How to build an external car alternator regulator? - Page 1
Forum section: electronics / projects

author: MarkS
author_rank: Unknown
timestamp: August 15, 2025, 09:50:08 pm
content: My 2010 Nissan Murano alternator has a bearing going out. While looking for bearing replacements, I came across someone that had removed the rectifier assembly and used an off the shelf 3-phase rectifier to move that portion of the electronics outside of the alternator to mitigate heat damage from the engine. I found that Digikey has a plethora of 3-phase rectifiers that would work for me, including some that have amp ratings far above anything I could ever use in a simple automotive application. The alternator has two sets of 3 phase windings in a wye or star configuration, with each set of windings paralleled at the rectifier. From this, I am confident that I could move the rectifier outside of the alternator with relative ease.However, I would also like to move the regulator outside the alternator. I've always looked at the regulator as going from the alternator to the engine, but have just learned that it is, in fact, used to regulate the alternator itself so that it doesn't overcharge the battery. Doing some more research, I have come to the understanding that it monitors the output voltage and through PWM, modulates the rotor windings so that at or around 14.4 volts, the effective duty cycle is near or at 0%. This seems easy enough as any simple microcontroller can do both of these things without breaking a sweat. However, those figures represent the upper bound of output voltage and lower bound of PWM duty cycle. In order to do this properly, I would need a voltage at which the PWM duty cycle is near 100%. Also, should the change from 100% to 0% be linear or PID controlled or...? I also read somewhere that the duty cycle transition from fully on to fully off should be more gradual than a square wave to prevent voltage spikes during transition. Would a triangle wave work? Then, I found out about something called load dump. From what I could tell, without a degree in electrical engineering, is that this is basically a flyback diode. I think? The papers I saw, from an older post on these forums, are way over my head. I need this explained in a more simplified manor.This seems like an easy and fun project, but I have obvious gaps in my knowledge. Can anyone help point me in the right direction?

author: moffy
author_rank: Super Contributor
timestamp: August 15, 2025, 11:31:47 pm
content: A simple linear transistion in PWM would be sufficient, typically you are just controlling the current going into the field coil, it is important to provide a path for the field current when the PWM is off, this is usually done with a diode. A linear solution is better in that it is more reliable than a micro which can suffer from glitches, it could be as simple as an LM555 timer IC. One thing to consider is how the current is limited out of alternator, you might want to add that.P.S. Here are some linear not PWM regulators, a good starting point:https://www.homemade-circuits.com/car-alternator-regulator-circuit/Previous discussion:https://www.eevblog.com/forum/projects/make-a-car-alternator-voltage-regulator/

author: CaptDon
author_rank: Super Contributor
timestamp: August 16, 2025, 12:01:57 am
content: A million times easier to just replace the alternator in kind with either new or rebuilt. I am sure Murano alternators typically last 150K miles or more. I run an aftermarket '1Wire' alternator on my truck. It is built in a GM size 120 case and never had a problem. There are some aftermarket '1 Wire' kits for many types and makes of alternators. They are very useful on boats!!

author: langwadt
author_rank: Super Contributor
timestamp: August 16, 2025, 12:04:15 am
content: how much is new one?

author: Benta
author_rank: Super Contributor
timestamp: August 16, 2025, 12:19:53 am
content: Good question.I love the "I read somewhere that..." ideas and projects that come up. I'm driving a 25+ years old MX-5 and both alternator and battery are fine.Battery is only 8 years old, though.I see no rational reason for doing further development on something that's worked reliably in billions of cars.

author: MarkS
author_rank: Unknown
timestamp: August 16, 2025, 12:21:43 am
content: Quote from: moffy on August 15, 2025, 11:31:47 pmThat's helpful, thank you.This isn't about money. This is about doing something fun that I've never done before. It will always be cheaper to replace than DIY anything. The side benefitis that the back of the alternator and thus the electronics is just centimeters from the left side exhaust manifold. Moving the electronics away from the heat can only be a good thing. I'll end up buying a used alternator for this project. In the meantime, I have the bearings for the current alternator. I'll replace those while I play around with this project.

author: floobydust
author_rank: Super Contributor
timestamp: August 16, 2025, 01:40:24 am
content: On a popular engine, Toyota also mounts the alternator very close to the exhaust manifold (pic). Not as tight as Nissan. There is the heat shield on the manifold, but the alternator still gets very hot, worse so in stop and go traffic where there is not much airflow, unless the cooling fan is on blowing 90°C air around lol.The electronics would be rated to +125°C/257°F. Rectifier diodes are very tough, and special in alternators that they are zeners to limit vehicle transients to around 40-50V. Running 4 wires for that, plus the regulator field wires is kinda messy. Problem is it might fail, the wiring can rub/chafe/melt and short out.Some alternators are ECU controlled. I don't see it for this Murano. Same Nippon-Denso? alternator used in a few different cars.I have made my own car alternator voltage regulator, to replace a mechanical relay one in a 1968 Ford. There are dozens of amateur schematics out there.It would best to use a OEM alternator and possibly look into what the rectifier diode failures are about. It could be like the Boeing AH-64 Apache helicopter, I thought it was vibration and the rectifier diode crimp connections failed and were arcing. The regulator module is more fragile in some ways.

