- Greasing up switches and connectors? - 7 Updates
- Transformer shot! (was scope SMPS/ capacitor venting) - 7 Updates
| "Ian Field" <gangprobing.alien@ntlworld.com>: Mar 07 06:15PM "N_Cook" <diverse@tcp.co.uk> wrote in message news:nbjbp3$uo0$1@dont-email.me... >> Thanks. > Can we summarise this thread by saying - > Any grease is better than no grease, Some mechanical engineering greases contain a significant proportion of water. Not certain - but that may open the possibility of corrosive decomposition products. Many greases are lithium based, its probably bound up in stable compounds, but very reactive if it gets loose. Molybdenum grease is probably OK except in high voltage or high impedance work - graphite grease is probably not OK for anything electrical. Graphite is the lubricant of choice for brass, such as locks etc. PTFE penetrating oil works well on contacts, as for grease the one I know of is Finish-line PTFE fortified bicycle grease. It works OK on heavy contacts, but may isolate the wiper on light duty switchgear. Silicone grease is exactly opposite to hygroscopic - it repels water. |
| Jeff Liebermann <jeffl@cruzio.com>: Mar 07 10:53AM -0800 >> Dave >I actually put it directly on the center conductor after the connector is attached and then screw it on the fitting. While the grease is an 'insulator', the metal parts touch and the grease prevents moisture getting to the wire. I did not put any grease on the rubber boot except for any residue that was on the outside of the connector. >G² <http://www.wisegeek.org/what-is-dielectric-grease.htm> "Besides being used to seal rubber covers on electrical connections, dielectric grease also prevents corrosion when applied directly to metal connectors. Though it works well for this purpose, it can sometimes cause a connection to stop working if not all of the grease is pushed out of the way between the points of contact inside the connector." Wiping off silicone grease from a connector pin is difficult, messy, and requires solvents. If you read other articles on the electrical uses for dielectric grease, you'll find that they all discuss how it is applied to everything EXCEPT the conductors. For example: <http://www.rx7club.com/2nd-generation-specific-1986-1992-17/fyi-about-dielectric-grease-electrical-components-979955/#post10895971> "one thing people have tried is dielectric grease on various electrical component connections. this is NOT a good idea! dielectric grease or "tune up grease" as you may find in auto parts stores is ONLY meant for high voltage connections such as spark plug wires, that is about the only place it belongs on a car. using it on electrical connections, eventually you may as well pitch the harness into the garbage.. it's almost impossible to get the stuff out once it's in there, dielectric grease does not conduct electricity very well and will in fact cause resistance issues and eventually failed connections." etc... -- 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-Del <ohger1s@aol.com>: Mar 07 01:10PM -0800 Interesting. I was always under the impression that *any* lubricant, whether a fine liquid to a grease would be pushed aside by a sliding electrical contact and electrical contact would be made on the molecular level. The lubricant would surround the contact points and deny air and moisture access to the contact. I've used dielectric grease on vintage automobile harnesses and bulb sockets and have never had a problem with contacts afterwards. |
| "Ian Field" <gangprobing.alien@ntlworld.com>: Mar 07 09:44PM "John-Del" <ohger1s@aol.com> wrote in message news:deb53566-c135-443e-8b84-04e7c620b327@googlegroups.com... > whether a fine liquid to a grease would be pushed aside by a sliding > electrical contact and electrical contact would be made on the molecular > level. Some technical journal informed me that this planet has a smoother surface than any ball bearing that can be manufactured - apparently; that includes the fact that centrifugal force gives the planet a greater diameter at the equator than at the poles. If you looked at an electron-micrograph of the contact surfaces - you'd think you were looking at a mountain range. |
