Cross posted with my teardown thread on ForABodiesOnly for those not on FABO. Here, I will dissect an aftermarket replacement for a Chrysler voltage regulator and post my findings. This is a MasterPro 2VR1, $32 from O'Reilly.



The black plastic sealing the unit is probably a two part urethane, as it cuts easily with a knife.



Cutting deeply into the potting compound with a box cutter revealed a layer of sand underneath it.



After cutting around the entire perimeter, I was able to pry out the layer of urethane.



The layer peeled off in one piece.



There is a circuit board underneath, wired to the connector with bare strands of wire. The one on the right broke off since it was stuck in the potting compound. The other two did not reach up into the potting until almost at the point they tied into the connector.



The circuit board is a single layer surface mount design underneath a layer of conformal coating. I'm not sure exactly what material it is, but I suspect it's FR2 or another laminated paper substrate.



There are only twelve components on the PCB. The next step is to put the circuit under a microscope and trace out all the connection.



Stay tuned for an analysis of the circuit.

Let me know if the pictures aren't working.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

My copy of KiCad is being stubborn today, so we'll need to make due with a hand drawn schematic.



This is a very simple circuit, using a large power transistor and a smaller transistor to switch the larger one. The switching transistor is controlled by a Zener diode, Z1 on the circuit. When the voltage rises high enough, it flows through the zener diode and turns on the smaller transistor, which switches the large one off. When the voltage is low enough, current through Z1 shuts off, the large transistor switches on, and grounds the field coil. There is a capcitive coupling between the output of the power transistor and the switching transistor that limits the maximum switching speed. The reason for this is that switching off the power transistor creates a large voltage spike, which the D1 diode dumps back into the supply voltage. If the switching is too rapid, this will send too much current through D1 and can burn out D1, or even the 12 volt feed wire.

This is a rather simple circuit and rather similar to Chrysler's original design. One conspicuously absent feature is any sort of temperature compensation; batteries often need more charging voltage at lower temperatures.

Next, I'll go over a more in depth analysis of what this regulator does well, and where it has room for improvement.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

Thanks very much for your investigations and storytelling, Matt. It is nice to see a serious electronics guy take one of these apart and analyze it. I am guessing you might try to make an improved version of this?

Cheers,
Lou

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Home of Slant6-powered fun machines

Yes, I wanted to cut one open to see how existing designs solved some of the challenges I found working on a voltage regulator from scratch. Exactly how close my final design comes to this will depend on just how big a priority people find the possible ways it can be improved.

So, first, here's what they did well with this regulator.

The soldering work on the PCB itself is first-rate. I'm guessing it was run on an automated production line using solder paste and a reflow oven. It's not impossible to hand place components like this, but getting them placed that precisely isn't easy. And the solder joints are almost certainly not hand-soldered with an iron.

The circuit itself is a very simple design with not much to go wrong and not much that can kill it. The most likely things that could damage the circuit are water intrusion or an alternator field coil that draws more current than the power transistor can handle. Unfortunately, I could not find any markings on the power transistor, so I don't know what its maximum current is. Even though there aren't any discrete components for protecting it against voltage spikes, this circuit should be able to withstand spikes to 40 to 60 volts without any problem, possibly even higher.

And here are the areas of concern.

While the PCB soldering is done very well, the wire soldering is second-rate. While the joints look functional, their technician seems to subscribe to the idea of "The bigger the blob, the better the job." The conformal coating job was also done poorly, leaving many areas of the board uncovered.

I don't like the idea of a sand filled box. Sand filled electronics have valid applications where there's a concern about a box getting filled with explosive gas, such as natural gas pipeline stations, but that doesn't apply here. While this box didn't show any signs it would leak, if you made a mistake like leaving a big greasy fingerprint around the area where the urethane fills the box, it's game over. On the upside, it does make teardowns easier - perhaps their warranty department insisted on this. It's not an unacceptable way to build electronics, but I don't like it.

As noted before, there's no temperature compensation. It runs at a fixed voltage.

And then there's the issue of tolerances. The resistors are cheap 5% tolerance pieces. Zener diode voltage tolerances are also around 5% unless you spring for something special. Theoretically, you could stack the tolerances so the voltage is off by 15%. That is unlikely to happen in practice, but it is theoretically possible. Most of these are probably going to be within 5% of their target voltage.

Heat sinking isn't ideal, but this circuit doesn't put out a lot of heat, either.

Last, areas where it could be improved.

Chrysler's original design used a thermistor to increase output voltage at low temperature.

An adjustable target voltage isn't necessary if the regulator is always at the voltage where it needs to be. Also, different batteries have different target voltages. 13.8 volts on a lead-acid battery may not charge quite as fast as higher voltage, but it reduces corrosion on terminals. However, a lithium-ion battery won't charge if the voltage is below the mid-14s.

Some other improvements wouldn't match factory Mopar wiring. For example, allowing the regulator to wire directly to the battery positive and ground would give a more accurate voltage reference, but you'd need a separate way to switch power so it doens't hold the alternator on. You could also add an alternator warning light output if it cannot hit its target voltage. Neither of those would work with a schematic at all like the one shown, but it's definitely possible.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

Nice work Matt, thanks for sharing.
I have seen pictures of the inside of the Ignition PCM, not pretty!

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Hyper_pak

Thanks for all of the good info there.

I would be interested in a similar teardown involving various brands / suppliers including the adjustable VR; to see if three is one brand that would be more reliable in real world use.


