Hi Guys

I need to use 70V to power a solenoid for about 1sec at a time. I
would like to controll it with a PIC microcontroller.

What would be the best to get the 5V of the pic to activate the 70V
circuit of the solenoid? Is there any super transistor or is the only
way to do it by using a relay? Can somebody give me some google
keywords to find the right component to use and the applicable
attributes that I need to look out for?

In addition to that, I don't know how to get 70V from anywhere.
Preferrably, I want to get it from the wall socket. The transformers I
can find is only betwen 3V and 24V. I'm in Europe. Where can I buy
something that I plug into the wall and get 70V out. Again a few
google keywords will be helpful.

Safety: The 24V doesn't seem to shock me at all. Will 70V give you a
shock?

Thanks!

Without the apparent knowledge of what, and where, you are attempting ot
accomplish, it may be best to refer your specific quest to a qualified
electrician. Even 24 VAC, (and even less) may be lethal if inappropiately
connected to the human body. IHMO!
wrote in message
...
Hi Guys

I need to use 70V to power a solenoid for about 1sec at a time. I
would like to controll it with a PIC microcontroller.

What would be the best to get the 5V of the pic to activate the 70V
circuit of the solenoid? Is there any super transistor or is the only
way to do it by using a relay? Can somebody give me some google
keywords to find the right component to use and the applicable
attributes that I need to look out for?

In addition to that, I don't know how to get 70V from anywhere.
Preferrably, I want to get it from the wall socket. The transformers I
can find is only betwen 3V and 24V. I'm in Europe. Where can I buy
something that I plug into the wall and get 70V out. Again a few
google keywords will be helpful.

Safety: The 24V doesn't seem to shock me at all. Will 70V give you a
shock?

Thanks!

Hi , thanks for your feedback.

Here's a diagram of what I more-or-less want to achieve (looks better
in fixed width font like courier):
-------- -----------
| | | |
5V | | 72V
| PIC---BBB |
| | | |
|------| ----SOL----

I have a 5V circuit with an intelligent PIC in it which will send out
a signal when the SOLenoid should be switched on. The solenoid needs
72V. The BBB is a big black box which, I suppose will either be a
transistor grouping thing or a relay of some sort.

The solenoid takes anything between 12 and 72V depending on how long
you have it working and how hard it should work. I have a 24V PSU that
plugs into the wall and converts 220Vac to 24Vdc. I think it's maximum
1A. I need something similar but in a 72V flavour.

And this is where I want to know, is this type of voltage getting
dangerous and which parts I should use for the BBB and the 72V
supplier.

On Wed, 21 Nov 2007 05:11:57 -0800 (PST),
wrote:

Hi , thanks for your feedback.

Here's a diagram of what I more-or-less want to achieve (looks better
in fixed width font like courier):
-------- -----------
| | | |
5V | | 72V
| PIC---BBB |
| | | |
|------| ----SOL----

I have a 5V circuit with an intelligent PIC in it which will send out
a signal when the SOLenoid should be switched on. The solenoid needs
72V. The BBB is a big black box which, I suppose will either be a
transistor grouping thing or a relay of some sort.

The solenoid takes anything between 12 and 72V depending on how long
you have it working and how hard it should work. I have a 24V PSU that
plugs into the wall and converts 220Vac to 24Vdc. I think it's maximum
1A. I need something similar but in a 72V flavour.

And this is where I want to know, is this type of voltage getting
dangerous

---
Yes.
---


and which parts I should use for the BBB and the 72V
supplier.

---
View in Courier:

Ideally, you could do something like this, but to get 72V into the
solenoid you'll need a transformer with a 51V secondary, which might
be tricky to find.

220AC---[FUSE]-- |
|S1A
O
| +-----+
P||S--|~ +|-------------+
R||E | | |
I||C--|+ -|--+--[BFC+]--+
| +-----+ | |
O FWB GND |
|S1B [SOLENOID]
220AC---------- | |
|
D
PIC--------------------------------------G IRL3215
S
|
GND----------------------------------------+


Transformers with 24V secondaries are very common, though, so here's
what I'd do:



220AC---[FUSE]-- |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+--------+
| R||E | | | |
| +--I||C-+ | | | [SOL]
| | | | | |+ |
| | T2 | | |[4700µF] D
| | O O | | | | G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|$ -|---+--------+ |
| +-----+ | |
O | |
|S1B | |
220AC------------ | | |
| |
GND---------------------------------------------+ |
|
PIC--------------------------------------------------+

That is, use two transformers with 240V primaries wired in parallel
and 24V secondaries wired in series aiding.

You could also use transformers with 120V primaries by wiring the
primaries in series.

A 4700µF reservoir capacitor will get you about 2Vpp of ripple
across the energized solenoid, and the transformers' secondaries
should be rated for about 1.8 times the solenoid load current, or
about 2A.

Also, there's nothing magic about the MOSFET, all you really need is
a logic level N channel device capable of handling the solenoid
current when it's turned on and holding off the solenoid voltage
when it's turned off.


--
JF

On Wed, 21 Nov 2007 09:44:18 -0600, John Fields
wrote:

On Wed, 21 Nov 2007 05:11:57 -0800 (PST),
wrote:

Hi , thanks for your feedback.

Here's a diagram of what I more-or-less want to achieve (looks better
in fixed width font like courier):
-------- -----------
| | | |
5V | | 72V
| PIC---BBB |
| | | |
|------| ----SOL----

I have a 5V circuit with an intelligent PIC in it which will send out
a signal when the SOLenoid should be switched on. The solenoid needs
72V. The BBB is a big black box which, I suppose will either be a
transistor grouping thing or a relay of some sort.

The solenoid takes anything between 12 and 72V depending on how long
you have it working and how hard it should work. I have a 24V PSU that
plugs into the wall and converts 220Vac to 24Vdc. I think it's maximum
1A. I need something similar but in a 72V flavour.

And this is where I want to know, is this type of voltage getting
dangerous

---
Yes.
---


and which parts I should use for the BBB and the 72V
supplier.

---
View in Courier:

Ideally, you could do something like this, but to get 72V into the
solenoid you'll need a transformer with a 51V secondary, which might
be tricky to find.

220AC---[FUSE]-- |
|S1A
O
| +-----+
P||S--|~ +|-------------+
R||E | | |
I||C--|+ -|--+--[BFC+]--+
| +-----+ | |
O FWB GND |
|S1B [SOLENOID]
220AC---------- | |
|
D
PIC--------------------------------------G IRL3215
S
|
GND----------------------------------------+


Transformers with 24V secondaries are very common, though, so here's
what I'd do:



220AC---[FUSE]-- |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+--------+
| R||E | | | |
| +--I||C-+ | | | [SOL]
| | | | | |+ |
| | T2 | | |[4700µF] D
| | O O | | | | G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|$ -|---+--------+ |
| +-----+ | |
O | |
|S1B | |
220AC------------ | | |
| |
GND---------------------------------------------+ |
|
PIC--------------------------------------------------+

That is, use two transformers with 240V primaries wired in parallel
and 24V secondaries wired in series aiding.

You could also use transformers with 120V primaries by wiring the
primaries in series.

A 4700µF reservoir capacitor will get you about 2Vpp of ripple
across the energized solenoid, and the transformers' secondaries
should be rated for about 1.8 times the solenoid load current, or
about 2A.

Also, there's nothing magic about the MOSFET, all you really need is
a logic level N channel device capable of handling the solenoid
current when it's turned on and holding off the solenoid voltage
when it's turned off.

---
Oops...

I assumed that the solenoid will draw about 1A when it's energized
with 72V, so the foregoing may be invalid.

Do you know how much current it will draw? Or what its resistance
is? Also, what will its duty cycle be?


--
JF

Hi. thanks for the detiailed response JF.

I'm using the following solenoid: www.radionics.ie : RS Part number
search (top of page): 431-7560
(19mm push, 12V)

I'm looking at about 3.5% duty cycle.
It says on the datasheet( http://docs-europe.electrocomponents...6b805c2a1f.pdf)
that the wattage increase by the square of the increase in voltage.
12-72 = 6x increase so 36x increase in wattage. (1/36 for the duty
cycle)
7W at 100% duty @ 12V so we're looking at 252W on 72V on a 3.6% duty
cycle.

Unfortunately they don't mention current or resistance in the
documentation but I can go and measure tonight.

On Nov 21, 4:20 pm, wrote:
Hi. thanks for the detiailed response JF.

I'm using the following solenoid:www.radionics.ie: RS Part number
search (top of page): 431-7560
(19mm push, 12V)

I'm looking at about 3.5% duty cycle.
It says on the datasheet(http://docs-europe.electrocomponents...900766b805c2a1...)
that the wattage increase by the square of the increase in voltage.
12-72 = 6x increase so 36x increase in wattage. (1/36 for the duty
cycle)
7W at 100% duty @ 12V so we're looking at 252W on 72V on a 3.6% duty
cycle.

I just measured and found the following:
On a 24V system, the current is 1.1A and the resistance of the
solenoid is about 23ohm.
So sounds like I'll need about 3A current on 72V. That sounds like A
LOT!

Now a far as I understand a wallwart power supply will keep on giving
juice until you reach the maximum current that it's designed for. So
clearly I can't get 3A out of a 1A psu. What about batteries? What
happens if I put 8x9V in series? That will give me 72V but what's the
maximum current that I can draw from it?

On Wed, 21 Nov 2007 08:20:59 -0800 (PST),
wrote:

Hi. thanks for the detiailed response JF.

I'm using the following solenoid: www.radionics.ie : RS Part number
search (top of page): 431-7560
(19mm push, 12V)

I'm looking at about 3.5% duty cycle.
It says on the datasheet( http://docs-europe.electrocomponents...6b805c2a1f.pdf)
that the wattage increase by the square of the increase in voltage.
12-72 = 6x increase so 36x increase in wattage. (1/36 for the duty
cycle)
7W at 100% duty @ 12V so we're looking at 252W on 72V on a 3.6% duty
cycle.

Unfortunately they don't mention current or resistance in the
documentation but I can go and measure tonight.

I found this,:

http://docs-europe.electrocomponents...6b805b88ed.pdf

so if yours is the 12V nominal unit it'll have a coil resistance of
20.7 ohms, so the current with 72V across it will be:

E 72V
I = --- = ------- ~ 3.5 amperes,
R 20.7R

and the power it'll be dissipating will be:


P = IE = 3.5A * 72V = 252 watts,


so the duty cycle must be limited to:


Pnom * 100% 7W * 100%
D = ------------- = ----------- = 2.778%
Pon 252W

or less to keep from overheating the unit.

So now we have enough to look at the power supply again,
but the energy stored in its magnetic field is going to generate a
nasty spike when the thing turns off and the field collapses. I
didn't see any inductance spec's in the data sheets, so can you
measure it or find out what it is?


--
JF

Hi John

This is brilliant to see that your calculations tie up with what I
measured on the 24V.

How do I measure the inductance? What do you mean about the spike?
Some magnetic force or a current? Is it the opposite of capacitance?
Then I guess the falling magnetic field will cause a current and then
probably in opposite direction...

BTW I'm using this to knock a little ball the same way as a pool que
hits a pool ball. I presume that a solenoid is the best electrical
component to do this?? My 72V plan should be able to give me the force
required but maybe there's some magical component that can give more
bang per volt.

I'm also considering a solenoid with a higher resistance, which to me
means it must have more wounds/windings to more work. (Surely this
logic is correct - If it's the same brand, looks more or less the
same, then, if the wattage is higher, it must work harder and maybe I
can get away with lower voltage and current for the same performance)

Anyway.. How do I measure inductance?

On Wed, 21 Nov 2007 12:34:24 -0800 (PST),
wrote:

Hi John

This is brilliant to see that your calculations tie up with what I
measured on the 24V.

How do I measure the inductance? What do you mean about the spike?
Some magnetic force or a current? Is it the opposite of capacitance?
Then I guess the falling magnetic field will cause a current and then
probably in opposite direction...

BTW I'm using this to knock a little ball the same way as a pool que
hits a pool ball. I presume that a solenoid is the best electrical
component to do this?? My 72V plan should be able to give me the force
required but maybe there's some magical component that can give more
bang per volt.

I'm also considering a solenoid with a higher resistance, which to me
means it must have more wounds/windings to more work. (Surely this
logic is correct - If it's the same brand, looks more or less the
same, then, if the wattage is higher, it must work harder and maybe I
can get away with lower voltage and current for the same performance)

Anyway.. How do I measure inductance?

---
There are several ways.

But first, before we get to the rest of your questions, what kind of
test equipment do you have?


--
JF

On Nov 22, 12:58 am, John Fields
wrote:
On Wed, 21 Nov 2007 12:34:24 -0800 (PST),
wrote:





Hi John

This is brilliant to see that your calculations tie up with what I
measured on the 24V.

How do I measure the inductance? What do you mean about the spike?
Some magnetic force or a current? Is it the opposite of capacitance?
Then I guess the falling magnetic field will cause a current and then
probably in opposite direction...

BTW I'm using this to knock a little ball the same way as a pool que
hits a pool ball. I presume that a solenoid is the best electrical
component to do this?? My 72V plan should be able to give me the force
required but maybe there's some magical component that can give more
bang per volt.

