Indicator Relay Number 3!

[Guest HS88]

I'm on relay number 3 now. I have fitted a fuse inline before the relay to stop it being burnt out.

 

I have since gone through several relays and cannot determine what is causing it!!

 

Would the most obviously answer be a loose connection somewhere? Or has anybody had this problem and found the cause(s)???

 

Thanks!

[edbond]

What wattage are the bulbs in the indicators and what's the relay rated for? (maybe a red herring, but where I would look first!)

[Guest HS88]

thanks. I have got 4 bulbs in total and I cant recall the numbers off the top of my head, but when I worked out the totals I'm sure they were less than the fuse and relay... I will check again!!

[sj-bradley]

The relay is obviously taking more through the coil than it's rated for so something is providing a short to ground somewhere.

 

I would take all the bulbs out first. You could also test the wires with the bulbs out for any low resistance as they should be open circuit.

 

Just a thought, does it blow the relay on left or right turn? Do the bulbs flash at the same rate on left and right? I think the slower side is the problem side as high resistance (no bulb) means low current and the relay flashes faster.

 

Simon.

[Guest HS88]

as far as I can recall from earlier both sides seemed ok and flashed at the same rate, and the first time tonight I think the Hazards caused the problem. Then again they broke but this was obviously one side or the other.

 

I will try taking all of the bulbs out, thanks for that idea.

 

I'll take a look around all of the indicator wires, for those in use and those not. (side repeaters from the original sierra)

 

Cheers guys

[Grim]

i don't know if the same applies to indicator relays as regular relays, but i have had a regular relay appear to work and then burnt out ofter a short period of time, due to not being wired up correctly. Make sure the relay terminals correspond to the correct wire!

[Guest HS88]

Thanks. I'll check although the relay is connected to the original sierra 3-pin socket.

 

It's odd how it can work then stop working which leads me to believe it could be a loose wire shorting out somewhere..

[fry61]

You only have 12/14 volts available so can't see how it's possible to apply too much voltage to a 12 volt coil; same with amps the resistance of the coil is the limiting factor not the load connected. A fuse can be over-loaded because its resistance is very low so more current can flow than its design load; a coil will be over-loaded by over voltage ,current is limited by its very high resistance, old age & a break-down of internal insulation can lower resistance leading to higher current & burn-out.

 

This lesson was brought to you by the Hoodyversity, others may dis-agree.

[Longboarder]

Well you knew it would be me! What happens if you connect up an indicator relay with 49 to 12v, 49a to earth and 31 to earth. ie. simulating a total short to earth. Would anything cook?

ps I don't know and don't have a spare indicator relay to test this.

 

Nigel

[fry61]

Post a diagram please Nigel, you know I can't work it out without a pencil.

[sj-bradley]

I would always be cautious about connecting a coil straight across a voltage supply as it is effectively a dead short across the supply. I would always put a rated fuse in there.

 

Coils only really have impedance in A.C circuits but the DC resistance (which you can measure) would give you a rating for how much current the relay will draw.

 

I.e a 6 ohm relay will draw 2 amps typical on a 12v supply which means it will also dissipate 24 Watts so needs to be rated for that.

(It will also get quite warm).

 

I suspect that the internal resistance of the relay coil will be much higher than that and consequently the power dissipated much lower.

 

(Ohm's law - just recently told to me as Van In Road and also Pig In Van which I'd never heard before ! )

 

The relay contacts of course switch a different circuit and are usually rated much higher.

[fry61]

Hope this is not going towards an LED situation. Coil is the load,so no dead short, fuse has little/no resistance so same applied voltage to coil; coil will have resistance in hundreds of ohms so fuse unlikely to be small enougth to protect against overload.

 

Good nemonics Simon but to make sense needs = sign in there -- V=IR & P= VA (or I)

 

Nearly tripped into impedance talk myself ( being in A.C all working life) but not mentioned in my above post;as there will only be back EMF at initial making/breaking of circuit.

 

Your worked example would give a very large temp.rise in a short time & coil would burn out;insulation break-down gives this result.

 

If I understand Nigel's post on connections the coil will be O.K but the relay switch contacts or the fuse will burn out.

[sj-bradley]

Hi Florin,

 

Oh, I understand completely about the ohm's law and such. Being old school I had to learn by rote and had never heard of the mnemonic way of learning the rules. It was entertaining when the tutor stated these. Even I learned a new one "CIVIL" for current / voltage phase lagging or leading which I had not heard of (I was always getting these the wrong way round - never again )

 

I was not sure about what the actual resistance would be of a typical relay coil and only gave the basics to the equation.

 

I know that if you want to energise a relay using transistors for example that a clamping diode is essential to prevent the back emf (Lenz' law) from destroying the transistors.

 

If the coil is in hundreds of ohms then there will be low current flow through that circuit.

 

Does the original poster say that the coil had burnt out or the relay contacts?

 

If the relay contacts, then that would suggest a very high current flow as these are typically rated to switch a higher current than the coil circuit. This would indicate a short somewhere (which would be found if the bulbs are removed yet a low resistance is still present through the circuit)

 

I'm not upset by discussing these problems as they are enlightening to both myself and others who are reading this thread.

 

Thanks you for helping to clarify this situation.

 

Simon.

[fry61]

Electronics is the black art --- give me a length of wire & a tungsten filament lamp (bulb in american) any day.

 

 

Best mnemonic I remember from school is " Silly Percy Has Competely Burst His Tiny Pink Ballon. But then some soul-less hurmourless computor nurd posted all solutions for trigonometry on line.

[sj-bradley]

Usually is - especially when potted up in that solid black stuff

 

Simon.