Flyback Diode to Protect Relay
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- čas přidán 27. 08. 2024
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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):
/ @juliansshorts
Adding a low value capacitor ( 0.1uF ) across the motor contact suppresses RF noise and also tames down the Arcing produced during the break contact times .
You could put a capacitor across the relay contacts to help with arcing.
The diode clamps the reverse voltage at ~0.7V long before the 33V transient suppressor would even start to conduct. A 1N400x should work fine and is cheaper to boot!
I use a 12 Dc motor through the relay. The motor is given through a separate power supply. It is controlled through the relay. When the 12 dc power supply is turned off, the relay turns off according to the time given by the potentiometer. But When the power supply to the motor is turned on, the relay will turn off before the scheduled time.
A capacitor in series with a resistor will do it too, you'll need a big diode for that shed fan as the freewheeling current will likely stress that little 1 amp job.
Looks like a snubber across the relay contacts is also needed :)
uK8cvPAq - how much reverse current do you think will flow? We use 1N4004 or 1N4007 diodes to suppress the back EMF from large 24V 375mA electromagnets and they last for many years. And some of them get switched off- on - off every two minutes.
@@Mark1024MAK That should be fine, generally the diode should be rated for the full run current plus stall/heavily loaded conditions for it to be bullet proof. The RC is generally preferred for larger motors as the diode itself can load them, try it for yourself by spinning a disconnected motor with your finger then connect the diode, it'll feel harder to spin with the diode connected.
@@JulianIlett Well, you might be able to get away with paralleling lots of 1 amp diodes but they should be clumped together to help with thermal balancing. Doesn't always work but its a cheap trick often used in AV power supplies.
Also look up RCD snubber.
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 😖].
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...
You can also put a fast acting diode (UF4007) across the contacts so that its reverse biased. This will also eliminate the back EMF from the long inductive wires.
Another thing: a diode like that actually slows down how fast the magnetic field collapses and keeps the relay engaged a like some milliseconds longer
Power Max - a diode across a load controlled by a relay does not slow down the operation of the relay, but a diode wired across the relay coil will delay the relay de-energising.
@@Mark1024MAK Yes, precisely; that clarification is important. Not sure how much it slows it down provided the high resistance of the coil and voltage drop of the diode though.
A diode across the relay contacts will do nothing for them as the back emf is positive with respect to the relay, the inductance wants to keep current flowing in the same direction. A reverse diode across the motor and RC snubber across the relay contacts is what's needed.
@@uK8cvPAq Your not understanding, you put the diode across the coil not the contacts. If +12V and 0.5A is flowing through the coil with the reverse biased diode in parallel, then when power is immediately disconnected the current through the coil wants to continue flowing and the voltage across it inverts to -0.6v, where the diode becomes forward biased for some period of time.
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.
OH ! that was weird, right when you switched ya shed fan on (hovercraft mode ) my room door slammed shut !...jumped out of my bloody skin, no diode across me...cheers.
Weird indeed :)
Andy aren't you his neighbour perhaps :)
@@maicod Hahah!...same country.
I knew :D
Must be an internet-enabled fan.
Julian, Diodes are really only useful for the reverse current generated when disconnecting the motor. Doesn't really help with the arc across the relay contacts. This is very much needed if you are using an electronic switch as they usually cannot handle the reverse voltage spike (the diode is absolutely needed across the coil to protect the arduino). What you want for protecting the contacts is some sort of RC circuit to slow down the in-rush current. There are small modules available from the usual China channels (this one has RC as well as a MOV for the big spikes):
Banggood: www.banggood.com/RC-Resistance-Surge-Absorption-Circuit-Relay-Contact-Protection-Circuit-Electromagnetic-p-1230922.html
just like they used to do in all the telephone exchanges when they were electromechanical RC network across the contacts by the truckload.
`I don't know much about electronics, I do have a rudimentary understanding; why not use a PWM signal and a FET to spin the fan upslowly?
Diodes are commonly used in fork lifts as the primary cause of sparking from the relays opening.
@@fernandgeenevan8773 the pwm itself need the diode in its circuitry also more complex circuit compaired to just a relay, also lower losses with relay
Thanks David, that's perfect. I'm going to keep the diode (or diodes) across the motor as it does reduce the spark intensity, but I'll also add this snubber across the relay contacts. That should be belt and braces :)
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.
The diode is also acting as a dinamic brake by short circuiting the armature of the motor when disconnecting.
