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.

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