Anyway, since you can buy a hundred 1N4007 diodes for $1.92, shipped, from China, and electrolytics are damn expensive these days, I'm just going to mount 30 or so diodes on a perf board to drop the charging voltage down to below 150V.
That way I can parallel-up a bunch of those 6,600 mfd 150v caps.
Wish me luck (or don't). I'm good either way.

Check out the IV curve of a diode and tell me what voltage will be across your diodes and the capacitors when the diodes stop conducting.

 

That won't bring back lost fingers. Engineering rule Rule #1, don't compromise safety items.

Exactly.
That's why I'm building a braking system for my brother's band saw, since his wife uses it as well.
I've seen too many industrial accidents, including band saw ones, over the past 60 years.
I have all of my fingers. A number of my friends do not.

 

Check out the IV curve of a diode and tell me what voltage will be across your diodes and the capacitors when the diodes stop conducting.

Will do.
Already thought of that.
I plan to bridge the caps with a resistor to keep the diodes conducting.

 

Will do.
Already thought of that.
I plan to bridge the caps with a resistor to keep the diodes conducting.

That would work if your resistor pulls enough current to make the diode voltages at least (170 - 150) / 30= 0.67V.

 

That would work if your resistor pulls enough current to make the diode voltages at least (170 - 150) / 30= 0.67V.

Roger that, Bob.
Ohm's Law will guide me on the path of enlightenment to selecting the proper resistance value.
Pray for Science, my brothers (and sisters).

 

My experience with induction motors is that instantly short circuiting the mains connection when a power contactor dropped out will create enough braking torque to roll it across the shop floor. Do not try it with the motor on a bench.
That was done with a 2 HP 240 volt motor that was listed as a high efficiency motor. The transfer time from line to solid short was about 50 milliseconds, the motor had no external load.The cord was about 8 feet of #10 wire with soldered crimp lugs for minimum resistance. I did have to hold my foot on the motor when it was started, that also would roll it over.
My mains powered electric mowers have had short-circuit braking to prevent fools from reaching inside while the blade is still spinning. That short stop shortens the motor life a lot, so I remove it. It is a simple matter to avoid sticking ones hands inside a mower.
I find it just as simple to avoid grabbing the bandsaw blade. The employer provides push sticks, along with a sign that explains how much they save by providing a supply of push sticks . The savings, back in 1988, were quite a few hundreds of dollars each time the saw was used.

 

My experience with induction motors is that instantly short circuiting the mains connection when a power contactor dropped out will create enough braking torque to roll it across the shop floor. Do not try it with the motor on a bench.

I wonder why then that the most popular effective method has always been DC injection for AC induction versions ??
When shorting would have been much simpler!!
https://www.engineering.com/story/how-regenerative-braking-works

 

I wonder why then that the most popular effective method has always been DC injection for AC induction versions ??
When shorting would have been much simpler!!
https://www.engineering.com/story/how-regenerative-braking-works

DC injection to stop an induction motor is more effective and will bring it to a complete stop much sooner. No question on that. But short circuiting does produce a rather interesting reaction. The DC bias continues to provide braking torque even when the motor is stopped, the short action is very short-timed.

 

That would work if your resistor pulls enough current to make the diode voltages at least (170 - 150) / 30= 0.67V.

The measured voltage across my 1N4007s is 0.685 v at 8 mA, a lower current than I thought would be required.
However, I wondered if the leakage current of multiple electrolytics would be high enough to keep the diodes conducting with a 0.69 voltage drop.

So, for fun, I asked ChatGPT about typical electrolytic leakage currents.
ChatGPT seems to think I won't need to bridge a resistor across the caps.

Here's what it had to say:

Dear ChatGPT, what is the typical leakage current in a 6600 MFD 150 volt electrolytic capacitor?

ChatGPT: The typical leakage current in an electrolytic capacitor depends on a number of factors, such as the capacitance value, voltage rating, and temperature.
That being said, a leakage current of 1-2 microamps per microfarad (uA/μF) is a common rule of thumb for electrolytic capacitors. Therefore, for a 6600 MFD (microfarad) 150V electrolytic capacitor, the typical leakage current could be anywhere from 6.6 mA to 13.2 mA. However, this is just an estimate, and the actual leakage current may vary based on the specific characteristics of the capacitor. It's always a good idea to consult the manufacturer's datasheet for more detailed information.

 

DC injection to stop an induction motor is more effective and will bring it to a complete stop much sooner. No question on that. But short circuiting does produce a rather interesting reaction. The DC bias continues to provide braking torque even when the motor is stopped, the short action is very short-timed.

