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Single wire alternator question

451Mopar said:
You both have good points. You don't want the alternator output to go OPEN / unconnected. On external regulated alternator the alter may output high and unregulated voltages that might damage the alternator diodes (depending on what voltage they are rated for.) The external regulator will also be applying maximum current that it can to the alternator field windings (this will happen when the regulator senses the ignition voltage is below the regulators set point. Either alternator open or short in alternator out or ignition sense. I am not sure how an internally regulated alternator would react to no battery load, but I would think the alternator output is going to be very noisy?

The fuses are not sized by the alternator current output, They are sized by the wiring gauge in the harness they are protecting.
With a short-circuit at the alternator, you are not protecting the alternator, but the wiring harness going to the alternator (sourced from battery.)
Alternator output should be routed to the battery, and then vehicle power taken from battery. A common point with low resistance. large wiring or bus bar is nearly the same as directly from the battery, but if you loose the battery connection, and the only the alternator is supplying power than the output is going to be noisy, maybe with high voltage spikes depending on the capacitor in the alternator (and any other capacitance in the connected circuit.)
As mentioned above, it would be rare that a 100+ AMP alternator will be operating at maximum output, unless you are operating a bunch of electrical accessories.
Usually 4AWG is good from alternator to battery is the cars actual constant electrical loads are < 100 amps, and a 100 Amp mega-fuse (slow-blow) will protect the 4 AWG wire.
It is fine to go with larger size wire because it will have less restive losses, but it will weigh more, cost more, and routing is more difficult.

What I am trying to say, For example, you have a 100 Amp alternator, and your electrical loads are normally < 60 Amps.
You could wire the alternator with 8AWG wire and a 60 Amp slow-blow fuse (or fusible link) at the alternator output, but not a 100 Amp fuse.
Although the alternator could supply the 100 amps if there is a short between the alternator and battery. The wire is not rated for 100 amps of current and will melt after a short time.

Also as pointed out above, if there is a short, normally the battery is the source supplying the power. A battery fuse (if even using one) is going to be very large so the starter circuit does not blow the fuse. Single ought (1/0) welding cable normally used in battery relocation is good for 300 Amps for a few minutes.
A 300 Amp Mega-Fuse can withstand short high currents around 1,000 Amps for about 1 second (non-derated.) At normal temperatures and say 400 AMPS through the 300 AMP mega-fuse, it would take a few minutes for the fuse to blow. It looks like a 250 Amp fuse may be a better selection?

I'm no expert, but I would need to do more research on wire size to fuse rating, and length/temperature derating (although most wires are fairly short compared to most derating graphs.)

https://www.littelfuse.com/~/media/...bolt-down-fuses/littelfuse_mega_datasheet.pdf
Click to expand...

I'm aware of the typical time-current melting curve for fuses. Because its based on a log-log graph, time is relative to the current interrupted, the higher the current, the shorter the time to interrupt. In addition, the ambient temperature along with the wire's insulation type affect the ultimate amperage the conductor can withstand. For example, look at the NEC for a given wire size and insulation types, THHN, THWN, MTW, or silicon in open air or conduit and if in conduit, the fill factor de-rating variable. True, automotive systems typically do not subscribe to NEC standards, but ambient temperature should influence conductor sizing.
My innitial point was Nacho-74RT, speaks in generalities without any actual figures to substantiate and without any fundamental knowledge of electrical systems operation. The unfortunate result is many of the forum's subscribers take his comments as "gospel".
And to a later contributor's comments re starter motor current draw, the amperage draw during cranking is influenced by: engine compression ratios, oil viscosity, temperature (as battery temperature decreases, the chemicial efficiency decreases and output decreases) of both the engine and ambient temp, 300 amps - 400 amps current draw is not unreasonable. The number mentioned is a typical or average value as noted in the FSM.
As a side bar, I have a B.S. drgree in Electrical engineering and a Professional Electrical Engineer credential, which, I believe, qualifies my comments. I'm sure others will disagree.....
BOB RENTON
 
RJRENTON said:
The number mentioned is a typical or average value as noted in the FSM.
Click to expand...
Nowhere in the FSM is it noted as “typical or average”. The numbers posted above are the acceptable current draw speculations as published by the manufacture’s service manuals. The specific conditions that need to be in place prior to testing are clearly detailed in the test procedure outlined in the service documents from the time. Current draw for these original Chrysler gear reduction starter motors in excess of ~200 amps is outside of this factory specification, is abnormal and would be considered an indication of some fault.

