Post by thread:current (was Car battery power help)

> changing the SUBJECT line...Tell me if this is correct...It doesnt matter > how much current your batter or what not can supply...it matters how much > you are drawing out of it (?) Exactly. The amount of current depends on the voltage and resistance. Having a power source that is capable of supplying huge current will not alone cause the current to increase. It can, however, do more damage in a fault situation. A circuit that shorts when connected to a little battery might do nothing more dramatic than briefly warming up the battery. With a big battery, it might smoke or even catch fire. The more current that's available, the more you might want to use a fuse. I actually once saw a prototype circuit board catch fire inside a PC. The board had a 5V to gnd short caused by a misalignment of its layers. The PC just kept right on working even with the flame and smoke pouring out! The circuit path on the board was long and thin enough that the PC's power supply was able to maintain 5V even with the short, creating enough heat to ignite the epoxy and keep it burning. The flame extinguished itself when the power was turned off. --- Peace, William Kitchen spam_OUTbillTakeThisOuTiglobal.net The future is ours to create.

"William J. Kitchen" wrote: > With a big battery, it might smoke or even catch fire. The more current that' s available, > the more you might want to use a fuse. I tell people who build my ignition controller to keep high current ground returns seperate from the one that powers the PCB. I have seen most of the PCB tracks vaporised in a fault condition. It's still got be beat how they did it though. -- Best regards Tony http://www.picnpoke.com Email .....salesKILLspam@spam@picnpoke.com

At 12:05 5/11/99 +1100, you wrote: >"William J. Kitchen" wrote: > >> With a big battery, it might smoke or even catch fire. The more current that's available, >> the more you might want to use a fuse. > >I tell people who build my ignition controller to keep high current >ground returns seperate from the one that powers the PCB. I have seen >most of the PCB tracks vaporised in a fault condition. It's still got be >beat how they did it though. Something is confusing me here Tony I thought that you have had no probelms with the 7805 approch nad over 1000 units Now you seem to indicate unexplainable faults. HUMM Maybe there is something in that for all of us... <GRIN> As for the question of what is a TRISIL. Basicaly is a bidirectional crowbar device (Like 2 SCRS) that clamps both rails together (To within 0.6V) one the breakover point is reached. These things come in 0.5kW and 1.5kW (Yep thats correct) versions (surface mount 0805, and SOIC8!). I love these things Dennis {Quote hidden}> >-- >Best regards > >Tony > >http://www.picnpoke.com >Email salesKILLspampicnpoke.com > >

If you'll forgive the OT, a shop I once worked in sold a kit with .040-over pistons to two guys with a .030 block. Undaunted, they hammered it together. Phone did'nt ring till they could'nt get it to start. There's talent out there. Regards, Jack Tony Nixon wrote: I have seen > most of the PCB tracks vaporised in a fault condition. It's still got be > beat how they did it though.

Dennis Plunkett wrote: > Something is confusing me here Tony > I thought that you have had no probelms with the 7805 approch nad over 1000 > units > Now you seem to indicate unexplainable faults. That's the thing I suppose. The leds were on an early version, and the other problem came from the fact that a kit design can be completely misused by a constructor. That's something no one has control over. I actually had someone ask me if it was ok to use one of them in an airplane. I hastily said no, but you never know what the outcome will be with some people. As for the 7805 approach, the zener blew off the board, and the 78L05 had to be replaced, but all else were ok including the PIC. -- Best regards Tony http://www.picnpoke.com Email .....salesKILLspam.....picnpoke.com

Dennis Plunkett wrote: {Quote hidden}> > At 12:05 5/11/99 +1100, you wrote: > >"William J. Kitchen" wrote: > > > >> With a big battery, it might smoke or even catch fire. The more current > that's available, > >> the more you might want to use a fuse. > > > >I tell people who build my ignition controller to keep high current > >ground returns seperate from the one that powers the PCB. I have seen > >most of the PCB tracks vaporised in a fault condition. It's still got be > >beat how they did it though. > > Something is confusing me here Tony > I thought that you have had no probelms with the 7805 approch nad over 1000 > units > Now you seem to indicate unexplainable faults. > > HUMM > Maybe there is something in that for all of us... <GRIN> > > As for the question of what is a TRISIL. Basicaly is a bidirectional > crowbar device (Like 2 SCRS) that clamps both rails together (To within > 0.6V) one the breakover point is reached. These things come in 0.5kW and > 1.5kW (Yep thats correct) versions (surface mount 0805, and SOIC8!). I love > these things > > Dennis DigiKey calls these Transient Voltage Suppressors (TVS) - they come unidirectional or bi-directional. Mark -- I do small package shipping for small businesses, world-wide.

part 0 828 bytes DigiKey calls these Transient Voltage Suppressors (TVS) - they come unidirectional or bi-directional.   Mark </UL> If it acts like back to back SCR's, then I'm guessing that this really is a crowbar device, i.e. once triggered it remains conducting untill current is removed?  If so not too usefull for spike suppression... Mike Rigby-Jones </BODY> </HTML> </x-html>

