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