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Voltage regulator correct output voltage?


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Hi all, just repaired the dynamo regulator (by passed intrnally for alternator) aftrr complete electical failure.Managed to gigger the electrics to get me home and have now repaired the connections with set screws and nuts as the soldering had cracked disconnecting power to the car.

Now I have an interesting problem. The temp gauge reads high and the elecric fan wont cut in, unless I earth out the sensor and it works fine. I cant see any obvious reason other than the fan switch in the bottom hose has failed. Or has it.

 

As the fuel tank is full I cant tell if the temp gauge is over reading or not. I've checkef the voltage at the gauges and it's 14.5 volts with the engine running and 12.5volts with engine off. Can I have buggered the voltage regulator with bypassing the faulty wiring or possibly the wiring failure giving full voltage only to the car (with no battery to absorb any excess ) as it failed over loading the instrument voltage regulator.

 

So after my meandering the question is should I be getting a stable 10 volts at the gauges as my 35 year old memory from collage tells me? What should the voltage reading be at the gauge.

Edited by MRG1965
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Hi decided to let it heat up and the fan cuts in at around 85 Celsius (30 70 100 gauge scale) and does not boil over, so suspect voltage regulator. Normally the fan would cut in at around 75 on thd gauge.

 

Mark

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MRG,

The OE voltage stabiliser supplies the gauges by switching the supply on and off with a bimetallic strip that is heated by the current. It provides an average 10V to slow-reacting gauges, but if you put a multimeter on it, you will see 12v-0v-12v-0v- etc etc that simulates a constant 10v, in the face of the changing output of the dynamo/alternator at different engine speeds, or when the engine is off. Modern solid state ones give out a constant 10V.

 

Failure of the stabiliser may be in 12v or 0v mode. You have full Volts to your gauges, so they read high, and you need a new stabliser. The OE type must have been invented by Faraday's apprentice, so look for a modern transistor version, as used in Land Rovers: http://www.ebay.co.uk/itm/SOLID-STATE-VOLTAGE-STABILIZER-Land-rover-series-2-2a-3-/131569828057?hash=item1ea22c40d9

 

JOhn

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MRG,

The OE voltage stabiliser supplies the gauges by switching the supply on and off with a bimetallic strip that is heated by the current. It provides an average 10V to slow-reacting gauges, but if you put a multimeter on it, you will see 12v-0v-12v-0v- etc etc that simulates a constant 10v, in the face of the changing output of the dynamo/alternator at different engine speeds, or when the engine is off. Modern solid state ones give out a constant 10V.

 

Failure of the stabiliser may be in 12v or 0v mode. You have full Volts to your gauges, so they read high, and you need a new stabliser. The OE type must have been invented by Faraday's apprentice, so look for a modern transistor version, as used in Land Rovers: http://www.ebay.co.uk/itm/SOLID-STATE-VOLTAGE-STABILIZER-Land-rover-series-2-2a-3-/131569828057?hash=item1ea22c40d9

 

JOhn

Thanks John, yes mine reads a constant voltage, effectively current battery voltage, without any cutout, so assume the contacts are stuck closed. Thanks for the link.

 

Mark

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if you make your own or buy on e of the Landy items it would be worth protecting the regulator from the erratic electrics in our cars.

 

Fit a capacitor from the input to earth - 100uF or thereabouts.

And fit another capacitor from the output to earth - 0.1uF or thereabouts.

 

This will stop the regulator 'ringing' and going bang.

 

Roger

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Hi Andrew, interesting idea, and if it comes with a wiring diagram or indication on the unit for the connections I could just solder it inside the existing case to retain the original look, one in stock a mile from my house, might have a play this morning, for £1.09, what have I got to lose.

 

Mark

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if you make your own or buy on e of the Landy items it would be worth protecting the regulator from the erratic electrics in our cars.

 

Fit a capacitor from the input to earth - 100uF or thereabouts.

And fit another capacitor from the output to earth - 0.1uF or thereabouts.

 

This will stop the regulator 'ringing' and going bang.

 

Roger

Cheers Roger, as always top tips, electronics is not my thing, but I'll add the the shoping list.

 

Mark

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There is a cct diagram here that matches what Roger mention above, albeit with slightly different value of capacitor. This is what I use.

 

http://www.circuitdiagram.org/24v-or-12v-to-10v-converter-lm7810.html

 

Cheers

Graeme

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if you make your own or buy on e of the Landy items it would be worth protecting the regulator from the erratic electrics in our cars.

 

Fit a capacitor from the input to earth - 100uF or thereabouts.

And fit another capacitor from the output to earth - 0.1uF or thereabouts.

 

This will stop the regulator 'ringing' and going bang.

 

Roger

Wrong way round Roger! Small cap on the input to reduce the HF noise, larger one on the output to smooth the DC.

 

Pete

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Pete - that is not what the output capacitors is there for. Output smoothing is not needed as this is a DC-DC application and the load won't care anyway given that it normally gets chopped DC from the bimetallic regulator. The capacitor is to improve the transient response of the IC and to prevent it oscillating. The makers data sheet recommends 0.33 microfarads on the input and 0.1 microfarads on the output (for an LM7810).

 

I expect Roger suggested 100 microfarads on the input because there can be a lot of noise coming from the dynamo/alternator/ignition which might upset the chip, but in fact a big electrolytic can have poor rf response, so the 0.33u should be used in parallel to take care of that.

 

Rob

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Rob, that makes sense. It's been a few decades since I messed around with these, although I'm named on a patent for using those regulator chips as instrument voltage regulators, that was in the 1970s! Yes, I used to design automotive electronic systems for a living.

 

Thinking more about it, I don't think I'd put an electrolytic in there, as they don't like transient overvoltage.

 

 

Pete

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Better to us a "Voltage transient Suppressor" these are very fast acting diodes which will protect the regulator from damage by over voltage.

I used to design electonic circuits for use in a range of vehicles from cars to tractors to ships, & these were always specified. A capacitor will smooth out the transient to some extent, a TVS will clip it.

 

https://en.wikipedia.org/wiki/Transient_voltage_suppressor

 

Bob.

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Hi all, quick update. Took the unit off and it worked fine on the bench, put it back on and works fine. Suspect poor earth was stopping coil heating up the bimetalic strip giving constant battery voltage. Simplest answer is usually the right answer.

 

Cheers

Mark

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