UPDATE May 2015 : If you have read it before, scroll down to UPDATE #1 & UPDATE #2 section of this article.

It all started with just a small 12V block battery and an extension cable with a cigarette-lighter plug at the other end. While I hooked this up to a telescope with a matching adapter cable you can use this same battery to power the AstroTrac and some of the small EQ-mounts. With a typ. power consumption of 0.3A, this 4Ah block would be sufficient to drive these mounts for one, ro two sessions without recharging. The only big problem I've encountered with this solution were the clips to connect to the battery's contacts. They weren't strong enough and I had several occasions where the mount accidentally lost power.
Another problem, and that partially is my own fault because I didn't recharge after every use, is loss of power to the mount because the battery was drained. The mount has no under-voltage alarm and at some point it just quietly stops. To recharge that battery, I used the car battery charger I already owned. There are smaller chargers available.
UPDATE #2 : This Lead-Acid battery cost ~$30 and has ~50Wh capacity. A Li-Ion battery with similar capacity currently costs $100, it is smaller, weighs less. But many power-packs cannot provide the high peak currents this block battery can because they use small cells & DC/DC-converters to generate 5V over an longer timespan.


A 12V battery can power other accessories besides the telescope -- but that becomes a bit more tricky. SLRs for example, they don't use 12V as their input voltage -- CCTV cameras and astronomy equipment usually do. WATCH CAREFULLY -- you don't want to fry a $2000 camera in an attempt to save $100. Different vendors, even different models all have different voltage & power requirements. Let alone different connectors & batteries. Nikon cameras even refuse to work unless the battery as a special chip inside. 7.5V...9V are common voltages and 3.0...5.0A, The D3 needs more power and requires 5A @ 13.5V.

My solution -- I've made one only for the Canon 650D -- utilizes a no-frills, 3rd-party battery grip and I've implanted a tiny DC/DC converter that has just the right electrical specs and by sheer luck can be squeezed into the room originally reserved for 4 x AA batteries. With a bit of soldering & wiring, this dSLR now runs on 12V battery or a 12V AC adapter. It is a more rugged solution than using a purely mechanical adapter and leave the DC-DC converter unprotected.

Thanks to power users draining their smart-phones & laptops, a new breed of gadgets emerged and I took advantage of those "Refueling Stations". Compact, high-capacity NIMH or Li-Ion batteries, with built- in chargers and occasionally even with adjustable output voltages. Those "tanks" are a welcome -- but expensive -- option as they have a higher capacity, often include a display to gauge remaining charge and replace the external battery charger with a built-in one (you still need a small AC- adapter). Instead of bare contacts, these devices have built-in plugs and an array of adapters to fit many different devices. For use with my astronomy gear, I still had to invest a bit DIY work but that was now limited to customizing cables and "standardize" them to all use the same type & size of connector.

When you pick such a battery pack, it is important to also look at the maximum output current these devices are rated for. Since they have built-in electronics and are intended to recharge other devices, the peak current may be insufficient to power the mount when it starts up both motors. Especially if you hook up more gear, that output current issue will be more serious. With a regular lead-acid battery, that usually isn't a limiting factor.

This issue of maximum peak current deserves more attention as the number of 12V-powered items increases. 1A...1.5A peak for the small EQ-mount usually isn't a problem for these "intelligent" battery packs. With a mobile, yet complex astrophotography setup, you have a couple of devices hungry for 12V DC power. When you add this all up, the power requirement very quickly will exceed the typical 2A or even strong 4A threshold. Here are some examples

• telescope mount : typ. 0.3A...0.9A, peak ~1.5A for medium, >4.5A for bigger EQ-mounts
• (main) imaging CCD camera : greatly varies, up to 4A. mine requires ~2A
• dSLR (via 12V adapter) : not specified,
• Adaptive-Optics / OAG : not specified, estimate 0.5A, short peak might be 2A
• Dew-Heater : greatly varies, max output exceeds 10A ...15A
• CCD- / dSLR cooler (in case you camera hasn't a built-in cooler) : 2...6A
• Laptop (either via AC-inverter or custom DC/DC converter) (< 100W)
  alternative : small PC + external monitor (< 120W)
• autoguide camera and other accessories (via USB-hub) < 1.5A @ 12V
• motorized focuser (also on USB)

The Dew-Heater's power supply clearly belongs into a different category, together with the small PC + monitor. For once, they are significantly larger than the rest but they also are a lot less sensitive to variations and even big power spikes won't necessarily crash the system (the tiny-PC is not as robust as a laptop). At the same time, they are also more tolerant to voltage changes as the battery drains.

