John, thank you=A0 Andre ________________________________ From: John Ferrell To: Microcontroller discussion list - Public. Sent: Friday, November 11, 2011 9:34 AM Subject: Re: [EE]: battery charge resistor value ? On 11/11/2011 10:57 AM, Andre Abelian wrote: > Hi all, > > in my board I have 2 AA batterys that I want to use rechargeable battery = instead and connect to > 5 volt power coming from outside make it slow charge. the schematic is si= mple "slow charge" > > > -+5------A--diode-K---resistor---------Bat+ > 5v=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0 =A0 =A0 =A0 =A0 =A0 2.4v rechargeable=A0=20 > > --------GND----------------------------Bat-=20 > > A=3D anode > K =3D cathode=20 > > > since there is no auto shut down etc I want to use it as continuously slo= w charge but not going to=20 > over charge the battery. my board run time takes 5 ma and when wireless i= s on it takes 100ma > 2.4v power is connected to boost circuit and output is 3.3v to pic. > my question is what resistor value should I use that slow charging is goi= ng to happen > and no thing will blow or burn?=20 > > any idea? > > thanks > > Andre I like C/15 or C/20 where C is the battery's rated capacity for NiCad or=20 NiMh chemistry. AA's are usually about 2 amp batteries now days so it might be even=20 safer with a C/40 rate without compromising circuit operation. It is prudent to install the batteries in a plastic bag to minimize the=20 impact of failure in any case. --=20 John Ferrell W8CCW "The man who complains about the way the ball bounces is likely to be the one who dropped it." =A0=20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .