Battery Voltage Gauge

Talk about the E-Type Series 3

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Richard560130
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#1 Battery Voltage Gauge

Post by Richard560130 » Mon Sep 09, 2019 4:35 pm

Yesterday SWAMBO was driving our SIII roadster along A roads, and dual carriageways at a steady speed. The dashboard battery voltage gauge was slowly oscillating (5 to 10 minutes) around the central 13volt mark , getting towards but not touching the red markings left and right. All the gauges were working ok, the ignition light wasn't on, and the engine was running smoothly. Is this normal, or is it a developing problem ???

Thanks for any advice ::: Richard

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cactusman
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#2 Re: Battery Voltage Gauge

Post by cactusman » Mon Sep 09, 2019 5:13 pm

At steady speed the voltage should remain stable at around 13.5 to 14 lots max. Either the alternator or alternator regulator regulator if you have a separate one is unwell, the battery is unwell and confusing the regulator or there is a loose wire...possibly ground wire somewhere.
Julian the E-type man
1962 FHC
1966 MGB....fab little car too

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Heuer
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#3 Re: Battery Voltage Gauge

Post by Heuer » Mon Sep 09, 2019 5:14 pm

:yeahthat:

The voltage with the engine running should be 14.3 volts. From what you describe it sounds like the alternator has failed and is no longer charging the battery. You can confirm this by putting a multimeter across the battery terminals with the engine running. It should register 14.3 v.
David Jones
S1 OTS OSB; S1 FHC ODB
1997 Porsche 911 Guards Red

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MarekH
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#4 Re: Battery Voltage Gauge

Post by MarekH » Tue Sep 10, 2019 8:07 am

The gauge can only move slowly because it is a bimetallic gauge. This means that when unpowered, the needle slowly drifts to the left and when connected and powered, it drifts slowly to the right.

What is not right is that it is oscillating. This means the voltage is being turned on and off, probably at the gauge itself.

The alternator's regulator is like an on/off switch which is constantly changing state, but it does this many times a second. (I posted a description recently on another thread.) You can verify whether the alternator/regulator is or isn't the root cause of your problem by running the engine and measuring the voltage pretty much anywhere you like away from the gauge. If it is constant (probably near 14v), then your problem is more local to the gauge; it it turns off completely and back on with the same periodicity, then it isn't a gauge wiring problem. Since the ignition happily carried on working during your drive, it is unlikely to be the latter, especially since you didn't report the red warning light coming on.

kind regards
Marek

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Richard560130
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#5 Re: Battery Voltage Gauge

Post by Richard560130 » Tue Sep 10, 2019 8:48 am

Thanks for the prompt replies, I will track down my voltmeter and investigate at the weekend.

Richard

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#6 Re: Battery Voltage Gauge

Post by Richard560130 » Mon Sep 16, 2019 2:35 pm

Hi, I started the engine at the weekend, (battery turned engine swiftly ,so was well charged), at 1500 rpm, voltage across the battery terminals was 12v, voltage gauge reading slightly left of vertical from the 13v central mark. Went for 25 mile run, dashboard gauge didn't deviate from the left of centre position, came home checked actual voltage with voltmeter, still reading 12v. Not sure why battery voltage gauge didn't repeat the oscillating behaviour, but from previous posts is 12volts too low anyway ??? Any further guidance appreciated

Thanks Richard

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cactusman
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#7 Re: Battery Voltage Gauge

Post by cactusman » Mon Sep 16, 2019 2:46 pm

As heuer says with the engine running look for 14.3 volts...although anything above 13.8 will be fine. Just wondering....you sure your multimeter is showing the correct voltage? Can you borrow another multimeter and pop both on the same source voltage...a small 9 volt battery for example...and see if both show the same +/- 0.1 volts or so? Cheap meters can drift or just be plain wrong....
Julian the E-type man
1962 FHC
1966 MGB....fab little car too

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Richard560130
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#8 Re: Battery Voltage Gauge

Post by Richard560130 » Tue Sep 17, 2019 4:02 pm

I have tested a new 9v Duracell battery. Reads 9.4v, so no reason to suspect voltmeter is faulty ? are there other tests/inspections anyone would recommend ??

Thanks

Richard

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#9 Re: Battery Voltage Gauge

Post by cactusman » Tue Sep 17, 2019 5:52 pm

Sounds like your multimeter is ok. So...if the battery voltage is less than about 13.8 volts with the engine running or obviously wonders around then the alternator and or associated wiring is suspect. If you have a separate alternator regulator...e.g. 4TR type....then this too may be faulty. I am assuming here that the battery is fully charged. Check all terminals are secure. Check all earth straps are secure. Failing that seek advice from an autoelectrician who should be able to test and diagnose your issue.
Julian the E-type man
1962 FHC
1966 MGB....fab little car too

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malcolm
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#10 Re: Battery Voltage Gauge

Post by malcolm » Thu Sep 19, 2019 5:57 am

Charge the battery on a separate charger to see if it reaches and holds 13.7'ish volts. If not, battery is duff. 12volts is flat. If it does, alternator probably duff
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S
2015 F Type V6 S

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jagwit
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#11 Re: Battery Voltage Gauge

Post by jagwit » Wed Oct 02, 2019 12:18 pm

I upgraded my Butec alternator to a modern ex LR unit because I trusted low readings from the Battery gauge...

Big mistake. Trusting the gauge, that is.

In the end, I need not have upgraded the alternator at all, had I known about the issues around the Battery gauge (which was calibrated correctly and not faulty!!!)

Here is a thread on what I found, and did to the fix the issue:
http://forum.etypeuk.com/viewtopic.php? ... 911#p76911
Best Regards
Philip
Jag: 72 S3 XKE, 74 S3 XKE OTS, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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jagwit
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#12 Re: Battery Voltage Gauge

Post by jagwit » Wed Oct 02, 2019 12:23 pm

Here are a series of pics that my Battery Gauge displayed on the bench with voltages applied directly to the gauge terminals and verified with my Fluke multimeter (ON the gauge terminals):

12V:
12V.jpg
12V.jpg (151.19 KiB) Viewed 4670 times
13V:
13V.jpg
13V.jpg (144.76 KiB) Viewed 4670 times
14V
14V.jpg
14V.jpg (150.81 KiB) Viewed 4670 times
Best Regards
Philip
Jag: 72 S3 XKE, 74 S3 XKE OTS, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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