"Larry Jaques" wrote in message
...
On Fri, 13 Sep 2013 10:01:37 -0400, "Jim Wilkins"
wrote:

The Schottkys are D1 and D2, in series between the panel and battery
on the positive side. When one failed short the charger kept working
normally. Q6 connects the negative side.

Why the 2nd diode on a DC-only circuit? Reverse polarity
protection?

Likely inadeqate current rating. They are 3A diodes in a 4A circuit.
The problem is that if one heats up its forward voltage will drop and
it will hog all the current, assuming they were initially matched and
shared evenly (Ha!). I may have caused that by adding two more solar
panels which pushed the current over 3A.
http://en.wikipedia.org/wiki/Thermal_runaway
"Typically, one device may have a slightly lower resistance, and thus
draws more current, heating it more than its sibling devices, causing
its resistance to drop further. The electrical load ends up funneling
into a single device, which then rapidly fails."

The replacement 10A diode is larger and doesn't fit under the heatsink
clamp. I hung it off the side of the board.

When I do get a day off, it has to be a real down day for
my body to come back and be able to handle the next week's work.
It's
hell getting old.

Monday I cleared some brush as volunteer work, then spent the week
nearly immobile while my knee healed. I need the exercise but not the
injuries, so I put in for the less physically demanding building
maintenance committee. I'm a much better carpenter, electrician and
plumber than landscaper anyway.

The kit can just about keep up with my laptop's
20W-35W demand.

Reminder to self: check -my- laptop's current draw.
...
I went the Amazon route. It's in the queue, too. I was going to
wire
it up at the controller, inside. Are you using it at the battery to
check charging rates per panel? Maybe I'll rethink this.

The analog meter is wired with 2-pin trailer connectors like the newer
plastic-framed panels use
http://www.newegg.com/Product/Produc...9SIA1SR0H18836
so I can insert it into the circuit indoors before the controller to
show that everything is still working, or out at the panels to aim
them for maximum output. I use a digital multimeter to check
individual panel output with much better accuracy.

*Testing a cigarette-lighter DC-to-AC inverter of Chinese origin
showed it would happily drain the battery down to 7V though it
claimed
to have a low battery shutoff.

Oops. g I'll have to check my finest HF product for that, too.

That inverter came from a second-hand computer store, marked down, in
an unlabelled bag. It tested OK except for the failed low-voltage
limit and should be fine in the car where the ignition switch controls
the lighter outlets. The HF inverters I have do shut off when the
battery drops to around 10V. Thus they make good battery discharge
test loads with a lamp or crock pot (safer) plugged in.

If you don't have a data acquisition system, this free program can
record the discharge of a laptop battery, and capture the time when an
inverter or UPS powering the laptop shuts off and it switches to
internal battery power.
http://www.hwinfo.com/download.php
The program's continual file writes keep the hard drive active, more
or less as you would if using the laptop on battery.

I tested the inverter's low voltage behavior with a 30V 5A lab supply
like this, bought locally:
http://smart-prototyping.com/index.p...product_id=177
Lab power supplies with adjustable current limits are great for
measuring component parameters IF you know what you are doing and are
careful. They are good fire-starters if you don't.
http://electrojumble.org/reforming.htm

That one makes me nervous with loud relay clunks from inside as I turn
up the voltage. I don't know if the output can briefly spike. It may
have a capacitor downstream of the current regulator because I've seen
readings start high and then settle to the regulated limit, and the
current readout isn't completely stable at high current and low
voltage such as measuring the forward drop of the Schottkys. Otherwise
it's been a good lab supply and universal battery charger / salvager
for the price.
http://batteryuniversity.com/learn/a...alizing_charge

I use my homebrew Variac power supply (0-40V, 20A) to check
flea-market laptop 12VDC laptop power adapters since they can draw
more than 5A, as can 100W cigarette-lighter inverters. A laptop's
current demand is beyond user control so I made a custom input jack
from brass tubing to connect the adapter to big Franken-rheostat
loads:
http://www.alliedelec.com/images/pro...l/70022534.jpg

In practice these Dells take 2A to 2.5A at 12V but once a D630 that
was recharging a low battery decided to pull all it could until the
adapter got very hot.
jsw