I'm also considering a solenoid with a higher resistance, which to me
means it must have more wounds/windings to more work. (Surely this
logic is correct - If it's the same brand, looks more or less the
same, then, if the wattage is higher, it must work harder and maybe I
can get away with lower voltage and current for the same performance)

Anyway.. How do I measure inductance?

---
There are several ways.

But first, before we get to the rest of your questions, what kind of
test equipment do you have?

--
JF

I have a digital Volt, Current and resistance meter. (Made by El
Cheapo). I see they call it a domestic meter:
http://www.maplin.co.uk/Module.aspx?...eter&doy=22m11
This is the only measuring tool I have. :-s

On Thu, 22 Nov 2007 01:16:21 -0800 (PST),
wrote:

On Nov 22, 12:58 am, John Fields
wrote:
On Wed, 21 Nov 2007 12:34:24 -0800 (PST),
wrote:





Hi John

This is brilliant to see that your calculations tie up with what I
measured on the 24V.

How do I measure the inductance? What do you mean about the spike?
Some magnetic force or a current? Is it the opposite of capacitance?
Then I guess the falling magnetic field will cause a current and then
probably in opposite direction...

BTW I'm using this to knock a little ball the same way as a pool que
hits a pool ball. I presume that a solenoid is the best electrical
component to do this?? My 72V plan should be able to give me the force
required but maybe there's some magical component that can give more
bang per volt.

I'm also considering a solenoid with a higher resistance, which to me
means it must have more wounds/windings to more work. (Surely this
logic is correct - If it's the same brand, looks more or less the
same, then, if the wattage is higher, it must work harder and maybe I
can get away with lower voltage and current for the same performance)

Anyway.. How do I measure inductance?

---
There are several ways.

But first, before we get to the rest of your questions, what kind of
test equipment do you have?

--
JF

I have a digital Volt, Current and resistance meter. (Made by El
Cheapo). I see they call it a domestic meter:
http://www.maplin.co.uk/Module.aspx?...eter&doy=22m11
This is the only measuring tool I have. :-s

---
Well, we're kinda stuck then, I think.

If you had a signal generator you could connect a capacitor in
series with the solenoid, sweep the LC, find the resonant point, and
then calculate the inductance knowing the resonant frequency and the
capacitance. Or, if you had a DMM which could measure inductance
you could do it directly.

But, now knowing your application, knowing the inductance doesn't
matter all that much.

What I'm thinking is that you could charge up a capacitor to 72V and
then dump it into the coil to get the action you want, like this:
(View in Courier)

..+V--[R]------+-------+-------+
.. | | |
.. [R] | |
.. | S |
.. +-----G PCH |
.. | D |+
.. [R] | [BFC]
.. | | |
.. C | |
..I/O--[R]--B NPN [COIL] |
.. E | |
.. | | |
..GND----------+-------+-------+



--
JF

Also, there's nothing magic about the MOSFET, all you really need is
a logic level N channel device capable of handling the solenoid
current when it's turned on and holding off the solenoid voltage
when it's turned off.

Hi John, I would like to get back to the MOSFET comment. This sounds
scary to me. About the current. Do you mean, as we both calucated that
if the 72V will use 3A current, the then mosfet may need 5V 3A, in and
that will allow the 72V 3A out?

So my pic needs to give 3A??? This sounds almost impossible. I'll have
to check the datasheets. Is this how all transistors work re current:
The current in the base needs to be the same as the current you want
in/out on the collector and emitter?

And then of course, my next question will be if you can suggest an
appropriate mosfet from my local shop: www.radionics.ie

Thanks & Regards
Evert

On Sun, 2 Dec 2007 08:03:56 -0800 (PST),
wrote:


Also, there's nothing magic about the MOSFET, all you really need is
a logic level N channel device capable of handling the solenoid
current when it's turned on and holding off the solenoid voltage
when it's turned off.

Hi John, I would like to get back to the MOSFET comment. This sounds
scary to me. About the current. Do you mean, as we both calucated that
if the 72V will use 3A current, the then mosfet may need 5V 3A, in and
that will allow the 72V 3A out?

---
No. What I meant was that when there's zero volts on the gate, the
MOSFET will be turned OFF and the drain will be required to stand
off the supply voltage. On the other hand, when the gate is at 5V
the MOSFET will be turned ON and the solenoid current will flow
through the MOSFET from drain to source.

There is no current required into or out of the gate except what's
needed to charge and discharge the gate capacitance.
---

So my pic needs to give 3A??? This sounds almost impossible. I'll have
to check the datasheets. Is this how all transistors work re current:
The current in the base needs to be the same as the current you want
in/out on the collector and emitter?

---
No. for bipolar transistors there's a characteristic named 'beta'
(or Hfe) which specifies the current gain of the transistor:

Ic
Hfe = ----
Ib

For example, if a transistor is specified as having a minimum beta
of 100 with 100mA of collector current, then the maximum base
current required to get that 100mA of collector current will be:

Ic 100mA
Ib = ----- = ------- = 1mA
Hfe 100

For MOSFETs, in this type of application, all that's necessary is to
raise the voltage on the gate high enough to lower the resistance of
the drain-to-source channel to the point where its resistance is
negligible with respect to the load.
---

And then of course, my next question will be if you can suggest an
appropriate mosfet from my local shop: www.radionics.ie

---
Which circuit are you planning on using?


--
JF

No. for bipolar transistors there's a characteristic named 'beta'
(or Hfe) which specifies the current gain of the transistor:

Ic
Hfe = ----
Ib

For example, if a transistor is specified as having a minimum beta
of 100 with 100mA of collector current, then the maximum base
current required to get that 100mA of collector current will be:

Ic 100mA
Ib = ----- = ------- = 1mA
Hfe 100
Ok, got that.

For MOSFETs, in this type of application, all that's necessary is to
raise the voltage on the gate high enough to lower the resistance of
the drain-to-source channel to the point where its resistance is
negligible with respect to the load.
Why am I talking about Collectors,Bases, Emitters and you talk about
drains and sources. Are these the same? Why the different naming then?

And then of course, my next question will be if you can suggest an
appropriate mosfet from my local shop:www.radionics.ie

---
Which circuit are you planning on using?

This seems the simplest. (stolen from your message above)
220AC---[FUSE]-- |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+--------+
| R||E | | | |
| +--I||C-+ | | | [SOL]
| | | | | |+ |
| | T2 | | |[4700µF] D
| | O O | | | | G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|$ -|---+--------+ |
| +-----+ | |
O | |
|S1B | |
220AC------------ | | |
| |
GND---------------------------------------------+ |
|
PIC--------------------------------------------------+

Thanks a lot for all your help. I really appreciate it.

