Post by thread:OT determining amount of cells

I have seen battery chargers that determine the amount of cells in a battery pack and then charge acordingly. The chargers is mp controlled, but I haven't opened it up to see it if it is a PIC. The battery packs are made up of 1.2V Nicad cells. But if the cells are discharged, it is not just a case of measuring the voltage. Anybody knows how? Quentin

>The battery packs are made up of 1.2V Nicad cells. But if the cells are >discharged, it is not just a case of measuring the voltage. Sure, Quentin. The basic chemistry determines voltage. A NiCd with no load on it, unless _very_ dead, will register around 1.2V. All they do is a no-load volt test. Some of the smarter units will apply a small charging current to it for a short duration, then measure the pack to determine cell count before starting charge. Even smarter ones will continuously monitor cell voltage. Note that a fully-peak-charged NiCd can exceed 1.2V by quite a bit, so as the cell count gets above 7 cells, these chargers become less accurate as charge approaches full. The real issue though is that they charge with the correct current. NiCd cells like constant current charging, not constant voltage (like lead-acid cells). Andy ================================================================== Andy Kunz Life is what we do to prepare for Eternity ------------------------------------------------------------------ spam_OUTandyTakeThisOuTrc-hydros.com http://www.rc-hydros.com - Race Boats .....andyKILLspam@spam@montanadesign.com http://www.montanadesign.com - Electronics ==================================================================

Quentin wrote: > > I have seen battery chargers that determine the amount of cells in a > battery pack and then charge acordingly. The chargers is mp controlled, > but I haven't opened it up to see it if it is a PIC. > The battery packs are made up of 1.2V Nicad cells. But if the cells are > discharged, it is not just a case of measuring the voltage. > > Anybody knows how? I'd look ate the rate at which the voltage climbs at a constant current. NiCd's voltages climb very quickly. You should be able to identify the curve without too much problem. -- Friendly Regards /"\ \ / Tjaart van der Walt X ASCII RIBBON CAMPAIGN tjaartKILLspamcellpt.co.za / \ AGAINST HTML MAIL |--------------------------------------------------| | GSM Technology for Positioning and Telematics | | Cellpoint Systems SA http://www.cellpt.com | | http://www.wasp.co.za/~tjaart/index.html | | WGS84 -26.0124 +28.1129 Voice +27 (0)11 2545100 | |--------------------------------------------------|