What's your volt meter reading when cruising around town? Options

[raynekat]

Just curious what the typical volt meter reading is:

1) when you're sitting at the stoplight

2) cruising down the boulevard at 3-4000 rpm

Trying to see if I'm seeing typical or low readings
Thanks

I just recently noted a low charging issue that I believe came down to an alternator/voltage regulator mismatch.
I was using a Bosch VR with my Motorola alternator.
Now I've switched to a Marchal VR and the charging voltages look better.
About 13.75 volts while cruising.

[Pursang]

When driving I think it runs around 13v or so. Warm engine idle is in the 10-11 range but turn signal or brake lights drop it even more. Headlights on is a huge drain. If you know of a shop in the Portland area (SW) that is proficient with the 914 electrical maladies, please let me know. Thanks.

[Mark Henry]

You're good at 13.75v

[dr914@autoatlanta.com]

13.6 is the standard. Anything over 14 volts means that the system is overcharging

Just curious what the typical volt meter reading is:

1) when you're sitting at the stoplight

2) cruising down the boulevard at 3-4000 rpm

Trying to see if I'm seeing typical or low readings
Thanks

I just recently noted a low charging issue that I believe came down to an alternator/voltage regulator mismatch.
I was using a Bosch VR with my Motorola alternator.
Now I've switched to a Marchal VR and the charging voltages look better.
About 13.75 volts while cruising.

[porschetub]

13.6 is the standard. Anything over 14 volts means that the system is overcharging

Just curious what the typical volt meter reading is:

1) when you're sitting at the stoplight

2) cruising down the boulevard at 3-4000 rpm

Trying to see if I'm seeing typical or low readings
Thanks

I just recently noted a low charging issue that I believe came down to an alternator/voltage regulator mismatch.
I was using a Bosch VR with my Motorola alternator.
Now I've switched to a Marchal VR and the charging voltages look better.
About 13.75 volts while cruising.

Not sure about that,my spare Hella unit (new) shows 14.4v on the cover.

[porschetub]

I seemed to remember there was a gold foil sticker indicating matching VR to altenator,don't know if it was on the 914/6 as it looks like a 911 part.
Found this pic;

[SO.O.C914er]

I’m seeing just under 14v day time driving but when I run my lights at night it drops to just above 12v is this normal....mind you this is coming from a guy who is abby normal haha (IMG:style_emoticons/default/av-943.gif)

[914Toy]

Question: what is the accuracy of these voltmeters? - I suspect not better than +/- one volt

[914Toy]

Question: what is the accuracy of these voltmeters? - I suspect not better than +/- one volt

[raynekat]

My 13.75 volts is coming from a voltmeter across the battery terminals.

With the Bosch VR's, I was only getting about 13.2 volts at 3000 rpm.
Driving at night with the lights on and wipers going, you could see the lights visibly dimming at a stoplight as the revs came down.

I also tried a modern Motorola VR that doesn't plug into the socket (had to do some creative wiring to get it to work) and it showed the same as the Bosch VR's.

Still looking around for a "vintage" Motorola VR to try, but perhaps the Marchal is doing a good enough job?
I'll get the car out at night again and check it out.

I've got one of those volt meters/USB things that plug into your cigarette lighter socket for reading voltage while I'm driving.
I'm assuming they are fairly accurate.
Anyone else tried one of those?

[Superhawk996]

My 13.75 volts is coming from a voltmeter across the battery terminals.

With the Bosch VR's, I was only getting about 13.2 volts at 3000 rpm.
Driving at night with the lights on and wipers going, you could see the lights visibly dimming at a stoplight as the revs came down.

Not trying to be an Dope here but welcome to 1969-1976. 13.75 volts is more than enough voltage. Even 13.2 is sufficient to charge.

What you have is a power defecit when you see lights dimming. Said differently you have a current defecit.

Minor dimming is to be expected . . . again welcome to 1970's tech.

