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Goosing a solenoid??

J

Jim Thompson

Jan 1, 1970
0
On 6 May 2005 13:10:29 -0700, [email protected] wrote:

[snip]

Interesting pseudonym. The original "Dagmar" was a couple of years
ahead of me in high school. The Egnor family barbershop... always
good for an illegal poker game ;-)

...Jim Thompson
 
B

Bob Eldred

Jan 1, 1970
0
Frank Bemelman said:
Is is possible to connect it to 48V only, and switch from initial 100% duty
cycle to something much lower duty cycle PWM, to drop to a current that is
equal to 12V/Rsolenoid?

Of course it's possible and desirable. This is especially true when there
are 24 solenoids to be driven. Using PWM and 48 volt drivers, the total
dissipation can be kept low and the parts count reasonable and the power
supply simple. A couple of inexpensive microprocessors can easily do this
and it should be given serious consideration. It would be the simplest,
cleanest and most versatile method if it is ever to become a commercial
product. See my above post. I have designed drivers like this. If interested
e-mail me directly for more on the subject. Please remove the ns from the
front of the email address.
Bob
 
M

Mike Monett

Jan 1, 1970
0
Of course it's possible and desirable. This is especially true
when there are 24 solenoids to be driven. Using PWM and 48 volt
drivers, the total dissipation can be kept low and the parts count
reasonable and the power supply simple. A couple of inexpensive
microprocessors can easily do this and it should be given serious
consideration. It would be the simplest, cleanest and most
versatile method if it is ever to become a commercial product. See
my above post. I have designed drivers like this. If interested
e-mail me directly for more on the subject. Please remove the ns
from the front of the email address.

I'm not sure if pwm is desirable or even needed. Here are three
examples of circuits that could be used depending on the performance
needed:

1. Capacitor Discharge

The schematic is shown in

http://www3.sympatico.ca/add.automation/misc/sol01sch.gif

The capacitor C1 is charged to 48 Volts through R1. Q3 connects the
bottom end of the solenoid coil L1 to ground. Capacitor C1 then
discharges through the solenoid to increase the initial current
rise. When the voltage across the capacitor falls below 12V, diode
D1 turns on to provide sustaining current to keep the solenoid
closed. Diode D2 and R6 limit the back emf voltage when the driver
transistor Q3 turns off.

The waveforms are shown in

http://www3.sympatico.ca/add.automation/misc/sol01wfm.gif

The top graph shows the capacitor voltage in red and the coil
voltage in blue. The bottom graph shows the solenoid current in
black.

This method offers good performance for low duty cycle applications.
The rep rate is limited by the time required to charge C1.
Considerable power is dissipated in R1 when the solenoid is
activated.

2. Switched Capacitor

The schematic is shown in

http://www3.sympatico.ca/add.automation/misc/sol02sch.gif

When the solenoid is not activated, transistors Q1 and Q2 keep the
capacitor C1 charged to 48 Volts.

The waveforms are shown in

http://www3.sympatico.ca/add.automation/misc/sol02wfm.gif

As in the previous example, the top graph shows the capacitor
voltage in red and the coil voltage in blue. The bottom graph shows
the solenoid current in black.

This circuit provides good performance for high rep rate
applications. A small amount of power is wasted keeping transistor
Q1 turned on when the solenoid is not activated.

3. Pulsed Voltage

The schematic is shown in

http://www3.sympatico.ca/add.automation/misc/sol03sch.gif

The R3, C2 network in the emitter of Q2 form a one-shot that briefly
applies 48 Volts to the solenoid when Q3 turns on. The D2, R4, D3
network provide protection against the back emf generated when Q3
turns off.

The waveforms are shown in

http://www3.sympatico.ca/add.automation/misc/sol03wfm.gif

As in the previous examples, the top graph shows the capacitor
voltage in red and the coil voltage in blue. The bottom graph shows
the solenoid current in black.

This circuit provides the fastest current rise into the solenoid,
since the voltage is held at a constant 48 Volts instead of decaying
as in the previous examples. The current fall time could be
increased by allowing a higher back emf when transistor Q3 turns
off. The quiescent current is essentially zero.

