Ongoing power drain issue

[jagnut66]

I  am still leaning towards a drain somewhere, however, reading everybody's comments has left me wondering if I'm not being pulled in the wrong direction and that it might be the battery after all. 

I don't know the answer yet. 

Sorry, I work during the week, so it may be the weekend before I get back on this. 

Best wishes,

Mike.

[johny]

Right Ive thought of an easier way to test the system for a drain:

With everything turned off disconnect the power lead from the battery terminal.

Set voltmeter to read 12v DC and connect it between the battery terminal and power lead.

If theres no drain you'll read zero while any greater reading indicates theres a circuit ie a drain.

You can test the meter by turning on the car lights and although they wont work the meter will show 12v.

Then turn everything off again before reconnecting the battery.  

[SpitFire6]

1 hour ago, johny said:

Right Ive thought of an easier way to test the system for a drain:

With everything turned off disconnect the power lead from the battery terminal.

Set voltmeter to read 12v DC and connect it between the battery terminal and power lead.

If theres no drain you'll read zero while any greater reading indicates theres a circuit ie a drain.

You can test the meter by turning on the car lights and although they wont work the meter will show 12v.

Then turn everything off again before reconnecting the battery.  

Hi,
That test might be too sensitive using a digital meter. 

[johny]

I thought we wanted sensitive to pick up the smallest leakage?

[johny]

Oh and Mike when you first connect the voltmeter you might get a reading but this should slowly reduce to zero or certainly a very low reading. Plus dont worry you cant do any damage damage to the meter or car electrical system with it set to >12 volts DC👍

[johny]

Oh and Mike when you first connect the voltmeter you might get a reading but this should slowly reduce to zero or certainly a very low reading. Plus dont worry you cant do any damage damage to the meter or car electrical system with it set to >12 volts DC👍

[jagnut66]

Hi, 

As an update on this I have now fitted two battery isolators, one on both positive and negative terminals. The positive one I have 'shielded' with an offcut of rubber mat I had to hand, due to the proximity of the heater matrix housing (it doesn't touch the housing, by the way, that is just the angle of the picture). 

See picture below.

Having had the engine running and the car moving (albeit slowly -- covered in another post), I then left the car for a week and unlike previous occasions it started readily, without the need to recharge the battery. The wary cynic in me will be watching this though...... 😉

Note this is with the memory circuit (permanent live) to the radio still connected, via two separated fused wires attached to the isolators, one of which should be visible in the picture, attached to the negative terminal.

Of course I realise, even if this does provide a (semi) long term solution, it is just a sticking plaster solution, the ultimate cure is a new wiring loom.

However, the isolators themselves are here to stay, as a security measure.

Best wishes,

Mike.

Edited May 19 by jagnut66
additional text added

[Steve P]

I had one of those on my Vitesse for a while as it lives in a lockup and didn`t want it to drain over longer periods, I found the screw on connector was getting hot when in use due to resistance between it and the battery connector. Now removed.

Steve

[jagnut66]

1 minute ago, Steve P said:

I had one of those on my Vitesse for a while as it lives in a lockup and didn`t want it to drain over longer periods, I found the screw on connector was getting hot when in use due to resistance between it and the battery connector. Now removed.

Steve

Thanks for the tip, I will keep an eye on it.

However, if they were that problematic then I'd have thought there would have been mention in the classic car press on the subject. Nonetheless I'm glad you told me.

Time will tell...........

Best wishes,

Mike.

[johny]

Yes unfortunately every connection in a circuit brings with it a volt drop although usually pretty small but nevertheless they have the potential for causing a problem which is difficult to detect☹️

Now your large and exposed positive battery connection makes me nervous Mike and I wonder if theres any plastic cover available that could shield it?

[Morgana]

I don't think anyone has mentioned that the measured battery voltage diminishing when the charging current is removed is not indicative of a fault. In fact, voltage is one of the less useful means of interpreting battery health as it can't be evaluated with any reliability during use.

The charging voltage of approximately 14V will not be maintained once the charging impetus is removed. What you're measuring at the battery terminals is the alternator's output potential. The battery is only charging because the voltage being applied is greated than the resting voltage per cell. To use the water analogy, the alternator is creating a higher head of pressure which is letting the 'water' pour into the battery. When the sluice gates are closed, the measured reading will reduce and settle until it attains the resting potential per cell, which will be around 2.1V. If the measured battery voltage is less than about 11.9V after a period of resting, then there is certainly a battery problem and its reduced capacity from deep discharging or simply age means it's time for a new battery, since each cell (six in a 12V lead acid battery) can't maintain its charge. Somewhere between that and 12.7V will be the normal range depending on battery age, chemistry and temperature.

Any leak great enough to cause issues with battery capacity and starting after short period of a day or so will certainly show up in a test light arrangement. Consider the amp-hour capacity of the battery and it would have to be a hefty draw of the order of headlamps to drain a battery below cranking capacity in that space of time. I use a little MES bulb and holder (the sort from school science experiments) as I have some on hand, with crocodile clips. With everything turned off, such that you would expect no battery discharging to happen, disconnect the earth lead, and clip or hold one bulb lead to the battery negative terminal and the other to a good body earth. If the bulb lights, there is a circuit drawing current. Applying the same bulb to each circuit in turn will reveal the culprit.