All other components are in close proximity and are used in conjunction and therefore it makes sense to combine the power-supply needs & cables. In my case, the typical power requirements can be ~4.5A but hopefully the camera won't be needing 2A all the time. The peak current is critical since a drop in voltage will cause all the USB logic & the telescope mount to reset -- often unnoticed. And I estimate my requirements (no laptop or dew-heater) to be ~6A and that is beyond the capacity of many "intelligent" battery packs I have seen. Despite its massive capacity and $200 price, peak current is "only" 4.75A : BiXPower-42500mAh -- many other Li-Ion solutions have a much lower peak current.
For "tethered" use in my driveway, I now have a 12V/8A power-supply. It has the same size connector than the cable coming from my heavy 12V car-battery. And if I travel light (SLR instead of CCD-imager), I can still use the lightweight NIMH or Li-Ion battery pack.

Another area that requires power -- but often is overlooked and a source of many, seemingly unexplainable errors -- are the USB devices and their drop in power [from own experience !!]. In many cases, the laptop can power the devices you directly connect to it. But in an environment like a telescope setup, you quickly need a hub to connect them all (distance as well as number). Several of these devices require varying, at times large, amount of power, and if you are not careful, these spikes in the power demand can exceed the USB limits and will cause the whole USB bus to crash. At home, you would pick a self-powered hub and plug the supply to the outlet in the wall. My DIY solution is more compact and uses 12V DC.

It appears, the telescope & astronomy accessories have the common sense to use the same size connectors for all the 12V loads. It is a "2.1x5.5mm" and when I add the term "CCTV Camera" search results get a lot better : 2.1 x 5.5mm. These connectors also fit the CGEM mount but tolerances there are quite large. The rubber band you see here adds tension and prevents the cable from sliding out. There is some risk in using this type of connector -- the 19V laptop power-supply uses the same size ==> careful not to mix up the different voltages. And you can accidentally create a short-circuit while plugging a connector in. This might cause permanent damage and even if not, it can cause a reset to all attached devices. Say goodbye to the telescope's alignment. There possibly are connectors with better separation of the two contacts
Anderson "PowerPole" connectors can avoid that issue but to attach your cable, you need a special crimping tool ($40 and up).


The grand-finale for my mobile setup is this DIY- build "Juice-Box" I've tailored to my needs. It houses the heavy bulk of the power supply section -- fortunately this box has wheels. And the size is just right : (more about "VANessa"). Storing a car-battery inside a box isn't a big accomplishment but to make this my 120V & AC power hub, I've added a few useful extras :

• regular car battery -- just the right size to fit this box
• 400W AC-inverter attached to that car battery (powerful -- but noisy fan)
  can power "all" : laptop, monitor and many battery chargers
• a powerful charger for that car batteries (up to 15A) -- requires AC.
  Literally cut it in half to save space : /stargazer95050/19370915
• embedded the chargers for my SLRs and other accessories batteries :
  ==> can recharge them while driving, less clutter
• hookup the "Juice-Box"-battery to the car's 12V DC
  ==> recharge that while driving
  MISSING : automatic disconnect. I must pull the plug manually
• lot's of storage room left inside this box
• moveable 100W AC-inverter (silent, fanless) when low noise is more important than power (e.g. overnight recharging while sleeping)
• when closed, the lid has 4 cup holders, a flat surface and looks just like a regular icebox.
• even when lid is closed, I can connect an external AC extension cord, thanks to a small incision I made (input to charge or output from DC/DC-converter)
• this box is heavy but can be rolled up to a more distant site thanks to the wheels. Most often my extension cables are sufficient to provide 12V & DC-power without removing the "Juice-Box" from the car. (less back-pain & quicker too)

So far, that 400W inverter has produced more noise than results -- the much smaller & silent 100W converter was sufficient nearly every time. Only when in a extreme hurry and needed to recharge 1 or even 2 laptops plus SLR batteries, the 100W output was insufficient. While driving, I now keep the 100W inverter easily accessible and use it to power GPS Navi or up to two small gadgets or the laptop without the annoying wizz from a cooling fan.

Providing power to the components is one part of the effort. If you travel, the issue of packing, safely storing and keeping track of things is just as crucial. You don't want a missing cable to ruin your trip. Since my favorite method of transport is a car and roads are bumpy & curvy, it is worth spending time on preparing for that as well. Furthermore, when planned carefully, you can quickly pack & unpack all your gear in between shoots. At times, I even carry the accessory-"tray" into a motel room to recharge all batteries over night. The recommendation I have is not to pack too many items into one box (gets too heavy) and possible "invest" a dollar or two and buy a pack of freezer bags to each hold one cable (avoids unwanted entanglements, one bag for the TINY stuff). Label each bag and when you pack, you easily can check your inventory. My setup includes a long (green) AC extension cord, jumper cables (just in case) and room for several AC poer supplies & chargers.

