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battery mystery.
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Ray White



Joined: 02 Dec 2014
Posts: 6285
Location: Derby

PostPosted: Tue Sep 29, 2020 3:03 pm    Post subject: battery mystery. Reply with quote

Hi all. My MG battery did something strange. It went from over 12 volts to zero overnight. The only thing the battery was connected to is the starter switch and starter. Nothing else at all.

What could have caused this drain?
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Tue Sep 29, 2020 4:16 pm    Post subject: Reply with quote

When you disconnect it does it show any voltage at all?

If not then I suspect it has gone open circuit internally.

Or is your meter acting up again? Can you light a bulb connected directly across the battery?

Peter
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1939 SS Jaguar 2 1/2 litre saloon
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Ray White



Joined: 02 Dec 2014
Posts: 6285
Location: Derby

PostPosted: Tue Sep 29, 2020 8:25 pm    Post subject: Reply with quote

Hi Peter. I mentioned it to my tame auto electrician today who said just the same as you. He thinks I just have bad luck as although he has seen it a few times in his long career it is pretty rare.

As far as my meter is concerned it is more a fault with the operator than the equipment!

the battery. was left on charge and it won't go above 0.02 volts - so it's pretty well knackered!
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petelang



Joined: 21 May 2009
Posts: 442
Location: Nottingham

PostPosted: Tue Sep 29, 2020 11:16 pm    Post subject: Reply with quote

If your battery has gone so low its unlikely your charger will be able to refresh it but, heres the trick.
Connect a pair of jump leads to it and another battery that has a bit of charge in it, need not be fully charged, just showing about 12 volts. Connect your charger on the pos and neg leads and leave it over a few hours and...hey presto, your battery will recover.

Now, make sure there is nothing draining your battery on the car. Put a 2.2 watt dash lamp bulb, or similar in series between the positive post and the positive lead. If it lights up, something has a circuit and is draining your battery.
Finding it is altogether another matter...
Peter
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47Jag



Joined: 26 Jun 2008
Posts: 1480
Location: Bothwell, Scotland

PostPosted: Wed Sep 30, 2020 1:07 am    Post subject: Reply with quote

Ray.

Is this a sealed battery?

Try this, Place one probe of your meter on the positive post and the other in the electrolyte of the adjacent cell, it should read around 2 volts. Then walk the probes along the battery measuring between the two electrolytes or the negative terminal again expect around two volts. Anything dramatically lower IE zero or thereabouts indicates that the cell is dead or dying.

Art
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Ray White



Joined: 02 Dec 2014
Posts: 6285
Location: Derby

PostPosted: Wed Sep 30, 2020 7:40 pm    Post subject: Reply with quote

petelang wrote:
If your battery has gone so low its unlikely your charger will be able to refresh it but, heres the trick.
Connect a pair of jump leads to it and another battery that has a bit of charge in it, need not be fully charged, just showing about 12 volts. Connect your charger on the pos and neg leads and leave it over a few hours and...hey presto, your battery will recover.

Now, make sure there is nothing draining your battery on the car. Put a 2.2 watt dash lamp bulb, or similar in series between the positive post and the positive lead. If it lights up, something has a circuit and is draining your battery.
Finding it is altogether another matter...
Peter


Hi Peter. It would be understandable if the battery had been fitted to a normal complete car but it wasn't. The battery was fitted to my unfinished TC which has no electrical parts connected to it other than the starter and switch. No ignition. No wiring. Nothing. The thing is that it drained down from fully charged to zero... OVERNIGHT!.
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Ray White



Joined: 02 Dec 2014
Posts: 6285
Location: Derby

PostPosted: Wed Sep 30, 2020 7:49 pm    Post subject: Reply with quote

47Jag wrote:
Ray.

Is this a sealed battery?

Try this, Place one probe of your meter on the positive post and the other in the electrolyte of the adjacent cell, it should read around 2 volts. Then walk the probes along the battery measuring between the two electrolytes or the negative terminal again expect around two volts. Anything dramatically lower IE zero or thereabouts indicates that the cell is dead or dying.

Art


Hello Art. No; it is not a sealed battery. The electrolyte is at the normal level but the cells are all dead.

At first I thought that the starter switch must have shorted out and current was being drawn by the starter. However, I have had both the starter and the switch checked out by the local auto electrician and they are fine. The switch is spring loaded and needs a strong tug to get it to work but it does work and - more importantly - it doesn't pass current when at rest.

