how long will my battery power me for?

I need some of you egg heads to help me work out how long my battery can power my rig.

I have this powertank: www.maplin.co.uk/Module.aspx?ModuleNo=49...urce=1&DOY=10m12

it outputs 12v and has a 17amp battery.

My mount is a Celestron CG-5 GoTo, is 12v and im unsure of any more of its requirements.

Im also going to add a Dew-Not 6" heat strip which is 12v and requires .47a and 5.6 watt.

I dont know how to go about working out how long my power tank can power all of that. can you guys please help me?

Fintan,

The key thing here is your battery is not 17amp but 17amp/hours. Meaning it can deliver 17amps for 1 hour (or of course 1 amp for 17hours) My recollection is that the CG5 draws .76amps slewing and around .45amps just tracking. Given your heater draws close to .5 amps that makes and average draw of about 1 amp. Meaning it should last in theory for 17 hours. BUT theory and fact can be different. These batteries rarely charge to their full capacity. Either way that should keep you going for a whole night on a full charge.

Dont forget that Amp/Hour rating dramatically reduces at temperatures hovering around zero.

You can find a "de-rating curve" to measure this.

Dont know where.

Peter.

Thanks guys. extreemly helpful and knowledgeable as always Dave, thanks a mil, exactly what I needed to know. I live with an electirican, and he couldnt help me work it out!

Because they never hold their full charge, I always keep in mind an error of 20% when planning long sessions using batteries/portable power supplies. That way, you're pretty sure to have a couple hours with perhaps time to spare before running out. On nights like last night, I reckon you could almost cut the supply by 1/3rd.