I got a bunch of USB sockets and voltage regulator ICs that will trim 12v to 5v, and thought it would be nice to wire in for charging phones etc. someone suggested that the ICs would fry due to transients. So I am wondering about wiring zener diodes as shunts across the feed and wanted to know what you thought. I am especially interested in voltage and wattage for the zener and perhaps resistance to limit current. Thanks!

Just build a simple voltage regulator circuit. You only need a few parts and would cost under $10. Or buy one for $6 http://www.getfpv.com/5v-step-down-voltage...0YaUaAgAu8P8HAQ

Just buy a cigarette light USB, cut it open and take out the board. Hard wire to 12v.

At least that's what I did.

What McMark said.

I just bought a female cigarette lighter socket at Radio Shack, wired it into the fuse panel under the dash, and plugged in one of those $5 cig lighter USB chargers.

Hey, I tell everyone this is the place where all of the super-sharp EEs with 914s hang out.

I bought a stick of Goldstar GL7805s, rated for at least an amp. I already have a couple bags of USB female outlets, and all the aluminum I need for heatsinks.

Good to get going. BUT on another board I read about voltage transients blowing out the ICs. I want a neat install and don't want to have to redo this all the time. The other board comment suggested a Zener diode to short out transients. OK. Now I am out of my depth. I don't know breakdown voltage, wattage or whether to run a current limiting resistor. Also I don't remember where I saw the original idea - probably megasquirt surfing.

My initial circuit is very simple, but maybe it should be improved?

How many do you need? My stereo has one in it and I have two more provided by the cigarette lighter plug.

$8 shipped.

http://www.amazon.com/Outlet-Charger-Socke...e/dp/B00MNGCDVS

Thanks for all of the ideas. It is helpful to get a glimpse of other approaches. I am still though wondering whether I need to protect the devices I have already purchased and perhaps learn more in the package. I think I will try an electronics board, but that will whizz so far over my head...

Or maybe I will just wire them in and see what happens. The plan is to have USB ports installed in the console face. It may in the end be easier to put in cigarette lighters, but I like the much smaller square look. I also am planning HUD.

The 7805 should work fine in this car as long as you dont have a CD (MSD) ignition in it.

I plug my arduino datalogger directly into the system 12VDC and I DO have a MSD.

MSD makes a transient surge suppressor for this very reason, but it is really for more modern cars that have a LOT of electronics in them:

http://www.msdignition.com/Products/Access...r,_26_Kufd.aspx

But it is really just about the same as some of the ultracaps you can find in the car stereo dept. at walmart.

Thanks Stu. I figured you would address the transient question. Do the ultra caps do much? Other than make for bling? This project is for the stock 3.2 conversion. I may eventually run MSD on the 4.

The audiophiles THINK the ultra capacitors help the audio (I am not convinced).

But putting one in as a transient surge suppressor near the front fuse panel would probably reduce noise to any modern electronics you may have.
I would have to experiment with one to be sure.
My guess is that the only noticeable effect would be some dash lights would remain on for a few seconds after turning off the ignition.

I would just try your idea and see if there is a problem.
If you have any trouble, I could throw a 7805 on my car and look at the output with an oscope to see how noisy it is.

You beat me to it. I have these installed in my motorcycle and center console of the Porsche.

The ready-to-go solutions noted are the easiest ways to get USB power.

If you want to design your own, the 7805 should work well. It is generally accepted in modern cars that 35-40V input voltage capability is adequate. This is partially because modern alternators have power zener diodes to limit the load dump (ISO7637-2, pulse 5) to 35V or so.

Further overvoltage protection could be accomplished not with a zener diode but a transient voltage suppressor (TVS). I use TVS's on my front LED boards to protect the blanking circuits.

You should also install a series diode to protect the 7805 against reverse battery application. The 7805 provides 70dB of attenuation of noise on +12V to provide a quiet +5V output. Filter caps near the 7805 are a good idea.

I highly doubt the USB power would be affected much by noise on +12V line. Audio units are more susceptible since they use +12V directly. The Ultra caps should only be used to provide instantaneous energy for bass and subwoofer applications.

The only reason I suggested the UltraCap is that I know they are available at walmart. And they would definitely provide noise filtering, but are way overkill. Some of us don't have any kind of electronics store nearby since a lot of the Radio Shacks closed.

We think alike; We should hang out together sometime; We could get lost in conversation others would find boring.

If you're willing to wait a month on shipping, you can get a buck for a buck, delivered from China.

http://www.ebay.com/itm/6-24V-12V-24V-To-5...-4AAOSwKIpWC0gl

Well that cheap is scary.

I started down the road thinking it would be cool to add some custom look USB ports. Thanks Folks! I will let you know when it actually happens.