Help on wire gauge for my new electrical system.

[green69rt]

I'm at the point of installing my new 130 amp alt.  So, I was checking the various size wires in the stock system and doesn't look good to me.  Lots of 10 AWG; don't know what the starter is but maybe 6 or 8 AWG (and that should be good.)  But what about stuff like the ground wires.  Engine to firewall is 10, Battery ground looks to be 4 or 6.  Any recommendations?  I think I'm going to have to rig a 4 or 6 AWG from the alt output to the battery.

[Nacho-RT74]

Your alternator will never feed 130 amps to the batt. The batt will suck whichever load its able to suck to keep charged. The alt output capacity won’t speed out more because is able to source 130 or 500 amps. Chemicals inside get its own speed to suck the load needed get recharged.

Same about the car needs. You can get 500 amps alt but if your car requires 35 amps, the alt will source just 35 alt. So the wire size must be according with the car loads requirements and not the alternator capacity.

The thickness of the wire between the batt and starter motor is because what the starter sucks. But at the same time on same batt you feed a sidemarker bulb with 16 gauge wire ( or even 18 ) once again because what bulb requires and not because the batt is able to source

[green69rt]

Your alternator will never feed 130 amps to the batt. The batt will suck whichever load its able to suck to keep charged. The alt output capacity won't speed out more because is able to source 130 or 500 amps. Chemicals inside get its own speed to suck the load needed get recharged.

Same about the car needs. You can get 500 amps alt but if your car requires 35 amps, the alt will source just 35 alt. So the wire size must be according with the car loads requirements and not the alternator capacity.

The thickness of the wire between the batt and starter motor is because what the starter sucks. But at the same time on same batt you feed a sidemarker bulb with 16 gauge wire ( or even 18 ) once again because what bulb requires and not because the batt is able to source

Yes, I understand that and I remember reading several of your threads about the subject.  The one thing that I wonder about is the fact that I am running twin cooling fans.  So here are my loads as far as I can tell.

Fans -50 amps.
Headlights/taillights ( guessing)  20amps
stereo - 8 amps
AC - 10 amps

Total is about 88 amps in the worst condition (with no battery charging.)  So #4 AWG is rated about 85 amp.  Too much?  Reason I asking about the battery connection is... most of my loads seem to originate at the battery, in fact the fan installation says to take its source directly off the battery (I know it would not use battery capacity, it's just a connection point).  So any current flow (the 88 amps) would be from the alternator to the battery (+) terminal and then to the various loads.  Ground loop would be from the various loads (fans, headlights etc.) to chassis ground, then thru the chassis-to-engine ground and back to the alternator which is grounded to the engine.  Right/wrong?

As far as I can tell the Chassis to engine ground from Y1 is 10 AWG.  FSM says the alt output wire is 12 AWG.  That may have been good for the old loads of headlights and a 5 watt radio, and heater fan but not my setup.

[nitrousn]

I am in the process of setting my car up now. I have a voltmeter conversion and will run the alternator directly to the starter relay connection with this kit.   https://www.painlessperformance.com/wc/30700

[green69rt]

I am in the process of setting my car up now. I have a voltmeter conversion and will run the alternator directly to the starter relay connection with this kit.   https://www.painlessperformance.com/wc/30700

That sounds like a nice little kit.  Attaching things to the battery terminal was never a good idea IMO.  That kit looks like it solves a problem.  Thanks for posting.

After reading more, it looks like it replaces the existing wire not just add a parallel wire.  I'll have to think about that.

[nitrousn]

I bought a reproduction RB harness even though it now has a Hemi. With my set up I decided to leave the factory alternator wire just not hook it to the alternator as it feeds the horn relay also. The heavier wire will run direct from the alternator in the new harness but will terminate at the new fuse block which gets its feed off the starter relay. I will try to post some pics when I have it wired. I have lots of changes so I wanted to be protected. Here is a pic of what I am working on. I hope to get the engine and the rest wired up in the next couple weeks.

[green69rt]

One question or thought.  So with the 6 AWG alt wire that sounds like it will work.  But,  all electrical circuits are loops so you got the output of the alt covered but what about the return?  On mine the return is thru all the various chasis grounds.  Then there is a wire from the firewall (the chasis) to the engine block,  Whatever goes out thru the alt output comes back to the alt thru that block ground so I plan on making it a 6 AWG wire.  Not the 10 AWG in the FSM.   With your little kit plus the bigger chassis/block ground I think I'm covered.  Thanks.


Nice setup you got going.  More pictures??  Got a thread on the build?

[nitrousn]

For the charging part the alternator grounded to the block and the battery ground direct from battery to block should more than cover it. Any add on equipment the ground would have to be adequate unless you ground it direct to the battery or the engine. Right now my electric fans will be grounded to the core support. With the engine to firewall along with the smaller negative off the battery mine should be Ok. The rest is all lower amperage draw items. I would not over think it.