On Mon, 3 Dec 2007 02:23:35 -0800 (PST),
wrote:

No. for bipolar transistors there's a characteristic named 'beta'
(or Hfe) which specifies the current gain of the transistor:

Ic
Hfe = ----
Ib

For example, if a transistor is specified as having a minimum beta
of 100 with 100mA of collector current, then the maximum base
current required to get that 100mA of collector current will be:

Ic 100mA
Ib = ----- = ------- = 1mA
Hfe 100
Ok, got that.

For MOSFETs, in this type of application, all that's necessary is to
raise the voltage on the gate high enough to lower the resistance of
the drain-to-source channel to the point where its resistance is
negligible with respect to the load.

Why am I talking about Collectors,Bases, Emitters and you talk about
drains and sources. Are these the same? Why the different naming then?

---
Bipolar Junction Transistors (BJT) and Metal Oxide Semiconductor
Field Effect Transistors (MOSFET) are two completely different
animals, but they each have three terminals with the bipolar's base
corresponding to the MOSFET's gate, the bipolar collector
corresponding to the MOSFET drain and the bipolar emitter
corresponding to the MOSFET source.

For the BJT:

http://en.wikipedia.org/wiki/Bipolar...ion_transistor

and the MOSFET:

http://en.wikipedia.org/wiki/MOSFET
---

And then of course, my next question will be if you can suggest an
appropriate mosfet from my local shop:www.radionics.ie

---
Which circuit are you planning on using?

This seems the simplest. (stolen from your message above)
220AC---[FUSE]-- |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+--------+
| R||E | | | |
| +--I||C-+ | | |+ [SOL]
| | | | |[4700µF] |
| | T2 | | | |100V D
| | O O | | | | IRL3215G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|$ -|---+--------+ |
| +-----+ | |
O | |
|S1B | |
220AC------------ | | |
| |
GND---------------------------------------------+ |
|
PIC--------------------------------------------------+

Thanks a lot for all your help. I really appreciate it.

---
You're welcome. Use an IRL3215.

Also, just to be safe,

220AC---[FUSE]-- |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+-------+-----+
| R||E | | | | |A
| +--I||C-+ | | |+ [SOL][1N4003]
| | | | |[4700µF] | |
| | | | | |100V +-----+
| | T2 | | | | D
| | O O | | | | IRL3215 G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|~ -|---+-------+ |
| +-----+ | |
O +--[ZENER]--+
|S1B | 1N4734A |
220AC------------ | | |
| [10K]
GND------------------------------------+ |
|
PIC-------------------------------------------------+


--
JF

Hi John

I thought I had all I needed but now I have one last embarrassing
question to ask...

Should the 5V ground be connected to the 70V ground? I.e should the
5V gnd be connected to the mosfet source? What is the reason for it to
be attached not attached?

On Tue, 4 Dec 2007 09:11:37 -0800 (PST),
wrote:

Hi John

I thought I had all I needed but now I have one last embarrassing
question to ask...

---
Don't be embarrassed. You knew you didn't know and asked for help.
That's commendable.
---

Should the 5V ground be connected to the 70V ground? I.e should the
5V gnd be connected to the mosfet source?

---
Yes.
---

What is the reason for it to be attached not attached?

---
The source is common to both the 70V supply and the supply providing
the signal the PIC will send to the gate, so their grounds both have
to be connected to the source.


--
JF

thanks. Got that bit about the grounds connected to the source.

Was reading art of electronics last night (rocket science to me!) and
then I saw something that you said as well:
"Always use a supression diode when switching an inductive load"

They had the following diagram:
+Vcc --+---COIL----+----C E----- GND
| | B
+---|------+ |

Ok. So I unleash the 72V through my favourite coil. When I stop the
voltage.... The magnetic field subsides. But according to you and the
book it generates somesort of spike.

So the way I figure it, is that the current must be generated in the
opposite way. So previosly the C of coil in my diagram was the + and
the L was -. Now I think the L will be + and the C -. So can I
'replace' the coil with a battery for the millisecond or two that the
field dissolves?

Anyway... that's the only way I can explain the use of the diode. When
the 72V is running through the coil it has no use. When it is switched
off, it will allow my new 'battery' with a + on the L side to short
circuit itself and that I guess takes care of the current generated...
Is this correct?

So if all this guessing of mine is correct then my question is... So
what? What will happen if the C of the BJT is more - than the E and B?

On Sun, 9 Dec 2007 15:31:13 -0800 (PST),
wrote:

thanks. Got that bit about the grounds connected to the source.

Was reading art of electronics last night (rocket science to me!) and
then I saw something that you said as well:
"Always use a supression diode when switching an inductive load"

They had the following diagram:
+Vcc --+---COIL----+----C E----- GND
| | B
+---|------+ |

Ok. So I unleash the 72V through my favourite coil. When I stop the
voltage.... The magnetic field subsides. But according to you and the
book it generates somesort of spike.

---
Yes.

the magnetic field doesn't just subside, it collapses very quickly
and when it does it cuts the turns of the coil and induces a voltage
across the coil opposite in polarity to the voltage impressed upon
it by the battery. That is, with the transistor turned ON the
voltage on the collector side of the coil will be close to ground,
but when the transistor turns OFF The voltage on the collector will
rise as described by:

dI
E = L ----
dt

where E is the voltage appearing across the coil, in volts

L is the inductance of the coil, in henrys and

dI
---- is the time rate of change of current in the coil.
dT

For example, I don't remeber all the details, but let's say your
solenoid has an inductance of 0.1 henry, there's 3 amperes of
current in it when you open the switch, and it takes 1 millisecond
for the current to decay to zero amps from 3 amps.

Then:

dI 0.1H * 3A
E = L ---- = ----------- = 300 volts
dt 0.001S

Which will more than likely punch a hole through the transistor if
the diode isn't there.

BTW, just for grins, take a look at what happens if dT is 100µS.
---

So the way I figure it, is that the current must be generated in the
opposite way. So previosly the C of coil in my diagram was the + and
the L was -. Now I think the L will be + and the C -. So can I
'replace' the coil with a battery for the millisecond or two that the
field dissolves?

---
Yes, but you've got it backwards. You have to put the + of the
battery on the collector and the - on the supply
---

Anyway... that's the only way I can explain the use of the diode. When
the 72V is running through the coil it has no use. When it is switched
off, it will allow my new 'battery' with a + on the L side to short
circuit itself and that I guess takes care of the current generated...
Is this correct?

