I've been unable to figure out why my charging voltage is so sporadic. Charging voltage ranges from 12.35 volts to 16+ volts. I first noticed this 2 months ago but it could have been going on since I got the car last November. I've tried 4 voltage regulators, the one that came with the car (after market), an original VR from a 74 1.8l and two different models from Transpo. The issue is the same with all VRs, with the voltage jumping around as RPMs change. Today I started it and the voltage at the battery was 12:35 with the car running. Voltage did not change as the increase RPMs while the car was still parked. When I took it for a drive I saw it was over 14V then later it was over 16V. Voltage does lower to the expected amount (< 14B) when I turn the head lights on which puts more load on the battery. I've redone three grounds, the one above the transaxle in the back, the one under the relay board and the one under the fuse panel under the dash. Has anyone else experienced this?

Check the belt and puleys. Loose/worn?
Next is to pull the alternator and have it checked/rebuilt.

Speaking of voltage regulators, maybe yours is shot.

Did all 4 VRs give the same results? Exactly the same?

Does the GEN light come on when starting then go out for all driving?

With the engine running, lights on, measure the 3 voltages on the VR connector to chassis, not engine case.

D+ should be 14V
DF should hover 5-10V
D- should be zero volts

The charging system is quite simple but the components are buried in the car.

D+ and battery voltage and B+ should be identical.

Measure all to chassis, not engine case or battery neg.

The belt is tight and I'm able to turn the crank using the 22mm bold on the alternator pulley to set TDC for valve adjusts. Removing the alternator and having it rebuilt might be what I end up doing since swapping VRs and checking grounds does nothing.

I've tried 4. 2 are new.

All VRs react the same.
The charging light hasn't come on today even with the key on not running. I have seen it come on before.

Here's what I've got

Right after startup.
D+: 0V
DF: 0V
D-: 0V
B+: 12.6V

After a 1 minute drive parked at idle.
D+: 12.6V
DF: 7V
D-: 0V
B+: 13.7V

Parked reved @3000 RPMs
D+: 16V
DF: 3.1V
D-: 0V
B+: 15.9V

Have you measured the alternator output vs. rpm & time?

I went for a drive tonight and the battery guage in the car shows normal voltages with the lights on. Well, I'm not sure if normal is right but it stays between 12.5 and 14.0. With the lights out I see it go above 16 whitch is the last #.

I'm not sure what you mean by "Have you measured the alternator output vs. rpm & time?". Is that different from what I did above? I haven't disconnected the alternater output yet. I've read not to run the car with the alternator disconnected. Maybe its fine for a short test.

I figured out my charge light on the dash gauge. The issue was with the new VR I got today. The mounting plate on this one doesn't reach the screw holes in the relay board when plugged into the relay board. I had read in another thread that you can turn the VR around and plug the alternator cable directly into the VR. doing that broke the circuit to the charging dash light. It might have been the reason I got 0 volts on D+ and DF on initial start up for my test. I don't know. After I plugged the VR to the board as designed my charging light eliminated with the key on and car not running then turned off after started. My D+ voltage did jump over 14 while revving in my garage. I'll test again tomorrow when I don't need my lights to drive.

OK without the GEN light in the circuit the VR may have a hard time starting up. The GEN light provides just that little bit of current needed by the armature to develop some magnetism to get the alternator started. This is called bootstrapping.

If you spin the motor fast enough even w/o the GEN light, a little bit of residual magnetism in the armature while spinning fast could get the alternator started.

Once started up, the alternator doesn't need the GEN light thus it's off during normal operation.

Your measurement of 16V is a problem. The battery voltage should never go much over 14V and unless loaded down with lights at low RPM, shouldn't go below 13V.

^ I didn't know about the operational details re alternator bootstrapping until just now, but just had this scenario happen as the Gen LED in my (old) custom Mark Surel quad-gauge failed. My mechanic was thinking using an LED vs incandescent bulb might interfere with proper charging system operations but it does seem to be working fine again with a new LED via NH Speedo and a new Hella VR.

Do not disconnect the alternator.

If I were a betting man, I’d bet alternator armature brushes are worn out or sticking based on the readings right after start up.

Would also explain the erratic readings as you drive.

The other weird reading is the 16v @ 3000 rpm with DF at 3.1v. Seems like the alternator is being full fielded but with very little voltage on DF. Could potentially be two issues with both a bad alternator and a sticky voltage regulator?

The more I look at the numbers - a sticking voltage regulator could also account for the numbers you see at at start up if contacts between D+ and DF are open. If they are stuck open, and DF isn’t even making it to the armature until then contacts rattle around / come unstuck and then the alternator can be bootstrapped to life.

I’d start by getting a good Bosch voltage regulator in to it. The fact that you have 4 of unknown quality and history isn’t helping convince me it’s not the voltage regulator based on your measurements.

914Sixer has a used Bosch solid state on F/S and sounds like a couple other NOS units on the way which will seem pricey but will be better than cobbled aftermarket units that don’t fit right.

