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.

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.

You're good at 13.75v

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

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

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;
Click to view attachment

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

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

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

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?

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.



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.

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

Lots of great info there Superhawk.

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

Click to view attachment

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.

Click to view attachment

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.....

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.

Dangerous territory. 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.

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???

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.

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.

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.

Glad to hear the Generator bulb is still incandescent. That takes one variable out of the loop. Seems to be working properly.

Don't underestimate a CDI current draw. Quick info I can find seems on Summit Racing site for a Mallory CDI indicate about 0.7 to 0.9A/1000 rev's. So at a 3000 RPM cruise, that is 2.7A just from that device alone.

We are measuring DC current.

With a current clamp it is super easy non invasive measurement.

Just place the clamp around the red wire that leads from the alternator to the B+ source (actually starter motor terminal IIRC) to see what the alternator is doing on its own (is it sourcing current to the battery, how much current, etc).

Likewise, if you want to see the net inflow/outflow of the battery, you can put the clamp around the large (like 4AWG gauge) red battery wire. This is where you would be able to see what your actual electrical loads are that the battery is sourcing current to.

There are hall effect AC/DC current clamps that can read both AC and DC current. The super cheap ones (like $30) usually are AC only - you don't want one of those. However, I think last I looked, you could find one that measure AC & DC for about $80.

Just be sure that it has something on the order of a 0-6A or 0-10A low range for DC current. Be sure to look at specs on low end units. Sometimes the range is 0-60A; depneding on the accuracy, something on the order of 6A load might very well be +/- a couple of amps which might make it difficult to see what is going on. Could definately tell current direction (charging or not charging) but it might be hard to see if the Li-ion BMS is throttling current by a couple amps.

Here's the current clamp I purchased.
Took quite awhile to find the right one as most on eBay, Harbor Freight, etc only do AC current.
I wanted DC current.

This Uni-T UT210E from China (oh why oh why can't Americans make something like this for a decent price?).
It was $62.48 delivered.
How can you go wrong?

The specs that I was most interested in:
DC current
2.000A with 1mA resolution and +/- 2%+8 accuracy
20.00A with 10mA resolution and +/- 2%+3 accuracy
100.0A with 100mA resolution and +/- 2%+3 accuracy

So the selector can choose between 3 ranges for current.

Click to view attachment

https://www.ebay.com/itm/New-Uni-T-B4Q094-U...353.m2749.l2649

Guess the next question is where exactly would I measure for current draw?
On one of the main cables coming out of the positive terminal from the battery?

On a positive note, I checked the charging at my battery with the car running about 2500 rpm.

It was measuring 13.85V which seems like a decent enough value for the alternator/voltage regulator system.

See my previous post for suggested locations.

Interested to see what results you get on actual current draw.

Superhawk....I think you were dead on about that Lithium Ion battery not being "big" enough.
It just doesn't have the reserve to keep up with the electrical usage on the car.
This is what I measured on one of the big cables coming off the positive terminal on the battery.
The values you see listed below is the total reading I read off the clamp meter....not what each additional component added to the total (i.e. engine running with running lights on was 6.6A....the running lights alone were something close to 3A).

At idle (baseline): 3.6A

Add running lights: 6.6A (only about 3A added, Spoke's LEDs in rear, normal in front, with LED side marker bulbs)

Add headlights: 9.2A (guess the 914Rubber LED headlights are fairly energy efficient...added 2.6A)

Add front fog light: 16.1A (these are normal bulbs...about 7A)

Add rear fog light: 18.2A (again a normal bulb.....only about 2A added)

Add wipers on low: ~25A (the meter was really jumping around with the wipers)

At idle with wipers only: 8-10A (about 6A added)

So the 30 Amp-hr rating on the Lithium-Ion battery is not enough to keep up with all these loads turned on at the same time. I didn't even try adding the defroster fan or higher wiper speeds as the car (or built-in circuitry of the battery) turned itself off pretty quickly after I added the wipers and got the load up in the 25A range.

Luckily the battery always keeps a reserve allowing a couple of restarts after it shuts itself off. So the battery operated as advertised it seems.

