Power source for Arduino in Car - Page 1
Forum section: electronics / beginners

author: symbianas
author_rank: Regular Contributor
timestamp: May 03, 2020, 03:54:52 pm
content: Hi, I am planning to install Arduino which reads CAN BUS data in the car. So I will need some kind of ~14-12V to 5V converter.I have these 2 at my disposal. Are they any good? Which one would be more efficient and reliable? Or would you recommend anything else?

author: tunk
author_rank: Super Contributor
timestamp: May 03, 2020, 04:15:31 pm
content: The one on the left looks a bit like this:https://lygte-info.dk/review/USBpower%205V%201A%20USB%20Port%20Car%20Charger%20JHY008%20UK.htmlThe one on the right looks like it's better quality.I suggest that you find the chip numbers and do a web search.

author: Ian.M
author_rank: Super Contributor
timestamp: May 03, 2020, 05:00:48 pm
content: Neither look to be particularly high quality, though the one on the left looks to be particularly crappy.For reliability its hard to beat aLM317HVlinear regulator, with a 36V unidirectional TVS diode protecting its input against spikes and other transients and a beefy 4.7R power resistor (>7W, opreferably pulse rated) and 300mA slow blow fuse in series with the feed upstream of the TVS diode. However that's only good for a couple of hundred mA out, needs some heatsinking (at 5V,200mA out with the engine running the regulator will be dissipating approx 1.6W) and of course efficiency sucks as you are throwing away 65% of the input power as heat. Don't be tempted to use an ordinary LM317 - you need the LM317HV's 60 V max input to output differential rating so there's enough headroom between the TVS diode worst case clamping voltage and the regulator's max. input voltage.The consequences of regulator failure aren't at all nice for a permanently connected CAN device - if it fails shorted input to output and while your CAN device is burning up due to overvoltage it lets through a differential voltage over 7V onto the bus, you risk blowing other CAN devices, which in a modern vehicle could do thousands of dollars worth of damage. Even if you have a good regulator, an almost paranoid level of over-voltage and over-current protection at the CAN transceiver IC + resistors in the data lines between it and the MCU are advisable.

author: symbianas
author_rank: Regular Contributor
timestamp: May 03, 2020, 05:19:42 pm
content: Quote from: tunk on May 03, 2020, 04:15:31 pmNice website. You are correct the one on the left is the same or similar to your link. The other one seems to be similar to this one (at least internals):https://lygte-info.dk/review/USBpower%20Bluetooth%20Car%20charger%20BC06%20UK.html

author: OamSlaugh
author_rank: Newbie
timestamp: May 04, 2020, 12:04:39 am
content: QuoteQuoteI second that. The automotive power bus is not a friendly environment and you will see some "mystery failures" down the road (haha!) without beefing up the input.My two cents would be to use a bidirectional TVS though, such as the SMBJ36ca or similar, and then add a diode inline with the power feed between the TVS and your regulator's input. This will give reverse polarity protection and still prevent damage to the device during negative transients.