The other method Most often used is Plugging, this extends right through to zero RPM of the motor, short circuiting is very short term and diminishes as RPM decreases.

 

DC injection to stop an induction motor is more effective and will bring it to a complete stop much sooner. No question on that. But short circuiting does produce a rather interesting reaction. The DC bias continues to provide braking torque even when the motor is stopped, the short action is very short-timed.

Stopping a brush type motor by means of short circuiting it WILL reduce the motor life. At least I have experienced that with mains powered electric mowers. The shorted circuit stop is well beyond the motor rating.

 

So, for fun, I asked ChatGPT about typical electrolytic leakage currents.
ChatGPT seems to think I won't need to bridge a resistor across the caps.

I worry for the future of humanity: "Shut off your brain and ask ChatGPT as if it were the great oracle."

I was in the store last week, and the woman ahead of me had a purchase that cost $3.28. She handed the cashier a $10 bill. For whatever reason, the cash register didn't tell her how much change to give back. The cashier said "I don't need the computer to tell me that."....as she reached into her pocket for her phone so she could use the calculator app.

 

I worry for the future of humanity: "Shut off your brain and ask ChatGPT as if it were the great oracle."

Whoa, Jon, that might be a little harsh.
I've been around long enough, at 77, to have heard that said about a number of emerging technologies, such as hand-held calculators, computers and production-line robots. Since I know that viewpoint has been around longer than I have, I thought that I had better ask ChatGPT for its view on the subject.

ME: What emerging technologies in the past have been derided as being a threat to civilization?

ChatGPT: Thanks for asking, John.
Throughout history, there have been many emerging technologies that were derided as being a threat to civilization. Here are some examples:

1. Printing Press: When the printing press was invented in the 15th century, it was feared that it would spread heretical ideas and undermine the authority of the Church.
2. Steam Engine: In the 19th century, the steam engine was seen as a threat to the jobs of craftsmen and artisans who relied on traditional skills.
3. Electricity: When electricity was first introduced, some people believed that it was dangerous and could cause fires and explosions. There were also concerns that it could lead to moral decay, as people could stay up late into the night instead of going to bed early.
4. Radio: In the early 20th century, radio was seen as a potential tool for propaganda and brainwashing. There were also concerns that it would lead to a breakdown in social order, as people could listen to whatever they wanted instead of being exposed to a common cultural narrative.
5. Calculators: When hand-held calculators came out, people feared that students would no longer feel a need to learn basic math skills.
6. Computers: In the 1970s and 80s, some people feared that computers would lead to mass unemployment as machines replaced human workers. There were also concerns that they would be used to control people's lives, either by governments or corporations.

Despite these fears, these technologies have ultimately proven to be transformative and beneficial for humanity. It is important to approach emerging technologies with caution and a critical eye, but also to recognize their potential to improve our lives and solve some of the world's most pressing problems.

ME: Well said, ChatGPT.

From my viewpoint, this technology, like every other new technology, is just another tool that can be used to increase an individual's personal productivity. To be certain, many individuals will use it to cheat, lie and steal, but that's no different than any other technology out there.

 

No, the danger is that all the underlying knowledge and fundamental concepts will be lost "because I can just ask the AI."

An example of that happens here every week it seems. If you understand the fundamentals, it's easy enough to calculate the series resistor for an LED. But every week, the question seems to come up again, and even when explained, it still seems to be a mystery.

How much easier it would be to just ask "I have a red LED on a 5 volt supply. What resistor do I need? Probably don't even need to specify a current and AI will make a recommendation. Why learn Ohm's Law and how to apply it to an LED circuit. Vf? I don't know what that even means and don't care.

 

You need to already understand what you are asking about, these things make mistakes and you need to catch them if you want to use them for any serious purpose.

 

Whoa, Jon, that might be a little harsh.
I've been around long enough, at 77, to have heard that said about a number of emerging technologies, such as hand-held calculators, computers and production-line robots. Since I know that viewpoint has been around longer than I have, I thought that I had better ask ChatGPT for its view on the subject.

ME: What emerging technologies in the past have been derided as being a threat to civilization?

