EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: max_torque on February 21, 2017, 08:04:27 pm
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If i had to put a 10k, 0.25watt resistor into a wire in a harness, what's the most robust method?
I'm thinking of 0805 smc resistor on small pcb, incoming & outgoing harness wires soldered to that pcb, strain relief and sealing done via adhesive heat shrink around complete pcb??
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I would have thought a standard 1/4w axial resistor wired in-line would be more robust. Heatshrink the solder connection at each end and then an overall heatshrink over the resistor and leads. That should spread any flex outside the solder wicking zone, something that will affect flexibility of the stranded wire near the joint, PCB or no PCB.
P.S. Too little info to give a definitive answer... Thickness of the wires, thinkness of the loom etc.
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I've done this before. I used a through-hole resistor, soldered it into the wire and put a piece of heatshrink tubing over it. Using a chip resistor and PCB is WAY overthinking it.
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a leaded resistor sounds like a disaster to me. The leads will have to support the mass of the harness wire, will vibrate and snap off.
However, a leaded resistor, soldered into the wire, and then potted into some sort of support (like a plastic tube) might work. In all cases the wire will have to be supported where it is soldered, and some distance up away from the joint to avoid brittle failures at the point the solder stops wicking up the wire. Not for nothing does no one solder looms these days, everything is crimped. In fact, i could use a crimp splice to attach wire to leaded resistor, and then pot that, which would be even better!
(http://www.meyette.us/splices-1crimp.jpg)
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For mass production I would suggest you try very hard to make it work without the resistor.
For personal / small batch, I'd go with crimping & strain relief as you thought.
Solder joints on wires are infamous for failure. And axial resistor packages are not designed for mechanical stress.
I do have one thought, though: can you integrate the resistance into the wire itself? You could get a wire with skinny copper and thick insulation to keep suitable mechanical behaviour.
- Depends on required resistance and wire length
- Would have poor parameter stability
- Not easy if you're using a mult-conductor cable.
\
- The crimps/connnectors at the ends could be difficult.]/li]
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I twisted the resistor lead around the wire and soldered it, very robust connection. The heatshrink over it provides most of the mechanical strength and prevents the resistor from vibrating. I've even done this in automotive applications and it never failed even after years in the engine compartment.
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If you are doing one for yourself, soldering directly and covering with heatshrink will probably last.
The next step up is crimping to a larger resistor. A 1/4 watt resistor may have very thin leads, while a 1/2 watt or 1 watt resistor is likely to be much stronger.
Older BMWs used in-line diodes with crimped on 0.250" connectors, one side female the other male, that blended neatly into the harness. They were little-known, so the approach must have been reliable.
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Hino, a major Japanese corporation, had resistor "modules" made with connectors. The harness merely had the mating connector. The excavator company did likewise, but they didn't have the money to make a nice, plastic molded module, so the resistor was crimped to the terminals, and the whole thing was potted and/or sealed with thick heat shrink.
The dozer company had a harness vendor solder or crimp the resistor directly in the harness. Neither had many problems that I could recall, despite being on off road equipment with significant vibration. They did use the "connector" method, but once chose a vendor that didn't understand that the resistor leads needed to be insulated. We had several CAN terminator "resistors" that were nearly zero ohms.
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I've done this before. I used a through-hole resistor, soldered it into the wire and put a piece of heatshrink tubing over it. Using a chip resistor and PCB is WAY overthinking it.
I would solder the resistor in so the wires go the lead on the opposite end, that way the heat shrink can hold on to more wire and there is further from solder to where it can vibrate
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Bob Nuckolls' take:
http://www.aeroelectric.com/articles/Homeless/Homeless_Components.htm (http://www.aeroelectric.com/articles/Homeless/Homeless_Components.htm)
http://www.aeroelectric.com/articles/In_Line_Resistor/ (http://www.aeroelectric.com/articles/In_Line_Resistor/)
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If you really want to do it as right as possible you might want to refer to the NASA spec for splicing wires. https://standards.nasa.gov/standard/nasa/nasa-std-87394 (https://standards.nasa.gov/standard/nasa/nasa-std-87394) page 69+ deals with splicing. while they don't explicitly call out your use case, manly because it should avoided in the hardware design, it does make a very reliable splice.
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I don't think I have a viable alternative to what's been mentioned for inlineing a resistor, but I'd ask again - are you sure it has to be inline with a wire?
It's basically always going to be a better choice to put it on a PCB or between two rigid points (directly to a connector would suffice) because then you can let the stranded wire deal with the mechanical stress. If you have to inline it, then the next best choice would be making it a separate module with its own connectors with strain reliefs and whatnot, of course it's probably the most expensive. A good bonding with the wire on either side and some rigid pieces attached across the joint and potted in place would probably next best or so, with something like the multi-heatshrink method would be ok for a temporary fix or something that needs a bit more robustness than just a straight bodge, but which isn't likely to stand up to significant stretching force or vibration.