Takeaway..... This battery is OK for race cars (autocrossing) and driving around town during the day in nice weather. Which is what I will likely only be doing. Any nighttime or distance driving and I'd want a different battery. I'll definitely be thinking about moving up to a 50-70 Amp-hr battery this Spring at any rate.

Nice work and great information for the community. Thanks for taking one for the team!

Yeah, that is definately too much for a 30Ah Li-ion battery.

So reported numbers are at idle, I know it would be hard to document running over time, on the road, but I'm 99% sure you will have two things occur:

1) Any battery (including Lead/Acid) will begin to lose cell to cell voltage as it discharges and current will drop accordingly according to Ohms law I= V/R where R is fixed by the components. Actually I'm 100% sure on this one!

2) Ultimately the battery managment sytem (BMS) will end up disconnecting the load (internally) to the battery so that the Li-ion battery doesn't completely discharge, which would harm the battery. On the way to that point, a Li-ion BMS MAY begin to throttle current to the load as cell voltages dip depending on how the BMS was designed to operate. I think it your case, it didn't throttle current since you said it allowed up to about that 25A draw and then just suddently disconnected.

Out of curiosity, did you get the current clamp around the alternator ouput wire (B+ that goes to starter)? I'm sure you're alternator is pumping out some juice to help offset the draw when you're running which explains how you are able to get more than say 1 hour of running time if you were indeed drawing 25A total on just the battery.

Alternator is 50A so in theory it should offset completely but the reality of stop & go driving is that you're probably spending more time idling than you think and at that point, the battery will have a hard time keeping up and you'll see the dimming that started the thread discussion.

Thanks for posting those number Doug! This is something I've been very curious about. Especially the draw with LED lights.

Makes me long for the days of ammeter gauges on the dash. I did install a voltmeter in the ashtray area to be able to keep track of system voltage at least. However, the glowing light is a good backup and much better than nothing.

Usually reads about 13.5 volts while driving. I don’t know how accurate the VDO voltmeter is in comparison to the plug in ones (but I do use one in the cigarette lighter socket on my 911.
Click to view attachment

I measured the VDO voltmeter in my car and found the voltmeter to be within 0.1V in the 8 to 16V range. The real error as we all know is connecting the voltmeter somewhere in the 914 wire loom where voltage drops are common.

I've got an Odessey PC925 battery in my car and I can confirm some of this for sure.

It works GREAT for trips where weather is not a problem, night or day, and has a TON of cranking power.
As soon as I turn on the wipers though I can watch my volt meter start to dip as I drive, until it settles in at about 10.5 volts.
The PC925 is listed as a 28AH battery. One of my tasks for this year is to get a more conventional battery with a better AH rating.

Zach

Here's what the "offending" battery looks like for those curious.
It's made by a company called Antigravity.
And this particular model, RS-30 with Restart, is no longer manufactured by them.
It's light weight....about 11.5 lbs and has a battery hold bracket available.
The bracket was slightly too wide to fit in the stock 914 battery tray, so I took it down to a local water jet company and had them carefully trim it to fit.
The bracket is aluminum.

Click to view attachment

A pic of the battery/bracket installed in the 914.

Click to view attachment

Unfortunately it will likely not be a great choice for more of a "daily" driver type of car.
For only the occasional Sunday drive (in nice weather), auto crossing or track days, I think this is a great option. It definitely starts up the car without any issues.

Scary part of the the Antigravity battery line-up is that the battery I had purchased was by far the battery with the largest amp-hr rating.
Most are much smaller than the 30 amp-hr the above battery has.
So they are indeed only "starter" batteries....for starting up your car and not much more.

Looking at one of these AGM batteries as a replacement for my Lithium-Ion.
Looks like it has plenty of AmpHr: 62.
Weight is a bummer (41 lbs), but that's what a daily driver battery weighs it seems.
And not inexpensive as automotive batteries go.
Terminals appear to be in the right locations....a big plus.
Will do a bit more research on them.
There is an Odyssey that would fit and has 55 Amp-Hr but the terminals are wrong.

Click to view attachment

Here are the specs:

D4700
MSRP: $321.99

12V BCI Group 47 AGM Battery, Max Amps 2,900A, CA: 760A, Ah: 62, 2000W / 3000W
Weight Lbs. – 41.19
Weight Kgs. – 19.14

Length – 9.49 in
Height – 7.48 in
Width – 6.93 in

MAX Amps – 2900
CA – 760A
RC - 110
Ah - 62

M6 Terminal Hardware Included

3 Year Warranty

Received my new battery today from JEGS.