ChatGPT: Thanks for asking, John.
Throughout history, there have been many emerging technologies that were derided as being a threat to civilization. Here are some examples:

1. Printing Press: When the printing press was invented in the 15th century, it was feared that it would spread heretical ideas and undermine the authority of the Church.
2. Steam Engine: In the 19th century, the steam engine was seen as a threat to the jobs of craftsmen and artisans who relied on traditional skills.
3. Electricity: When electricity was first introduced, some people believed that it was dangerous and could cause fires and explosions. There were also concerns that it could lead to moral decay, as people could stay up late into the night instead of going to bed early.
4. Radio: In the early 20th century, radio was seen as a potential tool for propaganda and brainwashing. There were also concerns that it would lead to a breakdown in social order, as people could listen to whatever they wanted instead of being exposed to a common cultural narrative.
5. Calculators: When hand-held calculators came out, people feared that students would no longer feel a need to learn basic math skills.
6. Computers: In the 1970s and 80s, some people feared that computers would lead to mass unemployment as machines replaced human workers. There were also concerns that they would be used to control people's lives, either by governments or corporations.

Despite these fears, these technologies have ultimately proven to be transformative and beneficial for humanity. It is important to approach emerging technologies with caution and a critical eye, but also to recognize their potential to improve our lives and solve some of the world's most pressing problems.

ME: Well said, ChatGPT.

From my viewpoint, this technology, like every other new technology, is just another tool that can be used to increase an individual's personal productivity. To be certain, many individuals will use it to cheat, lie and steal, but that's no different than any other technology out there.

Just a note:

This is terrible philosophy. Even if we accept, arguendo, all of the bullet points as accurate portrayals, the conclusion neither addresses the validity of the fears (did these things happen?) nor does it bolster the bald assertion made in it.

I am not taking sides on this, I am trying to do good philosophy. The answer is mere sophistry it just asserts something that, if you agree with it, seems “self evident” but if you disagree has no support at all.

As an example, the stocking frame, a machine that could make ribbed textiles, was seen as, and was in fact, a threat to the weaver’s guild. The members of the guild earned a good living, making them part of what would be today the middle class. The automated looms could do their work much faster, as well or better, and for much less money.

This existential threat lead to a rebellion lead by a possibly apocryphal character who was reported to have smashed a couple of stocking frames with a hammer in a fit of rage. Ned Ludd, who may or may not have existed and done this, nonetheless give the name to the Luddites, a resistance group known for smashing automatic weaving machines.

The Luddites lost, and so the victors painted them as “anti-progress“ when in fact they were narrowly protecting their livelihoods. It is extremely unfair to expect a class of displaced workers to see the sudden destruction of their social fabric to be “progress”, but most analysis of the Luddites today both poison the well by styling them as generally anti-progress lunatics before suggesting that “progress” is an unequivocal good.

Progress per se is unavoidable but it is emphatically far from an unalloyed good. Even in those cases where it leads to a general improvement in the standard of living it often, if not always, does so on the backs of those shunted aside by it.

So, the facile presentation of “things people thought were bad” followed by “but see, they were actually good” without facts and logic to back that assertion up, it sophistry, however effective.

 

No, the danger is that all the underlying knowledge and fundamental concepts will be lost "because I can just ask the AI."
An example of that happens here every week it seems. If you understand the fundamentals, it's easy enough to calculate the series resistor for an LED. But every week, the question seems to come up again, and even when explained, it still seems to be a mystery.
How much easier it would be to just ask "I have a red LED on a 5 volt supply. What resistor do I need? Probably don't even need to specify a current and AI will make a recommendation. Why learn Ohm's Law and how to apply it to an LED circuit. Vf? I don't know what that even means and don't care.

Jon, you bring up a valid point, and I do sympathize with your concerns, but keep in mind that what you get back from an AI depends entirely on what you put in to it. GIGO really applies more than ever to AIs.

For me, your LED on 5V question to ChatGPT would give me a quick and probably appropriate answer.

For someone learning electronics, however, a more nuanced question will deliver an appropriate educational response.
Take this example where ChatGPT was clever enough to assume that that it would be likely that I would be using a red LED on a 5V supply and would want to limit the current to a nominal 20mA.

ME: Explain why you need a series resistor with an LED and how to calculate its value.

ChatGPT: An LED (Light Emitting Diode) is a semiconductor device that emits light when a current passes through it in the forward direction. LEDs are commonly used in electronic circuits to provide visual indicators, illumination, or decorative lighting.

However, LEDs are sensitive to current, and if they are directly connected to a voltage source, they can be easily damaged. To prevent this, a series resistor is needed to limit the current flowing through the LED. The resistor will drop some of the voltage across it, allowing only the required voltage to be applied to the LED.

