Diodes?

[zeltus]

After my starter motor went berserk and shorted out a relay I had put in for my aux lights, I got to thinking...

The symptom (upon fitting a new motor from that nice German chap on eBay DE) was a nasty buzzing noise from the relay/fuse box area, the rev counter wavering unhappily at 2,000rpm and dull gleams from the dash lights. And of course, no power to the starter switch. Very scary, but after ripping out the relay, all came back to life. Serves me right for installing the almost-obligatory foglights on my 2002 GSA I s'pose!

But anyway, my question is, is there some sort of diode I can buy and put in along with a new relay, that'll stop the magic smoke going the wrong way down the wrong wire? Or should I just use a lower amp fuse? I am quite happy playing around with 12v non-CANBUS electrics up to a point and am keen to build protected circuits as and when I can.

As ever, all help gratefully received.

Bill

 

[Ian J Hartley]

It's a bit difficult getting involved in your home made electrical modifications.

But as a general rule, I would use a relay of 30amps or 40amps, to control lights.sounds a bit over kill on a circuit which probably only draws about 8 amps, but the internal contacts of the relay are more robust and can take the switching with minimal carbon build up. If you use a lower rated relay, there is a possibility of the contacts actually welding closed.

Some relays have diodes built in across the coil to prevent reverse voltage spikes, when the relay de-energises.

Use wire of a higher grade for your electrical mods than you comfortably need within reason of course.

Make sure every circuit is protected by a fuse of the correct rating for your circuit. This is the weak link that you want to protect everything from melting if you have a fault.

It is probably OK to use the existing wiring to Control your circuits, ie switching relays etc, but not to power them.

Lastly. Unless you know the original bike wiring can take the load, and that is rare. Manufactures add in tolerance for age and deteriation, not for after market mods. Then lay in new wire from the battery to power your circuits.

If you want to fit a diode in the power circuit then that diode is going to need to be at least of the same current rating, or higher than the load. I'm at a loss to understand why you would need to do that. When if your wiring modifications are done correctly there is no need.

 

[zeltus]

Ta for that... most of which I already do

I do need to double check the amperage rating of the relays... I guess I just used bog-standard ones form the local motor bits shop.

I only asked about the diode bit because, as you say, some relays have them internally. Also, I below my sidestand down detector circuit thingy has a diode in it. Somewhere. According to the wiring diagram.

My main problem is that one relay I carefully placed under the petrol tank. Where it couldn't be got at by anything* without removing the tank first. Idiot is a description that springs to mind of the fule wot done that. Looking in the mirror, I see the description is apt.

*anything that is, except the salt-infested road spray that splattered it every time it rained. It didn't seem to like that much. I specialise in lurning the hard way, each and every time.


Bill