Thoughts on which imaging rigs to concentrate on

[RichLD]

Gina, please excuse me if I sound really thick here, but is that ice on your sensor?

[Gina]

I don't know what it is but I did accidentally partly unscrew the camera sensor chamber taking it off a T2 adapter and may have crushed the desiccant tablets when I tightened it up again.  I have seen the odd bit on the sensor and had to shake it off.  I've only had this much detritus on the sensor since I put the camera on the Esprit scope.  I'll have to take it off and inspect it.  I've previously had the temperature lower and not seen this.

[ChrisLX200]

Yes that is a typical icing pattern...

ChrisH

[Gina]

Thank you Chris   Maybe I didn't get the camera tightened up enough and it's not sealed so the desiccant tablets have "worn out"   I'll see it I can see ice when it's off the scope and powered up with cooling on.  If so I guess I'll have to open it up and change the tablets.

[Gina]

Just looked at the data I collected overnight and 45 out of 100 150s subs look as if they might be alright but at that point something went wrong with the tracking and the rest were spoilt.  There are also 7 subs of 120s.

[Gina]

I have brought the camera and laptop indoors to test the camera for frosting up.  While I was out in the observatory I checked the supply voltage at the power distribution box on the scope and it was down to 11.6v rising to just over 12v once camera temperature set-point had bee reached.  I have volt drop all over the place.  At PSU its 13.8v, at battery it's 13.3v with another volt or so dropped in the cable from the warm room to the scope/camera.  No wonder my cooling is not as good as others have reported.  I think I'll have to do something about this.

The cable from battery to camera is about 4 or 5m and quoted "Resistance per metre at 20°c 0.0185 ohms" so if 5m that's 0.09 ohms.  Or near enough a tenth of an ohm.  That should be 0.4v at 4A not over a volt.  OK there's some drop in the earth cable but that's BIG stuff as used for house electrical earthing.  Connections are by 6.3mm spade terminals and XLR connector plus standard car battery screw clamp terminals.  These are supposed to be highly reliable for use in damp conditions.  BUT there would appear to be excess volt drop somewhere.

I guess I need to test further.  The cable in question only feeds the distribution box on the camera/scope - the mount is fed through a separate cable of the same size.  The only load I had on this morning was the camera cooler and EFW2 filter wheel (which only takes power when moving and very little then).

[ringz]

Gina,

Go into the device manager, click on ports and right click on the com port you want to change.

click on properties then port setting tab and then advanced.

that will show you the port number allocated, you can change it to a port number that will work for you, ignore any already in use messages

then reboot.

 

[SilverAstro]

It has been a long time since I used them, so something may have changed

XLR for power supply ? They have very small round pins so contact area is going to be very small, normally used for audio /signal application not power routing.

Can you measure the volts drop either side of your various connectors and when were the XLRs ( and other non-screwed down ones) moved to scrape off corrosion .

Edited September 17, 2016 by SilverAstro

[SilverAstro]

Better still, a loop-resistance check ! 4a isnt all that much

 

[Gina]

These are the big XLR connectors with 10A rating.  The XLR connection gets undone and remade every time I set up the rig - last night, just before the imaging run.  The pins and sockets are clean - I checked.  The connector also has a screw ring to clamp the parts together as well as the plug an socket being very tight and needing considerable force to connect and disconnect.

The pair of spade terminals have not been touched for some time.

I'll check all connections either side and see if I can find where the problem is.  Also the current wasn't 4A but 2A.  And there isn't a problem anyway!  The cooling electronics maintains constant power regardless of voltage by increasing the current at lower voltage.

I now have the camera on cooling test but ATM I can only get it down to -14°C due to the ambient temperature.  No sign of frosting or even dewing at this temperature.  I have the camera powered from a bench PSU with variable voltage and digital voltage and current displays.  When the voltage was lower the current was higher and vice versa so the power remains the same.  That means that the supply voltage doesn't affect the cooling power after all!

[Davey-T]

I use these connectors, not sure if the contacts are any better than XLR ones though.

I'm sure you know that DC doesn't travel as well as AC, and needs bigger cables, so I've run 240v to the obsy and reduce it all there.

My wifes garden railway has an 18v AC supply for long distance distribution.

http://www.maplin.co.uk/p/neutrik-powercon-20a-3-pole-mains-in-line-female-n54gb

Dave

[Gina]

Yes, I've run 240v AC mains to the observatory and convert to 13.8v DC there. 

As for AC v DC, it's the volts and amps that matter not whether it's AC or DC.  (From an Electronics and Electrical Engineering graduate with a career to match).

