Indicator Relay Number 3!

[fry61]

The lamp & indicators will work together at the wrong frequency & lower brilliance if all O.K when fault present no indicators & test lamp should be at full 12volt brilliance as long as fault is present,assuming dead short to earth;which it appears to be as you are blowing big fuses. HTH

[Guest HS88]

Thanks. So at least I might be able to use my indications in some fashion cheers for the tip. On a search for a 50w lamp tomorrow morning.

[Guest HS88]

I've probably got a few spare if 21w is sufficient...

Cheers.

[sj-bradley]

Any 12 volt bulb will do as it will drop the 12 volts and light up if there is a dead short in the circuit.

 

If you use a high wattage, you will also be putting excessive current down the wires so a lower wattage test lamp is better.

 

All it has to do is light up.

 

Simon.

[Guest HS88]

Brilliant. Thank you Simon.

 

Put my mind at ease

[sj-bradley]

Oh, and test the lamp before you do so on a circuit to make sure it isn't blown and actually works !

 

(D'Oh obvious moment there !)

 

(Light bulb moment)

 

Simon.

[fry61]

Any 12 volt bulb will do as it will drop the 12 volts and light up if there is a dead short in the circuit.

 

If you use a high wattage, you will also be putting excessive current down the wires so a lower wattage test lamp is better.

 

All it has to do is light up.

 

Simon.

Sorry Simon you're wrong --- Two equal resistors in series will halve the current, that's why I suggested high value test lamp -- indicators are 21 X 2 + 5 watts per side --so in this test I would use a head light or spotlight rated at 55/60 watts. And when short is found current will still not exceed "normal load" by more than an amp. Using a low value test lamp will not allow sufficient current for the relay to operate.

[Guest HS88]

ok spare headlamp not indicator it is then..

[sj-bradley]

I agree that two equal value resistors will halve the current.

 

Except for the fact that if the OP is blowing 30 amp fuses, I.e 360 Watts of power then the unknown short is not going to be equal by any means what so ever. It is also highly unlikely that the indicator circuits cabling can handle that much current without burning out and causing a possible fire or other weak spot which will cause problems later on.

 

So if there is a dead short, any lamp will do and the lower the wattage, the less current will flow through the short (and cables) which should help prevent the cables from melting.

 

I would actually prefer to use some form of multi tester to track down the problem, but then that's me. In a pinch a low wattage bulb will suffice.

 

Relays will operate on quite low currents as the cabling would be suitable for around 5 amps or so. The other side of the relay is meant to switch the higher currents required for the headlights and the cables are noticeably thicker in order to cope with the demand.

 

I hope I have clarified what I meant in my original post.

 

Thanks,

Simon.

[fry61]

Sorry again Simon, my test set-up will limit the amperage to 5A no matter what value the fault resistance is.

[sj-bradley]

I'd agree with your limit. But why not use a smaller bulb and halve the current again?

 

If the cable is only rated to 5 amps, why max it out? The drain on the battery would also be less as well.

 

Simon.

[fry61]

Think I'll finish here by agreeing, my post laid out what I did for a similar fault; your way may be equaly valid.

[Grim]

i think florin's point is that a higher wattage bulb will give more normal non-fault operation (lower resistance and dim) with a more noticeable faulty operation. Two bulbs of the same resistance in series would give two dim bulbs, not very good for indicating.

 

Is that right?

[Guest HS88]

I've just fitted a headlamp bulb inline before the relay. It flashes with the left/right/hazards.

 

Haven't managed to get the left indicator to short out and only the headlamp flash but I assume this will happen soon.

 

At least for now it can indicate (although at a slightly faster rate) and if the left shorts I will still be able to indicate right since the internal headlamp will flash.

 

Thanks for all the advice. Hopefully I'll find my short!