2 relays share the same ground ?

[Guest]

Hi,

I did the ignition coil relay modification some time ago, it was a very smart thing to do. To make sure that the charging circuit is monitored well, I installed a volt meter, also using a relay.

Both ignition coil and volt meter coil are set up the same way:

30: directly from battery
87: to device (coil or volt meter)
85: ground
86: signal (both taken from the existing wiring diagram O/W, switched power wire)

can the two grounds (85) from both relays be linked ?
meaning, on one relay the 85 is connected to the frame AND to the port 85 of the other relay (so that only 1 ground connection was needed)...

Is that OK ? what if I would link the 85 of one relay to the 86 of the other relay ?

The reason why I ask: went for a ride yesterday (before volt meter relay was inserted) and everything was fine. Now, after the volt meter relay installation, the damn thing will not start anymore (starter motor is turning ok, light are working, choke ok, petcock set on PRIME,...)

[BassCliff]

Hi,

Are you getting spark? You may have accidentally disconnected something from the coil relay while you were installing the volt meter relay.

A ground is a ground. I can't see where running a ground wire from 85 to 85 to frame ground would be a problem. Re-check all your connections on the original coil relay mod.


Thank you for your indulgence,

BassCliff

[OldVet66]

Make sure you use star washers between the ground lugs and your ground surface to insure a good ground.

[posplayr]

what those guys said, and you don't need a separate relay if you are just trying to create a switch sense point for a Honda 6 wire R/R. Use the same relay output.

[gert du prez]

found the problem, new question

Hi,

I ran the power from the battery to the coil relay using an 10 amp inline fuse.
While installing the volt meter relay (without inline fuse) apparently the fuse got blown (so no spark)...

Now I run the coil relay without inline fuse (always hot relay) and the volt meter relay with one (also always a hot relay, but fused)

what's the consequence of running the coil relay without inline fuse ? dangerous ?

[BassCliff]

Hi,

The inline fuse for the coil relay should be the same amperage as the bike's main ignition fuse. Is that 15 amps on your bike? Running without the fuse just means there is no protection. Any over-voltage (or over-amperage) will be passed on down the circuit. Instead of blowing the fuse you might melt your relay or coils.

Thank you for your indulgence,

BassCliff

[Matchless]

In addition to what BassCliff said, the fuse is your purpose made weak spot, that disconnects at the specified current before your wiring starts melting. Meaning it is the safeguard that prevents you burning up your wiring harness as well!

The fuse must always be as close to the battery or supply as is possible.

Never bypass a fuse, never bridge out a fuse, never fit a higher rated fuse!! This goes for bikes, cars, home wiring and every electric or electronic circuit that use fuses or should be using fuses.

Just imagine a smouldering wire, under 22 liters of fuel, between your legs, being fanned by a strong wind......

[BassCliff]

Just imagine a smouldering wire, under 22 liters of fuel, between your legs, being fanned by a strong wind......

Thank you for your indulgence,

BassCliff

[gert du prez]

I think I understood the picture

Hi,

15 amps for the main fuse,
10 amps for the ignition...

and I think I understood the picture...

any ideas on how this fuse got blown ?

[posplayr]

Hi,

15 amps for the main fuse,
10 amps for the ignition...

and I think I understood the picture...

any ideas on how this fuse got blown ?

Did you do the install with the battery disconnected? If not and you touched the live wire to a ground it could have easily shorted.

Do you have the fly back diodes installed in your relays. It is usually a good idea.

[gert du prez]

now you got my attention !
what's a flyback diode ?

it took me more than 1 shop to find an inline fuse, so please don't send me out looking for very sofisticated relays ! I use the simple 4-connection ones...

[Steve]

Any over-voltage (or over-amperage) will be passed on down the circuit. Instead of blowing the fuse you might melt your relay or coils.

Sorry, but it's time to quench a common misconception (or two).

First, over voltage will not blow a fuse.

Second, a fuse is not there to protect the relay or the coils.
It is there to protect the wiring harness between the battery and the fuse in case the relay or coils go bad.

For all practical purposes, the voltage remains rather constant, or, at least, in a very narrow range (12-14 volts). Nothing there will surge high to blow a fuse. The fuse blows because the resistance has been lowered in the circuit, allowing more current to flow. If the current is more than the fuse is designed to handle, it melts to protect the wiring. Let's face it, the coils are already bad, that's what caused the increase in current that blew the fuse. In other words, the fuse did not protect the coils.

.

[bakalorz]

now you got my attention !
what's a flyback diode ?

it took me more than 1 shop to find an inline fuse, so please don't send me out looking for very sofisticated relays ! I use the simple 4-connection ones...

Ignore the part about the flyback diode, it's bad advice.

When you stop providing the drive signal to the relay, the sudden drop in current and the inductance of the relay coil cause it to generate a very brief but relatively high voltage pulse in the circuitry providing this signal. A flyback diode is a diode added in parallel to the relay coil to short out this pulse.

Switches are generally immune to the pulse, but it could damage transistors if they were controlling the relay coil.

Your coil is controlled by the switch that provides power to the bike, it is not a problem.

I don't know why the heck POS even brought it up, ignore it.