Reducing Laptop Power Consumption

As I found out in an earlier post, my laptop uses about 2.1A when its battery is fully charged and about 5.6A when the battery is depleted. At typical lead-acid battery voltage (~13V) these translate to about 27 and 73 watts, respectively. This makes a laptop one of the largest drains on a battery when imaging. Is there a way to reduce this significantly?

The answer is definitely yes!  Let's start with a review of laptop power consumption as measured by another blogger. He found these amounts for a laptop very similar to mine:

• Laptop off, battery charging: 54w
• Laptop on, idle (display at full brightness, WiFi on, power management "balanced": 20w. 

Notice that an idle laptop that's also charging the battery will consume 74w, essentially the same amount I found. Your laptop may have different power use, but it will probably be in the same area.

Next he tried a few methods of reducing the power use with the following results:

• Set screen brightness to dimmest setting: 4w reduction
• Turn off hard drive: no reduction
• Disable WiFi: 2.5w reduction

It's possible to completely turn off the display saving a little more (the specifics in in a moment). My guess is that powering down the display will reduce power by about 6w.

The total reduction by turning off the display and disabling WiFi is therefore about 8w or so. That's about 2/3A when running off a 12V battery, and over a four hour imaging session it will amount to 2.7Ah. That's not a big amount, but it's not insignificant. Recall that my summer star party standard was 16 hours of imaging. The saving in that amount of time is 10.7Ah.

So how does one turn off the laptop display? Luckily there's a tiny program for Windows that does just that. It's appropriately called "Turn Off LCD" and it can be found here. Unzip it, put the exe file on your desktop and double click it whenever you want to shut off your display. This does not affect any programs that are running; guiding software and image downloads will continue normally. To restore the display just move your cursor or hit a key.

You can assign the program to a key stroke if you wish. The way I've done this is to use AutoHotkey. Here are the steps needed to do that if:

• Download and unzip Turn Off LCD, then move the exe file to the folder of your choice.
• Download and install AutoHotkey
• Right click your desktop and choose New / AutoHotkey Script. If this options isn't available it's probably because AutoHotkey isn't running; start it using the Start Button / All Programs / AutoHotkey / AutoHotkey
• Add your hotkey specification after the script's boilerplate. As an example, here's my script for binding Turn Off LCD.exe to the key combination of the Windows key and s:
    #s::
       run, TurnOffLCD.exe
    return
  Note that I've renamed the exe file to omit the blanks because I don't like file names that include blanks (I was raised in the era of DOS 3 world of 8.3 file names, what can I say?) You may need to specify a path to the exe file--it's just prepended to the exe file name.
  You can bind the exe to any key you want; more information is provided in the AutoHotkey help. Read it and learn.
• Save the script file with a name that makes sense to you. I called mine ScreenOff.ahk
• Right click it and choose Compile Script. This will create ScreenOff.exe.
• Move the compiled script to the Windows Startup folder so that it will be loaded every time your start your laptop.
• Hit Windows + s to turn off the display. Move the cursor or hit any key to resume.

Remember to disable WiFi and Bluetooth if you don't need them.

Any software that you don't need should be disabled or turned off, as it will only make your CPU, HDD, and graphics adapter work harder and consume more power. Software that should be disabled while imaging includes all security software, Windows Update, and Windows Defender. If you're not on a network none of that is needed or useful.

Unless your laptop's CPU is slow and feeble you can change its power settings to run slower and use less power. Windows usually supports three modes: High Efficiency, Balanced, and Power Saver (the one you want.) Be sure your laptop's battery is fully charged before you take it into the field.

Do all this and you may be able to reduce your laptop's power consumption by 1/3 to 1/2.

Messier Marathon Night Results

"Mission Accomplished!" to use a cliched phrase. "Goal Reached" might be a little better, or maybe "Dumbness Overcome."

This was one of my first attempts to use my DSLR in quite a while, and I managed to make a lot of mistakes early on:

• Forgetting to return to ISO 1600 from the composing setting of 6400
• Forgetting to set the shutter control to bulb
• Forgetting to increase the number of frames on the DSLR controller from the dark frame to light frame counts

And so on. The evening began with starts and restarts, but once it got going it went well. The time I lost meant I wouldn't go after the dimmer planetary nebula I had included on my object list in the last post, but that was okay.