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
At 75V 14A you probably should add a GPS, because your *shed* would be in hovercraft mode :)
Don’t forget the altimeter 😁
Put a diac across the motor, or just a 0.1 uF disk capacitor. You can also try a neon bulb; both diacs and neon bulbs have a “hold-off-until-sufficient-voltage” characteristic in either direction. Cheerios. 😊
These are all good for AC applications, a silicon diode is better for DC applications. A ceramic disc capacitor will however reduce RF interference to nearby radio equipment.
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.
You should place an RC snubber, same technique used on refrigerator compressor switching I think.
That’s an AC application... Diodes are more effective for DC applications.
@@Mark1024MAK Then it becomes an RCD snubber ( :
I would also try to add a capacitor parallel to the diode. It is ideal for high frequency signals and sparks.
From my memory of quite a long time ago, putting diodes in parallel does not share the current, the first diode to conduct will take all the current.
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.
Antiparallel Schottky gets my vote as worth a try
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.
The flyback current won't "peak extremely high". It is the exact motor current. A 1N400x can take a surge current of 30A (non repetitive, It's a thermal limit). I doubt the motor is running at more than 30A.
@@superdau You're right. I was confusing current and voltage. Brain-fade on my part. But my comments still stand in relation to the switch-off voltage which can peak well over the input voltage.
@@melkiorwiseman5234
No, a diode will clamp the voltage to 0.7V (or about 1V in the case of a 1N400x at higher currents). That's the whole point of the diode. The voltage only peaks, if you have nowhere for the current to flow.
@@superdau That works so long as the diode is rated to handle the combined voltage and current.
Melkior Wiseman - the 1N4005 diodes he is proposing to use have more than enough voltage rating. I’m not sure what the running current of that fan is, but myself, I would be happy with a single 1N4004 diode. The main current flow through the diode will only occur when the relay contact opens and the motor/fan is slowing down. So just for tens of seconds (with the current reducing as the RPM slows). And the number of times it will do this will be infrequent. More than enough time for the diode to cool down. The most important thing is to provide a suitable in line fuse (time delay / slow blow / anti-surge type) to the circuit, so that in the event of either a stalled fan or the diode going short circuit, the fuse will prevent a fire.
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.
That is not how electricity works. Ground isn't some kind of magical black hole. Doesn't matter which side you switch it; if there's an open circuit you'll get backEMF.
Forget the diodes, use capacitors, one from each pole to the case and one across the poles.
Or you could switch the motor using solid state relay and/or thyristor? Could be quite fun.
I maybe would have tried a cap across the contacts of the relay too/instead?
Or used a bigger relay/contactor. Used to deal with these things all the time, and gotta say, although relay contacts will fail, they don't do it very often. Looking at a modern contactor, the spec sheet says 'mechanical durability 15 Mcycles'.
You need to make an informational video on how to properly diode protect your automobile so the average consumer can fight back as shoddy mechanics treating them as cash cows...The comments youll get will be overwhelming when you educate people in a manner that hits them with a hard reality and aids them with a simple solution that saves them mucho deniero..
While you can use a regular "car" relay, why not use a MOSFET? They can handle the current and you maybe could even implement a variable speed control. Have the motor ramp up and down instead of just switching on and off. Why? Why not? ;-)
Look back through my 10 years of videos and you'll not find a single electric motor video. So I'm really enjoying the whole back emf, flyback, arcing, sparks malarky. Yeah, MOSFETs, PWM, all far too easy. But sparking relay contacts, quench diodes, snubber networks... woarhh :)
@@JulianIlett - LOL. I hear ya. But I just think your fans (LOL... not intended) would be more interested in seeing some cool Arduino --> radio link --> Arduino --> speed controller --> DC motor project. Maybe even feed back the current RPM of the fan? More options (thus videos!) make it more fun. This could be a fun *_series_* of videos.
*And then* add IR motion detection to turn the motor off when anyone approaches! If someone is snooping around looking for the source of the noise they won't find it! LOL. Plus it just keeps it off while you or the wife are there likely with the door open any way so you save power. Oh the options!
Julian, see the other comments especially David Granz comment. The question is if you are seeing sparks from inrush current or flyback current. I suggest you try with an actual relay to see if it arcing while closing or opening. What you are doing is rapidly causing both and the diode will only impact flyback current.
Done :)
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.
Which gave rise to radio transmitters...
"Radiant energy" eh? "Do a lot of good" , hmm? Sounds like quackery to me. Can it magically cure diseases?
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!
Hi There! Thanks for your video Would that be the same orientation if you install it on a 5 pin relay across the coil ? Many Many Thanks for your reply !
