Charging Issue, Sporadic charging voltage Options

[Dave_Darling]

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

[slapshot]

@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+.

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

[slapshot]

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?

@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.

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

[slapshot]

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

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.

[DRPHIL914]

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

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.

(IMG:style_emoticons/default/unsure.gif) time for (IMG:style_emoticons/default/sawzall-smiley.gif) (IMG:style_emoticons/default/smash.gif) (IMG:style_emoticons/default/welder.gif)

[slapshot]

(IMG:style_emoticons/default/unsure.gif) time for (IMG:style_emoticons/default/sawzall-smiley.gif) (IMG:style_emoticons/default/smash.gif) (IMG:style_emoticons/default/welder.gif)

Yes, there was lots of that.

[Superhawk996]

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?

@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.

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

[Superhawk996]

@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:

[Spoke]

@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

[Superhawk996]

@spoke

Cool (IMG:style_emoticons/default/beerchug.gif)

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?

(IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/idea.gif)

[Spoke]

@spoke

Cool (IMG:style_emoticons/default/beerchug.gif)

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?

(IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/idea.gif)

@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.

[Spoke]

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 #.

@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.

[Superhawk996]

@spoke

Cool (IMG:style_emoticons/default/beerchug.gif)

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?

(IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/idea.gif)

@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.

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 (IMG:style_emoticons/default/unsure.gif)

@spoke

[Spoke]

@spoke

Cool (IMG:style_emoticons/default/beerchug.gif)

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?

(IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/idea.gif)

@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.

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 (IMG:style_emoticons/default/unsure.gif)

@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.

[slapshot]

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.

[Superhawk996]

I wonder if the 7V on DF at idle after starting up was to recharge the battery after starting the car.

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.

[Superhawk996]

I tightened the gaps on the female connectors so it now takes some force to slid them on the board posts.

(IMG:style_emoticons/default/smilie_pokal.gif)

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.