All the hardware worked perfectly, although some went untested. The dry air and the gusty to breezy conditions meant the dew preventers weren't needed. It was only around 2 A.M. that frost began to appear, and my scopes stayed clean until the end a little before 3 A.M. The DSLR power supply worked perfectly and the 35Ah battery was barely tested running that and the mount. I used my laptop for PHD with its power supplied by it's own battery augmented with a Duracell 600 battery pack. The Duracell ran down pretty far in the five or so hours, so this might not be a good option for multi-night imaging. For more power conservation I need to find a way to turn off the laptop's display, not simply dim it.

The evening tally was six Arp galaxies and one planetary. In terms of Messier objects it was 9 1/2. Let's see some marathon images:

Leo Triplet (clockwise from NGC 3526 at top, M65, and M66) Together these are Arp 317. M66 is Arp 16.

M49 (right of center, Arp 134)

M60 (left of center, Arp 116) and M59 (right of center)

M87 (Arp 152)

M90 (Arp 76) and M89 at bottom edge

M97 (Owl Nebula) and M108 at bottom edge

All the images are based on 10 three minute exposures with a Canon T2i (at ISO 1600) riding on a TV 102 operating at f/7--except the image of M90, which was 5 three minute exposures at ISO 6400 (see list of mistakes above). These were calibrated with 20 dark frames collected throughout the night as the temperature fell from around 30°to 20°F. They obviously haven't been flatted. I reprocessed them to include synthetic flattening, and now they look a lot nicer!



An inspection of single light frames shows that they surpass visual observations, so why not bring back the idea of an Imaging Messier Marathon? Three minutes at ISO 1600 is about the same as 45 seconds at ISO 6400. 3/4 minute times 110 objects is only 82 minutes; out of a six hour marathon night that leaves four and a half hours for acquisition and composing images. Definitely doable.

That aside, the evening bumped my Arp list count to 26 and my planetary list count to 23. Both lists are about 1/4 done!

Onward to warmer weather!

Messier Marathon Plans

Tomorrow night is Messier Marathon night and it looks like it may actually be clear!

Considering what we often see for the MM, this will be relatively balmy (wind chills in the teens above zero) and dry (the observing field is a little mushy, but there's no snow). It helps that this year it's being held in April even if that's not best for getting a high count.

Having gone over to the imaging side, that's what I'll be doing. To keep in the spirit of things I'll do mostly Messier objects.

Because the Ms are fairly bright I'll be using my DSLR. The targets will be taken from the two Astronomical League lists I'm working on, Arp galaxies and planetary nebulae.

Here's the list, Galaxies first:

• M49
• M60
• M65
• M66
• M87
• M90

These all have surface brightness between magnitude 21.3 and 22.3, so I think they can be imaged fairly quickly for modest quality results; it is a marathon night. Because M65/M66 occupy the same field of a TV-102 and DSLR, they require only one image. So for the six galaxies I'm expecting four to five hours of clock time including time for acquisition, composition and dark frames.

Next the planetaries and their surface brightnesses:

• M97 (22.3)
• Abell 21 (24.9)
• Abell 36 (25.5)
• Abell 35 (26.2)
• PN G164.8+31.1 (26.6)

You can see why the last four are not Messier objects; they're not very easy to see. Abell 21 is about three times larger than M97, making it a good target for the relatively short focal length TV-102 (700mm). Given its location in Gemini it might be the evening's first object and will get up to two hours of photons. The other dimmer objects will probably get passed over.

A Battery Box Addition

The Battery Box got one refinement over the last couple of weeks: A built-in 7.5VDC power supply.

I had intended to use an external supply, but the little Drok unit gets good reviews and is much smaller than the adjustable supply I had planned to use. It was perfect for mounting within the box. All it needed was an output plug. For that I went with the same sort of plug used on many mounts, a lockable panel-mount socket and plug. (Both were purchased on eBay.)

Drok 12VDC to 7.5VDC step-down converter

5.5x2.1mm socket and plug

A built-in converter presents two problems if it's left connected to a battery: A continual power drain (0.1 to 0.12W) and possible interaction with a smart charger. The drain doesn't sound like much, but it equals about 7Ah per month; that's a lot for a 35Ah battery. To prevent these problems I isolated the converter using a rocker SPST switch. As a reminder to turn off the converter when it's not needed I added a tiny LED that draws a minuscule 3mA. Here's the switch and LED:

Switch and indicator light

As I said, it's a tiny LED! It's just bright enough to let you know that the converter is active.

12V sockets (above) and new 7.5V socket (below).

I made an extension patch cord that fits the plug and the power cord from the camera's dummy battery; this will permit me to use other power supplies.

