psu to board wire?

Hi, I am planning to replace my sangui with another ramps, this time with 'proper' 16awg wire. Last night I measured the resistance, it is 0.4ohm for about 5 meter in length, I plan to use it by about 60-80cm only. I am asking whether this wire is good? 5 meter at 0.4ohm? also it is a multi core flex cable, I guess silicon sleeves too

5 meters? Just remember that 0.4 Ohm x 10A is a 4V drop and 40W dissipated as heat... Not really a good idea.

I'm going to use about 50-80cm actually, it was still intact as 5 meters when I measured it. I'm no good in electronic stuffs

Please take a look at this thread here: [forums.reprap.org]

I got same cable as this guy over here [forums.reprap.org], based on the thread starter, he used smaller cable for his heated bed thus his wire can't sustain the current then melt the sleevings

I just found out that I can't use my multimeter to measure the wire resistance, even the supplied, stock psu to board cable shows me 0.4ohm resistance. I wonder if there's a way to measure wire resistance more accurately?

On runs that short, it's easier to just look at the current and length, and select accordingly . . . . wire sizing isn't rocket science . . . .

- Tim

Well, I just wanna avoid unwanted disaster due to selecting wire gauge without proper reference and knowledge. Smaller cable would give disaster. My place here don't use awg terms by the way, we use "how many amps you wanna run on that cable" term, then the cable for that requirement will be recommended, cable size may differ from awg though....

So much for the 'standards' used in this world

Micro ohm meters exist for this, but are prohibitively expensive (the cheapest I saw was over $500, many in the $1000's) . . .

[www.instrumart.com]

and thus my suggestion to select based on ratings. Cross sectional area largely determines resistance and current carrying capability, so AWG, BFD, FTS, or whatever really are not anything more than units of measure - IE 2mm wire is 2mm wire, and should behave similarly no matter what standard it is listed under.

So, get the mechanicals for what you have, find the closest rated size, and you should be close. Barring that, and since it sounds like you already have the wire, install it, and measure the voltage drop, which should be easier to get an accurate reading on. If you also know the current drawn, you can back into resistance for the run with Ohm's law (V=IR), and then determine ohm/s meter, foot, whatever.

The bottom line is that if it runs cool, and voltage drop is low, you are fine. And too big is only a problem ifnit won't fit the connectors being used. (My printer, for example, runs #10 for heaters, #14 for extruder, and #14 for motors, etc on about a 20mm run . . . brutal overkill on a 30A supply, but fits, cheap, and can't go wrong . . . And frankly, on cheap RAMPS-14 cards, the POS connectors are a far bigger problem than any reasonable wire will ever be . . .)

You don't mention where you are or what rating system is used . . . ? ? ? You did mention 16AWG, which, for a bed heater, at least, I would consider to be pretty small . . . here is a table, granted based on AWG, but just come into it with the copper diameter and it should help: [www.powerstream.com] Note that 16ga is listed as only good for 3.7 amps for 'power transmission' - IE sustained current applications, but for AC applications . . . DC is a bit different, not having skin effect.

- Tim

Edited 5 time(s). Last edit at 07/28/2015 01:21PM by tadawson.

I stay in Malaysia, noob in electrical as I don't have background but will learn for reference before doing it for real. Actually it is for the board instead of heated bed. I've been to one store only to buy some hardwares, so their methods is either amps to run on the wire or the diameter, yet I don't know which diameter should I compare to with the awg reference, cross sectional (some reference have this) or the diameter itself.

I'm sorry for asking this question which seem basic to you guys.

Board input, as in power goes in and the to heated bed or extruder, or just to power a board?

Cross section and diameter should be the same thing, I would think . . .

And again, unless it won't fit the connectors, or costs too much, you can't error going larger.

- Tim

Edited 1 time(s). Last edit at 07/28/2015 11:23PM by tadawson.

Just to power the board, my heated bed wire doesn't have a problem so far, my other thread used wrong type of wire, solid core type to power the controller board

I guess I will buy another slightly thicker copper cable, roughly 1.5mm diameter

If all you are powering is a board, no motors, heaters, etc. through it then the draw is so low that almost anything will work.

I do not however, happen to know of any 3d printer controller/board that does not handle heater/motor power, though . . . what is it?

- Tim

I mean, power up everything, my bad writing "just to power the board"

If it carries board/motors/bed/extruder, then 16ga is too small . . . If typical, and heat bed and *other* are separate, then perhaps you can use it for the motor/extruder feed, but for heated bed, I'd go with 12ga or 10ga myself . . . both supply to board, and board to bed.

- Tim

Erm... will it fit on to the terminal slot?

In case you didn't know : you can probably somewhat workaround the bias of your ohmmeter by making its two probes touch and putting it in relative mode - of if it hasn't got such a mode, remind the displayed value and subtract it of your following measurements.

---

Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

#10 fits a RAMPS, but is snug, #12, no problem . . . unless they used undersized connectors on your board . . . the Molex series that they are knocking off are rated for 16A, and have decent sized terminals.

- Tim

Quote
DeuxVis
In case you didn't know : you can probably somewhat workaround the bias of your ohmmeter by making its two probes touch and putting it in relative mode - of if it hasn't got such a mode, remind the displayed value and subtract it of your following measurements.

My multimeter can go down as low as 100mili ohm or 0.1 ohm resolution, I guess I'm unable to measure that as well if the actual cable resistance is about 50 mili ohms or 0.05 ohms

I try find #10,#12 and #14, flex core. so based on the gauge reference, #10 is 2.5mm, #12 is 2mm and #14 is 1.6mm diameter right? in terms of the copper inside the sleeves. I think I do have an audio grade thick copper and thick sleeve inside, the core is flex consists of probably hundreds of strands. I don't know the gauge of it and forgot the diameter as well. But the overall is that the cable I think not so flex due to its thick sleeving, transparent, sleeve.