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Sparky <see@thesig.net>: Feb 16 06:01AM -0800 Last year the alternator on my Toyota cooked the stator windings. I didn¹t look any further and replaced it with a rebuilt alternator & regulator from the local parts supplier.   Now (7 or 8 months later) the replacement has failed in the same mode. I¹m suspicious. Also confused:   If a diode opens there wouldn¹t be an increased load on the stator windings. If a diode shorts, there also wouldn¹t be any increase, just a decrease in DC output voltage.   If the alternator output is shorted, since it¹s connected directly to the battery (+) terminal, this would result in smoke and fire, at least a burnt fusible link. None of this has occurred. (Well, the windings are discolored and the smell is what clued me in to these problems.) When I put in a replacement alternator I¹m quite confident everything will look just fine. Until next time.     What could cause these symptoms? Twice?   Thanks!

"Rich." <rcres@XXnewsguy.com>: Feb 16 10:18AM -0500 "Sparky" <see@thesig.net> wrote in message news:0001HW.D1073825006CBD3AB01029BF@news.eternal-september.org... > Until next time.   > What could cause these symptoms? Twice?   > Thanks!   Did you change the battery any time after the alternator was changed or is it the same one still?

mike <ham789@netzero.net>: Feb 15 09:43AM -0800 On 2/15/2015 1:53 AM, whit3rd wrote: > as well, that's two half-cycles of the same polarity. The likelihood > of saturation is very high. Turn-on at peak V is a strategy that > minimizes saturation risk.   Well, I'll repeat what I wrote earlier in the thread:   I set the weld time by an integral number of cycles of 60 Hz.   The key word there is "integral" as in complete as in full as in you don't get two half cycles of the same polarity.   Designing your welder to avoid saturation is a strategy that minimizes saturation risk.

mike <ham789@netzero.net>: Feb 15 09:55AM -0800 On 2/15/2015 3:46 AM, Phil Allison wrote: > mike wrote:   >> if you say so.   > ** Wot a smug prick you are. Seems to be your opinion of everyone.   >> the main component of the >> primary current is due to the shorted secondary.   > ** The secondary is not shorted.   Once again, your signature condescending tone declares that the other guy is always wrong. Once again, you nitpick instead of attempting to understand. Communication is difficult enough, even when you try. When you try NOT to understand, you're just being you. I'm sure you win a lot of arguments when the other guy just gives up trying to influence your thinking.   My presence in this thread is to help others get the most out of their MOT welder. I gave up trying to influence you long ago. Just trying to give some balance to the view.   >> I think I'll give my SCR the benefit of switching on when there's zero >> voltage.   > ** More fool you. There it is again.

jurb6006@gmail.com: Feb 15 01:33PM -0800 >"Once again, your signature condescending tone declares that >the other guy is always wrong. "   That's not fair. I have seen Phil be nice to people a dozen times.   In the last thirty years.   Go ahead and hate the MF but respect him, he knows WTF he is doing and I know enough to know he knows WTF he is doing.

mike <ham789@netzero.net>: Feb 15 02:00PM -0800 > That's not fair. I have seen Phil be nice to people a dozen times.   > In the last thirty years.   > Go ahead and hate the MF but respect him, he knows WTF he is doing and I know enough to know he knows WTF he is doing.   One of the issues with people who know everything is that they often don't bother to understand the question before pontificating on the CORRECT answer. So you get a snarky response on their way to solve the problem that they inferred based on their experience. They have no trouble calling you names if you disagree with their interpretation. Since they know everything, anything you say is WRONG. And it's no use trying to support your position, cuz they ain't listenin'.   Communication is a two-way process. The objective of the mentor is to use terminology that the newbie can understand. Sometimes trying to state the exactly perfectly technically correct description obfuscates the key issue. The nitpickers jump on that to tell you that you're wrong...and stupid. It's not about education. It's not about being right. It's about telling the world that the other guy is WRONG!! Throw in a few of your favorite pet names for good measure.   I like to have technical discussions. That requires listening on both sides and supporting the argument with logic. Calling me stupid doesn't help anybody.