---
Kinda, but the + will be connected to the collector. What happens
is that when the coil voltage tries to rise past the supply plus the
drop across the diode, the diode clamps the transistor collector to
the supply plus one diode drop while the coil discharges through the
diode. So that'll be supply plus about 0.7V, which shouldn't bother
the transistor at all.
---

So if all this guessing of mine is correct then my question is... So
what? What will happen if the C of the BJT is more - than the E and B?

---
It won't go negative, it'll go hugely positive and let all of the
magic smoke out of the transistor.


--
JF

Hi JF

Again thanks for the info.

I went shopping the other day and they didn't have the parts I was
looking for. So now I'm searching online to try and find them on some
online shops.

I found a pretty good webites to get datasheets. But I have to open
every one to see if it qualifies.

Do you know:
1. It seems like there's an international product numbering system for
electronic components (or does every manufacturer number their own
way?)
2. Is there a place where I can search all MOSFETS (e.g.) and find the
code for the ones that qualify for me. E.g. 5V gate and 200V for the
supply.

Regards & Merry Christmas

On Thu, 20 Dec 2007 05:38:58 -0800 (PST),
wrote:

Hi JF

Again thanks for the info.

I went shopping the other day and they didn't have the parts I was
looking for. So now I'm searching online to try and find them on some
online shops.

I found a pretty good webites to get datasheets. But I have to open
every one to see if it qualifies.

Do you know:
1. It seems like there's an international product numbering system for
electronic components (or does every manufacturer number their own
way?)

---
AFAIK every manufacturer names their products in their own way.

Notable exceptions are second-sourced parts where the part numbers
from the second source generally mimic the original or, at least,
integrate the original manufacturer's part number into their own.
---

2. Is there a place where I can search all MOSFETS (e.g.) and find the
code for the ones that qualify for me. E.g. 5V gate and 200V for the
supply.

---
Not that I know of.

However, all is not lost.

Many manufacturers provide editable online parametric tables for
their parts which will allow you to define the search criteria and
which will display parts which meet those criteria.

Some distributors do also. Digi-Key is a good example, and their
engine will search across all the lines they carry, so that probably
comes as close to supplying what you describe as there is.
---

Regards & Merry Christmas

---
Thanks. You too. :-)


--
JF

On Wed, 21 Nov 2007 08:20:59 -0800 (PST),
wrote:

Hi. thanks for the detiailed response JF.

I'm using the following solenoid: www.radionics.ie : RS Part number
search (top of page): 431-7560
(19mm push, 12V)

I'm looking at about 3.5% duty cycle.
It says on the datasheet(
http://docs-europe.electrocomponents...6b805c2a1f.pdf)
that the wattage increase by the square of the increase in voltage.
12-72 = 6x increase so 36x increase in wattage. (1/36 for the duty
cycle)
7W at 100% duty @ 12V so we're looking at 252W on 72V on a 3.6% duty
cycle.

Unfortunately they don't mention current or resistance in the
documentation but I can go and measure tonight.


According to my RS website page RS 431-7560 is manufactured by
SAIA-BURGESS http://www.saia-burgess.com/2302/2303/2310/2316.asp which
owns the LEDEX brand http://www.ledex.com/ of STA linear solenoids
http://www.ledex.com/linear-solenoid...solenoids.html

(You will be requires to register)

The STA LEDEX part no. for the RS 431-7560 is 195225-230 for which the
data sheet is Metric STA 20 x 40
http://www.ledex.com/ltr2/access.php...20x40_Push.pdf

On this page
http://www.ledex.com/solenoid-applic...solenoids.html you
will find applications for linear solenoids some of which may be what
you are trying to accomplish.

Also, I would suggest that you read as much as you can on the LEDEX
website including
http://www.ledex.com/ltr2/access.php..._Section_M.pdf

When using your solenoid at the nominal voltage of 12V you can leave
it permanently connected without overheating but if you wish to
increase the voltage then you may be wise to use a LEDEX Hold-in
Circuit Module as described on page 6 of the last document link.

If you need help then I am sure that LEDEX will be able to answer your
queries.

Good luck!

Hi JF

I would have been happy to report that my 5V-24V switch worked with
the solenoid.
And it did...Until later that night that I discovered that my solenoid
must have gotten warm and melted in the middle and now the metal thing
is stuck in there. (that's what I deduce at least. After pulling out
the metal shaft, I can see brown discoloration in the inside of the
solenoid).

So I'm pretty sure I fried it with some sort of exhaustion. So now I
have the following questions:
- Is is possible that the diode can break it... I was wondering about
this befo If the magnetic field colapses and force current in the
opposite direction, does that mean the duty cycle extends further than
the amount of time that it is ON? So it is on for 0.5 seconds at 24V.
Then it colapses for 0.1 second at -200V. Should I add the power of
these together to calculate the duty cycle?
- Is is AT ALL possible that the MOSFET will allow some current
through if I have nothing connected to it (not necessarily negative
but just nothing).
- How does the mosfet 'decide' how much current to get through? Will
it just bridge the gap between the source and drain? Or will it put a
multiplier on the voltage or current of the gate? And then the
question that goes with this is: does is matter what size resister I
put in between my 5V pic and the gate?

One comment: I thought in the begginning that the gate is the middle
pin (like the base of a transistor). So I had my gate and drain the
wrong way around for about 10 iterations (and of course I was
scratching my head as to why the stupid thing didn't work). After that
it worked when I swopped it but maybe that introduced the timebomb
slow death for my solenoid.

-The final question I have is about my powersupply. Now it says it is
a 24V, 800mA, regulated power supply. (http://www.maplin.co.uk/
module.aspx?ModuleNo=48484&doy=7m1 --- the 24V one) This is a
switched mode PSU. Now, the bizarre thing is that despite all this 24V
talk theres a sticker on the power supply that say 24V and then also
"Typical voltage 21-35V" ---WTF?!?
I thought its 24 and that's it. Why would it be 35V sometimes?

Thanks again for your support and HAPPY NEW YEAR!

On Jan 7, 4:05 pm, wrote:
Hi JF

I would have been happy to report that my 5V-24V switch worked with
the solenoid.
And it did...Until later that night that I discovered that my solenoid
must have gotten warm and melted in the middle and now the metal thing
is stuck in there. (that's what I deduce at least. After pulling out
the metal shaft, I can see brown discoloration in the inside of the
solenoid).

