Make this Voltage Stabilizer Circuit for Your Car

In this post we learn about a car voltage stabilizer circuit which could be made and installed in all cars for ensuring a perfectly controlled and stabilized supply for the associated sensitive electronics and gadgets.

Understanding Car Electrical

A car electrical is probably more volatile than our house electrical, simply because it is generated from a source called alternator whose output considerably varies with the speed of the vehicle.

It means if you are driving your car with sudden changes in its speed or if you are often applying brakes, would consequently generate varying voltages from the alternator outputs.

Since nowadays our car and other vehicle interiors heavily involve sophisticated electronic gadgets, an unstable voltage conditions can cause serious effects on their performance and life.

The circuit idea was requested by Mr.Haziq, let's know more about the making of the proposed circuit (designed by me for the application).

Today we have some wonderful ICs at our disposal which are specifically designed for voltage regulation applications.

The LM317 and the LM338 are a couple of them which are versatile with their voltage regulation functions, I have discussed them elaborately in some my earlier posts.

The LM317 can handle up to 1.5 Amps while its big brother the LM338 can hold not more than 5 Amps.

However these values are quite meager when compared to the huge asks in automobiles.

By suitably modifying the configurations, the IC can be made to regulate any desired levels of currents though.

In the proposed car voltage stabilizer circuit we incorporate the IC LM317 and modify its standard design such that it enables the car electrical with sufficient power and yet restricts it from all possible dangers like overloads, over current, fluctuating voltages and short circuits, providing an ideal voltage conditions for the vehicle interiors.

Circuit Description

The circuit diagram shows a rather simple configuration where the IC 317 has been wired in its standard voltage regulator mode.

R1 limits the surge current, while R2 decides the triggering voltage to T1, if the current consumption crosses the 1.5 amp mark, T1 conducts and assists the IC by sharing the excess current through it.

P1 is set for achieving around 13 volts across C3.

R5 monitors over load conditions and short circuits, if the current crosses beyond 12 amps, sufficient current develops across R5 to trigger T2, which instantly switches OFF the IC so that the output voltage drops and restricts the current below 12 amps.

Ideal Specifications:

  1. Constant voltage = 13 volts
  2. Current Limit = 12 Amp
  3. Overload protection = above 12 amp cut OFF
  4. Thermal protection (if the transistor and IC are mounted on the same heatsink with mica isolation)
  5. Short circuit protection (fire hazard protection)

Parts List

R1 = 0.1 Ohms, 100 watts, made from 1mm iron wire.

R2 = 2 Ohms, 1 watt,

R3 = 120 Ohms, 1/4watts,

R4 = 0.1 Ohms, 20 watts, as explained for R1 (this resistor is actually not required, may be replaced with a wire short.)

R5 = 0.05Ohms, 20 watts, make  as R1

T1 = MJ2955 mounted on big finned type heatsink

T2 = BC547,

C1 = 10,000uF, 35V

C2 = 1uF/50V

C3 = 100uF/25V

P1 = 4k7 preset,

IC1 = LM317

D1, D2 = 20 amp diode (3nos. 6 amp diodes in parallel)

Simplified Version

Using the IC LM196, the above configuration becomes extremely simple, you may refer to the following diagram which illustrates a simplified version of the proposed car alternator voltage stabilizer circuit using bare minimum components.

R3 = 240 ohms
D1, D2 = 15 amp diodes
P1 = 10k preset
C1,C2,C3 as specified above
IC1 = LM196

62 thoughts on “Make this Voltage Stabilizer Circuit for Your Car

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Hi Sir, Thank you very much for this great circuit. I know it can easily being build only thing is I need to survey for the components R1, R2 and R5 in the market here, as for the diode I presumed it is 1N5408 in parallel. Other component is the Power Transistor MJ2955 which is PNP rated at 15Amps 60V.., is there any suitable substitution recommendation..? I know 2N3055 is among the same rated power but it's an NPN, please advise Sir..
    Regarding the R1, R2 and R5,if so it's not in the can diy it or where can I scavenged it! As for the rest of those components, I guess it shouldn't be a problem.,as for heat sink and mica isolation.. I have all lying around as I used to scavenged waste parts and
    Thanks again Sir for all the efforts given.

    • Hi Haziq,

      R1, R2 and R5 will need to be hand made using 1mm iron wire. You can make it by trial and error, by measuring and adjusting the value with an accurate digital multimeter.

      MJ2955 is the most commonly available so it's the best, otherwise you can try AD149, will also work here.

      Best wishes to you.

    • Hi Sir Swagatam,

      I need help.
      For project on my colledge I need to make AVR using microcontroller and relays.
      Do you have any idea how I can do that?
      I need some sheme or anything for this.

      Thank you!

