Yachting and Boating World forums: WTF strange electrical problem

OK, your engine temperature meter effectively works as a voltmeter and the 'voltage' that it reads is from the temperature sensor attached to the engine block (or radiator).

This temperature sensor is what is known as a NTC sensor (different colour ends, black, brown, blue, red, green etc) depict different operating parameters. NTC stands for 'Negative Temperature Coefficient and the resistance goes down towards zero as the sensor warms up. Sometimes and rarely PTC (Positive Temperature Coefficient) sensors are used but these are not so common. They work by an increase in resistance with a rise in temperature.

From what you say, the temperature gauge is reading a drop in resistance but as the NTC sensor is not dropping, it therefore appears that when you turn the fridge on, the temperature gauge then reads both the NTC sensor and also there seems to be a change in resistance when using the fridge.

You will possibly find that one of the fridge wires is wired via the engine block or that one of the fridge wired is causing an effect on the wiring to the engine block and this can include the engine earthing or bonding straps.

A lesser problem that causes this type of problem is the state of the electrics and wiring.

With the engine warm and running or not, use an AVO meter or DVM to read the voltage AT the battery terminals. Now turn on the fridge. Does the voltage at the battery fall or remain stable. Hopefully, it should be stable. If the battery voltage falls then your batteries need charging, servicing or replacing?

Finally, with the AVO or DVM, read the voltage between the ENGINE BLOCK (-ve meter lead) and BATTERY TERMINAL POSITIVE (+ve meter lead). Turn on the fridge as in the last test. Again, the voltage should remain stable.

If any of these two tests show a marked drop in voltage (more than say a tenth of a volt) you possibly have a high-resistance (HR) connection in the electrical circuit. This needs to be corrected. This would then point towards a loose connection or a corroded connection or terminal. Both can easily be corrected without spending too much money.

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regards David

"Away Sea-boats crew - Special Sea Dutymen, Close-up"

Skype: lenseman-uk

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