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Thread: Automotive power supply for Teensy

  1. #1
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    Automotive power supply for Teensy

    Seeking some opinions on the attached power supply schematic. suitability, functionality etc

    input voltage will be around 13.7v with engine running

    D1 1N4003 to provide protection against reverse connection

    TVS diode is a P6KE15A. datasheet [wrong symbol on schematic]

    OKI-78SR-5 dc/dc datasheet regulator to provide 5v to teensy 3.5 or 3.1 and some 5v sensors (mpx4250's or similar, outputs are connected to analog pins through voltage dividers)

    the 5.6v zener is to protect against reg failure, will need to be man enough to pop the fuse

    will be used in my data logger project. any advice welcome, i am a beginner

    Click image for larger version. 

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  2. #2
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    Name:  mdFZhAXw-llzAm2qRhaIXmg.jpg
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    This is what I use in my automotive project. It's an 8v-40v input and 5v 30a output dc-dc ~90% efficient psu, epoxy sealed and weatherproof. It also survives cranking, the lowest voltage I've tested for a drop out is 7.60 volts, however, once the voltage goes back up, it restores the 5v rail, and the voltage doesnt seem to fluctuate either on my DMM.
    Enjoy

    Also: Cut VIN-VUSB pad (Once you do that, Teensy only works with external power connected), or, option #2, get a data-only usb cable or make your own, by cutting it's red wire
    Last edited by tonton81; 12-18-2016 at 03:31 PM.

  3. #3
    Senior Member Jp3141's Avatar
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    15 V might be a little too low for the TVS -- as the battery goes bad (but not failed), the voltage could approach 15 V -- together with the TVS tolerance, it could cause some current to flow and it might overheat (and not blow the fuse). Try 18-24 V version.

    if you care about keeping operation during low battery (e.g when cranking the engine on a cold day), make the input cap larger -- to 1000 uF or more (but watch for the fuse blowing when you connect it initially -- may need a slow-blow fuse). The 78Sxx needs 0.1 uF caps also -- placed close to the chip. If your load current is only 10's of mA or so, it won't need (much of) a heatsink, but if you are driving heavier loads, it might (e.g. 50 mA ==> (14 -5 )*50mA = 450 mW

  4. #4
    Senior Member jimmayhugh's Avatar
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    Quote Originally Posted by tonton81 View Post
    Name:  mdFZhAXw-llzAm2qRhaIXmg.jpg
Views: 562
Size:  7.5 KB

    This is what I use in my automotive project. It's an 8v-40v input and 5v 30a output dc-dc ~90% efficient psu, epoxy sealed and weatherproof. It also survives cranking, the lowest voltage I've tested for a drop out is 7.60 volts, however, once the voltage goes back up, it restores the 5v rail, and the voltage doesnt seem to fluctuate either on my DMM.
    Enjoy

    Also: Cut VIN-VUSB pad (Once you do that, Teensy only works with external power connected), or, option #2, get a data-only usb cable or make your own, by cutting it's red wire
    got a link??

  5. #5
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    I Googled his description and found this.

    http://www.ebay.com/itm/SUPERNIGHT-W...-/331546742294

  6. #6
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    that one is 3A. get the 30Amp version, i buy em from ebay as well search for 150w 30a 5v dc-dc psu and you'll see the pic, they all look the same. make sure it says 150w 5v 30a

    heres a search list for you:
    http://m.ebay.com/sch/i.html?_from=R40&_trksid=m4084.l1313&_nkw=30a+5v+d c-dc+150w
    Last edited by tonton81; 12-19-2016 at 05:20 AM.

  7. #7
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    Quote Originally Posted by tonton81 View Post

    This is what I use in my automotive project. It's an 8v-40v input and 5v 30a output dc-dc ~90% efficient psu, epoxy sealed and weatherproof. It also survives cranking, the lowest voltage I've tested for a drop out is 7.60 volts, however, once the voltage goes back up, it restores the 5v rail, and the voltage doesnt seem to fluctuate either on my DMM.
    Enjoy

    Also: Cut VIN-VUSB pad (Once you do that, Teensy only works with external power connected), or, option #2, get a data-only usb cable or make your own, by cutting it's red wire
    i have used a similar part before but i wanted something smaller and on the pcb this time, also the modules still need input and output protection

    good call on cutting vin-vusb

    Quote Originally Posted by Jp3141 View Post
    15 V might be a little too low for the TVS -- as the battery goes bad (but not failed), the voltage could approach 15 V -- together with the TVS tolerance, it could cause some current to flow and it might overheat (and not blow the fuse). Try 18-24 V version.

    if you care about keeping operation during low battery (e.g when cranking the engine on a cold day), make the input cap larger -- to 1000 uF or more (but watch for the fuse blowing when you connect it initially -- may need a slow-blow fuse). The 78Sxx needs 0.1 uF caps also -- placed close to the chip. If your load current is only 10's of mA or so, it won't need (much of) a heatsink, but if you are driving heavier loads, it might (e.g. 50 mA ==> (14 -5 )*50mA = 450 mW
    yes i think i will bump up the tvs voltage

    the 5v reg is a switch mode replacement of a linear reg so doesn't need a heatsink. i will need to look into voltage drops when starting and whilst winching tho, it does have a pair of hefty batteries so should be ok and the reg works down to 7v.

  8. #8
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    I've used the LM2940 successfully in the past, it's designed for automotive use and has some cool features built in.

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