These examples are intended to show the basic operation. Additional
effort may be required to meet actual system requirements such as
worst-case supply voltages, temperature extremes, component
variation, etc.

However, it is difficult to see how pwm could provide higher
performance and lower component count.

Mike Monett
 
M

Mike Monett

Jan 1, 1970
0
Jamie wrote:

[...]
what ever happen to the simple 3 component network to drive a power
transistor with a peek and hold function ?

2 resistors in series to properly calculate the holding current of
the relay, one of the resistors will have a Cap coupled with it that
will be calculated to create a current lag long enough to give the
desired peek current, then as it charges the current will drop back to
the holding current when the cap gets charged.
having the cap coupled with a resistor allows it to discharge faster
for the next time.
ect.
old age analog electronics long forgotten i guess! :)

It would be nice if you provided a schematic. However, if I guess
correctly, your circuit was one of the first discussed in this thread.
The high power dissipation and long recovery time are the most serious
limitations.

"Peek" is probably spelled "peak" in this contxt.

Mike Monett
 
B

Bob Eldred

Jan 1, 1970
0
Mike Monett said:
I'm not sure if pwm is desirable or even needed. Here are three
examples of circuits that could be used depending on the performance
needed:

1. Capacitor Discharge

The schematic is shown in

http://www3.sympatico.ca/add.automation/misc/sol01sch.gif

The capacitor C1 is charged to 48 Volts through R1. Q3 connects the
bottom end of the solenoid coil L1 to ground. Capacitor C1 then
discharges through the solenoid to increase the initial current
rise. When the voltage across the capacitor falls below 12V, diode
D1 turns on to provide sustaining current to keep the solenoid
closed. Diode D2 and R6 limit the back emf voltage when the driver
transistor Q3 turns off.

The waveforms are shown in

http://www3.sympatico.ca/add.automation/misc/sol01wfm.gif

The top graph shows the capacitor voltage in red and the coil
voltage in blue. The bottom graph shows the solenoid current in
black.

This method offers good performance for low duty cycle applications.
The rep rate is limited by the time required to charge C1.
Considerable power is dissipated in R1 when the solenoid is
activated.

2. Switched Capacitor

The schematic is shown in

http://www3.sympatico.ca/add.automation/misc/sol02sch.gif

When the solenoid is not activated, transistors Q1 and Q2 keep the
capacitor C1 charged to 48 Volts.

The waveforms are shown in

http://www3.sympatico.ca/add.automation/misc/sol02wfm.gif

As in the previous example, the top graph shows the capacitor
voltage in red and the coil voltage in blue. The bottom graph shows
the solenoid current in black.

This circuit provides good performance for high rep rate
applications. A small amount of power is wasted keeping transistor
Q1 turned on when the solenoid is not activated.

3. Pulsed Voltage

The schematic is shown in

http://www3.sympatico.ca/add.automation/misc/sol03sch.gif

The R3, C2 network in the emitter of Q2 form a one-shot that briefly
applies 48 Volts to the solenoid when Q3 turns on. The D2, R4, D3
network provide protection against the back emf generated when Q3
turns off.

The waveforms are shown in

http://www3.sympatico.ca/add.automation/misc/sol03wfm.gif

As in the previous examples, the top graph shows the capacitor
voltage in red and the coil voltage in blue. The bottom graph shows
the solenoid current in black.

This circuit provides the fastest current rise into the solenoid,
since the voltage is held at a constant 48 Volts instead of decaying
as in the previous examples. The current fall time could be
increased by allowing a higher back emf when transistor Q3 turns
off. The quiescent current is essentially zero.

These examples are intended to show the basic operation. Additional
effort may be required to meet actual system requirements such as
worst-case supply voltages, temperature extremes, component
variation, etc.

However, it is difficult to see how pwm could provide higher
performance and lower component count.

