12V Power supply otions....

"Martin Brown" wrote in message
...
adm wrote:

"Martin Brown" wrote in message
...

adm wrote:

In my quest to have the LX200 and DSI set up outside but controlled from
inside, I am looking for a decent 240V AC to 12V DC power supply.

I use a nominally 13.8v ham radio PSU (the sort that Maplins and others
stock with two banana plug terminals on). Easily meaty enough at 4A for
my dewheater and fullrate slew to object.

Yeah - I saw one of those for £34 or something....but......isn't 13.8V
too high for the LX200GPS ? I though I read soemwhere (MAPUG ?) that it
needs to be 12V, not 13.8 and that it was the non GPS LX200s that used
13.8V

I don't know offhand what the voltage spec for the GPS LX200 is. The
original LX200 was *designed* for 12v nominal and "upgraded" to 18v with
no actual thought about the consequences. Several components are stressed
if it is run at full 18v (and the official Meade 12-18v DC converter is
one of the worst self-immolating pieces of shi^d^d^d bad design you are
ever likely to see).

Ah......after a bit more reading on the subject, I was confusing
myself......the orignal Lx200 was upgraded to 18V, not 13.8V.


I presume that 800mA will be OK for the scope itself, but the DewBuster
spec says it needs a 3A rated supply.

800mA will be marginal for the LX200 and may well blow its fuse on fast
slew if the thing momentarily stalls (and on 12v this is not uncommon).
Meade upped the voltage spec to nominal 18v to avoid motor stall issues.

If the GPS really is specced for 12v then they have changed the motors. I
would have thought they would make it so it could tolerate a nominal 12v
lead acid battery though since they are regularly used that way.

I guess it does - as that's what I use now ! I was confusing the 18V and
13.8V......


But it is noisy on 18v so I find 14v PSU (or a charged lead acid battery
about right). Halfords do a self contained charger and battery too.

I have one of those already ! I want to get away from lugging it outside
all the time, and especially being frustrated when I realise the damn
thing isn't charged up and needs to be charged for hours before I can
power my scope !!!!

Recharge it immediately after using (and once a month otherwise).

I try to. But at the end of a long night, sometimes I forget to do
so.....then I end up with a nasty surprise the next night.


Check MAPUG threads for additional details.

BTW I would not run signal cables parallel to 240v mains wiring.

It's non-optimal, I know ! I could run the data cables in a separate
conduit though - the distance is only around 10M or so.

And USB 2.0 will not like running very far and working either.

I know - but then again it isn't very far.... I wish I could find a
single 15m USB2.0 active extension cable rather than having to daisy
chain several together.

I think the longest I have ever seen are around 16' but I haven't really
looked very hard.

That's the longest I can find as well....

"Martin Brown" wrote in message
...
Colin Dawson wrote:
"JG" wrote in message
news:313030303331393042FA38AA83@crescentcomputing. co.uk...

"adm" said

In my quest to have the LX200 and DSI set up outside but controlled from
inside, I am looking for a decent 240V AC to 12V DC power supply. I
would
ideally like one with two or three 12V cigarette lighter style outlets

Lateral thinking here - if you are happy making up a breakout panel then
why not use a standard 400W Computer PSU? The +12V rail on that has at
least 4 outlets and is rated at 22A it also has +5V at 34A. The cost is
something like £10-12 retail. You would need to provide a method of
triggering the 'Power OK' signal though.

Some of them do not like having no load on the 5v rail though.

I ideally want to make up a single "umbilical" type ccable that will run
from the house to the scope itself - it would consist of power (240V
AC),
USB2.0 and the LX200 communications cable itself. This would probably be
buried in a conduit in my garden

As Martin has already said - not a good idea.

Rigging up a system to do this won't be difficult, there's plenty of
websites which show how to do this. Normally, electronics hobbiests do
this as a cheap bench power supply. So you'll get some pretty good and
safe ways to do this.

Though bear in mind that the new regulations require you to have an
electrician install all new mains wiring and for oudoors with ELCB.

I'd suggest that you place the power supply and scope as close as
possible to the scope. 12v DC doesn't tend to travel too well.
Something to do with resistance in power cables.

Although this is true, one option would be to have a nominal 13.8 5A
supply indoors and run the rough DC supply out to the scope and heater, if
necessary regulating down the scopes feed to a true 12v. A hundred feet of
cheapest solid copper core 20A house wiring cable will not drop too much
voltage (check this, but a back of the envelope gives 0.6 ohm/100'). Use
all the conductors in the cable 2 for + 1 for -.

(Negative DC cables always rot away electrolytically in the damp)

At 4A max load it should drop about 2.4v - perhaps a bit marginal so a
thicker grade of cable might be advisable. At least with low voltage DC
you don't have to worry about armoured cable and deep trench burial.

You would need to do the sums a bit more carefully and put a couple of
capacitors at the far end to decouple the supply but it should be workable
over short distances (and certainly over longer distances than USB2).

Regars,
Martin Brown