Hi Rod,
interesting design! Thanks.
How do you decide when to finish the charge? By the delta Peak. Have a
look at this (Fig 2):
http://www.maxim-ic.com/appnotes.cfm/appnote_number/680
It is a typical (fast) charging voltage plot. With the divide by 4
voltage Vsense, I will be loosing resolution, isn't it?
I mean, suposing that we have 0-5V in Vsense, 10 bit ADC gives 4,8 mV
per bit (adc step). Your resolution is divided by 4, so 4,8 x 4 = 20 mV
per bit + we must add the +- LSB ADC accuracy, thats a 40 mV error....
So I think I won't be able to detect the 10 mV delta Peak....
In the description of your circuit you mention an 84 mV delta peak. Is
that peak the result of Delta * Num of Cells?
Regards
Jean-Paul escribió:
> Hi,
>
> It looks like you don't think that the end-of-charge voltage is above the
> nominal voltage.
> On the schematics given in the link hereafter, it would be safer to put a
> zener diode across the lower resistor of the divider, to protect the
> controller.
>
> Le Jeudi 8 Mars 2007 21:51, Rod Boyce a écrit :
>
>> Markos,
>>
>> It is very simple I have done this many times in my days job, use a
>> resistive divider and work out the error by calibrating the input and
>> fix any error in software. One thing you have to be careful of is that
>> you monitor the temperature as well as many resistors vary their
>> resistance with temperature, but it depends on your application if you
>> are charging lead acid batteries then you may only have to calibrate the
>> circuit between the usable voltage range of interest.
>>
>> Have a look at
>> http://www.angelfire.com/electronic/hayles/charge1fig3.html note the
>> divide by 4 voltage sense connecting to the ADC input of the PIC
>> micro-controller.
>>
>> Regards,
>> Rod
>>
>> Markos wrote:
>>
>>> Hi guys,
>>> maybe this is a little offtopic, but i'm sure you could
>>> help me. I'm implementing a simple battery charger, and I need to
>>> messaure voltages ranges from 0 to 12 V.
>>> ¿Could I use the PIC integrated ADC to messaure above 5 V (provided that
>>> I use the voltage reference pins tied to 0 and 12 V, for example)? Most
>>> external ADC have a 0 to 5V input range....
>>> How would you guys solve this? Any Ideas?
>>>
>>> Thanks in advance.
>>>
>>>
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