At all times and under all conditions, all delays add. In addition, faster switching reduces the resistance heating as the device switches on and off.

 

You didn’t answer my question.

You asked me a question?

If you were a pinball wizard,...

Not sure about wizard (I'm not deaf, dumb or blind yet) but I could usually play for free as long as I wanted to in a typical pinball arcade.

To illustrate, tilt threshold and bumper angles are other attributes that contribute to successful play of at able. A wizard knows by muscle memory or feel, what that parameter is on a given table.

Certainly. The drain pitch is another sure-fire way to assess an arcade in a glance. You have to play a little to learn about the tilt sensitivity.

Ah for the days of 5 balls for a quarter, and all mechanical actions.

 

At all times and under all conditions, all delays add.

Can't argue with that.

faster switching reduces the resistance heating as the device switches on and off.

Not likely a problem for a MOSFET used to drive a pin-ball solenoid, even for a several microsecond switching speed.

 

So given the fact that the coil has resistance I1 = 3.7 Ω (powerful "kick") and I2 = 133 Ω (weak "hold") and the plunger is spring loaded. That I have an Arduino to power 5V and a DC power supply to 48V with a power filter/capacitor board, what do I need given the comment below?

My advice for the MOSFET is to go large. By that I mean, if you think you need 10A, spend a fraction more and get 20A. And/or spend to get a lower Rds-on.

The diode D3 is redundant - the other coils are already clamped with diodes?

Really, given that the purpose of the diodes is to protect the mosfet, it is D1 and D2 that are redundant.

OK, if those diodes are already part of the coil assembly then it is D3 that is redundant.

Also, the value of R1 will determine (possibly) the discharge rate of the MOSFET gate charge, depending on how the micro +5V pin operates. So, keep the value a bit on the smaller side, like in the 1k ohms range.
If using discrete through the hole MOSFETs, look into ones like the IRL540 which are common and relatively cheap. They are rated 100V and 28A at 25C with a very small RDSon of 0.077 ohms. With 4V on the gate, RDSon rises a bit to 0.11 ohms, but still very low for triggering relay coils

I have IRF540 on hand but I think I'll go with IRLZ44ZPBF for my next go-to MOSFET. Rated 55V, 51A and Rds of 0.023Ω. Just 99¢.

If a faster turn-off is really needed than a small resistor in series with the diode (say equal to the solenoid resistance) will significantly reduce the turn-off time
The trade-off is that it will increase the turn-off voltage across the MOSFET to twice the supply voltage.

Be careful with a 55V MOSFET when you are running/switching a 48V supply. Any spike on the voltage supply itself could damage the MOSFET.
IRF540 is not good for 5V gate voltages, it should be the IRL540 (or equivalent substitute) when using a 5V device to a MOSFET gate

1. No need for flyback diode D3 to protect the MOSFET due to the presence of diode D1 and D2 on the coil assembly
2. Pulldown resistor 1kΩ instead of the generally advised 10kΩ ?
3. Large voltage and current for MOSFET
4. Low RDSon for MOSFET
5. MOSFET that is usable for 5V gate voltages, but how do I figure that out ?
6. A N-channel enhancement-type logic MOSFET
7. As a common ground for the MOSFET, should I use the Arduino GND or the 48V power supply GND?

This is really helpful guys!

 

Since the mosfet is switching the current in the 48 volt circuit, use the 38 volt ground for the main connection, BUT ALSO be sure that the gate control loop ground is low resistance.. So really,you do need both grounds, one for the flipper power loop and one for the MOSFET gate control loop.

 

Since the mosfet is switching the current in the 48 volt circuit, use the 38 volt ground for the main connection, BUT ALSO be sure that the gate control loop ground is low resistance.. So really,you do need both grounds, one for the flipper power loop and one for the MOSFET gate control loop.

Sorry, I don't understand your comment... In all documentation I found it is mentioned that you need a common ground when using a MOSFET in order to be able to measure the voltages for both circuits. How do you suggest the design should look like inregards to the GND? Now I have the following:

 

Certainly it is true that the grounds must be common. It is also true that swiching a 3 ohm magnet coil across 48 volts will result in 16 amps flowing for a very short time.And 16 amps flowing through even half an ohm of connection wire resistance will develop 8 volts between the two ground points. THAT is why I suggested separate grounding loops, made common only at the mosfet source terminal. None of the coil current should pass through any of the wires connecting the processor board ground to the flipper current ground.
Keep in mind: Ground loops can KILL attached circuits.

 

2. Pulldown resistor 1kΩ instead of the generally advised 10kΩ ?

If the MOSFET is driven from a push-pull output, such as the Arduino, then 10kΩ should be fine.
1kΩ may reduce the output voltage from the Arduino.

5. MOSFET that is usable for 5V gate voltages, but how do I figure that out ?

Look for a "logic-level" type MOSFET.
Their Rds(on) in the data sheet is given at a Vgs of 5V (or less).

 

Certainly it is true that the grounds must be common. It is also true that swiching a 3 ohm magnet coil across 48 volts will result in 16 amps flowing for a very short time.And 16 amps flowing through even half an ohm of connection wire resistance will develop 8 volts between the two ground points. THAT is why I suggested separate grounding loops, made common only at the mosfet source terminal. None of the coil current should pass through any of the wires connecting the processor board ground to the flipper current ground.
Keep in mind: Ground loops can KILL attached circuits.

I partly do understand what you are saying, but I don't know how to draw that in a schematic.
Can you please show me how?

 

The line from the 48 volt negative supply to the arduino common would be removed, and instead it would go to the mosfet source terminal, or just below the terminal. So the resistor and the mosfet do not need to be so vary far from the arduino, and the entire section with the flipper and diodes could be flipped to the opposite side of D3, then the 48 volt source could be flipped to the righthand side of that vertical line thru D3.

AND, what kind of engineer are you? Your profile says "other".

 

The line from the 48 volt negative supply to the arduino common would be removed, and instead it would go to the mosfet source terminal, or just below the terminal. So the resistor and the mosfet do not need to be so vary far from the arduino, and the entire section with the flipper and diodes could be flipped to the opposite side of D3, then the 48 volt source could be flipped to the righthand side of that vertical line thru D3.

AND, what kind of engineer are you? Your profile says "other".

Please bear with me, I'm a SOFTWARE engineer

So is this what you mean (except I did not flip the coil part)?

 

So given the fact that the coil has resistance I1 = 3.7 Ω (powerful "kick") and I2 = 133 Ω (weak "hold") and the plunger is spring loaded. That I have an Arduino to power 5V and a DC power supply to 48V with a power filter/capacitor board, what do I need given the comment below?

Here's a pretty nice MOSFET that should be adequate. 100V, logic level, 63A $1.55

https://www.mouser.com/ProductDetai...IRLU3110ZPBF/?qs=9%2BKlkBgLFf3%2BbVpW4Q9n0Q==

 

The circuit in post #51 is much closer. But I would still split the two connections to the source terminal of the mosfet. Other than that, it does reflect much closer to how it should be wired. If the mosfet symbol included a circle to define it as a component then the two lined could come to that dot at the bottom (source) from different directions and the tech assembling the circuit could know just what to do. And this is not even mentioned in the EE classes, it needs to be deduced. The whole concept of "ground" is really novel, and mostly incorrect. "True Ground" is a mythical entity, often mentioned but very seldom seen.

 

The circuit in post #51 is much closer. But I would still split the two connections to the source terminal of the mosfet. Other than that, it does reflect much closer to how it should be wired. If the mosfet symbol included a circle to define it as a component then the two lined could come to that dot at the bottom (source) from different directions and the tech assembling the circuit could know just what to do. And this is not even mentioned in the EE classes, it needs to be deduced. The whole concept of "ground" is really novel, and mostly incorrect. "True Ground" is a mythical entity, often mentioned but very seldom seen.

Would it still be better to connect to the power supply GND (going to the wall socket) instead of the Arduino GND?

 

The power supply "ground" terminal must be connected to the green wire in the line cord, so that the power supply frame is safely grounded. It has no use in the internal wiring and so it should not connect to any part of the circuit. The power supply negative terminals can be connected to the arduino ground connection.
In this system really there is not a ground, but rather a common, which is the power supply negative terminals.

 

The confusion is that circuit common is often called "ground" but it has nothing to do with earth ground, or any other ground.

 

The power supply "ground" terminal must be connected to the green wire in the line cord, so that the power supply frame is safely grounded. It has no use in the internal wiring and so it should not connect to any part of the circuit. The power supply negative terminals can be connected to the arduino ground connection.
In this system really there is not a ground, but rather a common, which is the power supply negative terminals.

OMG DUH! I have this connected this way, obviously, but did not realize this when considering it as a possible GND.

 

OMG DUH! I have this connected this way, obviously, but did not realize this when considering it as a possible GND.

The meanings of words are really quite important and far to often overlooked. That is certainly a source of misunderstanding and results in a lot of confusion. That is why Itry to avoid using the term ground except for the "green wire" portion of electrical distribution systems, where it usually means an actual connection to the earth.

 

The meanings of words are really quite important and far to often overlooked. That is certainly a source of misunderstanding and results in a lot of confusion. That is why Itry to avoid using the term ground except for the "green wire" portion of electrical distribution systems, where it usually means an actual connection to the earth.

That high lights the terminology I was trained and grew up in, 'Ground' was very rarely used, it was 'Chassis" "Common" etc, for safety, you used "Earth" or maybe the qualifying, "Earth Ground".
It is also aggravated by those that randomly use the earth ground symbol in schematics to indicate the common power rail regardless whether it actually is or not!
Max.

 

Your terminology clarification really enlightened me! Using that I found proper explanations about what I needed to know:
- MOSFET source needs to be connected to Arduino GND to close 5V circuit
- MOSFET source needs to be connected to power supply V- to close 48V circuit
- Both circuits need to be connected to the Arduino GND to have a common reference point

By knowing this, reading back your comments do make so much more sense! I'm certainly going to update my glossary so that I know (and remember) the right terms to use.

My design now looks as follows:


I'll look into the components next...

Thanks for for all you help and patience with me!