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Using an SX proto board in a car's 12 volt system — Parallax Forums

Using an SX proto board in a car's 12 volt system

Basic JimBasic Jim Posts: 106
edited 2006-09-23 04:34 in General Discussion
Hello all,

I have an application in mind that would draw it's power from·a car's 12 volt system. I was woried that it would strain the proto boards regulator as the 12 volts in car system while running can get up to 14 volts. I checked the specs on the LM2940 and it says it can handle an input voltage of up to 26 volts!

·My question is, if thats so why does the board specify a six to nine volt adapter? A 12 volt adapter·should work fine right?

Just wanted to check with the experts before I go out and fry a board!· shocked.gif


Thanks,
Jim W. turn.gif

Comments

  • BeanBean Posts: 8,129
    edited 2006-09-13 01:00
    Jim,
    The LM2940 might handle 26 volts, but not at it's maximum current (1 Amp).
    That would be (26-5) = 21 Watts of heat !!!
    At 9 volts it would be (9-5) = 4 Watts of heat, alot but probably okay with a heatsink.

    [noparse][[/noparse]edit] Just checked the datasheet. The TO-220 with no heatsink can only handle a little over 2 watts of heat. With a decent heatsink it can handle about 9 watts of heat. (Those numbers are at 25°C).

    Bean.

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    Low power SD Data Logger www.sddatalogger.com
    SX-Video Display Modules www.sxvm.com

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    Make more than you spend.


    Post Edited (Bean (Hitt Consulting)) : 9/13/2006 1:09:18 AM GMT
  • Basic JimBasic Jim Posts: 106
    edited 2006-09-13 01:05
    So, If I put a larger heat sink I should be OK with 12 volts? that should be easy and cheap!

    Thanks,

    Jim W.
  • BeanBean Posts: 8,129
    edited 2006-09-13 01:09
    See my edit above. It depends on how much current you are using, but probably yes.

    Bean.

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    Cheap used 4-digit LED display with driver IC·www.hc4led.com

    Low power SD Data Logger www.sddatalogger.com
    SX-Video Display Modules www.sxvm.com

    There are only two guaranteed ways to become weathy.
    Spend less than you make.
    Make more than you spend.
    ·
  • Basic JimBasic Jim Posts: 106
    edited 2006-09-13 01:30
    My circuit won't draw much current. I'll keep a finger on the heatsink. I could also put a little cpu fan over it if it gets too hot. But, I think I should be OK without one.

    Thanks again,
    Jim W.
  • cbmeekscbmeeks Posts: 634
    edited 2006-09-13 14:48
    Ok, I am curious...what are you making?

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  • Basic JimBasic Jim Posts: 106
    edited 2006-09-13 23:40
    Hi cbmeeks,

    I want to tell you now but I need to do a little more research before I blab about it. It's kind of a dumb idea (at least my wife thinks so.) But I think there might be a market for it. Others I’ve shown it to think it's a good idea (or, they are humoring me.) You will probably laugh. (like she did). But, give me a little while to get back to you.

    Jim W.
  • StarManStarMan Posts: 306
    edited 2006-09-14 03:30
    At least you got a reaction from your wife.· If she were indifferent, you may need to think twice.

    Strong reactions, good or bad, are positive feedback.· If some people love your idea AND some people hate it, it's a winner.
  • BeanBean Posts: 8,129
    edited 2006-09-14 13:13
    If your wife thinks it's a dumb idea, that's better than a man thinking it's a good idea [noparse];)[/noparse]

    When I got my LPKF PCB milling machine, my wife thought it was the dumbest thing she'd ever seen.

    And just because it IS a dumb idea doesn't mean it won't be profitable. Someone made alot of money from the "Pet Rock"... And they still sell the "chia pet". What would your wife had said about each of those ?

    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Cheap used 4-digit LED display with driver IC·www.hc4led.com

    Low power SD Data Logger www.sddatalogger.com
    SX-Video Display Modules www.sxvm.com

    There are only two guaranteed ways to become weathy.
    Spend less than you make.
    Make more than you spend.
    ·
  • cbmeekscbmeeks Posts: 634
    edited 2006-09-14 13:37
    Basic Jim said...
    Hi cbmeeks,

    I want to tell you now but I need to do a little more research before I blab about it. It's kind of a dumb idea (at least my wife thinks so.) But I think there might be a market for it. Others I’ve shown it to think it's a good idea (or, they are humoring me.) You will probably laugh. (like she did). But, give me a little while to get back to you.

    Jim W.

    Hey, I had the idea of putting a small laser gun on a small robot car that had motion sensors. The car would pick up tiny bits of motion from insects (like roaches) and drive to them and shoot them. A tiny, laser shooting, roach killer. That would ROCK.

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    A place for programmers to hangout!
    http://www.codershangout.com

    METROID?
    Metroid Classic
  • Brian RileyBrian Riley Posts: 626
    edited 2006-09-14 14:18
    Basic Jim said...
    So, If I put a larger heat sink I should be OK with 12 volts? that should be easy and cheap!

    Thanks,

    Jim W.

    No you won't be that OK. I have used he SX48 with 12volts and it runs too warm over a period of time to my liking. Especially if its gonna be buttoned up some place or worse, under the hood. The easiest solution is to offload some of that voltage/power with a three to five 1N4000 series diodes in series with the 12V line, which will drop .7volts per diode. Rememeber that "12v" with regard to a car is a eumphemism for what in reailty is 13-14 volt system. The regulators put ot in the vicinity of 13.8volts. The batteries generally settle down in the low 12v range when the engine has been shut off. And it might not hurt to have a hefty choke in that line to beat down startup transients, as well as an overvoltage protection diode across the input. Automobiles are a very electronics unfriendly environment..

