Different reading on battery condition gague

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yellowpinky
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Different reading on battery condition gague

Postby yellowpinky » Thu Sep 19, 2019 3:05 pm

I noticed recently that the needle on my battery condition gague has moved. Previously the needle would be on about 13v while driving, which indicates 'on charge' on the meter. And now it reads 12v 'off charge' all the time... The battery should be ok... it's a big exide one, that's around a year old... I suspect there's a problem with the alternator, but could do with some advice to confirm before carrying out work etc... my main concern at the moment is that the cooling fan is electric, so if the battery died through not being charged, then I could overheat!

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Re: Different reading on battery condition gague

Postby StillGotMy1stCar » Thu Sep 19, 2019 3:21 pm

I have known the Smiths voltage gauge's fail.
I would check your voltage with a multimeter first.
Regards John

yellowpinky
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Re: Different reading on battery condition gague

Postby yellowpinky » Thu Sep 19, 2019 3:24 pm

Yes good idea, it is a smiths gauge

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Re: Different reading on battery condition gague

Postby StillGotMy1stCar » Thu Sep 19, 2019 4:33 pm

I took one apart and was surprised to find it works on the bimetal strip principle so can have a short life.
Regards John

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Re: Different reading on battery condition gague

Postby geoberni » Thu Sep 19, 2019 5:49 pm

StillGotMy1stCar wrote:
Thu Sep 19, 2019 4:33 pm
I took one apart and was surprised to find it works on the bimetal strip principle so can have a short life.
Regards John
Conversely, working on a bi-metal strip, rather than cheap Chinese 'electronics' it could last for decades. :wink:

I have a Smiths Temp gauge, working on a bi-metal strip, that I picked up at an autojumble. It's probably at least 70s, very likely older, it works fine and doesn't look out of place.


It's probably a darn site more reliable than this forum which has multiple posts far too often.
I see we have 3 of this topic posted at 3.05 this afternoon.
There might be a tendency to blame the members who make the multiple posts, but it's not something that I find with other forums... are our members more prone to finger trouble, or is it the forum software... :-? :-?

Edited to add the bit about the temp gauge.
Last edited by geoberni on Thu Sep 19, 2019 8:23 pm, edited 1 time in total.
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Re: Different reading on battery condition gague

Postby Banned User » Thu Sep 19, 2019 6:22 pm

It seems to have a slight delay before it reacts to the ‘submit’ button. It’s easily solved by waiting a nano second or by deleting the resulting multiple posts.

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Re: Different reading on battery condition gague

Postby StillGotMy1stCar » Thu Sep 19, 2019 11:08 pm

A note to Berni, I said I have known Smiths voltage gauges fail, which is perhaps relevant to this case.
I later added my surprise that it works with a Bi-metal strip. I was expecting a moving iron or moving coil meter movement being used as a volt meter.
I am not knocking Smiths gauges.
Edit; yes I did say “works with a Bi-metal strip so can have a short life.”
Perhaps I shouldn’t have.
Fuel and Temp gauges last well possibly because of a lower working voltage and current.
Last edited by StillGotMy1stCar on Thu Sep 19, 2019 11:54 pm, edited 1 time in total.

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Re: Different reading on battery condition gague

Postby yellowpinky » Thu Sep 19, 2019 11:49 pm

I'm not sure why this post duplicated three times, Sorry...
Anyway, I tested the battery with a multimeter & the reading didn't change between when the engine was switched off, running or being revved up. I also disconnected the earth terminal from the battery while the engine was running and the engine stopped. Fan belt is in good condition, but the alternator does seem to be making a slight grinding noise.
This may seem like a dumb question, but can I assume the problem is with the alternator?

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Re: Different reading on battery condition gague

Postby StillGotMy1stCar » Fri Sep 20, 2019 1:08 am

At the moment it is not charging, most likely nothing to do with the grinding noise, it is possible to change the bearings.
Anyhow do a few tests before you decide if the alternator is worth repairing:-
When you turn the ignition on without the engine running the red ignition light should come on.
The alternator won’t charge without the reference voltage supplied via the ignition bulb.
To test the bulb remove the small wire from the alternator and short it to earth and make sure it illuminates.
If it does illuminate all the time with the engine running this shows it isn’t charging, remove it from alternator to make sure it goes out (unlikely but if this lead had a short to earth it would light the ignition bulb but not give the reference voltage to the alternator).

