backchannel: AGM @ 80% depth of discharge

I’ve seen similar claims before, but I haven’t done the homework until I was inspired by this one:

>they are design such that you can use more of it without damaging the battery’s lifespan. So comparatively, AGM compared to FLA batteries with the same rated capacity (the same amount of lead in them) will have more USABLE capacity.

I could think of no particular reason that vanilla AGM should enjoy more cycles at very deep depth of discharge (DoD) compared to flooded, excepting maybe the exotic carbon-foam variant.

So I started doing the homework.  It took less than a day because Continue reading “backchannel: AGM @ 80% depth of discharge”

backchannel: island of misfit [solar] toys

Our unfortunate fellow has already spent hundreds on some stuff that won’t play well together.  Each component is fine on its own, interestingly enough.

good news first

The setup (other than the oversized inverter) is sized rather well.  200w of panel, 20A of b2b charging, and 100Ah of battery.   Good.

the less good news

Renogy needs to be horsewhipped Continue reading “backchannel: island of misfit [solar] toys”

solar yield in overcast conditions

Over the past few years I’d estimated that my system puts out about

  • 25-33% of normal max in bright overcast
  • 20% in overcast
  • 10% in dark overcast

It was guesswork, but then I saw this article that gave lux for various sky conditions.

I plugged the values into a spreadsheet to convert the lux into theoretical max yield for a 100w panel:

should be “lux” not “lumens”

That lines up pretty closely with my observations.



Mythtesting: higher voltage for additional yield in the mornings

I am a fan of higher-voltage panels, serial panel configs,etc for several reasons.   But I think there are some hyperbolic claims about their ability to collect extra power in the dawn/dusk shoulders.

The theory (and actuality), illustrated with 2x 100w 12v panels is that

  1.  solar panel voltage stabilizes above ~20% insolation;  below that it falls off into a trough precipitously.
  2. for our 12v panels wired in parallel, this “trough” voltage (not a real term)  is below battery charging voltage then the panel cannot charge the battery; zero power is harvested in these low light conditions.
  3. consider the same panels wired in series – their trough voltage is likely high enough to charge the battery;  some power is harvested.

The matter at hand today is to find how much power can higher-voltage configurations harvest in the trough?

I will illustrate with some sloppy, illegible charts.  I suck at those.

Continue reading “Mythtesting: higher voltage for additional yield in the mornings”

AGM for weekenders

Off-grid charging AGM is challenging and expensive;  doing it as a weekender can be easier and less expensive since we can ward off battery-murdering sulfation with vigorous and timely charging just before/after the weekend outing.


  1. make it through the weekend outings with power for light-to-medium loads
  2. without murdering AGM batteries due to undercharging, by using a minimum of C/5 (40A) charging.

Scenario:  camper has 200A of AGM and 200w of panels.  The panels are not intended to fully charge the batteries, only to support the batteries over the weekend and get them back to at least 12.7v during the day.  Vfloat would be nice.   Campground is an hour away from the house.   Batteries are fully charged at the house just before leaving and immediately upon return.  When not camping (ie, not cycling), 200w of panel will keep the house batteries maintained.


  • there is a huge cost difference between fully charging lead batteries to manufacturers specs in the field and keeping them alive in the field and fully charging at home.   We aim to exploit that difference.
  • Configurations with B2B (aka DC-DC chargers) can be fed at home with 12v power supplies, since they will step up voltage.    Configs with isolators will require a smart converter.

From most to least expensive, not including battery costs:

Continue reading “AGM for weekenders”

hot shower, hot laptop

hot shower


  1.  I have copious amounts of water here, and
  2. the weekenders left

I decided to take a hot shower.   I put a couple gallons in the solar shower bag and left in the sun for a few hours.  The water was actually a little too hot for comfort, but there was a brisk breeze that was a bit chilly.

The actual shower took about 3/4gal;  after I finished the formal showering I just stood there and let the rest run over me.  Small pleasures!

hot laptop

My daily driver laptop is a previous-generation refurb Chromebook, which I use because its power consumption is laughably low at 16w.  But I also have a real laptop (debian linux) for heavy lifting, compiling, media editing and playing Minecraft.  It’s an old business-class Dell Latitude which apparently cost $4,000 when new.  I bought it off eBay for $120 shipped, IIRC, and doubled RAM to 16BG.  Also slipped in a half-gig SSD drive a couple year ago.

It’s a beast, but tends to overheat and shut down when used hard at ambient temps above 77F.  I did some reading and it appears the thermal paste between the CPU and cooling gear was substandard and/or poorly applied.  Since it’s not my main PC I basically just avoided the issue, but I did order some well-reviewed thermal paste off Amazon.

Today I finally pulled the cover off, removed the old paste and applied the new.  I stress-tested with Minecraft at 78F and it didn’t get squirrelly, so hopefully it’s fixed.   I have some CBSRMT tapes I want to digitize and edit, which will push the CPU around a bit.  We’ll see.