"bob prohaska" wrote in message news:t5scbb$n1d$1...@dont-email.me...
As I think it over, it does not seem possible for a battery charger to
accurately charge a battery in parallel with a load. The charger needs
an independent measurement of battery current, along with voltage, to
get an estimate of SOC. Three-terminals-and-shunt appear to be required.
Certainly possible, but not with off-the-shelf units I've found.
You are right, the charger can't determine SOC if some of its output goes
into the load, that takes a separate meter monitoring +/- battery current.
This does the job for my two DC refrigerator AC/solar/battery power
One is an identical Drok 200320. It looks like I bought the last of them
from Amazon. Here it is with the optional protection relay on AliExpress,
which I've never bought from.
The current sense is in series with the battery and estimates SOC from the
difference between charge and discharge currents. It displays Ah and
percentage of discharge, 0.00AH and 0% is fully charged. You program OAH
with your estimation or measurement of battery Ah capacity and then it
displays State Of Discharge as a percentage of it. Although remaining
capacity would be more useful, discharge is easier and more certain to
measure after you zero the meter at known full charge. By stopping at zero
it ignores extra charge current that goes to gassing and replacing
Mine needs external Vext from a small DC-DC converter to remain accurate as
the battery voltage approaches full discharge. Calibration requires loads in
the range of 1A to 4A at 12V.
The charger and load are in parallel and you'd have to measure their
currents separately if you wanted to know it for setup and normal operation.
I have a KAW on the AC supply and this on the solar input from the panels.
The SIN9020s shows load current from the battery when the AC supply is off,
and charging current when the load is disconnected.
With experience you can judge SOC well enough from only the battery voltage
when idle or under load. The meters I mentioned provide that experience and
detect problems. You know actual Ah capacity only if you've recently run a
full discharge test and even then it's not consistent between runs, and
varies with the load.
I've decided to purchase the packaged Ampinvt 800 watt inverter-charger.
That device unloads the battery when AC is available, so it at least has
a chance of getting the SOC right.
I'll start by experimenting with an old Delco Voyager deep cycle lead
acid battery. If the inverter behaves well I'll look into LiPO4, though
the prices do make me wince. I've had a LiPO4 starting battery in one
of my motorcycles since 2011 and the damn thing still starts. Lead acids
didn't last more than a couple of years with reasonable if not meticulous
Thanks very much for your insights!
Good luck. I buy and integrate separate components and modules to learn,
plus I have the equipment to fabricate sheet metal enclosures for them, so I
don't know what is available as fully packaged plug-and-play. Generally it
won't do what I want anyway, such as the charger/inverters that can't
measure SOC or detect a 40W load. I've been building custom electronics for
industry and the government since the 70's.
Adequate battery care appears to be topping them off every month or two, and
equalizing occasionally if you have the equipment for it. Modern vehicles
may need more frequent attention due to higher key-off battery drain. An
Interstate battery lasted 15 years in my truck, until its measured starting
current became marginal for a cold start. I traded a pair of marine
batteries after ~12 years when their remaining capacity was barely enough to
run a refrigerator overnight.
Yesterday I got around to completing the battery backup circuit for one of
my DC refrigerators, and set up a recently bought and restored APC1400 UPS
to power the error check of a new 5TB external hard drive. A few hours later
they were on battery, disconnected from the grid, for thunderstorms. That's