On Thursday 29 July 2021 12:55:29 Chris Albertson wrote: > THis is actualy "on topic" for CNC controllers, read on. I've got a > good link below. > > I have an interest in old tube amplifiers. They went out of style > before I was old enough to know much and they never covered tubes when > I was in school. But there is an email group about tube technology > and many books available. I've learned to design audio amps and such. > They are not hard at all, much easier than solid-state audio design. > Inrush current is a small problem with large tube amplifies and other > kinds of power supplies. > > The way to deal with inrush today is to use a thermistor on the > high-current side of the transformer. (this applies to both linear and > switching supplies) These have about 1 Ohm resistance when hot and 100 > Ohms when cold and you size them so their temperature follows the > inrush current profile. They look like large size ceramic disk > capacitors (If you remember those) Think of a coin with legs made of > wire. They are thin disk-shaped for thermal reasons so you never see > them surface mounted. > > The thermisters are used in almost every modern electronic device that > uses AC mains power. Any TV set, monitor, computer power supply, > audio gear, you name it, if you look inside you find one. Anything > made in the last 30 years. > > These devices are cheap and ultra-reliable. You can use them any > place there is a high surge current and you want to limit the peak > current. When they are cold the resistance is high so they limit > current but after a specified time the resistance drops. It is like > if you switched in a resister then took it out, but it is analog and > continuous, not switched, and also 100X more reliable and 1000x > cheaper.
I will argue that point, Chris. When I was doing consumer electronics servicing in the later 40's thru the early 60's, that little gismo was the most common failure in consumer electronics by a factor of least 2, and its nearest competitor for that title was of course the low voltage electrolytic capacitor. In the tv's they used it to time the color tubes degausing coils by using also a varistor so as this thing warmed up, the voltage drop was no longer great enough to get thru the varister to drive the coil. So if everything worked, you had a nice clean color pix by the time the tube heater got warmed up and gave you a picture. That is, if everything worked. But those things did everything but start a fire and I expect some did, but the service shop never saw those, they went straight to the dump. Because of that experience, and the fact that they were never seen in broadcast gear which is typically turned on once in its life but is expected to work when it is used portably, I would never consider using one in my own designs. Period, end of discussion. The call backs and general unpleasantness they created is one of the reasons I closed up shop and went to broadcast engineering full time in the early 60's after I got my 1st phone ticket. which I got without cracking a book. And I did the same thing in '72, passing the CET test, missing 2 of the 125 questions given by a prof at Norfolk Community College who was teaching a class designed to generate new CET's because in several years of teaching it, not a single one of his students had passed the final. His problem as he obviously was not schooled in the subject, he was teaching by rote. I also made a 98 on the AFQT the armed forces were using in 1952, the middle of the Korean war. That did not go well as it got me classified 4F, they knew full well I would not follow orders to march out in front of a rattling machine gun just because some sargeant ordered me to. So that officer would have to shoot me for disobeying an order and then send me home in a box. That ended my dreams of furthering my education via the GI bill. So to this day, the closest I can claim to a high school diploma, is a GED. But if you want to discuss relativity, you will find me pretty knowledgeable as I have observed it for years while keeping a uhf transmitter on the air. Relativities effects on the speed's vs mass of an electron are on full display as the source of such a klystron based transmitters major distortion. We did not then know how to compensate for distortions in time, only in amplitude, but we've since learned how or you wouldn't have the tv's clarity you have today. We've also invented better high powered tubes with less of it because they are shorter. And somewhat cheaper. The last time I negotiated the purchase of a klystron, a 4KM100LA, it was $125,000. > You can place the device on either side of a transformer, but > typically on the side with the lower voltage as it will have the most > current. Heat is "i squared r" and you want to heat these things. > > Now the best part. If you are a hobbyist or make prototype or > one-off equipment like most of us here, Ametherm will give you a > lifetime supply of different kinds of thermistors for free as samples. > They have a ton of educational material and online calculators on > their web side and their engineers will talk to you. > https://www.ametherm.com/ They didn't exist back then, in fact it was difficult to obtain a replacement part even from the makers, they were not available at your common electronic parts houses until the tail end of the 60's. > These devices are not total magic but when combined with surge > suppression diodes will keep surges, static electric charge and back > EMI from crossing between devices. Assiadall modern electronics use > these and for good reason. > > You can also do things like epoxy one to a heat sink (or a motor > frame) and then it will provide a voltage based on temperature. They > are simpler to use than other methods. Ametherm will give you a dozen > out two for the asking. > > My first application was on the AC mains side of a vacuum tube-based > amp Makes a very nice "slow start" when you turn it on. That and > some other ideas allow people today to build tube gear that greatly > outperforms the old 1960s stuff. > > On Wed, Jul 28, 2021 at 3:26 PM Gene Heskett <[email protected]> wrote: > > On Wednesday 28 July 2021 15:25:01 Chris Albertson wrote: > > > Do you really need to worry about inrush tripping the breaker? > > > 1) If the DC supply is the old linear type, it will have a very > > > large filter capacitor and supply peak loads without a large AC > > > draw. The trick is to turn on the supply and then the motor a > > > second later. > > > > Now, imagine that supply consists of 4 toroid transformers each > > capable of developing the nominally 63 volts plus and minus, for a 1 > > kw analog audio amp. and the filter caps are 6 in each supply of > > 9200 uf at 65 volts, and each transformer is treated as a single > > supply. wired two in parallel and two tall for a combined voltage of > > around 126 volts and 220800 uf. Plug that into a 30 amp breaker and > > flip the switch. clunkiest switch you ever heard because that 30 amp > > breaker went down like a shotgun on the first half cycle of power, > > essentially simultaneous with the click of the switch. So I hit the > > junkbox and come up with two 40 amp SSR's and a 50 ohm 200 watt > > resistor, added a couple time delays controlled by hal and driven by > > the F2 state such that the 50 ohm is in series with the supply line > > for the first 4 seconds and is shorted after that. Now it runs fine > > on a 15 amp breaker, but will trip it if I ignore the motors > > chirping because the pwm-servo is set to about 17 amps but it takes > > several seconds, so I settled for a 20 amp in that slot. Thanks for reading my rant. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
