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”

backchannel: solar generators, charging AGM from alternator

OP is running a Yeti-style battery pack.

I charge a 20,000mAh external battery

Onlookers: 20,000mAh = 20Ah.

I’m out of the Van most of the day and charge that battery while I’m working

That is a perfect use case for such devices.  [not joking]

I do not yet own a refrigerator, but do plan to have a fridge and full house battery set up with AGM batteries within a few months hooked up with a solenoid to the alternator for charging. No solar panels for me as I’m stealth camping in New York City.

Something to consider when planning out the future setup: it will be tough to keep lead-acid batteries (including AGM) healthy with alternator charging alone. Possible workarounds:

  • charge the AGM periodically (2x/week or more if possible) from shore power at your work, using a converter. This will help limit damage from less-than-fully charging.
  • budget to replace lead-acid batteries more often.  Give real consideration to flooded batteries;  they are half the price and more resilient to abuse.
  • Normally I would encourage to a ‘dweller to grit their teeth and install a panel or two: the panel will provide high voltage, long duration charging to complement the high current, short duration charging from the alternator. BUT stealthing in NYC brings a special challenge — tall buildings make “urban canyons” that make direct sunlight a rarer occurrence than elsewhere.
  • Because of the urban canyon effect, I’d encourage you to think about switching to a battery chemistry that doesn’t care about state of charge. Both lithium and carbon-foam (a subtype of AGM) are much more tolerant about infrequent or incomplete charging.


backchannel: agm for vandwellers

Part of a response to a question I answered.  OP wanted advice on the short term only, and I’d overshared my thoughts on the long term.  I took it out and moved it here.

If you decide vanlife is for you, in the **long term** the biggest bang-for-buck in deep cycle batteries is 2x 6v golf cart flooded (wet cell) batteries in series, usually 200Ah+. They are able to take massive abuse and can be maintained (watered) when used hard. The purchase price is about half of what AGM cost, and they’ll likely last longer in this use case.

There are very few *actual* 12v deep cycle lead-acid batteries. The lead plates are so heavy they are not practical for humans to move. Hence splitting them up into two 6v batts. The 12v ones that do exist cluster on the high end: northstar, odyssey, rolls.

AGM weren’t developed for our uses; they were developed to for standby/backup applications where:

* normal liquid electrolyte would stratify when sitting still for long periods – this is not an issue for us because our batteries are agitated by vehicular movement.
* they could provide massive current suddenly when needed (ie, invert their power to AC to run cell towers when grid power goes out)
* would sit fully charged at float voltage (Vfloat) in perpetuity with limited damage

Our van battery banks are not still, do not stay fully charged, and generally speaking do not need the ability to dump massive current in a hurry.

exceptions to the rule

There really are situations where AGM is warranted but they are relatively rare in vandweller scenarios.

  • *  the ‘dweller installs the battery bank in a location where it is not reachable for normal maintenance
  • *  the ‘dweller needs to mount the battery on its side for some esoteric reason (or is 4×4 trekking so the RV itself can end up in weird angles)
  • *  the ‘dweller chooses to run heavier-than-normal loads like microwaves, electric coffeemakers, electric cooktops, etc. Note this means the battery can be drained faster (and bulk recharged faster), not that it provides more capacity.
  • *  the ‘dweller has has a chemical hypersensitivity.
  • *  the advanced ‘dweller is running a single battery for both house and starter systems (“shallow cycling”)  <– not for beginners!

backchannel: Lifeline batts and alternator charging

I follow the on Meryl and Me Hit the Road blog.  I read an article there today and thought some of the tech details would be worth talking about.  The article discusses the charging system[s] for the RoadTrek’s new house battery bank.

the isolator

[the battery seperator] is a “smart” switch – when the engine is running and the RV batteries need to be charged it connects the engine battery to the RV batteries and charges them through the van’s alternator. It also will charge the engine battery when the RV is plugged into shore power

This sounds like a dual voltage sensing relay (VSR).  Such a relay “senses” when either side has power to share and then connects the starter and house batteries.   The VSR is powered by the starter battery and is always “on” watching the voltage on both sides.

[A normal isolator (constant-duty solenoid) on the other hand gets power from the ignition wire so it is only “on” when the key is turned on. ]

Let’s unpack the quoted paragraph a bit; there’s a lot going on. Continue reading “backchannel: Lifeline batts and alternator charging”

Backchannel: AGM + bulk hole

from this thread:

I know it’s overcast, so I’m not expecting much but I’m having a heck of time keeping my batts charged. I’ve never had this problem before. My PWM controller is only showing that I’m harvesting 1.2 amps from 400watts of solar. I’ve called around, and even on a day like this, I’m told I should be pulling closer to 10amps.

Before folks start jumping in with “OMG what you need is hundreds of dollars of my favorite brand’s gear” I’ll bring up a couple general thoughts.  Continue reading “Backchannel: AGM + bulk hole”