Greg

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http://www.youtube.com/hyperpack

It would be interesting to see if brand makes any difference, or if they're all being made in the same or similar ways now. If anyone has a dead regulator (or ignition module, for that matter) they'd like to send me, I'd be glad to do an autopsy and post the results. One thing I won't have a good way of comparing are the transistor's current capacity (I might be able to if they have markings visible, but this one doesn't) and the QC procedures used at the factory.

If there is a difference in ignition module brands, some things I might expect to see in a better module would be:

- Better precision resistors
- Precision voltage reference device in place of a Zener diode
- Larger package power transistor for better heat dissipation
- Thermistor instead of fixed resistors, as Ma Mopar intended
- Some may use a regulator-on-a-chip design instead, but I expect most will use variations of the OE Mopar circuit.
- Fully potted instead of using sand

Things that might be in a high quality design, but I'm not expecting to see:

- A regulator circuit that is neither a pre-packaged solution nor copied from the Mopar design, such as a 555-based circuit or microcontroller
- Aluminum-core PCB for better heat dissipation
- Thermally conductive ceramic potting (think the white stuff on a ballast resistor)

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Matt Cramer
1966 Dodge Dart turbo / EFI project

1) I would expect the temp compensating feature would assist in improved ignition performance under cold start/run, electric-assist choke function, & battery charge recovery after hard cold starts.
2) Referencing at the battery is great for the battery, but short-changes all systems at the point of their regulated voltage connection, so referencing the ign."ON" provides full voltage to the components. As such, this is also the cause of common overcharging when bulkhead/column/ign.sw./splice connections are sub-standard, but the solution is correction(sometimes hard work), not an elegant crutch.
3) Thank You for investing Your time to learn & share with the Forums, look forward to the progress.

I was able to draw up a better view of the existing schematic. (Note - I forgot the capacitor between pins 2 and 3 of Q2, will need to add that.)

One way you could get more accurate voltage with a factory-type regulator would be if you used the field coil wire to trigger a relay to power the regulator from the battery. If I created a regulator with a few more pins, though, it could handle the switching internally with a couple extra transistors. It may indeed be a crutch... but there's a lot of voltage drops through 40 year old wiring, and adding a few extra parts can be less trouble than chasing all them down.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

Wouldn't a similar purpose be served more easily by doing as Chrysler did on their heavy-duty charging systems, bringing the alternator and regulator electrically closer by using a field-loads relay? Really easy. Get a good-quality, name-brand relay. Find the wire that presently feeds line voltage to the voltage regulator when you turn on the key. Cut it. If you've got the '70-up system, cut it upstream of the splice that also sends line voltage directly to one of the alternator's field terminals when the key is on. Upstream end goes to terminal #86 of a relay. The regulator/field end goes to terminal #87. The #85 terminal gets grounded. The #30 terminal goes to battery + (via an appropriate fuse of about 5A to 10A, depending on alternator spec). This way, turning on the ignition shows the regulator the actual battery voltage, not line voltage after dropping through the notoriously high-resistance ignition switch and master wiring weld under the dash (plus firewall connector, etc).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan - yes, that's a more detailed write up of what I was suggesting with the relay. If developing a regulator that uses a different plug and wiring, it would also be possible to do this internally with MOSFETs instead of a relay.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

I did a DIY solid state replacement for the alternator regulator about 40 years ago.

At that era early a-bodies were less than two decades old and for example I used
a Valiant as a daily driver here in Helsinki which is as north as Alaska. Not as cold
but real winters.

And we had really cold winters those days. The climate change has been got them away.

There was couple of problems in my Valiant electricity system. I lived in down town
so my car was standing at the side of the street. Not garaged. As well we got
a rule we have keep head lights on during day times. Even in sunny weather.

As the original Mopar alternator does not made any noticeable power at idle and the lights
will consume power the battery was going empty every this and then. I had couple
of options. Either I had to carry the battery to our apartment to 3rd floor for plug in
charging or I have do do a long road trip to get the battery full.

I did the 3rd option. I made my own solid state regulator with really aggressive
voltage increase after start and especially after COLD start. It started from about
16 volts and normalized to 14 volts with no steps within 15-20 minutes. 16 volts
occur when the temperature was well below freezing point.

As the wiring harness in an early a-body is loosing a lot of voltage for lights there
was no abnormal blew of bulbs.

I have not used the original alternator for long time. I rather use a modern alternator
of about 50-60 amps output with internal regulator and direct wiring in between
alternator and the battery. Also the ammeter issue has to be solved somehow.

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1966 Dart. 170 cu.in. 200 rwhp.

YES! I was hoping someone would do this. Hoping I see the diagram correctly would you assume that one could be made to be easily repairable? I know it may seem frivolous to do so but my curiosity gets the better of me. As a side note I have re-wired my slant as Dan recommended with running relays and such and it works flawless. My voltmeter (not ammeter) is as steady as a young man.

It's possible to build an easily repaired regulator, particularly if you used a through hole PCB. It would drive the cost up significantly since the cost of a sealed case is a lot more than simply using an open case and filling it with potting compound.

I've sometimes wondered if the sand fill was an effort to make this style of regulator repairable, but I don't think it is worth the possible manufacturing and reliability issues.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

I built something like this. By varying the quantity of diodes with the reference zener could cause more or less temperature coeffient to output voltage.

However the positive side drive to the alternator field has plenty of sensitivity to wiring harness condition. This is because the regulator will pass 2-3A to the field and this will cause several hundreds of millivolts change to the voltage the regulator uses for its operation.

So it is better to convert the alternator with 2 wire field which makes possible to drive the field to the ground.

OR just throw the old Mopar alternator and replace with new unit with built in regulator. But not too big unit because the old original wiring harness is not ready for BIG currents.

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1966 Dart. 170 cu.in. 200 rwhp.