Author Topic: Charging system check flow chart  (Read 3127 times)

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Online mervin

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Re: Charging system check flow chart
« Reply #1 on: November 09, 2014, 07:15:49 PM »

Originally posted by OW31 in reply to a query, surely to good to lose

Does this only happen when the ignition is switched on? Best to start by being clear how the circuit works.

The red wire is the DC charge output from the rectifier to the battery via the 20 amp fuse. If that was burning or blowing the 20 amp fuse all of the time (even when ignition is off) it would be caused by a shorted rectifier unit or a red to black (earth) fault in this circuit somewhere. CAUTION : If the fuse is not blowing it can often be just simply the battery or wiring is not capable of supplying enough current to blow the fuse. Instead the wiring just gets hot an smoulders but it is the same thing.

The regulation works like this: The regulator receives a 12 volt sense (sample) voltage via the ignition switch and brown wire. This same brown wire splits before the regulator and feeds one rotor field brush. This obviously must be insulated from earth at the brush (fibre/plastic washer mentioned). If it is shorted through a missing washer at the brush the 10 amp will blow (if the battery is healthy enough to provide plus 10 amps to blow it (sometimes not!!!) After flowing through the rotor and creating the magnetic field for generating it leaves via the other brush (which must also be insulated with a washer) back to the regulator on the Green wire. The regulator works by restricting/resisting the return circuit (Green Wire) thus reducing the field strength of the rotor.

IMPORTANT: Earlier A and B models do not work like this. The regulator in these models work by restricting the feed to the Rotor and the return is actually earthed at the stator/brush. If you fit an earlier A/B model stator to a C/D model you will have serious problems like this, it's happened !!! You can do it but you must insulate both brushes from earth.

If the Green rotor return wire is shorting to earth at the brush or wherever you will effectively have an unregulated charging output with the generator going into runaway as the output will rise to the max but at the same time the field/rotor will receive this high voltage and increase the field strength increasing the output even more and so on until something burns out. A healthy battery will go some way to suppress this extreme for a while until it too boils and creates high internal resistance making matters worse.

With any fault you start by asking "what has been done or changed since it was healthy" If it was fine before your strip down, then you would start by looking at your rebuild or the parts that have changed. So make sure all the wiring is correct and you cannot be sure the loom is fine, so you might have to check it through against the wiring diagram making sure slight shade different colours are in the right place.

Use a multimeter on ohms and measure the green wire at the brush to earth, it should not be a short as that is the most likely cause of this. If it is a short or thereabouts, unplug the regulator and see if the resistance goes to infinity. If not that green wire is down to earth somewhere if it does go infinity, it is pointing at the regulator.

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Re: Charging system check flow chart
« Reply #2 on: April 15, 2020, 10:42:12 AM »
Please note the link on Mervin's post is no longer working, try this one

https://www.nsr-world.com/workshop/wiring/electrex-fault-finder/Electrex_fault_finding.pdf

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