[help needed] harness extension system ideas?

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harness extension system ideas?

Post by AndreyB »

Looking for ideas for a nicer harness extension system.

Let's begin with what I have now:
Currently I have a 6 ft ECU harness extension - so, a male connector I took from a junk yard is connected to the car, then go the extension wires and then a female connector - so, I can connect the stock ECU as if nothing is there. This would have little value as is, but I also have an intermediate connector on each wire - so, if I choose to I can disconnect some wires and also I can put a T-type wire into the extension in order to sniff the data flow etc.

I know a picture would help but I do not have a picture right now :) The intermediate connectors are the 1/4" crimp terminals like
Image and Image

The problem with this is that I have 30 pairs of these crimp terminals hanging in the air in random order. I have the wires grouped & labeled, but it is still a mess. This really needs a picture but use your imagination :)

So, any ideas how I can re-do the same thing in a nicer & more reliable manner?

Please keep the price in mind, for the Cooper I would need maybe 40 wires. I would still need to be able to disconnect or sniff individual wires.

Maybe all I need would be zip-tieing these wires to a punch board & stay with the crimp terminals? But this would be kinda bulky. I am ready to invest in maybe even a small PCB to simplify my life, maybe even with individual switches to disconnect individual wires? Or maybe just a long narrow PCB with wires knitted to the PCB?

That's why I am looking for ideas :)
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Re: harness extension system ideas?

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Re: harness extension system ideas?

Post by AndreyB »

No hablo ingles for sure :( I guess I have failed to describe what I need. I will try pictures later.

How does the 50pin connector help me with EASILY connecting-disconnecting single wires when I choose to, with setting up T-connections for sniffing.
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Re: harness extension system ideas?

Post by hasse.69 »

If you buy two of those you could make a breakout harness , we use it att Volvo CE from time to time.
brteak_out_box.gif
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:)
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Re: harness extension system ideas?

Post by AndreyB »

So "breakout box" is the term.. We are getting closer :)
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Re: harness extension system ideas?

Post by hasse.69 »

This is more what i had in mind.
f50-aoa-box.jpg
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No habla ingles!!! :lol:
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Re: harness extension system ideas?

Post by skeeters_keeper »

I would think a breakout board with jumpers to select might be cheaper and cleaner. Breakout boxes are nice but you still end up with a bundle of wires that you have to plug/unplug individually.

I'm thinking a board with a 4 x (ecu pin count) array of male pins. The center two pins would go to the car harness, the outer pins would go to a connector on each side of the board. Then you could pick if you want to jumper each individual wire to a) the stock ECU connector or b) RusEFI connector or c) both.
The same thing could be done with switches but it would be much bigger/more expensive. Jumpers are cheap!

If all you want to do is connect a logic analyzer to sniff a particular pin you can put a female jumper wire on it.

The downside to this idea is you'd need a different board for each car type (if using the factory ECU connectors).
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Re: harness extension system ideas?

Post by AndreyB »

I like the idea with x3 (or x4) male pins board. Actually it would work great if I use jumpers to establish the connection.

But the 2.54 pins & jumpers are probably too small for ECU currents (are they?). Is there any larger system of pins/connectors/jumpers more suitable for our currents?
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Re: harness extension system ideas?

Post by skeeters_keeper »

Just a quick google search yields several results that say that the .1" headers are rated for 3a - do any of the pins in the ECU need more than that?

My intuition says that those headers/jumpers are larger than the pins in the ECU connector so everything should be fine. But I realize that isn't founded on anything! If there are a few pins that require larger current carrying capabilities maybe we could just use some heavier duty switches/jumpers for them.
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Re: harness extension system ideas?

Post by AndreyB »

3A should be enough: one injector is about 1A and with sequential injection we do not need to multiple this 1A

I am failing to google what would be the power rating for a jumper itself or for that sake to find these 2 position jumpers on eBay. But if the jumper is capable of transferring 1-2A between the pins and we make wide tracks on the breakout PCB, this might be the answer!

Is there a good technique of connecting wires to the PCB without any connectors? I guess 18AWG or 20AWG should work for all of these wires. I was thinking about drilling a couple of holes to knit the wire to the PCB but this might be a mad idea.
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Re: harness extension system ideas?

Post by abecedarian »

I wouldn't suggest anything smaller than 18 AWG carry more than an Ampere more than a few inches.
Not necessarily because it can't, but because of the heat build up.
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Re: harness extension system ideas?

