leaving ELP, adding battery bank capacity

final errands in El Paso

Did a few things; fueled up, filled water, ate Menudo one last time at L&J Cafe. Mmmmm.

the drive

I left Monday morning heading toward the Yuma area. Headwinds were strong so after a few hours I pulled over and napped and waited for the sun to go down. After sundown I drove a few more hours then stopped for the night.

Note that Monday’s driving (“two days ago” in the screenshot) meant the vast majority of charging was by alternator; the solar only needed to contribute 590Wh. The 14.01v overshoot was me failing to disable alternator charging soon enough. I try to disable it when the bank is closing in on 13.8v. The alternator is a bit of a blunt instrument and I’d rather let the surgical solar charge controller handle Absorption.

Tuesday I drove the last couple of hours. It was severely overcast all day and the solar made 800Wh but couldn’t finish Bulk. Today it is sunny and we should get to 100% SoC even dragging the additional +50Ah up to speed (see below).

Edited to add: during the dark overcast the Victron held Vmp (for ~45w) where the EpEver’s algo would have crashed ~7.5w). It’s only a 37w difference but in poor conditions every watt counts.

a grocery stop at Green Tree

One of my favorite things about the southwest is the presence of food salvage stores. When I find them I do my shopping there then fill in gaps at a regular retail grocery. I got a cart of stuff for $22. Examples:

  • 2.5lb box of grits for $1
  • 1lb Jimmy Dean sausage $2
  • bag of duritos (Mexican snack that Doritos were probably named after) $0.50
  • 3lb of coffee beans for $3. Purported to be Starbucks beans for cold brew (“70% Narino Colombia Supremo and 30% eastern African”) although they are bulk packed. I’m not a huge Starbucks fan but the beans are decent and they are aggressive about selling off the barely-expired ones. Yes, please. I’ll try them hot-brewed as soon as my current canister is done.
  • Topo Chico water for $0.50. I love this murderously-carbonated water but it’s to find for <$1.

I intended to stop by Walmart but the fridge was full after the salvage run. A good problem to have.

American Girl

American Girl Mine BLM area is a common wintering spot; the nearest town is literally called Winterhaven. Temps will start rising into the 70s which will nudge everyone further north and/or up.

adding to the battery bank

My 100Ah works well for my purposes, but I got donated a 50Ah Chins LiFePO4. Theoretically batts should all be of the same capacity, age, cell mfg, etc, but experiments by Will Prowse and Offgrid Garage suggest each will give/take according to its relative capacity.

I put the Chins on a bench power supply and got it up to the voltage of the existing 100Ah Rebel battery. When they were about the same I shut everything down.


I turned the Rebel 90deg so the smaller batt would get maximal contact with it. They are sharing the 16w mat and the temp probe is between them.

Then I hooked them in parallel with wires left over from the 2x 6v bank. For connection to the rest of the system I took POS from the Rebel and NEG from the Chins. It is possible this setup will limit throughput to the size of the smaller batt’s BMS (50A) but I have not considered it carefully. If that turns out to the case I will get additional wiring and connect both to a common bus.

When I reconnected the bank to the system most things powered right back up but two did not.

a moment of confusion

Two problems: the Battery Doctor VSR didn’t come back on and neither did the battery monitor. What the heck?

I sat for a few moments and tried to lower my heart rate. I broke out the multimeter and saw 12v everywhere I expected to.

Ahh. I had turned the VSR off with the switch, and had accidentally unplugged the monitor’s display plug while rearranging. :-) This reminded me to reset the monitor’s Ah setting from 100 to 150.

powering back up

I turned the panels back on and re-enabled charging in the new solar charge controller. It’s been pumping about 490w since then, very close to the 475w the math would suggest for this location and time of day.

It will be interesting to see if the isolator charging current ramps up (45A?) or will stay in the same ballpark. The stock alternator is 180A so it’s not like 30A vs 45A would make a difference to it.


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