Mike Monett

People can do whatever they want, of course. But keep in mind that there are
24 channels so your solutions are multiplied by 24 in parts count, money and
complexity. Secondly these methods are not versitile. Lets say you need a
bit more drive, what do you do? Change the 330uf caps to hold more energy?
Get a new power transformer? What you have described is the solution we used
back in the 1970's or before. The PWM solution I have used for a piano
playing mechanism uses a microprocessor to drive 12 channels, 12 solenoids.
For 12 channels, the parts count is one PIC microprocessor 12 gate
resistors. 12, IRF FETS and 12 fly back diodes. There is one powersupply, 70
volts, several small bypass caps, a 5 volt voltage reg chip and that's it.
Keep in mind that the micro provides the drive signal as well, a component
you have not even shown in your scheme. Also, a 3055 transistor has poor
current gain so if you need to drive several amps, the base drive is high as
well requiring more parts. I'm sorry, but your method is a klutsy, old
school solution. Of course you don't have write any code so that's an
advantage. If you want more information, please e-mail me. Remove the ns
from the e-mail address to respond, nsmontassocatyahoodotcom. Thanks for
the argument.
Bob
 
J

Jamie

Jan 1, 1970
0
what ever happen to the simple 3 component network to drive a power
transistor with a peek and hold function ?

2 resistors in series to properly calculate the holding current of
the relay, one of the resistors will have a Cap coupled with it that
will be calculated to create a current lag long enough to give the
desired peek current, then as it charges the current will drop back to
the holding current when the cap gets charged.
having the cap coupled with a resistor allows it to discharge faster
for the next time.
ect.
old age analog electronics long forgotten i guess! :)
 
M

Mike Monett

Jan 1, 1970
0
Bob Eldred wrote:

[...]
People can do whatever they want, of course. But keep in mind that there are
24 channels so your solutions are multiplied by 24 in parts count, money and
complexity. Secondly these methods are not versitile. Lets say you need a
bit more drive, what do you do? Change the 330uf caps to hold more energy?
Get a new power transformer? What you have described is the solution we used
back in the 1970's or before. The PWM solution I have used for a piano
playing mechanism uses a microprocessor to drive 12 channels, 12 solenoids.
For 12 channels, the parts count is one PIC microprocessor 12 gate
resistors. 12, IRF FETS and 12 fly back diodes. There is one power supply, 70
volts, several small bypass caps, a 5 volt voltage reg chip and that's it.

Yes, Bob, thanks for the reply. I see how you do it now. The PIC is definitely the
way to go.
Keep in mind that the micro provides the drive signal as well, a component
you have not even shown in your scheme.
Also, a 3055 transistor has poor
current gain so if you need to drive several amps, the base drive is high as
well requiring more parts. I'm sorry, but your method is a klutsy, old
school solution. Of course you don't have write any code so that's an
advantage. If you want more information, please e-mail me. Remove the ns
from the e-mail address to respond, nsmontassocatyahoodotcom. Thanks for
the argument.
Bob

I used obsolete parts in the SPICE analysis since I have them in the library. A
proper design would obviously use modern parts.

Mike Monett
 
C

cyBORG

Jan 1, 1970
0
You guys should check out some pinball machine operator's manuals, for
example, 1990's Williams pinballs used End of Stroke switches / Capacitors
to help with the main drive/"hold" circuit.

There are schematics in some of the scanned operators manuals. www.ipdb.org

-cyBORG



Mike Monett said:
Jamie wrote:

[...]
what ever happen to the simple 3 component network to drive a power
transistor with a peek and hold function ?

2 resistors in series to properly calculate the holding current of
the relay, one of the resistors will have a Cap coupled with it that
will be calculated to create a current lag long enough to give the
desired peek current, then as it charges the current will drop back to
the holding current when the cap gets charged.
having the cap coupled with a resistor allows it to discharge faster
for the next time.
ect.
old age analog electronics long forgotten i guess! :)

It would be nice if you provided a schematic. However, if I guess
correctly, your circuit was one of the first discussed in this thread.
The high power dissipation and long recovery time are the most serious
limitations.

"Peek" is probably spelled "peak" in this contxt.

Mike Monett
 
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