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    See the K107 Serial LCD Controller at
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  • Basic JimBasic Jim Posts: 106
    edited 2006-09-14 16:11
    Thank you Bean and Starman for your encouragement. The more I think about it the more I think it should be doable. What worries me most is that it isn't being done already so, there must be a reason. It's not rocket science.

    Thanks Brian,
    The diodes are an excellent idea. I'm not sure how hefty a choke I would need. Maybe I could scavenge one from an old car radio for testing purposes.

    Best,
    Jim W.

    Post Edited (Basic Jim) : 9/14/2006 4:15:44 PM GMT
  • Guenther DaubachGuenther Daubach Posts: 1,321
    edited 2006-09-15 09:14
    Having one or more diodes in series with the supply line has another advantage too: You protect the device against wrong polarity. This is why I usually put at least one 1N400x in series with the supply input.

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    Greetings from Germany,

    G
  • Brian RileyBrian Riley Posts: 626
    edited 2006-09-15 14:30
    earlier, I said...
    Automobiles are a very electronics unfriendly environment..

    I just want to expand on that a tad .... not too many years ago, chips came in basically two flavors ... chips and mil-spec chips ... Now they come in more flavors and for the most part the top of the heap, that is, the most demanding specs, is not the military stuff, but ... yup, you guessed it ... chips destined for automotive use!

    FWIW ... cheers

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    cheers ... brian riley, n1bq, underhill center, vermont
    See the K107 Serial LCD Controller at
    www.wulfden.org/k107/
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-09-15 15:55
    I was thinking that you could put a 7809 in front of the SX-48 and have that regulator dump the heat.
    Boy! Have I been wasting money.

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  • Basic JimBasic Jim Posts: 106
    edited 2006-09-15 16:27
    Gunther,
    That is a fantastic point! I will stock up on those little critters

    Best,
    Jim W.
  • Basic JimBasic Jim Posts: 106
    edited 2006-09-15 16:37
    Brian,

    Wow, I didnt know that. All this time I thought Mil spec was top of the line. Probably isn't much difference in spec. from military to automotive since both are subject to very extreme enviroments. Military might more robust in EMI surges I would think.

    Best,
    Jim W.
  • Basic JimBasic Jim Posts: 106
    edited 2006-09-15 16:46
    Kramer,

    You said, "I was thinking that you could put a 7809 in front of the SX-48 and have that regulator dump the heat."

    That's how I was going to tackle the problem originally. I glad I posted my question. This forum is a fantastic resource!

    Best,
    Jim W.
  • SteelSteel Posts: 313
    edited 2006-09-15 16:52
    Can you also just put a 9VZener in parallel to the circuit on the frontside, so that the Zener dumps anything over The 9V?

    Im just wondering for if my own circuits end up in that environment. It seems like a cheap fix to a noisy situation...
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-09-19 02:43
    Steel said...
    Can you also just put a 9VZener in parallel to the circuit on the frontside, so that the Zener dumps anything over The 9V?
    · No (that is, No Way.)· Zener current [noparse]/noparse][b]I[/b][sub]Z[/sub must be limited.

    · The Zener is like a regulator, once input voltage is greater than Zener voltage, then the difference will be across the limiting resistor.

    · Sometimes a Zener is used this way (in parallel with the input)·when the greatest expected input voltage is "just a tad" greater than the Zener voltage [noparse]/noparse][b]V[/b][sub]Z[/sub, intending to then clear a fuse as a result.

    · Also, "pre-regulating" with diodes (pl.)·isn't a panacaea, either (i.e. don't get carried away.)

    · Post Edit -- If you're interested in an experiment, try using a zener in series with your input to "pre-regulate" with, because it's the same "principle" as using a rectifier diode for voltage drop.


    Post Edited (PJ Allen) : 9/19/2006 2:50:26 AM GMT
  • BongoBongo Posts: 65
    edited 2006-09-19 17:18
    I would think that the back emf caused by your transport's starter motor is going to cause you far more grief than the reg running a little warm.· Would suggest a bipass diode as a bare minimum to some supply filtering.



    bongo
  • Guenther DaubachGuenther Daubach Posts: 1,321
    edited 2006-09-19 20:08
    In critical applications I place an overvoltage protection diode, like a P6KE6V8 across the 5V supply (cathode to plus, anode to minus). Such diodes can dissipate peak power pulses of up to 600W at very fast response times. For example, I'm using them in an application where an SX controls a concrete saw, where extremely high voltage transients can occur caused by a 400V, 16 Amps three-phase frequency converter. May be it's a good idea adding such a device to your automotive application.

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    G
  • Basic JimBasic Jim Posts: 106
    edited 2006-09-20 22:24
    When I think about all the elctronics people use in their car now it seems to me that my SX board should survive. I've seen people run their computers, cell phones and even TV's from the cigarete lighter. Seems to work for them. freaked.gif


    ·For now I will try one of Gunther's P6KEV8 with some 4001 and a choke and that should hopefully get me by.·yeah.gif·I have ordered a couple xtra proto boards just in case I'm wrong. If worse comes to worse I could break down and buy a DC-DC converter.idea.gif

    Thanks,
    Jim W.tongue.gif
  • Guenther DaubachGuenther Daubach Posts: 1,321
    edited 2006-09-21 08:14
    Jim,

    please find attached the schematic for a DC/DC converter. I'm using it in many of my applications, and it works great.

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  • TransistorToasterTransistorToaster Posts: 149
    edited 2006-09-23 04:34
    You can use the MC34063 switching regulator. It's real cheap.
    Frank
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