Chris Jones <lugnut808@spam.yahoo.com>: Feb 16 12:34PM +1100 On 16/02/2015 04:55, mike wrote:   >> ... Phil   Although he is rude, Phil is usually right, and this time is no exception.   I suggest you get a hall-effect current transducer connected to a DSO so that you can measure inrush current, and try out switching the transformer on at both the peak of the mains voltage, and also at the zero-crossing, and look at the current waveforms. When you run out of working triacs you could also google it.   The key to understanding this is to realise that the magnetic flux is proportional to the time-integral of the applied voltage, and that in continuous operation the flux is normally close to zero when the voltage is close to maximum, and the flux is close to maximum when the voltage is close to zero. Have a look at the first link here:   www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=13C3206_AppNote&DocType=CS&DocLang=EN http://sound.westhost.com/articles/inrush.htm http://en.wikipedia.org/wiki/Inrush_current#Transformers   Chris

Phil Allison <pallison49@gmail.com>: Feb 15 06:15PM -0800 Chris Jones wrote:   > continuous operation the flux is normally close to zero when the voltage > is close to maximum, and the flux is close to maximum when the voltage   > http://sound.westhost.com/articles/inrush.htm     ** FYI:   I had a large input to the writing of that article - Rod is a friend and colleague, we talk and email regularly.   The most surprising thing is how the in-rush surge of an unloaded transformer consists of brief pulses all with the same polarity - it's DC current.   Also, if you power a 240V tranny from 120V, surges are eliminated.       .... Phil

mike <ham789@netzero.net>: Feb 15 09:07PM -0800 On 2/15/2015 5:34 PM, Chris Jones wrote:   >>> ... Phil   > Although he is rude, Phil is usually right, and this time is no exception.   > I suggest you get a hall-effect current transducer connected to a DSO been there done that AEMC MR461 current probe. TEK TDS540 scope. I designed my first production forward converter ~40 years ago. so > that you can measure inrush current, and try out switching the > transformer on at both the peak of the mains voltage, and also at the > zero-crossing, with the secondary heavily resistively loaded, and look at the current waveforms. When you run out of > continuous operation the flux is normally close to zero when the voltage > is close to maximum, and the flux is close to maximum when the voltage > is close to zero. Have a look at the first link here:   Are we talking about inductors or transformers with load resistors that cause a steady state primary current 2X their design rating?   > http://sound.westhost.com/articles/inrush.htm > http://en.wikipedia.org/wiki/Inrush_current#Transformers   > Chris   Thanks for the links. I like to learn new stuff. I'm still trying to get my head around why the graphs in the first link are reversed in time, but if I stand on my head, it looks like the drive signal is optimized to maximize inrush current. I don't have any argument with that. You can certainly manage the drive so the core saturates.   My attempts were to arrange the drive signal to MITIGATE inrush current.   The key point is in the wikipedia link: "Worst case inrush happens when the primary winding is connected at an instant around the zero-crossing of the primary voltage, (which for a pure inductance would be the current maximum in the AC cycle) and if the polarity of the voltage half cycle has the same polarity as the remnance in the iron core has. (The magnetic remanence was left high from a preceding half cycle)." end quote   If you always turn off the current at the current zero crossing with a positive voltage slope, then always turn on the next weld pulse at zero voltage on the positive voltage slope, doesn't that leave you in a remanence position to avoid saturation at the next turn on? If not, why not?   The SSR is gonna turn off near zero current. About all I can control is the slope of the voltage sinewave when I give the command. To turn it on it's far easier to sense the zero crossing of the line voltage than the peak. Isn't a major portion of the primary current in phase with the primary voltage due to the resistive secondary load? Isn't it the leakage inductance that causes the phase shift?   Under the control conditions described above where we control both ends of the waveform to manage remanence and have a very low value resistive load, how much would I gain by waiting for the peak line voltage at turn on?   I'd go look, but it's stored behind a bunch of junk in the garage.   As I recall, I didn't make many measurements without load. But with the secondary (almost) shorted in the weld mode, I don't remember any horrible input current transients. I do know that synchronization with the line made a major improvement in the repeatability of the welds.     I'm up for some education.   My thinking was that, if not for saturation, the SCR would be less stressed if I turned it on at zero voltage when the primary current was zero. And from the unpowered state, the voltage and current can't be anything but zero. And that, if I could arrange the resting place on the B-H curve from the previous pulse such that the first half-cycle wouldn't saturate the core, that's the best I could do easily. Measurements didn't show any horrible first cycle inrush. Welds got more repeatable.   Let me say the same thing in different words. If the load is linear resistive, the transformer current and voltage will be approximately in phase. If the SCR shuts off at zero current, the voltage will also be near zero volts (plus whatever the leakage inductance allows). Case 1, you start the next pulse in a nanosecond. Isn't the initial current still pretty near zero? Isn't the point on the B-H curve still about the same? Case 2, you start the next pulse next week at the zero crossing of the input voltage headed in the same direction. What's the initial current? What's the initial point on the B-H curve? How is restarting it synchronously significantly different from just leaving it running?   I'm not disputing the articles you posted. I'm not saying anything about the general (worst) case. I'm suggesting that this is how you engineer a spot welder using a MOT.   Where did my thinking go wrong?

