Relay with or w/o diode?

[FJR Rich]

Hello,

Is there a rule/guideline when using a relay with a diode and without one? I understand the purpose of the diode to catch/prevent voltage spikes, but when looking at some posts, I don't see where the diode called out. Some actually call out a Radio Shack auto relay which doesn't have a diode.

My plan is to install the following through a relay switched fuse block:

- driving lights

- heated grips

- GPS power

Thanks,

Rich

 

[Geezer]

Hello,
Is there a rule/guideline when using a relay with a diode and without one? I understand the purpose of the diode to catch/prevent voltage spikes, but when looking at some posts, I don't see where the diode called out. Some actually call out a Radio Shack auto relay which doesn't have a diode.

My plan is to install the following through a relay switched fuse block:

- driving lights

- heated grips

- GPS power

Thanks,

Rich

I don't see any need for a diode, and it's probably just one more place for something to go wrong. A standard 12V automotive relay works fine and is readily available, not only for the initial install but also for replacement in the field.

I do recommend that you seal up the seams in the auto relay to keep moisture out.

 

[ionbeam]

Most AUTOMOTIVE relays are already weather sealed but you can 'belt and suspenders' seal it as you see fit. Unlike standard grade relays, automotive relays are weather sealed but more importantly, they are constructed so that vibration and shock will not cause the contacts to bounce and intermittently open.

I would recommend using a diode on any relay that is switched by a wire that goes directly to the ECU. I would also recommend using a diode on all relays that share a common +12 volt line with radio or entertainment units.

Use any Radio Shack diode between 1N4001 and 1N4005, these diodes are quite robust and should never create or cause a problem. Install the diode with the band end on the +12 volt wire and the other end going to ground.

Using a diode on any circuit connected to sensitive electronics is a layer of protection that is cheap and easy. In automotive/motorcycle applications you can usually get away without a diode, but these days with ECUs, ABS ECUs and other sensitive electronics it sure can’t hurt to improve protection.

 

[RonBB]

Ions got it right. Totally agree.

 

[0Face]

+1 for Ion.

Check out Fuzeblocks.com for a good fuseblock.

I'm not affiliated.

 

[BrunDog]

Most AUTOMOTIVE relays are already weather sealed but you can 'belt and suspenders' seal it as you see fit. Unlike standard grade relays, automotive relays are weather sealed but more importantly, they are constructed so that vibration and shock will not cause the contacts to bounce and intermittently open.
I would recommend using a diode on any relay that is switched by a wire that goes directly to the ECU. I would also recommend using a diode on all relays that share a common +12 volt line with radio or entertainment units.

Use any Radio Shack diode between 1N4001 and 1N4005, these diodes are quite robust and should never create or cause a problem. Install the diode with the band end on the +12 volt wire and the other end going to ground.

Using a diode on any circuit connected to sensitive electronics is a layer of protection that is cheap and easy. In automotive/motorcycle applications you can usually get away without a diode, but these days with ECUs, ABS ECUs and other sensitive electronics it sure can’t hurt to improve protection.

I usually don't reply to these because ion always fills in the gaps... He did, but there are a couple of nooks and crannies I might spackle and sand...

Relays are solenoids, and solenoids are coils, and coils are inductors. When a relay is powered, it stores a potential energy in it (which it takes from the power source in the form of an increased inrush current). When the power source is removed, that stored energy has to go somewhere, and on its own will induce a reverse current into the power supply. In a power switch application, like that of say, the horn switch, that energy cannot be dumped back to the switch because it is open, and so it dissipates back into the coils resistance (which results in heat, but not much). On the other hand, when a solid state switch, such as a transistor switches power to the relay, the released energy will try to flow backwards across the transistor, which could overload (read: fry) it. That is why ion says to use a diode on signals from the ECU - they are solid state switches. The diode forces the current back into the coil.

So, while it would never hurt to put a diode on everything, you only really need it on those which are powered by a solid state switch. A toggle switch, pushbutton, or ignition switch don't qualify, but the ECU certainly does.

Sorry if that's more than you care to know!

-BD

 

[ionbeam]

...I would recommend using a diode on any relay that is switched by a wire that goes directly to the ECU. ...

I usually don't reply to these because ion always fills in the gaps... He did, but there are a couple of nooks and crannies I might spackle and sand...

BD, thanks for filling in the details! I didn't go there because FJR Rich said: "I understand the purpose of the diode to catch/prevent voltage spikes, but when looking at some posts, I don't see where the diode called out." After being hammered recently for TMI in another thread I was being less loquacious than normal This can't last long... :lol:

 

[rushes]

...I would recommend using a diode on any relay that is switched by a wire that goes directly to the ECU. ...

I usually don't reply to these because ion always fills in the gaps... He did, but there are a couple of nooks and crannies I might spackle and sand...

BD, thanks for filling in the details! I didn't go there because FJR Rich said: "I understand the purpose of the diode to catch/prevent voltage spikes, but when looking at some posts, I don't see where the diode called out." After being hammered recently for TMI in another thread I was being less loquacious than normal This can't last long... :lol:

Hell no!

Spill it out!

Let the rest of us sift through! :thumbsup:

I did hafta look up "loquacious" tho.

But see, I'm learnin' new stuff!

Thanks! :clapping:

 

[Fred W]

After being hammered recently for TMI in another thread I was being less loquacious than normal This can't last long... :lol:

Yes, I'd say that should be short lived. Thank goodness...

 

[FJR Rich]

Thanks ionbeam for the explanation. So whenever a "use relay" is stated, it is implied to use a relay with a diode (either built-in or add-on). I do have the RadioShack Auto relay, I just need to buy the diode now.

OFace: Thanks for the Fuzeblocks info. I do know about them but already have an auto relay and regular fuse block to use. Although I probably will use a Fuzblock on my other bike.

Thanks again everyone!

Rich

 

[FJR Rich]

BrunDog, thanks for the explanation. Although I knew it at a high level, i.e. spikes, I appreciate the more detailed info.

NOTE: I didn't see your response earlier except as a partial quote in ionbeam's reponse and didn't know why. By chance I pulled down the "Options" menu and saw that my display option was set at "Outline". Once I changed it to "Standard" I saw your full response. Sorry about that! I also see Fred W or rushes responses now too. Yet another thing I learned today!

Thanks again!

Rich

 

[SkooterG]

Man, I can just feel the electro-geek love going on in this thread!

 

[Ignacio]

Man, I can just feel the electro-geek love going on in this thread!

Ditto. I was aroused and scared at the same time. Something tingling and I think it's more than just 12 volts DC.

If anything it makes me wish I'd paid more attention in the one electronics class I took in college.

 

[ionbeam]

Don't mess with us electrical guys or you B toast.

 

[ngarider]

Just don't decide to wire it up after a few pints, hook it up backwards, and let the smoke out. TRUST me.

 

[charismaticmegafauna]

Man, I can just feel the electro-geek love going on in this thread!

Ditto. I was aroused and scared at the same time. Something tingling and I think it's more than just 12 volts DC.

If anything it makes me wish I'd paid more attention in the one electronics class I took in college.

And that's just the beginning.....

There's magnetism and electromagnetic lines of force that want to make those rowdy outer valence electrons make the jump -- I tell ya', it's sooo exciting....!