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  1. R

    A PIC based Battery Management System

    Very nice work Peter. A slice of engineering heaven. Also thanks for posting the pictures and write up, it's much appreciated. One thought I had about having 50 opto isolator outputs ganged together is that leakage currents could become a problem at high temperatures since they are multiplied...
  2. R

    A PIC based Battery Management System

    The transistor level shifter is a current driven system, so it's relatively immune to dv/dt problems. Capacitances are so low compared to data rate that it should also be fairly immune to inter cell inductive spikes (output capacitance of small signal transistor is only around 5pF). In the...
  3. R

    A PIC based Battery Management System

    Read the thread. Per cell CPU approaches have been proposed and some people have tried implementing them. I'm not sure what the status of those projects is. Last I remember there was some problems with spikes on the supplies reseting or glitching the processors. You can use a transistor and two...
  4. R

    A PIC based Battery Management System

    Yes, a switched flying capacitor sampler would work but you run into the problem of finding integrated FET switches with enough voltage rating to do the job. They seem to max out at about 40V. That's what this schematic essentially is, a flying capacitor sampler that has been simplified and...
  5. R

    A PIC based Battery Management System

    Ok, here's a scheme to sample the cell voltages for the A/D converter on a single MCU system without having any current drain on the cells when you aren't actually reading them. The schematic is not complete, it's just enough to explain the concept, you'll need to add the rest of the cells and...
  6. R

    A PIC based Battery Management System

    and they are pretty. I'm curious as to what software you are using to generate them? Although I suspect the fact that they look so good is more dependent on your good artistic sensibilities. nice work.
  7. R

    A PIC based Battery Management System

    The schematic looks pretty good. You can drop the bottom LT1990 and read the lowest cell voltage directly. You also can just go with the 10 bit A/D in the cpu which will give you ~5mv resolution. 12 bit isn't really necessary. You are always going to have the slow battery drain from the Diff...
  8. R

    A PIC based Battery Management System

    That was what I suggested in the last paragraph of the previous post. The LT1990 works the same way the AD628 does, but it's cheaper.
  9. R

    A PIC based Battery Management System

    yes it has clamping diodes and if you limit input currents with resistors it won't destroy the part, but you will be getting large amounts of substrate current injection and I don't think they guarantee that the part will perform properly while it's clamping pins. It's very likely some of that...
  10. R

    A PIC based Battery Management System

    I figured you'd be calibrating it. It doesn't make sense not to take advantage of such a powerful tool that an MCU with EEPROM makes available. I just wanted to reinforce the fact that the accuracy of a resistor divider system will be very dependent on resistor tolerances. an ATMEGA168 has a 10...
  11. R

    A PIC based Battery Management System

    Heya Sheriff Jon! :) I don't know if it's more technical, but it's more electrical. Pretty schematics too. There's lots of interesting around this place, read Ho!
  12. R

    A PIC based Battery Management System

    You are going to have to watch out for the Common mode voltage rejection errors of your diff amp from resistor mismatching. Also the matching of the Mux channel resistances. You're also going to have more than 45V across your bottom MUX from Ch1b to ch16b when those channels are off. Similar...
  13. R

    A PIC based Battery Management System

    There are a few problem areas to the approach. If you need a 20:1 divider to scale the voltages to the A/D range you end up reducing your A/D resolution by 20, you amplify the effects of thermal drift by 20, even the resistor voltage coefficient amplified by 20 starts to be a noticeable error...
  14. R

    A PIC based Battery Management System

    these days most everything is surface mount, many newer ICs only come in surface mount packages. You might try using something like this http://www.futurlec.com/SMD_Adapters.shtml A good fine point soldering iron or hot air tool can be very useful. some SMD info...
  15. R

    Even Newer 4 to 24-cell Battery Management System (BMS)

    An inductor between the Power FET and the battery (and a freewheeling diode to handle the current when the FET turns off) would essentially turn it into a step down converter. The Inductor will allow you to actually limit the current effectively without dissipating too much heat in your FET and...
  16. R

    A PIC based Battery Management System

    The supply voltages are relative to ground, so Pin 4 needs to be connected to -9 to -15V BELOW ground, Pin 7 connected to +9 to +15V above ground. It needs 2 batteries. Using 9V batteries as an example, Connect the negative terminal of the 1st 9V battery to Ground. Connect the positive terminal...
  17. R

    A PIC based Battery Management System

    pin 4 needs to be connected to a -9 to -15V supply, pin 7 needs to be connected to a +9 to +15V supply. You can use 9V batteries for starters. The output voltage range of this op-amp is several volts less than whatever the supply rails are. A somewhat easier part to work with is the single...
  18. R

    Even Newer 4 to 24-cell Battery Management System (BMS)

    0.1uF is a bit big. I would start with 100-200pF. You don't want to stuff too much current into the input protection. If you only have 0.1uF, put a 1k resistor in series with it.
  19. R

    Even Newer 4 to 24-cell Battery Management System (BMS)

    Another way to reduce the current consumption of the IXDF404 is to put a small feedback capacitance from pin 5 (non-inverting output) to pin 2/ pin 4 (inputs). This will give you some switching hysterisis and slow down the rate of oscillation. Because you are driving the IXDF404 inputs with a...
  20. R

    Even Newer 4 to 24-cell Battery Management System (BMS)

    you can drop the dissipation in the KSC1009 by reducing the LED currents that it feeds, remember you are driving those with 12V now, increase the resistors. You can also shift some of the dissipation out of the transistor by putting a resistor in the collector lead and absorbing some of the...
  21. R

    A PIC based Battery Management System

    I don't see any obvious problems. The major concern I have is the slave CPUs connected directly across the cell for it's supply with no decoupling. High currents and parasitic circuit inductances are going to generate some voltage spikes and there is nothing to keep them away from the CPU...
  22. R

    A PIC based Battery Management System

    Your connector labeling is confusing. It's difficult to tell what connects to what. Where does Slave Data Initiate go?
  23. R

    A PWM Controller For Each Cell?

    what do you think a charge time of 20RC implies? No sane engineer relies solely on simulations. Reality checks with real world parts are required. Yes, I do expect you to go and build at least one or two functional blocks of your design so you can see what the REAL problems and limitations...
  24. R

    A PWM Controller For Each Cell?

    Does this look familiar? http://www.olino.org/us/articles/2006/11/22/charge-efficiency-capacitor it was posted in this thread earlier by dirtyd. Several times it was pointed out to you. Did you read it? no Charge pumps are capable of high efficiency, but only under very light loads. Your...
  25. R

    A PWM Controller For Each Cell?

    No, I meant that you will lose half your battery power as heat in your circuit. dirty_d already posted a link to a technical explanation as to why this happens. which you ignored or failed to understand. It was pointed out several times after that but apparently you aren't interested in...
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