Looking for DB25 cables w/decent wire thickness - Page 1
Forum section: electronics / general

author: forrestc
author_rank: Unknown
timestamp: August 08, 2018, 11:55:19 pm
content: I've discovered that a set of ~2 meter DB25 M-F cables that I purchased a couple of years back for a project is introducing an unreasonable amount of resistance (on the order of 10 ohms) into a circuit, causing issues since some of the conductors carry quite a few mA in this application (process control).Tearing one open I've discovered the wire inside appears to have very little if any copper, and also is so small that I couldn't even venture what gauge it is - probably 30GA or smaller.I have a couple other cables I recently acquired and have discovered a similar situation, although they are admittedly not as bad as the original cables.I'd really like to find some cables which use at least 24GA wire, if not something thicker. Unfortunately, it seems that all I can find for a reasonable cost are unspecified "generic" cables or cables which are 28AWG. It seems that if I find one which specifies a reasonable gauge, I'm looking at $50USD/cable or thereabouts for a fully-pinned cable, which isn't good considering there are around 25 of these used in this application.I've searched every source I can think of, wondering if there's somewhere I'm not looking....

author: tautech
author_rank: Super Contributor
timestamp: August 09, 2018, 01:15:48 am
content: Keep an eye open for some suitable for projectors as they often need long runs.One I have snipped from a classroom has ~10 strands of tinned copper for each conductor.It's heavy enough that I'd have no reservations on 1A/conductor for 2M runs.Maybe you just want longer/better ones and coil up the excess.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: August 09, 2018, 05:55:13 am
content: Some Digi-Key options that have datasheets showing 24 AWG wire:https://www.digikey.com/product-detail/en/phoenix-contact/2305486/277-14600-ND/4449879https://www.digikey.com/product-detail/en/phoenix-contact/2302159/277-5034-ND/2524922I hope it's a project for work. These are $76 a piece.

author: Halcyon
author_rank: Unknown
timestamp: August 09, 2018, 07:31:44 am
content: Could you not just use lengths of Cat 6 Ethernet cable with RJ45 to DB-25 adapters on each end?

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: August 09, 2018, 12:29:31 pm
content: These cables are for signals, you shouldn't expect them to carry power. You can find "db" shell connectors with high current inserts.https://electronics.stackexchange.com/questions/84962/how-big-current-i-can-commutate-using-d-sub-connectorsWhere you can find them is left as an exercise for the reader.

author: aargee
author_rank: Frequent Contributor
timestamp: August 09, 2018, 11:54:41 pm
content: Maybe the answer is to get the cables made for you, there are specialist companies who do this - or - make them yourself?

author: james_s
author_rank: Super Contributor
timestamp: August 10, 2018, 06:14:31 am
content: Are these new Chinese cables you are using? I've cut up various old cables to get the nice selection of different colored wires and it seems like the one I used for a whole pile of projects was 24 or 26 AWG, I think it was a DB-25 cable from the 90s.

author: Nauris
author_rank: Regular Contributor
timestamp: August 10, 2018, 02:09:54 pm
content: Amphenol has some low-smoke 24 AWG ones.The are only $29 a piece for 10 ft.https://www.cablesondemand.com/category/DB25/product/CS%2DDSLSZH25MF/URvars/Items/Library/InfoManage/CS-DSLSZH25MF.htm

author: forrestc
author_rank: Unknown
timestamp: August 15, 2018, 06:20:44 am
content: Quick reply for everyone....First, no, I'm not carrying much current here. 500mA/conductor is the most I'll see ever - most of the conductors which are 'current carrying' are ~200mA or so. The problem is that at 10and 200mA, the voltage drop across this cable is around 2V, which causes problems. At 500mA, it's 5V which is a real problem.And no, I don't really have a connector choice. On the other hand, DB25 isn't unreasonable for the currents involved, especially since only a few conductors are current carrying at any given time.Yes, these were cheap mostly chinese cables probably just from some random internet seller (don't remember my source, it's been a couple of years ago at this point). I'm mainly trying to find a source where I trust that the wires inside are reasonably sized. Amazingly very few actually specify the wire gauge, probably because they're mostly from chinese manufacturers trying to skimp on AWG, and in most situations it really doesn't matter.I considered making my own, but the problem is that we're talking around 20 of these cables. 20 cablesx25 conductorsx2 ends=1000 terminations. No thank you. I am considering IDC ribbon cable though...Custom cables would be fine, but I haven't found a resonably priced source.Nauris: I had forgotten to check on cablesondemand.com, usually use them just for Coax cables - thanks for reminding me, this seems like the best option so far.Back in the day when everything used DB25 cables, it was fairly easy to find a good quality cable, seems like that is harder and harder.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 15, 2018, 06:54:09 am
content: Quote from: forrestc on August 15, 2018, 06:20:44 amIf the ribbon has sufficient core than that would be the easiest way to go.