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 Post subject: Portable power pack
PostPosted: Thu Oct 03, 2013 8:39 am 
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Joined: Mon Oct 12, 2009 6:47 pm
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Location: Bolton
Keith was asking me yesterday about a suitable replacement for his "power tank" battery, which no longer holds a charge. Coincidentally, only last month Bill had the same problem with his, and on dismantling it found that the internal battery was just a 12V 7Ah sealed lead-acid gel type, like this: http://cpc.farnell.com/leoch/lp12-7/battery-lead-acid-agm-12v-7ah/dp/BT0551103 But I'd suggest that a rated capacity of just 7 Amp-hours (which would degrade significantly in the cold temperatures of a winter's night) is too weedy for the job of running a telescope mount, camera and heating-tapes.
I often use a 17Ah battery, more like this: http://cpc.farnell.com/leoch/lp12-18/battery-lead-acid-agm-12v-18ah/dp/BT0551303 but if I'm powering a laptop too (via a DC-DC converter) then I use an old 45Ah car-battery.

If you want to make up your own power-pack and incorporate the vehicle "cigar-lighter" sockets, then you can easily get individual sockets http://cpc.farnell.com/_/cigar-lighter-skt/cigar-lighter-socket/dp/AR70643 or banks of three http://cpc.farnell.com/carpoint/0523402/3-way-socket-12v/dp/CP05729 to fit to your battery.

Incidentally, if you're using one of the SLA batteries then it's best to use a charger like this: http://cpc.farnell.com/_/mw12cb042uk-01e/charger-12v-lead-acid-420ma/dp/BT0445603 since a charger designed for "wet" car-batteries could overheat a discharged SLA with too much initial current.


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 Post subject: Re: Portable power pack
PostPosted: Thu Oct 03, 2013 9:50 am 
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Joined: Sat Feb 25, 2012 10:57 am
Posts: 101
Great timing Ross as both of my power packs are struggling at the moment. I have managed to get everything else converted over to mains power except for my dew heaters which do deplete the power packs after a few hours.

I was wondering about running these of the mains also but the recommended (Kendrick) converter is quite expensive and i am not sure if a cheaper block or computer type ad.apter would do the job. http://www.kendrickastro.com/astro/dew_laptopheaters.html

I should be grateful of any advice please.

Regards


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 Post subject: Re: non-portable power
PostPosted: Thu Oct 03, 2013 10:43 am 
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Joined: Mon Oct 12, 2009 6:47 pm
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Location: Bolton
First a word of warning - don't be tempted to take any mains appliances (including DC adapters) designed for indoor use out into the garden where they will get soaked in dew!
But if you still want to take this (potentially shocking) approach, then at least keep all your mains bits in a waterproof box, like this DriBox: http://cpc.farnell.com/festive-lights/fl-1859-285/dri-box-285-ip55-weatherproof-black/dp/EN8256503 and make sure that you have an appropriate RCD protection device in the mains feed.

Now regarding the dew-heater tapes (and any other 12V DC kit), all you need is a power unit capable of a few Amps output - perhaps one from this range: http://www.ebay.co.uk/itm/UK-Stock-DC-12V-Universal-Regulated-Switching-Power-Supply-for-LED-Strip-CCTV-/161081134308. Keep this PSU indoors, and just feed its low-voltage output down to your 'scope (using decent thick wires).

And we've found that these low-cost PWM controllers are ideal for regulating the current to dew-heaters: http://www.ebay.co.uk/itm/LED-Dimmer-Controller-Brightness-Adjust-12V-For-5050-3528-LED-Light-Strips-UK-/400582168358 - in fact we've got one on the BBT.


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 Post subject: Re: Portable power pack
PostPosted: Thu Oct 03, 2013 1:35 pm 
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Joined: Sat Feb 25, 2012 10:57 am
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Thanks Ross and sound advice regarding the external power. I wrap everything and put plugs and connections etc inside luncheon type boxes with lids fitted and keep everything off the ground. The cables inevitably get dewed up but everything else is bone dry. My laptop is safely inside a shed.

Regards


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