Post by skeeters_keeper »

Here are some cheap ones on e-bay. Not sure of the quality and no current rating: http://www.ebay.com/itm/100x-Hard-Drive-Computer-CD-DVD-PCB-Panel-Test-Bread-Board-Shunt-Jumpers-2-54mm-/390368398749?pt=LH_DefaultDomain_0&hash=item5ae3c50d9d

Here are some on digikey. For the small difference in price, these are probably the ones I'd get, and the data sheet says they are rated at 2A: http://www.digikey.com/product-detail/en/969102-0000-DA/3M9580-ND/2071621


As far as hooking up the wires - how about using two 2x row of pins separated by a short distance (.25" or so) with vias between them to solder the wires into.
What size trace do you need on the PCB to carry 2A?
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Re: harness extension system ideas?

Post by AndreyB »

skeeters_keeper wrote:What size trace do you need on the PCB to carry 2A?
http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/ says 15.4 mil/0.4 mm?
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Re: harness extension system ideas?

Post by AndreyB »

skeeters_keeper wrote:As far as hooking up the wires - how about using two 2x row of pins separated by a short distance (.25" or so) with vias between them to solder the wires into.
Not sure how this would work. What would hold the wires? With holes and knitting the wholes would hold the wire.
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Re: harness extension system ideas?

Post by abecedarian »

A plated via sized appropriately should be sufficient to insert a wire and solder to.

18 AWG wire will carry a few Amps a foot without issue; 16 AWG can carry up to 10A a few feet as well.
In the engine compartment, runs up to 10 feet in length, I'd suggest 14 AWG to carry up to 10A, 12 AWG to carry up to 15A, 10 AWG to carry up to 20A, 8 AWG to carry up to 25A. For intermittent loads such as fuel injectors and such, you should be able to increase the loading by 50% without issue, and possibly up to 100% if the wire length is substantially less.

For comparison, normal house wiring is either 14 or 12 AWG, the former rated to 120V/15A up to nearly 100 feet, the latter rated 120V/20A... do note the difference in voltage though.

And before it gets brought up, my qualifications are based on nearly 5 years building recreational vehicles, during which I spent over two years designing the electrical systems including both the A/C side as well as chassis / 12v systems... including the 'load center', back-up battery charging systems and tow-vehicle interfaces.
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Re: harness extension system ideas?

Post by AndreyB »

I know that we only have couple of A consumed by the ECU ('hi-side A'), but what about the grounds we control - injectots etc? I guess the grounds would need to be more than 3A. On the other hand we can simply split the GND into multiple wires & run them parallel.

So, assuming couple Amps and say 10 feet as the wire limit (my current harness is maybe 8 feet - it goes from the driver side corner of the dash to the passenger seat behind the driver seat - that's for the blue Aspire) (for the cooper I might need even more since the ECU is in front of the engine and I would want to bring it again to the passenger seat), what kind of wires would we use? :)

I am still thinking a bit of knitting to make the wire-to-pcb connection more rigid.
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Re: harness extension system ideas?

Post by abecedarian »

Most likely, 14 AWG would work up to 20 feet / 4 meters, given just a few Amperes current. 12 AWG would probably provide enough for anything.
Similar for grounds- they're going to be landed either near the ECU or provide return paths for sensors and such.
Just look at your factory wiring to get an idea of what might be needed.

High-amperage devices like the starter relay, fuel pump and even power to injectors are switched through relays and such.
Small gauge wire switches circuits requiring high current through relays, right?

On the other hand, you can't really have "too big" wire, so maybe plan for 12 AWG? It's not that much more expensive than 14 AWG so...?




That previous job included purchasing materials as well as design so I do know a thing or two, and I was often tasked with cutting a few bucks off the cost of the trailers and I never cut $5 worth of wire out because the installation / build cost wouldn't change and function and safety over cost was my modus operandi. Lights have to work, batteries have to charge, et cetera, and saving $5 on an RV's construction costs wasn't worth the additional cost of the inventory to be maintained.
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Re: harness extension system ideas?

Post by skeeters_keeper »

Are we talking about making an entire harness, or just an extension? 18ga is more than adequate for a few feet, especially if it isn't bundled tightly in a harness. Of course if it makes you feel better you can use thicker. Sure won't hurt!

I'd be OK with just soldering the wires to the board through vias. After all this is meant to be "temporary" for development, right? There are other options too if you don't prefer to solder directly. Perhaps screw terminals?
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Re: harness extension system ideas?

Post by AndreyB »

Wire price is an issue here. ~50 wires x 10 ft = 500 ft. eBay says about $20 for 18GA and $40 for 16GA or 14GA. I guess this means I would have to use different wire sizes depending on the purposes, because $40 just for wires is too damn much.

Yes this is temporary but I want some piece of mind that this would not fall apart. Screw terminals would fall apart if the wire gets stuck along the way and I pull in the wrong direction...
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Re: harness extension system ideas?

Post by abecedarian »

It should go without stating that wiring is one place you do not cut corners.
It only takes one small piece of wire, sized incorrectly, to result in a fire you can't put out.

