[chbot] Car 12v supply to 5v VCC.

Geoff sdfgeoff at gmail.com
Tue Jul 9 07:51:43 BST 2019

I'm afraid I'm overseas and will be for the next couple months, so dropping
by for a chat isn't practical at the moment. Were I in town, I'd gladly
swing by for a chat.

I'm not sure my experience with a PI matches your intended use-case. Mine
is running as a server and I just happen to have a 12V powered external
hard drive. As a result I don't shut the pi down, well, ever. It's
currently at 173 days uptime, and over it's couple years of operation it's
only been rebooted a handful of times.
One thing that may help is that not much is on the SD card. In my case this
is because the SD card is tiny (2gb), so most of the data/programs are on a
secondary drive connected to it. I've heard reports that people have had
their SD cards being read-only and had the entire OS on an external drive.
Even though an SD card and a SSD are both based on flash memory, SSD's are
far more reliable. Of course, putting things on an external storage
increases the size and complexity of the build, so for automotive
applications where you have mechanical vibrations I probably wouldn't
suggest this approach. I'd say your thoughts about using an orangePi with
it's EMMC are pretty good. There are some other SBC's with onboard flash as
well (beaglebone etc) if the orange pi doesn't work for whatever reason.

Depending on what you're doing with the Pi it's possible that an embedded
system is a better solution. They tend to be more robust and reliable. It
sounds like you're building some sort of wireless datalogger? I'd say that
role can probably be filled by a micro-controller. Is this what you're
doing with the ESP or are these two separate projects?

I'm not at all familiar with automotive wiring, but things dying when you
disconnect the kill switch sounds like an inductive spike. If you've got
100A or so flowing out of your alternator there's a whole bunch of energy
caught up in those alternator coils, and when you disconnect the load it'll
create a massive voltage spike even if the RPM of the alternator doesn't
change. If it is an inductive spike, a fuse may not help due to the pulse
being high voltage but low current. The short duration of the spike also
means it may not show up on a multimeter - an oscilloscope would be the
only way to measure it. I'd be a bit cautions about connecting a scope to
that sort of power though.
You've already got a resistive shut. This will help, but a better solution
would be a flyback diode. A flyback diode won't suck power during normal
operation, but should catch the spike when it occurs.


On Tue, Jul 9, 2019 at 5:45 AM Daniel Powell <danielvieway at hotmail.com>

> Geoff, given your location (I’m in Gardiners road) you and I should talk
> over a light beverage. Would especially like to know how you are
> successfully shutting down your Pi and avoiding card corruption. Or even
> what you are using as a canbus transceiver (my PiCan is a little bulky).
> I’ve benched wireless telemetry and NMEA via my Pi, haven’t transferred it
> to the race car yet. Thinking I should port it to an Orange Pi and run
> everything on EMMC (will also avoid any vibration issues with the SD card)
> The offroad race car alt is a 110amp and barely able to keep up with the
> arrays of large fans and the occasional times I install the lights.
> The rules also require you to electrically isolate everything on kill.
> Even though I have a high resistance dump to ground when the kill switch is
> activated it occasionally pops the alt regs. Not the best of environments.
> I’m thinking of sneakily running the main alt line on a fused link and run
> the ECU, coils, pumps, etc, through a two pole kill switch…. Not legal, but
> at least I won’t keep on blowing alts with the 6 pole kill switch. It’s a
> new car, and a work in progress.
> http://www.powell.kiwi/main/images/19250450_1419407384817694_4263183785932437739_o.jpg
> The dash is currently designed to be installed within the steering wheel.
> However I think for the first installation I’ll mount one in the central
> console in the rally car (pic below) such that both the driver and co-dog
> can read it. It’ll also allow ease of replacement or configuration given
> it’s in an enclosed cabin.
> http://www.powell.kiwi/main/images/23592457_10156000416886579_231343381967206836_o.jpg
> Thanks for *all* the assistance gentlemen.
> Cheers,
> Daniel.
> *From:* Chchrobotics <chchrobotics-bounces at lists.ourshack.com> *On Behalf
> Of *Geoff
> *Sent:* Sunday, 7 July 2019 7:35 PM
> *To:* Christchurch Robotics <chchrobotics at lists.ourshack.com>
> *Subject:* Re: [chbot] Car 12v supply to 5v VCC.
> You can actually find 12->5v step downs locally in NZ for cheap enough.
> All car USB converters do exactly this, and can be had on trademe for a
> couple dollars:
> https://www.trademe.co.nz/computers/cables-adaptors/usb/listing-2220387680.htm
> <https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.trademe.co.nz%2Fcomputers%2Fcables-adaptors%2Fusb%2Flisting-2220387680.htm&data=02%7C01%7C%7C8e53c47e3db34b76bd1908d702adb305%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636980817374994911&sdata=g3JCdKLeErIfD1kF6JGapupIz6mZuv04ZtPEGtPgrCU%3D&reserved=0>
> If you have a dollar-store-thing near you, they probably have them as well
> for $4-5. In bishopdale mall there's a "Party Dollar Store" that I used to
> pick up this sort of thing from.
> Even if you're not using it in the cabin of the car, you can open it up
> and extract the PCB so you can solder wires to it. The ones I used had a
> single screw that held the whole thing together.
> Is the output stable? Well, from a clean 12V supply, I've been running a
> raspberry pi for the past two years, and it's still working. No idea about
> what a racecar would do to it.
> Geoff
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