The Mysteries of Electrickery

[RogerH]

The 4A has been going very nicely for sometime now. Haven't had the gearbox out for over a year and haven't needed an extra shed in the garden  for a good while.

However the other night I parked the car as usual. Came out yesterday and the temp gauge was either not working or was somehow registering the temp at the arctic pole by some transcendential phenomenon .

First thing, have alook at the wiring diagram.. There is not a lot that makes the gauge work.  10V supply, some wiring to the sender and the sender.

The 10V supply looked good as the Fuel gauge was working fine.

Next easiest thing to check was the sender. It measures apprx 750 Ohms in the cold state. Warmed it up under a hot tap and it dropped quickly to 250 Ohms. This suggests it is working.

I noticed that the little male spade end fitting was a touch loose.  Anyway I fitted a new sender and bingo all back to normal.

So, was the sender dicky or just having a larf. Could the ever so slightly loose connector really stop it working. Did the lose connector just happen over night.

I told you it was a mystery.

I put the old sender back in the spares box for future use, working on the theory that if it is ignored long enough it will get the hint and start working.

 

Roger

Edited April 11, 2019 by RogerH

[barkerwilliams]

Ah but did you check the resistance of the new sender to compare with the old?

Or is it just a presumption of innocence M'lord?

Alan

 

[stuart]

There can be a vast difference in the way those senders read, be interesting to see what the new one registers Roger.

Stuart.

[RogerH]

Hi Alan,

   the cold resistance or each was not too far apart.

 

Hi Stuart,

               I'm not holding my breath on expecting it to be the same. It is what it is.

 

Roger

[Lebro]

I would put it down to the dodgy spade terminal.

Bob.

[RogerH]

Hi Folks,

          who says repro' parts are rubbish. The new (probably 10 years old) temp sensor was taken for a decent run last night.

Once up to temp the needle went precisely to the calibration indicator - you know that little red square next to the letter 'H'  (I wonder what that stands for).

It remained at this position as steady as a rock. Very impressed.. All I need to do now is get out of the calibration mode.

Out of curiosity I fitted the old one from yesterday. The good news is, after a nights rest in a dark box it has sparked back into life - from hence forth it shall be known a Lazarus.

 

On a more serious note  (sorry about that) obviously there is a fair amount of variation in the build of these sensors (as Stuart hinted at yesterday).

They are sold in colour coded types. So why is it so problematic to get a  'red' sender to act like a 'red' sender. 

As the item I fitted was over reading it would be easy to add a resistor to bring it back to where it was needed - but why can't the manufacturers work out the correct value.

 

Roger 

[Steves_TR6]

Perhaps call the new sensor Icarus...