Query summary: The Maha MC9000 (~=MH-C9000?) NimH/NiCd battery charger/reconditioner recently recommended here looks somewhat like what I want. Use is to cycle new NimH AA cells to check their long term capacity trends. PC interface would be useful. Ability to charge for preset time would be useful. Both can be lived without. Can anyone suggest other chargers which may suit my purpose? ___________________________ I'd been about to "roll my own" battery cycling unit as I wasn't aware of anything available locally at a sensible price (or even at a non-sensible one). But this: > From: Dr Skip > I've started using the Maha MC-9000 and am very impressed. Many different ways > to set up the cycles, and it seems to have brought quite a few NiMH and NiCd > cells back to life so far for me. led me to discover that the Maha MH-C9000 is available here for $NZ114 ~= $US85. Manual here: http://www.mahaenergy.com/download/mhc9000.pdf While limited, it seems to do most of what I want. Remote data access would have been nice, but is not essential, and I can add a 'lash-up' interface that meets my needs if I wish.Main add on need is to monitor cycles and possibly to switch from charge to discharge mode after a set charging period. Can anyone suggest anything else that does similarly well or better. Substantially more cost may be acceptable if it has enough extra features. Main aims 1. and 2. below. Brief dream-spec outline at end. _________ "Charge" below refers to coulombic capacity - ie mAh. Voltage along the way during charge and discharge is interesting but less relevant to me. Cell ~~= battery ~~= cell. Processor interface (USB, serial, ... would be very nice but is not essential) My aim is to 1. Cycle sets of new NimH batteries / cells at controlled charge and discharge rates to observe initial capacity and changes in capacity with cycles of use. Charge to - delta V (preferably not to gross thermal rise) and discharge at defined voltage to defined* voltage endpoint would do for this test. A standard charger will do well enough for this. "Little things" like ambient temperature can be addressed external to the charger. 2. Charge at defined rate for defined period so as to convey an amount of charge no more than the battery's nominal capacity, and then discharge at defined rate to defined end point voltage and track capacity. This varies from a standard cycle in that the battery is provided with no more charge than a 100% efficient cell would require. The aim is to determine the coulombic efficiency of the cells under various charge and discharge conditions and with increasing cycle times. eg if I have a 2000 mAh cell and charge it at C/5 = 400 mA for *4* hours and discharge it at 200 mA until it reaches 1V loaded, what does the capacity variation look like with time. I anticipate that most chargers will not be able to meet this requirement and that a 'roll you own' will probably have to follow - possibly by 'fooling' an MH-C9000 or similar. (eg thermal pulse to sensor at end of defined charging period [[This measure is of relatively little importance when abundant energy is available and the cell energy content is of low value. eg it takes under 3 Watt-hour of energy to charge a 2000 mAh NimH cell. The energy cost the energy content using mains energy at say $US0.20/ kWh is thus around $0.05. ie you can charge 2000 such cells with $1 of electricity. At Chinese wholesale factory prices the amortised cost of the cell with a cycle life of 500 cycles (optimistic for rapid deep discharge, realistic under some scenarios) is about $US0.002 or 4 x the energy costs. At US retail battery costs the ratio is higher. In areas where mains energy costs are not so high the battery cycle cost still predominates for mains charging. Where total cost per cycle matters much then LiFePO4 look very attractive - as long as their limitations are acceptable (the most likely show stopper is temperature range in some modes in extreme conditions). Where energy is limited or extremely expensive (off grid solar etc where energy needs exceed availability) then coulombic charge efficiency can matter greatly. LiFePO4 can start at 99.5% and improve slightly with cycles (although cell capacity drops). Note this is coulombic efficiency and NOT energy efficiency - as charge voltage is not constant during the charge and discharge cycle and internal losses will affect this. When it comes to NimH cells not much is available on coulombic efficincy, what is available is inconsistent, and typical claims are wrong - as relatively simple analysis of the charging curves shows. (Discharge coulombic efficiency can be arbitrarily defined as 100% at a given discharge rate (you get out everything that you get out) and any inefficincies attributed to the charge cycle. Standard charging recommendations fior NimH often specify something like 40% coulombic overcharge, which is manifestly excessive, but safe enough if maximum battery cycles is not a priority. With manufacturers it is probably often not :-) ! ________________ Summary dream charger/discharger spec: - Charge at selected linear current rate 0 - 2A+ - Extra points for charge current profiling. - Discharge at selected current rate 0- 2A+ OR - Discharge at constant energy rate OR - Discharge at user defineable load curve. - Terminate charge on any mix of -dV, +dT, Temp, Time on charge, terminal voltage. - Terminate discharge on any of Vbat, time of discharge. - Flexible charge / discharge cycling. - Various conditioning and charging algorithms as per MH-C9000. - Monitor and record charge and discharge capacities per cycle. - Upload port (USB or serial or ... ) - Real time upload of current & voltage per cell and general stats "nice" - Remote ability to control processes as required "nice" eg PC control.. Russell - Apologies for all the 'defined"s - starting to sound like a patent document. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist