Probably the best place to post questions for many (and quite different) opinions is piclist: http://www.piclist.com/techref/piclist/index.htm or jallist: http://tech.groups.yahoo.com/group/jallist/ So far I didn't saw major problems in discussing pic related things or electronics at jallib, but here the number of answers will be limited. The topic of jallib is related to jal libraries and standards, Rob is the informal chief in charge here.
I can say only how I would do it: - I will choose a PIC running from 2V to 4V, there are many, also the other IC's should run at 3V +/- 1V (LCD, communication etc.) If this will not be entirely possible, then I'll choose your DC-DC converter (but my supply option will be 3.3V, PIC resources running at lower voltage are better, see only the hardware RTCC for example). - I will keep the LIPO voltage range between 2V and 4V (3.6V if mandatory) using a simple crowbar-like protection on the accumulator end and a high constant current generator driven from PIC. A TL431 (variable zener) and a high current MOS-FET can do the protection. Once the LIPO voltage reached 4V, the crowbar will source the entire charging current, until the PIC will stop the charging process. You always need two levels of protection: one hardware which should work even when the software (the PIC) has a malfunction (and will have until firmware versions will be greater than 10...20). - I will choose a power discharge resistor and a high current MOS-FET switch for the failure predicament. This will simplify the measurement (you will not need current measurement only voltage measurement). Also the version in which you'll use the available load for failure predicament and measure the voltage and the current between two moments of time is feasible. On Fri, Aug 10, 2012 at 8:41 AM, Bogdan Mihai Octavian < [email protected]> wrote: > Well, thank you for your answer! I guess that I'm responding back > to Vasile Surducan? Cause your book, "Microcontrolere pentru toti" was the > best book in the University and the book that help me started with PIC > programming. I am still writing code with the help of JAL.... > I wish to thank again for the good job writing that book! > Back to my problem now! After a few revises I have dropped Lead_acid > battery and switched to LiFePo, just one cell ( > http://www.all-battery.com/3.2V12.5AhLiFePO4PrismaticEnergyCell-30251.aspx). > Because Linear Technology as well as Texas Instruments had developed > already LiFePO gas gauges (http://www.ti.com/lit/ds/symlink/bq27501.pdf, > for example) my job just got easier. Because I will need to power my 5vdc > electronics just from a single cell LiFePo the boost converter efficiency > is not so bad especially If I use the converters from Murata ( > http://www.farnell.com/datasheets/369793.pdf). Because I will need to > power the 12VDC/1Watt coil of an servo-valve I will use isolated DC-DC > converters from XP POWER. The valve should work for 5 to 15 minutes every > 12 to 36 hours...not so bad. The other sensors (4-20mA pressure sensors and > the other two optical level sensors) will be powered from a different > isolated DC-DC converter that will be on for 2 seconds every 5 to 10 > minutes, not so bad also. > Just one cell LiFePO (LiIon are not doing it so well at lower temperature, > as -20 Celsius degrees) is easier to monitor and manage. The best solution > for MPPT charger from Solar panel comes from Linear Technology, LT 4000-1. > So, I am pretty much covered in this corner of the problem. > Now, I have the battery gas gauge with I2C communication, 12 bits > A/D converter for the pressure sensor and COG LCD on the same I2C bus. That > wouldn't be so difficult to control. > Any idea about what I2C COG LCD will work better with JAL COG > library? I have selected a few from Farnell, but it's my first time that I > have to send data to a COG LCD ( I have to display a few graphical > parameters of the process) > P.S.: I quite new with forums and threading so it would take a while > to accommodate myself with this. Should I move my thread to JALLIST forum, > as Rob mentioned? > > joi, 9 august 2012, 10:02:10 UTC+3, vasile a scris: >> >> Hi Bogdan >> In my opinion, failure predicament for Lead Acid accumulators is not too >> complicated, but I do know nothing about LiFePO cells so I can't >> pronounce... I've designed and manufactured as prototype, about five years >> ago (if I don't wrong) a charger-discharger for NiMH with one channel >> using a simple PIC12F675 and a PC for analyzing data.. I think you have to >> implement two things: a charging algorithm and a discharging algorithm on a >> known load. Both are quite simple. You can also measure dV on dt with load, >> but this might need more than 10 or 12bit AD resolution. >> The biggest problem I've faced over the time since I'm playing with PIC >> micro is not the algorithm itself, but the problems of long time running. >> For such application you'll have to consider deeply how a watchdog should >> help you against bottlenecks. >> >> best wishes, >> Vasile >> >> On Tue, Aug 7, 2012 at 5:56 PM, Bogdan Mihai Octavian < >> [email protected]> wrote: >> >>> Hello everybody! I'm not new into microcontrollers, actually all >>> my projects, personal or those built for the company I'm working for, were >>> built around PIC family. Now I'm working at a project that involves battery >>> management and battery failure predicament. It is a industrial process >>> automation powered from a Solar panel (UPS with MPPT charger and all the >>> other stuff involved). Because it has to work without the Sun, sometimes, >>> from the internal UPS powered from one or two LiFePO cells, I have not >>> decide yet, I have to know the battery condition. The automation it is >>> remotely located and it is visited by the maintenance stuff once a week or >>> in case that something goes wrong (radio communication also implemented). I >>> have founded some hardware solutions, battery gas gauge, provided by Linear >>> Technology or Texas Instruments or Maxim, but those are little too >>> complicated. I was thinking do do that myself and this is where I will >>> need some help. >>> So, does anybody have an idea how to do that? Measure the battery >>> capacity and predict battery failure..... >>> >>> Thanks for your time! >>> (Allocated to read this) >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "jallib" group. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msg/jallib/-/vxYiirFkNs4J. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]. >>> >>> For more options, visit this group at >>> http://groups.google.com/group/jallib?hl=en. >>> >> >> -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To view this discussion on the web visit > https://groups.google.com/d/msg/jallib/-/ERMbALr12soJ. > > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/jallib?hl=en. > -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
