Portable power for laptops in the field

Irish stargazer (John) · #1 13-01-2013, 08:37 AM

After almost 18 months without long exposure imaging I am very keen to get started again. When I was imaging at The Mornington Pensinula Astronomical Society site they had electricity conveniently at each observing platform so there was no need for batteries to run the netbook for guiding.
I have seen devices at Officeworks from Targus that can be used to power a laptop from a car lighter socket (so I presume a portable powerpack might work also). They look like big USB type adapters but are quire small and neat. The spec looks like they draw 10amps so the typical powerpack wont last long. Any idea what a typical 240V invertor would pull?
Any recommendatons on a portable power set up that would give 6-8 hours of use?

LewisM · #2 13-01-2013, 09:30 AM

Good question - I'd like to know too, as I plan a couple imaging excursions soon.

The powerpack I bought will typically run the mount alone for 8 hours on a full charge. It has 2 USB power sockets on the back also. I am sure connecting the laptop would decimate the stored charge quickly though

I have a 10 metre long cigarette lighter cable that could power the mount at least from the car battery, but then to figure out a safe way to do the laptop.

Astro_Bot · #3 13-01-2013, 10:00 AM

Do a search in eBay for "Laptop Car Charger XXXXX" where XXXXX is the model number of your laptop.

I bought mine for (I think) $25 delivered from these guys:
http://stores.ebay.com.au/ECR-COMPUTERS
(It looks like their online store is down for maintenance at the moment).

For a battery pack, I recommend a deep cycle battery in battery box - cost varies with capacity and battery quality (all are not created equal).

My laptop draws ~35W typically in use (idles at 19W) so I spec'd mine for a 3A draw at 12V (for the laptop, and, in my case, aslo 1A average for the mount). If yours is the same, then 3 x 8 hours = 24 Ah .... BUT .... you should never draw down below 50% charge to maintain battery life, and the battery will lose a little capacity with age, and performance will vary with temperature and draw rate, so, I (and others) recommend a 30% safety margin on top of everything else. That comes to 24Ah x 2 x 1.3 = 62.4 Ah. I recommend you measure your laptop power draw and adjust figures accordingly.

Allan_L (Allan) · #4 13-01-2013, 10:23 AM

Hi John.
I bought a Waeco Deep Cycle Battery. 33aH
It cost me $330 but I have seen them cheaper since.
It is designed to power a fridge continually for long periods, so is ideal to power a laptop for imaging purposes.

I have powered my laptop all night with a 150watt PURE SINE WAVE inverter and just plug the normal 240v plug into that.
(Don't get a cheaper modified sine wave inverter for sensitive electronics)

But if you can get a specific DC - DC power converter (to change from 12 volt to whatever voltage your laptop requires, with its correct plug type), that sounds like a cheaper option than PS Inverter.

naskies (Dave) · #5 13-01-2013, 12:22 PM

Using a 240V inverter is less efficient than straight DC-DC conversion, plus there's the extra safety concerns - especially since a lot of the cheaper equipment isn't rated for outdoor use in the dew.

Have a look at your laptop's power pack and see what the output voltage is (probably somewhere between 15-24V for most laptops, or less for netbooks). I think the laptop car supplies you're talking about are similar to this one from Jaycar (what I use)? The 150W rating is the maximum power consumption - if your laptop draws less, it'll use less.

Are you also going to be needing power for dew heaters, USB hubs (more reliable externally powered), cameras, mount etc? I run everything - mount, cameras, hub, Macbook, dew heaters, etc - off a single 110AH battery. During warmer months it can supply enough power for two consecutive nights, but in winter it'll start alarming low voltage half way through the second night.

Aussie Batteries & Solar currently have a deal going for a 120AH battery, only $289. Several people on IIS (and that I know of off forum) have happily purchased from these guys - including myself. They also have a kit including the 120 AH battery, 120W solar panel, regulator, etc for $649.

By the way, 100+ AH batteries are *HEAVY* (30 kg+) and somewhat difficult to move because of their shape. If that is going to be a problem, you can buy multiple 40-60 AH batteries and run them in parallel.

You'll also want a charger that supplies around 10-30% capacity of the battery, i.e. a 120 AH battery should have between a 12A to 36A smart charger (3 or more stages). If you'll be charging it via a generator in the future, you'll probably want one towards the higher end so it doesn't take too long.

Irish stargazer (John) · #6 13-01-2013, 12:27 PM

Quote:

Originally Posted by Allan_L

Hi John.
I bought a Waeco Deep Cycle Battery. 33aH
It cost me $330 but I have seen them cheaper since.
It is designed to power a fridge continually for long periods, so is ideal to power a laptop for imaging purposes.

I have powered my laptop all night with a 150watt PURE SINE WAVE inverter and just plug the normal 240v plug into that.
(Don't get a cheaper modified sine wave inverter for sensitive electronics)

But if you can get a specific DC - DC power converter (to change from 12 volt to whatever voltage your laptop requires, with its correct plug type), that sounds like a cheaper option than PS Inverter.

