Coil relay mod with a twist

[MrZig]

I know all about the coil relay mod and it seems like quite the good idea, however people have expressed conscerns about the relay quitting and being left stranded.

Some people have put in extra switches, or used the same connectors so they could simply reconnect the old wire. However, all of that takes extra wiring and effort if the relay does break.

Here's my proposition: What if you didn't cut the main +12VDC wire going into the coils, but simply spliced into it with the +12VDC from the relay?

I'm pretty good at most 12VDC applications, however I don't know what happens if you have two positives going into the same wire. It shouldn't double the voltage, but keep it constant at battery output, right?

This way you would have an automatic failsafe if the relay failed, since all you did is splice into it, the original wiring takes over.

[Russ' GS1000E]

Sounds sound to me,
but then I haven't been able to find a good drawing of the Coil Relay Mod.

[DMB]

but then I haven't been able to find a good drawing of the Coil Relay Mod.

This is the diagram that I used. It's from 80GS750. Just about the simplest diagram, and all that I really needed.




Here is a Link to the diagram and the original thread

Also, BikeCliff's site had a ton of info on this mod including a few more advanced schematics. Located here.

[82Shafty]

I certainly am not an electrical engineer, I believe there may be a few on here, but my assumption is that the 1.5V loss at the coils from the original wire would get back fed the additional B+ from the new spliced source wire.

One of my original coil wires is tap'd up and the other is used to feed the relay. All three of my switches produced the standard half of a volt drop, hence the relay mod.

I believe that if you were truly concerned, you could opt for something like a fuel pump relay, something that is normally on for many, many miles. I also believe there are some solid state controls out there that use less to power up and waste less through the points style connection, of course, at a greater cost.

Maybe someone with a MSEE will come along and fill in the details.

[posplayr]

I kinda remembered an issue with doing teh "twist"

I then went and asked someone what happens when you wire the Relay output to the control line input (I had the same idea at one point). The problem is that the relay will latch and never open again.

The output is tied to the input and so the input can't drop again.

The solution is to put in a diode between the control input and the relay output but then you drop about 1 volt.

Better solution is to carry a spare relay or a jumper to direct connect the harness.

Pos MSEE

[reddirtrider]

I then went and asked someone what happens when you wire the Relay output to the control line input (I had the same idea at one point). The problem is that the relay will latch and never open again.

The output is tied to the input and so the input can't drop again.

The solution is to put in a diode between the control input and the relay output but then you drop about 1 volt.

Better solution is to carry a spare relay or a jumper to direct connect the harness.

Pos MSEE

You are correct on all counts.

[SqDancerLynn1]

I put a relay on my 850 simillar idea, only I used relay to power the fuse block to eliminate a voltage loss. Relay was a 35A weather pack (sealed) with mounting bracket. A bit overkill, Probably cost me $45 don't remember, was from Painless Wiring Co.

[salty_monk]

Just carry a short connector with spades on the end as "jumper cable". If the relay goes out, toss it & hook up the jumper cable & you're back to "as original".
(connect 86 to 87 directly).

If the voltage drop is so serious "as original" that it won't run you can "hotwire" 30 to 87 & off you go, just don't leave it hooked up when you're not riding or you'll burn out your coils.

It's not a lot of effort, you can tape or cable tie it anywhere on the frame ready for use etc...

Dan

[BlackStar]

I used a relay socket, and carry a spare relay under the seat. Relay failures can be minimzed if it is not hard mounted. Run a tie wrap through the mounting tab hole and loosely mount it if you have to. Mine is not actually mounted other than by the heavy wires coming out of the socket. Vibration is what kills these relays. Vibration is what we use to qualify relays for avaition, that and thermal cycles. The weak ones typically fail vibration test.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=330-074

[salty_monk]

I used a socket & carry a spare relay too but the spare might also be killed by vibration even though it's not hooked up... the jumper cable is the only 100% sure failsafe. You can just jump across connectors in the socket.

Dan

[posplayr]

a Caveat

the jumper cable is the only 100% sure failsafe

Unless the original problem that caused u to do the mod in the first place still exists. Hopefully you can still limp home.

Aks me how I know .

Pos

[spyug]

I had been thinking off and on about this mod for over a year and finally got around to do it a couple of weekends back. In my research, I must have missed the discussions about failed relays. If I'd have known I might not have done it mainly because I endured several years of electrical issues and got stranded at least 5 times with the old virago I had. I also didn't consider the mounting and have it stuffed up under the tank close to the coils and zip tied to the frame.

Last night I made up the emergency jumper as recommended by Salty and on the weekend I'm going to get another relay and a socket and wire it back to under the seat for ease of replacement. I'll carry the 2nd relay as spare.

I still think the mod is great and I really notice a difference in start and running but now I'm going to have a niggling worry in the back of my mind everytime I ride.

Too bad you can't get an industrial strength relay. I kinda like the idea of fix it and forget it

Well maybe someday.

Cheers all,
Spyug.

[salty_monk]

Unless the original problem that caused u to do the mod in the first place still exists. Hopefully you can still limp home.

Aks me how I know .

Pos

If the original problem still exists it's still not an issue.

As I stated above connect 30 to 87 in the relay socket & you basically hotwire the battery directly to the coils. It will be like having the relay latched permanently.

That will get you home or to a store for a new relay, just remember to break the connection whenever you stop or you will burn out your coils....

As you can see, it really is a true failsafe to carry a jumper cable.

Dan

[MrZig]

What about using a starter relay? Sure it's not cheap, but finding one at a junkyard wouldn't be bad, plus it has to be a lot more reliable then a normal bosch relay, right?

[Steve]

Starter relays are meant to carry high current for a short amount of time.
The typical Bosch-type fog light relay will carry a modest amount of current (far more than the coils require) virtually indefinitely.
It's not just how much current a relay can handle that matters, you also need to consider how long it's able to stay energized.

.