One other add-on is intended to make this easier to use: An accessory cable for my charger that will let it charge through one of the sockets. Because this is a small battery it can be charged at a relatively low amperage of 1.1A. While I haven't yet recharged it from a state of deep discharge, I'm hoping that it will remain cool during charging even when left in the box. It's my hope to never need to remove the cover.

NEXT UP: It's the Messier Marathon, April 8 or 9! I plan on imaging some Messier galaxies as a part of the Arp galaxy imaging project. There are six Messier/Arp galaxies I haven't imaged yet: 49, 60, 65, 66, 77, 87, and 90. Only 77 is badly placed; it will set too soon for imaging. Because it's a marathon night, I'll shoot only luminance with my ST-8300M, and probably only an hour apiece at most using my TV102. Last year the MM had only so-so skies. Here in Minnesota we're overdue for some good Messier luck.

Box your Battery

Tired of lugging a heavy battery around by its carrying strap? Inconvenienced by connecting to it using alligator clamps? Messed up by dew getting the battery all wet? Make a battery box!

It's simpler than you might think and you can make it as fancy as you want. Here's my rather minimalist box:

A Simple Battery Box

At the right side under the lid protuberance designed to allow dew to run off are two 12V sockets. I may add a couple more on the far side. Each is individually fused so that if one device blows the rest keep working.
 

The voltmeter springs into action

The only other thing I added was an LED voltmeter that's actuated by a momentary-on push button. This helps me monitor the battery's state of charge.

Under the hood

The 35Ah battery (group U1) is dwarfed by the box, which is designed to handle batteries in groups 24-31. I've used rigid foam to hold it in place. I haven't done a deep recharge of the battery yet, so I don't know how warm it will get. I suspect it won't get warm at all--My charger is only 1.1A. With an accessory the charger can charge the battery though one of the sockets

What you'll need:

• The box: The one I used comes with a useful divider and can be used with a  battery that provides 75Ah and still have room for the sockets
• Sockets are found on eBay for about $6 each. I used waterproof ones that come with their own cables and fuses. I bought the kind that attach with a locking ring; they've been solid in use.
• The voltmeter (about $4) is also from eBay, waterproof, and also attaches with a ring.
• Connecting wire. If you run your own wire to the sockets, be sure to use 14AWG or heavier wire, and check that the fuses are appropriate for the wire and devices you plan to connect. Wire to the voltmeter can be much lighter as it will carry only a tiny current.
• Tools: The only helpful tool you may not have is a variable drill bit that will help make the socket and meter holes. You don't need one as large as the holes--it can be used the start the hole and ream it to proper size.

What you don't need:

• Battery terminals for jumper cables. This should be a deep-cycle battery, and it doesn't like jump starting. 
• A carrying strap. The box comes with handholds at either end. A 35Ah battery and box weighs under 25 pounds, so it's easy to carry.

As you can see from the above picture a U1-sized battery leaves a lot of room for accessorizing. An amp meter could be useful to install if you want to measure battery drain. If you have the need for other voltages, add some step-down DC converters. They're small and very inexpensive. You should probably isolate them from any charger, perhaps with a two-way rocker switch. Go wild and add lights and a radio and you have one of the overpriced commercial "power tanks."

I'll be field testing this battery over the summer at a number of star parties, and may modify it as a result.

My battery box delivers twice the watt hours of a commercial "power tank," and costs less (about $125 total,  $100 of which is the battery and charger).

Trying My New Battery; Color Balance Issues

The weather has been cooperating a little better this last week, and I've been able to try out my battery-based imaging setup. I haven't done much more than image an hour here, a couple of hours there, but the results are about as expected.

Here are two images from my inner red zone back yard,

M42:

As you can see I was unable to completely eradicate the sky brightness gradient.

The Rosette:

Both are taken without filters only because I don't have one. A decent filter would have improved these greatly.

Here are a couple from some distance north of the Twin Cities in a yellow zone,

75m of the M81/82 area:

I have this delusion that I'll be able to image the integrated flux nebula.

The southern portion of Auriga (including some dark lines from tree branches):

The first two images came out horribly red/magenta heavy, and it was a lot of work getting the color right. I passed that off as a consequence of the camera mod and light pollution. The second two appeared just as red on the display screen while working on getting the exposure right, but they came out fairly neutral because I chose the ImagesPlus RAW conversion that ignores the camera's white balance; I used "Bayer No White Balance" instead of "At Capture White Balanced Color."

