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Old April 30th 04, 09:50 PM
Colin Dawson
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If you start looking about for astro bits in the states. I think that I
should point out the Kendrick Dew system.

I've never seen this device directly, but it also has setting for how much
power is being used. The dew heater project on my website, uses a pulse
width modulator that pulses at about 2.5 Khz (down to about 1.5Khz I think).
The kendrick system, depending on it's settings, turns the heater on for 15
seconds, then off for 15 seconds. It's basically the same as doing it as
sub second pulsewidths BUT, and yes it's a big but, if you try to run your
scope and the heater off the same battery there's a voltage issue. Whenever
the Kendrick heater turns on there's a huge power drain on the battery (just
the same as a homemade heater), then when the kendrick turns off this stops.
This causes the battery voltage to drop when the heater is on, Then come
back up. I've heard from a posting on a NG a while back, that this can
cause the scope to do strange things (reset, motor faliure, autostar goes
haywire, not track properly). Using a Khz frequency for the pulse width,
means that the battery voltage will not fluctuate as much as the load
changes, in fact it's so quick that I'm not even sure if it will be noticed.

I've been given a circuit diagram by a very helpful poster from another NG,
which will monitor the load on the heater. I've not investigated this, but
decided to keep it for a later date, then try it out and retro fit it to my
power box.

Regards

Colin Dawson
www.cjdawson.com


"Andrew Cockburn" wrote in message
-service-com...
You're right, I'll make the dew heater, then I have a reason to make the
master project :-)

Problem is, work is looking sucky for the next 3 weeks - lots of
travelling so no time to do anything at all astro related except bug you
all with my posts !

The only plus is that I will be spending a week in the states so might
get a chance to pick up some cheap astro bits or components for the dew
heater - I'll be in Silicon Valley, and they have electronics shops
there you just wouldn't believe ;-)

Andrew

Colin Dawson wrote:

Cool.

Rather than spending time thinking about your main power project, it

might
be worth getting the dew heater built up and running. I remember that

it
took me about a week to of evenings to get the main ring and K8004

running.
You could also put a power lead to your scope from this box, or do

something
similar to my new box that I'm working on. Then have a single plug into
your start's socket.

Once you've got the K8004 working properly, there shouldn't be a problem
moving the circuit into your master project once it's ready. ;-)


I've got next week off work, so hopefully I'll be able to get my power

box
finished. It's taken a little thinking out, but I've got a rough plan

for
how the box is going to fit together. Fingser crossed that it works.

Regards

Colin Dawson
www.cjdawson.com


"Andrew Cockburn" wrote in message
-service-com...

Got my starter so power is sorted for the time being :-)

Now I have time to think about the main power project since there hasn't
been a break in the clouds for days :-(

Andrew

Colin Dawson wrote:


"Chris Taylor" wrote in message
news:6unjc.10$96.0@newsfe1-win...


Hi Colin

I own 2 GOTO scopes and both have their own 1.2Ah batteries. I've not
noticed any difference between the beginning of the evenings battery's
performance (slewing speed or sound), or the end of the session on


either

of


them. I do spend more time tracking with the LX90 given that the LPI


get's

used. Nonetheless, I've not had the battery go flat, or appear to be
labouring on the LX yet and I've spent from 8pm to 2am observing. The

C
Cells are an expensive way to do things so I bought the Lead Acid

before
they could go flat. On the Celestron GOTO the batteries (AA's!) used

to

go

flat in a few hours and were a waste of time and money; lesson

learned.



hmm, you're lucky. I think it's partly because I'm such a pickky


little

blank (insert bad word of your own choice)
but I've noticed that about 1/2 way through the session my scope starts


to

sound a less perky than at the beginning of the session. It doesn't


seem

to affect the performance though, but I'm definatly not making it up.

I've just checked the Duracell web site, and they rekon that the LR14's


will

work for 11 hours at 0.5 amp current.




There's also no reason not to get a 7.2AH and I'd have probably bought


one

if the closest shop i could find with a solution (B&Q) had sold them.


The

other alternative was a 45 Minute journey to Maplin, or a few day wait


for

an internet purchase to arrive.



From the information that you've provided, I think that the only need

to

a

bigger battery it to help power more toys.
Can't have too many toys.

Regards

Colin Dawson
www.cjdawson.com