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Basic Stamp used as a battery/solar charge controller? — Parallax Forums

Basic Stamp used as a battery/solar charge controller?

scribbscribb Posts: 8
edited 2004-12-08 05:32 in BASIC Stamp
Has anyone built a charge controller circuit for 12V lead-acid batteries?
I'm thinking about building one·using a PWM setup (with·a MOSFET as the switching device).· I plan to have it rated for at least 3 amps (at about 13.8 Vdc).
If anyone has done·a project·like this, then please feel free to show off your work.
If possible, I'd like to see a schematic or block diagram.

Thanks all.
Sheldon

Comments

  • scribbscribb Posts: 8
    edited 2004-09-16 12:44
    I was thinking something like what's in the attachment.
    BS1-CHARGE.gif
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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-09-16 20:12
    Scribb,

    ·· Tracy Allen posted some information regarding charging Lead Acid batteries at one point on the Yahoo Group.· In my application, which required a charge on an in-use battery, he suggested that I use a PB137 VR, which I got through Mouser.· It will keep a 12V lead acid battery charged, while providing great reverse leakage protection for when the AC power is lost...However, I don't think it will do more than 1 AMP.· Does your application require 3 AMPS continuous?



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • scribbscribb Posts: 8
    edited 2004-09-17 12:48
    I like what the PB137 does.
    But, I wish it were rated for more current (I have a 3A power supply).
    Also, it doesn't seem to be a switching regulator??· I take it that it will get pretty hot under full load?
    04vlt_03b.gif
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  • Tracy AllenTracy Allen Posts: 6,658
    edited 2004-09-17 15:59
    The PB137 is packaged in a TO220 case, so you would normally mount it on a fat heat sink. One nice thing about solar panels is that the voltage drops as you get near the rated capacity, so, for example, you have 13.7 volts output at 15.7 volts input at rated current, so with 1.5 amp current, that would be 3 watts. If your overall heat sink junction to ambient is 15 degrees C per watt, then the rise over ambient would be about 45 degrees C. If ambient is 25 degrees C, the junction will be at about 70 degrees C, which is well below the allowable thermal limit of 150 degrees C. However, without a heat sink, junction to ambient is 50 degrees C per watt, and at three watts it would overheat and shut down (it is thermally self protecting).

    You might be able to parallel a couple PB137s to get greater current, the 3 amps you need, if you put a small value resistor (~0.1 ohm) in series with the output of each one where they connect, to assure that they equalize the load. I haven't tried it, but I think it would probably work.

    The PB137 is strictly a float charger, and it does not provide any compensation for ambient temperature. It is not well suited for use in the extremes of weather you could find in an outdoor application. It is best suited for indoor charging.

    That said, you could make a much more sophisicated charger with your Stamp. You could add a rapid charging feature, but to do so you need to add means to monitor the charging current as well as the voltage, and also the temperature.

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    Tracy Allen
    www.emesystems.com
  • AntzAntz Posts: 7
    edited 2004-09-18 01:38
    There are plenty of cheap solar battery controllers/regulators out there.
    Most of them are the serial type, and work by simply monitoring the battery voltage.
    When the voltage drops below about 14.1 volts, it connects the solar panel to the battery, when it gets above about 14.4 volts it disconnects the solar panel. Most setups I have delt with will typically pulse the power on/off about twice a second. Most serial regulators of this type are rated at 10 amps or more.
    The only problem with this is it can introduce noise to the power supply as it switches.

    Lately I have been using parallel regulators that sit across the power supply and dump the excess load as heat. Each one is rated at 3 amps max dump load, so it is just a case of hooking up as many as is needed in parallel for the maximum charge available from the solar panels. It also means the extra regulators will provide quite a bit of redundancy should one fail.

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  • Jonny555Jonny555 Posts: 46
    edited 2004-09-18 03:31
    I've been having one hell of a time getting a solar lithium polymer charger going.
    Maxim closed the tap on their samples today too [noparse]:([/noparse]
  • Buck RogersBuck Rogers Posts: 2,175
    edited 2004-09-18 03:51
    Hello from Buck Rogers
    What do you mean by "Maxim closed the tap on their samples today too [noparse]:([/noparse]"? Normally there is a good reason why they can not send you a sample. Sometimes they actually need a reason why they can send you a sample, or not send you one. If you need small quantities of a part, anything over the sample lmit of eight per part number, you can buy them from their store, or a shop like Digi-Key. Which does sell Parallax parts.

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    Buck Rogers

    www.gregg.levine.name
  • Jonny555Jonny555 Posts: 46
    edited 2004-09-18 04:13
    Yes I ordered 8 samples in 90 days(a few adc/dac's, type k thermocouple ic and a few different voltage comparators). Digikey or Future are usually where I purchase larger quantities of ic's. Unfortunately I didn't notice I had ordered so many. When I came to order samples of their lithium ion charge ic's they emailed me saying I had reached the limit. I've tried a few charger circuits but I need something with ultra low voltage/current dropout and this is driving me nuts. The L200 and LM317 circuits have not impressed me at all. My last hope is the MAX1647 Chemistry-Independent Battery Charger(1-4 Li cells).
  • steve_bsteve_b Posts: 1,563
    edited 2004-09-20 16:57
    I've tried to get samples from Maxim a few times and have yet to receive any.·

    I'm in Canada....so I don't know if they're all sitting at the border...but I've not been contacted otherwise.



    sb

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    ·

    Steve
    http://members.rogers.com/steve.brady
    http://www.geocities.com/paulsopenstage

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • vir-technologiesvir-technologies Posts: 4
    edited 2004-12-08 05:32
    Sheldon,

    All the BSII needs is an ADC, and you can charge and monitor batteries. A 8-12 bit ADC will work fine, and code is fairly simple. Below is a link to battery management source code I have designed and used over the past several years, and the core functions have been used in NASA since the early 1990's. It can easily be modified for SLA, multiple Li or Ni packs.

    Please review the kit listed here, vir-inc.com/software.html, for circuits and source code which can be downloaded with the IPMCharge code - PBASIC SDK.

    This simple circuit could just snaps on to the BSII Carrier Board, and you have a complete solution for rechargeable batteries.

    I caution you to not look at battery voltage alone to determine low or high battery levels, as this does not provide any data on the efficiency of the cells to power the system. This applies to wireless phones, RC vehicles or SLA batteries.

    Regards,

    Steve Halla
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