When you really need a resistor jumper - Page 1
Forum section: electronics / projects

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 12, 2016, 01:18:12 am
content: Like, say you have an optional DC-DC converter in a power supply. When you assemble a variant without that option, you can simply jumper over the transistor/diode and inductor to bypass it. But if that jumper needs to handle an arseload of amps...http://www.digikey.com/product-detail/en/harwin-inc/S1911-46R/952-1740-1-ND/3131071Only problem: these things are ridiculously expensive: at 20mohm max, they'reat least$14 per ohm!(Yes, I know $/ohm is a meaningless quantity. That's why it sounds so good)They also come only in oddball sizes, not as replacements for ordinary chip components.It would be nice to substitute chip components with a similarly sized zero-ohm jumper, but they don't come in nearly as high current ratings. (Zero-ohm jumpers are just ordinary resistors, with the resistive enamel layer gooped on unusually thick, and no laser etching. They still have some resistance, typically in the 10mohm range, but they're only rated by maximum, so they aren't really useful, at least without calibration.)But, so... the thought occurs to me... drop in one of these:http://www.digikey.com/product-detail/en/vishay-dale/RCL06120000Z0EA/RCL0.0CCT-ND/2587726Notice it's a "wide" style. So, if you placed it over an 1812 footprint... the side electrodes will do the job of shorting things together... and, I'm betting, they'll do a better job than it would, right-ways-up, anyway!I'll have to ask the assembler guys how dumb they think this is...Tim

author: exmadscientist
author_rank: Frequent Contributor
timestamp: October 12, 2016, 02:10:59 am
content: I've never had occasion to use them, but Keystone makes a line of "true" zero-ohm jumpers in standard footprints:http://www.keyelco.com/category.cfm/Test-Points-Tips-Probes-Clips/Zero-ohm-SMT-Jumpers/id/1203. They look like a nightmare to hand solder, but at 200 uOhms specified maximum resistance, they sure can pass current!

author: qwaarjet
author_rank: Regular Contributor
timestamp: October 12, 2016, 02:28:11 am
content: why not a couple standard "zero ohm" chip resistor in parallel the cost per chip is <0.005$/ unit in quantity so you could use like 20 and still be cheaper that jumper you listed

author: Emrys
author_rank: Newbie
timestamp: October 12, 2016, 02:43:23 am
content: Two ideas:1. A wire.2. A connector that bypasses the DC-DC layout for that variant.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 12, 2016, 03:26:43 am
content: Quote from: exmadscientist on October 12, 2016, 02:10:59 amNice, if you can get ahold of 'em:http://www.digikey.com/product-detail/en/keystone-electronics/5108/36-5108TR-ND/5118869They're still $0.17 in thousands, though.On account of the low stock and price, I would try to avoid them.It is an option, though, especially where space is constrained: "unlimited" amps through a 1206 footprint!Quote from: qwaarjet on October 12, 2016, 02:28:11 amQuote from: Emrys on October 12, 2016, 02:43:23 amPlease. I'm not going to "save" $0.005 on parts just to spend an additional $5.00 per board in assembly costs.If it's not PnP, I don't want to hear it. I'm talking production here.QuoteI'm also not going to spend $1 (plus whatever the plug assembly costs!) for a full-blown connector.Let me put it this way: the baseline is currently hovering around $0.20 per part. An ideal solution is trivial to install (i.e., it's literally a chip-shaped part that drops in -- like the Keystone part above), and costs as much as the zero-ohm jumper or current-shunt resistor it's substituting.Unless you meant something else, in which case Idunno... could you elaborate?Tim

author: exmadscientist
author_rank: Frequent Contributor
timestamp: October 12, 2016, 04:05:55 am
content: Quote from: T3sl4co1l on October 12, 2016, 03:26:43 amDigi-Key has >600 in stock in 1206; Mouser has 1000. I wouldn't call that particularly low stock. DK says "7 weeks" manufacturer typical lead time, which isn't bad if you want thousands. The 0805 and 0603 variants are the same price but show >20,000 and >60,000 stock respectively, for what that's worth.I do agree that depending on a single-source for volume production is never fun.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 12, 2016, 04:18:33 am
content: Quote from: exmadscientist on October 12, 2016, 04:05:55 amYeah. I don't have any particular problems about Keystone -- they seem to be pretty reasonable (at least, from the outside; I haven't had any contact with reps, which is probably a good sign if anything), they have good products, and I've not heard anything bad about them. It's just not a preferred choice, for "meh" reasons like these (single source, price, stock and lead time).Tim

author: Monkeh
author_rank: Super Contributor
timestamp: October 12, 2016, 04:44:17 am
content: Several resistor manufacturers have a dedicated jumper part as well as a 0-ohm resistor. Stackpole HCJ, Rohm PMR, Susumu YJP, the Keystone ones.. Most of these are stocked in quantities of tens of thousands at Digikey.Admittedly the cheapest of these is $337.50 for a reel. But that's the price of a dedicated jumper rather than a resistor which wants to be more (or is it less?), apparently.