So I'm pretty sure I fried it with some sort of exhaustion. So now I
have the following questions:
- Is is possible that the diode can break it... I was wondering about
this befo If the magnetic field colapses and force current in the
opposite direction, does that mean the duty cycle extends further than
the amount of time that it is ON? So it is on for 0.5 seconds at 24V.
Then it colapses for 0.1 second at -200V. Should I add the power of
these together to calculate the duty cycle?
- Is is AT ALL possible that the MOSFET will allow some current
through if I have nothing connected to it (not necessarily negative
but just nothing).
- How does the mosfet 'decide' how much current to get through? Will
it just bridge the gap between the source and drain? Or will it put a
multiplier on the voltage or current of the gate? And then the
question that goes with this is: does is matter what size resister I
put in between my 5V pic and the gate?

One comment: I thought in the begginning that the gate is the middle
pin (like the base of a transistor). So I had my gate and drain the
wrong way around for about 10 iterations (and of course I was
scratching my head as to why the stupid thing didn't work). After that
it worked when I swopped it but maybe that introduced the timebomb
slow death for my solenoid.

-The final question I have is about my powersupply. Now it says it is
a 24V, 800mA, regulated power supply. (http://www.maplin.co.uk/
module.aspx?ModuleNo=48484&doy=7m1 --- the 24V one) This is a
switched mode PSU. Now, the bizarre thing is that despite all this 24V
talk theres a sticker on the power supply that say 24V and then also
"Typical voltage 21-35V" ---WTF?!?
I thought its 24 and that's it. Why would it be 35V sometimes?

Thanks again for your support and HAPPY NEW YEAR!

Ok, I read up on a few things so some of my questions are answered. I
know now that the gate never draws current becuase it is a FET. It
works with a field, the gate is insulated so no current flows through
it.

I think I find out why things went all wrong the other day. I realised
yesterday that I had the polarities of the 24V reversed. So I had 24V
at the source and 0V at the drain. In addition to mistaken the drain
with the gate pin, I think I had more than enough reason and flaws in
my little system to even break the MOSFET. I can confirm that the
MOSFET is not working now. Or at least: I THINK the MOSFET is not
working. Which brings me to another question: Is there an easy test
for a MOSFET to see if it's functioning properly?

On Tue, 8 Jan 2008 01:22:02 -0800 (PST),
wrote:

On Jan 7, 4:05 pm, wrote:
Hi JF

I would have been happy to report that my 5V-24V switch worked with
the solenoid.
And it did...Until later that night that I discovered that my solenoid
must have gotten warm and melted in the middle and now the metal thing
is stuck in there. (that's what I deduce at least. After pulling out
the metal shaft, I can see brown discoloration in the inside of the
solenoid).

So I'm pretty sure I fried it with some sort of exhaustion. So now I
have the following questions:
- Is is possible that the diode can break it...

---
No.
---

I was wondering about
this befo If the magnetic field colapses and force current in the
opposite direction, does that mean the duty cycle extends further than
the amount of time that it is ON? So it is on for 0.5 seconds at 24V.
Then it colapses for 0.1 second at -200V.

---
With a diode across it, it can't collapse at 200V since the diode is
clamping the voltage across it to about 0.7V.

Since the coil has a resistance of ~ 21 ohms, that means that during
the collapse of the field the maximum current through the coil will
be:

E 0.7V
I = --- = ------ ~ 0.033A = 33mA
R 21R

and the maximum power dissipation will be:


P = IE = 0.033A * 0.7V ~ 0.023W = 23mW

hardly anything to be concerned about since it's less than 1/10th of
a percent of what you normally drive the coil with.
---

Should I add the power of
these together to calculate the duty cycle?

---
I wouldn't bother.
---

- Is is AT ALL possible that the MOSFET will allow some current
through if I have nothing connected to it (not necessarily negative
but just nothing).

---
Yes. If the gate is charged positive WRT the source and that charge
is trapped, the MOSFET will stay at least partially turned on for as
long as that charge remains above the MOSFET's threshold voltage.

If the MOSFET Is just sitting there, though, with a charged gate and
nothing connected to it no charge (other than leakage) will flow.
---

- How does the mosfet 'decide' how much current to get through?

---
It doesn't. Once you've driven the gate sufficiently positive, the
only things which will limit the drain-to-source current will be the
impedance of the supply, the impedance of the load, the MOSFET's
drain-to-source resistance (Rds(on)), and the resistance of the load
side wiring.
---

Will
it just bridge the gap between the source and drain?

---
Yes. like a switch.
---
Or will it put a
multiplier on the voltage or current of the gate?

---
No. If it's fully turned on all that will appear between the supply
and the load is the MOSFET's Rds(on).
---

And then the
question that goes with this is: does is matter what size resister I
put in between my 5V pic and the gate?

---
It may, depending on how quickly you want to turn ON the MOSFET.

That is, since the gate looks like (is) a capacitor which has to be
charged and discharged in order to turn the MOSFET on and off, the
time it takes to do that will be:


T = RC

So the larger R becomes the longer it'll take to charge and
discharge the gate capacitance.

There's also the question of how much current your PIC's I/O can
source and sink, since the smaller the current the higher the port's
resistance will be and the longer it'll take to charge and discharge
the gate capacitance.
---

One comment: I thought in the begginning that the gate is the middle
pin (like the base of a transistor). So I had my gate and drain the
wrong way around for about 10 iterations (and of course I was
scratching my head as to why the stupid thing didn't work). After that
it worked when I swopped it but maybe that introduced the timebomb
slow death for my solenoid.

-The final question I have is about my powersupply. Now it says it is
a 24V, 800mA, regulated power supply. (http://www.maplin.co.uk/
module.aspx?ModuleNo=48484&doy=7m1 --- the 24V one) This is a
switched mode PSU. Now, the bizarre thing is that despite all this 24V
talk theres a sticker on the power supply that say 24V and then also
"Typical voltage 21-35V" ---WTF?!?

---
It doesn't say anywhere that it's regulated, only that it's a
switcher.
---

I thought its 24 and that's it. Why would it be 35V sometimes?

---
If it's unregulated, the output voltage will be load dependent and,
lightly loaded, it'll rise.
---

Thanks again for your support and HAPPY NEW YEAR!

---
:-)
---

Ok, I read up on a few things so some of my questions are answered. I
know now that the gate never draws current becuase it is a FET. It
works with a field, the gate is insulated so no current flows through
it.

---
Hitting the books, huh?

As my friends from Oz say, "Good on you!"
---

I think I find out why things went all wrong the other day. I realised
yesterday that I had the polarities of the 24V reversed. So I had 24V
at the source and 0V at the drain. In addition to mistaken the drain
with the gate pin, I think I had more than enough reason and flaws in
my little system to even break the MOSFET. I can confirm that the
MOSFET is not working now. Or at least: I THINK the MOSFET is not
working. Which brings me to another question: Is there an easy test
for a MOSFET to see if it's functioning properly?

