On Sunday, 16 July 2017 18:36:48 UTC+1, Jeff Liebermann wrote:
On Sun, 16 Jul 2017 02:28:25 -0700 (PDT), tabbypurr wrote:
On Sunday, 16 July 2017 02:24:07 UTC+1, Jeff Liebermann wrote:
On Sat, 15 Jul 2017 17:58:46 -0700 (PDT), tabbypurr wrote:
Charge control depends on battery chemistry & size.
NiCd & NiMH can be charged by just limiting current
delivery to C/16, so measure your panel output current
in full sun as well as offload voltage. Lithium is
much more fussy, hence some of the circuitry.

I beg to differ. You might be able to trickle charge NiCd, but NiMH
is considerably more picky:
http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride
"It is difficult, if not impossible, to slow charge a NiMH
battery. At a C rate of 0.1C to 0.3C, the voltage and
temperature profiles do not exhibit defined characteristics
to trigger full-charge detection, and the charger must
depend on a timer. Harmful overcharge can occur when
charging partially or fully charged batteries, even if the
battery remains cold."

In other words, C/16 or 0.06C charge rate for NiMH screws up the NVD
(negative voltage detection) mechanism used to detect EoC
(end-o-charge), which can easily overcharge a NiMH cell or battery.

My cordless phones use NiMH with no charge control.

Maker and model please. I want to see if I can find a schematic.

They
get charged or discharged all the time. Last set of cheap
cells lasted at least 1500 cycles. So you can do it.
NT

I hate to admit it but you are probably correct.

My AT&T EL52210 Dect 6.0 handset
https://www.google.com/search?q=at%26t+el52210&tbm=isch
uses two AAA 2.4v 400ma-hr NiMH cells. The battery label demands that
I charge the battery for 16 hrs prior to use. Doing the math and
assuming constant current charging, that's a C/16 charge rate.

I disassembled the charger base and took some photos:
http://www.11junk.com/jeffl/pics/repair/AT-T%20charger%20base/index.html
Not much inside. 6VAC 300ma wall wart, diode bridge, filter cap, and
some unidentified diodes and transistor. I'll trace out the circuit
and identify the parts if I have time. Without an IC to do the NVD
detection, this charger is rather crude and probably does not follow
the recommendations from the Battery University site.

Incidentally, the phone is 5 to 8 years old and shows no sign of
battery problems. The handsets spend most of their life in the
charger base and the batteries have never been discharged to the point
where the handset complains. Open circuit battery voltage is now
2.68V which is very much full charge for NiMH.

Very strange.

BT graphite 1100 series. I saved you the time & googled, no trace of a circuit anywhere. So I could be wrong, but I'd be surprised if there were any charge control electronics in such equipment. Such non-ideal battery charging schemes are widespread, more or less universal really, in many types of equipment.


NT