Upgrading 65A Alternator to a 130A

[ferrall]

I have a 1994 Volvo 5.8Fi PMDA and was looking to replace the alternator. I have a Prestolite 65A in it now which now failed for the second time in 4 years. I have a feeling that running 2 amps and subs must take a toll on it. Would going to a 130A alternator solve this problem and would I have to modify any wiring moving up in amperage?

 

[alldodge]

I have a 1994 Volvo 5.8Fi PMDA and was looking to replace the alternator. I have a Prestolite 65A in it now which now failed for the second time in 4 years. I have a feeling that running 2 amps and subs must take a toll on it. Would going to a 130A alternator solve this problem and would I have to modify any wiring moving up in amperage?

You sure there isn't something else going on. Putting out heavy all the time will take it's toll, and if it's burning the diodes or windings then I'll agree. If you go to the 130amp ALT increase to 4 AWG wire, and also increase your ALT fuse on the starter or put one in line

 

[ferrall]

Well, now I think there's something else going on. I installed the 130A alt. and nothing changed. I'm getting around 11V on my meter off the battery. Doesn't look like it's charging. At this point I have no idea. Electric stuff is not my forte'.
Regarding the "going to a 4 AWG wire," how would I do that when it's all wrapped up in the wiring harness? And this fuse on the starter, I have no idea what you're talking about. Sorry, just not familiar enough with this stuff.

 

[alldodge]

Well, now I think there's something else going on. I installed the 130A alt. and nothing changed. I'm getting around 11V on my meter off the battery. Doesn't look like it's charging. At this point I have no idea. Electric stuff is not my forte'.
Regarding the "going to a 4 AWG wire," how would I do that when it's all wrapped up in the wiring harness? And this fuse on the starter, I have no idea what you're talking about. Sorry, just not familiar enough with this stuff.

As I was thinking all along. Start with your batteries, hopefully your have at least two in parallel. Check them to make sure there are holding a charge, give them a couple hours off the charger before checking.

If your using the meter on the boat, this could be suspect. Need to use a handheld meter.

Factory ALT's have an output, ground, power and sense leads going to them. If you have a one wire ALT (only uses one wire) then the regulation is all done inside. To run a larger wire you need to remove the ALT output lead from the ALT, also remove the other end from the fuse on the starter, and tape them up. Run a new wire from the ALT output terminal all the back to the starter fuse. Your current fuse is 90amps, and you could leave it there, but it will blow if the ALT ever needs to put out more then the fuse can take

Edit: also check the reading at the ALT

 

[ferrall]

I did use a handheld meter and the batteries are fine. I have a load tester and they tested fine. I have a 3 wire Alt. Output, ground and a purple. I'm not positive what the purple goes to because it wasn't labeled on my old alt. I'm assuming it goes on the exciter terminal.
So, you're saying there's a wire that goes from the alt to the starter? I'm unaware of any starter fuse and where it would be. Like I said, the output wire from the alt goes into a wiring harness which is all wrapped up and I lose sight of where it even goes. If this fuse you're talking about is blown right now, would that cause my issue I'm having right now?

Thanks!

 

[alldodge]

Your purple wire goes is your exciter for the field winding of the ALT. All of the purple wires on your motor go hot when the key is turned to on. The ALT output goes directly back to the battery via the starter connection. Here is how Merc does it and VP does it the same way. Look for the fuse on the starter as in the pic below. Now there is a possibility your motor does not use the fuse. This is for an electric fuel pump but just note the ALT wires

 

[bruceb58]

Post a picture of the back of your alternator.

 

[ferrall]

No Title

The 2 terminals in the black area are the exciter (EXC) on the left and "S" on the right. The other 2 are "B" and "E" on the far right in the silver area

 

[ferrall]

My gut feeling with this whole thing is that I have a bad ground somewhere because I have other electrical issues which I won't go into now. I'll get that that 4 gauge wire put in and look at grounding in more depth and look at the wiring diagram of the alt and starter you gave me

 

[bruceb58]

So what do you have hooked up to the excite and the sense terminals? BTW, the E terminal is ground but you likely already know that.

 

[jeffnick]

Instead of replacing to 4 gauge, how about just adding another wire?

 

[muc]

This is a Ford fuel injected engine. It is wired different from the MerCruiser diagrams posted above. DO NOT use those diagrams. The alternator output doesn’t go to the starter.

You should really take a look at Volvo Service Bulletin 37-2-3 before running this boat. Especially since you have doubled alternator output without increasing wire capacity.

“Instead of replacing to 4 gauge, how about just adding another wire?” NO you should not. It's not safe.

Sorry if I’m coming across like a jerk. But the path you are on could lead to the death of innocent people.

Please get the proper service manual, wiring diagram and electrical training. Or hire somebody who has those things.

“My gut feeling with this whole thing is that I have a bad ground somewhere because I have other electrical issues which I won't go into now.”
Electrical issues can be interrelated and all of them should be taken into account when troubleshooting.

Service Manual P/N 7796456 is what you want

 

[bruceb58]

Alternator output connects to a wire at a circuit breaker. It then connects to another wire that goes to the starter. it does NOT go trough the circuit breaker. If you are going to replace the wire with 4ga, you pretty much have to bring it down to the starter. The wire that connects the alternator to the input of the circuit breaker should be removed.

I agree with Muc that you should look at a Volvo manual to see how it is wired if you are unsure.

 

[K-2]

The ground wire(s) also should be 4 gauge on this alternator upgrade.

If you "just add another wire" the load could/will take the path of least resistance which means 1 wire will get used to carry the load , so you didn't gain anything.

 

[alldodge]

While I do see a difference I don't see how it can be a catastrophic failure. Goes from the ALT output to the circuit breaker, then a direct connection to the starter. So the issue is the same and there is not a 90amp fuse, and it does connect to "one" side of the assist solenoid, it does go straight back to the starter, then the battery. There is a bit of difference in the ALT hook up.

 

[jeffnick]

If you "just add another wire" the load could/will take the path of least resistance which means 1 wire will get used to carry the load , so you didn't gain anything.

I'm not sure this is the case...
I ordered a winch that required a 40 amp breaker. It came with 2 20 amp breakers in parallel, similar to multiple wires carrying the load as I suggested above. I've never had one kick out even when the winch stalls.

 

[ferrall]

No Title

This is my old 65A alternator. It doesn't have a sense terminal though there is a label for where it would be just opposite of the excite terminal. Right now I have my purple wire connected to the excite terminal on my new alt.

I did notice in the latest wiring diagram that the excite and sense terminals look to be jumped or connected together. Am I reading that correct?

 

[bruceb58]

yes, they need to be hooked together.

 

[alldodge]

The wiring diagram shows a connection between them, it may be connected internally. Measure ohms across the two terminals, should be zero ohms.

 

[bruceb58]

If you "just add another wire" the load could/will take the path of least resistance which means 1 wire will get used to carry the load , so you didn't gain anything.

A larger wire will take most of the current only because it will have less voltage drop for a given current. The ratio of current by the two wires is a ratio of the resistance of each wire.