Rectifying the rectifier

I was surprised to find that leaving the battery in connection overnight resulted in a flat battery. Clearly there is a current leakage. Testing potential sources showed that the rectifier was shorting to ground. A replacement is clearly needed. The existing rectifier is the original disc-shaped Wipac item. This is bolted onto a heat sink mount inside the battery compartment. This type of rectifier is no longer made ad expensive as a used item. Also there's no real guarantee that a used one would be any better than mine!  I decided to replace it with the Lucas equivalent choc-box rectifier- or more accurately a pattern version since the Lucas item is likewise no longer available.

 This type of rectifier is applicable to 6 and 12v systems and also positive or negative earth. Its also very cheap at around £5 and worked well in the tiger cub I used to own. 
Lucas style choc-box rectifier
If you look at the 4 terminals on this rectifier you will se that two are both parallel and diagnonally opposite each other. In the pic above these are top right and bottom left. These are the two AC in posts. The others are + and - and at least one of them should be marked as such.
Marking on this rectifier identifies 2 terminals but..


I marked the others to avoid confusion!

First step -as always- disconnect the battery.
The original rectifier is post-mounted at the rear of the battery compartment- its a 2BA nut


In case you are refitting t note that there is an insulation washer below the nut. This isnt needed on the new box style because the case is insulated from earth.


The old rectifier just pulls off- note the traces of heat-sink grease on the base and also on the heat sink stud plate.



I cut the wires to detach the rectifier as these were soldered on.


I could then test it with the diode function of my multi-meter it should read voltage in one direction (testing between either of the AC in to + or -) but not in the other- in my case I got low readings in all combinations and the item seemed clearly to have failed.

I had intended to fit the new rectifier onto the old stud but this was too short so I was forced to replace it. The old stud is just bolted below the body panel and easily removed. 
Heat-sink rectifier base- note the base plate is fixed on the stud

I used a large repair washer and an M6 screw to replace this assembly- nut quite as good because its not welded together and so more awkward to fit. I mounted it with the screw head exposed inside the battery compartment for ease of access but make sure that the bolt length that protrudes below is not so long that it would contact the tyre under suspension load.

New heat sink arrangement- note large repair washer to go under the rectifier and M6 screw with various washers to mount through the rectifier and secure beneath the panel.

Do not forget thermal conductive grease between the rectifier and washer and the washer and body panel to unsure efficient heat dump.
I added fresh Lucar terminal connectors and insulating sleeves and connected up.
New rectifier in place and connected
Leaving the battery overnight now resulted in no loss of charge so job done I think. I still need to sort out some aspects of the loom as it seems that the ground wire from headlight to earth is broken, although that from lighting switch to earth (via the resistor wire) is intact. In the end I gave up trying to find and fix the break and just ran a new white wire alongside the loom. Transparent sheathed wire appears to be unavailable now in anything but speaker rating  and I didn't want to overload that with headlight current.





























 


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