12V battery charger+power supply w/ current/voltage monitoring + etc

Discussion in 'The Projects Forum' started by YetAnotherGeek, Jul 15, 2015.

  1. YetAnotherGeek

    Thread Starter New Member

    Sep 16, 2014
    Hello all,

    I'm starting work on a 12V power supply that I've been assigned as part of a summer research project. These are the specifications I've been given:

    -Needs to take a ~12V (11V-14V) input from a car battery.
    -Needs to charge a lead acid battery and then a lithium ion battery from the 12V input.
    -The power sources have the following order of preference:
    1. 12V input
    2. Lead acid battery
    3. Lithium ion battery

    -Power output needs to be rock-solid. It is very likely that the 12V input is going to disappear suddenly. This power supply will be used in car crash reenactments to power sensors.

    -Current and voltage needs to be monitored. I have an Arduino design that I plan on just dropping onto the PCB. I don't have anything to sense this.

    -Current and voltage need to be displayed.

    -Anything that can stabilize power output needs to be added on. Safety features (thermsistors, etc) need to be included.

    -The PCB needs to fit within a 180x120x80 mm case.

    -All power sources need to have switches on them.

    I'm using Altium Designer. It's my third PCB project ever and I'm still new to this. I'm a computer science/electrical engineering double major. I'm much better at the CS side than the EE side - right now. So I have a lot of silly questions and not a lot of experience with hands on applied stuff. I.E. I'd never heard of a "buck boost converter" until I started on this.

    Right now I'm looking at an LTC 4000-1 https://cds.linear.com/docs/en/datasheet/40001fa.pdf as my controller. On page 34 it starts showing typical applications. I've also looked at the LTC 4000, which has a few more circuits available, http://www.linear.com/solutions/LTC4000?type=circuit .

    I've also looked around on Linear's site as I wrote this post and found things like http://www.linear.com/product/LTC4417 and https://cds.linear.com/docs/en/datasheet/4020fb.pdf that look promising, but I've not seen any that look like they could handle multiple batteries simultaneously, so it's looking like I'm going to have to have multiple ICs.

    I've Googled around a bit for other designs to look at and what I've seen has not seemed robust enough for what I'm doing.

    I'm new to this. I need guidance through this project, so I figure this thread's going to be sort of a chronicle of me figuring out how to do this, hopefully with assistance from you all.

    My first questions are: What chips would you suggest I look at? What keywords should I go and learn? What advice do I need to hear that I'm not asking for because I don't know?

  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    Maybe a few more specs.
    What are the voltage and capacity ratings of the batteries to be charged?
    Both at the same time?
    Fast charge or just trickle charge?
  3. #12


    Nov 30, 2010
    Maybe start with a block diagram? Lines and boxes communicate a lot better than words. Later, showing a schematic will communicate better than talking about a schematic.
  4. YetAnotherGeek

    Thread Starter New Member

    Sep 16, 2014
    Voltage ratings on the individual cells for the lithium ion battery are flexible so long as the output is 12V. I think the lead acid battery is just going to be 12V.

    I've not been told the capacities of the batteries, just given hints. I believe the expectation of the lead acid battery is to be able to push 6A for 30 minutes, and that the li-ion battery is going to be something far less than that.

    Whichever charge prolongs the life of the batteries the most. I'm not sure, but if I remember right lead acid batteries have a 3 stage charging process that includes a fast charge and then a trickle charge at the end. If I'm wrong about that, we're probably looking at a trickle charge since these are intended as swappable back ups.
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
    Seems like a strange request to charge 2 12 volt batteries with a third. But hey. :D
    A couple of these would do it along with a balance IC for the lithiums.
  6. YetAnotherGeek

    Thread Starter New Member

    Sep 16, 2014
    Thanks! This is cool!

    From my understanding, the 12V main input source (the car battery) is going to be from a running vehicle that gets wrecked as part of a test. It's highly possible the car battery will be disconnected.

    The power supply's powering sensors, a kinematics computer, and other things. They need to stay up even after the wreck's done. The power supply's going to be moved from car to car for several wrecks.

    My understanding is that the lead acid battery will be changed out a few times during the day and the li-ion is just meant to hold things up while the lead acid battery's being changed out. My understanding may be flawed.

    I'm going to compare the controllers we've looked at so far and come back with questions! Thank you very much for your time!
  7. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    If I understand you correctly...

    1. There can be up to three separate sources available to power a single pile of electronics: the car battery, the backup lead acid battery, and the backup backup lithium battery, correct?

    2. There is a preferred order to the power sources: car battery first, backup LA second, backup backup Li third, correct?

    If these are true statements, and you already are reading up on LTC's buck-boost line, then the energy manager sounds pretty straightforward - three ideal diode controllers, a big capacitor, and a buck-boost circuit.

  8. YetAnotherGeek

    Thread Starter New Member

    Sep 16, 2014
    Yes on both counts!

    Ideal diode controllers are new vocabulary to me. I see how they work now. I think.

    While I'm reading up on the controllers, the next tricks are to add an Arduino voltmeter (using a voltage divider to increase the range) on one of the analog pins. This is simple. After that I'm looking at an ammeter. I've done some Googling around, http://www.instructables.com/id/DIY-Amp-Hour-Meter-Arduino/?ALLSTEPS is what I'm looking at. I've never messed with Hall effect sensors before. Are they as worry-free as they seem?

    I'm thinking that, for the Arduino Uno SMD, that I'm going to look at assigning the 6 analog pins as such:

    A0: Current from 12V source
    A1: Current to load
    A2: Voltage from 12V source
    A3: Voltage from lead acid battery
    A4: Voltage from Li-Ion battery
    A5: Unused

    Also, I need to look at using a screen that's visible in bright sunlight.