Any electronics nerds interested in Arduino/Atmel?

[franken]

Originally Posted by dmjlambert

Well I don't know about PWM for AC, I think it is for DC motors only, but I may be mistaken. It will be interesting to find out how it goes.

Look into a triac for AC PWM... https://www.google.com/search?ei=6ko....0.okNKgaixWr8

As for BJTs vs FETs they use a bit different terminology but the basic difference is the former operates on base current, and the latter on gate voltage. FET tech typically uses less current and higher voltage.

[davepl]

Originally Posted by dmjlambert

Well I don't know about PWM for AC, I think it is for DC motors only, but I may be mistaken. It will be interesting to find out how it goes.

It works for light bulbs, I'm just not sure about electric motors. I think if the PWM wave is fast enough (like 1000Hz at least) and the relay fast enough, it should work perfectly!

Since I have two phases I'd need two relays, though.

[87Skier]

Originally Posted by davepl

It works for light bulbs, I'm just not sure about electric motors. I think if the PWM wave is fast enough (like 1000Hz at least) and the relay fast enough, it should work perfectly!

Since I have two phases I'd need two relays, though.

I'm not entirely sure what you want to achieve.

Do you have a AC (alternating current not air conditioning) motor that you want to soft-start? Are you trying to drive DC cooling fans with PWM for speed control? Is the fuel pump supposed to be variable output?

[dmjlambert]

What is the purpose of soft-starting an AC motor? What does it achieve?

[87Skier]

Originally Posted by dmjlambert

What is the purpose of soft-starting an AC motor? What does it achieve?

Motors have high inductance, so when you power them on by just connecting it to line voltage, it is essentially a short for a small window of time. This causes a voltage drop in the system while the motor comes up to speed, and also means that the current in the motor is extremely high during this time.

Soft-starting drastically reduces the startup current and the current through the motor coils.

[oldgold70c10]

Originally Posted by 87Skier

Motors have high inductance, so when you power them on by just connecting it to line voltage, it is essentially a short for a small window of time. This causes a voltage drop in the system while the motor comes up to speed, and also means that the current in the motor is extremely high during this time.

Soft-starting drastically reduces the startup current and the current through the motor coils.

Although it sounds good, it is probably not a great idea to try soft starting a split-phase motor (cap start-cap run, or cap start-induction run) like is used on an air compressor. These motors pull a lot of amps on start up because they are high torque motors, and need to come up to speed quickly.
The type of motor usually used for soft-start is a 3-phase motor, and they are available with built-on or separate inverters/vfd module, so you can operate them from a single-phase power source

[87Skier]

Originally Posted by oldgold70c10

Although it sounds good, it is probably not a great idea to try soft starting a split-phase motor (cap start-cap run, or cap start-induction run) like is used on an air compressor. These motors pull a lot of amps on start up because they are high torque motors, and need to come up to speed quickly.
The type of motor usually used for soft-start is a 3-phase motor, and they are available with built-on or separate inverters/vfd module, so you can operate them from a single-phase power source

I forgot to mention this.

Also, soft-starting reduces the average current, not the peak current through the coils.

[davepl]

Can someone explain cap-start? Does it store a bunch of surge energy in a cap for the initial inductive "kick" when the motor starts?

I decided not to monkey with my big compressor. I have a small desktop compressor I used for tires and air brushing that I will play with instead!

I built a switched outlet box with a 30A Craydon SSR in it to play with, we shall see. I searched and paid extra for a non-zero-cross relay. Normally they don't switch until the next time the AC crosses zero, which is OK as a switch but wouldn't work for AC slicing.

I've also been tinkering with a bunch of old retro displays and trying to interface them to modern electronics. Here are some of my results!

Little saga on the VFD display: it's a Japanese unit from Noritake and uses hand-coded timing loops to drive it that I could only get to work on the CPU they designed it for (which I'm not using because it's ancient). So for the $1.75 they cost, I dedicated an Atmel 328P (which it works with) just to controlling the VFD. It then exposes the standard LCD interface across the i2c bus so that the ESP32 can call it as if it were a local display. Works great, but was a bit of an investment.

I'm a software guy, so every one of these little wires is a victory ;-)

[oldgold70c10]

Originally Posted by davepl

Can someone explain cap-start? Does it store a bunch of surge energy in a cap for the initial inductive "kick" when the motor starts?

I decided not to monkey with my big compressor. I have a small desktop compressor I used for tires and air brushing that I will play with instead!

I built a switched outlet box with a 30A Craydon SSR in it to play with, we shall see. I searched and paid extra for a non-zero-cross relay. Normally they don't switch until the next time the AC crosses zero, which is OK as a switch but wouldn't work for AC slicing.

