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Rechargeable battery circuit with Prop — Parallax Forums

Rechargeable battery circuit with Prop

Chicago MikeChicago Mike Posts: 88
edited 2007-12-19 10:07 in Propeller 1
Can anyone guide me to the most basic of basic recharging circuits. I have a propeller application I've built for which I would like to use a Ni-MH 9V 150mAh rechargeable internal·battery. As the application is rather extensive·already, I'd rather keep my parts related to this charging circuit to bare minimium (PCB real estate is the issue at this point), and I do still have·program space, and 3 pins available on the prop to assist with any logic that may be needed.

I guess my problem is that I don't have a good understanding·of the design/implementation of charging circuits.

The battery will be in the device, and ideally I just want to give a jack to charge the battery. I already have a routine checking the voltage of the battery for a low level indicator.

Google searches have yielded many very complex and elaberate solutions for, what seems like stand alone solutions, not integrated device solutions. Has anyone built a charging circuit with a prop yet? Anyone has some good sources of rechargeable battery theory?

Thanks,
Mike.
·

Comments

  • Fred HawkinsFred Hawkins Posts: 997
    edited 2007-12-18 14:56
    try here: http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=84&superGrpID=Power%20Mgt%20Battery%20Chargers
  • parts-man73parts-man73 Posts: 830
    edited 2007-12-18 16:52
    I've been contemplating the same issue, and that link provided me with some valuable information. Thank you.

    I was wondering about the implications of having the circuit being powered connected to the battery and/or charging circuit at the same time as the battery is being charged. I do plan to read over some datasheets, but if someone knows...please share.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Brian

    uController.com - home of SpinStudio

    PropNIC - Add ethernet ability to your Propeller!

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  • deSilvadeSilva Posts: 2,967
    edited 2007-12-18 18:21
    Good "in-place-charging" is a contradiction in terms...
    (1) You should never force current into a full rechargeable! It will not only turn to heat but destroy the whole battery in the long run.
    (2) You should discharge a battery to just above the point of "low discharge" to avoid the memory effect. ALL batteries are bound to the memory effect; it is a myth that NiHM or Lithium batteries are not.

    Both are "chemical" effects...

    So you should either "charge" a battery or "discharge" it to the fullest.
    Whether a battery is "fully charged" or "at the point of low discharge" is not obvious a-priory. It is generally tested by trying to charge it and observe its reaction to it.

    And: All batteries are different! I do not mean: There are different types.. I mean: Each single battery differs from all others!

    The - bad! - standard solution used in many simple devices is this (12V input):
    InPlaceCharging.JPG
    150 x 200 - 7K
  • RaymanRayman Posts: 14,865
    edited 2007-12-18 18:39
    Here's a nice page on regarging AA's from USB:
    http://www.stefanv.com/electronics/usb_charger.html
  • deSilvadeSilva Posts: 2,967
    edited 2007-12-18 19:12
    @Ray: Yes that is a very comprehensive description how many commercial chargers without microcontroller work. The most important thing is to shut it down when having reached full charge.

    I still avoid to post my own selection of 42 more or less useful links to similar projects...
  • Nick MuellerNick Mueller Posts: 815
    edited 2007-12-18 19:33
    As deSilva said, not very practical to charge in the circuit.
    But you can do it if you charge with C/5 to C/10 and monitor the temperature. If a NiMH is going above 50°C, it's time to stop charging. Quite primitive! KTY-81 as temp sensor, for example.

    Read the data sheets at sanyo, they do give a lot of information.


    Nick

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    Never use force, just go for a bigger hammer!

    The DIY Digital-Readout for mills, lathes etc.:
    YADRO
  • deSilvadeSilva Posts: 2,967
    edited 2007-12-18 19:47
    Many (all?) LiIon batteries have this included.. Its the third (generally middle) lead-out you may have wondered about all the time...
  • Nick MuellerNick Mueller Posts: 815
    edited 2007-12-18 21:50
    > Many (all?) LiIon batteries have this included..

    With "this" do you mean a temperature-sensor?
    AFAIK, no, not (just) temperature sensor. Much more. Battery ID, capacity, number of charges and and and. I think with "LiIon battery management IC" you should find better information than mine. smile.gif


    Nick

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Never use force, just go for a bigger hammer!

    The DIY Digital-Readout for mills, lathes etc.:
    YADRO
  • deSilvadeSilva Posts: 2,967
    edited 2007-12-18 23:37
    Cheap one-cell Li-Ion batteries (3.7V) seem to have a thermistor only... AFAIK.
    Multi-cell "smart" batteries - as in lap tops - have the intelligence you describe. They have 4 to 5 pads. Simple chargers use the thermistor pad only. The controller bus is used from the laptop or VERY expensive chargers only...
  • Chicago MikeChicago Mike Posts: 88
    edited 2007-12-19 03:18
    Has anyone gave the MAX712 or MAX713 Fast-Charge Controllers a shot? Expensive in general (Around $8.00 for the SOIC model), but seems, in theory to have everything needed with minimal external parts.
  • Fred HawkinsFred Hawkins Posts: 997
    edited 2007-12-19 04:52
    Nice overview pdf from microchip: http://ww1.microchip.com/downloads/en/AppNotes/01088a.pdf

    They argue convincingly that LI-ion are perfectly suited for portable apps: 
    "Besides the cost, the Li-Ion batteries have significant advantages over the NiMH batteries. The 3.6V nominal voltage also makes Li-Ion a perfect supply voltage to most portable devices. Cell balancing can be an important issue when more than one battery cell is required for the system. For NiMH batteries to supply 3.6V, 3-cell NiMH is usually needed to maintain the voltage. A single-cell Li-Ion battery supplies the same voltage while taking less space and without worrying about cell balancing. "


    Post Edited (Fred Hawkins) : 12/19/2007 4:57:09 AM GMT
  • Nick MuellerNick Mueller Posts: 815
    edited 2007-12-19 09:30
    Adding to the temp-controlled charging I wrote about:
    Maybe C/10 is a bit slow for charging and it doesn't get warm enough when full. Better try it with C/2 ..C/5.
    You can vastly improve that, if you do detect the end of charge with dU/dT. When NiCd or NiMH are charged, their voltage rises. At the moment they are allmost fully charged, the voltage drops (thus the dU/dT). So if you monitor the voltage (the absolute value does *not* matter) and switch off if the voltage *drops* (by a magnitude of 10mV) the battery is full (disregarding the fact that it should be overcharged with reduced current).
    You still need the temperature sensor, because you don't know in what state the battery is.

    So with two ADCs, you get a quite good charger.

    Nick

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Never use force, just go for a bigger hammer!

    The DIY Digital-Readout for mills, lathes etc.:
    YADRO
  • deSilvadeSilva Posts: 2,967
    edited 2007-12-19 09:56
    Charging all kinds of batteries is well understood. What is not so well understood is how to do it best "in-situ"
  • Nick MuellerNick Mueller Posts: 815
    edited 2007-12-19 10:07
    As long as I_out << I_in and the R_i of the cell is low enough (kinda doubt that with 9V 150mAh) it still works. And you always have the temperature for safety.

    Nick

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Never use force, just go for a bigger hammer!

    The DIY Digital-Readout for mills, lathes etc.:
    YADRO
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