backchannel: Solar Systems Charged and Challenged

from this article in Truck Camper magazine.

What these folks don’t realize is that many RVers don’t need a solar panel system and would be better advised to upgrade their battery banks.

No warning bells, but wakes me wonder how he’s proposing to fully charge lead batts offgrid without solar.

Is a solar panel system a cost effective option for truck camping?….the answer in most cases is no

Solar is expensive per watt, but if it’s the only effective solution to a particular problem then cost effectiveness is not paramount. Continue reading “backchannel: Solar Systems Charged and Challenged”

backchannel: nothing crazy

>nothing crazy just like charging phones maybe a toaster or a hot plate

It never ends.

  1.  searching the group would reveal the previous umpteen times it’s been asked/answered (ie, hopes dashed)
  2. charging phones takes about 10w and can be run off a $5 cigarrette lighter USB port.   Running a toaster or hot plate typically takes over 1000w and thousands of dollars of gear.


Also neverending, clueless poster is a druggie.


electric kettles

Wifey wants an electric kettle.

There are, generally speaking, two ways to boil non-trivial quantities of water in a campervan:

  1. propane – a $40 method that works all the time.  Also accepted:  butane.
  2. off-grid electric – $1000+ method that works some of the time

You’d think this would be a no-brainer, but “electric kettle” comes up over and over.   I think this is a framing error, the failure to realize that a campervan is not an apartment.




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”

the problem[s] with 1:1 solar charging

this is a draft

1:1 rule of thumb

There is a rule of thumb that says a 1:1 ratio is the minimum amount of solar needed to charge a deep cycle bank.  The long form is 1w:1ah, which means 1 watt of solar panel for every amp-hour of lead chemistry deep cycle battery capacity under good insolation.  So if you had 150w of panel and 100ah of battery it would be 150w:100ah, or 1.5-to-1.  Yes, I know the case on the unit abbreviations is wrong but it’s easier to read.

As with all rules of thumb, it serves as Continue reading “the problem[s] with 1:1 solar charging”

laptop cooling update

The thermal paste fix has made a huge difference.  I played Minecraft in 92F ambient the other day (hottest day in Twin Springs just before I bailed).  No issues.

Normally I use the chromebook because of the low power consumption, but I’m getting such good sun here in Boise NF that I am running the laptop this morning.  This means I can do some extra stuff:  Continue reading “laptop cooling update”

backchannel restraint

So proud of myself.  Didn’t post the following:

It’s not “hidden in the manual”, the manual doesn’t say “it’s bad”  and it’s not a “bad controller”.  This situation derives from a failure to understand product specs.

To paraphrase Dave Chappelle, “that’s how PWM works;  that’s what PWM is for.”   I encourage you to slow down on buying components until you have a fuller understanding of how they work and how they support whatever it is you want to accomplish.


To give you an idea what he’s up against,  in the same post he says “Keep in mind that for now I’m only feeding the one single Optima Blue Top AMG battery“.  This is an idiot trifecta (quadrafecta?):

  1. it’s a “marine hybrid”, not a deep cycle in any normal sense
  2. AGM is a poor choice for solar-only charging
  3. it’s AGM not AMG
  4. Optima is hype, overpriced for people who thrive on marketing pap. The Optima he bought is roughly 6x more expensive than a normal solution, and will underperform.

An Optima battery icon could be the avatar assigned to offgrid folks who make counterproductive choices.


backchannel: new guy nails small solar setup

Most of my backchannel comments are lamentations about bad decisions and techncal ignorance.  But this newcomer did a great job designing a small system: and it’s worth talking about.

> Just need enough power to charge a phone and occasionally a laptop, power the roof vent fan, and a small rv fridge would also be nice.

It’s nice to see someone have a reasonable expectation of what can be powered from a small setup.  No electric cooking, no A/C, etc.   Carry on.

Here are the parts he picked out, and my comments on them: Continue reading “backchannel: new guy nails small solar setup”

solar challenges


I mentioned that I am in the NF above Midway, UT.

Solar power yield had been marginal due to partly cloudy conditions and partial shading from the (birch?) trees.    The rare pullouts on this forest road are shallow and don’t leave a lot of room for solar-friendly placement:

shadecloth “awning” clipped to rack

Under normal circumstances I finish Absorption around noon.  In this spot, though, full charge had been completing around 4pm.

The weather turned bad Continue reading “solar challenges”

backchannel: panel rated output is “a marketing ploy”

from a comment on an amazon review

>Thus 175W is just really a misleading a marketing ploy to take advantage of dumb consumers, and the number is nowhere realistic.

No, 175w is the measured output in lab conditions which customers can use to compare apples to apples.   The company can’t help it if customers are idiots.  The best they can do is provide correct information.
Consider these analogies:
  • “The pamphlet says the car has 400hp but it only makes 45hp when I have the cruise set on the highway.”
  • “The pamphlet says the car’s top speed is 200mph but it only goes 15mph when I tow it with a tractor.”
A given customer’s ignorance does not mean measured ratings are marketing ploys.
> Wouldn’t it be great if the solar industry came of with , and used, a realistic “actual 12V delivered” (A12D) power spec that consumers could really trust (and respect).
“Actual 12v” delivered in what conditions?  With what controller?  What battery voltage?  What insolation?  What weather?  What panel tilt?  What ambient temperature?  Output is affected by all of these.
Counter-query:  wouldn’t it be great if customers understood the products they bought and didn’t shit on sellers out of ignorance?
The panel’s specs are published right in the listing, dingus.  Learn what they mean, and learn how they apply to your very specific (and always changing) situation.