The only other thought I had was that there was not a good enough earth. I have now fitted an earth strap from the engine to the bulkhead which is what the battery is earthed to.

I think I need a new battery.
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Wed Sep 30, 2020 8:01 pm    Post subject: Reply with quote

Ray White wrote:

I think I need a new battery.


I agree.

Peter
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Peter_L



Joined: 10 Apr 2008
Posts: 2680
Location: New Brunswick. Canada.

PostPosted: Wed Sep 30, 2020 10:13 pm    Post subject: Reply with quote

The same battery as mentioned here ?

Ray White wrote:
Churchill Johnson wrote:
If your battery drops that much it's a bin job, again decent battery with jump leads would temp fix that, as for switch take leads off from it then hold them together yes will be sparks if batt ok that will soon show if motor will turn over..


I suspected it was no good. So far I have had a faulty starter motor (now o.k.) two duff cable pull switches and a knackered battery.

...I just keep smiling and saying things like "worse things happen at sea". !
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Ray White



Joined: 02 Dec 2014
Posts: 6285
Location: Derby

PostPosted: Sat Oct 03, 2020 3:47 pm    Post subject: Reply with quote

...so I fitted a new battery and I am now in all sorts of trouble. When I connected the earth terminal I soon noticed smoke coming from somewhere and the throttle linkage went red hot. I quickly disconnected the battery.

The problem MUST be the starter switch.

I say that because the switch is mounted to the bulkhead through two brass brackets that hold the throttle linkage. I think there must be a short to earth through the starter switch.

My local auto electrician tested the switch the other day and gave it the all clear.???????

It looks like the suggested low voltage route is the way to go....
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Peter_L



Joined: 10 Apr 2008
Posts: 2680
Location: New Brunswick. Canada.

PostPosted: Sat Oct 03, 2020 4:54 pm    Post subject: Reply with quote

Ray.. Knowing that I keep repeating myself. 21W Bulb in series with main lead from battery. If there is nothing switched on and the bulb lights up, you have a short. If you remove a connection and or a component and the light goes out, that is where the short is happening. You may have been fortunate that your old battery had so little stored energy that it went flat before the a fire could start. Going from a high current application of the switch to a low current one will not remove the problem area but will make its easier, via fuse, to prevent some really bad pyrotechnics.
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Kenham



Joined: 12 Mar 2012
Posts: 209
Location: Kent

PostPosted: Sat Oct 03, 2020 5:44 pm    Post subject: Reply with quote

I had a Morris van do that, the choke cable was like an electric fire, in this case it was a bad earth connection.
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MVPeters



Joined: 28 Aug 2008
Posts: 822
Location: Northern MA, USA

PostPosted: Sat Oct 03, 2020 6:07 pm    Post subject: Reply with quote

Ray
Just to add:
If the throttle linkage is heating up, it must be providing an electrical path. Perhaps the strap you added is not down to bare, bright metal?
Mini choke cables used to heat up if their engine earth strap broke. It was the only other metal electrical path since the engine was entirely rubber-mounted.
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Peter_L



Joined: 10 Apr 2008
Posts: 2680
Location: New Brunswick. Canada.

PostPosted: Sat Oct 03, 2020 6:12 pm    Post subject: Reply with quote

Kenham wrote:
I had a Morris van do that, the choke cable was like an electric fire, in this case it was a bad earth connection.


I saw that once on a Ford 105E. Broken engine/gearbox to chassis earth strap. There wasn't much life in the starter but the spring loaded throttle linkage at the carburetor was glowing. The replacement and I think perhaps later models was plastic. I remember we fitted a new earth strap from the chassis to one of the engine/gearbox bolts high. The original which was below.
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Ray White



Joined: 02 Dec 2014
Posts: 6285
Location: Derby

PostPosted: Sat Oct 03, 2020 6:17 pm    Post subject: Reply with quote

This afternoon I did some more checks. I can now show how this second switch is also faulty.

While previously checking I had been simply holding the probes against the threaded terminals and found no fault.

It was not until I pressed the wire connector against the boss of the terminal on the switch that I discovered a short. The fault was only showing up when the cable was tightened.

It has been suggested that I need not spoil the appearance of the dash, in that I should leave the cable knob as a dummy - and fit an accessible electric switch out of sight.

I think Peter L wins the day.

Very Happy
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