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Old May 1st 04, 10:22 AM
Andrew Cockburn
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I saw that post as well, and came to the same conclusion - a high
frequency PWM design should give a roughly constant load that won't
trouble the scope at all, so I am sticking with your design and planning
for one big battery rather than 2 separate ones. Same should be true of
the laptop inverter - I assume that it will be working roughly at
50hz, which again is near enough a constant load, especially when you
factor in the smoothing effect of the battery. Worst case I can add a
regulator to the scope supply.

Andrew

Colin Dawson wrote:
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