So was noticing I have less voltage while the car is running. I am use to seeing 13/14 volts as the pretty much normal. I have a fairly new marchel alternator and this year I am seeing 13v on the high side. Now I do have more electrical items, wide band o2, mega squirt, and active exhaust. Regulator going bad? Pictured in upper left. Hmm maybe I have them on the wrong pins? Might have messed that up?Click to view attachment

All consumers off ? Belt too loose ?
I can't describe how it's done but I understand there is a way to test output of an
alternator before the VR.
Maybe someone can chime in ?

That would be great if someone would. It would suck to have to change the alternator now

Ben, why are using a remote regulator....Arn't they all in the alternators on 911s. or 914-6 went the same way as the fours. Mark

No none of them until the mid 80s went to integrated regulators. The external regulators actually work really well. I just need to relearn it

Wait ... someone makes a brain fart regulator? I could use one of those at work! Where can I order one?

Since your regulator isn't part of your alternator, can't you just put a voltmeter at the output of the alternator & measure it's output voltage as you rev the engine?

What am I missing here?

Subscribed (FWIW)

What are the normal voltages? All I'm getting from my alternator is 13.6V

Well it’s AC coming of the alternator then the regulator /recitifier turns it to DC

Ben,

I’m on vacation with no access to my technical documents but happy to see what I can find on-line to help.

I don’t recognize that regulator. Is is just a 3 pin mechanical regulator or is it something different?

You should be seeing higher than 13v with say rev’s higher than 1500-2000 rpm.

As others have alluded to - make sure you don’t have some high current draw somewhere loading the system heavily. I doubt that is the case - it would take a heck of a lot of load but something like heated seats or something like an active exhaust actuator that is stuck might be pulling high current????

"All I'm getting from my alternator is 13.6 V."

???

Then measure the AC voltage which will be either rms or peak depending on your voltmeter. The rms voltage is peak/1.4.

What you measure at the wall socket is rms. FYI.

The fuses to the active exhaust are 5 amp so that’s not it. I will check connections and then I will probably dissect the regulator and see if it needs cleaning etc

Well I know I am getting some charging just not as much as I want so the alternator is producing power

Let me clarify here. If your voltmeter reads 120 V at the wall socket, then it measures rms voltage.

Speaking of power, 1 watt = 1 volt amp. Measuring current is a PITA since you need a really beefy ammeter that has to be placed in series with the circuit that you're testing. This is old school like me.

On the other hand, you can go with one of these:

https://www.amazon.com/Fluke-302-Digital-Cl...72629&psc=1

Assuming you’re running a 3 pin mechanical regulator here’s the 911 factory manual diagram / color code

Not at all uncommon to get some corrosion on the regulator contacts that can inhibit charging. In the past I’ve hit them with 400 grit and revived an in-op regulator.

Your regulator appears to have the cover riveted on unlike the Bosch /4 regulators there just have a taped on cover
Click to view attachment

One last thing to keep in mind is the charging voltage is dependent on battery state of charge. So if your battery is fully charged, you’re not going to develop 14v of charging voltage.

Does your charging voltage change as you load the alternator with headlamps or blower fans?

This guy knows his shit.

I’m going to post one more which is Spoke’s simplified schematic for an alternator and 3 pin regulator

I did a strike through on a line that has no bearing to your issue.

As previously noted the voltage on the field (DF) will vary based on battery state of charge and the electrical load the system is seeing. A higher voltage on DF indicates the system is “pushing” the alternator harder and trying to increase alternator output.

Click to view attachment

Note: color codes on this reflect the /4 914 regulator wiring. The other illustration is from a 911 factory manual and 911 wiring, thus the difference in color of wires.

Note 2: the voltage measurement of DF is referenced with the regulator plugged in and functioning by rapidly energizing and de-energizing the solenoid coil within the regulator.

Battery healthy? In some cases the alternator just cannot find enough charge to push against.

That’s a good possibility the battery is a pretty old optima. Switching to a new battery shortly. Good thought as well.

Thanks that will help me track it down

Yeah, that's what I was hoping to learn about.

Where are you taking the voltage reading from? If it's the standard center console gauge, it's normal for it to read low. And change a lot depending on the electrical load on the system, particularly turn signals and such.

