17 amps is not going to hang much gear on for very long
All batteries are rated in amp-hours. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH.
add up all your gear power usage and apply the above formula
Going through an inverter then back to 12 Volts will incur at least a 20% loss in efficiency. If you don't have a need for 240V then simply run the LX from the 12 Volt battery.
17 amps is not going to hang much gear on for very long
All batteries are rated in amp-hours. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH.
add up all your gear power usage and apply the above formula
it is a good rule of thumb to double the rated amp hours in sizing an appropriate battery
Mark,
Super Cheap Auto sell a 1200Amp 24Ah Jump starter for $129 and we have found this more than enough to run the LX90 for 3 or 4 sessions in a row and still have plenty in reserve, but an LX90 from memory only draws about 1.5amps at max. slew so power drain is minimal. As for your laptop I don't know but I reckon a seperate power supply would be the way to go.
I have a 17amp projecta brand {without inverter}power tank from kmart {hmm price cant remember maybe 80-90 bucks} from real field experiance it delivers enough power for my LX200 for a night no worries . Powering a LX scope with something else from the same source is advised against in some forums , i decided not to anywhy so its your risk . I orginally got a inverter to power a laptop but was worried about power spikes ect and safety aspects and got a Kerio adaptor from Dork Smith instead , now with just running the laptop from the projecta i get roughly 2-3hrs before the recharge led comes on and thats the same with a Orion dew zapper.If you decide to run a scope and laptop i doubt you would get more then 2 hrs even if the numbers suggest otherwise .I ended up getting a second battery {35amp golf buggy battery}for the laptop and dew heaters
I have a 35Ah battery and a 120Ah battery. I find the meade really sucks the juce slewing around with dew straps and whatever added. lasts me a nights viewing
Havent noted a drop in performance yet of the powertank with my LX with guidescope etc aboard but for more energy drawing devices like heaters its probarly more economical in the end purchasing a lead sealed battery {deep discharge type} or if the budget allows a gel battery instead of a powertank variety . Even with my 35 amp battery with 2 heaters running at max {got the adjustable kendrick type controller and heaters} id get no more then 6hrs, at half strength which is usally all thats needed it will cover all night.Powertanks are good and convenient but for the heavy stuff spend a bit more to get it right in the first place so you dont have to drive back from a dark spot because your power has let you down.
Bunnings or M10, 550 watt continuous running generator at $98 coupled with a good or very good surge buster or one of the new permanent magnet generators from scorpions (computer friendly) have a varience of 1% on 240 volts. too noisy?? about 60 dbA???
All batteries are rated in amp-hours. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH.
add up all your gear power usage and apply the above formula
Close but not quite. Battery ratings are usually given on a 20 hour discharge curve. Whilst a 20Ah battery will give 1 amp for 20 hours, you wont get 2 amps for 10 hours, or 4 amps for 5 hours. As the current drain increases the real amp hours available reduces.
Hi Mark, Why not 'KISS'? Just buy a large capacity 2nd car battery,(can get them 2nd hand from wreckers), install it in a convenient place & have the isolator wired up. Your laptop will happily run on one of the attached adjustable voltage converters. HTH. L.
ps. Davo, Could this be a petrol driven 240 volt alternator set that you're actually recommending? Cost of petrol,oil,maintenance,spare parts,exhaust gases & CONSTANT NOISE at a quiet observing night! Worse than the Meade SCT's....... L.
pps. & IMHO, Too many pieces of equipment needed for such a simple job.
I have been fiddling with different power supplies for almost 6 months, and I have come to the view that I will have to pony up the cash for a decent gel cell 100AH battery and battery box. I have had second hand batteries recommended to me, both car batteries and gel cells, and I have found that they are insufficiently reliable and do not always pump out 12v. The auto power packs are designed to start cars and provide cold cranking amps, not a consistent reliable supply of power. They do work, but I wonder about their longlivity. I know some people have had problems with the supercheapauto chinese models. You get what you pay for. Car batteries also have a limited life if they are deeply discharged. A decent 100AH gel cell will not leave much change from $300. The higher the AH the batter to avoid deep discharges. I would recommend this path rather than spend money on car batteries or power packs and the like. I have been told that most car batteries have about 45AH in them, although they don't list it on the side anymore. Those who have used them report that they have a limited life for astro use. Just my experiences.
I think you are probably right there. Some time ago I stumbled on a link from Cloudy Nights on this subject. This bloke had clearly done a lot of work on this subject not to mention a lot of money poured into power sources, many of which failed after a short time.
The gist of what he said was that absorbed gel mat (AGM) batteries are best when it comes to powering scopes and other accessories over long periods and are more cost effective over the long haul. Gel cells were second best.
****** things certainly aren't cheap though. Not much change out of $300.
Battery Power?
L.
L.
