Rembrant Posted March 25, 2022 Share Posted March 25, 2022 I was just reading the section on the 3G alternator conversion as I was trying to find out what size fuse holder and fuse I was going to need. Then I spotted Gary's note that the 1996 harness had a fusible link in the grey wire. I have the 1996 alternator harness, but the guy that pulled the engine cut the end of it off. There's currently only about 2" of it there. I don't think it was much longer to begin with. I saw one last weekend and it looked like it was only about 3" long to the ring terminal (the grey part, that is). So should I still put a fuse on this? I assume yes?... If yes, what size? I don't know for certain, but from what little I've read, I believe the factory alternator on this engine was 95 amp? Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 25, 2022 Share Posted March 25, 2022 The 1996 charging system is shown below, and it has a 12 gauge fuse link. But that begs the question of what size fuse to replace it with. In the 1985 EVTM there's a note that says: Note: (Fuse Link D) 14 gauge with 70A alternator. 16 gauge with 40 or 60A alternator. So 12 gauge would seem to be about right for a 95A alternator. (The diesel must have gotten a much bigger alternator as it has two 12 gauge fuse links in parallel.) Given that I'd say go with something like 110A. Fuses aren't precise and don't take overcurrent like fuse links do, so you have to err on the high side. Wait just a cotton-pickin' minute. There's also a page for a 200A alternator and it has a 300A fuse. Not a fuse link. That's 50% more, which would say you should have something like a 150A fuse. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 25, 2022 Share Posted March 25, 2022 The 1996 charging system is shown below, and it has a 12 gauge fuse link. But that begs the question of what size fuse to replace it with. In the 1985 EVTM there's a note that says: Note: (Fuse Link D) 14 gauge with 70A alternator. 16 gauge with 40 or 60A alternator. So 12 gauge would seem to be about right for a 95A alternator. (The diesel must have gotten a much bigger alternator as it has two 12 gauge fuse links in parallel.) Given that I'd say go with something like 110A. Fuses aren't precise and don't take overcurrent like fuse links do, so you have to err on the high side. Wait just a cotton-pickin' minute. There's also a page for a 200A alternator and it has a 300A fuse. Not a fuse link. That's 50% more, which would say you should have something like a 150A fuse. That's interesting. I know that many of us are using a 175A fuse with the 130A 3G, and that would suggest ~1.3x the alternator rated capacity. It would make sense to me the 95A alternator should be fixed right around 125A.... But I'm also sure my 2/0 cables are fine with that kind of current. What size charging cable do you have with the '96 harness, Cory? 6Ga? This chart seems to suggest that 6Ga can handle 150A at 4.4 feet long... https://jascoautomotive.com/automotive-wire-amperage-capacity-chart/ Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 25, 2022 Share Posted March 25, 2022 That's interesting. I know that many of us are using a 175A fuse with the 130A 3G, and that would suggest ~1.3x the alternator rated capacity. It would make sense to me the 95A alternator should be fixed right around 125A.... But I'm also sure my 2/0 cables are fine with that kind of current. What size charging cable do you have with the '96 harness, Cory? 6Ga? This chart seems to suggest that 6Ga can handle 150A at 4.4 feet long... https://jascoautomotive.com/automotive-wire-amperage-capacity-chart/ Yes, it is interesting. And it may suggest that the alternators are capable of kicking out more current than their ratings would imply on a short basis. Perhaps the rating is a continuous rating? I know my voltage goes up higher than the long-term set point right after starting, but then comes down pretty quickly. So I'm wondering of there is a "map" in the regulator that tries to give the battery a quick hit of power right after starting but then tapers off. And maybe at times that can exceed the rating of the alternator? Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 25, 2022 Share Posted March 25, 2022 Yes, it is interesting. And it may suggest that the alternators are capable of kicking out more current than their ratings would imply on a short basis. Perhaps the rating is a continuous rating? I know my voltage goes up higher than the long-term set point right after starting, but then comes down pretty quickly. So I'm wondering of there is a "map" in the regulator that tries to give the battery a quick hit of power right after starting but then tapers off. And maybe at times that can exceed the rating of the alternator? Ryan's old videos used to show the 130A putting out over 160A under load testing. I don't know how long it could keep that up without the diode board having a meltdown. Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 25, 2022 Share Posted March 25, 2022 Ryan's old videos used to show the 130A putting out over 160A under load testing. I don't know how long it could keep that up without the diode board having a meltdown. That's what I'm talking about. I doubt it could do it very long as the heat would build up very rapidly, but a fuse has a hair trigger compared to a fuse link, so I'd bet that's why Ford put a 300A fuse on a 200A alternator. And that might be a really good rule of thumb. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 25, 2022 Share Posted March 25, 2022 Ryan's old videos used to show the 130A putting out over 160A under load testing. I don't know how long it could keep that up without the diode board having a meltdown. My 160 amp on Darth has been there for around 10 years. Only issue was a set of brushes in the regulator. I did switch to a soft start regulator and a larger alternator pulley as the initial load was hard on the polygroove belt (black dust all over the alternator). If it does quit due to diode failure, I have an extra 130 amp 3G left over from my Taurus. Link to comment Share on other sites More sharing options...