Check the Large wire or wires (it may have two) hasn’t become disconnected, be careful not to short this one to earth.
The Large alternator terminal/s should be a direct connection to the battery normally via the starter solenoid or pull switch whichever is fitted, so test for continuity of this lead. An easy way would be to check the voltage or use a test light at the large terminal of the alternator, the engine doesn’t need to be running.

Sorry to ramble on, to sum up you need proper ignition light function and continuity from the battery to the large alternator terminal/s for the alternator to work.

Importantly alternators don’t like running without a load, best not to disconnect the battery with the engine running.

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Re: Different reading on battery condition gague

Postby geoberni » Fri Sep 20, 2019 10:57 am

StillGotMy1stCar wrote:
Thu Sep 19, 2019 11:08 pm
A note to Berni, I said I have known Smiths voltage gauges fail, which is perhaps relevant to this case.
I later added my surprise that it works with a Bi-metal strip. I was expecting a moving iron or moving coil meter movement being used as a volt meter.
I am not knocking Smiths gauges.
Edit; yes I did say “works with a Bi-metal strip so can have a short life.”
Perhaps I shouldn’t have.
Fuel and Temp gauges last well possibly because of a lower working voltage and current.
Fair enough. :) I don't think moving iron/coil meters are suitable to vehicles bouncing along the road; they're a bit more sensitive and I think would be wobbling all over the place. Damping the movement would be possible but no doubt add to the cost too, making them too expensive for the typical motor. Might find such in a vintage top range motor.
You comment about relevant working parameters could be valid though. :wink:
Here's an image of the Voltmeter wiring diagram
https://3.bp.blogspot.com/-gcJUyUVEfPk/ ... age+v2.jpg
Obviously different to the way a fuel or temp gauge uses the bi-metal.
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Re: Different reading on battery condition gague

Postby oliver90owner » Fri Sep 20, 2019 1:07 pm

If the alternator is issuing unwanted noises, it seems like it is dead.

There are not many failure modes with alternators. Bearings, slip-ring/brushes, voltage controller and rectifier.

If the ignition light is not illuminated, the most likely fault to look for (after a blown bulb) is the brushes contact with the slip-rings - usually one new brush (the outer one) is all that is actually needed. But if the bearings are failing (usually only the drive end) it may be sensible to change the slip-rings at the same time as the non-drive end bearing, if this is renewed. I generally change both non-drive items, if one or the other needs repair.

Things like disconnecting the battery terminal, while running, or electric welding close by (without disconnecting the alternator wires) can easily affect the rectifier. The voltage regulator either works or not!

If your battery failed, the ignition would, too. But do not allow your battery to get discharged - modern automotive lead-acid batteries will soon fail if not kept fully charged.

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Re: Different reading on battery condition gague

Postby geoberni » Fri Sep 20, 2019 3:01 pm

oliver90owner wrote:
Fri Sep 20, 2019 1:07 pm

If your battery failed, the ignition would, too. But do not allow your battery to get discharged - modern automotive lead-acid batteries will soon fail if not kept fully charged.
That's a very good point. I recently replace the leisure battery in my caravan as it was boiling off instead of charging properly :o and the leaflet with the new one said the warranty was void if the battery was discharged below something like 12.1 volts, because below 12v it's likely unrecoverable.

I think that's what had happened with the old one.
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Re: Different reading on battery condition gague

Postby yellowpinky » Thu Sep 26, 2019 7:28 am

Thank you everyone! All fixed now :) It turned out to be the ignition bulb, I cleaned up the bulb holder & popped a spare bulb in & the alternator sprung to life. It happened during a super busy time, so bought & fitted a new alternator in haste, but with no regrets as it was only about £40 & is quieter & is reading about 14v rather the the old one at 13v. The electrics on the van just seem to have a bit more ooomph generally. Another good thing was detecting an issue with adjustment of the alternator as past of it was bumping into a bracket from the engine, so after bending the bracket slightly I was able to get the belt tightened properly.
I hope the battery isn't damaged during this problem. I took it off to charge when I could, but I had to abandon the vehicle for a couple of days while the battery was flat...
I've been charging it off a mates fairly cheap battery charger, mine is a vintage one unwisely lent to another friend. I'm thinking to invest in a better charger for better battery condition a less stress if this happens again. I'm thinking something that cuts out once the battery is fully charged... any recommendations what to look for? atm what's the need for a high rampage one if it's better to charge a battery slowly...
I'm also thinking of getting one of those lithium battery jump starts...
Going back to the light bulb, I've been experimenting with off white led light bulbs in the dashboard... I know it's a small detail, but maybe a more durable bulb for the ignition light is a good idea... I'm also interested in ways to maintain the battery condition, but I'm not a who's with electrics, but have made sure connections are good etc & am gradually going over all the connectors & cleaning or replacing... I've lined the battery box with rubber. I heard on YouTube keeping a battery clean is good as the dirt on a battery casing is conductive... I clean out the battery tray area with spray silicone as it kind of soaks into the rubber & looks tidy.

