Circuit Protection and the "Shunt wire" by-pass

[72RoadrunnerGTX]

There’s been some recent discussions circulating lately about the “Shunt wire”, or under-hood direct battery to alternator, by-pass for the original Chrysler charging system. Claims of a simple fix that makes the stock charging system and related wiring/components safer by having this by-pass in place. Apparently, with little to no understanding of how this by-pass defeats the original circuit protection designed into this stock system and in fact creates an extreme risk of an electrical fire in the event of a short anywhere in the stock unfused wiring or components, even with a fusible link in the by-pass. Some basic electrical fundamentals involved, Ohm's law and Kirchhoff’s laws come into play here in understanding how this parallel by-pass effects the designed circuit protection on this stock system. Correct circuit protection is a must for any electrical circuit design to be considered safe, especially any circuit where the current potential can be in the hundreds of amps. There are much safer ways to harden, improve, or correct the real or perceived weaknesses of this stock charging/electrical system.

Another attempt to explain in a video format.


Parallel Circuits and the Application of Ohm’s Law
https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/simple-parallel-circuits/

 

[Nacho-RT74]

That parallel/straight path ppl tipically adds thinking is the correct fix just saves the load to recharge the battery when it discharges and sources all added accesories incorrectly sourced from batt when ammeter is present. But the car loads demands are still inside the cab running throught the bulkhead.

Ppl thinks it fixes because that extra charge load tipically is constant when revving up due the constant previous discharge stage that should be saved getting a better power source plant able to keep the battery out of the game, is not running anymore through the system as MUST be.

Hence why is still incorrect, aside the fuse link is also being bypassed (not just the ammeter) as you point out.

 

[bee71]

Jamie at Dead Dodge Garage has a good video on this and he adds a fusible link to the shunt wire.

 

[72RoadrunnerGTX]

Jamie at Dead Dodge Garage has a good video on this and he adds a fusible link to the shunt wire.

Can't agree with your assessment of that video. You and he are missing the point, adding a fusible link to the shunt wire still defeats the original correct circuit protection for the stock wiring and wires will still burn in the event of a dead short. BTW, he doesn't always use a fusible link, admits to "living dangerously", his use of fusible links in his shunt wire is a recent thing, plenty of his older vids make no mention of it . Did you watch the technical explanation video I posted?

 

[dvw]

Many current production cars have no method of fusing the alternator hot side. Easy enough to do with a Mega fuse. Agreed the method shown won't allow the amp gauge to function. The biggest issue with the factory wiring are the bulkhead terminals. The contact becomes corrode or loose. Then yhey heat up and melt. What have I used with success? Remove the 2 terminals in the firewall connector that feed the amp gauge. The 2 wires (red and black) are cut on each side of the firewall. The existing terminals are removed. Drill thru the empty terminal locations to allow wires to slide thru the cavities. Splice a new section of wire between both sides of the firewall to the remaining wire using quality splice clips and shrink tube. Leave the wire longer than need on the inside of the fire wall. Then if you have to disconnect a bulkhead connector you can pull it back for access. Make sure the amp gauge nuts are tight. Granted the wire is still thinner than it really should be. However this setup has been on my Challenger with a 110 amp alternator for 21 years. It has worked flawlessly. If you really wanted to you could run completely new thicker wires You would need to leave the exiting black wire connecte to the amp gauge as it is the major power feed under the dash.
Doug

 

[bobsgtx]

Many current production cars have no method of fusing the alternator hot side. Easy enough to do with a Mega fuse. Agreed the method shown won't allow the amp gauge to function. The biggest issue with the factory wiring are the bulkhead terminals. The contact becomes corrode or loose. Then yhey heat up and melt. What have I used with success? Remove the 2 terminals in the firewall connector that feed the amp gauge. The 2 wires (red and black) are cut on each side of the firewall. The existing terminals are removed. Drill thru the empty terminal locations to allow wires to slide thru the cavities. Splice a new section of wire between both sides of the firewall to the remaining wire using quality splice clips and shrink tube. Leave the wire longer than need on the inside of the fire wall. Then if you have to disconnect a bulkhead connector you can pull it back for access. Make sure the amp gauge nuts are tight. Granted the wire is still thinner than it really should be. However this setup has been on my Challenger with a 110 amp alternator for 21 years. It has worked flawlessly. If you really wanted to you could run completely new thicker wires You would need to leave the exiting black wire connecte to the amp gauge as it is the major power feed under the dash.
Doug

This was the fix back in the day. I did it a few times when I worked at a gas (service) station.

 

[RJRENTON]

There’s been some recent discussions circulating lately about the “Shunt wire”, or under-hood direct battery to alternator, by-pass for the original Chrysler charging system. Claims of a simple fix that makes the stock charging system and related wiring/components safer by having this by-pass in place. Apparently, with little to no understanding of how this by-pass defeats the original circuit protection designed into this stock system and in fact creates an extreme risk of an electrical fire in the event of a short anywhere in the stock unfused wiring or components, even with a fusible link in the by-pass. Some basic electrical fundamentals involved, Ohm's law and Kirchhoff’s laws come into play here in understanding how this parallel by-pass effects the designed circuit protection on this stock system. Correct circuit protection is a must for any electrical circuit design to be considered safe, especially any circuit where the current potential can be in the hundreds of amps. There are much safer ways to harden, improve, or correct the real or perceived weaknesses of this stock charging system.

Another attempt to explain in a video format.


Parallel Circuits and the Application of Ohm’s Law
https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/simple-parallel-circuits/

It is obvious that many, if not all, of these "self proclaimed experts" have little understanding of Ohm's Law and Kirchoffs Laws and how they are interrelated. These published "fixes" are self perpetuating, started and maintained by inexperienced people using word of mouth and incorrect "seat of the pants reasoning" and the "this is what my buddy did" examples......sad excuses all......if these "experts" do not understand the fundamentals, all they have to do is ASK. More damage is done with the "guess and by golly" approach.....but their mistakes are never revealed........
BOB RENTON

 

[gkent]

So, for a 90 amp alternator with a trunk mounted battery, what's the proper method ?!?! Starter cable is live only in "start" mode. Battery is fed by a 2 ga. cable.

 

[72RoadrunnerGTX]

So, for a 90 amp alternator with a trunk mounted battery, what's the proper method ?!?! Starter cable is live only in "start" mode. Battery is fed by a 2 ga. cable.

Is that a serious question? Not sure I’m following, what would your described modified electrical system have to do with the subject of this thread, an unsafe band aid fix to an all-stock original electrical system?

 

[72RoadrunnerGTX]

Many current production cars have no method of fusing the alternator hot side. Easy enough to do with a Mega fuse. Agreed the method shown won't allow the amp gauge to function. The biggest issue with the factory wiring are the bulkhead terminals. The contact becomes corrode or loose. Then yhey heat up and melt. What have I used with success? Remove the 2 terminals in the firewall connector that feed the amp gauge. The 2 wires (red and black) are cut on each side of the firewall. The existing terminals are removed. Drill thru the empty terminal locations to allow wires to slide thru the cavities. Splice a new section of wire between both sides of the firewall to the remaining wire using quality splice clips and shrink tube. Leave the wire longer than need on the inside of the fire wall. Then if you have to disconnect a bulkhead connector you can pull it back for access. Make sure the amp gauge nuts are tight. Granted the wire is still thinner than it really should be. However this setup has been on my Challenger with a 110 amp alternator for 21 years. It has worked flawlessly. If you really wanted to you could run completely new thicker wires You would need to leave the exiting black wire connecte to the amp gauge as it is the major power feed under the dash.
Doug

To be clear, for this circuit protection subject on an original stock electrical system, the battery is the bigger current potential device, hence the system circuit protection needs to be located as close as possible to the battery. No real need for system circuit protection at the alternator.

 

[RJRENTON]

To be clear, for this circuit protection subject on an original stock electrical system, the battery is the bigger current potential device, hence the system circuit protection needs to be located as close as possible to the battery. No real need for system circuit protection at the alternator.

I agree with your premise......Some people just do not seem to comprehend....
BOB RENTON

 

[dvw]

To be clear, for this circuit protection subject on an original stock electrical system, the battery is the bigger current potential device, hence the system circuit protection needs to be located as close as possible to the battery. No real need for system circuit protection at the alternator.

With the original design I don't think the worry was a ground of tis circuit in the engine compartment as much as the possibility under the dash. Thus the factory fuseable link location. Always best to protect at the source of potential.
Doug

 

[451Mopar]

Can't agree with your assessment of that video. You and he are missing the point, adding a fusible link to the shunt wire still defeats the original correct circuit protection for the stock wiring and wires will still burn in the event of a dead short. BTW, he doesn't always use a fusible link, admits to "living dangerously", his use of fusible links in his shunt wire is a recent thing, plenty of his older vids make no mention of it . Did you watch the technical explanation video I posted?

I commented on Jamies video to let him know of the issue. I originally did the same on my car and later when pointed out I understood the problem.
Because I'm too lazy to go under the dash, I just pop the alternator wire terminal and battery fusible link terminal out of the engine side bulkhead connector, and make a new fusible link that connects to new terminals going into each bulkhead cavity so alternator and battery terminals at the bulkhead are connected together and protected by the fusible link. The original alternator wire is disconnected and not used. Still has the new alternator wire to battery.

 

[451Mopar]

So, for a 90 amp alternator with a trunk mounted battery, what's the proper method ?!?! Starter cable is live only in "start" mode. Battery is fed by a 2 ga. cable.

There are many ways you can wire the car, alot depends on what your trying to do.
Normally you want the alternator output wire going directly to the battery.
On a car with large starter cable that is live, the alternator out could connect to that in the engine compartment, but that can be an issue with killing the engine with a battery cut-off switch depending on how everything is wired.
Usually those who want to totally isolate all electrical at the battery with a cut-off switch, power is controlled through relays.
On the charger, I use a dual pole cut-off switch that disconnects the battery power, and also kills the ignition
https://www.digikey.com/en/products/detail/cole-hersee/75907/6347520

 

[Nacho-RT74]

The only source to feed constantly a short no matter what is the batt, hence why the fuse link is on that side.

If the car was riding around without batt and just alt, a short will stall out the engine because will draw all the power regulator handles from ign circuit to keep the engine/alt running, so the source would disappear by itself.

 

[451Mopar]

The only source to feed constantly a short no matter what is the batt, hence why the fuse link is on that side.

If the car was riding around without batt and just alt, a short will stall out the engine because will draw all the power regulator handles from ign circuit to keep the engine/alt running, so the source would disappear by itself.

I see what you are saying about the original wiring.
Talking about the alternator by-pass of adding wire from alternator to battery "without" disconnecting the original alternator wire the the bulkhead connector, like in Jamies dead Dodge garage video.

 

[Nacho-RT74]

Since the beginning 72RoadrunnerGTX is saying just add the wire between alt and batt what is what EVERYBODY tipically makes jumping out the amm and also the fuse link ( or any other protection ) is simply wrong. It needs deeper mods, like he in fact mentions on video, to keep the protection, Althought still eliminates the amm function.

Add a fuse link on the jumper wire without any other mod doesn’t help a lot either, because still with that added protection on that jumper wire between alt and batt it gets also two paths to feed the eventually short. Doubling the wire and doubling the fuse link makes also double time to blown the protection (if ever) so more damage will be produced. Once again, if just adding the path without any other mod as shown.

Dunno what that guy Jamie’s says and I won’t take my time to heard about what he says LOL.

About what you say that there are many ways to wire a car as far meets your requirements. Totally true!. But there are also many ways to make it WRONG and still meeting your requirements, however being unsafe or incorrect if some considerations are not taken in mind.