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PowerSupply.md

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Power Supply

Astrid with the OTEStamper board should be powered via the 12-15 Volt 2.1x5.5mm DC Input Jack on the OTEStamper board, which is common on astronomy equipment. This input jack is "center positive" and has a self-resettable 2A polyfuse. Power to the input jack is reverse polarity protected.

Supply voltages outside of this range will likely damage the board and the Raspberry Pi and may corrupt the SD Card. We recommend against using 12V Cigarette lighter-type connectors, as they often disconnect easily and can lead to SD Card corruption when that happens.

5.1-5.2VDC is generated internally by the OTEStamper board for the Raspberry Pi to run. Please make sure that any wiring and the connector you use to supply Astrid can handle at least 2A. For reasonable run length, this means 16AWG or thicker for the wire, and likely 14AWG if you're supplying a larger mount too. 18AWG is really the least that should be considered and only for short runs and for only powering Astrid.

Power Banks / Power Packs

Power Banks / Power Packs are NOT Batteries

IMPORTANT: It's strongly suggested to avoid Power Banks or Power Packs for powering Astrid. Power Banks / Power Packs (e.g. TalentCell) are most often made from cheap batteries with substandard electronics that are incapable of supplying regulated power to Astrid. This also applies to powering Astronomy Equipment in general (Mini PCs, Astro Cameras, Mounts, etc.).

Common problems with Power Banks/Power Packs are:

  • Misrepresented Battery Capacity (specified at 3.7V not 12V)
  • Power outputs auto switch off with low power drain, removing power from Astrid
  • Low and/or varying voltage due to current limiting, poor boost conversion
  • Fire risk/explosion risk
  • Insufficient size

Any Power Bank/Power Pack that contains Lithium Ion or Lithium Polymer batteries can also cause fires and can explode. Lithium fires often can't be put out with water or chemical fire extinguishers.

Examples:

There is no support/assistance available for Astrid setups using Power Banks / Power Banks if the problem is suggestive of being related to power issues.

Also, any larger power bank/power packs that have a 120V inverter are often square wave and not the correct sine wave output. This can permanently damage any device plugged into it (such as a laptop power supply, or 12V DC power adapter).

Using LiFePO4 (Lithium Phosphate) 12V batteries instead is safer, significantly cheaper, and works (see below).

There is one exception to this recommendation, and that is the Celestron Lithium and Lithium Pro LiFePO4 power banks(only), which are designed for astronomy applications. However, as of now, only the Lithium Pro has been tested with Astrid and they are significantly more expensive than an equivalent battery.

Household Power

Astrid can be powered at home with a 4A or greater 12V DC regulated center positive good quality power supply, for example:

Batteries

Field deployments will typically need a battery, here are our suggestions. We use a 10Ah Dakota LiFePO4 12V battery.

Be sure to use the correct charger for the battery recommended by the manufacturer to avoid damage and fuse with a 5A fuse. Ensure the wiring used is large enough to handle the current required to avoid overheating, insulation melting, and voltage drops. The fuse is a safety measure and is to prevent the situation where the output jack may touch the positive terminal accidentally and short the battery.

LiFePO4 (Lithium Phosphate) battery chemistry is recommended for safety, cold weather performance, and battery longevity. You should also verify that the battery has a BMC (Battery Management Controller) on board. Lithium Ion and Lithium Polymer batteries should be avoided due to safety concerns, fire risk/explosion.

We particularly like the batteries made by Dakota, and we own a few due to their exceptional cold-weather performance and warranty. The same batteries that are ideal for Astrid are also used for Fish Finders/Sonars and can be found in Outdoors Stores and on Amazon.

If traveling by air with lithium batteries, be aware that there are regulations depending on the size of the battery, and you should verify with your airline before traveling.

For example, the TSA guidelines

Do not attempt to use Alkaline batteries (or Zinc-Carbon/Zinc-Chloride) to run Astrid, the internal resistance of these batteries (AA's for example), mean that they are unable to supply the peak current required. It may be possible to run good quality NiMH AA batteries like the Eneloop Pro, but only for around 2 hrs when configured as 10 batteries in series in a battery holder with solder lugs and 16 gauge wiring... at which point an LiFePO4 is cheaper anyway, runs longer and is less prone to problems.

Runtimes are approximate. "Runtime" means Astrid alone (typically tripod mount). "Runtime with Mount" assumes a mid-sized mount (EQ5/AM5) with a current draw of ~1Amp.

Battery Capacity Tested Runtime (hrs) Runtime With Mount (hrs) Meets FAA Carry On Regulations Comments
Dakota 12V 7Ah 84Wh No 12-14 3.5-4.5 Yes
Dakota 12V 10Ah 120Wh Yes 17-20 5-6.5 Yes
Dakota 12V 18Ah 216Wh Yes 32-36 10-12 No
Dakota 12V 54Ah 691Wh Yes 90-100 30-34 No Expensive
Sealed Lead Acid Gel Battery 120Wh No 14-17 4.5-5.5 No Heavy
Celestron PowerTank Lithium (18771) 84Wh No 12-14 3.5-4.5 Yes Expensive (untested)
Celestron PowerTank Lithium Pro (18768) 158Wh Yes 23-26 7-8.5 Yes Expensive. Tested by Steve Conard and Brian Heimes. The telescope port requires 250mA draw minimum to stay on and the cigarette lighter port requires 420mA minimum. Suggest powering Astrid from the telescope port. If the power tank is cutting power to Astrid, then a dew heater can be added to increase current. Also the 5.5 x 2.1mm connector does not have enough length for proper engagement, you should add an extension chord with a longer jack. Capacity indicators on the Celestron Power Tank are not accurate, otherwise runs fine.
8 Energizer L91 Lithium AA 36Wh No 5-6 Not feasable Yes Buy at destination. Good to -15C, lower with less runtime. Batteries are expensive and require a solder lug battery holder as most battery holders have small gauge wiring. A small lithium battery you can carry on a plane (e.g., the 10Ah Dakota listed above) is often the most cost-effective option if used more than once.

Power Connectors

The recommended way to connect a smaller LiFePO4 battery to Astrid is via a 5A Fuse and DC 5.5mm x 2.1mm male barrel plug with 16 Gauge (or thicker wiring). The fuse is there to protect the battery from accidental touching of the barrel plug to a battery terminal.

Often people will make their own power connectors or have connectors already available to them. Here are some suggestions if you prefer to purchase an a mostly assembled connector without soldering / heat shrinking (you'll still need to crimp 2 terminals):

Parts

Cable Construction

  • Cut off the barrel socket close to the end of the socket (leaving just the 2.1mm plug that goes into Astrid. Split wire and crimp on 2 x 0.25" quick disconnect terminals to connect to the battery (do not connect to battery yet)
  • Plug in 2.1mm extension lead
  • Replace fuse in the lead with the 5 Amp Fuse