{Quote hidden}> Michael Rigby-Jones wrote: > > <snip> > > As for the question of what is a TRISIL. Basicaly is a > bidirectional > > crowbar device (Like 2 SCRS) that clamps both rails together > (To within > > 0.6V) one the breakover point is reached. These things come in > 0.5kW and > > 1.5kW (Yep thats correct) versions (surface mount 0805, and > SOIC8!). I love > > these things > > > > Dennis > > DigiKey calls these Transient Voltage Suppressors (TVS) - they > come > unidirectional or bi-directional. > > Mark > > If it acts like back to back SCR's, then I'm guessing that this really > is a crowbar device, i.e. once triggered it remains conducting untill > current is removed? If so not too usefull for spike suppression... > > Mike Rigby-Jones TVS's act just like a fast, cheap, very high power Zener, they're a little sloppy on triggering voltage (not quite as precise as a Zener, or at least weren't at one time), these work well for Auto circuits. A TVS won't clamp down to 0.6V (maybe a Trisil is a different beastie?) TVS's are rated by power & Vbr (breakdown / avalanche voltage); 1 pSec avalanche time for unidirectional units, the bidirectional's are slower, and at $0.72 in onesies for the 1.5kW units, you can do worse. General Semiconductor makes the ones I've looked at, other co's make these; http://www.digikey.com/EC/V3/250.pdf for Digi-Key's catalog page, FYI. Other places may be cheaper. <G> The wattage rating IS, btw, a "Peak power pulse" rating - I wouldn't try to use one at a steady state power dissipation of 1.5kW, "it wouldn't be pretty!" - I haven't blown one up yet, I'm sure someone will here <G> Mark -- I do small package shipping for small businesses, world-wide.

<x-rich>At 09:06 5/11/99 -0000, you wrote: >>>> <excerpt>RE: current (was Car battery power help) <fontfamily><param>Arial</param><bigger><<snip></bigger></fontfamily><color><par am>0000,0000,ffff</param> <fontfamily><param>Arial</param><bigger>> As for the question of what is a TRISIL. Basicaly is a bidirectional</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>> crowbar device (Like 2 SCRS) that clamps both rails together (To within</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>> 0.6V) one the breakover point is reached. These things come in 0.5kW and</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>> 1.5kW (Yep thats correct) versions (surface mount 0805, and SOIC8!). I love</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>> these things</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>> > Dennis</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>DigiKey calls these Transient Voltage Suppressors (TVS) - they come</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>unidirectional or bi-directional.</bigger></fontfamily> <fontfamily><param>Arial</param><bigger> Mark</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>If it acts like back to back SCR's, then I'm guessing that this really is a crowbar device, i.e. once triggered it remains conducting untill current is removed? If so not too usefull for spike suppression...</bigger></fontfamily> <fontfamily><param>Arial</param><bigger>Mike Rigby-Jones</bigger></fontfamily> </color></excerpt><color><param>0000,0000,ffff</param> </color>This depends on the devie that you go for. Yes the hold current is low once tripped. If you use a TRANZORB then it will clamp one over voltage. And release once under. Dennis </x-rich>

At 10:02 5/11/99 -0800, you wrote: {Quote hidden}>> Michael Rigby-Jones wrote: >> >> <snip> >> > As for the question of what is a TRISIL. Basicaly is a >> bidirectional >> > crowbar device (Like 2 SCRS) that clamps both rails together >> (To within >> > 0.6V) one the breakover point is reached. These things come in >> 0.5kW and >> > 1.5kW (Yep thats correct) versions (surface mount 0805, and >> SOIC8!). I love >> > these things >> > >> > Dennis >> >> DigiKey calls these Transient Voltage Suppressors (TVS) - they >> come >> unidirectional or bi-directional. >> >> Mark >> >> If it acts like back to back SCR's, then I'm guessing that this really >> is a crowbar device, i.e. once triggered it remains conducting untill >> current is removed? If so not too usefull for spike suppression... >> >> Mike Rigby-Jones > >TVS's act just like a fast, cheap, very high power Zener, they're a >little sloppy on triggering voltage (not quite as precise as a Zener, or >at least weren't at one time), these work well for Auto circuits. A TVS >won't clamp down to 0.6V (maybe a Trisil is a different beastie?) TVS's >are rated by power & Vbr (breakdown / avalanche voltage); 1 pSec >avalanche time for unidirectional units, the bidirectional's are slower, >and at $0.72 in onesies for the 1.5kW units, you can do worse. General >Semiconductor makes the ones I've looked at, other co's make these; >http://www.digikey.com/EC/V3/250.pdf for Digi-Key's catalog page, FYI. >Other places may be cheaper. <G> > >The wattage rating IS, btw, a "Peak power pulse" rating - I wouldn't try >to use one at a steady state power dissipation of 1.5kW, "it wouldn't be >pretty!" - I haven't blown one up yet, I'm sure someone will here <G> > > Mark I have <G> But in an power induced envorionment, where one of the tests was to place 415VAC on a line for 15 minutes Dennis > >-- >I do small package shipping for small businesses, world-wide. > >