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Re: Different reading on battery condition gague

Postby Banned User » Thu Sep 26, 2019 8:24 am

Using an led bulb for the ignition light can cause the alternator to stop charging. They don’t draw enough current and you end up in the same situation as you had with the blown bulb.

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Re: Different reading on battery condition gague

Postby oliver90owner » Thu Sep 26, 2019 8:33 am

The alternator is, as you have found, initially energised by the current through the ind. bulb. I have no idea what the minimum current requirement might be, so while an LED lamp might work it may not supply sufficient excitation for the alternator to operate. If you decide to try it, do let us all know if it works.

Don’t know when they stopped supplying a starting handle with Minors, but that was the alternative to the starter motor in days when jump starters and the like were relatively unheard of.

Modern battery cases do not suffer from the same ills as early ones. They do not lose charge in that way. However it is still good practice to keep the terminals clean and dry. Maintenance-free batteries have made losses along the cells at the top of the battery a thing of the past.

There are lots of battery chargers that can be left connected permanently - they float charge, not so much ‘cut out’ when the battery is fully charged. Quality varies about as much as the price point. Some of the more exotic ones (read expensive, too) can charge in a different mode to the usual ‘run of the mill’ chargers and can do a better job of maintaining a battery. Clearly, most choose a simple type as they are not generally required on a regular basis - as alternators do a good job of maintaining battery charge. The days of the dynamo is long past as an effective battery-charge maintainer. Mostly used by those who like to keep things original!

Do check the charging voltage with a decent meter. Battery voltage is generally maintained at 14.4-14.6. Too little and the battery life may be shortened by sulphation and too high by electrolysing the battery electrolyte. Different battery construction may require slightly different optimal terminal voltages.

Edited to add: Pool Guy got there first. But I will add that low current will not stop an alternator charging - it just may not start it charging. A very subtle difference, but a difference all the same!

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Re: Different reading on battery condition gague

Postby Myrtles Man » Thu Sep 26, 2019 9:09 am

yellowpinky wrote:
Thu Sep 26, 2019 7:28 am
I'm thinking to invest in a better charger for better battery condition a less stress if this happens again. I'm thinking something that cuts out once the battery is fully charged... any recommendations what to look for?
Have a look at the 'CTEK' range.

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Re: Different reading on battery condition gague

Postby mogbob » Thu Sep 26, 2019 11:40 am

I'll second the CTEK recommendation. A good piece of kit Bob

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Re: Different reading on battery condition gague

Postby Shropshiremoggie » Thu Sep 26, 2019 2:51 pm

Another option is Optimate . I have used one for years with great success .

geoberni
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Re: Different reading on battery condition gague

Postby geoberni » Thu Sep 26, 2019 4:54 pm

Alternator and Charging Light relationship....


Traditionally, the Alternator required the charging lamp to pull some current, perhaps 1/2 amp if I recall correctly, as part of the Field Winding circuit to kickstart the Alternator into working.
Technology has moved on and modern cars have fancy control units to do such things.

But for Moggies and early generation alternators, fitting an LED just causes problems as there's not enough current flow.

There's also an issue that the lamp will light if the current flows either direction, but the LED only works with current flow in one direction.

If you search for "Alternator charging lamp LED problems" or similar phrases you'll find loads of articles and forum chat, with all sorts or wizardry being proposed. For example, this one: http://www.mg-cars.net/mg-midget-sprite ... 161550.htm

Simple answer, stick with a filament lamp....
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Re: Different reading on battery condition gague

Postby oliver90owner » Thu Sep 26, 2019 11:57 pm

I think one will find the ind. bulb is 2W? Current will be according to Ohm’s Law. Approx 1/6 amp.


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