(ET) Multi-bank 12V chargers

[Ken Olum <kdo cosmos phy tufts edu>]

   From: "David Roden" <etpost drmm net>
   Date: Thu, 18 May 2017 01:49:21 -0400

   12V CHARGERS: This might be the cheapest route.

A related possibility is to get a multi-bank charger with isolated
outputs, so that you can charge three 12V batteries at once.  This is
probably more convenient but may not be cheaper than just getting 3
chargers.

I posted about this several months ago and there was a brief discussion.
I'll follow up eventually when I had some experience with my charger,
but here's a brief update.  I bought the Minn-Kota MK460 to charge four
12V AGM batteries in my Electric Ox.  It generally looks like a good
charger, but I have not got much chance to try it out because my tractor
is at the mechanic's with gearbox problems.

However, there is a very unpleasant issue, which is that the details of
the charging algorithm are secret.  I spoke to Minn-Kota and they told
me that in order to prevent someone from competing with them they will
not disclose the exact algorithm used in their charger.  It is a
bulk-absorption-float-off algorithm, with some odd properties.  It is
very slow to start up, not reaching full charging current for about 10
minutes, and the transition from absorption to float seems to me to be
at a rather low current.

I'll have more to say later when I have some more experience.

As David said, using 12V chargers only makes sense if you get rid of
your 18V tap, and you need to make sure before using your tractor
that the charging process didn't fail on any of the batteries.

                                        Ken