This is not an engineering site with PEE creds required to post, it’s an automotive enthusiast site. Most questions posted do not require a full electrical theory dissertation as a response. While his English diction/language skills may make his posts a challenge to read at times, it is clear Nacho has good practical knowledge and experience about what he responds to. Many here, and on other sites, have benefited and clearly appreciate his assistance. Really do not see the need for your constant berating of his efforts to help others.
 
My interest in this is because I'm doing a battery re-location to the trunk.
I also have a PowerMaster 170 Amp One Wire Alternator.
Planning to use 1/0 Gauge Welding cable from battery to Engine compartment / Starter. Already have 4AWG alternator wire. Looking at fuse sized now.
 
72RoadrunnerGTX said:
Nowhere in the FSM is it noted as “typical or average”. The numbers posted above are the acceptable current draw speculations as published by the manufacture’s service manuals. The specific conditions that need to be in place prior to testing are clearly detailed in the test procedure outlined in the service documents from the time. Current draw for these original Chrysler gear reduction starter motors in excess of ~200 amps is outside of this factory specification, is abnormal and would be considered an indication of some fault.

This is not an engineering site with PEE creds required to post, it’s an automotive enthusiast site. Most questions posted do not require a full electrical theory dissertation as a response. While his English diction/language skills may make his posts a challenge to read at times, it is clear Nacho has good practical knowledge and experience about what he responds to. Many here, and on other sites, have benefited and clearly appreciate his assistance. Really do not see the need for your constant berating of his efforts to help others.
Click to expand...
I totally disagree with your premise.....the guy has zero fundamental knowledge of electrical systems and how they function....specifically regarding the Mopar ammeter and how it functions in relationship to the balance of the car's electrical system. ...basically he's a "one trick pony". Maybe specific credentials are not important to some, but having them, qualifies the holder (me) a fundamental knowledge and understanding of how things are determined, and knowing the correct method is better than an approximation or "guess" based on nothing. Which ever aspect you prefer, the choice is yours.
BOB RENTON
 
BAFRAID said:
View attachment 1102357 Putting a one wire internally regulated alternator in my car. 69 super B. I know it only needs a battery wire hooked up. Can I hook the battery wire from the original wiring harness to it for this purpose? Looks like there are two wires on the battery connector.
Click to expand...

Answer is "not by itself". If you want to just connect the original wire to the alternator then you also need to run another large wire directly from alternator to battery, so it would be "parallel" to the original "alternator/ammeter/fusible link/battery" circuit. This is not the "optimal" configuration, but it is easy, and doesn't require changes to the original wiring harness. In general the new alternator to battery wire would divide the load on the original wiring by about 1/2. If the new wire is larger size and shorter (lower resistance) it should take slightly more load off the original alternator wire. The modification will reduce the Ammeter movement to almost nothing, making it pretty useless as a gauge. If any new heavy loads are added, get their power from the battery through a relay so you don't overload the original dash harness and bulkhead connector. Adding headlight relays will also really help take a load off the bulkhead connector, dash harness, and the headlight switches.
 
BAFRAID said:
Oh Lord, I just wanted a simple answer.
Click to expand...




:rofl:


( would be nice with the B.S. degree he at least learnt how to spell my nickname someday LOL )

By the way if some of you guys think I can get a better english diction on some specific phrase, please let me know how to "rephrase it" better. Remember I think mostly i spanish and all my enviroment is in spanish, except around here.

