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nevertwobig

Wiring A New High Output Alternator

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nevertwobig

I have a 97 sunsetter with the 320 monsoon. I picked up a new 105 amp alternator to replace the 55 amp. I know I have to upgrade the wiring but can I bypass the wiring to the starter and go directly to the batteries or the perko switch? Also the sense wire could it go directly to the batteries? Looking for some imput, Thanks in advance!!

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Bobby Light

You need to replace the Orange wire as well. Make sure you use 0/2 wire if your batteries are in the passenger observers compartment.

Edited by Bobby Light

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nevertwobig

The orange needs to be 0/2 also?

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shawndoggy

As long as your current wiring is in good shape, an alternative is to double up your power and ground current runs, so you don't need to go all the way up to 0/2 if you currently have 2awg, you'd just do a second parallel run of 2awg power and ground.

That 0/2 wire is EXPENSIVE!

(thanks to DONTW8 for this tip... it's what I did in my old boat when upgrading my wiring).

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nevertwobig

Thanks, But I could eliminate the power going to the starter and go directly to the batteries, correct?

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shawndoggy

Thanks, But I could eliminate the power going to the starter and go directly to the batteries, correct?

as long as the current wiring to the starter is sufficient. The starter is just a bus stop for the electrons that are flowing from the battery or from the alternator.

EDIT: but it's more expensive that way because you don't get the benefit of electrons flowing from the alternator to the starter and to the batteries... you'd be solely relying on the upgraded wiring.

Edited by shawndoggy

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Bobby Light

The orange needs to be 0/2 also?

No I think it's 4 awg, and you have to have that wire installed. The wire on a 55 amp alternator going to the starter won't be sufficient for a 105 amp alternator.

Edited by Bobby Light

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nevertwobig

Thanks for the help! Hoping to get the boat out of storage this weekend and do the swap!

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shawndoggy

No I think it's 4 awg, and you have to have that wire installed. The wire on a 55 amp alternator going to the starter won't be sufficient for a 105 amp alternator.

I think on my 06 (70a alternator) it was 8 or 10 awg. Definitely not 4. I remember wondering how that wimpy little wire was going to get power to the batteries.

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Bobby Light

I think on my 06 (70a alternator) it was 8 or 10 awg. Definitely not 4. I remember wondering how that wimpy little wire was going to get power to the batteries.

I was talking about the wire size for the 105 amp alternator.

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nevertwobig

Yes it is pretty small. Can I just use the battery post on the alternator and skip the small-a** one coming out?

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shawndoggy

I was talking about the wire size for the 105 amp alternator.

No I know, I'm just commenting on how small they are on the factory wire on the lower output alts.

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Bobby Light

Yes it is pretty small. Can I just use the battery post on the alternator and skip the small-a** one coming out?

Are you talking about the little wire that goes from the starter to the alternator? If so no you can't skip that one and it needs to be beefed up, it's the charge wire.

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nevertwobig

If I remember correctly, I only have the 3 wires coming off of the 55 amp. purple and orange plus the ground. The new one has red battery sense, black ignition switch wire, ground and a batt+ post. that is 1 more than the old one. confusing!

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Slurpee

If I remember correctly, I only have the 3 wires coming off of the 55 amp. purple and orange plus the ground. The new one has red battery sense, black ignition switch wire, ground and a batt+ post. that is 1 more than the old one. confusing!

OLD Purple = New Black Ignition

OLD Orange = Batt+ Post

OLD Ground = Ground Post

NEW Batt Sense is debatable. In theory it goes to the fuse panel near the battery so that the alternator regulates the correct voltage at that point taking into account the voltage drop in the wiring. In a boat things are a bit different. I'd say protect the battery and make sure that the batt sense wire runs right to the battery. It's low current so don't worry about a really beefy wire. Just use something rugged enough to make the run and not ever get knocked loose easy. Any other opinions out there?

I'd also say that YES you can run straight to the battery and leave the connection to the starter from the OEM wiring capped. The reason is that there is most likely a really beefy power cable already running from the battery to the starter. If you make a really beefy connection from the alternator to the battery then the starter is still getting it's connection to the alternator via the run to the battery and it'll be a thicker connection than what you had before.

I'm about to drop a 200A 3 wire alternator into my engine this weekend. Finally got the belt and pulleys to upgrade the crank and water pump to a serpentine belt. Yay. So now I have a question. The whole engine block is grounded so WHY is there a black GND wire in my old OEM wiring harness from the alternator? I assume it's the circuit return for the Excite connection or the BATT- sense????

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nevertwobig

That's a good question slurpee! I don't know the answer to that. Thanks a lot for the help! I was hoping to run straight to the batteries. The only question now is I have two batteries, can I run to the Perko switch to charge both?

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nyryan2001

He needs to upgrade both the + and the ground wires, all the way up to the batteries correct? only doing the + can still burn up and overpower the ground wire?

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nevertwobig

I plan on upgrading the ground too with 0/2 wire. Just was unsure about bypassing starter. Thanks!

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Bozboat

As long as your current wiring is in good shape, an alternative is to double up your power and ground current runs, so you don't need to go all the way up to 0/2 if you currently have 2awg, you'd just do a second parallel run of 2awg power and ground.

That 0/2 wire is EXPENSIVE!

(thanks to DONTW8 for this tip... it's what I did in my old boat when upgrading my wiring).

Since your the "Internet Mechanic" and I am electrically challenged, here is my question: I am assuming that the Wire/battery cable from battery to Starter must be large enough to carry the full surge of the battery when the starter is engaged. 500 or so amps? So it must be a large battery cable.

The wire from the alternator pushes only 105 amps and that is only occasionally when you hit the right rpms, so why would the wire from the alternator have to be large? I understand that the old alternator pushed 55 amps maybe, and the new one is double that maybe. So a 4awg should be fine and an 0awg or a 2 awg would be more than needed?

When you hit the key large amps flow to the starter but when the motor is running the alternator pushes smaller amps to the starter on a smaller wire and then back to the battery on the battery cable???

link someone used for wires

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nevertwobig

I would rather error on the side of caution and go bigger on wire.

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WakesetterE

Your starter doesn't draw anywhere near 500 amps! It likely draws around 40-60 amps

Cranking.

The alternator should be able to output full current by 3000 rpm or less. It will only put out what is needed up to its capabilities.

The wire from the output lug on the alternator to the battery positive terminal or starter positive must be able to handle the full alternator current (105amps in your case). Goggle a dc wiring load chart to verify your size....but remember bigger is cheap insurance.

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nevertwobig

Is it really necessary to upgrade the ground wire? It is attached to the outer shell of the alternator. The alternator should ground through the mounts correct? What do you think?

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Bozboat

Apparently all wires should be 0 awg, tinned.

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