If you feel the dimming is excessive, you have to address the current defecit. The 1st suspect would be the battery. When there is a current defecit the battery acts a temporary current source. It should be providing sufficient electrons to keep things powered if the alternator output droops temporarily. Weak battery can start the vehicle and then sill have problems sourcing extra current under continious running load (like lights, wipers, etc.)

All alternators have a current output curve. The 914 alternator doesn't put out much current at idle and/or low revs. I don't know what the specific 914 curve is but the point is they all have a curve. During this low output condition, the battery is expcted to either be just barely charging or with a heavy load (lights, wipers, brake lamps, etc.) it could be net negative for short periods of time. The battery fills the void until the engine rev's come back up, and more current is sourced from the alternator.

If you already have a fresh battery, you could put a current clamp on the battery terminal and monitor it. Current flowing INTO the battery means the battery is charging. Current out of the battery is discharging. Excessive battery discharge with a 13.2 - 13.75 volts across the terminals is a sign that you have a bad alternator this isn't able to keep up with the current demand. Batteries go bad far more often than alternators. A bad battery can act like an excessive load on the alternator due to internal cell shorting within the batttery and can destroy and alternator in short order.

As a theoretical conversation, if your battery were a dead short, the alternator would output maximum current yet the battery voltage across the terminals would read ZERO. The continued max output of the alternator would eventually overheat the windings, brushes, diodes, until the alternator fails some internal component.

The last resort is to replace your alternator but remember, you're replacing it with 1970's tech.

Whatever you do, don't expect a 914 to behave like a modern vehicle. You will have some minor light dimming on a perfectly operating 914 whereas that is not accepted anymore on modern vehicles. Modern vehicle have very elaborate load managment systems. So elaborate that they can for example turn loads off & on without you even knowing in order to keep the voltage and current flowing within the system at an optimal level to protect the battery, and to minimize the fluctuations you see.

For example, your heated seats draw a lot of current. If there is a current defecit, the seats can be turned off yet the heat doesn't go away immediately. They can then be turned back on for a bit to keep them warm, and then off again a few minutes later. All this is done while the LED on the instrument panel remains lit. You have no idea the seats are effectively being pulse width modulated to control the sytem voltage and current. Don't expect this type of system management in a 914.

I've got one of those volt meters/USB things that plug into your cigarette lighter socket for reading voltage while I'm driving.
I'm assuming they are fairly accurate.
Anyone else tried one of those?

Yes, it will be more accurate than the analog VDO gauge thanks to the mircale of modern electronics. The circuit to monitor voltage accurately will fit on a surface mount chip that only costs pennies and is no bigger than a gnat's ass.

[SO.O.C914er]

Extremely good input (superhawk) this really answers what I’m seeing with my car.

[raynekat]

Lots of great info there Superhawk.

I have one of those new fangled Lithium batteries from Anti-Gravity.



They are pretty high tech and super light weight, but are not designed for cars with large loads.
I don't believe an early 914 utilizing mostly LED lighting (headlights, turn signals, brake lights), no AC, no heated seats would draw that much current.

But maybe with all the lights on and the wipers going, I'm starting to get a pretty good load on the battery?
What are your thoughts on that?

With the key off the battery shows about 13.2 volts.

I was thinking about testing the battery's load capability with one of these load testers.



It's entirely possible that this battery will not work for me unfortunately and I'll have to go with a more "conventional" style battery.....

[porschetub]

It's entirely possible that this battery will not work for me unfortunately and I'll have to go with a more "conventional" style battery.....
[/quote]

Could well be your problem,I have a similar issue even with rebuilt altenator,reconditioned relay board ,new engine loom and NOS Bosch VR,have AGM compact battery,someone who knows more than I do told me they don't play well with older charging systems?,I connect my spare wet cell battery and always appear to have less issues.
Its kinda like the system isn't reading the battery fully ,it will take load when forced to i.e. all high load items on but seems to have a mind of its own under normal conditions.
Having said the above this battery has never gone flat and left me stranded so some charging must be holding it up.
My VDO gauge isn't that accurate and reads lower than the battery but its still a reasonable indicator.