Thanks Guys

I have seen the Waeco units used to power a big Dob with heaters, fans and Argo Navis for several nights before. One of these units is on my hit list. What brand of inverter as you using Allan?
A netbook wont pull as much power as a full laptop so 33AH should be adequate (I think)

Astro_Bot · #7 13-01-2013, 12:35 PM

Quote:

Originally Posted by Irish stargazer

A netbook wont pull as much power as a full laptop so 33AH should be adequate (I think)

Maybe, but ... "measure twice, cut once". You can get a plug-in digital power meter from JayCar for ~$20.

hotspur (Chris) · #8 13-01-2013, 12:45 PM

I have a 97 amp hour battery and 120 watt solar panels,and a good inverter-make sure you get a very good sine wave inverter,it does not have to be a huge one for a laptop-around $150-$200 will get a good on for your needs-and power up camera batteries as well.

The battery I got was second hand,the 120 watt panels from ebay-around $225-but make sure you go back on to ebay and buy a regulator-I got mine for $110-its a 'Mason' brand I think-its important not to rely on the one that comes with panels-they are crap-the $110-has a digital read out-tells you so much-very very handy.

I've used the above kit in the field,to help make a documentary ove rlast 6 months.

I'll post some images and links if needed,and I get time

Allan_L (Allan) · #9 13-01-2013, 01:22 PM

Quote:

Originally Posted by Irish stargazer

Thanks Guys
I What brand of inverter as you using Allan?

Well ...
Being ultra safety concious, I bought a Compaq brand inverter. (I had a Compaq Laptop at that time)
It converts 12vDC to 110 volts AC (American standard).
It cost more than my latest Notebook.

But that was 10 years ago.
I would not suggest that is the way to go now.
Any Pure Sinewave inverter should be fine.

But I do like the idea of a 12vDC to whatever vDC power converter, especially if it comes with the particular plug for your laptop.
That should be the most efficient way to do it.
DISCLAIMER: But I am no electrical expert!

Irish stargazer (John) · #10 13-01-2013, 01:26 PM

I saw these in a few places. Too good to be true???

http://www.officeworks.com.au/retail...ers/TAAPD046AU

http://www.targus.com/pdfviewer/temp/APD046AU_10.pdf

Astro_Bot · #11 13-01-2013, 01:29 PM

Quote:

Originally Posted by Allan_L

That should be the most efficient way to do it.

It is.

Astro_Bot · #12 13-01-2013, 01:33 PM

Quote:

Originally Posted by Irish stargazer

I saw these in a few places. Too good to be true???

http://www.officeworks.com.au/retail...ers/TAAPD046AU

http://www.targus.com/pdfviewer/temp/APD046AU_10.pdf

Output voltage is fixed at 19.5V. What is your netbook's input voltage? Also, I don't think you need to spend that much unless you really need USB power.

Allan_L (Allan) · #13 13-01-2013, 01:34 PM

That looks good John!

Dual charging (19.5v main and 5v USB) !

And from someone like Office Works i would feel comfortable that it wont fry the computer.

Make sure to check the compatibility list for your PC.

Irish stargazer (John) · #14 13-01-2013, 01:36 PM

Samsung Netbook. 19V @ 2.1A (40W)
The battery (new) usually gives a few hours before charging is needed.

Astro_Bot · #15 13-01-2013, 01:41 PM

That should be alright (but +/- 0.5V variation is about all I'd suggest for a laptop - the designers usually skimp on input circuitry to save weight, space and heat, and put all the conditioning in the plug-pack).

Irish stargazer (John) · #16 13-01-2013, 02:07 PM

Targus also produce an in-car invertor

http://www.officeworks.com.au/retail...gers/TAAPV11AU

mithrandir (Andrew) · #17 13-01-2013, 02:12 PM

It appears no-one makes a 12V charger for my Toshiba Qosmio X770, so there's no option but to use an inverter to get 240V to run the charger. It takes about 180W and has a custom plug.

Irish stargazer (John) · #18 13-01-2013, 02:19 PM

Quote:

Originally Posted by mithrandir

It appears no-one makes a 12V charger for my Toshiba Qosmio X770, so there's no option but to use an inverter to get 240V to run the charger. It takes about 180W and has a custom plug.

That's a beast of a machine though-eats a lot of juice.
In fairness, I would not personally use such an expensive laptop in the field (dew, dropping it etc..). That's why I use a $300 netbook. If it breaks I can just pick up another one. Great for planetary AVI capture as you can hold the screen up to the focuser and the battery lasts for hours on a full charge (just replaced the battery after 3.5 years)

Eggmoon (Geoff) · #19 13-01-2013, 02:42 PM

OR... if your laptop has a removable battery, buy a second laptop battery. Places like battery world do them for most models. Sure you will have a short downtime while you swap batteries... but only a minute or so.

I am holding off on another battery for my laptop only becasue I am waiting for the new Samsung ATIV Smart PC Pro to arrive in a 3G version. These are claiming quite long battery life, around the 8 hour mark, so that should get you through a nights work.

These are one of the new breed of laptops that the screen and keyboard seperate, so you can use it as tablet or laptop.

I have netbook that has a second battery... but find it a bit slow and light on for RAM.

Astro_Bot · #20 13-01-2013, 02:51 PM

Quote:

Originally Posted by mithrandir

It appears no-one makes a 12V charger for my Toshiba Qosmio X770, so there's no option but to use an inverter to get 240V to run the charger. It takes about 180W and has a custom plug.

Have you seen these?
http://www.ebay.com.au/sch/i.html?_t...at=0&_from=R40