mike <ham789@netzero.net>: Feb 15 09:21PM -0800 On 2/15/2015 6:15 PM, Phil Allison wrote:   > ** FYI:   > I had a large input to the writing of that article - Rod is a friend and colleague, we talk and email regularly.   > The most surprising thing is how the in-rush surge of an unloaded transformer consists of brief pulses all with the same polarity - it's DC current.   Why is that surprising? In the steady state, it is traversing a very nonlinear B-H loop. If you restart it from a place different from where you left it, you drive it "off center". To regain steady state, you have to apply a DC, component.

Phil Allison <pallison49@gmail.com>: Feb 15 09:38PM -0800 mike wrote:       > > I had a large input to the writing of that article - Rod is a friend and colleague, we talk and email regularly.   > > The most surprising thing is how the in-rush surge of an unloaded transformer consists of brief pulses all with the same polarity - it's DC current.   > Why is that surprising?     ** Most people are *very* surprised to find this out.   Just like YOU were surprised that zero switching produces maximum surges in transformers.   It's counter intuitive in both cases.       .... Phil

Phil Allison <pallison49@gmail.com>: Feb 15 10:11PM -0800 mike wrote:     > Thanks for the links. I like to learn new stuff. > I'm still trying to get my head around why the graphs in the first > link are reversed in time,     ** Figures 3 & 4 showing scope screens have been published up side down so need rotating by 180 degrees.     > but if I stand on my head, it looks > like the drive signal is optimized to maximize inrush current.   ** By simply switching the AC supply on at zero volts.   > I don't have any argument with that. You can certainly manage > the drive so the core saturates.     ** By simply switching the AC supply on at zero volts.     > My attempts were to arrange the drive signal to MITIGATE inrush > current.   ** Bollocks.     > a positive voltage slope, then always turn on the next weld pulse > at zero voltage on the positive voltage slope, doesn't that leave > you in a remanence position to avoid saturation at the next turn on?   ** Nope.   Read the link.     > To turn it on it's far easier to sense the zero crossing of the line > voltage than the peak.   ** Then allow a 4mS delay before firing the triac.     > ends of the waveform to manage remanence and have a very low value > resistive load, how much would I gain by waiting for the peak line > voltage at turn on?   ** Try it and see.   Most of the transformers I see are under heavy load at switch on, charging hefty filter caps. Only makes the combined switch on surge worse, compared to no load.       .... Phil

