Re: External Power #starparty #EXOS2 #TECHNICAL


 

Scott,
 
It really depends on how much power you plan on drawing, and for how long, and at what voltage, and at what temperatures.
 
My setup (AP-only, PMC8, DewNot dew heaters, usb hub, DSLR, Guide camera) bounces around a bit, but on average draws not much more than 1A.  Really pretty frugal - the DewNots are not power hogs, and a little heat goes a long way, at least for me.  My power is measured and distributed by a Pocket Powerbox (which also controls the heaters), and I really do not want to run my overall setup below 11v.
 
I read all the glowing reports about Talentcells on CN and picked up their 12v/11000mAh model.  Charged it up, and it dropped below 11v on me, after couple of hours.  In June, not winter.  
 
Basically, it still had lots of power left, but only at lower voltages.  If I'd been charging USB devices off it, it would have been a different story.  It wasn't so much the total power the battery could store, as whether it could maintain that at the voltage I needed over time.  That voltage drop seems to be a feature of Lithium-ion batteries as a species.  As far as I can tell, the Talentcells are good Li-ions, but they're still Li-ions...
 
After figuring out what was going on, I returned the Talentcell, and got a battery from another mfr, using LiFePo4 technology.  Much flatter voltage when discharging, and sadly, more expensive.  I've done 6+ hour sessions so far, in colder temps, with it still holding in the high 11's (voltage).  I do not know how much farther out the failure point is, but so far, good enough for me - although I may need to wrap it up with a handwarmer when we get down into the -10/-15C range.  First winter coming, so we'll see.  
 
So...think about your requirements and be cautious about capacities and voltages.  I went for LiFePo4 because I did not want the weight of a lead-based battery, but if I had larger power or endurance requirements in my environmental conditions (winter is coming...), I think I'd have to go to lead.
 
FWIW...
 
- Bob
 
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2-IMX224C
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64

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