I've also been tinkering with a bunch of old retro displays and trying to interface them to modern electronics. Here are some of my results!

Little saga on the VFD display: it's a Japanese unit from Noritake and uses hand-coded timing loops to drive it that I could only get to work on the CPU they designed it for (which I'm not using because it's ancient). So for the $1.75 they cost, I dedicated an Atmel 328P (which it works with) just to controlling the VFD. It then exposes the standard LCD interface across the i2c bus so that the ESP32 can call it as if it were a local display. Works great, but was a bit of an investment.

I'm a software guy, so every one of these little wires is a victory ;-)

You have to have some way of setting up a rotating magnetic field in a single-phase motor. Otherwise, the field just alternates without rotating. In a cap-start motor, there are 2 windings, a run and a start. The run winding is across the ac line, the start winding is across the ac line with a capacitor in series with it. The capacitor causes a shift in that winding (along with the winding being wound slightly different than the run) so that the field will rotate, to start the motor. On many motors, once the motor comes up to about 75% or running speed, a centrifugal switch cuts out the start winding, This is a capacitor-start, induction run. For loads requiring more running torque, a capacitor start, capacitor run motor is used. These have two capacitors, one for starting and one for running. The run capacitor stays in series with the start coil all the time. Air compressors and table saws often use cap-start, cap run motors. Another type of capacitor motor for low-torque loads like fans omits the start capacitor and has just a run capacitor. These are called permanent split capacitor (PSC) motors and they are very efficient.

[davepl]

Aha! That must have been what my EE friend at the power company was talking about when he was trying to dissuade me from doing this on my big 240V compressor... he talked about the potential of a centrifugal switch.

I need to read up a little more on single-phase induction motors, as with brushes and no moving fields, they're a little mysterious!

[dmjlambert]

So, bringing up this older thread to continue discussion. It's a slow process to work on the truck, but now that I finally got the air conditioning going I can think about other things. I was forbidding myself to work on other things until I got the darned A/C going. Here in Texas for a daily driver truck, A/C is pretty important for comfort. Although I usually roll down the window and stick my arm out, there are a few dozen days here where it is HOT.

Anyway back to the electronics and programming nerd discussion, I have in my truck's future the idea of power window for the passenger side. I have such a strong passion for rolling the windows down while I drive, if it's not too hot. And it rains a lot here. So when it starts raining, I need to pull over in a parking lot, put the truck in park, and scoot way across the truck and roll up that window. So, when I do the power windows as described in the "power windows on the cheap" thread, I will want to add a controller. I'm not too much into the idea of mounting typical power window buttons, I just don't like the look. So, I got a cruise control stalk. They reproduce these now, but I got an old used one off eBay.



Now I am working on the idea of using that button to roll the window up and down, and I've also considered hiding my garage door remote and operate it via a relay, and perhaps temporarily turning on windshield wipers (mist control), and perhaps one day in the future install cruise control. Do all those things and more with one button.

The code:
https://pastebin.com/dPbVhxqk

Demo video of the code:
https://www.youtube.com/watch?v=xDpqLDz1xEk

So what are the best button press patterns to use to do the various things? My initial thoughts are the cruise control pass through as described in the program is likely to work fine. That is a slow press followed by slow release, and is sent to the cruise control as a fast press followed by finger controlled slow release. Then the next most frequent thing I would do is rolling that passenger window up and down. So I would probably do that with a fast press to start the window moving, and release the button to stop the window rolling. I will program it so every time I operate the window it would move in the opposite direction compared to the previous movement. Quick press and release can do the garage door remote.

[pjmoreland]

Does that cruise control button have two contacts in it? It's got three wires for some reason. Could it be that pressing the button part way does something different than pressing the button all the way? If so, then that might give you more options on how to control multiple things with one button.

[dmjlambert]

Yes, 2 sets of contacts, at different depths of button press. It appears to be most useful to detect how fast you are pressing or releasing the button. I can have the Arduino recognize slow press followed by slow release, or slow press followed by fast release, or fast press followed by slow release, or fast press followed by fast release. Partial press and release is also possible, but a little harder to reliably do with my finger without accidentally hitting the deep contact some of the attempts.

[pjmoreland]

Originally Posted by dmjlambert

Yes, 2 sets of contacts, at different depths of button press. It appears to be most useful to detect how fast you are pressing or releasing the button. I can have the Arduino recognize slow press followed by slow release, or slow press followed by fast release, or fast press followed by slow release, or fast press followed by fast release. Partial press and release is also possible, but a little harder to reliably do with my finger without accidentally hitting the deep contact some of the attempts.

That's nifty