Need 520H Electrical advice

[formariz 11,849]

While doing maintenance on my 96 520H, I noticed that the 30AMP fuse is discolored from overheating particularly on one leg. Tractor works perfectly with no problems. Previous owner had problems with 9 pin connector so he bypassed the two red wires from it. First question is what would be the cause of fuse discoloration. Bad contact perhaps? I cleaned all fuse terminals now and used dielectric grease on them. Second question, is whether the 9 pin connector fix is correct and it will not potentially in the future cause any problems.

[953 nut 51,682]

10 minutes ago, formariz said:

Bad contact perhaps?

                A lot of the fuse holders are located near the battery facing upward so they become a receptacle for battery acid. Just a tiny bit at a time over the course of a few decades and then you see the result of a poor design.    

The dielectric grease should have been used from the factory.    

[formariz 11,849]

3 hours ago, 953 nut said:

                A lot of the fuse holders are located near the battery facing upward so they become a receptacle for battery acid. Just a tiny bit at a time over the course of a few decades and then you see the result of a poor design.    

The dielectric grease should have been used from the factory.    

Looks like you are absolutely correct. The fuse leg on the battery side is the one overheating, and all of the terminals on that side show corrosion while the opposite side is much better.

Edited August 8, 2019 by formariz

[953 nut 51,682]

2 hours ago, formariz said:

battery side is the one overheating,

One of our members who hasn't posted lately @Save Old Iron had a great post on that subject that I saved. Here it is:

 

Think about it - if you forced a sudden surge of lets say 35 amps thru a 30 amp fuse - the fuse internal element slowly "melts" - usually within a few seconds - you see a melted wire in the fuse body and the fuse body and leads remain looking like they originally did ( give or take a little). If you dead shorted the battery thru the fuse to the chassis, you may blacken the inside of the fuse but the fusible element melts long before you have a chance to cook the entire fuse body like in your picture.

Same idea for the white plastic engine harness connector - the brown discoloration is from cooked plastic - where is the heat coming from ?? The "Molex" style connectors used in this tractor series are in a harsh, corrosive environment. Vibration causes the connections to loosen - corrosion starts within the metal terminals and a voltage drop develops across the corrosion.

If you have a 10 amp current flowing across a 1 ohm resistance (contact corrosion) the electronics formula to calculate power = current squared times resistance

so 10 amps x 10amps x 1 ohm resistance = 100 watts !!

100 watts of connector heating is the same as laying a 100 watt soldering iron on the connector.

[squonk 38,929]

Yeah bad connection. As for the molex, I tore one out and used 2 4 pin connectors instead

[Jerry.Guzzi 6]

On 8/8/2019 at 8:12 PM, 953 nut said:

One of our members who hasn't posted lately @Save Old Iron had a great post on that subject that I saved. Here it is:

 

Think about it - if you forced a sudden surge of lets say 35 amps thru a 30 amp fuse - the fuse internal element slowly "melts" - usually within a few seconds - you see a melted wire in the fuse body and the fuse body and leads remain looking like they originally did ( give or take a little). If you dead shorted the battery thru the fuse to the chassis, you may blacken the inside of the fuse but the fusible element melts long before you have a chance to cook the entire fuse body like in your picture.

Same idea for the white plastic engine harness connector - the brown discoloration is from cooked plastic - where is the heat coming from ?? The "Molex" style connectors used in this tractor series are in a harsh, corrosive environment. Vibration causes the connections to loosen - corrosion starts within the metal terminals and a voltage drop develops across the corrosion.

If you have a 10 amp current flowing across a 1 ohm resistance (contact corrosion) the electronics formula to calculate power = current squared times resistance

so 10 amps x 10amps x 1 ohm resistance = 100 watts !!

100 watts of connector heating is the same as laying a 100 watt soldering iron on the connector.

Wow, this must be what my 520 H done. Got so hot it's burnt fuse block, 30 amp fuse was welded to fuse block. I ordered Stator from Cummings, going to rewire like my converted 417/520 H next month.