A short video describing the purpose and benefit of using a diode with your battery contactor or starter solenoid. How and where to wire the diode to the contactor is shown with a simple circuit.
Almost. What you need is a snubber. A snubber is a diode in series with a resistor. So, why do you need the resistor. In many electronic circuits, devices are protected from inductive kick back by a diode. The coil in a contactor is not puny like 100 turns of #35 wire on a ferrite coil, it is probably as big as the coil in many magnetos. So, in effect, the diode is shorting out a spark plug when it fires. The diode has a junction that will breakdown because of very high currents in the microsecond range. So, the diode case won't show excessive heat before failure. When the diode junction breaks down, it becomes a resistor and current flows in both directions, shorting the power supply and you have a classic smoke test. A resistor in series with the diode is chosen to limit the current through the diode while also limiting the voltage spike in the surrounding circuit.In most cases, reducing a thousand volts to say 50 volts wins the day. Since the resistor has a higher resistance than the conducting diode it is in series with, most of the energy is dissipated as heat in the resistor instead of the diode. Since resistors are designed to get hot, they can withstand energy dumps that the diode's junction cannot. A diode alone always works for coils connected to delicate printed circuit board leads. That is a low power situation, contactors in aircraft are not comparable. One last thought, make sure you use a non-inductive resistor. Wire wound resistors have measurable inductance.
When you talk about the direction of electric flow do you mean “ Conventional “ current flow ( actually proton flow direction ) or actual electron flow ?
I was involved in building "specialist" vehicles for over 20 years We used contactors sometimes referred to as Klixons to conect dual charge or auxilliary batteries and as generator starters Beware! do not buy a cheap contactor, our buyer, being a cheapskate started ordering chinese components because of price After numerous failures we cut open a few units, the core inside the coil was a simple bolt! This contacted the heads of the two bolts that the wiring was attached to In a couple of instances the bolt heads fused together causing the starter to engage all the time burning out the starter or destroying the ring gear, if in the battery master situation it might mean not being able to switch off systems Buy the best, you will not be dissapointed, also it could save an engine or a life!
@@mmichaeldonavon trouble is, a diode slows the operating of the opening contacts, and this leads to burning of them and premature wear. Use a Diode in series with a resistor.
It just kills me to see relays mounted in the vertical fashion in aircraft. One hard landing and a bounce and you can engage the starter, sheer a few teeth or worse. Relays should be mounted in the horizontal fashion. Especially in aircraft. Just my 2 cents.
Umm, no. If you mount them horizontally, you are asking for a sticking solenoid. So how to over come this? Mount the starter solenoid so that gravity pulls it open (usually looks like upside down) and the opposite for the master. I've pulled apart a couple old relays and there is quite a bit of shavings (or something) in there that best fall to the bottom.
The diodes I have seen always have letters and numbers on them. These numbers must indicate the types, sizes or strengths of the diode. So what "size" and type of diode is appropriate for this application?
ZManMD Use a 1N5408 That will give a 1000 volt repeated reverse voltage spike protection and 3 amps of forward current. The 5400 only provides 50 volts protection, the 1N5404 provides 400, the 5406 provides 600, 5407 is 800, 5408 is 1000.
Sam... I use starter solenoids in some 4x4 upgrades to remote solenoid applications with a pb start. So (big lug) #1 goes to starter, big #2 to the batt, and "s" start trigger to the push button. the "i" (ignition??) terminal is always left bare. Where is the diode in this relationship? (And to make matters more confusing... [why are solenoids always unmarked???!!!] on some constant duty installs others have done for me... they run the "i" to ground. I don't get it...) Thanks in advance. GotScout@gmail if easier.
@@samualwhittemore228 Diode do not provide the protection in voltage. What you mean with the voltage its the maximum reverse voltage the diode is built for.
Do not use a diode!! Use a 24 to 40 volt MOV! (Metal Oxide Varistor) The MOV is specifically designed to deal with spikes in current, the diode is not. The diode works, but it also alters the operating characteristics of the relay, slowing their reaction time down. The MOV does not change how the relay works, it's not polarity sensitive, and is what nearly all off the shelf lightning suppressors for home use are made with.
Is grounding the circuit through the switch shown here a uncommon way of wiring the circuit? Most times I see running power to the switch---to the solenoid and THEN to ground. There is no information given as to the # of the diode (specifications) to use either. For the uninformed, like me, what size of diode should be used on a 12 or 24 volt starter solenoid??
Don't use a diode! Use a 24 or 40 volt MOV! (Metal Oxide Varistor) It's not polarity sensitive, and is designed specifically to handle voltage spikes. For a 12 volt system you could use a 24 volt MOV, and a 40 volt MOV for a 24 volt system. The voltage spike from a relay that has been de-energized can reach 10's of thousands of volts! To install an MOV, just bridge the two terminals of the relay coil.
Not a stupid question. There are D.C. solid state relays as well as the familiar A.C. SSRs. The advantage of using mechanical relays though, is they are immune to voltage spikes and short surges of high current, but SSRs may not be so forgiving.
