Circuit Breaker Upgrade question

**TRBenj** · 10-01-2008, 09:53 AM

RE: Circuit Breaker Upgrade question

Im going to assume that the basic '97 (GT40?) wiring is similar to the older/simpler carb'd PCM Fords (ignition/computer/sensor stuff excluded, of course).

Sounds like you need a bigger alt to keep up with the increase load from the stereo. A bigger battery would be highly recommended as well. If you run the stereo for a significant amount of time with the boat not running, strongly consider going with duals- keeping the starting and stereo batteries isolated would allow you to start the boat after running the stereo battery low.

All new loads (stereo, etc) should be run directly off the battery and fused appropriately. Ratings for fuses should always be chosen to be slightly lower than the rating of the WIRE coming from it. IE, figure out how much current your loads will draw (worst case), size the wire accordingly, then fuse it (closest to the source) just under the rating for the wire.

When splitting the loads like this, there are now 2 paths to consider. One is the new wiring for the stereo. The second is the wiring and fusing for the loads already attached to the charging system (IE, everything in the dash). The stock breaker is sized according to the size of the wire running to the dash. While you could certainly upgrade the wire running to the dash and run everything off of one upsized breaker, thats probably not the easiest way to go. Its also not necessary to upgrade the wire running to the dash since there has been nothing done to increase the load there.

Instead, one option to consider would be a dual breaker system. The stock breaker could still be used to protect the wiring and loads at the dash. A second (larger) breaker could be used on the charging circuit between the new (larger) alt and battery/batteries. I would recommend a system like this:

**mrbobolina** · 10-01-2008, 12:39 PM

RE: Circuit Breaker Upgrade question

Hmmm I think I understand all of that. Where I got lost is how the electric current is controlled between the 100a breaker and the current 60a breaker?

In the diagram it seems as though the 60a current is coming from the 100a breaker. This would lead me to believe 100a are being allowed to the 60a breaker and would cause it to pop?

Electricals are not my specialty so bear with me if I am off in left field on that one.

**TRBenj** · 10-01-2008, 05:27 PM

Re: RE: Circuit Breaker Upgrade question

Originally posted by mrbobolina

Electricals are not my specialty so bear with me if I am off in left field on that one.

A load will draw current. Without a load, current will not flow. There are 2 current sources- the alternator and the battery/batteries. If there are no loads on the alternator, it will not supply any current (even when running). Same goes for the battery.

Like I said, there are 2 paths that you need to look at with the addition of a large load (stereo) and upgraded electrical system. The first is the obvious one- the path that feeds and recharges the stereo. In this path, the stereo amps will draw current, the battery will supply it, and the alternator will replenish the battery back to full charge. The battery is both a source (to the stereo) and a load (on the alternator). The path goes alternator-->100A breaker-->battery-->stereo. Note that the load from the stereo will not be drawn through the 50A breaker. Also note that the wires running between the battery and stereo arent breakered- that is why they need to be fused individually.

The second path is the stock path to the dash. All of the stock loads (lights, gauges, etc) are fed by this. The path goes alternator-->50A breaker-->dash. When the engine is off, those loads are fed by the starting battery instead of the alt. Note that in either case, that current running through the wire to the dash passes through the 50A breaker. This protects the 10awg wire in the case of a dead short at the dash (or somewhere in between).

The only wires not breakered/fused in the system are the ones between the battery and starter. This is the "unprotected" side of the system. These wires are sized large enough to handle the very high current draw of the starter for a short period of time- which is generally several hundred amps.

**bchesley** · 10-01-2008, 09:30 PM

RE: Re: RE: Circuit Breaker Upgrade question

There is a 100 amp upgrade from PCM that includes the alternator and new wiring harness. Do a search for alternator upgrade by wake_fun.

**mrbobolina** · 10-21-2008, 01:48 AM

TRbenj - I am going with your two battery suggestion. I called Nautique and Mastercraft; asked what battery setup the new boats come with which have the crazy sound systems built on them as well as more than typical electrical requirements. They both described what you suggested.