| Jeff Liebermann <jeffl@cruzio.com>: Mar 07 05:50PM -0800 On Mon, 7 Mar 2016 13:10:22 -0800 (PST), John-Del <ohger1s@aol.com> wrote: >sliding electrical contact and electrical contact would be made >on the molecular level. The lubricant would surround the contact >points and deny air and moisture access to the contact. Or trap moisture if it was wet when you inserted the connector. Based on my limited automotive and marine radio experience, I think grease is a bad idea. However, there are places where it will do as you suggest. If there's AC or DC current going through the connection, and the connection is under some pressure, you can get a reasonable connection. Dry loads such as TV/cable/RF don't work well or for very long. If the connection moves, and is designed for self cleaning operation, such as in a switch or relay, it will work for a while. The problem is not only from the insulating properties of the dielectric grease, but also from the dirt and grit that are attracted by the grease. As the dirty grease builds up, it becomes thicker and thicker. Eventually, the grease hardens sufficiently to force the contacts to ride up onto the layer of dirty grease, instead of making a connection. This is a very common problem with potentiometers that are lubricated with greases diluted by solvents. When the solvents evaporate, the remaining grease is almost thick enough to cause the wiper to ride up onto the grease. Few people do this, but as I mentioned, the grease gets thick enough from being mixed with carbon particles scraped off from the resistance element to cause a problem. If you need to be convinced more, please buy some phosphorescent powder on eBay. <http://www.ebay.com/sch/i.html?_nkw=phosphorescent+powder> <http://www.allureglow.com.au/powder.php> <http://www.crimescene.com/store/index.php?main_page=product_info&products_id=76> Try to get the finest grain powder possible. Most of my pile is 10 and 15um. I haven't tried the criminal investigation stuff, but I'm fairly sure it will work. Also get a UV (365nm) flashlight. Mix a little with your grease of choice and apply to a flat piece of steel, aluminum, or copper (so you can see what you're doing). Rub it in and then wipe the grease off without solvents. Use the UV light to see how much is left. There should be plenty. Now, try some common solvents. More will disappear, but you'll still have plenty of grease left on the surface. If you have a microscope handy, you can see a microscopic thin layer of glowing grease. >I've used dielectric grease on vintage automobile harnesses and bulb >sockets and have never had a problem with contacts afterwards. I bought an Isuzu Trooper cheap from someone that took it to Burning Man. When it came back, many of the electrical connections were intermittent. The cause was dielectric grease in the connectors, mixed with fine desert sand and dust. After some experimentation, I used a small ultrasonic clean and trichlorethylene to dissolve the grease. I initially made the intermittents worse, but after two more applications, the contacts were finally deemed clean. Diversion: Of all the connectors available, the common F-connector is the only one that is made from enough dissimilar metals to insure galvanic corruption. The connector shell is made from aluminum or brass. It is plated with alodine 1200, nickel, chrome, gold, pyrite, or nothing. The coax center wire is copper plated steel or solid copper. The foil and braid shields are aluminum. With this mix of dissimilar metals, if you get any water inside, something is going to corrode. -- 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 |
| DaveC <not@home.cow>: Mar 07 06:31PM -0800 > Grease is more easily pinched through than corrosion. It extends the > life of sliding switches by reducing friction. > Kevin Mc And by extension, oil is better at preventing corrosion while not sticking up things. This research found that simple mineral oil reduced contact resistance dramatically: http://www.te.com/documentation/whitepapers/pdf/p154-74.pdf I (op) decided I'm going to cleans out this mode switch and try Caig DeOxit. Thanks for all the great discussion. |
| Jeff Liebermann <jeffl@cruzio.com>: Mar 07 07:13PM -0800 On Mon, 07 Mar 2016 17:50:17 -0800, Jeff Liebermann <jeffl@cruzio.com> wrote: >copper. The foil and braid shields are aluminum. With this mix of >dissimilar metals, if you get any water inside, something is going to >corrode. I forgot to mention the center connection, which is made from tin plated brass. -- 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 |
| Cursitor Doom <curd@notformail.com>: Mar 07 06:08PM And before anyone suggests it: I've frequency swept the primary circuit just in case there's a second resonance peak at around 25kHz and there isn't one. |
