote... >> > > WW is a bad idea, you want a bulk-style resistor. > Like Ohmite's OZ and OY series, they are even > rated to handle 14 to 20kV for a short while!My problem with bulk resistors is that they are bulky. We're putting 32 SSRs on a VME module, with vibration requirements. Looks like a Vishay 5-watt wirewound is reliable at 17 kilowatts, 1 msec, 17 joules/shot, 0.1 Hz. After a day or so more, I'll crank the voltage up and see what happens at higher energy. I think our FPGA can shut off the mosfets before 5 joules. We won't even promise to survive that kind of abuse. -- 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
On Tuesday, September 26, 2017 at 3:15:19 PM UTC-4, Winfield Hill wrote:> John Larkin wrote... > > > > WW is a bad idea, you want a bulk-style resistor. > Like Ohmite's OZ and OY series, they are even > rated to handle 14 to 20kV for a short while! > > > -- > Thanks, > - WinI think JL wants a smaller R. But searching DK under ceramic R's I found these cement resistors. http://www.yageo.com/documents/recent/Yageo%20LR_SLR_2013.pdf Tempco stinks. George H.
Reply by ●September 26, 20172017-09-26
On Tue, 26 Sep 2017 12:57:44 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Tuesday, September 26, 2017 at 3:15:19 PM UTC-4, Winfield Hill wrote: >> John Larkin wrote... >> > >> >> WW is a bad idea, you want a bulk-style resistor. >> Like Ohmite's OZ and OY series, they are even >> rated to handle 14 to 20kV for a short while! >> >> >> -- >> Thanks, >> - Win > >I think JL wants a smaller R. But searching DK under ceramic R's >I found these cement resistors. >http://www.yageo.com/documents/recent/Yageo%20LR_SLR_2013.pdf > >Tempco stinks. > >George H.I'm pulsing the Vishay 5-watt axial wirewound now at 22 kilowatts for 1 millisecond, 0.1 Hz. There seem to be no indications on a data sheet of how resistors will survive extreme pulsing; just gotta try it. I did blow the top off a Vishay 5-watt power-pad metal plate resistor. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●September 27, 20172017-09-27
On Tuesday, September 26, 2017 at 9:17:15 AM UTC-7, George Herold wrote:> On Tuesday, September 26, 2017 at 11:45:14 AM UTC-4, John Larkin wrote: > > On Tue, 26 Sep 2017 07:37:09 -0700 (PDT), George Herold > > <gherold@teachspin.com> wrote:> > >Can you solder to nichrome? ... (fabricating your own > > >resistors would be spendy.)> > No, nichrome has to be welded. > > I was just wondering if one of the stainless steel fluxes would work.It might make a joint, but 'normal' operating temperatures would crack the solder. One either hard-solders (silver/copper alloy) or welds to make a good electrical connection. Welding is cheaper.
Reply by ●September 27, 20172017-09-27
whit3rd <whit3rd@gmail.com> wrote:> On Tuesday, September 26, 2017 at 9:17:15 AM UTC-7, George Herold wrote: >> On Tuesday, September 26, 2017 at 11:45:14 AM UTC-4, John Larkin wrote: >> > On Tue, 26 Sep 2017 07:37:09 -0700 (PDT), George Herold >> > <gherold@teachspin.com> wrote:>> > >Can you solder to nichrome? ... (fabricating your own resistors >> > >would be spendy.)>> > No, nichrome has to be welded. >> >> I was just wondering if one of the stainless steel fluxes would work.> It might make a joint, but 'normal' operating temperatures would crack the > solder. One either hard-solders (silver/copper alloy) or welds to > make a good electrical connection. Welding is cheaper.What about titanium. I have some sheets. Absolutely amazing metal. Extremely difficult to work with. Doesn't want to weld or join with any other material. Very good high temperature performance. Used in the SR-71. Extremely sensitive to chlorine embrittlement. Needs to be protected. Could probably make good high surge resistors. The problem would be the welds.