Chris Jones <lugnut808@spam.yahoo.com>: Feb 16 11:52PM +1100 On 16/02/2015 16:07, mike wrote: >> transformer on at both the peak of the mains voltage, and also at the >> zero-crossing, > with the secondary heavily resistively loaded, If there is unnecessarily large inrush current that is due to core saturation late in the first half-cycle, then adding a resistive load on the secondary won't fix that.   >> is close to zero. Have a look at the first link here:   > Are we talking about inductors or transformers with load resistors > that cause a steady state primary current 2X their design rating? It doesn't much matter whether we are talking about transformers or ungapped inductors, in that the transformer with its secondary unconnected can still draw a lot of inrush current, and adding a load on the secondary won't fix that.   > I'm still trying to get my head around why the graphs in the first > link are reversed in time, but if I stand on my head, it looks > like the drive signal is optimized to maximize inrush current. Yes I don't know why they put the scope plot backwards. It adds unnecessary confusion, though at least they do mention it in the text. I can only assume they lacked the ability to flip it easily in their chosen method of document preparation.   > the drive so the core saturates.   > My attempts were to arrange the drive signal to MITIGATE inrush > current. I know, and I was just suggesting that turning on when the mains voltage goes through zero is not the best way to do that. Turning on at the zero-crossing of the mains voltage is good if your load is capacitive, e.g. the input of a SMPS.   > at zero voltage on the positive voltage slope, doesn't that leave > you in a remanence position to avoid saturation at the next turn on? > If not, why not? I think the remanence is clouding the issue. It is a relevant effect but even without it, there are good and bad times to switch on the transformer primary, and it would be better to consider remanence only after the basic situation with a soft-magnetic core is thoroughly understood. You might be able to use the remaining flux in the switched-off transformer to choose the least worst of the two zero crossings to switch it on at, but even then, I think you would do better to switch on at a different time. Why not seriously try it out with a current transducer and DSO, (and a vastly over-sized triac or even better a pair of big SCRs, just in case!). It would be nice to see the plots, and it is one way to end an argument.   > is the slope of the voltage sinewave when I give the command. > To turn it on it's far easier to sense the zero crossing of the line > voltage than the peak. The mains frequency (or period) is accurate and stable enough, and microcontrollers or even 555 timers are cheap enough that as Phil mentioned, you can figure out the time of the voltage peak from the zero crossing.   > Isn't a major portion of the primary current > in phase with the primary voltage due to the resistive secondary load? > Isn't it the leakage inductance that causes the phase shift? That sounds reasonable, but if the core saturates then that's the least of your worries. The primary current is not necessarily a good way to determine the core flux density, as you can make the primary current be whatever you want by choosing the secondary current.   > ends of the waveform to manage remanence and have a very low value > resistive load, how much would I gain by waiting for the peak line > voltage at turn on? Time for an experiment. It depends a lot on the transformer design. I have read that toroidal transformers produce more problematic saturation effects than E-I types, and if the core was nominally run at less than half of its saturation flux density then there will be no problem. Due to the more uniform geometry I think they can run toroidal transformers close to saturation in normal operation.     > As I recall, I didn't make many measurements without load. But > with the secondary (almost) shorted in the weld mode, I don't > remember any horrible input current transients. I wonder whether they even bother to switch the transformer on at the right time in a microwave oven. The current that your transformer draws in steady state might be so high (due to the secondary current) that saturation doesn't make it all that much worse, but given the choice (or given a bigger transformer than your circuit breaker likes), you might as well make it optimum if that is just a matter of inserting a small delay.   I have an arc welder that sometimes trips the breaker if I turn it on at the wrong time (with a mechanical switch), and it would be nice if it didn't.   > stressed if I turned it on at zero voltage when the primary current was > zero. And from the unpowered state, the voltage and current can't > be anything but zero. The risk of saturation occurs well after the zero crossing when the voltage is turned on. If the load is not capacitive (not a big SMPS) then the SCR won't mind if you turn it on when there is voltage across it, and later on in the cycle it will be much happier.   > will be approximately in phase. If the SCR shuts off at zero > current, the voltage will also be near zero volts (plus whatever the > leakage inductance allows). And the magnetizing current too.   > Case 1, you start the next pulse in a nanosecond. This is not the same thing as I was discussing. If the transformer is in steady-state operation and if you were able to turn off the primary at a zero-crossing of the mains voltage, that is a time when there is maximum flux in the core. If you instantly switch it back on again, sure this will be pretty much a continuation of steady-state operation.   If instead you turn it off for an integer number of mains cycles that adds up to a few seconds, the core flux will not be the same when you go to switch it back on again.   > Isn't the initial current still pretty near zero? Perhaps but that doesn't really matter as regards the risk of saturation.   > Isn't the point on the B-H curve still about the same? Yes, if you only switch it off for nanoseconds. No, if you wait a few seconds until you have repositioned your parts for the next weld.   > What's the initial point on the B-H curve? > How is restarting it synchronously significantly different from > just leaving it running? The flux in the core is different.   Put a big inductor (maybe a car ignition coil) across a 12Vrms AC supply and make sure you are holding the terminals a nanosecond after you disconnect the supply, at the instant when the AC supply is at zero voltage (and the inductor is carrying maximum current).   Then give it to me and I will hold the terminals a week later.   I think you will notice the difference. The state of the flux in the core matters.   Note that in the case of a transformer, it is possible that some value of secondary current could result in the primary current being zero (or any other chosen value) at the zero-crossing of the mains voltage. That is not relevant to my point, which relates to the flux density in the core, which won't be affected much by the secondary current if a low-impedance supply is driving the primary winding.   > I'm not saying anything about the general (worst) case. > I'm suggesting that this is how you engineer a spot welder using a MOT.   > Where did my thinking go wrong?   It may just mean that you need a larger rating for your fuse or circuit breaker and more expensive triac or SCRs than you could otherwise get away with.   When I tried spot welding, I was never able to get enough current from a MOT-sized transformer with a few turns on the secondary. I could sort of weld things if I applied very light pressure so that the workpieces made poor contact with each other and the resistance was high enough for the (insufficient) current to heat them, but this wasn't really satisfactory because getting the force and contact resistance just right was not reliable.   If I made a transformer big enough to weld thick workpieces with proper contact pressure, it might cause excessive drop in my mains supply, and/or trip breakers.   I think the best option for me is a series-parallel array of Maxwell boostcaps. This would eliminate the requirement for a large mains supply capability. The 3000F ones are rated for 1900 Amps each, so about 5 in parallel would probably supply about enough current for any normal sheet metalwork up to a couple of millimetres thick which seems to require close to 10kA capability. (Aluminium welding requires several times more current so I won't try that.) Most of the references that I have seen tend to suggest that the weld itself requires somewhere in the region of 1.5 Volts, but the electrodes etc. will have some resistive drop so I think at least 2 banks of boostcaps in series will be desirable. Due to the capacitors holding more energy than the total that you would want for one weld, it would be necessary to find a way to switch them off, and it would also be very useful to be able to adjust the current by PWM during the weld. Therefore a lot of MOSFETs would be required. It seems that the best current rating per dollar occurs for individual MOSFETs rated at about 100A, so about 100 of these in parallel would be required for 10kA. I think a totem-pole style half-bridge topology might work, using the output cables as an inductor to smooth the output current. A multi-phase PWM arrangement with multiple output inductors could make better use of the current rating of the caps. It would be an interesting project but I don't have time to do it yet. I am somewhat concerned about what would happen in the event of one failed MOSFET, and I would like to think of a way to mitigate that. Perhaps the bondwire or package pin would be an adequate fuse.   Chris