Do you know what kind of regulators you’re currently using are - solid state transistor or the original mechanical solenoid style? Original mechanical regulators are sometimes repairable by cleaning the contacts between D+ and DF if you’re inclined to try to troubleshoot a mechanical regulator.

http://www.914world.com/bbs2/index.php?showtopic=367286

Edit: just seeing this in context of initial readings after start

Yet another reason to stop screwing with aftermarket voltage regulators that don’t fit and may not work properly:

The more I look at your post(s) and the measurements - the more I’m leaning toward a bad voltage regulator regardless of what I said initially about armature brushes.

Click to view attachment

I didn't have a chance to look at it today.

The VR I just bought and have on it now is

https://www.amazon.com/dp/B09KSCGLZV?psc=1&...product_details

The one I bought last month is

https://www.amazon.com/gp/product/B09KSD9YH...=UTF8&psc=1

I have an original Bosch from a 74 1.8L. The one that was on it when I bought it was aftermarket. Its at the landfill now.

I'm leaning towards removing the alternator and see what the condition of the brushes are in. The alternator was replaced in 2010. If all looks good there, I'll go back to the VR.

Just a heads up getting to alternator diodes and brushes isn’t easy. More often than not the alternator pulley is seriously tight on the armature shaft to the point that you will bend the pulley trying to remove it.

Of the regulators you posted links to the first appears to be solid state but shows some sort of adjustable potentiometer on the bottom - weird that a potentiometer would be left exposed like that. The second regulator looks to be more like mechanical solenoid based in a taped can.

Both made in China and I wouldn’t trust either of them to be working unless they were bench tested and verified to be working. Neither has any statistically significant user reviews to know how the quality of these units is.

Why the opposition to a decent Bosch unit?

The other thing that I’d verify is that all the spade terminals in the relay board and the alternator feed to the board are clean and tight. Loose connections, not making proper contact can lead to regulation problems. Are you absolutely sure the regulator is making positive contact with the terminals in the relay board?

Thanks for the info on the alternator, Sounds like I'd be getting into more than I want or should.

I'm not opposed to a Bosch VR. I just felt that with 4 VRs giving the same result I should look elsewhere. I'm going to PMB Performance tomorrow to get some wheel bearings and will buy the VR they sale. I will also ask if they are able to test my VRs.

My relay board isn't in perfect condition but I wouldn't say its in poor condition either. I think you make a great point with connections being a possibility. That's something I can work on.

@slapshot
@Superhawk996

I wonder what this potentiometer is for. Was there any information of how to set this pot?

Does yours even have this pot? Maybe this is a stock photo.

I have to imagine that there could be a gain setting in a VR to provide exactly the correct DF voltage given the voltage feedback at D+.

@Superhawk996

Yeah I noticed the low voltage at DF at high RPM too. Not quite sure what to make of it. I kinda looked beyond that assuming a high RPM armature would couple to the stator much more efficiently at high speed thus requiring less voltage at DF. Makes me want to start up my 914 and do this test at idle and 3k RPM.

When you talk about the voltage in your car reading all over the place, are you talking about the stock voltmeter in the center console, or a multimeter connected across the battery posts?

The stock meter is hooked into a circuit that gets lots of voltage droop from lights being on. It is best used for entertainment purposes, or to notice if you have a bulb out.

Going up to 16V at any time is a problem. This is boiling your battery, and is likely to be dripping acid down into your "hell hole". Baking soda and water is your friend now, and rinsing it all off thoroughly afterwards.

Not having the alternator light come on when the engine is off is a problem. It could be a problem with the wiring, with the light, with the voltage regulator (or the VR may not be plugged in!), or with the alternator itself.

--DD

Yes, mine has that adjustment. There were no instructions and it didn't effect my measurements.

If you have time, I'd like to know what yours measures.

The center gauge is where I first saw it and is why I starting troubleshooting. I have been taking measurements on the battery as well to validate its accuracy and the voltage at the battery does follow the gauge.

I've been watching the battery for leakage and haven't seen any yet. I'm going to take the battery out and get a full view. I just fixed the hell hole this spring. It had gone all the way through.

Lights and other loads definitely effects the voltage measurements. With the lights on the measurements are good and stable with the battery charging between 13.6 and 14.0V. Its with no or little load when the voltages jump around and reach 16+V.
Click to view attachment Click to view attachment

time for

Yes, there was lots of that.

Click to view attachment Click to view attachment

I’ve got some downtime coming my way over the next few days. I’ll try to bench test my mechanical Bosch VR and see what DF is with 16V D+. I believe it would be very close to 0v.

@spoke

@Spoke

Couldn't find my old mechanical regulator - buried somewhere in storage.

Bench test of the Bosch 1/2 size solid state has the regulation point set about 14.4v. Up until that break point, DF is tracking D+. By the time D+ reaches 14.6v, DF is in the millivolt range and would have the alternator field windings shut off.

Will be interesting to see what you get on a running vehicle to see the interplay as the field is shut off / turned on very quickly around the regulation point. Can't imagine it would be anywhere near 3v on DF by the time you get to 16 Volts on D+. The catch is you'll never see 16v on a properly operating vehicle.

Video link:


https://www.youtube.com/watch?v=/wLwfuzusBJM?si=Z7YaiCQu2yiMNqXH



I’ll look for mechanical regulator next time I’m at my storage unit.

