Protecting electronics in vehicles

I'm designing a circuit for an ambulance my volunteer ambulance corps, a basic temperature sensor reporting back values to a server. It's working great so far, but I'm worried about protecting the circuit from load dumps, spikes, and other over-voltage situations that I've read about in vehicles.

I've tried to do a lot of research on this, but can't find straightforward answers. Based on what I've found, it seems like a TVS diode can offer the protection I need?

Something like this? http://www.digikey.com/product-detail/en/TP6KE20A/F6845CT-ND/5492185

If in fact this will "do the job", are there any other considerations I need to take into account? Or is this sufficient and I'm all set?

Thanks!

You should protect against voltage reversals and electrical noise as well. I’ve used this circuit http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Automotive_Filter.png (the 1.5KE18 Zener diode can withstand short term surges of 1.5 kW)

Here is a summary from one of the manufacturers of surge protection components: http://www.digikey.com/Web%20Export/Supplier%20Content/Tyco_8004/PDF/Tyco_AutoNetwork.pdf

People who build automotive electronics for a living, and want their stuff to last, take this advice very seriously.

You have to treat every single wire that goes outside of your box as a potential path for high frequency interference, static electricity, glitches, spikes and some idiot jump-starting the vehicle with a 24V truck battery hooked up backwards. You often end up with several protection strategies in layers.

The TVS diode is good for static electricity discharges. Someone with a nylon sweater climbs into the vehicle and zaps a big spark into one of your wires. Fifteen thousand volts, thankyouverymuch. It won't protect against a direct hit by lightning*.

A simple resistor is often the best protection against most other types of spikes and surges. They carry a lot more energy spread out over a longer time, so the TVS diode can be destroyed by relatively low voltages. But a resistor will stop high currents getting into your box.

Have a look at the Ruggeduino, to see how they protect against some of these hazards.

*If you have to design against direct lightning strikes, the best you can do is try to make sure your box doesn't have a lot of combustibles to burn when it gets hit.

Thanks Morgan!

I'm having a bit of trouble understanding the Ruggeduino circuit design. Also, when you say a simple resistor can handle other voltage spikes, what size are you thinking? By what mechanism does it do this protection?

What exactly can the TVS diode not protect against?

Learning as I go, and I am not taking for granted that this is a very complicated subject.

Thanks!

In my van I've got a Arduino running sound-activated lights. It's just powered directly by 12V through the barrel jack, and in my particular vehicle the Arduino's voltage regulator seems to provide enough protection. It's been running a couple of years.

The only external input is the sound input, so there's not much danger there.

I do have [u]protection diodes[/u] at the Arduino's analog input. That's to protect against excessive or negative voltages from an op-amp. The op-amp, is run off the 12V with no special protection. A DC-DC converter also connects directly to 12V, and it provides negative 12V to the op-amp.

The output connections are to solid state relays, so they are safely isolated.

seems to provide enough protection.

So far, but it [u]will[/u] fail.

Read these:- http://www.thebox.myzen.co.uk/Tutorial/Protection.html

http://www.digikey.com/us/en/techzone/microcontroller/resources/articles/protecting-inputs-in-digital-electronics.html

Note it says in the data sheet for the processor:-

Atmel products are not suitable for, and shall not be used in, automotive applications.

This is from the automotive temperature grade (-40C to +125C) Atmega328P-15AZ (still in 32-TQFP package), the widest temperature range part one can purchase:

"Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in, automotive applications. Atmel products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life. SAFETY-CRITICAL, MILITARY, AND AUTOMOTIVE APPLICATIONS DISCLAIMER: Atmel products are not designed for and will not be used in connection with any applications where the failure of such products would reasonably be expected to result in significant personal injury or death (“Safety-Critical Applications”) without an Atmel officer's specific written consent. Safety-Critical Applications include, without limitation, life support devices and systems, equipment or systems for the operation of nuclear facilities and weapons systems. Atmel products are not designed nor intended for use in military or aerospace applications or environments unless specifically designated by Atmel as military-grade. Atmel products are not designed nor intended for use in automotive applications unless specifically designated by Atmel as automotive-grade."