$40 or $50 for wire... if $10 makes that much of a difference, you shouldn't be doing this at all.
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Re: harness extension system ideas?

Post by skeeters_keeper »

The ampacity for 18ga wire is 14a. No offense, but your implication that 18ga wire with >2a current is a fire hazard is absurd. Can you share the calculations you've used to back this claim??

For example: I wire industrial control systems running 24v at ~1a with 22ga wire (short, 3-5' runs). Max panel temperature there is 135*f. The temperature under the hood of the car may get up to that in the summer or if the wire is running too close to the engine, but if its that hot inside the cabin - I don't want to be there!
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Re: harness extension system ideas?

Post by abecedarian »

skeeters_keeper wrote:The ampacity for 18ga wire is 14a. No offense, but your implication that 18ga wire with >2a current is a fire hazard is absurd. Can you share the calculations you've used to back this claim??

For example: I wire industrial control systems running 24v at ~1a with 22ga wire (short, 3-5' runs). Max panel temperature there is 135*f. The temperature under the hood of the car may get up to that in the summer or if the wire is running too close to the engine, but if its that hot inside the cabin - I don't want to be there!
Hmmm 24v... AC or DC? And you mentioned 'short' runs ( < 5'). Didn't I mention "short runs" up to a few feet for 18 AWG and a few Amperes? And even up to 10-15 feet under the hood? Sheesh.

My calculations are 'experience', as in I might get by with lighter gauge wire, but chose not to because 'safety' takes precedence over cost... as I mentioned.

And when you quote "ampacity" please also include voltage- 14A at 240V is VERY much different than 14A at 12V, and the latter will heat the wire much more than the former, much like even the same voltage DC will heat the wire more than the same voltage AC. But let's not discuss "wattage", okay?

In my previous job, I dealt with code compliance and building inspectors for California, Arizona, Nevada, Colorado, Texas, Oregon, Washington, New Mexico, Wyoming, Utah and Idaho, as well as Florida, Alaska and Michigan... took me a while- had to remember where I sold trailers to. None had any complaints regarding my calculations, and matter of fact would often approve my wiring designs after a short phone call and a few references to books with "ANSI" and "NEC" in their titles. It was my job. ;)

So, even though you say you can run 24v @ 1A with 22 AWG, I don't care. I wouldn't do it, preferring to go to 20 or 18, but that's your prerogative.

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Re: harness extension system ideas?

Post by skeeters_keeper »

abecedarian wrote:I wouldn't suggest anything smaller than 18 AWG carry more than an Ampere more than a few inches.
Not necessarily because it can't, but because of the heat build up.
You clearly said "an Ampere" and " a few inches".

Nice of you to change your story though.

I'm not trying to get into too much of a tiff here - from some of your posts you clearly do have at least a little background in related areas. But telling someone that something is a "fire hazard" when its nothing even close to that is wrong. There is a big difference between safety and making something way overkill just because it isn't designed properly from the start.

The circuit I mentioned was DC (which tends to generate more heat that AC) and I don't mind taking a few minutes to calculate the power dissipation if it would entertain you. It would just help re-einforce my point.
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Re: harness extension system ideas?

Post by abecedarian »

skeeters_keeper wrote:
abecedarian wrote:I wouldn't suggest anything smaller than 18 AWG carry more than an Ampere more than a few inches.
Not necessarily because it can't, but because of the heat build up.
You clearly said "an Ampere" and " a few inches".

Nice of you to change your story though.

I'm not trying to get into too much of a tiff here - from some of your posts you clearly do have at least a little background in related areas. But telling someone that something is a "fire hazard" when its nothing even close to that is wrong. There is a big difference between safety and making something way overkill just because it isn't designed properly from the start.

The circuit I mentioned was DC (which tends to generate more heat that AC) and I don't mind taking a few minutes to calculate the power dissipation if it would entertain you. It would just help re-einforce my point.
Not exactly sure I changed my story, and I don't require your calculations.
I said I wouldn't suggest using wire like that... more than a few inches and more than a few Amperes if I remember correctly, then later went on to say it would probably work within the engine compartment, and gave further recommendations. Take it for what you will.

Within the ECU enclosure, I'd probably stick with 14-16 AWG wire. Outside, depending on things, where heat can be rather easily radiated, 18 might be usable, but then again, I'd probably go with 12-14 AWG. Point being, use what's appropriate, and even then error on the conservative side.

I used 10 AWG on the 30A charge line from the tow vehicle, between the plug and batteries, and also had a self-resetting circuit breaker inline; USDOT and the various housing authorities for the states I mentioned were perfectly fine with, and approved, what I designed. I skimped when I could but at no time did I undersize wiring when it made no sense, for safety, for me to do so despite multiple requests by the bosses to pinch a few pennies, and that's literally what it would have been- maybe 5 feet of wire at $0.01 cheaper; couldn't and wouldn't do it. And to date, I don't think neither Weekend Warrior nor Carson Trailer has had an electrical fire resulting from improper design: those are the companies I worked for.

