bears and batteries, oh my

Yesterday was eventful.

hi bear

On my way out of the campsite to pick up the new battery in town (see below) I saw my first bear running across the trail about 100ft ahead. I checked later on the dashcam footage and caught this image. The cam was set to 720 so it’s hard to make out. There’s another shot of him continuing across a trail to the right but it’s even harder to make out because of the vegetation.

Based on his small size, timidity, and known activity in the area I’m pretty sure he was a black bear. I’d guess he was about 4ft long and maybe 200lbs?

hi 280Ah bank

pick-up

I picked up the SFK battery shortly after it arrived. It looked like rain when I got to the UPS store and was hailing when I walked out. :-( Not an auspicious start!

The box was 60lbs so I lifted/carried it for the countergirl. /makes man noises

unboxing

The battery was lovingly double-boxed and padded with open cell foam. The inner box was taped and the outer box secured wth big staples.

The rope carry handles made for easy extraction, other than it just being heavy, around 55lbs.

None of the lights on the GEN2B switch were on so I

• enabled Bluetooth
• and set the active balancer to HI BALANCE mode, which only balances above 3.3Vpc as far as I can tell. There is no visibility into that balancer other than watching the cell voltage deltas (see below).
• [I did not opt for the internal heating pads so the heating controls are not functional. I already had an external heating setup and so did not pay more for internal warming.]

I used the SFK app (see below) to connect; the batt arrived at ~43% SoC / 13.17V as seen in the pic.

installation

I shut down everything and installed the new batt right there in the parking lot. It took a while because I had to move stuff out of the way, etc.

Fired everything back up with no problem.

heading back to camp

Not much sun but the mounted array did make a little progress on the way back to camp.

By the time I made it back to camp and plugged in the portables it was dark enough that both arrays were down to single-digit wattage and the bank was discharging.

overnight

By morning I was down ~49Ah, pretty typical for my evening and overnight loads.

morning, charging

I started the van to see what charge acceptance through the relay would look like. I saw 34A, slightly more than the previous bank. This suggests that the resistance in the rest of the circuit is dominating the equation and the battery resistance itself is nearly immaterial. I’d like to get ~60A out of the alt so I’ll think about how I might get the circuit resistance down.

I’m still hiding in the treeline so I only have full sun on the main array until 10AM. After that the main array (and the van) is shaded while the portables stay in the sun. Until about 5pm when the tall trees get those, too.

It’s Friday now, but between the shade and the monsoon rains it might be Monday before I see 100% SoC. I’m not in love with 100% but it will allow me to sync the battery monitor and stress test the active balancer..

cell balance

I’ve only seen it between 28% and about 57%, but cell voltage delta has been 1-2mv. Sometimes dropping to 0mV or rising to 4mV. I will update this later as I see the delta at higher SoC.

Update: thunderstorms took over in the afternoon. Ended up getting ~110Ah stuffed into the bank. The shunt and BMS disagree, but I think the bank is ~58% SoC going into sundown.

Update on Saturday: got up to ~73% before the rains started again. Highest delta I saw was 5mV, and that just for a moment. In general it’s staying around 2mV.

charging plan going forward

Since I now have excess capacity I can start running the bank more in “the middle SoC”. The hard part will be targeting 80-90% SoC off a variable charging source like solar.

charging C-rate

with my existing setup

• solar max charging¹ is ~40A, or ~0.14C.
• alternator is 34A, or ~0.12C.
• theoretical combined might be 74A, or 0.26C.²

So I might try 13.6v or 13.7v with varying amounts of Absorption to see if I can ballpark the 80-90% SoC figure.

in case of inclement weather

The above settings should be fine in normal use, but if solar harvest is compromised in the immediate future I would charge to 100% then.

It would be possible to save two different versions of the Victron config for each of the two controllers and swap them out as needed. Or I could repurpose the equalize function which I have disabled. I defined it as 14.0v so I could pseudo-equalize ahead of the Bad Solar Days.

the SFK app

The Sun Fun Kits BMS app works only with their JBD-related BMSes. There are a couple interesting features:

• the ability to combine multiple SFK batteries into on “virtual battery” with combined info. I only have one so this isn’t for me.
• discharge test. I use the bank full time and will have no opportunity to use this.

… but overall I think the Overkill-enhanced JBD app is more practical for my uses.

comments

mastodon comment thread for this post
lemmy comment thread for this post

1. net charging after loads ↩

2. in pratice the current pulled from the alternator is strongly affected by the solar charge controller pushing up bank voltage. The reduces the apparent resting voltage between the bank and charging source, thereby reducing current from the alternator. I=V/R and all that. My general observation is that strong solar contribution reduces alternator current by about half. So maybe 57A (0.2C) combined? ↩