Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 9 of 9

Thread: 5V overvoltage protection for high power device howto?

  1. #1
    Senior Member
    Join Date
    Feb 2016
    Location
    Australia
    Posts
    219

    5V overvoltage protection for high power device howto?

    Helllo.
    I have an 8x8 ws2811 cube I've been building that is nearing completion.
    It will have 1024 Leds so around 50A at 5V.

    It runs a teensy3.6/octows2811 and piZero.
    I'm scared of a power supply failure and overvoltage destroying many hours of work.
    How would I make overvoltage protection.

    Thanks.

  2. #2
    Junior Member
    Join Date
    Aug 2019
    Posts
    3
    Gibbedy


    It would be useful if you could share a general schematic.

    At first I could think of a comparator, a TL431, an opto coupler (maybe some logic gates) and a power MOSFET that switches off when the voltage exceeds an established limit.

    Share more info with us

    dzalf

  3. #3
    Senior Member
    Join Date
    Feb 2016
    Location
    Australia
    Posts
    219
    It’s 1024 leds in parallel that are rated at 5vdc.

    At the moment I finish a row 128 leds, plug my adjustable power supply in and test.. but I have fears of bumping a preset button on the supply and it switching to 12vdc... also polarity protection would be good....

    I just cant risk a mistake at some point in the future killing all my leds at once.
    The simpler the solution the better for me..

    I’ve tried googling for high current zener diodes but 50W is the biggest I saw. I’ve got a few ideas but I’m not sure.
    Thanks dzalf.

  4. #4
    Senior Member
    Join Date
    Apr 2013
    Posts
    1,899
    Clamping a 5V supply when 5.5V is Vmax is tricky since most basic options will need 20-50% over to do anything.

    Along with having a fuse or circuit breaker on the power supply sized as close as possible for your worse case load so in theory a 12V supply will trip it before dumping enough current to cause damage you can consider a crowbar protection system
    https://en.wikipedia.org/wiki/Crowbar_(circuit)
    Basic idea is that if an out of tolerance happens you short circuit the power supply (possibly also disconnecting your output). This obviously risks the power supply but is cheaper than a new cube and if fitted this definitively will trip the circuit breaker/fuse, and properly designed will do so before to much energy from the overvoltage is dumped into the LEDs (since it is all flowing through your chrowbar, which is why they work better then trying to quickly disconnect via FET etc)

  5. #5
    Senior Member
    Join Date
    Feb 2016
    Location
    Australia
    Posts
    219
    Ok thanks..
    Ill get a high current thyristor and experiment.
    Thanks.

  6. #6
    I'd ask about the power supply you're using, and what that has built into it. From the sounds of it, we're trying to protect against user error, where you (or someone else!) sets the power supply to the wrong voltage. Why not swap it for a fixed voltage PSU that can only supply 5V?
    For example
    https://www.robotshop.com/uk/switchi...ly-5v-50a.html
    looks like it fits your numbers at first glance. I notice the voltage is adjustable over a range, so you might want to pop a bit of glue/thread lock on the adjustment pot

    If you do strap you're own protection to the front of another supply, check to make sure they'll agree. Strapping a fuse to a PSU that has built-in Over current protection may not actually give you what you want.

    Polarity protection, is much easier than current protection (IMO). You can do this entirely with physical things. Most beefy connectors can only be inserted one way round, then properly using red+black wires, PCB labels, and looking before turing the system on can be more than enough. If you (really) want to add protection to the circuit -

    You can put a shotky diode in series that will block reverse current. You'll have to increase the supply voltage a bit to get 5V the other side (~0.3V) and you'll probably need to heatsink as it'll waste ~50Ax0.3V = 15W. It's wasteful but foolproof, as it doesn't matter what the supply does, neither the supply, nor the load can be damaged.
    Or reverse bias it accross the supply, where it will conduct if the power is reversed. You then need to know what the rest of the supply is going to do when shorted, often you can use this to blow a fuse very quickly, or trigger the supply's built in protection. This does absolutely nothing untill the supply is reversed which is good, but something can be badly damaged if it's done wrong. The maths has to be done on fault current, fuse blow times, etc.

  7. #7
    Senior Member
    Join Date
    Feb 2016
    Location
    Australia
    Posts
    219
    Hi Edward.
    For testing I’m using my adjustable supply,
    For running I’ll use something fixed.
    I’m running xt90 connector and so reverse polarity protection shouldn’t be needed but I’ll have it if it’s simple.
    During the build process I was testing 1 x column of 16 leds and managed to supply reverse polarity. It made me feel rather unpleasant.. I just don’t want 64 x that feeling.

    I’ll come back here after I aquire some high current thyristors and have thought about it more. I just want something perminantly attached to my cube that prevents overvoltage.

    I’m probably overthinking it. I run thousands of leds on another project and don’t worry about it there.

  8. #8
    Senior Member crees's Avatar
    Join Date
    Dec 2016
    Location
    Utah
    Posts
    169
    We use automotive fuses on all pixel feeds with the appropriate rating. you could get something like this between your pixel + Feed and your power circuit

    https://www.amazon.com/KOLACEN-Autom.../dp/B072MFTZ1X

  9. #9
    Senior Member
    Join Date
    Feb 2016
    Location
    Australia
    Posts
    219
    Yeah I’ll get something like that.
    Thanks.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •