Discovery 2 Alternator and Battery Monitor Modification.

Here are the voltage drop readings between the vehicle battery terminals and the connector in the dashboard monitor modification. The measurements were taken using two calibrated 4 1/2 digit digital voltmeters, which showed identical voltages as each other, but were still changed over for a second test procedure to eliminate any inaccuracies.

Voltage measurement points-------------Battery-----Monitor----Voltage drop
Ignition on, engine off:----------------------11.87v------11.82v-------0.05v
Ignition on, engine running:---------------14.52v------14.48v-------0.04v
Engine running, heated screens:-------14.22v------14.17v-------0.05v
Engine running, heated screens +
headlights + heated seats:---------------12.97v-------12.92v------0.05v
Various vehicle electrical devices:----14.18v-------14.12v------0.06v
-----------------------------------------------------14.2v---------14.14v------0.06v
-----------------------------------------------------13.62v-------13.58v------0.04v

The maximum measured voltage drop was 0.06v. I think a paltry 60mv voltage drop is perfectly acceptable. A direct connection from the dashboard monitor modification connector to the vehicle battery terminals using 20-amp, 75/0.19mm, 2.12-sq/mm-CSA cable gave exactly the same voltage drop.

Sorry stainless, but you must be doing something wrong because you should not have had ANY VOLTAGE DROP if you wired direct to the battery.

This is because a volt meter does not draw current, so there is no way you should have registered any difference in the voltage reading at the battery and at the meter in the dash if you had run a dedicated set of wires from the dash mounted meter to the battery.

The use of thick 20 amp wire achieves absolutely nothing, you can use the thinnest figure 8 speaker wire and still get the exact same voltage reading at the battery and at the end of the speaker wire.

Again, you must be doing something wrong.

Returning to your original point, ( your 1 volt or more, against my 0.06 volt, voltage drop) comparing your own tests with my voltage drop table, what voltage drop did you actually measure between the vehicle battery terminals and the photographed relay terminals in the internal cabin fuse panel ?

Hi stainless, and I’ve been working on vehicle electrics for over thirty years and I have never seen a vehicle that did not get at least a 0.5v voltage drop at the dash wiring and 1 volt is common place.

Won’t comment further on your voltage readings, but when I had my D2, it had around a 1 volt drop at the dash wiring once you turn a few things on.

I’ll leave it at that.

Likewise, I have spent over 40 of my 60 years in electro-mechanical engineering, and try to never criticize other people, unless I have had personal experience of the actual subject being discussed.

If you repeat my test of actually measuring the voltage drop between the TD5 Discovery 2 battery terminals and the internal cabin fuse panel (not the dash wiring - wherever that might be), you will get a voltage drop reading of around 0.06 volts.

Make sure there are no bad battery feed to fuse panel connections on your test D2 TD5 vehicle, actually do the exact voltage drop test in question, take the measurements, and I will then accept your apology.

Talking of apologies, I am very surprised that thread hijacking ( as on page 1 of this thread ) is allowed on this otherwise popular and excellent Land Rover Forum.

As a comparison just (well earlier) went and checked the figures against mine and as follows.

Voltage measurement points-------------Voltage drop---Battery vs fuse box
Ignition on, engine off:--------------------------0.92v
Ignition on, engine running:---------------------0.78v
Engine running, heated screen (rear only):-----0.96v
Engine running, heated screens + headlights:-- 0.98v

Photograph 1. (On previous comment) both DVMs connected across Vehicle Battery Terminals.
Photograph 2. Drivers side DVM connected to Vehicle Battery Terminals.
Photograph 3. Passenger side DVM connected to Dashboard Monitor Mod Connector.
Photograph 4. Ignition turned on without engine.
Photograph 5. Engine running.
Photograph 6. Engine running with Headlights Main Beam.

Stainless, you may have found a wire that has nothing connected to it, but as pointed out, repeatedly now, you should never use dash ( fuse box ) wiring to try to get accurate battery/alternator voltage.

It is NOT good practice to source your voltage readings anywhere but at the battery itself.

If anyone has a D2, try your luck, but anybody interested in getting accurate battery voltage readings, no matter what type of vehicle it is, go to the battery terminals to get your voltage source from.