Using relays in parallel circuit in a motorbike. Help please.

Thread Starter

tech_guy

Joined Jun 16, 2017
7
Hi guys
I'm a noob and need help with some wiring in my motorbike. It involves a dual filament bulb and a set of horns.
About the bulb first:
The bike has two 35/35W dual filament bulbs. The one on the left has all three wires going in (high beam, low beam and ground) but there's no low beam wire to the other bulb. So when I need light from both bulbs I have to turn on the high beam which sometimes creates problems for other road users. I wish to have low beam on the right side as well. The plan is to have a branch wire from the low beam wire of the L bulb, connect it to a relay and power the low beam filament of the R bulb with a fresh line from the battery.
And now the horn.
The bike currently has a single horn which I think is rated at around 3.5 amps. It produces the old 'meep' sound which sometimes doesn't catch people's attention. I wish to replace it with a 2A+2A dual horn set using the typical relay circuit.

Please see the planned wiring diagram and suggest any changes that might be required.
wiring.JPG

I have a few doubts.

1. I'm using a single live wire and ground wire to connect both devices in a parallel circuit. Would a thick wire (like gauge 10) handle the job? Please do note that the horn circuit would only work for a short period of time and I don't know if there would be enough space for separate wires in a small 3.5Ah battery terminal.

2. How much current does a relay typically draw to turn the main circuit on? Would it affect the performance of the lender circuit in any way?

3. What would be the best way to get the supply wire from the L bulb circuit? It has a spade connector at the end. I don't have any splitter to attach to it so I'm thinking why not remove the insulation at a segment of the wire and connect from there.

4. What should be the ideal fuse rating for a circuit like this. The total load is (2x2) + 3 = 7A. The horn is rated at 2A. Is it the maximum current the horn will draw at any point in time?

5. Would grounding to the chassis give me any advantage? It's something I've never done or seen in real life. The distance from the devices to the battery is around 1m. The bike has a powder coated frame.
 

bwilliams60

Joined Nov 18, 2012
1,330
I would first watch a good video on automotive relays such as this one:
I would also look at the American Wire Gauge table and find the right sized wire for the job. 10 gauge is overkill.
An automotive relay typically draws about 100mA depending on design and manufacturer
 

Thread Starter

tech_guy

Joined Jun 16, 2017
7
I would first watch a good video on automotive relays such as this one:
I would also look at the American Wire Gauge table and find the right sized wire for the job. 10 gauge is overkill.
An automotive relay typically draws about 100mA depending on design and manufacturer
Thank you very much for the reply. I Googled a bit and landed on this page : https://www.jamestowndistributors.com/userportal/document.do?docId=1098
Based on the table at the bottom of the page I'd be fine with 12-14 gauge I guess. And 100mA additional load I think is not going to do any harm as I've seen people directly splitting the wire to power the low beams of both bulbs :rolleyes:. And they claim everything is fine.

Is my wiring diagram fine? Or do I need to change something? An expert's approval is very much necessary as this is my first electrical DIY on an automobile :)

After some pondering I've decided not to mess with factory wires. I've decided to use a wire with female and male spade connectors on the ends to extend the existing low beam wire and use the resulting joint to connect a wire to the relay. I think it'd be a lot more neat that way.
 

bwilliams60

Joined Nov 18, 2012
1,330
#12 has provided you with a much improved drawing. I would suggest you look at some weatherproof connectors such as weatherpak, metripak or deutsch. The latter is used in aerospace as well as the automotive industry. Both are readily available.
 

Thread Starter

tech_guy

Joined Jun 16, 2017
7
Gosh that drawing is hard to read, but it's correct.
Consider this style:
View attachment 129696
Thank you very much. Your diagram is much better. I was worried about my post being too silly compared to the super advanced topics here. Glad to know I managed to complicate it:D.

I follow the SWG and have some 1.5 sqmm wire (between gauge 14 & 16 I guess) lying around. Would it do the job for 7A load, 10A fuse circuit or do I need to go for a thicker one? The next size available is 2.5 sqmm.

#12 has provided you with a much improved drawing. I would suggest you look at some weatherproof connectors such as weatherpak, metripak or deutsch. The latter is used in aerospace as well as the automotive industry. Both are readily available.
Thanks a lot. I have some insulated connectors but haven't heard about the weatherproof ones. Will look for them on Amazon.
 

#12

Joined Nov 30, 2010
18,210
7A load, 10A fuse
That'll work.

Just remember, the fuse protects the wire. You always size the wire for the fuse, or the fuse for the wire. Of course you size both of them for the load, but the really important thing is, if something goes wrong, the wire must not be allowed to burst into flames, and you don't control that from the load end. You control that at the fuse end.
 

Thread Starter

tech_guy

Joined Jun 16, 2017
7
That'll work.

Just remember, the fuse protects the wire. You always size the wire for the fuse, or the fuse for the wire. Of course you size both of them for the load, but the really important thing is, if something goes wrong, the wire must not be allowed to burst into flames, and you don't control that from the load end. You control that at the fuse end.
Thanks that basically clears all my doubts. I'll do the wiring in a couple days. Please don't close this thread for a week as I may need help if I run into something complicated.
 

Thread Starter

tech_guy

Joined Jun 16, 2017
7
Hi I've completed the wiring and there's good and bad news. There ain't an inch of spare space near the battery so had to say goodbye to the mini fusebox. Using an 'inline fuse holder' now. It's working but I have no idea about its reliability. The glass fuse inside it is 15A.

Bought a new 3 pin HS1 socket and connected to relay. Both headlamps have low beam now . Thanks guys.

Now the bad news. The horn. There isn't enough space for two horns. The fairing is very close to the bike's body. I had to join the brackets/clamps into a 'V' shape and connect both horns to that. The horns are producing a scratchy sound :(. The sound is normal when they're operated individually on the same bracket. So the issue might be using the same bracket for both horns? If yes is there any workaround (or even horns that don't vibrate so much) other than fitting them separately? Please share your thoughts.
 

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Thread Starter

tech_guy

Joined Jun 16, 2017
7
OK so I can now confirm that the issue is with both horns being mounted on one clamp. When the horns were taken off the clamp they did produce the right sound. I'm yet to find a solution to mount them on the same clamp though. Don't know if some dampening material would work.
 

#12

Joined Nov 30, 2010
18,210
You depending on the mounting bracket for the ground?
Not a good idea. Make a redundant ground wire that doesn't wobble because of vibration.
 

Thread Starter

tech_guy

Joined Jun 16, 2017
7
You depending on the mounting bracket for the ground?
Not a good idea. Make a redundant ground wire that doesn't wobble because of vibration.
Hi
No I have a wire running from the negative terminal. Interestingly I didn't see a chassis ground anywhere on the bike.

The problem is the lack of space. So I have mounted both horns on the same bracket by extending it. It's producing a very unpleasant sound. The horns when mounted independently sounds nice. The problem is that there just isn't enough space or the right spot for mounting them independently. I'm looking for ways to prevent the bracket from vibrating so much. Possible? Another solution would be to look for some other type of bracket.
 
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