On Fri, 2 Feb 2018 20:11:26 -0500, "Jim Wilkins"
wrote:
"Larry Jaques" wrote in message
.. .
On Thu, 1 Feb 2018 19:37:14 -0500, "Jim Wilkins"
wrote:
.....
I finally found a fairly decent and inexpensive battery monitor for
home energy projects:
https://www.amazon.com/DROK-Multimet.../dp/B01M5CWR2P
...
Yes, charge current is a good indicator of SOC. UPS batteries seem
to
last longer with their stingy system chargers, a good thing.
I've heard that power wheelchair batteries may not last very long
because the user charges them only while in bed, so they rarely reach
full charge.
Huh? Not fully charged after 8-10hrs?
The numbers are 1-2 years, compared to maybe 5 years for
the same battery in a golf cart that has longer to recharge. I know
from a job repairing medical equipment that the owners buy the
cheapest wet batteries when the original AGMs die. Supposedly that's a
consequence of the slow and fussy bureaucracy of government
healthcare.
My neighbor found out that Medicare won't allow things to be recycled.
They will fund new items only. 2-month old hospital beds, 6 month old
3-wheeled electric scooters, etc. which are perfectly serviceable are
just tossed. That sickens me. Penny wise, pound foolish, as the
saying goes.
My backup system could have the same charging problem. I hope a week
or so at partial discharge followed by a full equalizing charge
outdoors after the grid returns won't hurt the batteries much.
It shouldn't, but with _your_ batteries... LOL
While dedicated Lithium battery fuel gauges can self-calibrate this
one has to be told the battery's Amp-hour capacity. The capacity
indication appears to ignore the excess A-h charge when a lead-acid
is
on float and starts the discharge percentage at your programmed
value
of 100%. It looks like the A-h total will drift due to full charge
float current unless reset. I'm hoping the A-h total will remain
useful while the battery is partly discharged during an outage..
These sounded smarter, at first, than their Bayite predecessors.
More importantly the VAC-1100A measures bidirectional current in the
ground lead of the supply that powers it, meaning that one current
sense input functions at as much as -37.5mV below the negative power
supply rail. The other +/- current meters that I have need an isolated
power supply that lets them float the negative-lead shunt up to their
+1.2V reference voltage. However the meter vendors don't offer a
suitable step-down switching power supply with an isolated output.
I've been using cheap surplus cell phone chargers with obsolete plugs,
which are fine for bench testing but not for running on DC during
power outages.
I've mentioned both this power supply problem and the poor/absent
manuals to Drok. Perhaps they listened.
That's good.
I tested it with full discharge cycles on an old 12V 18A-h AGM that
has deteriorated to 2.5 Amp-hours,
A test bed is a test bed, but 1/6 cap? snort
It was the best one remaining from a bunch of second-hand exit light
AGMs I acquired around 2010. Its low capacity minimizes cycle times
while I check out the discharge testing hardware.
OK, it does what you need.
What was wrong with the relay version, circuitry or relay contact
failure?
A flaky USB connection, and possibly intermittent measurement errors,
I only checked it briefly and may have misread the tiny display. It's
for unattended discharge capacity testing using the relay to
disconnect the battery at 10.5V, but those tests are time consuming
and way down on my to-do list.
It's hard to stay attentive to long-term monitoring. I tend to set my
watch for a handful of minutes, then go check, resetting the watch
alarm each time.
Previously I used separate unidirectional meters to measure
Watt-hours
in and out. The problem is that a lead-acid discharges at a lower
voltage than it charges, which creates a difference between the
Wattage totals.
Yeah, that sounds self-defeating, with the lead/lag A/V play, but
now
you know.
I thought I could correct the Watt-hour difference with a simple
factor like 12/13, but the discharge voltage drop also varies with the
load current, SOC and battery age. For example after that old AGM
drops out at 10.5V @ 5A it recovers to about 12.1V. I pulled 5 A-h out
of it at lower current.
Internal resistances play havoc with everything, triggering dropouts,
alarms, etc. Batteries can be perfectly good for most things, but try
to start a car with one and it will go TU in a heartbeat.
What do you make of these: 12 Volts Lead Acid Battery Desulfator
Assembled Kit | eBay
https://is.gd/5cBjNg $8 (120Hz pulse)
Voltage would be a good indicator of state of charge
if I could leave the battery alone to settle for a few hours, but
not
when I need to be using the power.
True. What are you going to do with all that -power-, though?
2.5Ah!
Wow. gd&r That's enough to idle your laptop with the monitor
off.
I have nominally 4 KWH of storage and a measured 300 Watts of 24V
charging power, slightly more than enough to keep up with the fridge,
two computers and the TV or to replace what the fridge used overnight.
Whew! I'm glad it's not just that one battery. :-) What does that
4kwh work out to in ah? 166.7? Not a bad set. (Pair of group 27s?)
--
Stoop and you'll be stepped on;
stand tall and you'll be shot at.
-- Carlos A. Urbizo