How Long Can a Car Battery Power a Fan
#1 
Posted 30 September 2011 - 01:28 PM
I am finishing my 12" F/7 which will have dew heaters strips for the main mirror, secondary, eyepieces, likely two at a time for the binoviewer, telrad + two fans. That's 5 strips and two fans. Since I have no experience with dew heaters, I am wondering, if used of a car battery, how long would this last, would it exhaust the battery (would not want to have to walk 70km back to Stockholm). Is it necessary to buy a separate power source for this set up?
Thanks!
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#2 Achernar
Posted 30 September 2011 - 01:49 PM
Do not use your car battery, that can result in freezing to death or at the very least one very unpleasant walk until you find help. Car batteries will be run down fairly rapidly by the sort of load a few heaters and a cooling fan would create, and even worse, using a car battery to power them will ruin your car's battery. You might get away with it, but if the battery is getting old you might get stuck somewhere when it's -40 degrees F. They are meant only to supply lots of power for brief periods, but there is an alternative or rather two. A 12-volt power tank is one, and they are similiar to the "booster" packs used to start cars with weak or dead batteries. Or you can simply use a 12-volt "Gel-Cell" or deep-cycle battery to power your heaters. I use gel-cell batteries used for alarm and video survielliance systems to power my cooling fan, dew heaters and digital setting circles. I use a DewBuster controller for the heaters, it allows exact control of how much heat you are applying and greatly extends how long you can observe on a full charge. It will even let you know when it's time to recharge the battery. A 12-volt, 18 Amp-hour gel-cell battery runs everything all night, and if I connect them to a charger when I'm done, the battery will be recharged in time for the next night. There is no electrolyte to spill and the batteries can be placed out of the way without interfering with the telescope's movements. If you use a deep-cycle marine battery, you can run the heaters, cooling fan, even a lap top computer all night long even in the cold. Whichever battery you choose, you need to get the right charger for it and charge it properly, but it will ensure you'll never have to worry about running down the battery in your car and facing a very bad situation in the deadly cold of a winter night.
You can buy the power tanks from any number of sources, the gel-cell batteries from an battery supplier or electronic supply store, and the deep-cycle marine battery from a battery supply store or a business that caters to boaters and mariners. You can get these batteries in a wide range of Amp-hour ratings, I would use at least a 12-Amp hour battery if not a 17 or 18-Amp-hour battery. Deeply discharging a battery repeatedly ruins it, so you will want to make sure the battery will not be over taxed, especially in the cold where batteries lose power.
Taras
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#3 gaidash
Posted 30 September 2011 - 02:54 PM
Great, thanks for the reply! I already found online several types of gel batteries in a chain store around here in Sweden
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#4 Don W
Posted 01 October 2011 - 09:15 AM
You can run them all night. The question is, will you have enough power to start your car when you're done observing. I strongly recommend a separate battery to run your astro gear.
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How Long Can a Car Battery Power a Fan
Source: https://www.cloudynights.com/topic/344630-how-long-can-i-run-heatersfans-on-a-car-battery/