Battery Pack for Portable Imaging

[RustierOne]

I wanted to share some images of the battery pack I've assembled for portable imaging. It's built around a 12 volt, 100 amp-hour deep-cycle lead-acid battery. While it is heavy at 55 lbs. (25 kg) it has enough power to last through a long winter night's imaging. The loads being carried include:

• Telescope drive (Losmandy G-11/ Gemini-1) - around 1/2 amp maximum
• Four-channel controller for heated dew shields (either 8-inch or 11-inch S-C telescope plus heater strip for 50 mm guide 'scope) - around 2-3 amps max
• Inverter to power laptop charger - 7 amps max

While over 10 amps might be required, the draw would usually be much less. The battery pack was assembled in a plastic battery box sized larger than the battery to give room for wiring , sockets and meter.


Battery Pack with lid attached, showing the three 12-volt receptacles


Battery Pack with lid removed showing charging through hardwired charging line


Top view showing battery, sockets, meter and some of the wiring.

The positive feed wires for each of the sockets are soldered together, then going through a 30 amp fuse (above right of meter) which is wired to the positive terminal with heavy red wire. All three negative feeds are hard wired to the negative battery terminal. The meter is also hard wired to the battery terminals. Finally the battery charging wire is connected to the battery terminals with a fuse (seen between the two battery terminals) on the positive feed.

The analog volt meter is of limited value due to its poor accuracy and limited resolution. I plan to replace it with digital panel meter with resolution to 0.01 volt. This will help determine the battery's state of charge. When not in use, the battery pack sits on my work bench with the charger attached to a timer which enables charging 8 hours per day. This was arranged so as to reduce the long-term power usage.

While this heavy power pack might seen to be an overkill, I have found it useful when attending a multi-day star party. Being oversized should also prevent deep discharging, which is detrimental to battery longevity.

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Best Regards,
Russ

 

[Carsten Pauer 2]

The Battery Box locks a bit to small for the Accumulator.
Have You add a Accumulator Heater to keep the Accumulators in the Winter warm ?

 

[ChrisLX200]

Looks a hefty battery Russ, but personally I don't like those inverters (safety reasons) and prefer to use a voltage converter for a laptop. You can get simple devices that will output variable voltage (my laptop needs 15V if I remember) and I have a second of these converters actually built into the mount base to output 18v for the G11/Gemini which works better on 18v than it does on 12v.

ChrisH

 

[RustierOne]

The Battery Box locks a bit to small for the Accumulator.
Have You add a Accumulator Heater to keep the Accumulators in the Winter warm ?

Hi Carsten,

I'm not familiar with the term accumulator. If that is the same as battery, what you suggest is interesting - using some of the battery's power to keep itself warm. Of course that increase in temperature would increase its performance. I wonder what the tradeoff would be. But I have not added any source of heat in the box. Maybe placing my inverter in proximity to the battery would help a bit. You are right, there is not much room for anything else with that battery box. At 25 kg (55 lbs) it's heavy enough.

I suspect a big help regarding battery temperature would be to store the battery pack in my heated house rather than the unheated garage. That way it would be warmer before going out in the night-time conditions. Perhaps a bit of insulation around the battery would help it retain that heat better.

--
Best Regards,
Russ

 

[RustierOne]

Looks a hefty battery Russ, but personally I don't like those inverters (safety reasons) and prefer to use a voltage converter for a laptop. You can get simple devices that will output variable voltage (my laptop needs 15V if I remember) and I have a second of these converters actually built into the mount base to output 18v for the G11/Gemini which works better on 18v than it does on 12v.

ChrisH

Thanks, Chris for the suggestion. While I don't know which would be more efficient in its use of battery power, the DC to DC method might well be safer. It's certainly worth being careful with 110 volts AC. That's also a good point, placing the converter in the G-11's base. There is certainly plenty of room there.

While I've never noticed any problem running the G11/Gemini on 12 volts (actually closer to 12.5 volts), running at a higher voltage might be an improvement. Particularly as the battery nears being exhausted, the voltage could drop well below 12 volts. If that should happen, the supply voltage would be below what is required by the Gemini. But by then the battery is nearly dead anyway. When I'm at home I'm running at 13.8 volts using a mains DC supply.

Unfortunately my laptop charger runs as 20 volts. So I can't use a single DC converter to power both mount and laptop.

--
Best Regards,
Russ