Man is it ever heavy (~42 lbs) compared to the Lithium I'm replacing (~11 lbs).
The new battery has a bunch more Amp-hr.
62 Amp-hr vs 30 Amp-hr for the Lithium.
Should do a lot better keeping up with the electrical load while driving around, sitting at stop lights, etc.

So it's an XS Power battery, model D4700.
This is one of those AGM batteries so acid leakage won't happen.
Specs:
12-Volt
CA: 760
CCA: 668
Ah: 62, 2000W / 3000W
Max Amps: 2900
Reserve Capacity: 110 Minutes

I purchased mine for $279.99 including shipping.
I think the price is very competitive for this type of battery.
Also needed is a set of battery terminals for another ~$10.

Some might not like the flashy looks, but I think it's fine.
You could always come in with some cut vinyl to hide them....

Click to view attachment

ps I did have the battery terminals reversed for this pic. The larger one goes on the positive terminal. Ha

So the real important thing for me is fit in the car.
I obviously did all my measuring before purchase and this battery looked perfect.

And it was.
Fits the stock battery tray perfectly.
Even the stock hold down clamp works nicely.
This battery has the necessary "cleats" front and back such that it is very secure when clamped in place.
Not too tall.
Can't tell you if the rain tray would get in the way as I don't run one with my six.

Another super important thing is that the terminals are in the correct location with the negative closest to the firewall.
It was like this battery was meant to go in a 914.

I may get a bit creative with some vinyl and some graphics to change to cosmetic looks of the battery, but that's a minor issue in my mind at this point.

Time to drive and enjoy the car without worrying about the battery any more.

Click to view attachment

Kitty Forman : So, what do you want for your birthday?

Red Forman : Whatever you want. Money is no object, as long as it's reasonable.

Eric : I want a cassette player for the car. A cassette player, not an 8 track. NOT an 8 track. Okay?

Kitty Forman : Why don't they put record players in cars?

Red Forman : OK, Eric, if you don't want an 8 track, you won't get one.

Kitty Forman : Oh, but Red, he wants one.

Eric : No, I don't. I don't want an 8 track.

Red Forman : You'll get a Delco. A genuine GM part for a genuine GM car.

My car had 2 issues.
1) non matching voltage regulator to the alternator
2) battery with insufficient Amp-hr rating

Now all is well in the Kingdom of Oz.

@raynekat - that's a really good find and while I think the graphics are a bit "much" I'll say that the white doesn't look bad at all in your setup. Do you think it would work in a /4 with a rain tray? I'm guessing with it being the right code and size to fit the battery tray, it would....

Also - maybe one of the original 914 HO Campaign battery covers would fit and cover up the graphics on the top?

I agree that the white looks fine in my car. Actually the XS wild graphics go with my tartan seats to some degree.

Good idea about the battery cover.....just ordered one with the band to hold it on.

I think I may come up with a fun Bosch vinyl graphic for the side of the battery and it will finally look the part.

This battery is only 7.5 in tall, so it would likely still fit with a rain tray as well.
I have a lot of room between the top of the battery and the bottom of the engine lid.

This battery was incredibly easy to install....it fit that well.
Like it was designed for the 914.

Here's what the battery looks like with one of the covers on it....
Helps to clean up the look a bit.
Got cover from AA and it fits perfect.
Wonder how long the rubber band will stay in one piece?

Click to view attachment

Looks good!

Final iteration with a bit of black vinyl and a fun Bosch decal I found on Ebay.
Looks proper and most wouldn't know I didn't have a Bosch battery in there.
Stealth all the way.....

Click to view attachment

Slick. Nicely done!!

Glad to see its running properly for you now. Battery cover looks good. Well done!

Yes Superhawk.
You were definitely the motivation/inspiration to upgrade my battery/voltage regulator on my car.
What I had was fine for a dedicated track car, but not so much for a street car.
I learned a lot on this voyage.
Many, many things I just didn't know about it.
Sometimes knowing enough to be "dangerous" is just that....dangerous! Ha