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I would use 2 pin male and female connector. Crimp leaded resistor in one of them, wire in other and just plug it in.. Connector will take care of mechanical part, resistor part with it's connector will be replaceable and serviceable. All will be automotive grade harness with same quality as the rest of job.. Schematics and documentation will be easy, production too. You can make it hermetic too with right connector.
Regards,
Sinisa
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a leaded resistor sounds like a disaster to me. The leads will have to support the mass of the harness wire, will vibrate and snap off.
However, a leaded resistor, soldered into the wire, and then potted into some sort of support (like a plastic tube) might work. In all cases the wire will have to be supported where it is soldered, and some distance up away from the joint to avoid brittle failures at the point the solder stops wicking up the wire. Not for nothing does no one solder looms these days, everything is crimped. In fact, i could use a crimp splice to attach wire to leaded resistor, and then pot that, which would be even better!
You're not exactly helping us to help you!
First you're saying that you're going to break every wire and solder it to a PCB, then you're saying that no one does soldering on wiring looms these days because of brittle failure (which is why I suggested sufficient length of heatshrink to take you outside the wicking zone). Now which is it? :palm:
As I said, you need to give information. How big is the loom? how big are the wires (in relation to a 1/4W resistor)? How much support? How much flex? How much vibration? Application? Picture?
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http://www.aeroelectric.com/articles/In_Line_Resistor/ (http://www.aeroelectric.com/articles/In_Line_Resistor/)
here we've been doing it for years when it was unavoidable. no customer ever complained as far as i know.
Though making it work without the resistor is the best responce. it adds a lot to the cost of the harness
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If i had to put a 10k, 0.25watt resistor into a wire in a harness, what's the most robust method?
I'm thinking of 0805 smc resistor on small pcb, incoming & outgoing harness wires soldered to that pcb, strain relief and sealing done via adhesive heat shrink around complete pcb??
If you use a leaded resistor then use a 2W resistor minimum.......the 0.25w resistor even with heatshrink at the hands of some rough assembly might not even make it to testing.
Also, fold the wires back on the resistor and cable-tie in place. I.E. take as much stress of the resistor leads as possible.
Ian.
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At the moment i'm trying to make the probelm go away by any means possible, but their is still a possibility i'll need to put a 10K resistor inline into something like a 22awg wire
My pcb suggestion would obviously use the pcb for strain relief, by supporting the wires for a good distance away from the point they are soldered to the pcb. However, i think i prefer the crimp option to avoid dodgy soldering and long term fatigue failures.
I don't really want to add the cost and "eyesore" of a separate connector, ideally the resistor bodge should be hidden as far as possible.
A 2w resistor, with chunk leads, crimped to the wire, and then inserted into a bit of stiff tubing and potted in looks to be the best (but still pretty horrible) option!
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There is almost no good solution to this if you need the wiring harness to survive harsh environmental conditions (vibration, humidity, ocean spray), and you can expect a real-world incremental cost of +10-20USD for bodging in an inline resistor.
Perhaps posting the relevant part of the circuit board that this wiring harness connects to will reveal a way to kludge something at the board level (unless this product is already in the field, in which case replacing the harness might very well be the least-costly solution, irrespective of the hit to longevity/reliability).
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The current issue is that i need a pull-up on an slave device monitoring/diagnostic input wire, and that pull up voltage must come from an external source (for various reasons too complicated to go into here) to the controller (which already monitors the existing diag input but without the pull up resistor). The existing enclosure simply has no free pins, meaning to put the pull up in the controller will require not just a complete redesign, but all moving to a larger enclosure with a larger pin count connector (with the knock effects of a physicals redesign for mounting, loom rerouting, and significantly increase in the cost of the enclosure and connectors).
The controller is just high enough volume where peice costs start to matter, but not high enough to get an enclosure supplier to tool up for a new connector set in the same sized enclosure |O
So, for a silly $0.001 resistor, i'm looking at a significant increase in unit cost, size, and the requirement to design a new controller to suit the new pin count (And possibly re-do EMC cert as well....) All in all a lot of cost if avoidable!
Against that, the end user is a large, prime mover contractor, that needs a very robust product because infield failures cost them big time. So, if there is a suitably robust method of putting the resistor in the loom, i'd do that ;-)
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Hi;
What I do is put a resistor inline with short shrink on the joints.
Then fold both wires back along the resistor so the whole thing forms a Z.
Then slide a longish piece of shrink over the whole thing.
https://www.amazon.com/Ginsco-152Pcs-Adhesive-Lined-Shrink/dp/B01N07O1GO/ref=sr_1_1?ie=UTF8&qid=1487798583&sr=8-1&keywords=adhesive+heat+shrink+tubing (https://www.amazon.com/Ginsco-152Pcs-Adhesive-Lined-Shrink/dp/B01N07O1GO/ref=sr_1_1?ie=UTF8&qid=1487798583&sr=8-1&keywords=adhesive+heat+shrink+tubing)
Any strain is be on the wire only,
( To clarify: both wires go past the resistor inside the shrink. )
Mick M
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solder it into an inline fuse holder?
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solder it into an inline fuse holder?
This idea gets my vote.