Oh, and my statements never have been taken as a gospell really, just some ppl consider them reasoneable and some other ppl thinks the same than me way before have known my statements ( you can check some Mattax's posts on some boards and his own website ), another guy called "71deputy" around, and here 72RoadrunnerGTX is agree with me on some stuff although we can be not 100% aligned on every detail. What has been taken as gospell since ever is the ammeter blame myth, and MADelectrical website statements, which I just try to clear up as what it is, a myth.

We must respect our olders, and I know you BOB are not youngster anymore, but respect must be earnt too, maybe not because what each of us is able to say, but also how to say it. And thats not part of the degree.
 
Last edited:
451Mopar said:
The fuses are not sized by the alternator current output, They are sized by the wiring gauge in the harness they are protecting.
Click to expand...

actually related to the devices circuit is sourcing... which of course also relates to the wiring somehow. But you can find a 20 amps fuse into a 16 wire gauge network, same as a 5 amps fuse. Sometimes is just about wiring simplicity, so the wire gauge can be taken as a clue but not allways as the definite answer.
 
Wiring, is sort of like engine building, there are alot of compromises and exceptions.

With wiring, there are so many choices of wire type, size, sleeves, connectors, bundling, and more.
I like some of the wiring information seen in HP Academy, but the wiring they show is more professional motorsports / aerospace, and overkill for most normal vehicles, not to mention the high cost of the harnesses.
On the other hand, we have all seen videos of wiring disasters in cars using lamp or speaker wire with just the wires twisted together. Although it might be OK for a short term repair, it is likely going to case problems over time.

In another post I tried to show how GXL/TXL wire is a good value for most car wiring, because it is not that much more expensive than PVC wire, but way less than Tefzel wire.

Because our old cars originally used mostly Packard 56 connectors, replacement wiring normally uses the same.
In the HP Academy videos they are using very expensive Deutsch autosport (like mil 38999) connectors.
Currently I am liking the cost/benefits of the Metri-pack connectors if I need to use a new type connector.

On wire sleeving, I don't care for electrical tape as it makes the harness stiff, but there is a large selection of braided sleeving with many different properties.
Again HP Academy uses Raychem DR 25 shrink tubing which is again expensive, but good for sealing out moisture.
 
I just finished mine yesterday. I'm running a Powermaster 95A. I ran a 6 AWG directly from alternator to battery and a branch going through the firewall attached to a relay activated by ignition. I then installed a modern fuse box in my glove box and I run all electrics through it. I want to minimise any current going through the bulkhead connectors. Next up is running relays on my headlights.
 
Nacho-RT74 said:



:rofl:


( would be nice with the B.S. degree he at least learnt how to spell my nickname someday LOL )

By the way if some of you guys think I can get a better english diction on some specific phrase, please let me know how to "rephrase it" better. Remember I think mostly i spanish and all my enviroment is in spanish, except around here.

Oh, and my statements never have been taken as a gospell really, just some ppl consider them reasoneable and some other ppl thinks the same than me way before have known my statements ( you can check some Mattax's posts on some boards and his own website ), another guy called "71deputy" around, and here 72RoadrunnerGTX is agree with me on some stuff although we can be not 100% aligned on every detail. What has been taken as gospell since ever is the ammeter blame myth, and MADelectricalwebsite statements, which I just try to clear up as what it is, a myth.

We must respect our olders, and I know you BOB are not youngster anymore, but respect must be earnt too, maybe not because what each of us is able to say, but also how to say it. And thats not part of the degree.
Click to expand...

With regard to respect, especially of our "olders".....know this, in this instance, respect has nothing to to with age, but with the fundamental knowledge of the subject (electrical systems and their functionality and derivation), as taught by the precepts of the electrical engineering discipline. Perhaps, you can share your precepts and disciplinary knowledge and formal educational levels with us so, we, especially me, can put some credence to the largely inaccurate statements you profess as "gospel".....enquiring minds want to know..... and im not afraid to use my real name.....
BOB RENTON
 
Nacho is my real name because Nacho is the shortname for Ignacio... if you didn’t know that
 
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