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BS2 and a car battery — Parallax Forums

BS2 and a car battery

BuckelburyBuckelbury Posts: 4
edited 2006-05-25 03:11 in BASIC Stamp
I have a farely simple question. Is it safe to connect a bs2 to a 12 volt car battery? If not, what would I need to do to make it safe?

Thanks
a...

Comments

  • VladimirVladimir Posts: 64
    edited 2006-04-23 20:13
    you will burn out ur BS2 instantly! that is if you don't have a 5 volt regulator installed. If you do, its safe.

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    Thanks,

    Vladimir
    ·
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2006-04-23 20:30
    The BS2 module can handle 12 volts, but it's not a good idea for a couple reasons: it puts a lot of strain (heat) on the Stamp's regulator, and a car's electrical system is very noisy; the introduction of that noise may do damage to the BASIC Stamp. If you have to use the car's electrical system you should put one of those LC filters desired for car audio systems inline to protect the Stamp.

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    Jon Williams
    Applications Engineer, Parallax
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-04-23 20:32
    Yes, you can connect the voltage connector of a BOE to a 12-volt battery. The BOE has an on-board voltage regulator.

    If you want to build your own board, you'll need a 1000uF capacitor across Vin and Vss (to filter some of the noise on the car's 12-volt line). And DON"T connect the 12-volts to the Vdd pin, as that WILL blow up the BS2 in short order.
  • BuckelburyBuckelbury Posts: 4
    edited 2006-04-23 21:00
    I will not actually be using the basic stamp in an auto or through the electrical system. I am simply using the car battery as a power source. During the day the car battery will be recharged via a solar panel, but at night I need to run the basic stamp off of the battery. I am not so concerned with interference as I am with the 750 Cold Cranking Amps that the battery can produce. So do I need to put a voltage regulator or some sort of circuit between the car battery and the basic stamp to prevent blowing up the basic stamp?
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-04-23 21:14
    12V, no matter the source, is a wee bit on the high side, and that's all for voltage matters.·

    The best way to keep from drawing too much current is to use a fuse.· There are fast-blow fuses in many ratings less than 1/2 A.· That's what will save your bacon.
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2006-04-23 21:17
    If you're going to use 12v from the car, you MUST use the Vin connection (pin 24 on the module). And don't be worried about the amps of your battery -- you cannot force amps through a device, a device demands amps (lower resistance, more amps). The noise in the electrical system can wreak havoc with digital electronics, though, so use a filter.

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    Jon Williams
    Applications Engineer, Parallax
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-04-23 21:17
    The BS2 is 'voltage driven'. By that I mean, for a given voltage, it will only pull as much current as it needs.

    So, though your 750 Amp battery has that much 'juice' inside it, it CAN put that out at 12 volts. But that's only if you put a (let's see, V = IR, 12 = 750 * R, R = 12/750, R == 0.016 ohms) 0.016 ohm resistor across it.

    If you put a BS2 across it (connect +12 to Vin, 0 to Vss) -- then that BS2 will only 'suck' a milli-amp or less. This means the battery should run down really-really slowly. Probably the battery will 'self-discharge' (Lead-Acid car batteries do this) more current than the BS2 is pulling out of it.

    Otherwise, a car battery (withouth a car's electrical system attached -- all those spark plugs, aiee!) is a really GOOD, zero-ripple voltage source.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-04-24 17:02
    allanlane5 said...(trimmed)
    If you want to build your own board, you'll need a 1000uF capacitor across Vin and Vss (to filter some of the noise on the car's 12-volt line). And DON"T connect the 12-volts to the Vdd pin, as that WILL blow up the BS2 in short order.
    Allan,

    ·· It is likely that for that type of noise the more important range of filtering capacitor would be around .01uF, .1uF, 1uF and maybe 10uF.· 1000uF is god for low frequency ripple, but the lower values filter the higher frequency noise.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-04-24 17:02
    ·If not attached to an auto, please reconsider.
    They tend to leak acid and burn holes in your clothes that you only discover after your next laundry shows the damage.
    Even a small motorcycle wet cell will do these nasty things.