One more 12V accessory that you might need -- but not very often -- is a small camping hair-dryer. Not to get the dew out of your air but instead to de-dew lenses, eye-pieces or telescope front elements. A slightly warm breeze can remove the dew without you touching the surfaces. This can be especially beneficial if you already have aligned the mount and are imaging. You don't want to use too much heat and also be careful not to drain your battery -- DO _NOT_ hook that up to a small battery or NIMH unit as those usually cannot deliver the 10A...15A needed.

Also be careful not to drain your car's battery with your astronomy gear. It may be tempting to avoid buying & carrying a dedicated heavy battery but gettnig stuck because the car won't start is not worth these savings.


Also, is not enough to have all these power-supplies & (rechargable) AA & AAA batteries, you still need a large collection of different (non-rechargeable) batteries :

• SR-54 / GP189 / L1131 (x3) are used in one of the illuminated crosshairs
• GPA76 (x2) are used in the other illuminated eye-piece -- at least both illuminators use the same screw so I can swap them as needed
• CR2032 (x3) inside the electronic angle gauge
• SR44 (x1) for the digital caliper I use to measure the focus position
• CR123A are used in various laser collimators, flashlights and lamps
• 9V block to power the manual focus motor controller and also for the DVM (Multimeter)

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Update #1 :
Not everyone has the time or know-how to put together a DIY power-supply for a SLR. There are off-the-shelf solutions but those usually require more components. A battery with an AC-inverter plus an AC-adapter to generate your camera-specific voltage and a mechanical "dummy-battery" adapter or custom connector for the camera. The battery + AC-inverter can be cheap and high capacity -- they are heavy and found as automotive accessories or "Power-Tanks" from astronomy vendors. Or you can pick a more expensive and more portable model designed for (fashion) photographers on location to power their flash-strobes -- for example the "Vagabond Mini". $300 for an 8Ah model. OTOH, you can get 18Ah capacity for ~$120, if you pick one of the heavier "Jumpstarter kits" from the automotive section.
The AlienBee's / Vagabond units are designed for smaller loads than many of the automotive units -- that isn't an issue until you decide to add a laptop or other accessories. Another criteria that is often overlooked is the acoustic noise !! -- often the AC-inverters use high-pitch fans and the Vagabond is no exception. Good designs minimize the noise and use the fan based on temperature -- the cheap car accessories usually don't have this. I don't own a AB Vagabond, so I can't tell how annoying their sound is, my Jumpstart unit is annoying, even when idle and gets worse with increasing load ==> I'm not using it any more.

The issue having a noisy fan in the AC-inverter bothered me a lot. It is no fun to sit at a stargazing session and have that dentist-drill sound in your ear. Or get annoyed by that sound while driving & recharging a laptop or other accessories. Fortunately, there are AC-inverters WITH NO FAN and they still can produce sufficient power for most tasks, including powering a laptop. To accomplish this, these units need sufficiently large metal surface. If quite operation is important, so far the best solution I found is a 100W AC inverter. You will have to add your own 12V battery or hook it up to your car's cigarette lighter.


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Update #2 :
Batteries have increased in capacity and their reduced size and these improvements have trickled down to other products. You now can find a huge selection of portable "power-packs" delivering 5V via a USB connector but the choices for 4A @ 12V are much more limited. Given the power demand of a motorized mount, there is a trade-off between price vs size & weight. A cheap car battery can exceed most of these power requirements but it is awfully heavy.
eBike batteries are tempting ($300, 300Wh, 5lbs) but their proprietary connectors make adaptation difficult and you need a DC/DC converter to get the 12V.
Other models also have high capacity. You pay ~$300 for 220Wh (4lbs) and it gives you 15V and up to 4.7A to power the EQ-mount. As an alternative, you can switch to 19V to recharge a laptop.
There's another category of Li-Ion batteries I find suitable for in my astro use. The vendors claim those can jumpstart a car (I doubt that !!) but with a small hack-job you can can convert them for other purposes. DO THAT AT YOUR OWN RISK. You gain a very compact, light-weight battery with 50...60Wh capacity only 42Wh and the strength to deliver high peak currents. Charger is built-in, but it isn't fast. Cost ~$90, 42Wh, 3lbs

The photo shows the modification I did to one of the $90 models ==> I cut off that extra protective circuit -- it interfered with my use. After that I replaced those clamps with two pair of cables and different plugs. This battery has powered the power-hungry EQ6 mount plus attached dSLR for several hours (1/2 night). Not too bad for such a low-weight unit and this can be sufficient for occasional observations.
The battery claims 12.000Ah capacity and that likely refers to the 3.5V cell voltage and results in 42Wh capacity -- that's a poor price/performance ratio.


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Update #3 :
Other Li-Ion batteries can deliver sufficiently high peak current to power the EQ-6 mount _OR_ a laptop _OR_ a CCD camera and has a respectable 120Wh capacity. The cables don't need a hackjob to fit the other tools and $150 for 120Wh is a better deal. Output voltage is adjustable in increments between 12V....20V and meet popular notebook demands. Various adapter plugs are included.

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