jkenny23 via EV wrote:
Another very important note; diodes don't drop voltage the same at all
current levels. Meaning; they will NOT stop your 4.5V panel from
overcharging your battery to 4.5V if you don't have a dedicated charging IC.
If you want to charge your battery to an unusual voltage, I highly recommend
using an adjustable CC/CV (constant-current/constant-voltage) buck
converter. They're widely available from China on eBay and Aliexpress, and
probably available from the US through Amazon. This way you can set a safe
current limit (say 400mA), and a voltage limit that is lower than 4.2V (say
3.9 or 4.0V). Then you could even use multiple panels in series and not
worry about charging, the input limit for the common LM2596 modules is 35V.
Here's some data for a common 1N5819 Schottky diode illustrating the issue
of voltage drop as current tapers down at the end of charging:
1.0A - 0.41V
0.5A - 0.35V
0.1A - 0.28V
20mA - 0.23V
Yes; diodes are far from "perfect" regulators. But they are predictable
and reliable (if not misused).
A cheap buck converter will have better regulation; but it will also
have lots more failure modes. It will also drain the battery when the PV
panel is not supplying power. The whole point of a series diode is to
prevent this.
Batteries don't require precision regulation. The 0.2v change for a 50:1
change in current is pretty good... maybe good enough for Peter's
application? That's what testing is for. :-)
Lee Hart
--
When something bad happens, you have three choices: You can let it
define you; let it destroy you; or you can let it strengthen you.
-- Theodor Seuss Geisel
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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