author: amyk
author_rank: Super Contributor
timestamp: August 16, 2025, 01:55:23 am
content: They are usually linear regulators.https://www.amsterdamhouseboats.nl/voltage_regulator.htmhttps://www.xs650.com/attachments/delco-12si-06-jpg.94743/Code:https://www.youtube.com/watch?v=by5cL9NPruw

author: floobydust
author_rank: Super Contributor
timestamp: August 16, 2025, 02:21:13 am
content: They've been PWM for at least a 10-15 years now.I'm not sure what regulator IC Nippon Denso is using.OP could look at some alternator regulator IC datasheets to learn how it is done:https://www.st.com/en/automotive-analog-and-power/alternator-regulators.htmlhttps://www.onsemi.com/pdf/datasheet/cs3361-d.pdfhttps://www.infineon.com/part/TLE8881-3TN124 pg. datasheet, pretty complicated.If you build a linear regulator, you'll find it switching on/off the field winding and not in a linear-mode as expected.

author: jh15
author_rank: Frequent Contributor
timestamp: August 16, 2025, 03:20:01 am
content: In the 60's i replaced the generator with a newer alternator, external regulator. i used a popular electronics or equivalent magazine to build a solid state regulator for a school lab project.was fun, had a pot on it and could vary headlight brightness at will.

author: MarkS
author_rank: Unknown
timestamp: August 16, 2025, 04:24:06 am
content: One thing I failed to mention is that this is also a safety concern. My car has a cvt, which shouldn't matter, but does. In the case of this model of Nissan's CVT, when the battery voltage drops below a threshold, a threshold at which the engine still operates, the TCU flat out shuts off the transmission. Most automatic transmissions go directly into limp mode. This one just cuts all power. I found this out when the prior alternator's regulator gave out. I was going down the highway at 60 MPH, when I lost power. The engine was still running, but pressing the accelerator peddle just caused the engine to overrev. I thought I may have accidentally bumped the shifter into neutral, so I was looking at that and by the time I figured out that something more was wrong, I found myself at a stop in 60 MPH traffic. In order to get the transmission into limp mode so that I could pull off the highway, I had to cut power to the engine. I almost couldn't get it to start back up. I fortunately did and was not hit.The alternator had been giving me symptoms that something was wrong, so a few days prior I removed it and took it to my local auto parts store to be tested. It came back as functional. Not convinced, I took it to another store and got the same results. I could have been seriously injured or killed. I could have seriously injured or killed someone else. Knowing what I know now, I want the electronics not only away from the heat, but easily accessible.

author: moffy
author_rank: Super Contributor
timestamp: August 16, 2025, 05:23:01 am
content: You need a warning before that happens, the battery should give some time for a low voltage detection and the final shut off of the CVT by the TCU. Didn't the dash give some indication of a problem before the final shutdown?

author: David Hess
author_rank: Super Contributor
timestamp: August 16, 2025, 06:31:18 am
content: Back when alternators had external mechanical voltage regulator which needed to be replaced periodically, I became frustrated with mine and designed and made a new one, twice.My first one used a 78S40 switching voltage regulator, predecessor of the MC34063, with external PNP power transistor. This limited the field current to less than 80%, so later I designed a better one using voltage mode controller from Unitrode with an external LT1007 error amplifier, reference, power MOSFET, and a stud fast recovery rectifier across the field winding. This later design used a 4-wire Kelvin connection to the battery terminals and achieved better than 10 microvolts of regulation from zero to full load on the alternator, which was way overkill. It used just the I part of of a PID loop but with pole/zero compensation for good transient response, which had a side effect of removing almost all alternator whine. This was overkill also.The alternator can be treated as a current amplifier, amplifying the field current to produce an output. Maximum field current could be 4 amps with a gain of 15 to produce a 60 amp output.I got quite a look from a neighbor when I was outside measuring the inductance of my alternator with an impedance bridge, and then later tuning the frequency compensation with an oscilloscope.

author: MarkS
author_rank: Unknown
timestamp: August 16, 2025, 03:51:40 pm
content: Quote from: moffy on August 16, 2025, 05:23:01 amIt was a case of the car that cried electrical problems. The battery and brake lights would come on, which is typically indicative of an alternator issue, and then go off, sometimes for days. That's why I removed the alternator and had it checked. All of the typical checks with it installed were either showing that everything was fine, or that things *might* be bad. The light came on in this instance, but by that time I was not taking it too seriously. Even then there was no indication that the transmission would just shut off.