# power pack Time for field power but help needed.

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Hi all,

for the time being while away from home I have been using my car's own battery to power my setup but last time out I noticed some curious happenings & only recently have put it down to what I think is a power issue.

I had setup my equipment as usual & my scope seemed to be tracking just lovely. I got a bit chilly & decided to sit in my car for a while to warm up with the engine running & heater on.

After some time and slightly warmer I switched the ignition off, left my car & took a peek through my scope, it was way off target. At this time I didn't associate this error with a power issue.

Once again, started and achieved alignment, scope was tracking beautifully for a long while, again, after getting cold again I did the same as before and got in my car, started it up and sat there to get warm. Some time passed.

Upon checking the scope again, again it was off target. By this time the sky was getting light & I didn't want to bother starting a new alignment procedure so I packed up.

It wasn't really until I got home that it dawned on me that the process of me starting my car whilst my equipment was connected directly to the battery could have been the cause for the tracking glitches.

I understand that the process of starting a car alters the voltage in the battery and I am wondering if this either drop off or surge in voltage disrupted the tracking of my scope. Could this be the case?

So anyway, I have decided to build a field power pack but just want to clarify some details with you brainy lot.

CPC Mount

12V x 1.5A = 18W (i'll allow 20W) info from: http://www.rothervalleyoptics.co.uk/celestron-cpc-925-xlt-telescope.html

Laptop

INPUT 19V x 2.37A = 45W

OUTPUT 14.8V x 2520MAH = 37.3WH

estimate of power need through normal 6hr battery life (( 45 x ( 37.3 / 45 )) / 6 ) = 6.2W

DSLR

INPUT 8V x 3A = 24W

OUTPUT 7.2V x 1040MAH = 7.49WH

estimate of power need through normal 4hr battery life (( 24 x ( 7.49 / 24 )) / 4 ) = 1.9W

DEW HEATERS (ASTROZAP)

1 x SCT9.25 12V x 1.3A = 15.6W

2 x 1.25" 12V x 0.25A each = 6W total

1 x 2" 12V x 0.35A = 4.2W

So far I calculate a total of 54W per hour or allowing for a 12 hour stint 648W total

I was also wondering if I need to factor in my ZWOASI224MC camera which runs via USB3 on my laptop & also my Flat Panel Maker, which runs via regular USB power?

That said, I have been considering these batteries: https://www.amazon.co.uk/dp/B00XNC7KZ0

which are a pair of 12v 33AH AGM Scooter batteries which should allow a total of 792W which should cover my needs.

Do all my above calculations look OK?

Do I need to place any type of voltage regulator between the batteries and the outlet?

Regards..,

Kirk

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Starting the car can drop the battery voltage by quite a large amount, a quick check with a voltmeter will tell you how much or look to see if an internal light dims.

Alan

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Bad bad idea to start car While all your kit is connected....I am amazed it's all still working, as well as a drop to about 9 or 10 volts across the battery when you start, which will stop your kit in its tracks, when it has first started there can be a big surge to the battery....

i would seriously think again before you do that, it sounds like you have been very lucky...

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20 minutes ago, LightBucket said:

Bad bad idea to start car While all your kit is connected....I am amazed it's all still working, as well as a drop to about 9 or 10 volts across the battery when you start, which will stop your kit in its tracks, when it has first started there can be a big surge to the battery....

i would seriously think again before you do that, it sounds like you have been very lucky...

Yep, realise that now.

any tips on my proposed build?

Edited by 1CM69
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Can't really help there as I don't Image out in the field, I have a pier set up in my garden, so use a bench supply, to a power hub which supplies all my kit..

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You can't really go wrong with a decent leisure battery - designed to give smooth power for a long time and not mind being reasonably deeply discharged. 100ah for about £65. Any caravan place or chandlery sell them.

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14 minutes ago, Skipper Billy said:

You can't really go wrong with a decent leisure battery - designed to give smooth power for a long time and not mind being reasonably deeply discharged. 100ah for about £65. Any caravan place or chandlery sell them.

Thanks for the tip

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