Any ideas anyone? I have a wiring diagram for a 12v vehicle system, The diagram seems to say there is a relay that has a variable resistor between the input of the relay and ground.

In reality it looks like there is what I think is an orrange disk type capacitor. (has 30v stamped on it, but can't read anything else)

What do you think it will be? a Capacitor or resistor?

Also why would either be fitted?

Thanks

pic would be handy?

I can't provide a pic as the vehicle is at work, but it's a yellow version of one of these in the link.

http://image.ecplaza.net/offer/s/suntanju/4862575_s.jpg

all I can see stamped on it is 30v

Cheers

i meant the circuit diagram symbol:rolleyes:

it could be some type of thermistor, do a google picture search for disc thermistor.

what does the circuit do?

The circuit releases a hydraulic handbrake. The relay energises a soleniod.

As for the diagram Its the typical resistor with an arrow on an angle like the one here http://www.gcsescience.com/Test-Circuit.gif

All I can think is that it's a capacitor to protect the relay.

Basically its leg has snapped off, but not sure how important it is.

Just googled the disc thermistor and it could be that yes (but yellow!!)

Cheers for this Teflon.

Edited 9 March, 200917 yr by L&KDET
More info

What is shown in pic (I'm pretty certain) is a ceramic disc capacitor /metalised ceramic capacitor ,and if memory serves is 15nano farads ( 15 is the value ,4 is the power of 10 ).

Without seeing the circuit ,can only surmise that it's possibly( if a capacitor of that value ) (at that sort of value ) got some rf suppression purpose .Then again there are two types of thermistor -one gets less as it heats up, the other type does the opposite .So without knowing which type it is -how long is a piece of string .

re: the above post..

thinking about i further i cant see how that could be a thermistor, more likely to be a capacitor which forms ome sort of de-bouncing function to stop the relay from mis-triggering

We foung the part no. in a book and have ordered one, its is also listed as a vari resistor, but its a translation from German, so what ever it is we got a new one on it's way.

It does work without it but hey!

Cheers for the help though Teflon.

If the relay has a timing function, it could well be a thermistor to provide a delay.

If the relay has a timing function, it could well be a thermistor to provide a delay.

Or to reduce the current through the relay after initial operation to that required to hold ( i.e cold ,thermistor has zero resistance ,after set period ,relay has operated and only requires a small current to hold ,thus saving on overheating on coil ---only a thought )

In my industrial control days, we sometimes put a capacitor across a relay coil to introduce a small delay when the coil powers up. The only other component I've ever seen a cross a relay coil is a diode, to protect the surrounding electronics from spikes from the coil.

Phil

a cross a relay coil is a diode, to protect the surrounding electronics from spikes from the coil.

Yes, that was going to be my guess. If it's between one of the legs of the coil and earth, it will be to send the back-EMF spike (generated when the coil de-energizes) to ground.