---
An easy test would be:

D------+
0-15V----G NCH |+
S [OHMMETER]
| |
GND--------+------+

With the gate at 0V the ohmmeter should read infinite ohms or "OL".

As you make the gate-to-source (Vgs) voltage more and more positive
the drain-to-source resistance (Rds) should get closer and closer to
zero ohms.

If you're using a logic level MOSFET the channel should become fully
enhanced with Vgs ~ 3V , otherwise it should become fully enhanced
with Vgs ~ 10V. "Fully enhanced" means the channel's ON resistance
(Rds(on)) will drop to no more than the value specified in the data
sheet for the Vgs specified.

A better test would be:

+24V--+----------------+
| |
[560R] 15V [20R] 30W
| / |
+-------+ +--------+
| | | |
| | D |
[1N4744A] [10K]---G NCH [VOLTMETER]
| | S |
| | | |
GND--+-------+--------+---------+

With the 10k pot cranked to ground,the voltmeter should read 24V.

As the pot is rotated toward 15V, the voltmeter reading should
decrease to almost zero volts and the 20 ohm resistor should get
hotter and hotter.

There's more if you're interested, but I think you've got enough to
keep you busy for a while!


--
JF

On Jan 8, 6:38 pm, John Fields wrote:
On Tue, 8 Jan 2008 01:22:02 -0800 (PST),
wrote:

On Jan 7, 4:05 pm, wrote:
Hi JF

I would have been happy to report that my 5V-24V switch worked with
the solenoid.
And it did...Until later that night that I discovered that my solenoid
must have gotten warm and melted in the middle and now the metal thing
is stuck in there. (that's what I deduce at least. After pulling out
the metal shaft, I can see brown discoloration in the inside of the
solenoid).

So I'm pretty sure I fried it with some sort of exhaustion. So now I
have the following questions:
- Is is possible that the diode can break it...

---
No.
---

I was wondering about
this befo If the magnetic field colapses and force current in the
opposite direction, does that mean the duty cycle extends further than
the amount of time that it is ON? So it is on for 0.5 seconds at 24V.
Then it colapses for 0.1 second at -200V.

---
With a diode across it, it can't collapse at 200V since the diode is
clamping the voltage across it to about 0.7V.

Since the coil has a resistance of ~ 21 ohms, that means that during
the collapse of the field the maximum current through the coil will
be:

E 0.7V
I = --- = ------ ~ 0.033A = 33mA
R 21R

and the maximum power dissipation will be:

P = IE = 0.033A * 0.7V ~ 0.023W = 23mW

hardly anything to be concerned about since it's less than 1/10th of
a percent of what you normally drive the coil with.
---

Should I add the power of
these together to calculate the duty cycle?

---
I wouldn't bother.
---

- Is is AT ALL possible that the MOSFET will allow some current
through if I have nothing connected to it (not necessarily negative
but just nothing).

---
Yes. If the gate is charged positive WRT the source and that charge
is trapped, the MOSFET will stay at least partially turned on for as
long as that charge remains above the MOSFET's threshold voltage.

If the MOSFET Is just sitting there, though, with a charged gate and
nothing connected to it no charge (other than leakage) will flow.
---

- How does the mosfet 'decide' how much current to get through?

---
It doesn't. Once you've driven the gate sufficiently positive, the
only things which will limit the drain-to-source current will be the
impedance of the supply, the impedance of the load, the MOSFET's
drain-to-source resistance (Rds(on)), and the resistance of the load
side wiring.
---

Will
it just bridge the gap between the source and drain?

---
Yes. like a switch.
---

Or will it put a
multiplier on the voltage or current of the gate?

---
No. If it's fully turned on all that will appear between the supply
and the load is the MOSFET's Rds(on).
---

And then the
question that goes with this is: does is matter what size resister I
put in between my 5V pic and the gate?

---
It may, depending on how quickly you want to turn ON the MOSFET.

That is, since the gate looks like (is) a capacitor which has to be
charged and discharged in order to turn the MOSFET on and off, the
time it takes to do that will be:

T = RC

So the larger R becomes the longer it'll take to charge and
discharge the gate capacitance.

There's also the question of how much current your PIC's I/O can
source and sink, since the smaller the current the higher the port's
resistance will be and the longer it'll take to charge and discharge
the gate capacitance.
---

One comment: I thought in the begginning that the gate is the middle
pin (like the base of a transistor). So I had my gate and drain the
wrong way around for about 10 iterations (and of course I was
scratching my head as to why the stupid thing didn't work). After that
it worked when I swopped it but maybe that introduced the timebomb
slow death for my solenoid.

-The final question I have is about my powersupply. Now it says it is
a 24V, 800mA, regulated power supply. (http://www.maplin.co.uk/
module.aspx?ModuleNo=48484&doy=7m1 --- the 24V one) This is a
switched mode PSU. Now, the bizarre thing is that despite all this 24V
talk theres a sticker on the power supply that say 24V and then also
"Typical voltage 21-35V" ---WTF?!?

---
It doesn't say anywhere that it's regulated, only that it's a
switcher.
---

I thought its 24 and that's it. Why would it be 35V sometimes?

---
If it's unregulated, the output voltage will be load dependent and,
lightly loaded, it'll rise.
---

Thanks again for your support and HAPPY NEW YEAR!

---
:-)
---

Ok, I read up on a few things so some of my questions are answered. I
know now that the gate never draws current becuase it is a FET. It
works with a field, the gate is insulated so no current flows through
it.

---
Hitting the books, huh?

As my friends from Oz say, "Good on you!"
---

I think I find out why things went all wrong the other day. I realised
yesterday that I had the polarities of the 24V reversed. So I had 24V
at the source and 0V at the drain. In addition to mistaken the drain
with the gate pin, I think I had more than enough reason and flaws in
my little system to even break the MOSFET. I can confirm that the
MOSFET is not working now. Or at least: I THINK the MOSFET is not
working. Which brings me to another question: Is there an easy test
for a MOSFET to see if it's functioning properly?

---
An easy test would be:

D------+
0-15V----G NCH |+
S [OHMMETER]
| |
GND--------+------+

With the gate at 0V the ohmmeter should read infinite ohms or "OL".

As you make the gate-to-source (Vgs) voltage more and more positive
the drain-to-source resistance (Rds) should get closer and closer to
zero ohms.

If you're using a logic level MOSFET the channel should become fully
enhanced with Vgs ~ 3V , otherwise it should become fully enhanced
with Vgs ~ 10V. "Fully enhanced" means the channel's ON resistance
(Rds(on)) will drop to no more than the value specified in the data
sheet for the Vgs specified.