Classic method to quench EMF
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 1N54×× 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
I think I would just go for a relay designed to switch DC at a current higher than that required by the motor. the motor when running is butting the current all the time so there should be no need for a magnetic arc quenching relay. When you think of all the cars running fans on 12V it's normally just a big relay. the relays can often break less current than they can make! also watch out for the normally closed contacts, they are often smaller than the normally open contacts. so you cant just swap the on-off function of a relay by just swapping the NO for NC contacts, without checking first the data sheet of the relay to check if the switching capacity is the same. Still can't beat a video with sparks in it. the electrical type not the old group :)
Not a fan of Ron Mael's moustache then, eh?
@@massimookissed1023 this town ain't big enough for a moustache like that ;)
On my mobile phone display, the spark was noticeably brighter with the 1st diode in circuit
Why don't you use a vdr. (Voltage dependent resistor) such as S14K60.
A VDR is slower than a silicon diode.
@@Mark1024MAK Yes but then you can use an S14K40. It starts reacting at 40 V spike. Maybee use it in conjunction with a bipolar condensator.
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.
To ensure current sharing, wire a low value resistor in series, for this application, the resistor can be thin flexible wire, just make sure that both the wires to each diode are all the same length.
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??
A relay and silicon diode is fine, and cheap and simple.
Hey Julian, i am curious if you are still planning to release a teardown of the Ozito/Einhell PowerXChange battery at some point? Or did you already and i just missed it?
How can i make my rotary motor faster and powerful..pls help
So, are you going to take this all the way and have the fan turn itself on and off according to detected humidity levels?
Yes, eventually :)
I'm puzzled how a forced draft will reduce humidity in the shed. My understanding of your weather is that it's humid most of the year. Seems that a dehumidifier would be your project.
I think he is using the fan to suck damp air out of the shed and draw fresh air in. And buying a dehumidifier may be a better solution, but not much of a video for an electronics channel.
Isn't the fan only running when humidity outside is lower than inside the shed?
Cold damp air out - even colder damper air in!
A desiccant dehumidifier might work in the shed, but a refrigeration type won't do much at all - it's far too cold. Ultimately there will have to be 2 humidity sensors - one in the shed and one under my corrugated plastic roof measuring the ambient outdoor humidity :)
@@mikebarrett2621 This is a thing. You might want to read up on "relative humidity".
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.
A relay!? For low current DC!!?? Oh Julian! Low side switching N-channel MOSFET!! Even an NPN Bipolar will do a much better job. Cheaper, more reliable, faster, smaller, and completely non arcing. But STILL (MUST) use a reverse biased rectifier diode in addition!
I don’t think that fan is “low current”!
@@Mark1024MAK the relay is only a "low" current relay, probably a Chinese one "rated" at 10A (that's TOTAL capacity i.e. just 5A per contact pair).
That's LOW current in 5v or even 12v power terms, and even for tiny 8-pin MOSFET chips that's not difficult to achieve.
In my book HIGH current requires 4mm^2 cable for ~30A plus. Solar battery wiring is often (but doesn't have to be) high current, >100A in some cases, but even then, MOSFETS can handle that FAR better than a relay!
@@Mark1024MAK even if the fan were mains 240v powered, a relay is not the best solution, an opto-triac would be far better and also directly driveable from an Arduino (a relay is NOT!)
Bob Lewis - “low current” is a relative term. In terms of *electronics*, “low current” is a current substantially below the levels you are talking about. In power engineering, very different figures are meant by “low current”.
I never said anything about MOSFETs not being able to cope with such current levels. Julian is well aware of the use of MOSFET use. He has featured them in past videos.
As with any problem, there are multiple solutions, each with pros and cons.
anyone know how to do flyback protection with a bidirectional dc motor
Is this required for ac fans?
The ventilator from the miner would not make any sparks, use that one!
I've recently bought more Antminers (they're so cheap) so I'll be doing more experiments in that direction soon :)
What ever happened to a hoofing great snubber ?
Hoofing great snubber ordered :)
Use mosfet for zero sparking
Try irf640 with 10k to ground to control fan
@Julian you might want to have a look how the RC model community is dealing with this for ages.. ;)
You use relays?
@@JulianIlett Nope, a small ceramic capacitor from the positive terminal to the motor body, the same for the negative terminal and then one between +ve and -ve should do the trick.
Tiny Workshop, Big Ideas - that’s done to reduce the RF interference. A silicon diode is better to clamp the back EMF.
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 .👍😀
4:10 yep, definitely growing weed lol
Growers use considerably better quality fans.
@@Peter_S_ not all, I fabricated some pretty decent home built inline extractors myself back in my home grow days :)
Still illegal in in our rather backward looking country :)
@@JulianIlett stuff the law, if I still smoked it I would grow my own again, who are the government to tell us what we can or can't do that has no affect on anyone else!
Ah, you're an anarchist - me too - oh no wait a minute - I'm an atheist not an anarchist :)