[Superhawk996]

Lots of great info there Superhawk.

I have one of those new fangled Lithium batteries from Anti-Gravity.



They are pretty high tech and super light weight, but are not designed for cars with large loads.
I don't believe an early 914 utilizing mostly LED lighting (headlights, turn signals, brake lights), no AC, no heated seats would draw that much current.

But maybe with all the lights on and the wipers going, I'm starting to get a pretty good load on the battery?
What are your thoughts on that?

Dangerous territory. (IMG:style_emoticons/default/happy11.gif) I'm sure to create a debate with this one.

Li-ion batteries haven't made prime time in OEM automotive circles for a lot of reasons.

Here's a couple quick facts:
Antigravity RS-30 is listed as a 30 amp-hour battery.
An Optima 34R is listed as a 50 amp-hour battery.
A group 42 Lead Acid battery would typically be 50-70 Amp hours.

A 30 amp-hour battery is a rating that IMPLIES that it would have the ability to deliver 30 amps for 1 hour or 1 amp for 30 hours. However, batteries don't work that way in practice. A 30 Amp hour battery cannot deliver 30 amps for 1 hour. It's output will fall off drastically as it discharges and the voltage potential of each internal cell declines. There are also issues with the internal battery chemistry occuring when it is discharced too fast or too long. Especially so with Li-ion.

So as a starting point your chosen RS-30 Li-ion battery is at a disadvantage with respect to it's ability to deliver lots of current over time. Your chosen Li-ion only has about 3/5 (60%) the power capacity (i.e. current draw over time) of the Optima AGM and let's just round to maybe 1/2 the power capacity of a Group 42 Pb-Acid wet cell battery. I don't know what your actual load is with your updated LED lighting. It can be measured with a simple current clamp. You are correct that the lighting probably isn't a huge load but also know that LED' ligting can be deceiving - the total draw is less than conventional lighting of the same light ouput but you're still probably drawing 5-8 amps total between headlamps and tail lamps. @Spoke may have more info on what LED total draw is for headlamps, taillamps, and Instrument lighting.

The wiper motor on the other hand is going to draw significant power. More so if the bearings & linkage bushings are worn and creating more motor drag. Again, a current clamp would let you measure the load of the wiper motor.

Li-ion batteries are not great at maintaing their power capacity over time. Especially if they are allwed to become deeply discharged.

You can try the load tester but Li-ion will be a bit deceiving. Li-ion batteries are good at providing lots of instant energy but are not so great at providing high power over long periods of time. Those simple load testers are "calibrated" for Pb-acid. So it may say that it is great when you instantly connect the Li-ion but if you leave it connected, it may drop off quite quickly. If you decide to use that load tester for an extended duration, I'd stay within eyeshot of the battery (with safety glasses on) and have have a fire extinguisher handy. Just as a precaution. Li-ion batteries deserve more respect than Pb-acid for sure. I use Li-ion them in RC cars high discharge & charge rates and I've definately had cells buldge which is the precursor to a thermal runaway. I store them in a vented metal ammo box . . . just in case.

Li-ion batteries are a completely different animal. They have their uses but I'm not sure I'd recommend one for a 914. For racing - definately yes to reduce weight. For a daily driver no, beause they can be fickle and I have no idea how well thier internal battery managment system (BMS) is doing at maintaining internal cell to cell balancing and you don't have any control over the power capacity drop off over charge cycles. In fact, I'm not sure how the BMS works in these batteries. It is conceivable that as current continues to be drawn out of this Li-ion battery, it may reduce the current just to protect itself. Honestly, I have no idea how the BMS in these aftermarket batties is set up. Maybe others with more knowledge on that could chime in.

[raynekat]

Superhawk....again some great comments and insights.

The Antigravity Rs-30 has 1200 cranking amps and weighs 11.5 lbs (one of important reasons I chose this battery....possibly the wrong one).

The Optima 34R has less at 800 cranking amps and weighs in a whopping 37.9 lbs. Obviously this is necessary (the added weight) to get the higher amp-hr rating.

