Shop OBEX P1 Docs P2 Docs Learn Events
Battery Pack for Propeller — Parallax Forums

Battery Pack for Propeller

Nick McClickNick McClick Posts: 1,003
edited 2010-02-02 16:31 in Propeller 1
I'm working on a battery pack for the propeller platform, I just wanted to get a second opinion on my calculations;

I want to use an MCP 1700 Linear LDO regulator (3.3v - datasheet). I want to recommend using 3xAAA nimh batteries for the pack (3.6v, 900mAh).

Assuming the Prop burns 100 mA, the regulator is going to shed 30mW (300mV @ 100mA) in heat, well within the limits for the package.

My total current draw should be somewhere around 115 mA, so the power life should be around 7 hours (rough estimate, looking at this AA nimh discharge curve.)

I've attached the board layout (I did a schematic, but it's not very interesting). C1 & C2 would be 47uF Al electrolytics.
battery_platform.png


Anything I'm missing? Look good?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Propeller Forums RSS Feed!

Gadget Gangster - Share your Electronic Projects
pdf
pdf
battery_platform.pdf
44K

Comments

  • RaymanRayman Posts: 14,600
    edited 2010-01-25 02:18
    looks good. As long as you don't need +5V, it'll work fine.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • Nick McClickNick McClick Posts: 1,003
    edited 2010-01-25 02:51
    Correct. I'd like to have 5V, but it's either going to require a step-up converter that's going to be expensive (like this one), or 5 batteries.

    Of course, you can always use something like an R/C Car battery pack and connect it straight to Vin...

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Propeller Forums RSS Feed!

    Gadget Gangster - Share your Electronic Projects
  • hinvhinv Posts: 1,255
    edited 2010-01-25 03:02
    Hi Nick,

    why are you using AA discharge curve to find out what your time will be under AAA batteries?

    Doug
  • Miner_with_a_PICMiner_with_a_PIC Posts: 123
    edited 2010-01-25 03:09
    >It might be cool to add a header connection (for optional use?) somewhere on the board that is connected directly to the batteries so that the batteries could be charged without removal of the batteries from the board. This would also offer an option to users that want to use an external source but want the batteries there as a back-up.

    >No fuse...if those batteries short pre-regulator (regulator limits to 550 mA, I believe) those traces are going to fry open. A poly could fix that issue well, but consider their nominal resistance and voltage drop if adding one to the design.
  • JonnyMacJonnyMac Posts: 9,098
    edited 2010-01-25 03:36
    I'm confused, Nick, the Propeller Platform has a beefy 3.3v regulator on it -- why not just connect to V50 and not have to worry about a secondary regulator? Am I missing something?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Jon McPhalen
    Hollywood, CA
  • mctriviamctrivia Posts: 3,772
    edited 2010-01-25 03:39
    Why not use a lithium battery pack. You can get much higher voltages and if you place a diode from the pack to the Vin pin and use an input voltage higher then the pack you can have it auto switch from wall to battery.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    24 bit LCD Breakout Board now in. $24.99 has backlight driver and touch sensitive decoder.

    If you have not already. Add yourself to the prophead map
  • Nick McClickNick McClick Posts: 1,003
    edited 2010-01-25 03:55
    @JonnyMac - it does, but it has a 1V dropout, so I'd need to add another battery. It would also have to dump 1.5v. But it would be nice to have near 5v (4.8v) and 3.3v.

    @mctrivia - recharging is an issue, so is price. I'd like make it easy to recharge and inexpensive.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Propeller Forums RSS Feed!

    Gadget Gangster - Share your Electronic Projects
  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2010-01-25 04:28
    looks good in general, but I do have a couple ideas that popped into my head when looking at it........

    I don't have a propeller platform board (yet), but if I did, I would not want to have my battery pack in the add-on board area (P0-P31) as that increases the number of headers for the stackup to make use of other add-on boards. Since you will need access to the batterries, this would always have to be on top, unless you designed it to mount upside down on the bottom. That may be a wise idea?

    Any thoughts on designing the pack to utilize a 3 cell plastic holder connected by wires to the actual PCB and have the PCB only take up the real estate on the left end? (Vin, V5, V3.3, GND)

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Andrew Williams
    WBA Consulting
    WBA-TH1M Sensirion SHT11 Module
    Special Olympics Polar Bear Plunge, Mar 20, 2010
    Propeller-Based Reverse Geo-Cache Birthday Present Project
  • Nick McClickNick McClick Posts: 1,003
    edited 2010-01-25 06:02
    I'll use longer pin headers (like I used with the ProtoPlus), so you'll be able to stack it under without flipping it over, but you can still flip it over and it will work, too.

    Because it's stackable, it's better if it has all the connections, so you can stack another module on top and/or underneath.

    I think Jon has the right idea - I re-revved it so the battery goes to 5V and the regulator on the Prop Platform. This will let the battery pack power stuff like the LCD UI module. with 4.8v output.

    battery_platform2.png

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Propeller Forums RSS Feed!