Now, I build cell sites. My last 'major' work was adding battery back-up capacity. Yes, big transition, but now I work on 'live' 24-48VDC @ 1200A instead of 12VDC at 30A.
"Live" as in they're not disconnected while I'm doing my work, and in nearly 20 years I've taken 2 sites off line by accident.
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Re: harness extension system ideas?

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For fire prevention, in the ambient temperature of a house, with wire rating for a house like THHN, you can run the 12awg at 20A, and 14awg at 15A. This is because the wire temp is 90C and you have wire with insulation rated for 90C. The fire rating depends heavily on the wire insulation you are using, and the wire that folks are likely to find here here for automotive use is probably not the same insulation categories. So when determining the max current carrying capability, you don't want generic rules, you want to look at your insulation rating and make sure the wire stays under that. For example, in your kitchen stove you provbably have some wire that's around 18awg and running close to 20A, see this for reference. http://www.mcmaster.com/#8209k11/=q6rsev note it's 20awg nickle plated copper rated for 840F a is UL listed to support 23A at 89F. Silicon jacketed wire typically has a much higher temperature rating and much higher voltage rating. You really need to look at the insulation when determining if a wire is safe.

Also beware the mechanical strength of the wire insulation. The NFPA70 specifies both temperature ratings and physical stress tests of the wire at the same time, while many UL standards only specify either temperature or mechanical strength. So if you have a hot wire, that's under some stress, that may not be specified by the UL standards.

In our case, you really need to consider what's being wired and what's acceptable electrically. From this page http://www.powerstream.com/Wire_Size.htm we see that 10A on 8ft run of 12awg will have a voltage drop of .261V. Bouncing your GND around by this much as you turn on and off injectors or ignition devices can be a problem for the analog circuits. Especially if you have a shared GND for that sensor. This is why I have a tendency to run the GND wire back to the ECU harness. Most MCU's are ratiometric devices, which means they are a proportional indicator of your + rail and - rail. If you power your sensor with that same rail, you can often allow the GND or + rail to wonder a bit with out seeing it in the sensors digital numbers after that ADC. However with some wire length, and with some capacitance and inductance, you can see variations caused by various signals delays. So you want to avoid fast transients, but slow wondering is generally OK. The rising edge and falling edge of the injector pulse would classify as a fast transient.

So for a injector, the + lead at 18awg and 1A is fine for both fire and electrical parameters. However the GND wire at 1A would be questionable as it would induce .026V of ripple into the ECU's analog signals.

About a suggested approach, I would suggest spinning small PCB with both connectors on it, with screw terminals. You would start with several short jumper wires under the screw terminals, then you could add change and remove them as requires. I don't like the crimps or the flat spade faston approach as those crimps can be a hidden source of issues. You really need proper crimp tools and proper practices to ensure a good connection, With out those controls, you often induce mOHM's of resistant in places that can cause problems. A couple mOHM's might not sound like much, but You can get into tank circuit issues with stepper motor used for IAC or similar. It's common that the mOHM's in the connector will allow a 12V driven stepper to exhibit more than 300V internal to the stepper motor, which usually results in fire. If you connect a scope at the stepper driver, you'll only see 12V as you would expect, but if you put a sensing wire internal to the stepper motor, you'll see the 300V. If you use a screw terminal, it generally reduces the potential for these mOHM issues. As well it's very flexible and doesn't require special crimp tools or anything like that.
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Re: harness extension system ideas?

Post by AndreyB »

So I guess there would be two kinds of modules on these PCB - a low-current module with 0.1 jumper

for the high-current module, a cool idea from the Russian sub-forum is to use the 'mini' fuse like http://en.wikipedia.org/wiki/Fuse_%28automotive%29#Size_groups - assuming we would find a cheap PCB housing for it, maybe a double or triple housing. This would be more convenient than screw in terminals.

Update: http://www.digikey.com/product-detail/en/BK-6013/BK-6013-ND/2330532 looks fine
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Re: harness extension system ideas?

Post by kb1gtt »

The style from the top right of this datasheet might be of interest. http://datasheet.octopart.com/3563-Keystone-datasheet-15715963.pdf
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Re: harness extension system ideas?

Post by hasse.69 »

Maybe you know a English site where this is on.
I give to you , the Nomogram. Ta da :D
http://www.docentdecibel.se/faq/beraekna-kabel-area/info_7.html

I think you all can handle some Swedish.
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Re: harness extension system ideas?

Post by kb1gtt »

I tend to use this English calculator with a pile of table all on one page. http://www.powerstream.com/Wire_Size.htm
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