Color balance isn't an issue when CCD imaging, particularly if your filters are balanced by the manufacturer to give equal white signals in each channel.

The question is now which is better, a custom white balance or using the "no white balance" processing option. There's only one way to find out, and that will require a sunny day, a few sheets of white printer paper, and a clear night. That's my next task.

Oh, and the battery worked perfectly. It's nice to have the power right there in such a light package. 35Ah, less than 23 pounds. My little battery case now has two power sockets, but the volt meter has yet to arrive.

The Lust for Power, Part 3: Generators

Last time I found two imaging configurations that called for the use of big, heavy, and expensive deep cycle batteries. The common alternative is to buy a generator; it will supply 110V AC, and then your AC adapters will feed your equipment.

Generators as the primary power source

Generators come in a variety of sizes. The factors to consider, roughly in order of their importance, include:

• Amperage rating (AC). While some generators have DC outputs, you'll probably be using the AC side.
• Running and peak wattage (W). Wattage is easily computed by taking the product of amps times volts. [Energy is watt-hours (Wh); A battery's available Wh is just the product of its Ah and voltage. For example, a 100Ah 12V battery has a capacity of 1200Wh, of which about 60% is available before recharging.] 
• Sound level. If you're at a remote site, chances are you'll have people camped nearby. Running a loud generator could get you booted out.
• AC regulation. Is the ouput voltage well regulated, and is it in the form of a relatively noise-free sine wave? This is difficult information to come by.
• Available low-energy modes. Does it reduce fuel consumption and sound level if the demand is small?
• Subjective things like ease of use, noise level, fuel consumption, reliability, etc. Generally the more you pay the more you get in terms of these.

What kind of power will we need? Configuration 1 (CCD, guided large telescope) required 6A. At 12V this is only about 72W. Peak amps is about twice that and demands 150W. Configuration 2 has an even smaller demand (130W peak).

The smallest generators have about 800W peak power and a price point around $300. The PortaSource IG800W ($313) has marginal amps; the Generac ix800 ($287) gets mediocre reviews and a lot of 1-star votes on Amazon.

Medium-capacity generators have around 1600 to 2000W running power and twice the amperage that I require. Prices range from $400 to $600, although some brands can demand about $1000. It's not clear that the added cost is worth it. These generally weigh 50 pounds or more.

In this class I think the Wen 56200i ($429) fits my needs best .

Generators with greater capacity are not needed for imaging, but can also serve as emergency generators. I'm not going to consider them. 

Generators to recharge batteries

It may make some sense to get a small generator and then use it to recharge a battery. because the recharge takes place during daytime noise is relatively unimportant. What matters is the amperage of the charger, since that will be "restocking" the Ah lost overnight. Because some chargers operate at lower amps than your imaging use, you may be able to get by with a generator that doesn't meet specs as the primary power supply.

The required charging time will be the number of hours you imaged  times the amps used while imaging divided by the charger's charging amps.

Example: Imaging at 6A for four hours and using a 1.1A charger. The recharge time is 4h x 6A / 1.1A, or almost 22h. The most you would probably recharge for would be 12h, so you could recover only 13Ah of the 24 you used the night before. Not practical.

Now imagine imaging at 2.9A for four hours and the 1.1A charger. Recharge time is now 4h x 2.9A / 1.1A, or  10.5h. That's actually doable.

I've used a relatively slow charger in this example. A 3.5A charger would cut these times by 2/3 , to 7 and 3.5 hours. A 50Ah battery and 800W generator could make a nice tandem.

Generators to Augment Batteries

Okay, why not power things from both a battery and small generator, thereby easing the power demands on both, then using daytime to top off the battery? Let's see some examples.

Let's consider Configuration 2, small telescope, CCD, guiding, dew prevention: 5.2A. the two big power consumers are the laptop and CCD. Let's let the generator power the laptop and mount (3A), the battery handle the CCD and dew prevention (2.2A). 3A is easily within reach of the small generators, and the nightly Ah drawn from the battery is 8.8Ah. Recharge time is 8 hours. Suppose it's fall and you can image for 6 hours; you'll pull 13.2 Ah out of the battery and need 12 hours to put it back. The generator will run a lot--18 hours a day.

The downside is that nighttime running of the generator brings noise back into consideration. And you'll be running the generator quite a bit--both during imaging and the daytime. It's an interesting approach to powering your gear, but I think either battery or generator is better than a hybrid solution.