Making a Leisure battery a safe external power source

[PESKYWAABBIT]

Right guys so i'm in need of some power in the fields as I'm restricted to just my houses courtyard. I have been told to look at leisure batteries but what other equipment is needed in order to make it into a safe power source for external use. I'm not great with electrical systems but what would be the best solution for me?

The things I need to power from this would be a Laptop and a HEQ5 Pro mount.

Thanks!

 

[happy-kat]

How many hours of continuous use will the battery be expected to run? Any dew shields?

So you can with out the size of what you need.

[PESKYWAABBIT]

1 minute ago, happy-kat said:

How many hours of continuous use will the battery be expected to run? Any dew shields?

Currently I run the mount for about 4 hours, without dew shields and just a laptop. So far I'm not long enough for dew to start build up on my optics. Maybe that's a fluke of where I'm living though. When I'm out in the field  of a dark spot it may be different but currently req's are just for my mount and a lappy. 

[carastro]

You'll need an invertor for the laptop.  

I normally put all my electrics in a large plastic box when I am at Astro camps it keeps them off the damp ground and if it gets really damp I sometimes put a cover over the box which has a cut out for cables to pass through under the lid.

Carole 

 

[jambouk]

There are plenty of websites and blogs on this kind of thing. You need to have a read of them and decide if you are happy to proceed and confident in your ability to be able to put an in-line fuse in the circuit, check and re-check the polarity and do some basic soldering (as you may want to change the types of terminals used).

If not, then either get someone else to do it, or buy a commercially available one.

You'll need to so some maths to work out how much "power" you need to run your kit. You need to list everything which will need powering, work out how much "power" each of these items need per hour of operation, and then work out how many hours you need the kit to operate for before a re-charge of the battery. Then jiggle the units around and end up with "amp hours". So at the end of this you'll say something like "I need 10 amp hours", but then I would multiply this by at least 4; so 40 amp hours. Then look online and see how heavy a 40 amp hour battery weighs; find something of equal weight at home and see how heavy it feels and think about how you are going to lug it around - if it doesn't feel very heavy, go up a few increments (52amp hours, 60 amp hours, 72 amp hours etc) and see how these weights feel. You'll never regret having a battery that has too much capacity assuming you are able to lug it around OK.

If you are on a tight budget and happy to go down the DIY option, and assuming your power requirements are under 20 amp hours or so, I'd say get hold of an old car battery from a friendly garage (get one with a resting voltage of >12.4v or so) and give the garage £5 which is the same as the scrap man gives them, but pick one which has a capacity of 4x your requirements. There are lots of nay-sayers about old car batteries, but they work a treat if you get hold of a good one and give it some TLC and pack it up nicely in box and insulate it with polystyrene and re-charge it each time you've used it and don't use more than say 25% of its capacity. You'll need a trickle charger like this one (https://www.amazon.co.uk/Streetwize-Motorcycle-Automatic-Trickle-Batteries/dp/B0012U5BO2/ref=sr_1_10?ie=UTF8&qid=1491986861&sr=8-10&keywords=trickle+charger+12v) which you will also need for the deep cycle battery. Car batteries tend not to tolerate serial deep discharges well and over time the battery furs up inside and over the years will carry less and less capacity, but if you avoid discharges of more than 25% and re-charge each time you'll get several years of service from one.

If you have more dosh and are happy with the DIY option, get a dedicated deep cycle battery which are designed to tolerate you using more of the capacity of the battery, but you won't get one for £5; I suspect it will be >£60.

Else, get something ready made, but these generally cost a lot more and you are unlikely to get a large capacity battery this way for under £200.

So, you need to do a bit more thinking about your skills and desire to tinker, versus the ease of just paying out a much larger sum and having less hassle. You also need to think if you go down the DIY route if you are happy with the car battery option or will be swayed by the nay-sayers and get a deep cycle battery at greater expense.

