| Author | Message | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
I finished the new gauge panel for my Bluebird today, and in the process of putting it together I thought it'd be nice to add a little indicator light across the engine fan clutch to tell me when it is on. So I stuck one in. Today was the test, everything worked but I noticed the bulb was burned out for the fan clutch light, so I replaced it. Then I tested it again... this time it worked but as soon as I turned the fan clutch off, POOF it went. AAh, no diode!! For those of you that don't know, the way any coil works, be it fan clutch, solenoid, relay or any other kind of electromagnet, is that when you turn it on a magnetic field is established. Then when you turn it off, the field collapses. This collapse induces a voltage in the coil and if it finds that it has no-where to go, the voltage will simply get higher and higher until it finally finds a path from one end of the coil to the other... this can actually result in hundreds of volts or even a spark, even if the coil was only energized with 12 volts. Granted the effect is short lived, microseconds to milliseconds, but it is a spike that can mess with electronics or in my case, even burn out lightbulbs. The cure? ANY coil, solenoid, relay, clutch or electromagnet, etc on a bus (Jakes too!) should have a diode hooked across it, with the (+) end of the diode hooked to the side of the coil that gets hooked to (+), and the (-) side of the diode hooked to the coil wire that goes to (-) or ground. Simple. What happens is that while the coil is energized, the diode is hooked in a direction that it won't conduct any electricity so effectively it's not even there. BUT when you disconnect power to the coil, conveniently the way the diode is hooked provides a perfect path for the electricity generated by the collapsing field to find it's way home to the other side of the coil, without making any electronic killing (or in my case bulb killing) spikes. For most relays or solenoids, a simple 1N4001 diode will do. For larger things like my fan clutch, a 3 amp diode is more in order. Because 3 amp diodes have thicker wires and are constructed a bit more heavily, I like to use them for everything. Ok so you're all hot to go get some diodes... where? Well from me of course. In the process of closing my electronic manufacturing company a bunch of years ago, I ended up with thousands of the 3 amp versions that have been sitting in my shop forever, getting used 3 or 4 per year on things like my fan clutch. So for the price of a SASE, I'll be happy send any of you all you'd ever need to properly do up your solenoids, clutches and relays (a lot of cube relays already have them these days) free for the asking. Just drop an envelope in the mail with one inside that has your address and an apropriate stamp (for a few ounces at least) and I'll send em to you. Click on my profile and email me if you dont have my address from the spacers post.... (Message edited by boogiethecat on June 21, 2006) | ||
| Brian Brown (Blue_velvet)
Rating: N/A |
I learn the most amazing things from your posts, Gary. And you're so generous to boot. Get 'em while they're FREE folks. Rock on, Gary! bb | ||
| David Hartley (Drdave)
Rating: N/A |
Metal Oxide Varistors work also and are not polarity specific. ( MOV ). Clamps in either direction, some of the newer automotive relays have them in them now. | ||
| herman Rating: N/A |
Yeah, but don't MOVs wear out? | ||
| Arnold J Molloy (Ayjay)
Rating: N/A |
Hi Gary: Great "heads UP" on the diode application, the only change I would suggest to your recommendation is that you use 1N4007's Vs. 1N4001's. The 1N4001 only has a PIV of 50 volts where the 4007 has a PIV of 1000V....a lot more insurance for just a few pennies more. P.S. I haven't stocked any 1N series diodes but 4007's in 25 years, use them for everything. AyJay 79 RTS | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
Hi Arnold, Actually the PRV isn't very important in this application, at least not nearly as much as the reverse recovery time. As long as it never sees it's PIV it'll really never matter, and a 50 volt diode is fine on a 12 or 24 volt system. That said, I agree with you that in any application a 4007 is always better than a 4001. The TRR is actually more important in a "catch diode", and a 1n4001 will work but it's awfully slow compared to some of the faster diodes you can get. But you won't find faster ones at Radio Shack... What happens is that the "spike" can get fairly high in voltage until the diode turns on, generating a bit of EMI in the process. But practically speaking, 4001's are good enough most of the time for this kind of app. Interestingly I've tested thousands of 1n4001's with a breakdown tester and most break over above 200-300 volts anyway. Manufacturers basically make high voltage diodes for everything and label them to lesser specs just to fill the need, rather than make lots of differnet kinds. FWIW, the diodes I'm sending everyone are rated 3A 400V and 150ns Trr... nice 'n fast, high PRV- actually quite overkill for this but what the heck, I have thousands I'll never use and they will certainly do the job really well!!! Cheers! | ||
| Phil Dumpster2 Rating: N/A |
Gary, exactly how many diodes do you have? You see, I'm building a bunch of current sensing detectors for a model railroad and am collecting various components as I find great deals on them. Not just diodes, but chips like LM324, 74LS244, 74LS373, 74LS138. By the by, inductive kickback from a coil is used in those battery desulphators you see on eBay. | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
I dunno, maybe 5,000? A lot anyway... probably more than you or I will ever use. I used to design and manufacture high power switchers for the laser industry. This is just leftover stuff I haven't offd yet on ebay, and they come in so handy for busnuts I thought I'd give a bunch away first. I don't have any of the LS stuff, I was a CMOS guy myself. I may have a few LM324s but you find those on ebay all the time. I always liked TL074's better... Stuff, huh  | ||
| motorcoach1 Rating: N/A |
The Diode things sounds great. I'm working on VOX switches to turn on CT V's and use a timers switch to control the on time for security systems and use the LM324 chips all the time. i just hate to have to buy so many to get the discount on them. | ||
| Phil Dumpster2 Rating: N/A |
Do you have any diodes in the 6 to 10 amp range? If not, how much would you want for 1000 of the 3 amp diodes? | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
Sorry Phil, as soon as they get into that ampere range, practically speaking they go into TO220 packages or bigger. There are some made at 5-6 amps in a axial package but I don't have any. Lets email off-board about "the deal".. Cheers gary |