Hi all.
I've recently had a few queries relating to using US equipment
(designed for the US mains voltage of 110V) in the UK (with a mains
voltage of 240V) and vice versa, and as this appears to be a common
problem, I'm posting this as an informative message on how to handle
this problem. Here's a quick ASCII circuit diagram which I'll refer to
in the following notes - you'll need to read this with a fixed width
font such as COURIER to make any sense of it:
BATT+
|
LIVE ---o><o----\ ||| /--------+ o...o---------+
FUSE / ||| \ | / |
\ ||| / o----o |
A ----/ ||| \--o--+ | / \
||| | | / \
T1 ||| | | N ----< BR1 >---- P
||| | | \ /
B ----\ ||| /--o--|--+ \ /
/ ||| \ | |
\ ||| / | |
NEUTRAL --------/ ||| \-----o-------------------+---- BATT-
|
EARTH -------------+
I understand that in the US, the EARTH connection is regarded as
optional. However, in the UK, and in most of Europe, it is MANDATORY
for metal cased equipment, and is RECOMMENDED for non-metal cased
equipment.
You may recognise T1 as a standard dual-primary, dual-secondary
transformer, and BR1 is the standard bridge rectifier arrangement,
with P +ve and N -ve as usual. However, were you aware that it can be
connected for either 115V or 230V operation - or, with the help of a
2P2T switch of suitable ratings, as one switchable for both.
In addition, note that the 115V setting is in practice 100-130V and
the 230V setting is in practice 210-250V - in both cases, the centre
voltage gets quoted.
Basically, for 115V operation, connect NEUTRAL to A and LIVE to B,
which you're probably used to doing. For 230V operation, connect A to
B and make no other connection to them.
For switchable operation, connect the switch as follows:
A
NEUTRAL------+ |
| |
o---o...o--------+
115V 230V |
o---o...o--------+
| |
LIVE --------+ |
B
The dashed connections are made when in the 115V position, and the
dotted connections when in the 230V position. Note specifically that
NEUTRAL and LIVE are swapped over here relative to the first diagram.
Also, if the transformer secondaries are rated at 12V, they normally
deliver around 13.8V which is the standard rating of a car battery, at
least in the UK. The connections labelled BATT- and BATT+ would go to
a connector for plugging in an external 13.8V source, and if a
switched connector is used that switches across when the connector is
plugged in, and it is wired up as shown - with the solid line being
connected when the battery is not plugged in, and the dotted line
connected when it is plugged in, then both mains and battery operation
are available.
Note in particular that as the battery would be connected before the
bridge rectifier, it doesn't actually matter if the connections are
reversed as BR1 will deal with that, and the correct polarity will be
seen in the rest of the circuitry.
Best wishes from Riley.
+----------------------------------------------------------------------+
| There is something frustrating about the quality and speed of Linux |
| development, ie., the quality is too high and the speed is too high, |
| in other words, I can implement this XXXX feature, but I bet someone |
| else has already done so and is just about to release their patch. |
+----------------------------------------------------------------------+
* ftp://ftp.MemAlpha.cx/pub/rhw/Linux
* http://www.MemAlpha.cx/kernel.versions.html