James

[jambouk]

To run the laptop, either use something like this: http://www.ebay.co.uk/itm/like/170945596136?chn=ps&adgroupid=39613511478&rlsatarget=aud-295856145004%3Apla-279121811481&abcId=923836&adtype=pla&merchantid=114919488&poi=&googleloc=9046404&device=c&campaignid=737386489&crdt=0 (I use a similar version, or something like this and use the standard three pin plug to charge your laptop:
https://www.amazon.co.uk/d/Car-Accessories/BESTEK-Power-Inverter-Adapter-Charging/B00RV69O0I/ref=sr_1_14?ie=UTF8&qid=1491988083&sr=8-14&keywords=12v+dc+to+ac

James

 

[bottletopburly]

This is a link to sgl members  marci website  https://dirtyastro.com/2016/11/26/project-battbox-diy-powertank/ may be of use

[cjdawson]

You don't need an inverter to power a laptop from a 12v battery.

There is an alternative method that you can use here's a couple of links to the power supplies that I use for my laptops.

I have one of these for my MacBook Pro

http://www.coywood.co.uk/apple-macbook-pro-in-car-charger-85w-magsafe2-dc-adapter-14837-p.asp?gclid=CjwKEAjwoLfHBRD_jLW93remyAQSJABIygGpL_b4umnG1m5QE52KKI3k3Vi48Egna7BXdRiqfWSw1xoC2U3w_wcB

 

I have one of these for my HP Laptop

http://www.coywood.co.uk/hp-pavilion-15-car-charger-for-90w-65w-45w-15572-p.asp

 

there are plenty of other available from this site too.

http://www.coywood.co.uk/car-chargers-1318-c.asp

 

These are much better and safer than using an inverter to power the laptop.  For a start no need to 240v.  The second thing is that the DC-DC conversion is much more efficient than going via AC.

[michael.h.f.wilkinson]

+1 for using a car-charger for the laptop. I do the same and it avoids using higher voltages which is never a good thing outside, unless proper safety measures are taken. There are some universal ones that can provide almost any voltage you need, for almost any connector you can think of. This means all you really need is a 12V battery, and a couple of standard cigarette-lighter style sockets. Any 12V leisure battery should be perfectly safe outside, you cannot electrocute yourself with 12 V. If you can install it into some plastic crate, with suitable connectors on the outside that is ideal.

[cjdawson]

Just one more thing that I have found with 12 (input) laptop power supplies.  Some of them can be very tempremental as to the range of voltages that they work over.  The ones I linked about, I've tested in real life so know that they work just fin with a battery to power the laptop scenario.  Some other that I had in the past, worked when the input was from a running car engine, but would quickly turn off when the engine isn't running, or when connected to a deep cycle battery.  This was one of the reasons why I went down the whole "keep a laptop away from my scope" approach for a long time.

[jambouk]

And if you have the DIY ability and are able to solder, I'd change the standard cigarette-lighter style socket on both your leads and on your battery end to the screw-locking ones to minimise the risk of disconnection:

 

[JOC]

jambouk - that's a neat connector, but if you get tangled up to the stage of risking disconnection, isn't it better that the leads disconnect rather than potentially pulling over a whole telescope/tripod assembly because they can't disconnect?

[jambouk]

6 hours ago, JOC said:

jambouk - that's a neat connector, but if you get tangled up to the stage of risking disconnection, isn't it better that the leads disconnect rather than potentially pulling over a whole telescope/tripod assembly because they can't disconnect?

 

Well this is a risk assessment one needs to make. For me, the risk of a transient power outage from the dodgy fag lighter connector is greater. You can get versions which have no screw collar, but still provide a better fit than the old fashioned cigarette lighter type. I'm just offering options and my opinion. I'm also very lucky that my mate who I more into practical astronomy than me and who lives in the next street is also very skilled at electronics and soldering... a handy mate to have

[JOC]

I am just a little wary of a connection that won't disconnect as I have already in just a few uses had my system rotate to a point where it has started to drag the power pack towards the telescope, the only thing that saved things from going more pear shaped than they were about to was the connector pulling apart - hence my concern.

[jambouk]

That's fine. I know there is enough slack in my leads so no tension could be placed on any connection. As I say, we all have individual set ups, and different expectations/requirement.

James