Electrical over heat

Have just got my 40 back on the road after a year in the shed . So yesterday per mot gave it a good clean ran it for a while and all was fine. Today the smiths water temperature is reading 90 at rest and then around 140 when running. I know this is incorrect as the temperature controlled fans come on at 90 and as they are not the fault must be on the electrical side.
Thinking about the simple circuit evolved is it most likely to be the voltage regulator as the gauge normally runs on a ten volt circuit ant the reading I'm getting seems to be a percentage increase as if its using 12 volts
Has anyone experienced similar
 
Still got issues .the voltage stabiliser reads an output of 12 volts where it should be 10 however,the input voltage from the battery is 13.9 volts which explains the lack of voltage reduction to the required 10 volts.
My question is where else will there be a voltage control to ensure none of the instruments are working incorrectly or being damaged I believe there is voltage regulation on the alternator but would this affect the voltage from the battery .Remember everything was working perfectly then there war a sudden change so a component must have become faulty some where
Help!
 

Randy V

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Huw,

I've never heard of electrical gauges that run on 10v. 12v only and 13.9 to 14.5 output from the alternator is normal.

Where I have had problems with electrical gauges for temp, it's always been a grounding issue if the sender is good and matched to the gauge it is assigned to.

Make sure your system is well grounded. Pull the sending unit out and clean all the threads on the sender as well as where it is screwed into - then put a little sealant towards the top of the threads of the sender and reinstall. The object here is for the bottom of the sender's threads to be well grounded and the top of the sender's threads to be sealed.
 
See where your coming from but the smiths fuel and temperature gauges run from a voltage stabiliser which converts a 12 volt system down to a ten volt system . This used to be achieved
by using a 12 volt input into a small device that contained a bimetallic strip with a small coil around it . The coil was on 12 volt to earth connection . So 12 volts entered the strip and the coil at the same time ,the coil heats the strip which the bends and pulls away from the 12 volt source ,the coil is then not powered cools allowing the strip to reconnect to the 12 volt input and the cycle repeats itself several times a second .the take off of the stabiliser is the other end of the strip which averages 10volts due to its rapid on off connection .
It's a really odd set up but used to work well now adays we use a solid state device to achieve the same .
My main problem is I can get a reading on all my gauges but suddenly they are too high on temp and fuel and I was hoping the stabiliser was at fault as it is the common denominator in the system
Will definitely look at the earth situation and make sure it's ok
 
Hi Huw

Generally speaking it is not good to have too many regulators working at the same level or cascaded for that matter. Is there only one 10V regulator which creates a 10V bus, which you then feed to all the Smiths gauges?

Earthing is always an issue to check. However I would suggest you change the regulator to a solid state one. If the frequency varies your '10V' will vary, as it is an electromechanical device, vibration can cause a change. If you have a capacitor failure, the voltage is likely to become spikey and cause issues down the chain, although I guess the gauges have some form of input voltage protection.

The regulator on the alternator will not affect the battery voltage when the car is not running, it simply regulates the voltage output from the alt into the battery. The alt regulators can fail in several ways, going short circuit and draining the battery, going open circuit and not regulating the voltage out of the alternator.

13.9V is a good healthy battery voltage (maybe slightly high, is it a new battery??), start the car and let it idle, the batt voltage will rise a bit (due to a slightly higher alt voltage, charging the battery), see what it rises to, rev it a bit and again see what it goes to, if it goes high more than about 14.5V, stop immediately,..... faulty reg on the alternator.

I've just read that some alts may output just over 15V, which I have never seen.


Regards


Keith
 
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