N_Cook <diverse@tcp.co.uk>: Feb 16 11:57AM I use a variac with an AC ammeter in line. I like to heat test kit using a hot air gun on low setting. But for the low heat range, a diode is in series with the mains, the one-sided "switching" 50/60 times a second causes horrendous magnetising current problems that would overheat the variac I'm sure, used on the same mains ring main. Replace that diode with a preset triac for balanced "switching" ? I one time niaively thought putting a 1N4007 in series with a 50W, 24V soldering iron Tx would give a low temperature iron for melting plastic, ended up melting the 24V Tx. What effect , if any , would such diodes in say hot air guns, falsely? register on a moving disc mains kWh meter or the recent "smart" meters / monitors ?

fransehv <frans@noemail.com>: Feb 16 12:05PM +0100 Thanks for the links I registered to vynilengine en downloaded the AL-F350 service manual. The PCB seems to be different unfortunately. I'll check how far I will come   Frans       --- Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware. http://www.avast.com

bleachbot <bleachbot@httrack.com>: Feb 16 02:13AM +0100

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larry <johnmcandrew66@gmail.com>: Feb 15 10:31AM -0800 Hi everyone!   I have a Philips 21GR2350/05b TV which is very old and served me well up to now.   But a few months back, it would completely switch on and off at around 2Hz when I first turned it on, eventually remaining on after say 5 seconds with a perfect picture. Today it takes up to a minute before finally switching on, but now there doesn't appear to be an image from the green raster with the image rather dim.   I've a feeling it's something to do with the power supply possibly not turning on properly, but I'd like to know for sure from you guys.   Thanks in advance,   Larry

jurb6006@gmail.com: Feb 15 01:22PM -0800 If it is a newer one, it is possibly a weak CRT. Alot of the last CRT TVs out there had AKB which is Automatic Kine bias which adjusts the greyscale continuously. This allowed them to use crappy CRTs and have the set be unwatchable after they got to a certain point of weakness. This would necessitate the purchase of another set, which is their goal.   You could try wrapping the fly, which means to put a inding around the core to substitute the filament supply to the cRT but a higher viltage. this is the same thing as putting a brightener on it in the old days. There should be some instructions on the net somewhere. You'll need some wire, a razor knife and a soldering iron and solder.   It doesn't always work, and soetimes induces an interelectrode short oin the CRT, but you probably got nothing to lose. These days, CRT TVs are worth about five bucks if they work well. Some really nice vintage models more, but that ain't what you got.   Really, if you got a car, look on Craigslst in "free". They are giving away $3,000 HD home theater projection TVs these days. And I mean working. That's why I don't work on TVs anymore.   If you are out to learnelectronics, that particular unit is not the best thing in the world to start on, audio equipment would be better. Get you a used scope off eBay or something if you really want an education. A CRO, (cathode ray) not an LCD.   Actually, TVs have become almost ipossible to service. Some of them don't just blank the picture if the CRT is weak, they go into protection and you have to unplug them to get it back. The manufacturers really stuck it to people. I wouldn't give a dollar for any TV built within the last two decades. I was going to restore my vintage Sony XBR (KPR36XBR) built in 1989 which sold for two grand new, but I blew that off. And let me tellya, I would pit the picture on that thing with anything when working properly. No HD needed, it was that sharp. If any TV of that era could be called a collector's item that would be it.   But it went out to the curb last year. Still have a good blue CRT for it on Craigslist. No bites.

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