A better test would be:

+24V--+----------------+
| |
[560R] 15V [20R] 30W
| / |
+-------+ +--------+
| | | |
| | D |
[1N4744A] [10K]---G NCH [VOLTMETER]
| | S |
| | | |
GND--+-------+--------+---------+

With the 10k pot cranked to ground,the voltmeter should read 24V.

As the pot is rotated toward 15V, the voltmeter reading should
decrease to almost zero volts and the 20 ohm resistor should get
hotter and hotter.

There's more if you're interested, but I think you've got enough to
keep you busy for a while!

--
JF

Thanks again for the info. This gives me another possible scenario for
why I toasted the solenoid.

I was 'driving' the gate with 5V+ a resistor and a switch. I didn't
have a pulldown resistor. I gather that it may be possible that the
field still existed on the gate even after I opened the switch. So I
guess with a pull down resistor on the gate I'd be more safe. What do
you think?

On Tue, 8 Jan 2008 11:51:41 -0800 (PST),
wrote:


Thanks again for the info. This gives me another possible scenario for
why I toasted the solenoid.

I was 'driving' the gate with 5V+ a resistor and a switch. I didn't
have a pulldown resistor. I gather that it may be possible that the
field still existed on the gate even after I opened the switch.

---
Not just possible, that's exactly what happened. :-(
---

So I
guess with a pull down resistor on the gate I'd be more safe.

---
Of course.
---

What do you think?

---
Since you're driving the 12V, 100% duty cycle coil with 24V, that
mandates a 25% (or lower) duty cycle so, assuming it's going to be
working 100% of the time, I think a good idea would be to drive it
with something like a 555 wired like this:

+24----------------------------------------+
|
VCC--+--------------------------------+ |
| | +------+
[20k]R1 +---------+ | | |K
| |_ | | [COIL] [1N4001]
+-------------7-O|D Vcc|-8---+ | |
| R2 | _| | +------+
+---[82k]---+--6-|TH R|O-4--+ |
| | |__ | | D
+-[1N4148]-+-2-O|TR OUT|-3---|--G NCH
| | GND | | S
[C] +----+----+ [0.1µF] |
| |1 | |
GND--------------+---------+----------+----+

Note that a pot can be substituted for R1 and R2, so you can adjust
the frequency, as required, to accommodate the inductance of the
coil, by choosing the end-to-end resistance of the pot and then
choosing the duty cycle by cranking the pot.

Also, if you can't find a pot with the end-to-end resistance you
need, you can always do this:


V---+
|
[R1]
|
[POT]--
|
[R2]
|
GND--+

Since we don't know the inductance of the coil it's impossible to
determine the pulse repetition frequency but, assuming it's 100
millihenrys:

Version 4
SHEET 1 880 716
WIRE 160 -32 -752 -32
WIRE 256 -32 160 -32
WIRE 160 16 160 -32
WIRE 256 16 256 -32
WIRE -272 176 -624 176
WIRE 48 176 -48 176
WIRE 160 208 160 96
WIRE 256 208 256 80
WIRE 256 208 160 208
WIRE 160 224 160 208
WIRE -624 240 -624 176
WIRE -576 240 -624 240
WIRE -464 240 -496 240
WIRE -272 240 -464 240
WIRE 16 240 -48 240
WIRE -464 304 -464 240
WIRE -432 304 -464 304
WIRE -320 304 -352 304
WIRE -272 304 -320 304
WIRE 112 304 -48 304
WIRE -16 368 -48 368
WIRE -464 400 -464 304
WIRE -416 400 -464 400
WIRE -320 400 -320 304
WIRE -320 400 -352 400
WIRE -320 464 -320 400
WIRE 16 464 16 240
WIRE 16 464 -320 464
WIRE -624 496 -624 240
WIRE -16 496 -16 368
WIRE -16 496 -624 496
WIRE -752 512 -752 -32
WIRE -624 512 -624 496
WIRE -320 528 -320 464
WIRE -752 640 -752 592
WIRE -624 640 -624 592
WIRE -624 640 -752 640
WIRE -320 640 -320 592
WIRE -320 640 -624 640
WIRE 48 640 48 176
WIRE 48 640 -320 640
WIRE 160 640 160 320
WIRE 160 640 48 640
WIRE -752 688 -752 640
FLAG -752 688 0
SYMBOL nmos 112 224 R0
SYMATTR InstName M1
SYMATTR Value IRF7468
SYMBOL ind 144 0 R0
SYMATTR InstName L1
SYMATTR Value .1
SYMATTR SpiceLine Rser=20.7
SYMBOL voltage -752 496 R0
WINDOW 0 42 56 Left 0
WINDOW 3 42 84 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 24
SYMBOL diode 272 80 R180
WINDOW 0 -43 35 Left 0
WINDOW 3 -101 -5 Left 0
SYMATTR InstName D1
SYMATTR Value MURS120
SYMBOL Misc\\NE555 -160 272 M0
SYMATTR InstName U1
SYMBOL voltage -624 496 M0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 0 -73 53 Left 0
WINDOW 3 -65 76 Left 0
SYMATTR InstName V3
SYMATTR Value 10
SYMBOL res -448 288 M90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 58 VTop 0
SYMATTR InstName R1
SYMATTR Value 8e4
SYMBOL res -592 224 M90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 2e4
SYMBOL cap -304 528 M0
WINDOW 0 -33 32 Left 0
WINDOW 3 -39 58 Left 0
SYMATTR InstName C1
SYMATTR Value 1e-6
SYMBOL diode -416 384 M90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D2
SYMATTR Value 1N4148
TEXT -610 666 Left 0 !.tran .2 uic


--
JF

On Tue, 08 Jan 2008 17:25:49 -0600, John Fields
wrote:


---
Since you're driving the 12V, 100% duty cycle coil with 24V, that
mandates a 25% (or lower) duty cycle so, assuming it's going to be
working 100% of the time, I think a good idea would be to drive it
with something like a 555 wired like this:

+24----------------------------------------+
|
VCC--+--------------------------------+ |
| | +------+
[20k]R1 +---------+ | | |K
| |_ | | [COIL] [1N4001]
+-------------7-O|D Vcc|-8---+ | |
| R2 | _| | +------+
+---[82k]---+--6-|TH R|O-4--+ |
| | |__ | | D
+-[1N4148]-+-2-O|TR OUT|-3---|--G NCH
| | GND | | S
[C] +----+----+ [0.1µF] |
| |1 | |
GND--------------+---------+----------+----+

Note that a pot can be substituted for R1 and R2, so you can adjust
the frequency, as required, to accommodate the inductance of the
coil, by choosing the end-to-end resistance of the pot and then
choosing the duty cycle by cranking the pot.

---
Or, change the frequency by selecting an appropriate 'C', duh...


--
JF