Hi Regis,
Those chargers that employ purpose-designed NiMH algorythms is what I would look for. Kinda tough to recommend any particular marque over another.
Regis White wrote:
"Efficient cells like the KAN's do not induce a voltage depression adequate enough to trip the peak-detect, so the charger keeps pumping in the current."
That explains why the packs got hot.
"The above applies to NiMH cells used for normal(?) operation, as opposed to propulsion applications (F5B, etc)."
So, is there a truly automatic charger for "Efficient" NiMH cells?
Regis
-----Original Message----- From: Simon Van Leeuwen [mailto:[EMAIL PROTECTED] Sent: Tuesday, November 09, 2004 5:30 PM To: Cameron Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: Re: [RCSE] Battery food-Charger
Since the A4 was released, the charge protocol for NiMH has changed significantly to better represent the characteristics of the cell chemistry. If memory serves (I owned one, then ditched it) only the peak overvoltage was dropped by a few mV as compared to the NiCD algorythm.
The current accepted regime for NiMH is similar to:
Stage 1: Charger algorythm applies a zero (slope) delta, essentially turns off the charge phase as soon as the fully charged state is reached (based on a V value, no overcharge above rated V). This brings the cell to ~80-90% of rated capacity (this value will decrease the more current pushed into the cell, as the rated V is reached sooner with an elevated charge V) Stage 2: Same charge current (or another lesser rate) is pulsed (duty cycle) to bring the cell >95% of rated Stage 3: Maintenance rate - same charge current (or another lesser value) is pulsed (shorter duty cycle) to maintain a fully charged state.
The above applies to NiMH cells used for normal(?) operation, as opposed to propulsion applications (F5B, etc).
Quoting Cameron <[EMAIL PROTECTED]>:
To quote Litco Systems directly from their manual for the Alpha 4
charger:
PLEASE NOTE: ALL DEVICES ON A-4 EXCEPT "W" DEVICE ARE INTENDED FOR
NI-CADS.
ONLY "V" AND "W" DEVICES MAY BE USED WITH WET AND GEL CELLS (LEAD-ACID BATTERIES). ALL DEVICES EXCEPT "A","S"& "W" ARE SUITABLE FOR NIMH
BATTERIES
(NICKEL-METAL-HYDRIDE). TO BE ON THE SAFE SIDE USE ONLY "I" AND "C"
CHARGER
WITH NIMH CELLS.
:-) *smile*
Cameron
-----Original Message-----
Date: Tue, 9 Nov 2004 11:43:28 -0800 From: Simon Van Leeuwen <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Cc: "[EMAIL PROTECTED] com" <[EMAIL PROTECTED]> Subject: Re: [RCSE] Battery food-Charger Message-ID: <[EMAIL PROTECTED]>
That's the probelm with employing a NiCD charger that peak-detects for
NiCD
instead of NiMH. NiMH are endomthermic, while NiCD technology is
exothermic.
This means as an NiCD becomes fully charged, the increase in heat
causes an
increase in internal resistance, which lowers the charge V, which
trips the
peak-detect circuitry.
Efficient cells like the KAN's do not induce a voltage depression
adequate
enough to trip the peak-detect, so the charger keeps pumping in the
current.
NiCD chargers are great at ruining perfectly good NiMH cells. Then the
cells
get blamed for poor performance...
-- Simon Van Leeuwen RADIUS SYSTEMS PnP SYSTEMS - The E-Harness of Choice Cogito Ergo Zooom
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