Why are relay pins numbered like that?

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Steve answers the question ‘Why are relay terminals numbered 30, 85, 86, 87?’ He also has a funny way to remember them. Plus: a quick demonstration on how they work.

Amazon Affiliate link to the OTC relay pliers:

If you click the link, it supports the channel, but won’t cost you more.

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It is German automotive wiring system. 15 is hot with ignition on, 30 is hot at all times, 31 is always grounded and the wires are brown.

albatross
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I've been on the planet for 60 years and I've been using relays for over 50 of those years. In all that time I didn't know where the numbers came from, until now. Thanks for enlightening me!

nicholashacking
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Great video. I have taught this class many times. One little but important thing was left out though.
Some relays have a diode rather than a resistor. The diode protects other devices on the circuit that may contain a microcontroller (computer). While a relay with a diode will work in any circuit it is critical to only replace a diode relay with another of the same type.
Practical example- A relay had been replaced on the air conditioner of an off-road construction vehicle. The vehicle's engine began stalling intermittently. Diagnostics found no fault with the engine but an operator noticed that the engine stalled when he changed the air conditioner setting repeatedly. A resistor relay had been installed in place of a diode relay and the small voltage spike from the relay would sometimes cause the ECU to reset, stalling the engine.

Miata
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On most, but not all, Bosch relays, 85 and 86 are interchangeable, meaning you can connect them in reverse order with no problems. Some of the older ones use a clamping diode instead of the resistor to control the flyback voltage, thus requiring wiring in the correct polarity.

rampy
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People are gonna flame me for this correction: Voltage and Amperage are measurement units. Basically, you use Volts to measure Electrical Tension and Amperes measure Electrical current. Didn't mean to sound pedantic, just to share information, just like @Tool Demos did. Great info on the realy numbering! Enjoyed it.

IscuAndrei
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Close to correct, but not quite. Yes, pin 85 is ground (-) and pin 86 is the positive (+) to the energizing coil to "turn on" and close the relay. But, pin 30 is usually used as the supply source (12v + or Ground -) and most circuits use pin 87 as the switched (NO Normally Open) item. Pin 87a is connected to pin 30 when the relay is off or (NC Normally Closed). [Note: Pin 87a (NC Normally Closed) may be missing on some relays]

ajseusa
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10 year old me, with Walkman parts all over the table, would be overjoyed to learn that 30 years in the future I can watch on-demand videos of people pulling things apart to learn how they work. Thanks for the education!

JamieBainbridge
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You have a brilliant approach to explaining why numbers like 87 are assigned to the pin numbers of relays using the DIN system, BUT, for dummies like me, you didn't actually explain why they didn't use "123" (as you mentioned) instead. I think you suggested they were just numbering circuits as they went along and when they got to relays, they had a number left to use like 87. I would like more light shed on that, like, what came before 87, and after, and the most important question. WHY?

claylong
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WOW! After more than 50 years working with electronics, and DIYing my cars, I still only knew about the inscrutable and unexplained numbers on the relays. This is my eye=opener for the week... maybe month. Subscribing, of course.

flagmichael
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All is explained in DIN 72552, and there's even a Wikipedia page for it.

ehsnils
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Thank you!!! I can now understand how important these little relays are for automotive purposes. A thinner wire(s) can be threaded throughout the vehicle instead of thicker wire to basically do the exact same thing, like running a fuel pump. It's cheaper to use relays and saves weight. Amazing engineering.

MustangFord
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As a matter of fact, I wasn't wondering why those numbers.... BUT NOW THAT YOU BROUGHT IT UP...!

BlackEpyon
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Every day you learn something new from the internet. I have played with those relays for decades and didn't know about the numbering. That Back To The Future memorizing hack was cool. In my native language, Finnish, there's one nice memorizing thing. Black is "musta" and red is "punainen". So the color names begin with the same letters as plus and minus. Easy to remember for beginners.

ohmp
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Had a car that the horn relay went out. New one was a whopping $80!
So I bought a fog light relay and wired it in. That relay was $10.

Worked like a champ too.
Probably better since it could handle more amperage than the OEM one.

crazysquirrel
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Haven’t watched the video yet but I’m pretty sure it’s a German wiring standard because that’s all I have worked on since 1992 so I see those pins in my sleep. I remember in high school my sisters BMW wouldn’t start sometimes it was a interment problem that I found was a short on the trigger wire. It was the fuel pump relay so I made a jumper wire and used a paint marker to mark the 2 terminals she needed to plug into. It got her by for a few months until I was able to get a service manual for the car and then I was able to use the schematic to diagnose it. Great video though.

rbmwiv
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In the UK we call the diodes back or reverse emf protection diodes, also relays with this protection usually show the diode symbol on the relay along with the connection diagram.

altvamp
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The reason for a diode suppressor relay is to protect the circuit from the high voltage field that is present when a coil is shut down. It protects electronics from a voltage spike like a one way check valve.

billmoran
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Late 1960's onwards Skoda cars, Jawa & CZ motorcycles use the DIN automotive terminal coding.

30 = Battery live.
15 = Horn switch & flasher can power feed.
54 = ignition system power.
86 = Tail & parking lights.
87 = headlight switch power feed.

CZtuner
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Interesting video! Also worth mentioning is that some of these relays have an internal diode mounted parallel on the contacts of the coil. A so called freewheeling or flyback diode. This is to reduce inductive voltages when the relay is turned off and so preventing to do damage to sensitive components in the system. High quality automotive relays also come with sheelding on the inside, to block off RF signals produced by the coil when switching. Also the closing/opening from the contacts cause 'spikes' in the RF spectrum which can cause interference. At the same time, the inside is protected from RF signals coming into the relay. Years ago I had quite some issues with VHF radiotranceivers that interferred with relays. For instance, when the PTT button was pressed and the direction indicator was on, the blinking speed of the indicator doubled. Another one... airbags popping out when the radio was operated. Therefore, we always did a small test. We took the car for a spin at a low speed and crossed our fingers. Fortunately, I never had an airbag going off, but I know some cases...

PhG
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A lot of this information is misleading. There are 2 different kind of shunts on relays. The rare diode type and the far more common resistor type. The resistor type doesnt care if 85 or 86 coil termainals are positive or negative. Because you'll run into a resistor type 500x before you run into a diode type, its basically assumed that all relats have resistor shunts. (Thats the component in the relay that prevents large inductive flyback voltages on the coil control leads.). 30 is not always connected to power. There are a lot of cases where this is true. For example, window lift motors and door lock actuators commonly use 2 relays. 85 and 87a on both are connected to ground. 87 is connected to positive, and 30 on each relay is connected to each motor lead. At rest, both relays ground both of the motor leads. This acts as a brake on the motor if not anything else. When you apply positive to 86 on one relay at a time, you will make the motor spin one way or the other depending on which relay is being energized. If both are energized at the same time, the motor does nothing because both leads are shorted together while tied to positive. So, no.... You are providing a lot of misleading information...

85 and 86 are the coil. Polarity is not specific except in the very rare case that you have a diode type shunted relay.

30 is common, 87a is normally closed (87a is connected to 30 when relay is not powered.) And 87 is normally open. (When the coil is powered, the relay will connect 30 to 87)

Because 30, 87a and 87 are simply switch contacts, they have no polarity and are not polarity specific. Just like any other toggle switch in existance.

If you're going to put information out in the world to educate people, make sure you're not feeding them bullshit.

gadgetdeez