backchannel: explorist life video on alternator charging


his upcoming upgrades


later this year we are doing some electrical system upgrades that are NOT going to include alternator charging.

This is a weird phrasing, since in the comments he says:

We are absolutely going to be putting alternator charging in our Transit.

Are we talking about two different campers here?

charging rates


The first thing I want to talk about is the three charging rates of different alternator chargers

He arbitrarily picks:

no mention of non-Victron DC-DC

no discussion of direct charging

A 300Ah bank charged by relay2 will charge at an average of 0.33C, or 100A. So let’s add a couple more options where appropriate:

I personally charge my bank with a Battery Doctor VSR left over from the original FLA bank. $1.41/A. I added a switch to disable at will so to be fair my actual cost is $1.67A.

I do understand he may not want to expose unsophisticated users (see below) to direct charging, but a mention would have been more honest.

how long does it take?

He explains that, yes, it will take 10 hours at 30A to replace 300Ah. This is grade-school math and I am a little concerned his intended audience needs a calculator (with sliders!) to do it.

Note that it would take exactly the same amount of hours to charge that bank with 30A, 100A, or 200A of solar. Except 100A and 200A solar is exceedingly rare on campers.

Also note he must be talking about lithium here, because lead-chemistry charging takes what it takes to finish Absorping and the time doesn’t vary much when charged between the minimum and maximum current rates.

This would be a great place in the video to discuss how driving patterns affect the practicality of alternator-charging installs.

how much solar


another consideration … is how much solar do you have?

That’s half of it; the other half is how much insolation do you have?. Having 1000w in winter in Finland isn’t going to do much. OTOH, 1000w in the desert Southwest may meet needs year ‘round.

the Victron tour trailer example


The trailer had

  • 2000w of solar
  • buck/boost 100A DC-DC

In a real world scenario that 100A buck/boost is only 1200w

How much does he think that 2000w array will be pumping at 8am or 4pm? Even at local solar noon it might max at 138A (using his 12.0v constant). How much did the array and Victron solar charge controllers cost?

… it would have been more beneficial just to let solar do the charging and not even use alternator charging…


  • solar ~1660w
  • solar+alternator ~1660w + 1200w = ~2860w.

And that’s best-case scenario for the solar. Run those numbers again for 8am.

solar <800w


now if you’re in a campervan or something much smaller and you can only really only have 400w to 800w of solar then alternator charging is pretty much always going to be a good idea

I think ≤800w covers the vast majority of RV solar installs, not just campervans.

I think he should pull and reshoot or recut the video to more clearly lay out alternator charging options.


mastodon comment thread for this post

  1. I linked to the 50A version. 

  2. negative return through the chassis