Electronic circuitry wizard needed.

[JRLesan]

I have an old truck which I converted from 6V to 12V nearly 50 years ago. A good friend and electronics wizard put together a regulator for me which reduced the 12V (approximate) voltage to 6V (actually 7.2V no load) with a current output high enough to power the heater motor, wiper motor and gauges simultaneously. I still get 7.2V output with no load but as soon as a load is put on the device output drops to ZERO or slightly above; thus the title. I can send pictures to anyone interested. NOT interested in experimenting with ballast resistors or buying some Chinese *** that won't last another 5 years let alone 50.

[lancem]

Clear some privet message space and I'll send you my email to send pics to.

[JRLesan]

Box cleared; am heading out to shop to remove device...

[Rizzo]

Shooting from the hip.....
Most voltage regulators are short circuit proof.
If one of the loads on the output has an issue (short circuit?), then I would expect the output of your 6 volt regulator to go to zero volts (there abouts).

I'd start lifting the load wires on the output of the regulator one at a time to see where the problem is. It may not be your regulator but some other issue.

[MaryB]

Drop me some pics via PM. I sent 40 years repairing electronics as a career.

Modern DC to DC converters from a name brand will last quite awhile... but like all electronics they will fail with time.

[45_Colt]

Mr. 45,
If you'd bother to read my original post, I said REGULATOR, not big ass resistor. My device is a transistorized regulator which was working fine until recently.

I read your post, a voltage variation of 17% is hardly being regulated.

As far as a transistorized 'regulator', a 2N3055, some resistors and a zener should cover it. But is wide open to self destruction should a short circuit occur, or just plain old fatigue from in-rush currents.

45_Colt

[rbuck351]

If you don't like resistors or regulators you could use two 6v batteries and a series parallel switch. This would give you 6v to run everything but the starter and 12v to the starter. This would last 50 years and then some as they were made for semi trucks using 24v starters and 12v for the cab and will handle loads far above what you could have on your truck.

This is not a cheap fix but would last longer than you or your truck.

[JRLesan]

Not a 'voltage variation' at all; 6 volt auto systems were designed at 7 volts or slightly over as were 12 volt systems designed at 13 1/2 volts or slightly over. Can't charge a 12 volt battery with 12 volts and a 12 volt wet cell in good shape is actually around 12-3/4 volts.

[popper]

Yup, probably a short someplace. A decent regulator will have protection and shut down.

[MaryB]

From the description he gave me I suspect it has current monitoring and the shunt resistor may have changed value enough to make it think to much current is being drawn. That resistor usually runs hot and they eventually break down.

[JRLesan]

There is no resistor (unless a transistor can act as a resistor) in the circuitry. two transistors in parallel beyond a 10 pin regulator, a 3rd transistor and a cap between two regulator terminals which, I'm guessing, is to 'smooth' out input. I can pencil a rough circuit diagram but symbols would be incorrect. Device will light a small lightbulb but will immediately shut down if a load is applied. The device worked fine, powering a 6 volt heater motor, windshield wiper, and dash gauges for a number of years without problems. I parked the truck in a barn around the year 2000 and only recently brought it out and got it running again. I know my friend gave me a parts list and we went down to his lab on a Sunday afternoon in MAY81 and he put it all together without incident and without instructions; just knew how to design circuitry. I have part numbers and have replaced the three transistors which I had extras os left over from the original build. Any additional help appreciated...

[n9tkf]

Is the capacitor electrolytic? These can dry out over time and cause problems. Do you know the part numbers of the 10 pin regulator and transistors? Might help to figure out the problem.

[JRLesan]

Capacitor is ceramic about the size of a pea and marked: Z5U 2200P 1KV
Two transistors 2N3055
One transistor 2N3054
One regulator ECG923 - Only part I did not have on hand so not yet replaced.

[45_Colt]

One regulator ECG923 - Only part I did not have on hand so not yet replaced.

Odds are it is the ECG equivalent of the LM723 regulator chip. DigiKey has them in stock, be sure to be seated when you check the price.

45_Colt

[n9tkf]

Odds are it is the ECG equivalent of the LM723 regulator chip. DigiKey has them in stock, be sure to be seated when you check the price.

45_Colt

It is a LM723 equivalent in a metal can configuration since OP states it has only 10 pins.

[JRLesan]

Are y'all saying that odds are the ECG923 has failed? That would explain why replacing the three transistors had no positive effect.

[n9tkf]

Are y'all saying that odds are the ECG923 has failed? That would explain why replacing the three transistors had no positive effect.

Could be a possibility. A few more questions. Is the output close to 7 volts?

What is connected to pin 1 and 10? This is the internal current limit circuitry. Pinouts attached.

[popper]

ECG923 Jap replacement for LM 723. Power resistors usually go open, not shorted, which will shut the regulator down. It will be a very low resistance (0.1ohm) so hard to measure. Output cap is for spike protection, they seldom go bad. 2n3035's die from spikes. Also make sure the wiring is clean, sitting a long time they get conductive dirty. Assume this is run from alternator vs generator? Generators sitting a long time have to be 'poled' to get them to work.

[MaryB]

The 10 pin regulator has current sensing as other have mentioned so either it is bad or whatever it is using to sense the current draw is bad.

Sounds like the standard pass transistor power supply circuit used in millions of 12 volt power supplies...

Data sheet for the 10 pin VR IC

https://www.ti.com/lit/ds/symlink/lm723.pdf

[JRLesan]

Pin 1 goes to ceramic cap and then on to the two 3055 transistors in parallel. Pin 10 is unused. Now, I may have that reversed as I can't tell from the data sheet which is ten and which is one; suffice to say they are next to one another and one is used and one is not.