On Wed, 21 Dec 2016 14:24:36 -0500, "Jim Wilkins"
wrote:

"Michael A. Terrell" wrote in message
...
Jim Wilkins wrote:

The HF carbon pile has a 15 second timer to warn you to grab the
reading and turn the current down. Since it's unstable at low
current
/ light pressure I didn't attempt to determine how much power it
could
handle continuously. My guess is less than 100W, from comparing the
disk stack to wirewound rheostats of similar size. The timer
circuit
limits the voltage it could withstand.

The manual specifies:
"15 seconds per test with 1 minute cool down"
"3 tests in 5 minutes maximum"

500A is claimed to test a battery rated at up to 160 amp hours or
1000
cold cranking amps.

When the battery on my main vehicle was drained by leaving the
hatch
ajar for a week I replaced it to avoid the risk of getting stuck
somewhere in frigid weather - right now it's 3F outside.

I traded in a junk battery and kept it and it's still good for 150A
at
16 years old. The HF load tester is to help me squeeze more life
from
batteries I don't depend on.


https://archive.org/details/73-magazine-1976-11 page 159 Has an
adjustable solid state load. You can add more pass transistors to
increase the current it can handle. You could add an op-amp and a
DAC to set the current from a computer if you want to get fancy.

Have to check that out.


I used a large water-cooled active load to test battery packs at
Segway. I don't need that much expense and complexity at home since I
don't sell a product that I have to guarantee. I do have enough large
fixed and variable power resistors to pull up to 65A continuously from
a 12V battery.

Ceramic wirewounds? That's some watts! I'm switching to a 20gal
water heater and using the 1kW of solar to heat it with a 900w 24v
element. One of the two original 3,800W elements will be left
installed and put on a timer to run for one hour (while power is
available) to bring it up to heat if the solar doesn't make it. The
bursitis is easing so I'll be back on the project some day soon,
weather permitting.


Instead I use DC-AC inverters as constant-power discharge loads with
low voltage shutoff to protect the battery. My standard loads are a
30W soldering iron to imitate a laptop and a 100W crockpot which
approximates the laptop, keyboard light and an external TV/monitor.

The inverters draw more current as the battery voltage drops and
reflect the available runtime of a real load better than a
non-compensating constant current or resistance load would, although a
resistor load is simpler and may be a better long term indicator of a
battery's age deterioration.

I bought a battery protector that I haven't tested yet, too many
outdoor projects. It's intended to switch a boat or RV to a backup
battery before the primary one drops too low to start the engine. I'd
have it switch the battery under test from the discharge load to a
charger. The datalog will capture the time of the jump.

Why would you run accessories on anything -but- the acc battery, Jim?
Relay charges both when power on/engine running, but only the acc
battery is used when the engine is off. Your main starting battery
stays full at all times. Install that protector, mon. They should
draw no power when the switch is off, and the coil only takes a dozen
or two watts when it's on, so it's not a noticeable drain on the
alternator. That's a half hour project.


Serial- or USB-connected DVMs are fine for logging batteries because
their 1 or 2 readings per second rate is good enough and being
optically isolated they're unaffected by the common-mode ground
voltage differences that high currents produce in cables.

Good call.


Plus they can't accidentally short-circuit the battery through the
laptop. I was fortunate to be facing away and slightly outside the
fireball when the tech next to me caused that type of accident with
scope probes.

Oops! Lucky man, you are.

--
....in order that a man may be happy, it is
necessary that he should not only be capable
of his work, but a good judge of his work.
-- John Ruskin