--DD

Ben your VR and Alt are both SEV Marshal...so should be compatible.
You're in a certain era of 911 equipment ('74-'77 ?) so keep that in mind.
I feel for you... I recently did the whole job ....engine in the car only to discover a
loose wire on the back of the alternator. My own mistake from 2009

Ben,

I would suggest running a "full field test" on your alternator. Disconnect the regulator, and start the car. With a DVOM connected to the battery posts, apply positive voltage to the DF wire that attaches to the voltage regulator using a wire from it to the positive battery post. You should hear a whine as the alternator goes to maximum charge, and you should see 15 Volts or more on the DVOM.

If you don't, you have a bad alternator. If you do, it is a problem with the regulator.

Right at the battery

Bingo!
It's been a LONG time since I full fielded one.

Only way to go with an external regulator.

All alternators have a "thermal cut" in speed.

You need 1500-2000 rpm to properly load test an alternator/generator.

I want to quantify a few things. As rpm increases I do see charging just not what I would expect, alternator has a few thousand miles on it from @mepstein and his rebuild source, the charge voltage was spot on last fall when I put the car away for the winter, I just cleaned up wiring but did change out the voltmeter I had for an integrated unit from John bell, the battery is 10 years old just confirmed this morning, I am changing that out today, one thing I noticed a few weeks back as the battery tender was on the battery isolated from the car is that the tender was charging the battery for a day and getting hot. I assumed it was a bad tender and bought a new one. It’s the name brand battery tender so not sure what was going on. I will verify everything today maybe. It’s like Texas up here not sure how you guys work in that temp on the regular

Dude.. you get used to it. And we adopted the Mexican's siesta mentality. If we have to work outside, we get up early and work until noon, then sleep in the hot afternoon and go back to work in the evening when it cools down.

Me personally, I put AC in my garage.


I can't see how you can survive the winter cold up there. I am bundled up in a heavy coat when it gets below 40 degrees F. And I HATE snow!

That’s a good idea. Did a little bit this morning after the gym, then maybe a nap today then back at it. Gotta figure out autotune on megasquirt as well but tuning in this weather sucks

Just know that if you full field it - you will get an uncontrolled voltage well over 14v.

If you have other electronics in the car that aren’t over voltage protected (not sure on MS specs) disconnect them before full fielding.

Good point that would be bad

So verified some basic connections and ohms tested the wiring. The 12v wire all good. Ground good. dF is weird as I get different values depending on what 12 pin connection I check. I know that’s not a field test but now concerned I could blow something out with over voltage

Oh but the interesting thing is the battery light does go out when the car starts. Gonna verify tomorrow that it has the right bulb in it though

The DF varying by where you test it may be a sign you’ve got some voltage drop going on. Either within the relay board multipin connector (pin 2) or within the board between pin 2 and DF. Might try a quick clean up of pin 2 and its female counterpart.

I wouldn’t worry about it going over voltage from varying DF due dirty connections. If anything voltage drop might be why you’re seeing only 13v instead of something more solid like 13.6 - 14 volts.

One other thing about DF is that it usually isn’t a rock solid stable voltage. It’s the nature of the beast (mechanical regulator) due to the regulator solenoid serving as a sort of very crude pulse width modulation of the field. Some fluctuation is normal as DF leads and lags the actual alternator output. Example if you measure pin 2 and then take a minute or two to remeasure over at 3 pin DF connection, the voltage may have already changed a volt or two.

The ultimate judge is what’s coming off D+ and B+ (alternator output to battery positive).

A hair off topic, and not to hijack, but why is the vdo volt meter so wonky? Mine is running right off the battery but it still isn't reliable (it just doesn't respond to the brake/turn signals anymore).

I’m confused. So you want it bouncing around?

If you are running it right off the battery it should be stable. The battery (in theory) is an infinite current source and its voltage should remain unaffected by minor loads like a turn signal bulb.

The OEM red / white wire that supplied the volt meter ran a convoluted route from battery to fuse 9, to the stop switch, and then to the volt meter and is subject to variance and voltage drops across lots of wire and the fuse. That red / white wire also went to a number of other locations that could load it down.