Edited September 17, 2016 by Gina

[SilverAstro]

25 minutes ago, Gina said:

These are the big XLR connectors with 10A rating.  

Also the current wasn't 4A but 2A.  And there isn't a problem anyway!  The cooling electronics maintains constant power regardless of voltage by increasing the current at lower voltage.

Oh OK !

Oh um,

" No wonder my cooling is not as good as others have reported.  I think I'll have to do something about this.
That should be 0.4v at 4A not over a volt."

I'm sure you will overcome

 

 

[Gina]

I shall certainly be investigating the connections - I don't like too much resistance in my power lines!

[Gina]

The camera sensor now has condensation around the edge which would become frost at lower temperatures.  The end cap was definitely not fully closed and damp has got in so I will need to change the desiccant tablets and also clean out some bits.  I've opened the camera sensor chamber and see that one tablet was slightly damaged and the stick-on cushion has been displaced.  I found some of the glue on the cover and a few tiny bits in the chamber which I shall blow out with a puffer.  The weather is dry, warm and sunny so the humidity indoors should be fairly low.

I think not having anything to stop the cap unscrewing when trying to unscrew the camera from whatever it was screwed on to, is a design fault so I can't mark this camera as 10 out of 10.  This problem has been mentioned before and maybe ZWO will change it in their next version of the camera.  The end cap is only a few mm wide so it's not really practical to hold this to detach the camera from the rest of the optical system.  The surface is smooth too.  If it had some lugs or even a serrated surface it might be possible to grip it but as it is it's virtually impossible.

That then is the first fault I've found.  Anyone using the F-F gender changer adapter may be able to get something in to hold that and unscrew it from the rest of the rig but it's only 11mm wide so you can't get fingers in - it would have to be some sort of tool.  If using the ZWO mini FW even that isn't an option as the adapter isn't used.

Edited September 17, 2016 by Gina

[Gina]

The replacement desiccant tablets and rubber pads had a moisture indicator card together with a desiccant bag in the sealed packet but the dot which is supposed to be blue is white.  Wording says warning if the blue dot has gone completely pink - well not quite - not like the rectangular pink panel so maybe the tablets are alright.  Anyway, I have now put them in the camera and screwed the cap on as tight as I can.  "Proof of the pudding" will come tonight when I get the temperature to -30°C!  FLO might be getting an email...

I've also been back out and checked connections but my DMM only goes down to tenths of ohms.  I found the spade connector a bit loose so I've tightened it up.  That could have been where the problem was - again I'll find out when I get the camera back outside and connected up.

[RichLD]

Oh dear, hope you've found the issue and that everything goes well tonight! 

[Gina]

Thank you   I have some small colour-change desiccant bags and might be able to fit two of them in the sensor chamber if the tablets don't work.  I imagine these tablets are supposed to be better that the standard silica gel.

Edited September 17, 2016 by Gina

[SilverAstro]

23 minutes ago, Gina said:

The replacement desiccant tablets

and the ones already in the chamber : there was discussion on the forum somewhere where ice was suspected and much research led to the conclusion that they were Silica Gel based, dont want to be teaching eggs, I'm sure you know that  low oven, a tad over 100C (not too much) may be quicker than getting fresh through the post ie. I second Rich's best wishes for tonight, oh hang on

you are typing as I am, standard silica gel as we used to know it had cobalt as the indicator till you-know-who banned it, as far as I know and the ref. discuss suggested that it was still silica gel.

I will now try to find that other discussion for you   > > 

 

Edited September 17, 2016 by SilverAstro

[SilverAstro]

It was for Atik cams tho' I 'spect it is the same stuff ? Here is FLO response in that topic confirming the bake-off winner baking method  

https://stargazerslounge.com/topic/276540-atik-414ex-artefacts/?do=findComment&comment=3029866

[Gina]

Thanks

[Gina]

The camera is now running at -24°C and no sign of anything wrong - just taken 100 flats with gain of 500 and 0.03s exposure with Ha 3nm filter ready for an imaging run of Crescent and Soap Bubble later (clouds permitting). 

Here's a single flat sub.

And histogram stretched from black to white.

Edited September 17, 2016 by Gina

[Gina]

Just been out and covered the scope and now taking 100 Bias frames.

[Gina]

Bias frames done and now taking darks for 120s g500 and t-24.  Here's a couple of single frames just resized.

Edited September 17, 2016 by Gina

[ChrisLX200]

The Soap Bubble is going to be really difficult with the Full Moon up Gina! The 3nM filter is a great asset on nights like this but it's no magic wand

ChrisH