Alternator, fuse panel power, battery wiring question

[jdcaples]

This is just a few theory questions.

I'm not trying to solve a malfunction problem; just trying to learn, to understand the reasons behind a design depicted by the diagram.

This diagram is in a Painless Performance document (#30700) for alternator charge system upgrades

View attachment 19172

My questions:

Why are wire #915 and the main chassis fuse block on the alternator side of the 200 Amp MIDI fuse?

Is the fuse just protecting the battery from a catastrophic alternator amperage surge? If so, why not protect the main fuse block too?

What is the reason that wire #916 is on the opposite side of the MIDI 200 Amp fuse from the battery?

What would happen if wire #916 and wire #915 were moved to the battery side of the MIDI 200 Amp fuse, like this?

View attachment 19173


Thanks!

-Jon

 

[Lumpy Grits]

IIWY(if I was you)I'd call Painless, and ask them.
Would like to hear back what their response is.
LG

 

[73CJ]

The only problem I can see is if the 200A fuse blew power would still trying to energize the alternator. The one wire alternator needs 12V to get things started to produce current. It might back feed the alternator and who knows what would happen.

Why would you want to deviate?

On Jegs $81 ouch for a fuse block and chuck on wire? Man they charge a ton.

 

[jdcaples]

<snip>


Why would you want to deviate?

On Jegs $81 ouch for a fuse block and chuck on wire? Man they charge a ton.

Not that I want to deviate, just trying to understand why the fuse doesn't protect the main panel too.

Thanks for the idea about energizing the alternator.

Haven't purchased the kit figuring if I want to rewire for better efficiency, I could do it myself cheaper with bigger wires where it counts.

For now, it is just thinking, not doing.

I may call since I do have a Painless product, just not 30700. I havent yet because it is hard to get away during work hours.

Thanks for the brain share!

-Jon

 

[HackFabrication]

Power to the main fuse block on older vehicles is delivered through a fusible link. Perhaps the diagram does not show it?

Although I have a different setup:



In the above pic, you can see where the original fusible link was attached to the mega fuse.

Since then I have went to a maxi fuse to protect the main fuse panel:



I'll be swapping that over to a Slo-Blo type fuse. Second fuse is for the electric fan setup.

 

[jdcaples]

I have an email out to Painless' tech support and am waiting an answer.

I spoke with a couple of friends who say the fuse panel and the alternator need to be protected from the battery by the fuse. Why? because people sometimes short the battery terminals, meaning they will sometimes put a wrench on the battery while working on something and that wrench can accidentally bridge the + & - terminals. Another accident that happens frequently: they'll reverse jumper cables while being good Samaritans. Reversing the booster cables will energize the wiring back to the alternator with more battery amps than the alternator can take, popping diodes or other components.

When the Jeep was wired up with a new Painless harness, the instructions said to notice the fuse panel wire from the alternator output was spliced into two wires. One side of the splice goes to the fuse panel, the other to the positive side of the battery (actually, the battery side of the remote starter solenoid relay).

I suspect wiring that to the + side of the battery is wrong. As the Painless document suggests, the fuse panel needs to be entirely on the alternator side of the fusible link; otherwise - in the event of someone shorting out the + & - sides of the battery - dangerous amounts of current can go from the battery to the alternator via the fuse panel/alternator wire.

We'll see what Painless says, but I do like HackFabrication's design.

Bottom line: the battery regulator wire (terminal two on the alternator's excite/batt reg connector) needs to be energized with the ignition. It doesn't need to be connected to the positive side of the battery 24x7, as it would in my hypothetical circuit. Also, that design provides a path around the fuse, back to the alternator negating the protection of the fuse from stupid battery shenanigans.


If you disagree with the above, I'd love to hear your thoughts.

Thanks!

-Jon

 

[jdcaples]

My question to Painless:

My question is in regards to wiring design.

The diagram provided for Painless Performance High Alternator Upgrade kit 30709 shows the battery charge wire being attached to one side of the MIDI fuse.

The alternator and the wire(s) to the chassis main fuse panel are on the opposite side of the fuse; thus both alternator and fuse panel are opposite the battery.

My question is: Why isn't the chassis fuse panel connected to the battery side of the MIDI fuse, opposite the alternator?

Painless' response:

It is for dual direction protection.

If you were to put the fuse panel (916) wire on the battery side then you would be bypassing the fuse.

The 915 and 916 are connected together through the fuse block.

I probably should have worded my question more clearly, but I've been thinking about this a lot and am a burned out on the topic.

If I uppfit the alternator charge wire, I'll just get components off the shelf and follow the circuit design in the doc.

If I really don't trust the alternator, I might add additional protection between the alternator and the fuse panel, but I'm not a fan of additional points of failure, esp for what looks like the corner case of an alternator going berserk, shoving oddles of amps down a 10 gauge fuse panel harness wire.

-Jon

 

[Torxhead]

I like using the fusible links for protection in these areas. I also moved the "Sense" wire on the alternator to the hot line on the fuel gauge. This prevents voltage loss as it goes into the cab.

 

[jdcaples]

I like using the fusible links for protection in these areas. I also moved the "Sense" wire on the alternator to the hot line on the fuel gauge. This prevents voltage loss as it goes into the cab.

Smart. Find an ignition switch activated hot wire so the alternator adjusts output for far-off destinations.

What gauge wire did you use for that and was it a simple splice, or did you did you use a ring connector to terminate the wire on the fuel gauge?

I'm tempted to do terminate on the blower motor since 1) my fuel gauge went on sabbatical and 2) I did the blower motor upgrade so that fan has the honor of being biggest electrical hog in the Jeep right now. Except the fan's not on all the time like the fuel gauge. Damn. Do I get anything besides a back ache and an additional point of failure if I split the sense wire across the a working fuel gauge and the blower motor?

-Jon

 

[Torxhead]

I would think any hot line to the inside of the cab would work. I think I used a #12 fusible link and was able to solder it to copper wires and ring terminals. I have installed those fusible links to the alternator "Sense" wire, alternator hot line to the battery, and ignition wire at the relay to the battery. When the engine is cold I get 15 volts inside the cab and 14.5 when it warms up. I picked this stuff up reading the great book of Jeephammer some time ago.