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Automotive 6 Volt Generator Transistor Voltage Regulator

Danwvw

Active Member
Not to stray too far here, I put new bearings and brushes into this Motorola Alternator back in 2013, It may have blown a diode though a couple of years ago as my dome light seems to have a rapid rpm related blink near idle: It's not so easy to remove one of these from the car because of the engine cooling fan running off one end of them. I should pull it off though and change the diode but it still keeps the battery up fine. IMG_4017_Carbs_Switched_to_Correct copy.JPG
 
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Danwvw

Active Member
Yeah, I was thinking, since it's the rainy season of setting inside the VW Bus with the scope and looking at the ripple at the Dome light.
 

Danwvw

Active Member
Here is a Idea for a Adjustable Regulator using the LT6700, I have found a SOT-23-6 BreakOut board for a DAC with mounting holes I can use to make the prototype easier to build.
SOT23-6 BreakOut Board.png
LT6700Adj.jpeg
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
You don;t need all of that front end stuff.

try the following:
make r1 =180K
make the potentiometer 20K
make r2=13K

Loose the th451 and the 150 ohm thing
Adustment should be 5.4 to 8V

They might not be standard values.
 

Danwvw

Active Member
Huh? That wouldn't work! (Only would have 37ua, it would be noisy) I think I see where you are coming from though and I have already been there. (We discovered using a zener to measure the generator output voltage provides a more stable operating generator output.) Probably The 150 ohm should be 15 ohms though to get the TL-431 IKA current up a little more The TL-431 operates between 1-100ma sink current and 15 ohms is 26ma at 8 volts. Remember the voltage drop across the input to ground is never going above .4 volts regardless of the circuit used here. But yes the input network could be just resistors or it could be just a 7 volt zener and that 15 ohm resistor for a fixed regulator voltage. Considering A TPS3700 Window Comparator instead of the LT-6700 because it has higher Temperature ratings. The Voltage Regulator area in the car gets up to about 155' F. maybe even more at times. Thanks for the comment.
Actually my TL-431 References are type C which are rated for only 70' C So I will use a 47 ohm resistor to keep the current through it below 10ma. The 150 ohm would give 2.6ma still enough it would work maybe better since the TL-431C is being used.
 
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Danwvw

Active Member
Actually Other components are marginal including the STPS40L15's I think I may have seen one lock on once with the key off after having the headlights on. As a component they read a lot lower forward bias voltage on the meter diode check after having been in service. With the Head Lights on The STPS40L15's are close to maximum 40 amps and in fact If the battery is low they may need to handle 50 amps or even more. (One reason I like the current limit designs but they wouldn't current limit well enough to stay below 50 amps without introducing considerable generator output voltage drop with the headlights on. It's an area that needs more testing the LM393 design may have helped that, it's better but I don't have an Amp Meter on it's prototype.) The STPS40L15 heat sink I have been using is just the B+ Terminal on the Old Mechanical Voltage Regulator base. It's a pretty solid piece of copper and it can transfer some heat back up the 2 big wires that connect to it but it does heat up to 155' F about 70' C. Its forward voltage drops with temperature > which helps too. The early LM 317P design would output a climbing voltage with how hard I drove, about 200mv or so Voltage >. I don't seem to see that happening now with the LM393 design in the car though.
DigitalAmpMeter.jpg
 
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Danwvw

Active Member
Been waiting on parts, storms let up, took the car out for a drive today. LM393 Voltage Regulator Design is working nicely with 7.0 volts up front and 6.5 volts with the Headlights which cause enough heat in the STPS40L15 Cutout Diode to raise the 7.0 volts to 7.13 volts when I turn off the lights but over a minute or two it cools down and the voltage up front goes back to 7.0 where it is adjusted to run.

More on my mind lately is A Engine Temperature Circuit if anyone is interested.
 

Danwvw

Active Member
The LT-6700 chip and its SOT 23-6 BreakOut board arrived and here is a Mock-Up of the Prototype. Note a 1K 10 Turn Voltage Adjust Pot is located on the underside accessible through access tube.
LT-6700 Prototype 1.jpeg
 

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