- MOVs - 2 Updates
- DVD Rewinder - 5 Updates
| Cursitor Doom <curd@notformail.com>: Apr 22 08:11AM Hi, I've noticed a high failure rate in appliances built-in mains filters. These are the filters that are typically found at the point the power lead enters the appliance. They're silver coloured things about the size of a matchbox and they tend to fail short and blow the fuse. The ones I've seen are usually rated for 1A since the only stuff I do is low power. However, some of that low power stuff is test equipment with SMPSs that initially look like a short circuit at power-on. I think this is what blows those filters. Early SMPS designs didn't seem to pay much attention to surge prevention so I'm wondering if it would pay to retrospectively fit MOVs at the beginning of the SMPS section to prolong filter and power supply life (hopefully). Any thoughts on the advisability of doing this and which MOVs are best suited to this purpose? Thanks. CD. |
| Jeff Liebermann <jeffl@cruzio.com>: Apr 22 08:20AM -0700 On Fri, 22 Apr 2016 08:11:21 -0000 (UTC), Cursitor Doom >Any thoughts on the advisability of doing this and which MOVs are best >suited to this purpose? >Thanks. I think you're mixing up MOV and NTC Thermistor (surgistor or inrush current limiter). The MOV is an overvoltage limiter and goes ACROSS the power line. The NTC thermistor goes in SERIES with the AC power and limits the initial inrush current. You'll need to trace out the schematic of the power line filter to see which one (or both) you're dealing with. In normal use, I've never seen MOV's or surgistors blow. I've seen pleny of them blow up when the AC line conditions are all wrong, such as lightning hits, unbalanced phases causing the voltage to increase, power supply overload causing the surgistor to draw too much current, and such. I've also seen a few design errors, where the surgistor specs were inproperly selected. I can guess my way through your problem, but I'm busy/lazy and would prefer you to do the dirty work. Do some measurements such as a scope picture of the inrush current, normal operation, extreme operation, etc with a line current sensor. Get the numbers off the MOV and surgistor and I'll see if they were properly selected. Read some design articles on selecting inrush current limiters. <http://powerelectronics.com/community/how-do-you-choose-right-type-ntc-thermistor-limit-inrush-current-capacitive-applications> Incidentally, most (not all) of the devices I've seen that have inrush current problems also use slow blow fuses. Good luck. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Jeff Liebermann <jeffl@cruzio.com>: Apr 21 10:31AM -0700 On Thu, 21 Apr 2016 09:24:15 +0100, MJC <gravity@mjcoon.plus.com> wrote: >Perhaps someone should invent caiman clips. Ideally they would be sold >duty-free (=Cayman; geddit?). >Mike. Yuck. Hook clips work fine until one gets to boards full of SMT components. I have a box of spring loaded probe tips, originally from a bed of nails test fixture, positioned with the flex plastic hose used for coolant hose and camera tripods. The board is secured to a PCB holder and spring pressure makes the connection. Much better and easier than tack soldering wires. I'll be at home for a while longer so no photos but here are the components: PCB holder: <http://www.comtreeinc.com/pv324_LG.gif> Spring loaded test probe/pin: <https://www.tindie.com/products/upgradeindustries/10x-spear-tip-spring-loaded-pogo-test-pin-p160-b-/> Flexible plastic hose: <https://www.google.com/search?tbm=isch&q=machinery+coolant+hose> -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Jeff Liebermann <jeffl@cruzio.com>: Apr 21 11:18AM -0700 On Thu, 21 Apr 2016 10:31:46 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote: >Spring loaded test probe/pin: ><https://www.tindie.com/products/upgradeindustries/10x-spear-tip-spring-loaded-pogo-test-pin-p160-b-/> More... The magic buzzword is "pogo pin": <https://www.google.com/search?q=pogo+pin&tbm=isch> <http://www.ebay.com/sch/i.html?_nkw=pogo+pin> Note that there are also receptacles (sockets) for the pins, to make them easy to replace: <https://www.google.com/search?tbm=isch&q=pogo+pin+receptacle> Lots of different sizes and tip types. Once you get into using these pins, you'll find yourself addicted. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Heisenberg <Barry@saymyname.com>: Apr 22 05:35AM +1000 On Thu, 21 Apr 2016 11:18:00 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote: ><https://www.google.com/search?tbm=isch&q=pogo+pin+receptacle> >Lots of different sizes and tip types. >Once you get into using these pins, you'll find yourself addicted. Are you familiar with IDS and wirewrap? =-=- "Humans will have advanced a long, long way when religious belief has a cozy little classification in the DSM*." David Melville (*Diagnostic and Statistical Manual of Mental Disorders) |
| Jeff Liebermann <jeffl@cruzio.com>: Apr 21 02:44PM -0700 On Fri, 22 Apr 2016 05:35:02 +1000, Heisenberg <Barry@saymyname.com> wrote: >>Lots of different sizes and tip types. >>Once you get into using these pins, you'll find yourself addicted. >Are you familiar with IDS and wirewrap? Insulation Displacement Something. Yep, been there with every ribbon cable connector. I even have the proper IDS compression tools for most of the connectors used in PC's. Wire Wrap. Yep, I still have my spools of #30 wire, which I now use for soldering breadboards. I still have my manual tools as I sold my battery operated wire wrap gun. Now, are you familiar with my policy of ignoring one line questions? The problem is that one line questions usually lack any content, value, understand, detail, and are generally not worth reading. Since your nom de plume implies uncertainty, I'll make an exception this time. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| John Robertson <spam@flippers.com>: Apr 21 07:40PM -0700 On 04/21/2016 10:31 AM, Jeff Liebermann wrote: > <https://www.tindie.com/products/upgradeindustries/10x-spear-tip-spring-loaded-pogo-test-pin-p160-b-/> > Flexible plastic hose: > <https://www.google.com/search?tbm=isch&q=machinery+coolant+hose> I'd enjoy seeing pictures of your test bench setup with those pogo pins. Near as I can figure you use those semi-stiff hoses to hold the pins on the UUT (unit under test). For me, not su useful as I am mostly fixing TTL stuff (not many folks still do that), but I can see it being very useful on SMT products. John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
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