    Consider this. . .
    I am using an 8volt 9amp Lead battery on my BasicStamp.
    It is a gell cell and sitting right next to me on my desk. Very clean, no leakage.
    And it is less waste in heat due to the lower battery voltage.
    Much smaller solar panel requirements too.

    This one is quite a lot of juice for the Stamp project, but I don't like to work with draging power leads to my computer desk.
    I tend to jump up and pull everything to the floor in a tangle.
    The amp/hour rating only comes into play if you make a dead short [noparse][[/noparse]lots of sparks].

    With this battery I can easily leave my Stamp running for a week or more between recharge.
    As I have need to verify that what I am doing will work properly for days, it is optimal.

    It is nice to only occasionally have to charge one big cell rather than constantly charge little ones, like the NiMh, for bench work. And much cheaper than a bench supply.

    And as said, no ripple too.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 4/24/2006 5:07:33 PM GMT
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-04-24 19:12
    Yeah, I agree with Walter. The Gel-cells are very nice, very clean, very safe.

    I managed to acid-burn a hole in an old winter coat I was wearing when I replaced a car battery at AutoZone. You really have to be careful with the "real" lead-acid units.

    P.S. Just remembered the brand on the Gel-cell -- Yuasa.
  • FranklinFranklin Posts: 4,747
    edited 2006-04-24 19:47
    You also need to remember that car batteries put out 13.8 volts and charge at up to 15 volts. I would build a robust off board regulator for your project to be safe.

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    - Stephen
  • john_boyjohn_boy Posts: 1
    edited 2006-05-23 02:17
    Could you not drop the voltage by putting several diodes in the path. Each one drops the voltage by 0.6 volts. Put in say 5 of them them to drop it by 3 volts and you have a nice 9-12 volt range (down from 12-15)
  • Shawn LoweShawn Lowe Posts: 635
    edited 2006-05-23 14:37
    Yes, you could drop the voltage that way, but with all those diodes it would probably be as cheap to just add a voltage regulator to the output of the battery.

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    Shawn Lowe


    My last words shall be - "NOT YET!!!"
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-05-23 14:54
    You can use another 5 volt regulator (7805) and go directly to pin 21. It will get hot and dump the extra voltage. In that way it will take all the 'heat stress' that would otherwise be occuring on the BasicStamp.

    Alternatively, you could step down the 12 volts with a 9 volt regulator (7809) and use pin 24. Seems a bit silly unless you have a reason to need 9 volts for something else.

    The diodes would work, but they too would be getting hot. Why not use the 5 volt regulator that has a surface to attach a heat sink and is engineered to do the job well?

    I am using an 8 volt lead acid battery rated at 9amp and have included a 1 amp fuse because an accidental short will melt the insulation off the wire. These batteries have a lot of stored energy; not at all like a AA cell. When you make a mistake everything converts into heat and sparks. So think about how to get the power under control. This is an important basic part of designing good circuitry.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • bushibushi Posts: 12
    edited 2006-05-23 18:14
    Not to hijack the thread, but I have a question about the LC circuit. I'm just starting a project where I'll have the BS2 in a very noisy environment ('72 VW Super Beetle). Could anyone give a suggestion as to either a pre-built LC module or a schematic for an appropriate circuit? Lots of good info in this thread that I hadn't considered in my initial design.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-05-24 10:09
    bushi,
    I good osilloscope will greatly enhance verifying things.

    The following are quick and easy fixes:
    Some of the available voltage regulators will block all the noise or at least claims have been made that they do. You need to find which ones. There was much discussion about this two years ago!

    I know most EMI filters are rated for 120VAC or 240VAC, but have you considering trying to use the pre-packaged noise filers.
    I believe these are called COR-COMMs EMI filters and are essentially low pass, high power.

    You can always add a graphite bead near the power's point of entry, too.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • bushibushi Posts: 12
    edited 2006-05-25 03:11
    @Kramer - Thanks for the reply. I took a look at the CorComm filters and they look good. I did some more digging and came across a nifty little DC/DC power supply. I'd like to have 5V and 3.5V (for a SmartCard writer) so I could run the power supply at 7.5V and use regular liner voltage regulators. If you get the time, take a look and tell me what you think.

    www.opussolutions.net/catalog/product_info.php?products_id=33
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