On Mon, 22 May 2017 08:34:11 -0400, "Jim Wilkins"
wrote:

"Jim Wilkins" wrote in message
news
"Larry Jaques" wrote in message
news
On Fri, 19 May 2017 16:13:34 -0400, "Jim Wilkins"
wrote:

....................

I bought this which has an easily set low voltage disconnect and
handles up to +/-30A,
https://www.amazon.com/DROK-Display-...ct_top?ie=UTF8


Previously I was using a rewired Battery Isolator I bought from
Quicksilver Radio for $5 at a hamfest to disconnect the load when the
voltage dropped. This describes the idea:
http://www.fridge-and-solar.net/The-...-Start-VSR.htm

Great price!


The rewiring changed it from switching the load to the second battery
when the main one's voltage dropped to switching one battery from the
load to a charger.

Discharge in series? Sounds like a plan.


As a discharge controller it has the disadvantages of still drawing
current from the main battery to operate the relay after it has
discharged to the disconnect voltage, and needing an adjustable power
supply to set or check it.

Those I've seen only engage the relay to switch to the secondary
battery. Are you talking about when the secondary battery is
discharged/cutoff and the relay continuing to be engaged? I see that
as a problem, too. Perhaps rig up a kickout relay to disengage when
the cutoff hits on the secondary?


I haven't seen that remaining for an hour or so at full discharge
would further harm a battery and want to record the voltage it
recovers to without any load as an indication of true remaining
capacity and a safety check that I haven't set the disconnect voltage
too low and drained the battery too far.

Yeah, that's a fly in the ointment of capacity measurement. Are you
saying "full discharge to cutoff point" there?


If not for its poor current resolution the 30A Drok unit would be a
fine discharge test controller when powered from an external 12V
supply that separates its operating current from the test circuit. The
circuit board was drilled but not properly connected for an SPDT
version of the SPST NC relay it comes with. I'll set the Battery
Isolator to a lower disconnect voltage as a backup on the load side of
the Drok.

There ya go!


Based on Amazon comments, it seems the 3-wire / 2-wire jumper may
select battery circuit or external power to operate the device.

It didn't look like that was fully populated in the pic I saw. IIRC,
it had only one pin/solder joint out of the 3.


A DC-AC inverter powering a safe resistive load like a crockpot can be
used as a discharge test load though you can't set the dropout voltage
and it may cycle back on when the battery recovers.

Hmm, yeah.

--
I started out with nothing and
I still have most of it left!
--anon