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. 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/ 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. > > And for Ralph's problem with the Washington inspectors, I suspect they > are reading the rules wrong, here they don't care about the load, the > only thing they checked outside of the box was the ground wiring to the > rods. > > And for lack of any other pressing duties, helped me bore 2 holes thru > about 8" of green concrete the required 6 feet apart to make it meet > code. After he ok'd hooking up the drop so we had power to run the > hammerdrill. > > Cheers Chris, 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