taskswap Posted March 25, 2022 Share Posted March 25, 2022 Yes, it is interesting. And it may suggest that the alternators are capable of kicking out more current than their ratings would imply on a short basis. Perhaps the rating is a continuous rating? I know my voltage goes up higher than the long-term set point right after starting, but then comes down pretty quickly. So I'm wondering of there is a "map" in the regulator that tries to give the battery a quick hit of power right after starting but then tapers off. And maybe at times that can exceed the rating of the alternator? I don't know if this helps or distracts, but alternators can also do what's known as a "load dump". I remember from my aviation days that a huge deal was in battery disconnect switches, BlueSea and others sell special versions that have alternator field disconnect terminals. They're designed to break that before breaking the main battery connection because without a battery connected, alternators can go bonkers and put out 100V or more, frying anything still connected. In cars that's rarely an issue because who disconnects their battery while the engine is running? (In small aircraft this is a common checklist step during an emergency landing or fire.) Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 25, 2022 Share Posted March 25, 2022 Yes, it is interesting. And it may suggest that the alternators are capable of kicking out more current than their ratings would imply on a short basis. Perhaps the rating is a continuous rating? I know my voltage goes up higher than the long-term set point right after starting, but then comes down pretty quickly. So I'm wondering of there is a "map" in the regulator that tries to give the battery a quick hit of power right after starting but then tapers off. And maybe at times that can exceed the rating of the alternator? I don't know if this helps or distracts, but alternators can also do what's known as a "load dump". I remember from my aviation days that a huge deal was in battery disconnect switches, BlueSea and others sell special versions that have alternator field disconnect terminals. They're designed to break that before breaking the main battery connection because without a battery connected, alternators can go bonkers and put out 100V or more, frying anything still connected. In cars that's rarely an issue because who disconnects their battery while the engine is running? (In small aircraft this is a common checklist step during an emergency landing or fire.) 3G alternators still have the "ground here to test" screw on the brush holder. This causes the alternator to go full field and you will see 20V or more as it tries to boil your battery. (NOT recommended!) But it will show if failure to charge is because of the regulator. This is also why I always suggest looping the y/w "sense" wire straight to the output stud. If you have it going beyond the fusible link (or Mega-Fuse) like Ford installs it, the alternator is not seeing the system current riseand will quickly overheat. Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 25, 2022 Share Posted March 25, 2022 My 160 amp on Darth has been there for around 10 years. Only issue was a set of brushes in the regulator. I did switch to a soft start regulator and a larger alternator pulley as the initial load was hard on the polygroove belt (black dust all over the alternator). If it does quit due to diode failure, I have an extra 130 amp 3G left over from my Taurus. Bill - Is Darth's alternator a "160" because it has diodes capable of handling that much current? I'm asking because I'm wondering how, or even if, the regulators take the output rating of the alternator into account. Looking at Rock Auto's site I don't see a different regulator for the 95A alternator vs the 130A unit, even though a 95A alternator is shown as standard equipment. (The 165A units appear to take an outboard regulator, and I see no regulators for a 200A alternator.) So do the regulators sense the temp of the rectifiers? Link to comment Share on other sites More sharing options...
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