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The orange wire connecting the alt output to the "battery cable" at the starter solenoid should have some sort of circuit protection (fuse/breaker/fuseable link) at the starter solenoid end. Hard to find a good schematic, but of the ones I found, some show a 90A fuse (looks like a 1" cube) and others just show being connected directly.
The wire size should be able to withstand the alternators full output (35A, 55A, etc) so circuit protection at the alternator end of the orange wire is not needed. (This is why the wire size needs to be increased if installing a larger capacity alternator) If the alternator shorts to ground internally (or orange wire gets grounded somehow) and there's no circuit protection at the starter solenoid connection of the orange wire, the batt can flow hundreds of amps thru that wire. That's my WAG as to what happened. IMHO, If the ops new harness doesn't include a 90A cube type fuse, he should seriously consider installing one, even if it's not shown on the applicable schematic. |
Originally Posted by compedgemarine
(Post 4928938)
most times a fusible link on the alternator is at the battery or starter post. problem with this is if it shorts between the link and alternator (wire rubs thru on the engine mount or such) the alternator is the source of power so it can just go to full output and the link never sees that load. fusible links work great when the short is on the opposite side of the power source (battery) but the alternator is also a power source and if it is spinning then it is powering. I guess if the link is on the alternator end of the wire it would work but that is not how most are wired.
Originally Posted by zz28zz
(Post 4928952)
The orange wire connecting the alt output to the "battery cable" at the starter solenoid should have some sort of circuit protection (fuse/breaker/fuseable link) at the starter solenoid end. Hard to find a good schematic, but of the ones I found, some show a 90A fuse (looks like a 1" cube) and others just show being connected directly.
The wire size should be able to withstand the alternators full output (35A, 55A, etc) so circuit protection at the alternator end of the orange wire is not needed. (This is why the wire size needs to be increased if installing a larger capacity alternator) If the alternator shorts to ground internally (or orange wire gets grounded somehow) and there's no circuit protection at the starter solenoid connection of the orange wire, the batt can flow hundreds of amps thru that wire. That's my WAG as to what happened. IMHO, If the ops new harness doesn't include a 90A cube type fuse, he should seriously consider installing one, even if it's not shown on the applicable schematic. https://www.ebay.com/itm/13543601365...55-0&loc=82786 Seafordguy, did you notice if you had that fuse in place? On a side note, I looked into this for my high output alt and it's showing installing a fuse between the alt output wire and less than 12" from the battery. |
Originally Posted by xlint89
(Post 4928964)
You guys are correct. I do remember seeing that square block on the starter relay post.
https://www.ebay.com/itm/13543601365...55-0&loc=82786 Seafordguy, did you notice if you had that fuse in place? On a side note, I looked into this for my high output alt and it's showing installing a fuse between the alt output wire and less than 12" from the battery. can you confirm instal? funny the diagram that Hardin sends with that harness does not show this fuse. im wiring according this diagram, the only thing im apparently not using is the “12v sense wire” coming from the alternator and the purple “Excite wire to alt” which is consistent with the other motor- those are taped off. https://www.hardin-marine.com/instru.../620-08904.pdf Looking closer though at that Diagram, I’m not sure how that provides more protection given it is after the 50AMP breaker which I would assume would trip first anyways since it’s the most direct route from ALT, through Batt Post up through breaker unless I”m missing something? |
https://cimg1.ibsrv.net/gimg/www.off...6a7ab12979.jpg
In series with the starter, I had the alternator wire on the starter but it could be run on top too.. not sure if it would help when an alternator short circuits but can`t hurt . |
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Originally Posted by seafordguy
(Post 4928967)
definitely did not have that. I’ll order two right now.
can you confirm instal? funny the diagram that Hardin sends with that harness does not show this fuse. im wiring according this diagram, the only thing im apparently not using is the “12v sense wire” coming from the alternator and the purple “Excite wire to alt” which is consistent with the other motor- those are taped off. https://www.hardin-marine.com/instru.../620-08904.pdf Looking closer though at that Diagram, I’m not sure how that provides more protection given it is after the 50AMP breaker which I would assume would trip first anyways since it’s the most direct route from ALT, through Batt Post up through breaker unless I”m missing something? I looked up my gen VI HP 500 (carb) engine and it does NOT show the 90A fuse on any of the parts diagrams. |
Originally Posted by xlint89
(Post 4928997)
What year and model engine do you have?
I looked up my gen VI HP 500 (carb) engine and it does NOT show the 90A fuse on any of the parts diagrams. |
Not sure what to look up for your application.
Was it a gen 4 454 or 502? |
God - it’s been so long, but I believe they are Merlin blocks, basically IV. Manual fuel pumps, but I think based on the Mark IV.
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I guess it might have been a blessing in disguise.
Installing the 90A fuse on the starter on the motor that didn’t catch on fire and I noticed the starter was loose. Turns out the bolts that clock the starter had backed out. Undescribably unpleasant getting that thing off the port engine with them in the boat. If I read the technical pages right, those things are 50-inch pounds - ripe for someone to strip them out, which one was. I had to put a nut on the backside and put locktite on both. https://cimg2.ibsrv.net/gimg/www.off...1b0b0f514.jpeg on the backside and I put them both back in with Blue Locktite. |
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