Hi my name is Michael and I've built me a Porsche 914 with a 427 Stroker Motor, and I've burnt 2 key switches, so a friend of mine that owns another Porsche Shop told me to put a starter relay like the Ford type, naturally I wanted the best so I went on Amazon and bought a MySpare relay 4 post they gave me to diodes one bigger and one smaller, I couldn't get it to work then I was reading the reviews, and a old farmer said that ya have to ground one of the small posts,so I've done more homework wich led me to your RU-vid, and I'm aware of better Quality Relay, and I am all about better and nothing burning up ,I run Holley Snider Fuelinjected and Msd Timing and Control, that has to go Straight to the Battery, I'm thinking perfect spot for the Diodes, also what type of Lamar or Skytech should I use Before it goes to the Stater Solinoid on the starter ,and the for post do I ground one of the small posts and still run a Diode across both small Terminals ? Aircraft stuff is the Quality I want to be at Overkill every thing no Fires no frying all my Electronics I have a lot of money in it just like Aircraft, can you help me please
And, my two cents. I see that your explanation used "Conventional Current Flow" theory - From Positive to Negative. In all reality, the negatively charged particles, the "current" will flow from ground (the air frame, effectively) through the coil, to the Positive terminal of the battery. No big deal, in that the diode is "reversed biased" across the coil, in its installation, then forwarded biased (i.e. the short ckt) when the mag field collapses. Good info though. Thanks. N-6395T
Michael Donavon Yea but if you explain it that way people will put the diode in backwards - because of it's conventional labeling. my guess is that muy mucho confusion is setting in about now for the electrical neophytes. Ha Ha ;))
You only confuse people with facts. LOL Although you are 100% correct, electron flow is usually only considered when designing, and even then not all the time. I use electron flow all the time, but then again, I'm a Ham Radio operator, and it's the best way of dealing with RF circuits. Conventional Current Flow is a hold over from a time when we didn't understand what electricity truly was, and it's relationship to the structure of the atom. But because it was in such common use, it was too difficult to suddenly tell everyone to change. It's like the VHF radios in aircraft. If only they went FM! But to change all aircraft world wide would be near impossible, like changing the concept of current flowing from positive to negative, to Negative to positive.
The Diode has a Stripe on the exterior, closer to one lead than to the other. Electrons will flow through from the side furthest from the strioe. They will NOT flow in the opposite direction. I hate Comments from people who don't know and won't learn first.
Use a 24 or 40 Volt MOV instead of a Diode! (Metal Oxide Varistor) It is not polarity sensitive, and keeps the operating characteristics of the relay (contactor) intact! What that simply means, is if a diode is used, it holds the magnetic field intact for upwards of 250 millisecond, allowing the field to collapse slower, thus reducing the voltage spike! The MOV does not slow the response time of the relay like the diode does. FYI, your common variety surge and lightning suppressor uses two 250 Volt MOV's to protect your electronics at home. Diode use for surge suppression is NOT the recommended way to address this problem of voltage spikes from relays. Use the device designed for that purpose, use a 24 or 40 Volt MOV!
@@daleyoung87 MOVs are good and they are better than a diode on their own, but if you want the best result, ie fast closing time, fast opening time, and the least amount of induced voltage, use a Diode in series with a resistor. An MOV on its own will still allow spikes of 2-3 times that of the supply voltage, much better than no protection of around 5-10 times a back emf of the supply voltage, sometimes more. For a 12v supply a diode and a series 120-150ohm resistor.
I do not understand why the diode is connected between the pos, that activates the coil, and the ignition post if the coil as it is a different circuit and would not be effected. Shouldn't the diode be in series with the positive wire that feeds the coil? My application automotive. Oh, I see you are keeping the solenoid powered by the jumper wire.
Actually 4:30 the Diode presents an OPEN Circuit to the reverse current. The open switch means that the Diode has NO connection to Ground so it cannot _"[present] a short circuit"_ to Ground nor to any other node. 4 years of it in college then I switched to Software.
Look a little closer! While I misspoke about shorting to "ground", it does indeed short the current across the coil itself, not to ground. The effect is the same - the switch does not see the reverse voltage spike. Make sense?
@@arcanondrum6543 Yes - we agree on that! While the coil is energized, the diode is reversed bias and looks like an open switch. The reason to have this diode is that when the coil is de-enrgized, the electromagnetism of the coil collapses - a strong REVERSE voltage is induced in the coil - which the diode NOW CONDUCTS - and shorts the current. This phenomenon is the whole point of this video. This diode bleeds off (shorts) the otherwise high reverse voltage that otherwise would spark across the switch.
Totally incorrect on your explanation. 1 - The diode does NOT go in series with the ground power lead. 2 - - Where did you get 100 times lager from? YES there is a large Reversed Induced Voltage (RIV). 3 - It is the RIV that you want to ground out. But the diode has to be connected in reverse bias so the collapsing field is in forward bias and grounds out.
