stress-testing the new setup under a forest canopy
It was creeping back into the high 80s F in El Paso (~4,000ft) so I made about a 2.5-hour run up to Cloudcroft (~8,500ft) where highs are around 60F this week.
Cloudcroft is surrounded by the Lincoln national forest where I’d escaped many times from the heat when I was working in ELP.
selecting a site
I needed a site with a few hours of sun and at least 1 bar of either Verizon or Tmo.
I found a spot with 3 bars of Tmo. According to my guestimate of the Sun Surveyor sun track I’d get about 3 hours of full sun between the trees, mostly in late morning. Theoretically that should be enough.
and so to bed
The tree canopy meant the solar was making minimal power in the afternoon, so each night we would hit the sack at about 85% State of Charge. It’s a 100Ah battery with practically no Peukert effect so the Ah remaining number and State of Charge number will be the same.
We ran the 10” LCD monitor to watch a couple shows and ran the heated mattress pad on LO all night.
morning
Each morning we’d be at about 45-50%, well above my personal 20% limit. Outside temps were in the 40s but the battery temp was in the low 50s; no chance to test the battery warmer (set to kick in at 45F).
recharging the bank
There are two openings in the canopy when I get sun:
- 0900 - 0915, when the panels can make about 180w
- 1100 - 1400, when the panels can make about 500w
At both 0900 and 1100 when the sun was emerging from behind the canopy the controller would get very confused. It was trying all kinds of power points and every change made more power, no matter the direction. This is because available sunpower was ramping up quickly as the sun emerged but the controller had no way to know that.
Charging in earnest kicked off at 1100. This screenshot from 1139 shows the info we need to know:
- the battery is charging at ~33A. BMS max is 100A, Rebel recommends ≤50A for longevity, and my preferred target is 20A for extreme longevity and balance. 20A happens when charging can start while the sun is low in the sky; not going to happen in the forest.
- the battery voltage is 13.6v
- cells are nicely balanced (8mV delta between highest and lowest; balancing commences at 15mV)
- the BMS estimates a this rate the battery will be 100% in 1 hour, 3 minutes.
As the sun rose charging current maxxed a little over 40A so it was done about 1230.
assessment
time
Recharging the LiFePO4 bank took ~1.75 hours of direct sun. The GC2 FLA bank would have taken ~5 hours due to lengthy Absorption. The available 3.25 hours of sun was sufficient fully to charge the LFP but could not have fully charged the FLA.
The LFP bank has done it’s job, allowing me to camp in areas of limited sunlight.
usability
Can’t put numbers on usability of the new battery bank, but it requires much less thought from me. Lithium doesn’t care about partial stage of charge, so I no longer worry about going into sundown at 100% SoC. I don’t run any major loads without sun support but I do find myself running smaller loads when I want to rather than when the battery can best support them.
battery monitor congruence
The $20 75A battery shunt I had in place tracks the battery’s voltage, state of charge, and time to full/empty surprisingly closely.
bonus - daily cardio
It’s mainly conifers (pinyon?) where we are camped. Muffin and I walked about an hour further up the road to a spot that had more aspens (?). They were dutifully dropping their leaves as colder weather approaches.
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