IC Voltage Regulator Question

[vwadad]

Hello Forum Members,

I have an old Jeep that originally had a 6 volt electrical system. That vehicle was converted at some point to a 12 volt system. I am installing an original 6 volt fuel gage, and therefore need to drop the voltage in the fuel gage circuit (prior to the gage) to 6 volts. In order to do this I am using an NTE962 IC voltage regulator. The wiring seems simple enough, but I am having problems. With no load, Vin of 12V and the center terminal of the regulator grounded as required, there is indeed 6 volts as measured between the Vo terminal and ground. But with any load applied to Vo, the voltage immediately drops to about 1 volt. This happens when the fuel gage is connected (approx .5A), or when a small 6V bulb is the load. The NTE962 is attached to a piece of aluminum as a heat sink, so I don't think temperature is a problem.

Any suggestions?

Thanks, Brian

 

[MikeMl]

Do you have the required bypass caps on the input and output. It might be oscillating.

 

[KeepItSimpleStupid]

For one use a real datasheet, in your case a 7806 regulator: https://www.electro-tech-online.com/custompdfs/2013/02/LM7805.pdf

Note the small caps on the input and output. These will generally prevent oscillation. It's good that the tab is ground. Is this a 6V negative ground vehicle or was it a positive ground vehicle?

If this is indeed a positive ground vehicle a to220 mounting kit should be used. In any event a silpad, mica or thermal washer and or heat sink grease if required. The silpad doesn't require grease. The kit contains a shoulder washer to insulate the tab and usually contains a domed washer as well.

The regulator is good for an amp, BIT a tungsten bulb's cold resistance is about 10X lower, thus it requires a LOT more current to trurn on. About 10x.

So, aside from oscillation (the device should be hot), positive ground (A definate possibility), Load too high (A definate possibility for the lamp).

Fuel gauges are a different story. Some had their own regulator, some pulsed a current and used a fluid filled gauge.

I'd certainly check the wiring diagram for the car and even try a fixed resistor to substitute for the fuel reostat. Positive ground is a possibility.

The regulator is good for an amp,



The 1V or 1.2 V generally indicates an overload.

 

[KeepItSimpleStupid]

From this forum:

https://www.naxja.org/forum/archive/index.php/t-1022359.htm

All North American XJs are 12V Negitive ground. Most Jeeps and Cars made in the US using 6 volt systems were positive ground. Them's the facts.

I was a very small child when 6V electrical systems were around.

If that's the case you have other issues to deal with. You would have to isolate the gage set and you might have to use an isolated switching regulator.

So you may have two issues:
1) Bulb - real draws 10x current on start-up (Bulb #)?
2. 6V positive ground vehicle