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... > > > > Quoting Regis White <[EMAIL PROTECTED]>: > > > > > > > I bought an Alpha 4 about six or seven years ago and have been quite > > happy with it. But (there is always a but) it did not have a > > separate discharge function - it only cycled (once). NiCads like to > > be left discharged I have been led to believe. Ni-MH on the other > > hand like to be fully charged - and can be harmed if fully > > discharged. So I have replaced most of my NiCads. What I learned > > was that I could not safely charge them on the Alpha 4 'Peak' > > function or even the 'c/10' function - only the 'Fast charge' > > function. Recently I acquired two KAN Ni-MH 7 cell packs and was > > surprised to find that the Alpha 4 could not automatic charge them > > safely - they got very hot. Since both packs got very hot, I suspect > > the KAN cells are just not compatible with Alpha 4 technology (which > > is easily 20 years old). (I mean we can plug in a cell phone to > > charge and just forget it.) Is there something about the KAN type > > cells that are different or is this an anomaly? Regis > > > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and > "unsubscribe" requests to [EMAIL PROTECTED] Please note that > subscribe and unsubscribe messages must be sent in text only format with MIME > turned off. > Radius Systems Cogito Ergo Zoom RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