  3. Hi Sir,
    Oh..ok got it..but onto what shall i wound it to..? The digital multimeter is to measure the ohm, what about the wattage..? how do I measure that.. or is it the 1mm iron wire can stand the extreme heat (wattage)produce..? I really like to learn more on how to wound or diy it.. I really hope you can show me the way or at leased point me to the right link about how to do this hand made thingy.
    My appreciation in advance for all future advise and assistance from you.
    Thank you Sir.

    • Hi Hazoq,

      I assume that a 1mm wire will easily withstand the load of 100 watts, the wire can be wound on a mica former.

      The former must be heat resistant that's all, nothing is critical except the resistance value and the wattage.


  4. Thank you Sir, I'll build it once I get all the components in hands and would present it to you and of course to the link given earlier.

    • There's no formula for making resistors….you will have to use special digital meters for measuring the resistances while making them, or you can use many resistors in parallel, for example you can connect 10 nos. of 1 ohm 10 watt resistors in parallel for getting 0.1 ohms/100 watt

  5. I am interested in using this circuit to stabilize the voltage on my 1939 chris-craft. I am using an 8 volt battery so I would want to stabilize at 9.2 volts. What changes to your circuit would you recommend for this application? Thanks! Steve

  6. Hi Swagatam

    All cars/trucks are equipped with a Voltage Regulator which supply regulated to the battery and the entire electrical system of the vehicle.

    Earlier these voltage regulator were mechanical relay type, installed as an individual component. But nowadays, these v/regulators are mostly electronic type (much simpler based on three transistors) and are built within the alternator.

    Furthermore, all the gadgets are duly protected with their respective fuse.

    I wonder what extra benefit we can get with above-mentioned circuits.

    • Hi Abu-Hafss,

      the above designs hopefully show a simpler approach to making these devices, anybody who may be interested to manufacture them or has a damaged system in his car can try this design.

    • Hi Swagatam…

      Do you mean to say that the above-mentioned circuit can replace a car's damaged voltage regulator? Or do you have a specific automotive voltage regulator circuit design that can be used to replace damaged alternator's built-in regulator?

      My alternator's built-in regulator is damaged thus I would like build my own which is capable of charging my battery at a maximum rate but with all the necessary features found in all built-in regulators.

      Your help would be highly appreciated.

    • Hi Dan,
      The circuits explained in the above article are extremely reliable and advanced with their discussed voltage regulation features.

      You can try the last circuit using the IC LM196 for replacing your car's damaged unit.

      However I am assuming the function of the car voltage regulator to be just voltage regulation only, and not something more complex than this, like monitoring the alternator field winding triggering states etc which the above circuits won't be able to do.
      I'll research more on this and try to get an appropriate answer soon.

  7. thanks for all this posts……now i want to make a ckt which can turn off the switch (a wall switch controlling a 3 point plug is connected)using a wireless i can turn off the switch without touching the switch …

  8. Hi, I have an old car that has a dynamo with only a standard cutout. i.e. no voltage or current control other than an adjustable third brush in the dynamo to control the maximum current output to 11 amps. When the battery is discharged following starting the maximum voltage generated for a short period is about 17 to 18 volts.
    I want to use an electronic ignition system and this is designed to operate between 8 and 16 volts. I would like to put a voyage stabiliser in the positive feed to the ignition to control at about 13 to 14 volts. I estimate that the amount of current taken by the coil and electronics would be 6 to 7 amps. What circuit would you advise please to very robust under these conditions.

    • Hi, Thank you for your reply.
      Doe the fact that I am using a dynamo rather than an alternator make any difference to your recommendation?
      Does the ideal spec you quoted at the start apply to this circuit?
      Will it handle the continuous load of 6 to 7 amps and does the ic need a heat sink?

  9. Hi, Thanks for your advice.
    1. Does it make any difference that a dynamo and not an alternator is being used in my case?
    2. Does the ideal specification you quoted, particularly the current overload protection, apply.
    3. Can it safely handle the continuous load of 6 to 7amps?

  10. This looks like what I've been shooting for to stabilize the system voltage in my truck. Is your circuit designed to connect in parallel to the charging cable, or in line so all system current passes through it?

    • It depends whether you want to stabilize the entire electrical of the vehicle or just a single gadget. If it's the entire system then the voltage must pass through the circuit, if it's for a particular device such as a battery, then it could be positioned in between the source and the battery.
      However the above circuit is applicable for 12V vehicles only, if your truck operates at this voltage then you can try the second design in the above article.

    • the input side needs to be connected to the battery (+)(-) and the output side with the load or whatever electrical/ electronics you may be having in your car….briefly, the circuit should be in the middle of the battery and the car electrical units, the supply needs to pass through the circuit before reaching the car gadgets.

    • actually the (-) of the battery and all the loads could be made common and joined to the car chassis….only the positive from the battery needs to be connected with the input (+) of the circuit and the output (+) from the circuit can join with the car gadgets for powering them with the desired stabilized supply

Leave a Comment