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Power supply recommendations

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#1 MHummel

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Posted 18 August 2019 - 12:43 PM

My son and I seem to have been bit by the astronomy bug. The last month or so since we got our Onesky has been quite an adventure including getting another scope from a neighbor (Tasco 130) price was right and couldn't pass on it even though I sill haven't figured how to collimate it yet but its working okay for him.

For now we are enjoying planetary viewing since the light pollution here in Stevens, Pa seems to be keeping dimmer objects out of view. We have been using phone holders to take pictures of Jupiter and Saturn with okay results but would like to try to get some better pictures and increase our experience with a Cmos camera and a lap top. Obviously on nights away we would need to power the computer and camera. 

The equipment I have so far is just the laptop, however I am looking at a ZWO ASI120MC-S camera, other than that I'd like to keep it pretty basic to learn stacking photos which would be done at home. I'd like to be able to power them for 2-4 hours, probably less at this point. For now I'm not running any electronic goto or tracking bases so its strictly planetary, with quick bursts while they are in frame. 

My thoughts at this time are using a led acid or possibly a deep cycle 12v battery and a converter. For now I don't care about the weight, just looking for advice on what you would recommend for power supply just to get us on our feet to see where this goes. 

Thanks,

Mark

 



#2 sg6

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Posted 18 August 2019 - 01:26 PM

Ignoring the laptop - what is it precisely that you want to do ?

Astrophotography is a bit "strange", in that you take 60 images of an object each say 60m seconds long and stack (add) them to get a result and the object/object is moving. And not moving in a straight line either.

 

In all this the sensor taking the images gets warm/hot and produces thermal noise that adds noise and crud to the images.

 

From what you have described the other difference is no "lens" on the camera, the scope is the lens. Phones etc have an inbuilt lens that hasnto be accounted for - I guess you had an eyepiece in then the phone?

 

Requirements for AP are simple: Good equitorial mount (very good is better), small fast good quality scope, camera of some variety. Other bits like nosepiece and T-ring, maybe a flattener.

 

Before any more the 120 has a small sensor, so may fail in areas.

 

Scope: Many decide to run off and buy a good big visual scope. Usually with a long focal length for big images (seem to be thinking magnification for some reason). The William Optics Redcat is a good AP scope. It is 51mm diameter, f/4.9m so about 250mm focal length. Should fit easily in a coat pocket. So not a big long focal length scope. They are just (generally) wrong.

 

So the "power". For AP you are powering the mount and the camera, and it reads also the laptop.

Could use a DSLR - most start with that as they have one around and the sensor is big(ish).

 

Back to the opening question: What is it that you want to do?



#3 Phil Sherman

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Posted 22 August 2019 - 05:56 AM

Without the laptop, a 17-18ah agm lead acid battery should provide you with the power you'll need. If you need voltages other than 12v, use dc-dc buck or boost regulators. Better regulated 12v can be obtained by using a buck/boost regulator. If you have to go the ac route in the field, the newer pure sine wave inverters using a lithium battery are the best approach. They're not cheap.

 

For a few hour session, the laptop's internal battery should suffice. If you have to supplement it with external power, a separate 17ah battery and a dc (automobile) power supply for it should give you enough power. Converting 12v dc to 120v ac then using a plug in power supply involves two voltage conversions and wastes the limited power available from a battery.

 

A 30ah lithium battery is an alternative to the sla batteries. It'll be a lot lighter than the sla ones but a lot more expensive. The internal construction of these (3 vs 4 cells in series) may make use of a 12v buck/boost regulator mandatory. A 4 cell in series battery actually has 1/3 more power available than a 3 cell if the batteries have the same ah rating.

 

If you have a recent Canon dslr, you can use its movie mode for planetary imaging. "Images Plus" astro imaging software has a camera control module that easily does this and can process the captured files for stacking. The end result of this can then be processed by the software's image processing facilities.




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