Low voltage vs. low voltage (but higher) - Page 1
Forum section: electronics / beginners

author: Falcon69
author_rank: Super Contributor
timestamp: June 11, 2015, 02:32:41 am
content: So, my question is this....higher voltage > lower voltage (i.e. 24vdc vs. 5vdc) to help prevent noise down a length of 50ft cable?I am debating redoing a project. Currently, it runs at 5 volts with a length of up to 50 feet.If I ran that at 24 volts, would the signals going to and from see less noise in the line with the upped voltage? Or would it not really matter? The cabling is double shielded (Both braid and foil) with the braid grounded at one end (the main circuit board) but not grounded at the sensor on the other end of the 50 feet.Currently, at the 5 volts, it works perfectly. But if it is better I'd rather go with 24 volts. Sometimes this cable would be routed near noisy electronics like VFD's and Routers/servos/stepper motors.

author: slateraptor
author_rank: Frequent Contributor
timestamp: June 11, 2015, 03:27:08 am
content: Your description is painfully vague.Sensor type?Signal type?Cable type? Specs?Purpose of DC level?Application?

author: Falcon69
author_rank: Super Contributor
timestamp: June 11, 2015, 03:32:36 am
content: just in general. Does a larger voltage have less chance of noise being introduced into a cable, then a lower voltage? Or, with something that only operates at such a low mA (50mA or so) along a 50ft cable not matter what voltage? Noise will still be introduced or not be introduced?I know that noise does enter through cables, just from my car stereo days. I remember that alternator noise was a real problem on some installs, until I connected a cable/wire from the point where the amp was grounded, to the point of where the battery was grounded to the frame. But, this might be completely different than what I was asking, as this problem is a ground loop problem.But in any case, just in general, my question.

author: slateraptor
author_rank: Frequent Contributor
timestamp: June 11, 2015, 03:59:27 am
content: Uncle.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 11, 2015, 04:56:35 am
content: If this is still on the same project I remember...Then as I recall, your signals are such that, there is little or no sequential logic (i.e., clock signals to worry about tripping with extra edges), and the bandwidth is quite low (i.e. does it light an LED or not), so it's basically not a problem.Yes, higher voltages do have higher thresholds, assuming you wire them that way. Drawing real current at the same time is also a good plan (e.g., industrial 24V and 4-20mA controls).When it comes to dumb on-off signals, big voltages aren't ever going away. 120VAC is common in industrial panel level design, since it can be used to directly operate relays/contactors, lights, small motors, etc. 24V (AC or DC) is common for the same reason, with the advantage of being SELV.As for communications, you're often better off combining signals into a few pairs, usually with something like asynchronous serial over RS-485, or a high level protocol (CANbus, Ethernet, etc.). These are very common in industrial communications, and most PLCs offer built-in support or IO modules with these functions.Tim