| Dimitrij Klingbeil <nospam@no-address.com>: Mar 07 08:21PM +0100 On 07.03.2016 19:08, Cursitor Doom wrote: > And before anyone suggests it: I've frequency swept the primary > circuit just in case there's a second resonance peak at around 25kHz > and there isn't one. Hi News indeed. Something must be amiss, and quite heavily amiss, that's for sure. It looks like the resonant circuit considerably out of tune. Driving a 17 kHz LC with 25 kHz would not make sense to me, and it looks like the circuit does not like it too much either, since it overheats. If it was indeed tuned for 25 kHz, then the currently set 22 (or 20) kHz pulse rate setting could at least make some sense. It would be slightly below resonance, but probably not too far away. I was assuming that the resonant circuit was ok-ish and the frequency somewhat matched, but this turns out, now, not to be the case. Now I've looked in the TDA1060 controller datasheet again, and checked the adjustment range (with the trimpot set from 0 to 10 kOhm and the 11 kOhm fixed resistor and 3.3 nF timing capacitor) and the calculated resulting range of frequencies happens to be from 17.3 kHz to 33 kHz. With a 17.3 to 33 kHz range, that would put 25 kHz quite well in the middle. A 17 kHz resonance frequency does not fit anywhere though. It can't even reliably be adjusted (even if it were correct, which it surely isn't) because it's simply out of the trimpot's range. But it would not make any sense to pulse a 17 kHz LC at 25 kHz either. The LC will be heavily capacitive, the power factor will be down in the ditch, and that will overload (-heat) the driver (just as it happens). Therefore I can only think that 17 kHz is wrong. The LC is out of resonance. If it were OK, it should never have a 17 kHz SRF. That leaves either a measurement error (now rather less likely) or a heavy stray capacitance somewhere, that brings the resonance down. I can only think of C1806 and C1807. They are in series. If one of them has an isolation problem, that would leave the other one alone in the circuit - and therefore double the capacitance. Also there are the resistors in parallel - R1817 and R1818. They should be 10 Megaohm. But if one of them is either shorted or improperly replaced (maybe it formed an isolation breakdown from over-voltage or someone put in a wrong value like zero Ohm instead), then that would also short out the corresponding capacitor, and have the same effect. Usually resistors are reliable, but sometimes, some old ones of the "carbon composition" variety, do form a "hot channel" and break down. Doubling the capacitance would almost halve the resonance frequency. Actually it won't *exactly* halve it, because there is still a third capacitor in parallel, namely the stray winding capacitance. This looks quite enough to be realistic. If one resonance cap is shot, the LC frequency will go down by a great deal, and (assuming it was initially slightly higher than the pulse frequency), a change from some 25 or 27 kHz to the 17 kHz that you are now seeing, could happen. It could also explain the overload on the resistor - a heavily capacitive out-of-resonance load would easily do that. Can you get these two caps out altogether, connect a known good 15 nF (or two of 30 nF in series) instead and sweep again? Also, to avoid unforeseen measurement errors, can you do that out of circuit? Just the transformer and the capacitor(s) on the primary. This would also nicely avoid the resistors too, they too may be questionable. You won't need a high voltage cap for sweeping - any good 15 nF one will do. But don't power it up with "any 15 nF". To run at full power it needs something like a FKP1 or MKP-4C with proper ratings (see my earlier post, there are some suggested models that can work there). Regards Dimitrij |
| legg <legg@nospam.magma.ca>: Mar 07 02:23PM -0500 On Mon, 7 Mar 2016 13:46:27 -0000 (UTC), Cursitor Doom >confine myself to just replacing the flaky polyester caps for the time >being. Be interested to hear how you think I should proceed now in the >light of this... You are refering to manual component numbers from the 3262 manual and schematic. The 3264 does not have the same schematic or part numbers. The schematic is functionally similar, but uses a different control IC and different components are present/selected to set the IC's function. Part type for the main transformer/size and pinout, the size of resonant/snubbing components, along the actual supply power ratings may vary with model number, as well. One example is the different resonant cap size used. 3262 PSU adjustment begins with para 3.4.4 on 3262 manual page 115. (do not ignore preceding setup instructions re scope settings) You can assume the sequencing