How to charge 3.6VDC battery with DC Power Supply
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From: jg on 2 Mar 2010 14:45 > > So, your first step is to figure out your battery chemistry. Without > that first step, there is no second step. They are NiMH. Battery pack is made up of 3 cells. Each one rated at 1.2v, for a total of 3.6v. (I have actually opened up one of the packs. They are the same height as AA and about 20% fatter.) So would it be OK to push to 4.2 vdc and set max current to something like 200mA? I would prefer formulas rather than a straight answer. (Teach me how to fish.) jg
From: Tim Wescott on 2 Mar 2010 14:54 jg wrote: >> So, your first step is to figure out your battery chemistry. Without >> that first step, there is no second step. > > They are NiMH. Battery pack is made up of 3 cells. Each one rated at > 1.2v, for a total of 3.6v. (I have actually opened up one of the > packs. They are the same height as AA and about 20% fatter.) > > So would it be OK to push to 4.2 vdc and set max current to something > like 200mA? I would prefer formulas rather than a straight answer. > (Teach me how to fish.) The classic way to charge NiMH batteries is either with a constant current for a good long time (this works a lot better with NiCd batteries, but you can get away with it on NiMH if you don't charge at too high a rate and if you're willing to accept a shortened cell life), or charge with a constant current until the cell voltages stop rising (NiCd battery cell voltages actually peak and then drop, NiMH batteries technically peak, but really discernibly just plateau). Fancy chargers pulse the current, and measure the cell voltage between pulses, looking for a peak and/or plateau. Charging at capacity / 10 hours is the rule of thumb for 'slow charging' -- so 250mA for your 2500mAh capacity pack. You can 'fast charge' at higher rates, but _only_ if you're using a peak detect circuit, and what the fast charge rate can be depends on the particular battery. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: bw on 2 Mar 2010 15:09 "jg" <juangarcia(a)sacbeemail.com> wrote in message news:517619b5-7eca-4e54-b462-836f4afd2721(a)y7g2000prc.googlegroups.com... > > So, your first step is to figure out your battery chemistry. Without > that first step, there is no second step. They are NiMH. Battery pack is made up of 3 cells. Each one rated at 1.2v, for a total of 3.6v. (I have actually opened up one of the packs. They are the same height as AA and about 20% fatter.) So would it be OK to push to 4.2 vdc and set max current to something like 200mA? I would prefer formulas rather than a straight answer. (Teach me how to fish.) --------------------- The cell size is 4/5A, about 1500 to 2000 milliAmphour Standard charge is 1/10 capacity (150mA) for 14 hours. It's more than 10 hours because charging efficiency is not 100 percent. Do not let the cells get over 40 degrees C on charge. Heat is not good to NiMH You can charge faster as long as the cells don't overheat. Faster charge profiles require more careful design, with thermal safetys.
From: jg on 2 Mar 2010 16:21 > --------------------- > The cell size is 4/5A, about 1500 to 2000 milliAmphour > Standard charge is 1/10 capacity (150mA) for 14 hours. > It's more than 10 hours because charging efficiency is not 100 percent. > > Do not let the cells get over 40 degrees C on charge. Heat is not good to > NiMH > You can charge faster as long as the cells don't overheat. > Faster charge profiles require more careful design, with thermal safetys. Thanx, what about voltage? More than 3.6v right? jg
From: jg on 2 Mar 2010 16:25
On Mar 2, 11:54 am, Tim Wescott <t...(a)seemywebsite.now> wrote: > jg wrote: > >> So, your first step is to figure out your battery chemistry. Without > >> that first step, there is no second step. > > > They are NiMH. Battery pack is made up of 3 cells. Each one rated at > > 1.2v, for a total of 3.6v. (I have actually opened up one of the > > packs. They are the same height as AA and about 20% fatter.) > > > So would it be OK to push to 4.2 vdc and set max current to something > > like 200mA? I would prefer formulas rather than a straight answer. > > (Teach me how to fish.) > > The classic way to charge NiMH batteries is either with a constant > current for a good long time (this works a lot better with NiCd > batteries, but you can get away with it on NiMH if you don't charge at > too high a rate and if you're willing to accept a shortened cell life), > or charge with a constant current until the cell voltages stop rising > (NiCd battery cell voltages actually peak and then drop, NiMH batteries > technically peak, but really discernibly just plateau). Fancy chargers > pulse the current, and measure the cell voltage between pulses, looking > for a peak and/or plateau. > > Charging at capacity / 10 hours is the rule of thumb for 'slow charging' > -- so 250mA for your 2500mAh capacity pack. You can 'fast charge' at > higher rates, but _only_ if you're using a peak detect circuit, and what > the fast charge rate can be depends on the particular battery. > > -- > Tim Wescott > Control system and signal processing consultingwww.wescottdesign.com Thanx, I'll try this over the weekend as I want to be awake to monitor for heat. Still wondering what the voltage should be though. |