So for clarity I took your diagram and adjusted it so that I can show you what I am understanding you to be saying.

- The alternator I have is a 140 amp alternator from DB Electric. (s10 model $150, shipped) - fits perfectly

- The secondary battery is a Die Hard platnum 31M (higher spec than the Optima, and I did not have to mail order it so it was actually cheaper - $249 - ouch).
Yes I know way overkill...

- 8501 Perko switch is being shipped ($30 ebay).

- Combiner - still shopping.

- 100 amp breaker still have not ordered it. Aside from protecting the solenoid, which I believe you indicated is fine as it only gets power for a very short period of time; what is the point of the 100a breaker in a two battery setup? FYI the perko switch can handle a 350 amp load.

What I changed on the diagram is the amp on the main breaker which is stock 60amp not 50amp (just being anal), and the alternator which now reflect the 140amp.

I also adjusted the stock wiring (60amp line) to reflect that it is connecting directly to the alternator and not to the 4awg line which is connected to the 100 amp breaker.

lastly I adjusted the diagram of the line from the 100 amp breaker going to the perko switch. I am not sure this what you intended, however based on what I read I believe this what you described. At the end of the day should this line connect directly to the SOLENOID, the perko switch (as I have drawn), or should I splice the line going from the solenoid to the perko switch (as originally drawn in the diagram), with something like a distribution block? Or at the end of the day it really does not matter so long as the connection is solid.

I appologize if these questions should be fundamental, I just want to fully understand and do it right one time only.

Attached Files

**TRBenj** · 10-21-2008, 03:55 PM

Originally posted by mrbobolina

Aside from protecting the solenoid, which I believe you indicated is fine as it only gets power for a very short period of time; what is the point of the 100a breaker in a two battery setup? FYI the perko switch can handle a 350 amp load.

What I changed on the diagram is the amp on the main breaker which is stock 60amp not 50amp (just being anal), and the alternator which now reflect the 140amp.

I also adjusted the stock wiring (60amp line) to reflect that it is connecting directly to the alternator and not to the 4awg line which is connected to the 100 amp breaker.

lastly I adjusted the diagram of the line from the 100 amp breaker going to the perko switch. I am not sure this what you intended, however based on what I read I believe this what you described. At the end of the day should this line connect directly to the SOLENOID, the perko switch (as I have drawn), or should I splice the line going from the solenoid to the perko switch (as originally drawn in the diagram), with something like a distribution block? Or at the end of the day it really does not matter so long as the connection is solid.

I appologize if these questions should be fundamental, I just want to fully understand and do it right one time only.

Answers/Comments:

-Wiring coming from the alt should be rated beyond the max spec of the alt, or fused appropriately (as close to the alt as possible). 4awg is only rated for 135A, so consider going to 2awg instead for the 140A alt.

-The purpose of the 100A breaker is to protect the 4awg (2awg) wire coming from the alt from the battery/batteries in the case of a dead short (a battery can source a LOT of current). The 60A breaker protects the smaller (10awg?) wire running to the dash.

-I didnt realize that the Perko switch has such a marginal current rating. I dont know what the starter will draw exactly, but I bet its close to 350A. You'll probably be fine, but that may be one part that would be worth upgrading at some point.

- The diagram that I drew doesnt necessarily show the physical connections- its a schematic of sorts. If you want to run 2 wires off of the alt (1 to each breaker, both should be 2awg) thats fine- but it would be easier to run one to a single breaker and a shorter wire to the second breaker, assuming theyre mounted close together at the rear of the engine. Same goes for the wiring to the Perko- its only necessary that the 100A breaker go between the batteries and 4awg coming from the alt, and that the Perko be installed between the solenoid and 2 batteries. Just remember that all of those wires should be 0awg since theyre on the unprotected side of the breakers. Shorter runs are better than longer ones- theres less voltage drop, and the wire is expensive!