"a basic temperature sensor reporting back values to a server. " doesn't seem a Safety-Critical Application and it would likely be approved by Atmel. Automotive-rated 328P datasheet: http://www.atmel.com/images/atmel-7810-automotive-microcontrollers-atmega328p_datasheet.pdf

To elaborate on the protection resistor, consider the basic Atmel chip that has built-in protection diodes from each input to the power rails. If an input goes above the power supply voltage or below zero, then one of those diodes will start conducting and "clamp" the input to that maximum.

However those diodes are just tiny circuit elements inside the chip. They can't take a lot of current. In this context, 20 milliamps is a lot of current. If your fault current is higher than this (think 24V battery applied to a 12V system) then the diode will be destroyed and you have to replace the entire chip, or the entire Arduino.

But if there was a resistor of 10K value on that input, then the fault current is now less than 2mA. The protection diode can handle this all day, every day. A 10K resistor won't make much difference to your digital input as it normally flows microamps and it will still see a full logic voltage on the input.

Now this isn't appropriate for every input - analog inputs need to know the "real" voltage on the other side of that resistor - which is why there are many other methods of doing this. I seem to remember that the Ruggeduino uses polyswitches, which are pretty clever variable resistors.

Bob and Mike: thanks for the heads-up on proper usage. Bob, you're absolutely right, my board has nothing to do with safety systems or patient-related equipment. Just sensors that transmit information to a server.

Morgan: makes total sense, and I can see how that would protect the input pins. My bigger concern is protecting the power input which is coming straight from the alternator/battery. I need 5V/1A, and want to shut down the incoming power if it goes above 15V-18V - want the circuit to be completely isolated at that point.

This is why I thought the LittleFuse TVS Diode would help. I also say this and thought it made sense, but I need it in through-hole and they don't have it in that package, and can't find something similar: http://www.ti.com.cn/cn/lit/ds/symlink/tps2400.pdf

So, for V+ power protection, does everyone think that the LittleFuse diode is all I need?

Thanks!

So, for V+ power protection, does everyone think that the LittleFuse diode is all I need

Well I think it is way more complex than that. Did you read those links?

So, for V+ power protection, does everyone think that the LittleFuse diode is all I need?

No. It is quite obvious that you have not read the links.

Ok. Back to square one. Can anyone give me a definitive power protection solution? A list of components to use?

  1. Transient/surge protection diodes and/or MOVs
  2. Regular diodes
  3. Inductors
  4. Capacitors
  5. Shielded cable.

What's the difference between #1 and the TVS diode I mentioned earlier?

Is there any manufacturer that says "Our products are designed for and may freely be used in connection with any applications where the failure of such products would reasonably be expected to result in significant personal injury or death, because we're so awesome and are sure that our product will in fact never ever fail under any circumstance"?

Honestly, those disclaimers sound rather generic, just like the warning manufacturers put on the packaging to alert us that their product may contain peanuts, when the product is peanut itself.

jremington, can i pay you for a complete circuit diagram with part numbers?

What don't you like about the circuit I already posted?

osmosis311: Ok. Back to square one. Can anyone give me a definitive power protection solution? A list of components to use?

No nobody can give you a definitive list because all situations are unique. It is an art rather than an exact science because you do not have a measure of exactly what interference you have nor what degree of degradation you can stand.

Read the links, understand them, do some experiments and test the results.

Mike,

I understand and agree with what you're saying. However, given that I'm still learning, and that takes a lot of time, and, given that the total cost of these "modules" I'm building will be around $50 and it's not the end of the world if one of them gets destroyed, at this point I'm looking for best effort, and then will experiment as you say, refining the solution over time as needed.

As a start, I'm trying to understand jremingtons circuit so I can apply that (don't know what all the component in the diagram are yet).

Not looking for shortcuts here, just simplicity, at the end of the day my ideal would be one part or Ic that is meant for this solution, and has all those components built into it.

Thanks.