Test setup:
Click to view attachment

@Superhawk996

Started up the 914 today but didn't blip the throttle and the GEN light stayed on as the alternator hadn't started up yet. The voltage at D+ was 1.8V. I didn't measure DF. The dash voltmeter was sitting at 12V.

Once I blipped the throttle, the GEN light went out and the voltage on my dash voltmeter went to 14V.

At idle:
V+ = 13.8V
VF = 7V

At 2k RPM:
V+ = 13.9V
VF = 3.1V

At 3k RPM:
V+ = 13.98V
VF = 2.7V

Turned headlights ON for the rest of the tests. Headlights are LEDs

At Idle:
V+ = 13.87V
VF = 5.5-6.5V

At 3k RPM:
V+ = 13.95V
VF = 3.1V

@spoke

Cool

So how is he getting 16v D+ and 15.9 B+ on a 3v(ish) DF? Measurement error? Some sort of current leak into the alternator field windings that becomes self energizing?

@Superhawk996

The only thing I can think of is if the DF voltage of the VR cannot go lower than 3.1V or so. Just like some dc/dc converters have a minimum duty cycle, maybe VRs do too. Plus the one he has has a pot on it which looks like it could be adjusted. Not sure what that is.

@slapshot

Could you repeat your D+/DF/Battery measurements at 3k RPM with lights on and lights off? Are your lights standard incandescent lights? Mine are LED and draw much less power than incandescents.

Even so - DF is really just a pulse width modulated average of D+ right?

That means using 12v (for easy math) a 3v DF means we have a 25% duty cycle of D+ between field on - mechanical VR contacts closed (12v applied to field) vs open (0 volts applied to field).

So what if the 3v DF coming out of his voltage regulator was an actual continuous 3v DC (non PWM) voltage? Would that 3vdc 100% duty cycle be enough to full field an alternator? Personally, I don’t think so but I’ve never tried it on a bench or in a car. I’ve only full fielded using 12v directly off a jumper. Wonder what the curve looks like of field voltage vs output.

Based on your start up measurements - it seems to be taking 7v to get you up to “normal” output so it sure seems like even a 3vdc constant voltage would get a full field output.

Crazy

@spoke

@Superhawk996

I wonder if the 7V on DF at idle after starting up was to recharge the battery after starting the car. I didn't rev the engine at all during starting thus the alternator didn't start up. I just blipped the throttle a bit to get the alternator started then let it idle for a bit.

Your comment about PWM has merit. Voltmeters are great for dc measurements but all other waveforms like PWM or ramps the voltmeter will just integrate the output to give a dc voltage. My next measurement (probably next week) I'll do with my oscilloscope.

It's not unusual for 914 owners to have troubles with different types of VRs with many resorting to OEM VRs to get their charging systems working correctly.

First, thanks all for all the info and data.

Last night I took the wires out of the connector form the alternator that plugs in to the relay board. I feel the wire connectors could be loose on the posts on the board. The plug slipped on without really any resistance. I tightened the gaps on the female connectors so it now takes some force to slid them on the board posts.

I took it for a quick ride this evening before dark and the center gauge was stable somewhere between 14 and 14.5V. It seemed promising that the issue was with the connections.

Heres my readings tonight.

Startup
Battery: 13.9
D+: 13.25
DF: 9
D-: 0.03

At idle after 5 mins
Battery: 14.7
D+: 14
DF: 7.5
D-: 0.03

@3000 RPM
Battery: 14.3
D+: 14.2
DF: 3
D-: 0.02

Lights on @idle
Battery: 13.7
D+: 13.3
DF: 9.6
D-: 0.05

Lights on @3000 RPM
Battery: 13.8
D+: 14.0
DF: 4.6
D-: 0.06

I have LED headlights and dash lights. All other lights are standard lights.

I went for another drive tonight after dark and the center gauge held steady between ~13 and 14V with lights on. When I got back and after I turned off the lights the gauge jump higher than I want to see. I put a meter on the battery and it was at 14.9V. That's pushing it. Maybe it was just trying to charge the battery after using the lights for the 20 minute drive. I'd like to keep it below 14V if possible. I think you are right that I need a better quality VR. PMB didn't have one in stock. Their parts guy says they get them from a supplier in Canada. I don't think its made by Bosch.

100% sure DF will always be elevated right after a cold start. Battery will be down slightly from sitting and then it just had lots of juice pulled out to start. As a result the field will need more “drive” to get current back into the battery and to bring state of State of Charge (SOC) back up. At initial start the battery acts like a load on the alternator.

Once SOC is back up, the field voltage (DF) will diminish.

You can see this in both your data and the new data Slapshot provided with terminals tightened and the voltages looking more normal.

I suspect his DF voltages are incrementally higher either because of the voltage regulator itself and/or his battery may not have been near 100% SOC due to the irregular charging he’s been experiencing.

Looking promising - keep an eye on it.

I really would try to find a NOS Bosch regulator. 914Sixer usually finds them from time to time - he’s a magician at sourcing NOS parts as they pop up around the world. His prices are reasonable and he’s an awesome resource for this community.