backchannel: this week in battery mistakes

not a deep cycle

> I put a single 1400Ah (700 useable) wet cell in my travel trailer at 170 pounds. No solar yet

Uh, no.  OP bought a marine battery with 1400 CCA.  Not a deep cycle, as s/he will find out within a year.


killing me softly

> 655ah of  batteries! … I got 960w of solar on the roof to charge them too!

  1. it’s a mismatched bank of one excellent AGM (Lifeline) and two other SLAs, presumably AGM.  Good luck with that, and my condolences to that nice Lifeline (excellent batteries, this example is ~$650)
  2. AGM requires C/5 charging current at a minimum.  Example:  lifeline says they require a minimum of .2C (C/5) charging or “the cycle life of the battery may be negatively affected”.  Ie, they will die early.
  3. The solar will provide  70A of charging on a good day (960w – at least 15% heat derating and DC-DC losses  = 816w,   816w / 12v = 68A.    .2C charging would be 131A for a 655Ah bank.   Kids in grade school can tell you that 70 is much less than 131.  About half.

backchannel: thoughts on gnomad home’s epic guide

FIrst off, much respect to them for tackling such an extensive article.  I don’t have the patience or talent to do it.

This post describes what we did with our own system based on our own research

A good start.  It does not claim to be gospel.

main components

The 400w Renogy kit is fine.  Could be sourced cheaper by the piece, but no biggie.

I like the 400w:155Ah ratio, especially since we are going to have an isolator installed.   The 155Ah AGM is ~$360.  For that money I would much rather have a set of Trojan T-105.    Longer life, lower cost.  If he really needs AGM I’d pony up another couple hundred for 6v AGM.  Still less expensive than the 12v by the lifetme kAh.  Continue reading “backchannel: thoughts on gnomad home’s epic guide”

backchannel: DC-DC charging myths

Outbackjoe’s info is excellent.  Here I will address some of his points about what he calls DC-DC charging myths.

 The most commonly reported myth is that your alternator cannot fully charge a battery.

It can, given enough voltage and enough time, as on a powered cruiser (boat), that spends many hours a day running the engine.   To some degree, time can be substituted for voltage (ie absorption takes longer at lower voltages).

Having said that, Continue reading “backchannel: DC-DC charging myths”

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!

abused GC2s finally died

I’ve mentioned that a year ago I bought some used 6v (golf cart) batteries for basically core price. I limped along with them since then, but the last month’s heavy use finally did them in.

I’m shocked they lasted this long. When I got them they were watered but had been stored discharged for months; they have voltages in the 2.x range (ie, seriously dead/sulfated).

Continue reading “abused GC2s finally died”

article: it’d be easier to get a job

from this article:

State police said they saw Griffen and Pohl in a vehicle and stopped them. They discovered the 17 batteries, police said. Police said Griffen and Pohl admitted to thefts at numerous trailer facilities in the Capital Region. According to police, the pair had been taking the batteries to local scrap yards…

“They were breaking into our yard and taking them off the front of the travel trailers… All of the batteries come with a core charge, worth somewhere between $10 and $15,” Heck said…. You’ve got to steal a bunch of them for it to add up to anything.”

That’s some low efficiency thieving right there.  One would think they’d look for something lighter and more valuable.

Maybe police should look for vehicles that appear to be overloaded?








Backchannel: seeking simple and correct answer

from this ill-fated thread:

I had a 300w Renogy Solar system installed at the Van build but I only had one battery hooked up. I have now bought a second battery to install into that system. I do not know how to do this. Do you have a simple answer that I can understand and follow as to how to install the second battery.

There is no way we can know what the OP can understand and follow.

Given that Continue reading “Backchannel: seeking simple and correct answer”

backchannel: single battery systems

from this post:

Can a portable solar system be used to charge your existing vehicle battery and then continue using the vehicle as your primary source of power? If that is possible it might eliminate the need for secondary battery (weight and space).

Yes.  I describe that usage in the Shallow Cycling rvwiki article.  Trebor and Sternwake on CRVL have both done it successfully.

I’m guessing that might shorten the life of traditional vehicle battery, IDK…..

We don’t know.

My reading suggests that starter batteries average about 36 months of useful life.  The main failure modes are: Continue reading “backchannel: single battery systems”