The value of the series resistor can be calculated using Ohm's law, which states that V = I * R, where V is the voltage across the resistor, I is the current flowing through the resistor, and R is the resistance of the resistor.

The formula to calculate the value of the series resistor is as follows: R = (V_source - V_LED) / I_LED

where V_source is the voltage of the power supply, V_LED is the voltage drop across the LED (typically around 1.8-3.3V), and I_LED is the desired current flowing through the LED (which should be within the LED's specified maximum rating).

For example, suppose you have a 5V power supply and a red LED with a forward voltage drop of 1.8V and a maximum current rating of 20mA. To calculate the value of the series resistor needed to limit the current to 20mA, the calculation would be:
R = (5V - 1.8V) / 0.02A = 160 ohms

Therefore, a 160 ohm resistor should be used in series with the LED to limit the current to 20mA and protect the LED from damage.

(Back to me)
Not a bad answer at all. Almost as good as having an electronics instructor as your next-door neighbor.

Personally, I am looking forward to using ChatGPT to expand my capabilities to finding answers to questions quickly and more efficiently. No more trips down to the local library like in the 1960s when I was learning electronics. No more endless fruitless Google searches for incorrect information.

I used to program in FORTRAN, BASIC, then in Visual BASIC starting back in 1969. A few years ago, I started working with the Arduino and C++.
When you have a moment, ask ChatGPT to write you a program for an Arduino. What it can do is amazing. There will be some coding errors, as to be expected, but you will get a solid 95% head start on what you need with all of the fussy little diddly bits sorted out and working.

You can either embrace a new technology, or you can rail against it.
It's your choice, just like it has always has been for everyone else throughout history.

 

Progress per se is unavoidable but it is emphatically far from an unalloyed good. Even in those cases where it leads to a general improvement in the standard of living it often, if not always, does so on the backs of those shunted aside by it.

Mr. Ya'akov, your thoughts are well-expressed and I could not agree with you more.

As an aficionado of history, I truly feel for the plight of;
Rock-throwing hunters who were put out of jobs by the invention of the spear and bow-and-arrow.
Gatherers who were put out of jobs by the invention of agriculture.
Stone-age tool makers who were put out of jobs by the bronze age.
Bronze-age tool makers who were put out of jobs by the iron age.
Scribes in the middle-ages who were put out of jobs by the printing press.
Iron-age tool makers who were put out of jobs by the industrial revolution.
Candle and lantern makers who were put out of jobs by the invention of the light bulb.
Wheelwrights and farriers who were put out of jobs by the invention of the automobile.
Women (and a few men) in typing pools who were put out of jobs by the word processor.
The list is endless.

Technological progress is a cruel mistress indeed, and we should all observe a moment of silence for those negatively affected by it over the millennia.

 

@J-Erbes it sounds like you have a plan, I wish you well. In case you haven't considered this I bring it up for your safety.

The saw blade will have a lot of inertia and if your plan works as well as you hope (or better than you hope) then when you stop it could potentially unthread itself from the arbor and go on a rather energetic tour of your shop. A saw designed to coast to stop will have no safeguard against this. You may want to put some distance and obstacles between yourself and the saw while testing, at least until you've verified that the concern is unwarranted.

 

@J-Erbes it sounds like you have a plan, I wish you well. In case you haven't considered this I bring it up for your safety.

The saw blade will have a lot of inertia and if your plan works as well as you hope (or better than you hope) then when you stop it could potentially unthread itself from the arbor and go on a rather energetic tour of your shop. A saw designed to coast to stop will have no safeguard against this. You may want to put some distance and obstacles between yourself and the saw while testing, at least until you've verified that the concern is unwarranted.

Thank you, Mr. Strantor. Your concerns are warranted and very real.

To avoid that issue, the typical DC-injection braking circuit has a power resistor of some 50 to 100 ohms in series with the braking capacitor(s) to limit the initial peak current through the motor windings during capacitor discharge to something less than the normal current draw of the motor. The goal is to stop the motor over a time period that would be, say, three to four times as long as it takes to bring the saw up to speed.

Back in the old days, I heard a story from one of the auto tech instructors at our local vocational school. The students had taken apart and reassembled a V8 engine, and had it running on a test stand in the shop. As the instructor held the throttle wide-open, the harmonic balancer, a 8-lb chunk of steel on the end of the crankshaft, came off the engine at 6500 rpm and scooted across the shop floor where it bumped up against a wall and sat there spinning for quite a bit of time. Valuable lessons were learned that day.