190E 2.6 5V electrical source? - PeachParts Mercedes-Benz Forum

Matej · #1 07-29-2016, 02:48 AM

Hello,
Can anyone please tell me if there are any good usable 5V sources I can tap into in the 190E? I would like to install a wired dashcam, and possibly add a hidden USB port.

My car will actually be converted to diesel, so that should open up some more potential sources, since I am still keeping the gasoline ECU for RPM signal and such. I believe the TPS is powered by a 5V source, but I am not certain if it is constant or variable depending on the throttle signal.

The ECU pin for the TPS voltage supply is number 18, it seems.
http://www.justanswer.com/uploads/JHoop/2008-04-14_120419_fuel.pdf

If you gentlemen have any other recommendations, I would be glad to hear them.
Thank you.

Mxfrank · #2 07-29-2016, 08:47 AM

AFAIK, there are no readily available 5V sources. There must be a 5V PWM controller in the dash pod assembly, as most gauge systems operate at a regulated 5V (otherwise the instruments would vary as system voltage goes up and down). But I don't know where you could tap in. For the same reason, there would probably be one internal to the EDS computer (when you install your Diesel and discard the gasoline ECU). Again, no way to tap in. It would be easier to build one, or just hardwire a USB phone charger, which are widely available. If you will be using it to charge an Iphone, you will need more than a 5V source anyway: Iphones also require 2.8V and 2.0v sources to charge correctly. Dashcams should have a 12V interface, unless you plan on building one from scratch.

Think about something like this, which can be tucked away unobtrusively:

https://www.amazon.com/Cllena-TOYOTA-Dashboard-Charger-1-2A-2/dp/B01CTOKI06/ref=sr_1_2?ie=UTF8&qid=1469792720&sr=8-2&keywords=dashboard++usb+socket+12v+dual

Elektri · #3 07-29-2016, 11:18 AM

You can also search for what is called a "DC to DC converter" - including the voltages.

Like: 12V to 5V DC to DC Converter

Mxfrank · #4 07-29-2016, 12:13 PM

For that matter, a 7805 chip is all he needs for a basic 5V power source.

optimusprime · #5 07-29-2016, 12:39 PM

I may be missing something but why not purchase a 12 volt d/c ? Everything i have seen over here is 12volt.

Matej · #6 07-29-2016, 08:41 PM

Quote:

Originally Posted by Elektri

You can also search for what is called a "DC to DC converter" - including the voltages.

This is going to be the probable solution, but I just wanted to know if there is an OEM source I could tap into to keep the system simpler without having to add extra components.
If there is not, it seems I will go with a converter after all.

On a related note, what are some good sources to tap a relay into that will close with the key in Accessory and On modes? Fuel pump relay? Klima Relay?
Thank you.

lsmalley · #7 07-30-2016, 03:08 AM

Why not just use a resistor to convert a 12v source to 5v and add a fuse and regulator. I needed a 3v source to test out some LED bulbs from radio shack and the resistor worked perfectly. Might want to consult James Dean as well on the forum as I believe he may have some knowledge with electronics.

Mxfrank · #8 07-30-2016, 07:11 AM

A resistor will produce a voltage drop, but not a regulated voltage. The simple way to build a regulated 5V source is with a 7805.

To wire a relay that's energized in either the accessory or run position, you need to tap a circuit that's powered in either the accessory or run position...so why are we talking about fuel pump and Klima, which aren't powered in accessory? Further, the fuel pump relay is eliminated in a diesel conversion and the Klima circuit would be rewired. How about the radio or lighter? That takes care of energizing the coil. The contacts should be powered directly from the battery, with an inline fuse, or you could used a fused relay.

Why are you going about things in this odd way? Any electronic equipment you buy will run on 12V and handle it's own voltage regulation. And if you were capable of developing your own electronics, you wouldn't be asking these questions.

97 SL320 · #9 07-30-2016, 09:54 AM

Pulling 5V from the ECM is an emergency last resort source, you might end up with all sorts of odd engine behavior.

For USB power, there are lighter plugs that have a USB power converter in them.

A recent thread on this site discussed where a power converter was making electrical noise causing the radio to be noisy so that that into consideration.

duxthe1 · #10 07-30-2016, 10:55 AM

Even if you're not using the ECM I highly doubt its 5V rail could provide enough current to be of any use. In general most sensors are high impedence and consume just a few milliamps. The 5V rail current capability will reflect that.