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anyone know where to source diode packs for a land rover series 3 ffr generator?


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I can probably give you equivalents if only I could access my frozen PC. In the meantime are you absolutely certain that the diodes have failed by direct testing? Rather than just my suspicion that they have failed, you need to ensure the associated connectors & wiring are satisfactory before. Major generator surgery:-)

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so far running all the checks i could it seems to suggest your diogionas was correct. further investigation is needed to confirm that they need replacing but as i use this landie reguraly i am trying to get it back on the road asap so gathering all details i can so i can order and recieve as soon as i know what i need.

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You don't need a diode pack, you just need to replace the 3 small relatively low power diodes, which are actually rather insignificant in size.

 

Dscf2192a.jpg

 

I see I have mislabelled the pic in ACU. When you look at the 3 diode packs each has 3 studs. The studs at each end of the trio are the high power diodes. They are functionally identical to each other although one in each trio is the reverse polarity of its partner.

 

This is because they share a common heat sink so one has the cathode (-ve) on the stud & the other partner diode has the anode (+ve) on the stud.

 

But the central stud of the 3 studs is not a diode it is the stud attached to the stator winding. So my picture is misleading & I need to correct it.

 

The low power diodes have the cathode to the stud connecting each directly to the heat sink & each stator.

 

The original low power diodes were Lucas DD3026A = CV8871, these are obsolete & were replaced by 5961-99-833-9958 = FV636048 which are used by a number of vehicle manufacturers.

 

No doubt if I gave a list of part numbers one could spend a lot of time chasing distributors reluctant to deal with an individual customer & wanting to charge hefty prices, fancy handling charges to cover all the invoices a paper work. So I would forget that.

 

There is nothing special about these diodes, the DD3026A is just a silicon diode rated at 1.5 amps able to withstand a PIV (Peak Inverse Voltage) of 400 volts. In order to dissipate heat in these early diodes they had to be bolted to a heatsink. Modern diodes are more robust looking in the Maplin catalogue there are diodes which look man enough AND THEY ARE ONLY 29p :D:D:D

 

As long as they don't get hotter than 150 deg C they don't have a heatsink stud & can just be wired in. They are rated at 3A & 1000 PIV.

 

http://www.maplin.co.uk/3a-glass-passivated-rectifiers-46407

 

http://www.maplin.co.uk/media/pdfs/Module%2046407.pdf

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I am watching this thread with a great deal of interest, as when my Series 2A comes back, with it's new genny fitted, I will need to look at the old one which does not charge. I did send two emails to a company which seems to do a lot of military stuff, but got no reply, even to say No!

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Well the obsolete Maplin diode was 1N5408G, which was a glass version of 1N5408. This is still available at 29p however the maximum working voltage has dropped from 150 deg C to 125 deg C.

 

Although it can withstand short term high temperature soldering, given the heat in the vicinity of engine, it would be best to have as high a temperature rating as possible. Moving to 6A diodes, the P600J is rated at a PIV of 600v & a maximum operating temperature of 150 deg C. The price rises to 99p but that is still good value.

 

http://www.maplin.co.uk/6a-silicon-rectifiers-46413

 

Click on "Specifications"

 

Although this is Hobson's choice having a diode rated to withstand a much higher current means it will not be struggling & overheat. These 6A diodes are rated at 600PIV whereas the original Lucas diodes were rated at 400PIV so there is an additional safety margin. It may seem curious that diodes with such a high PIV are used, but it has to be remembered that inductive loads (coils, motors, alternators etc) can produce high voltage transients & can destroy diodes if their PIV is too low.

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I am watching this thread with a great deal of interest, as when my Series 2A comes back, with it's new genny fitted, I will need to look at the old one which does not charge. I did send two emails to a company which seems to do a lot of military stuff, but got no reply, even to say No!

 

Is uour S2a Gen 40 amp or 90???? I believed that the diodes are in the 90amp and replace the selenium rectifier??? Clive can you clarify???

 

Regards

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I believed that the diodes are in the 90amp and replace the selenium rectifier??? Clive can you clarify???

 

Yes Wayne you are correct. The 40-amp alternator AC724/1 has no internal rectifier of any type & relies on the external selenium full wave rectifier. In the event of the selenium rectifier failing it would of course be possible to cook up an equivalent bridge rectifier using silicon diodes. They could be discretely mounted into the fins of the old rectifier preserving the look of a toastie. I feel a toastie with no rectifier behind the grill is a bit of a let down.

 

The 90-amp alternators of course have integral silicon rectifiers.

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Yes Wayne you are correct. The 40-amp alternator AC724/1 has no internal rectifier of any type & relies on the external selenium full wave rectifier. In the event of the selenium rectifier failing it would of course be possible to cook up an equivalent bridge rectifier using silicon diodes. They could be discretely mounted into the fins of the old rectifier preserving the look of a toastie. I feel a toastie with no rectifier behind the grill is a bit of a let down.

 

The 90-amp alternators of course have integral silicon rectifiers.

 

I thought so....Just wanted to flag as a S2a Gen is not the same as a S3 due to amperage and the good old Toastie Selenium rectifier.

 

Couldn't agree more about a Toastie without a working rectifier on show.....Hence why we are precious about genuine Toasties in the Warburtons camp ;);)

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I thought so....Just wanted to flag as a S2a Gen is not the same as a S3 due to amperage and the good old Toastie Selenium rectifier.

 

Ah but a late 2A will have a 90-amp system.

 

Pleased that you will be keeping the real thing behind your toast rack.

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Ah but a late 2A will have a 90-amp system.

 

Very correct, but they are even rarer I believe as short life before S3???

 

Pleased that you will be keeping the real thing behind your toast rack.

 

I couldn't and you wouldn't approve of me doing anything else. Hence why I have sensibly aquired a few 40amp Grade1 working Gens and NOS Selenium Rectifiers ;)

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sorry another question re diodes

i am doing the tests given in all charged up part 4 and getting the following results

first multimeter giving resistance across probes as 25

across the terminals on a new alternator (out of truck) i am getting the usuall very high readings but when reversed i am getting nothing as in the two probes are not connected. this is happening across all diodes on a newly refurbished alternator.

am i missing somthing or is there somthing worng with my multimeter or am i just making a schoolboy error

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