"Larry Jaques" wrote in message
...
On Fri, 19 Feb 2016 20:54:47 -0500, "Jim Wilkins"
wrote:
....................
AFAICT, MPPT isn't cost-effective below 200W. I intend this small
system for power-outage backup and mainly use it to keep my battery
zoo well fed, for which a homebrew adjustable linear voltage
regulator
with Volt & Amp meters works fine. I built a 10A 0-35V adjustable
power supply to handle any deep discharges.
Yes, I concur, both for sub 200w cost-effectiveness and keeping my
little zoo fully fed from the HF trash rack. But I recently
invested
in an $11 "30A MPPT" controller from China, as a last-gasp backup.
g
I'm curious to see how long the deep cycle marine battery from Wally
World lasts in this environment, too. Quarterly battery level
checks
are now on my calendar, too.
My Bayite VA meter came yesterday, and I'll use it on the new solar
package (2kW, split 540w water heating/1620w household) once I
purchase and set it up. The solar water heater element will be run
through the AODE since I don't really need it on the HF setup. The
Bayite is a nice little meter. It comes with a 100A shunt, so a 50
is
on order for $5. It should give a bit more accuracy. An existing
20A
PWM controller will work fine for the water, but I want a good MPPT
controller for the larger array with the larger stack of batteries.
The 2kw of Sharp 180w panels is $1,550, a good controller $300-600,
and batteries likely another $500-1k. Eek, does it add up!
I put the shunt in a 1" PVC conduit tee like this:
http://www.amazon.com/Thomas-Betts-E.../dp/B000KKVTJG
The leads to the display are in-line fuseholders coming out the center
opening. The power leads out the ends are an octopus of all the
various sized Anderson connectors in my system, so it also serves as
an adapter hub.
I tried swapping the sense leads with a DPDT switch to read in either
direction, but the meter's operating current drop in the low sense
lead affects the current readout too much. A 3PDT switch that swaps a
separate ground wire might work, at the risk of connecting a sense
lead before the ground and maybe ruining the meter. I haven't found a
comparable meter that reads current in both directions, which would
probably require isolated DC-DC converter power to raise the current
sense above meter ground.
At this moment I have one of these recording the discharge -
recharge
calibration cycle of the APC's batteries:
http://www.amazon.com/UNI-T-Multimet.../dp/B007THZMWI
Interesting. Did you write your own datalogging prog, or use someone
else's?
I wrote the core that reads the COM port and hashed the LCD segments
to numbers, based on the method shown here for a Digitek DT-9062.
http://www.franksteinberg.de/SOURCE/DT9062.BAS
My German isn't good enough to completely translate it. I think Ziffer
is Digit and Zahl is Number.
That is QBasic which integrates some structures from c, even pointers.
It runs best under DOS where you have better access to the hardware
ports than Windows allows. If you install Win2K or XP on a FAT32
partition, dual-booted with DOS, it can access the whole hard drive
and share files with Excel.
I could easily save the readings to a file but I haven't yet figured
out how I want to graph multiple readings on different scales in real
time, so I just run each meter's separate program and combine the logs
in Excel (or OpenOffice) by aligning their time stamps.
This is supposed to read multiple meters:
http://www.ultradmm.com/
I've gotten a few correct readings back in Test mode but can't
otherwise make it run.
Normally the voltmeters on the batteries are enough to judge their
state of charge and tell when they need attention. The charge and
discharge of Lithiums is nearly 100% efficient and worth monitoring,
but lead-acids charge too inefficiently near full voltage to bother
with datalogging..
I thought reviewed data logs might be able to show me signs that my
battery stack was aging in time to replace them before suffering
downtime.
Between R&D jobs I tested field-return medical Lithium batteries that
datalogged themselves. Initially the users would charge and discharge
them according to instructions, then after a few months recharging
apparently became random and opportunistic and the batteries' internal
model of their capacity would drift off. They needed a full discharge
cycle to recalibrate the "fuel gauge", but that decreases their life.
APC suggests fully cycling only older batteries for recalibration,
maybe yearly. I used the apcfix program to reset the cal to the
initial factory value (9A), from what the dead batteries it came with
left it at (4B).
My batteries are 5+ years old and this was their first full discharge.
The UPS is still set for sealed VRLAs that shouldn't be charged high
enough to gas, so after the rain I'll have to lug them outdoors and
top off the charge to the higher wet battery level, and confirm if the
table I downloaded of the gassing voltage threshold is correct for
them.
Since sitting partially discharged allows lead batteries to sulfate, I
think the answer is to keep them topped up to 100%, with grid power if
necessary. The cost in lost battery life may outweigh the savings in
electricity from waiting for a sunny day. Tesla's Powerwall Lithium
batteries should be more tolerant of partial charge. However they cost
10x as much.
https://www.teslamotors.com/powerwall
I'm not convinced that solar electricity is cheaper than grid power
when using lead batteries.
--jsw