Actually, after the current (or voltage) drops low enough in the Antigravity battery, it turns itself off saving enough power to do 2-3 restarts. Supposedly you'll never get stranded. ??? When I was driving around at night with all the lighting on and the wipers going, my little LED gauge plugged into the cigarette outlet was dropping down to 10V. That got my attention as well as the lights dimming quite a bit while idling at the stoplight.

Sounds to me, a larger amp-hr battery may be in my future.
You are likely right that this would be a great battery for a race car.
It's very lightweight and starts the car.

Wonder if this Antigravity will fit in my Vespa??? (IMG:style_emoticons/default/idea.gif)

[Superhawk996]

Superhawk....again some great comments and insights.

The Optima 34R has less at 800 cranking amps and weighs in a whopping 37.9 lbs. Obviously this is necessary (the added weight) to get the higher amp-hr rating.

Actually, after the current (or voltage) drops low enough in the Antigravity battery, it turns itself off saving enough power to do 2-3 restarts. Supposedly you'll never get stranded. ???

Yup, to steal from my previous post: Li-ion batteries are good at providing lots of instant energy (i.e. cold crank amps) but are not so great at providing high power over long periods of time.

The restart / shut off below a voltage limit is the battery managment system. What we don't know is if the BMS is throttling back the maximum current draw allowed as the battery state of charge drops with your loads applied. Sounds like it is, if you're getting down to 10 volts! Would be really interesting to put a current clamp on it and monitor how much current is being delivered as time goes on.

What I don't have a good answer for is what the voltage regulator will do in response to a Li-ion BMS system and it's interactions. At 10 volts It should be applying full field to the alternator trying to generate more current. The problem is the BMS might also be limiting current into the battery if the BMS is sensing that the internal Li-ion battery cell temperatures are too high either from too much charge rate or too much discharge due to load. I honestly don't know on that one.

Out of curiosity are you using an LED to light the gauge generator light? If you are using an LED for generator lamp lighting, do you have a resistor in that generator lamp circuit to allow the alternator to begin fielding current initially at start up?

FYI - not sure what your budget is but you could pick up a cheap AC/DC current clamp with sometthing on the order of a 60A range and tell what is going on for sure if you don't already have one.

[Spoke]

As far as LED current is concerned, my brake boards burn about 5W when on. Turnsignals about the same. So worst case is sitting on the brakes with turnsignals on. That would be

5W x 2 + 5W x 2 = 20W which is a bit lower than 2 amps.

Not sure about LED headlights. I would assume 15-30W each. 1.5-2.5A each.

[Superhawk996]

As far as LED current is concerned, my brake boards burn about 5W when on. Turnsignals about the same. So worst case is sitting on the brakes with turnsignals on. That would be

5W x 2 + 5W x 2 = 20W which is a bit lower than 2 amps.

Not sure about LED headlights. I would assume 15-30W each. 1.5-2.5A each.

So let's call that 7 amps for LED exterior lighting. But we still have some higher legacy loads:

Anyone ever meausured the following items?
Wiper Motor - TBD
Ignition coil - TBD
Radio and/or auxillary amplifiers - TBD. I know my modern radio is fused 10A (4 ch. x 25 watt RMS). Probably draws 4A steady state.
Fog Lamps - depends of LED or conventional.
Other goodies - radar detector, phone charging, etc.

[raynekat]

My car still has normal light bulbs in all the gauges including the generator light. The generator light appears to act normally. Turn the key, and the generator lamp lights up until you start the car. When I first start it up, I get a small glow until I blip the throttle and get the revs up, and the light disappears. After a few minutes warming up on the hand throttle, upon release of the hand throttle and idling at about 700-800 rpm, you don't see the generator light.

The engine is your standard MFI with the CDI box arrangement.

When I had my issue, I had the headlights on, brakes on and wipers on plus the engine of course.

I'll pick up one of the current clamps that you mentioned here in the next day or so, and report back on what I find. Is it easy to measure DC current? Or are we measuring AC current? Thought most everything on the car was DC.