    Gadget Gangster - Share your Electronic Projects
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-01-25 09:17
    Look at what the quiesant current of the Reg does when it gets to the LDO bit. Some go nuts and take 100mA+. You will be better off with an extra cell, overall.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Style and grace : Nil point
  • JRetSapDoogJRetSapDoog Posts: 954
    edited 2010-01-25 17:06
    I'm just curious = ignorant. What are the advantages of running the Prop (in this case) through a voltage regulator as opposed to straight on DC from the series connection of the batteries? Would 3.6+ volts possibly be too much? I thought it could handle somewhat over 3.3V (Yes, I should check the specs, but...). Would the regulator be able to maintain voltage even when the batteries dropped below 1.1V? I don't recall if a standard regulator can "boost," but maybe some (need to check the spec.). Anyway, just wondering if one could omit the regulator in certain ideal and low-load conditions. I think people have. Obviously, the regulator would be necessary if the battery voltage was too high (such as those new 1.6V rechargable cells I read about on Engadget, etc), but would that be a problem with standard 1.2V NiMH (or similar) cells?· * Update * I meant the foregoing for the 3-cell version.
  • Nick McClickNick McClick Posts: 1,003
    edited 2010-01-25 18:09
    A few advantages;

    1 - you won't blow anything up if you plug in the wrong batteries. 3 alkaline cells would provide 4.5v, which is too high.
    2 - you're able to provide 5v and 3.3v with the same set of batteries.
    3 - nimh's will sometimes start their discharge above 1.2v (say 1.4v), running the prop @ 4.2v sounds like a bad idea.

    two disadvantages I can think of;

    1 - you're losing (a bit) of energy heating up the linear regulator
    2 - the prop will run under 3.3v, but the reg. will drop-out before that. This isn't a big deal, though: When the voltage starts dropping on the cells, they're pretty much dead, anyway.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Propeller Forums RSS Feed!

    Gadget Gangster - Share your Electronic Projects
  • RaymanRayman Posts: 14,600
    edited 2010-01-25 18:17
    I'm thinking about a very similar problem: Providing AA power to my PSB device. I think I've decided to use 3-AA cells and one of those $5 chips to generate +5VDC... This also allows the battery pack to be trickle charged from the 5V regulator output...

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-01-25 19:44
    Oh for the perfect world, where the Prop is happy to run on a Li Ion cell. 4.2 Volts down to 3.7.

    Actually I have run one via a diode to drop the 0.7V, giving 3.5 V to 3.0V. I did have one on 4.2 Volts as an experiment with a Z80, but when the 9 Volt test failed I got a bit more careful with my remaining two Props.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Style and grace : Nil point
  • JRetSapDoogJRetSapDoog Posts: 954
    edited 2010-01-25 20:58
    Thanks, Nick.· Yeah, at a minimum, I forgot about the possibility of inadvertantly inserting alkalines.· Guess I'm just itching to blow something up (maybe with a 9V) like when I was a reckless kid.· Hmm...guess I should have sprung for the fail-safe mechanism when I worked·at Three Mile Island afterall (j/k).· Actually, that reminds me that a nuclear power plant somewhere ironically·failed as a result of·malfunctioning safety equipement, so bad·example.· That leads me to something I like to call Good's Safety Law (which I hereby introduce to a waiting world):· "Every safety measure has·at least one·inherent (often hidden)·danger associated therewith."· However, that doesn't mean that we shouldn't take safety measures, just stop and think about the possible danger scenarios·beforehand in order·to try to avoid them.· For example, it's probably a good idea to remove one's hands from one's pockets when walking down stairs (to free one's hands for balancing or fall-bracing).· But don't get so preoccupied with removing them that one loses their step.· Anyway, I'm always interested in how to make a minimal-parts system, which seems quite consistent with the spirit of the Propeller (with it's relatively easy video output and so forth).· However, yeah, skipping a voltage regulator is probably not a good idea in most cases.· Thanks again·for the response and for not berating me for even considering·the possibility of skipping one:· "Not use a voltage regulator???· Are you crazy!!!"· We now return to your regularly scheduled program....
  • BADHABITBADHABIT Posts: 138
    edited 2010-01-26 03:36
    You could use this buck/boost converter and run it from 2 or 3 nimhs.

    The Iq is a bit higher, but it should deliver enough power. Another advantage of this is that it would run the batteries lower.



    http://focus.ti.com/lit/ds/symlink/tps61121.pdf

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    BH skull.gif
  • Nick McClickNick McClick Posts: 1,003
    edited 2010-02-01 20:18
    Just want to double check my power calculations on this;

    1. A Prop @ 80MHz with all cores will use 80mA @3.3v (264mW)

    2. Converting 4.8v to 3.3v with an 80mA load will cause the vreg to burn up 120mW in heat (1.5V * 80mA)

    3. That's a total of 384mW, which should draw 80mA from the 4.8V power source.

    4. The nimh should drop under 1.1v per cell @ about 95% of total discharge. Depending on the cells used, there's about 900mA/h of total storage.

    5. I should get about 10.6 hours (855mA / 80mA) of power with 8 Cores @80 MHz.


    Running 3 Cores @ 80MHz should take about 30mA (100mW), 45mW lost in heat on the vreg is a total load of 145mW, or 30mA @ 4.8V = 28 hours of power.

    I am skipping Quiescent Current, but I'm also assuming everything is running in spin. As an estimate, though - does this sound about right?

    8 Cores @ 80MHz = 10 1/2 Hours
    3 Cores @ 80MHz = 28 Hours

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Propeller Forums RSS Feed!

    Gadget Gangster - Share your Electronic Projects
  • CannibalRoboticsCannibalRobotics Posts: 535
    edited 2010-02-01 22:40
    What about current loads on ports?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Signature space for rent!
    Send $1 to CannibalRobotics.com.
  • Nick McClickNick McClick Posts: 1,003
    edited 2010-02-01 23:02
    This is a baseline - any other components / parts / etc. connected would increase current draw, depending what the user connects.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Propeller Forums RSS Feed!

    Gadget Gangster - Share your Electronic Projects
  • nohabnohab Posts: 96
    edited 2010-02-02 15:18
    I assume one of the reasons to use 4,8V instead of 3,6V would be to support a LCD display, so I hope the regulator will cope with the current a display needs?!
  • nightwingnightwing Posts: 56
    edited 2010-02-02 16:31
    Does look nice!
Sign In or Register to comment.