Mep-005a trying to find power diodes

[Gordy1ID]

I only had 50 volts going to my generator to ground so I open up the back of my generator head and found two bad power diodes for the static excitation. They look like they have quarter inch threaded shafts. But I believe they are quarter inch fine thread studs. They are not the pressing kind. I'm wondering if anybody has a part number or if there's even a better product out there that will fit. The last photo is the diode stud compared to a 1/4-20 Bolt.
They have some on Amazon but I'm not sure if they will work for me. Any info will help guys. Thank you in advance Gordy

 

[Scoobyshep]

if you cant find an exact match, get something higher rated. that being said I usually go to digikey for parts like this.
here is an example. You also need to make sure they are pointed the right way. I dont have the TM in front of me at the moment so I cant say what the ratings were.

https://www.digikey.com/en/products/detail/vishay-general-semiconductor-diodes-division/VS-85HFR60/360047

 

[Gordy1ID]

if you cant find an exact match, get something higher rated. that being said I usually go to digikey for parts like this.
here is an example. You also need to make sure they are pointed the right way. I dont have the TM in front of me at the moment so I cant say what the ratings were.

https://www.digikey.com/en/products/detail/vishay-general-semiconductor-diodes-division/VS-85HFR60/360047

Thank you for this great information. I very much appreciate it. The guy I spoke to about the voltage regulator knows a lot about generators and said go with the higher voltage ones. The original ones were rated I think 30 amp 400 volt. So 6 or 1200 volts is great. Thank you very much bud!

 

[peapvp]

3 Diodes are standard polarity and 3 Diodes are reversed polarity!

 

[Guyfang]

What two were bad? Dont forget there are two different diodes back there.

 

[Gordy1ID]

What two were bad? Dont forget there are two different diodes back there.

One on the left side and one on the right side of the ring. So one was positive and one was negative. I'm going to replace all six with hopefully a better quality higher rating diode. Already on order. But good call thanks for looking out!

 

[peapvp]

@Gordy1ID test all your exciter winding's for resistance and megger test as described in Manual ARMY TM 9-6115-464-34

 

[peapvp]

Note:

The lacquer based insulation of the copper wires used can break down over time and can cause a near short at higher voltages

The only way to check this is with a 374 megger tester as described in Manual ARMY TM 9-6115-464-34

 

[peapvp]

The test procedure is on page 3-296

(20) Use a double bridge to measure resistance of each phase of exciter rotor. Resistance of each phase shall be 0.1473 to 0.1627 ohm at 77°F (25°C). Difference between phase reading shall not exceed 2 percent.

(21) Using 374 megger, ground test exciter by applying 300 Vac at 60 Hz RMS for 1 second between one terminal and ground (frame). There shall be no evidence of dielectric breakdown.

(22) Using a double bridge measure resistance between terminals of exciter stator, Resistance shall be 4.50 to 5.50 ohms at 77°F (25°C).

(23) Using 374 megger tester, ground test stator assembly by applying 750 Vac at 60 Hz RMS for one second between all leads (tied together) and the frame. Apply 500 Vac at 60 Hz RMS for one second between phases with neutral open. There shall be no indication of dielectric breakdown in either test.

(24) Use semiconductor test set to test rectifiers for inverse current leakage at peak recurrent voltage of 600 volts. Leakage shall not exceed 20.0 milliamperes at 77°F (25°C). Check forward voltage drop. Voltage drop shall not exceed 1.2 volts at 77°F (25°C ).


The Diodes should be rated at 1200V! This applies to both polarities.

Disconnect the soldered wire leads from Diodes and Diode Ring assembly before doing the above test's!

 

[Gordy1ID]

I finally got my generator up and running. I replaced all six diodes with the higher voltage and amperage rating. Everything works great and the voltage output is great also. Thank you very much for everybody's help. Especially you pete! But a big sincere thank you to everybody! This is a wonderful form. Gordy

 

[Scoobyshep]

I finally got my generator up and running. I replaced all six diodes with the higher voltage and amperage rating. Everything works great and the voltage output is great also. Thank you very much for everybody's help. Especially you pete! But a big sincere thank you to everybody! This is a wonderful form. Gordy

Glad to hear you got it running

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