Digest for sci.electronics.repair@googlegroups.com - 3 updates in 3 topics

9:41 AM Penedão
legg <legg@nospam.magma.ca>: Aug 04 08:20AM -0400

>care to do math. I just want a simple piece of free software for
>windows.
 
>Any suggestions?
 
https://joshmadison.com/convert-for-windows/
 
Convert anything.
 
Allows user-designated unit conversions to be added. . . .
 
RL
legg <legg@nospam.magma.ca>: Aug 04 08:16AM -0400

On Mon, 2 Aug 2021 10:57:20 -0400, Ralph Mowery
 
>I know they are not the output transformer of a push pull audio stage
>that may have had the speaker wires cut off, but that is what they
>resemble.
 
Tapped series chokes were once used for voltage selection under very
dedicated load conditions ~ fan speed control or heater settings.
 
Perhaps it's a tube heater (12 - 6V) range.
 
RL
Jeff Liebermann <jeffl@cruzio.com>: Aug 03 10:58AM -0700

On Tue, 3 Aug 2021 22:34:01 +1000, Clifford Heath <no.spam@please.net>
wrote:
 
>> always, just usually. With small lead-acid batteries, it will charge.
 
>It could be something as simple as self-discharge being much larger when
>a battery has been "substantially drained"...?
 
Much as I like to speculate about things I'm not quite sure, I'll take
a chance and add a few guesses:
 
1. Extremely crude battery maintainers are common. Just fixed
maximum voltage source and a series resistor. As the battery voltage
approaches the voltage source voltage, charging slows down and
eventually stop. Pick the wrong voltage or series resistor and it
might never get to full charge. Variations in line voltage can also
create problems with unregulated battery maintainers.
 
2. Flooded cell batteries are quite sensitive to temperature. The
better chargers have circuitry to compensate for temperature effects.
The really good one's have an external thermistor sensor that attaches
to the battery. The best have individual voltage and temperature
sensors for each cell. Crude temperature compensation assumes that
the battery and charger are at the same temperature. That's often not
the case, such as the battery sitting on a cold concrete floor, while
the charger is in a relay rack full of very hot radios. I've seen
this all too often at radio sites.
 
3. Self-discharge in flooded cells batteries increases with
temperature. See Fig 6:
<https://batteryuniversity.com/article/bu-802b-what-does-elevated-self-discharge-do>
 
4. Flooded batteries that have lost water and have exposed the tops
of the plates to air act weird. One effect is an increase in self
discharge rate, possibly caused by internal self-heating from
self-discharge. For example, losing 50% capacity from a flooded
lead-acid battery in 6 months would be half of the manufacturers rated
capacity of perhaps 70 amp-hrs or 840 watt-hrs.
420 watt-hrs / 180 days / 24 hrs/day = 0.1 watt/day
That doesn't seem like much, but that's under fairly ideal conditions,
with a new battery, no sulfation, etc. The self-heating will be
slight, but if it causes additional self-discharge, the effect is
positive feedback and might result in enough self-discharge to
interfering with low level charging.

>Yes, I use LiFePO4 also. Self-discharge is 1-2% per annum, and the
>columetric efficiency is very high also (you get back almost all the
>charge you put in). Great batteries.
 
Yep, they're amazing with the added bonus of having a 3.3V nominal
voltage which produces almost the same voltage as a common automobile
battery (4S = 13.2V). They're also good for a much larger number of
charge cycles than ordinary LiIon cells.
LiFePO4 = 2000 cycles
LiCoO2 = 400 cycles
Lots of other advantages (such as not catching fire or bulging), but
there are also problems. Plagiarized from:
<https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/>
- Keep the battery temperature under 45 Centigrade (under 30C if
possible) - This is by far the most important!!
- Keep charge and discharge currents under 0.5C (0.2C preferred)
- Keep battery temperature above 0 Centigrade when discharging if
possible - This, and everything below, is nowhere near as important as
the first two.
- Do not cycle below 10% - 15% SOC unless you really need to.
- Do not float the battery at 100% SOC if possible.
- Do not charge to 100% SOC if you do not need it.
 
My plan for an emergency generator starting battery is quite
different. I plan to use a fairly small battery pack. It can be
almost anything. Initially, I'll start with a 12V 7AH AGM battery.
Across the battery are 6 super caps:
<https://www.ebay.com/itm/193649838256> $21
I'm not sure of the size needed yet. The super caps provide the high
motor start current needed. The AGM battery keeps the caps charged. A
small float charger keeps the AGM battery charged between starts.
 
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
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