and intention of these instructions to mirror those needed for 3264, however numbers and test conditions that reflect operating power and typical frequency can be expected to vary. This includes chip reference pin voltages - TDA1060 internal reference is 3V62. The converter runs at a fixed frequency, above resonance. The frequency only needs adjustment if the output voltages lose full power low-line voltage regulation. This is also the protective power limit. The two model control circuits do not limit in a similar manner. The 3262 manual describes a latching power limit that occurs after repeated continuous overload. This does not appear to be present in in 3264, as it is chip-based feature. RL |
| Dimitrij Klingbeil <nospam@no-address.com>: Mar 07 08:48PM +0100 On 07.03.2016 20:21, Dimitrij Klingbeil wrote: > capacitor in parallel, namely the stray winding capacitance. > This looks quite enough to be realistic. If one resonance cap is > shot, the LC frequency will go down by a great deal... P.S. There may be another failure mode that I did not consider right away, that can make it a little harder for you to test the caps. These high voltage impulse-rated capacitors are usually made with three metal layers and two layers of isolation internally. Mains "X1" and "X2" rated capacitors are also made in this way. They are like two capacitors that are connected in series inside. When one isolator breaks down, the whole capacitor won't be destroyed catastrophically because there's still the other internal half in series. But it can happen (depending on the construction of the capacitor, if it has a continuous metal layer between the isolators) that the capacitance will "double itself" instead. If one of your 30 nF caps has failed in this way, it will "become 60 nF" instead of becoming short-circuit. So you won't see it on an Ohmmeter. But that would also be reason enough to detune the resonance a lot. So, my advice would be, do not trust them, and do not trust their parallel resistors too much either. Take a known working 15 nF cap and sweep the transformer with it. If you get anything significantly above 17 kHz with a new cap, look for the main problem in this direction. Dimitrij |
| Dimitrij Klingbeil <nospam@no-address.com>: Mar 07 09:55PM +0100 On 07.03.2016 20:21, Dimitrij Klingbeil wrote: > ... Also, to avoid unforeseen measurement errors, can you do that > out of circuit? Just the transformer and the capacitor(s) on the > primary. P.P.S. If you decide to sweep the LC part in circuit instead of out of circuit (because the transformer is difficult to solder out etc...), you can use a small voltage source (a 9 V block battery) connected to the power supply's "AC" input. This will precharge the circuit enough to get the parasitics down. It won't start the power supply controller, but it will reverse-bias various diodes and also the base-collector junction of the main switching transistor. That will make these semiconductor parts non-conducting (at small signal levels) and prevent them from rectifying the test signal from your sweep generator, and messing it up in various ways through leakage paths. It's an easier alternative to removing the switching transistor from the circuit. Dimitrij |
| Cursitor Doom <curd@notformail.com>: Mar 07 10:30PM On Mon, 07 Mar 2016 14:23:22 -0500, legg wrote: > resonant/snubbing components, along the actual supply power ratings may > vary with model number, as well. One example is the different resonant > cap size used. OMG you're right. I've had this issue before when looking at manuals from .pdf files on a screen rather than hard-copy. Well that's just dandy I must say. Now I'm *really* confused. Once again I'm really tempted to just scrap this thing as it stands, salvage the transformer and start afresh in a year's time with a conventional non-resonant PWM design using a MOSFET instead of a BJT and a more up-to-date controller. :( |
| Cursitor Doom <curd@notformail.com>: Mar 07 10:36PM On Mon, 07 Mar 2016 21:55:56 +0100, Dimitrij Klingbeil wrote: > ways through leakage paths. It's an easier alternative to removing the > switching transistor from the circuit. > Dimitrij Sorry, Dimitrij; as you were. Legg has spotted I was mistakenly referring to the wrong diagram in fact. They look very similar and when you don't have the physical hard copy manual in front of you then errors like this are far more easily made, I regret to say. Sigh. I've had enough for today, I'll take yet another look at it again tomorrow. :( |
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