Easy enough to go back to original if you miss the variability dependent on load.

Today I am digging into to gauges. That is the other area I messed with over the winter.

@ClayPerrine thanks for this. Was super nervous about doing this but checked this morning and appear alternator is perfectly fine so need to get a regulator I guess. I did pop the cover off my regulator not sure what to check so may have to go digital but at least the engine doesn’t need to come out

Not sure if this will help...

The late model Miatas have a generator and the voltage regulator is the ECU.

Megasquirts can be arranged to provide this. You end up setting a "target voltage" in parameters in the squirt.

Don't know if this is applicable to a Porsche generator but the hard work may have already been done.

If you want to try it look to the Mazda solution for directions/ideas.

"Late" Miatas mean NB1s and NB2s for me. So, the years I'm referring to are 99-05.

I think some of the NAs pre 99 also did this as one of the old school mods to make this work was installing a 90-93 alternator in the newer model.

After they figured out how to work it in the squirt no one puts the old alternator in anymore.

Hmm that’s interesting and good to know. I am learning MS right now. It is an amazing ECU for the money

Yeah, I don't miss that, it's just that it isn't accurate. It's like it has to warm up or something. I will have the multimeter on the battery and it will be showing 13.7 and the gauge will be down around 12.5, and 5 minutes later it will be up at 13.5ish. eventually it gets its crap together but I can't really trust it. I cleaned up all the connections today and it's still like that. Maybe it's some kind of ballast to keep it from bouncing around?

@emeryGT350

That doesn’t seem right. Let me check my gauge against bench power supply and DMM. Give me a couple days - away on vacation but I’ll post result when I get back.

You can control an alternator with Megasquirt. I have it in process for my 4.0 engine. It can't be done with the later internally regulated alternator, but it can be with the external regulated alternator.

From the MS3Pro manual:

High speed feedback field control: A different method of closed loop alternator field control, similar to an
electronic version of a points type regulator. The MS3Pro monitors the battery voltage at 20 kHz and switches
the field off if it is above target voltage, and switches the field on if it is below target voltage. Often easier to
set up than closed loop field control, as there are no PID parameters to tune - you just need to select this
mode and set a target voltage.
If the ECU is controlling the field coil directly, we recommend running the output through a solid state relay or external
power transistor. Many alternator field coils may require 10 amps or more, which is more than the MS3Pro’s
recommended output current.

You can replace the voltage regulator with a solid state relay, and use the Megasquirt to control the relay. the DF wire should be connected to pin 87 of a Bosch solid state relay, and pin 30 connected to the battery positive post. Pin 85 would connect to the ECU and pin 86 would connect to ground (I think...It may have to connect to 12v. Consult the Megasquirt manual). The programming should be fairly simple.

You will have to make the generator light trigger from the ECU if you want to have it work.

If you do it, let us know how it works.

Clay

1st thing is first and get a regulator on there and tune the car. Then I will tackle that. I am learning autotune now.

I'm in agreement!

I'd start with a stand-alone power generation system if I had the option.

Having less stuff in the squirt at initial light up is easier IMO.

If I continued to have regulator issues I would try to incorporate it into the squirt.

I would agree with that. Keep it simple at first, then add things like this later.

I honestly thought you already had it running well on the Megasquirt.

Clay

Decent not great. Was working on that and my voltage levels became subject and that reason for this post

What does the 12 pin connection have to do with DF? In the 914/4, DF goes between the alternator and the VR and goes through the 3 pin connector between them. That's it.

Did you do some tests on the 3 VR voltages while running? This can tell a lot about your system.

When running, measure these voltages at the VR:

D+ should be 13-14V
DF should vary between 5-10V depending on electrical load.
D- should be 0V

Also measure the battery voltage:
B+ should be 13-14V and follow D+

Measure all voltages with respect to a chassis lug, not the engine case.

For the field test, remove the VR and short DF to D+ then start the engine. This should force maximum voltage of about 16V on D+ and B+. Do this for a short burst as it's hard on the battery and alternator.

As an aside, my '86 930 was showing low battery voltage (12V) and slow starting. I bought a new battery and immediately got 13.5V steady. You mentioned you were going to replace your 10 year old battery. Did you replace it and did it make a difference?