JLCPCB Prototype for $2(Any Color):

Using a 1N4005 diode to quench the high flyback voltage from a 12V fan motor. But the 33V transient suppression diode didn’t work.

My other channel (Julian’s Shorts):




  1. For the 1N400x series of diodes, there's little sense in buying anything less than the 1N4007 (1000V!), unless you're a manufacturer trying to save pennies. On the other hand, in my years of salvaging stuff I've accumulated a bunch of different members of this series. This particular application is probably the only place I'd be using the lower-rated parts like the 1N4001.

  2. The other issue with diodes is their speed. If they're not fast enough, the voltage builds up while they're waiting to conduct. Pulesjet suggested a capacitor and that will definitely help a lot.

  3. If you are using a relay, why are your low-side switching? If you leave the low-side intact, the motor's inductive current bleeds off to ground when you cut power. If you low-side switch then you do need a reverse biased diode because the inductor will discharge the magnetic field as fast as necessary to keep the current constant. If it hits an infinite resistance it will push current to raise the voltage till it arcs over. But the low voltage drop of the reverse biased diode gives it a benign path to cycle through the inductor until dissipated. This may be a bit more complicated with a motor as the rotor motion will induce a current in the stator while it winds down.

  4. By putting the fan hovercraft style you are aerodynamically stalling the fan causing it to draw a lower current. Block the nozzle of a vacuum cleaner and you will hear it rev up as the fan stalls and starts to spin the air in the fan rather than blowing it.

  5. No point adding diodes in parallel. The forward voltages will all vary by some amount and the one with the lowest Vf will conduct first and so keep the voltage below the conduction point of the others, ie that one diode will still take all the load. 1A diode should be plenty, if you are still worried use a 1N54xx

  6. POST 17 MAR 2020 – Hi Julian – Spark suppression is achieved with Capacitors in parallel not diodes – Diodes in parallel are used for protection, If someone is reversing the Pos and neg, it's called an IDIOT Diode, Then any in line fuse should then become O/C, unless the IDIOT Rapped the fuse in silver foil because it had O/C before and that means the IDIOT Diode is probably O/C as well. Having done it's job but expired in the process. P.S. – I got 1 LBC for watching via LBRY, so .5 LBC is coming to you via a TIP or SUPPORT – LET ME KNOW which to send it to via my LBRY Discussions link – – Also Youtube Like 521

  7. We use 1N4004 (or 1N4007) diodes to suppress the back EMF from very large 24V 375mA electromagnets. If no diode is used, you get a VERY impressive blue spark when disconnecting…! [And if your finger happens to be in the way, it’s very painful πŸ˜–].
    So in your application, you may only need one or maybe a couple of diodes. Try it and see how warm they get. See also my other comments…

  8. I did a lot of testing with an oscolloscope with different diodes and configurations. Each have their advantages and disadvantages. For a coil backfeed i chose a high speed diode. And for a large inductor i used a combination in series. I forget what the results were for each test tho. Do some testing and show us the results! Edit: i think i put 2 diodes facing each other as the large inductor (was a spot welder leads) was causing the contacts to weld. It wasn’t just the negative spike but a positive spoke too!

  9. That flyback / inductive spike / back emf, is the Impulse, Nikola Tesla worked with to generate radiant energy. It can do harm yes, but if properly used (impulse injected into series resonant coil) it can do a lot of good.
    This is what I am researching. results, on my channel.

  10. Hi, I remember an appnote recommending using 2 anti-parallel schottky diodes in series with the transzorb. This reduces the overall capacitance of the transzorb and helps better transient response.

  11. Genuinely didn't know about your 2nd channel… have subbed now πŸ˜„πŸ‘

  12. You need to make sure that the diode can take the peak flyback current and not only the voltage. When the relay disconnects the power to the motor, the flyback current will peak extremely high and although diodes can take a momentary over-current, there's a limit to that tolerance. You can easily "blow" the diode into an open-circuit condition if it can't take the peak current.

  13. Hi Julian I hate to be a bother lol I'm trying to make the arm with gripper claw on my robot "smart" or artificial intelligence.I have the pi 4 b+ with the camera the i2c enabled on the pi and a mega2560 for the servos and the pca 9685 servo motor driver I have the camera mounted behind the claw and also a bi directional data converter for the pi and mega my main question is will this combination of components work for what I am trying to achieve ?thanks for any suggestions .πŸ‘πŸ˜€

  14. Julian, If I hadn't watched your videos you sound like a guy in their 20's. When are you going to grow up? 😁😁😁😁😁😁 Live long and prosper. Luv your stuff.

  15. Forget the diodes, use capacitors, one from each pole to the case and one across the poles.

  16. Using more than one diode in parallel in this situation smacks of witchcraft. If you don't think a one Ampere diode will do it switch to a 1N54Γ—Γ— diode. (3 Amperes) If you want to run the motor in either direction put the snubber diode across the motor's power supply at the input of the polarity reversing switch or relay. Ron W4BIN

  17. emmm…..
    don't think putting those diodes in parallel helps to relief the load current on just one because though silicon starts to conduct at 0.7V but all diode will have a different voltage tolerance. and if one turn on at a lower voltage than the rest, the particular diode will clamp voltage and will still end up just one diode that actually doing the job.

  18. At 75V 14A you probably should add a GPS, because your shed would be in hovercraft mode πŸ™‚

  19. Wouldn't the oscilloscope be better to see what your looking at with a switch, and maybe your seeing inductive start up arcing and not flyback? I cant help but think a SSR would be better suited for this damp application and a mosfet??

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