[nitrousn]

Fans -50 amps.
Headlights/taillights ( guessing)  20amps
stereo - 8 amps
AC - 10 amps

On your fans that is a lot of draw. I think both of mine are about 6 amps each for 12 amps. At least that is what they are rated for. I am adding two relays for the headlights so there will be no excessive draw on the headlight circuit. I have a small 4 circuit ATO style fuse panel that will be also hooked to the starter relay stud. I would recheck your fan draw to be safe and you may consider what I did with the headlights. Again once I get into it I can take some pics.

[Nacho-RT74]

let's see... all depend how will you wire your car!

I don't think fans will suck 50 amps... I can think on 15 amps each. AND THATS AN EXAGERATED RATE.

A/C itself to feed the compressor clutch barelly suck couple of amps... now the stock blower, 9-11 amps but just at max speed, because old motors are not efficient. The more voltage the less amps will suck, meaning with this depending on contacts and wires conditions, engine on or off.

do you need to wire a 8-6 gauge wire from alt to the batt ? no really. But where will you install the junction point to feed the extras ?

will the fans work with engine off and being cut by a temp sensor just like modern cars? or will turn off with ignition switch ?

will you keep the ammeter ? yes you still can keep the ammeter with a 130 amps and all those devices. I have talked a lot about this.

for example, if you keep ammeter, and cut of the fans with ign switch off while engine is still hot, you still can splice the power for them straight to alternator post, and run the wiring reinforcement to ammeter asi the thread you know. At the end the stock fan system also stop working with engine off. Batt won't feed EVER the fans being sourced at alt post if they are cut by ign switch. And with ign switch on and engine on, the alt will feed them completelly... assuming a 130 amps alt is able to source around 70-80 at iddle. The only critical moment will be while engine is not cranked yet and engine is hot by a recent ride around ( i.e.: at gas pump starting back on the engine )

If fans will be still running still with engine off and just cut by a temp sensor... then, could be an option run the power from batt and bypass the ammeter. IF the load they suck is what you say. Not necesarilly if the load is way less, as I really think. I REALLY doubt with modern systems a fan system will suck 50 amps EVER!!!

Can the dual fans wired independiently ? if so you can get a dual temp sensor, which will make to work a primary one on the regular operating temperature and the secondary with a higher temp rate. Let's say one at 160° and the other one at 200° or so ( if they exist ). The primary one will work so nice on the operation temp rate that the secondary will hardly see the life.

You can also make to work the secondary one with the Compressor clutch using a diode to isolate the compressor circuit when secondary fan turns on by itself by temp.

If you source both fans independiently,  and STILL running self countroled by temp sensor my opinion is you still can run safe the ammeter and the regular wiring upgrade for it, being sourced from alt post ( or a junction point from there ), because on a regular operation just one of the fans will be working and the stock ammeter and wiring will hold that easily. Aside will be a temporally load by couple of minutes or so untill water reachs the temp at sensor.

those are my thoughts. From there, is at your choice

[green69rt]

let's see... all depend how will you wire your car!

I don't think fans will suck 50 amps... I can think on 15 amps each. AND THATS AN EXAGERATED RATE.

A/C itself to feed the compressor clutch barelly suck couple of amps... now the stock blower, 9-11 amps but just at max speed, because old motors are not efficient. The more voltage the less amps will suck, meaning with this depending on contacts and wires conditions, engine on or off.

do you need to wire a 8-6 gauge wire from alt to the batt ? no really. But where will you install the junction point to feed the extras ?

will the fans work with engine off and being cut by a temp sensor just like modern cars? or will turn off with ignition switch ?

will you keep the ammeter ? yes you still can keep the ammeter with a 130 amps and all those devices. I have talked a lot about this.

for example, if you keep ammeter, and cut of the fans with ign switch off while engine is still hot, you still can splice the power for them straight to alternator post, and run the wiring reinforcement to ammeter asi the thread you know. At the end the stock fan system also stop working with engine off. Batt won't feed EVER the fans being sourced at alt post if they are cut by ign switch. And with ign switch on and engine on, the alt will feed them completelly... assuming a 130 amps alt is able to source around 70-80 at iddle. The only critical moment will be while engine is not cranked yet and engine is hot by a recent ride around ( i.e.: at gas pump starting back on the engine )

If fans will be still running still with engine off and just cut by a temp sensor... then, could be an option run the power from batt and bypass the ammeter. IF the load they suck is what you say. Not necesarilly if the load is way less, as I really think. I REALLY doubt with modern systems a fan system will suck 50 amps EVER!!!

Can the dual fans wired independiently ? if so you can get a dual temp sensor, which will make to work a primary one on the regular operating temperature and the secondary with a higher temp rate. Let's say one at 160° and the other one at 200° or so ( if they exist ). The primary one will work so nice on the operation temp rate that the secondary will hardly see the life.

You can also make to work the secondary one with the Compressor clutch using a diode to isolate the compressor circuit when secondary fan turns on by itself by temp.

If you source both fans independiently,  and STILL running self countroled by temp sensor my opinion is you still can run safe the ammeter and the regular wiring upgrade for it, being sourced from alt post ( or a junction point from there ), because on a regular operation just one of the fans will be working and the stock ammeter and wiring will hold that easily. Aside will be a temporally load by couple of minutes or so untill water reachs the temp at sensor.

those are my thoughts. From there, is at your choice

Now you've given me a lot to think about, plus I have to look up how the fans are controlled..  Just a couple of things to begin.  My amp meter is gone, I installed a Dakota Digital dash and when I did that I took out all the amp meter wiring so there is just one feed thru the bulkhead for the rear of the car (lights, heater blower, etc.)  Added a Classic Air AC/Heater unit,I need to check its amp draw.

The specifications for the radiator fans call out 49.6 amps.  Yes, that's probably the extreme condition.  They use a pulse width modulation to control fan speed based on coolant temperature.  The fans do run after the engines shut off, like modern cars  I don't know if the fans run independently, I'll have to check. I would expect that you are right, probably never run over 30 amps.

You point about where to connect the loads (especially the fans) sounds like a key point to me.  1. Off the battery post.  2. off the alt output post  3. Starter relay post.   I was leaning to the starter relay post because that's where all the loads come from now.  Thanks for you help, it's important to me to get this right.

[nitrousn]

What fans are you running. I was never in favor of running anything off the alternator stud. Just does not seem correct or right to do so. Relay stud to me is optimal and correct. I have the classic air also. I do not think that blower draws more than the factory. What controls are you using for the a/c?

[Nacho-RT74]

Relay or not, with ammeter, everything MUST be sourced from alt side except starter motor, never from batt side. RELAYS INCLUDED. Only exception could be power windows and similar stuff since they just work while you get them up and down and is not a constant load.

Without ammeter, won't really care anymore, but better do it on a middle point of the charging line. Will save wire stress, resistance and voltage decay along the line. Starter relay stud is a good option, but another juntion point around firewall could be good too.

Dunno what you have made inside the cab to source everything.. Stock wiring modified for the new cluster ? Some ideas come into my mind.


Now you posted more details of the fans system we can to post beter opinions/options for the setup. Never thought it had a control unit or modulation system to change the speed, that changes the deal a bit.

I can make a small diagram based on what I can suggest for the wiring.

They can be conected OR NOT before or after the ign switch depending on your preferences.

[green69rt]

Relay or not, with ammeter, everything MUST be sourced from alt side except starter motor, never from batt side. RELAYS INCLUDED. Only exception could be power windows and similar stuff since they just work while you get them up and down and is not a constant load.

Without ammeter, won't really care anymore, but better do it on a middle point of the charging line. Will save wire stress, resistance and voltage decay along the line. Starter relay stud is a good option, but another juntion point around firewall could be good too.

Dunno what you have made inside the cab to source everything.. Stock wiring modified for the new cluster ? Some ideas come into my mind.


Now you posted more details of the fans system we can to post better opinions/options for the setup. Never thought it had a control unit or modulation system to change the speed, that changes the deal a bit.

I can make a small diagram based on what I can suggest for the wiring.

They can be connected OR NOT before or after the ign switch depending on your preferences.

Just looked at the installation instructions.  The fan power supply insists that the power come directly off the battery terminals.  Two wires, one to each and it includes a breaker.  It states that the warranty is void for other arrangements.   Isn't it fun working on these old cars and trying to make them better?

[Nacho-RT74]

Can you upload the instructions sheet... or tell us where to download them... or the brand and Pn of the setup?

[b5blue]

I used a junction box and 40 amp control relay system. Your on the right track, wire size involves length also so 8AWG on the fans should be plenty. How big are the wires on the fans? Look at any connectors used closely, many are electrical choke points of thin metal. Marine grade/rated is a better spec. to find.

[Nacho-RT74]

This is what I would make on your car. Just talking about the Charging network

Fuse link can be a fuselink or not... maybe maxifuse... just your protection system preference

This setup will allow yout install relays on either side of the firewall with the double sided junction. I did all my relays upgrades into the cab ( headlights and blower ) attached to amm stud of course after the basic upgrade on stock system. Of course fans relays would be into the engine bay side.

both Black wires running to the juntion into the cab side are the black wires on 12 gauge originally running to ammeter and bulkhead. The red wire to ammeter won't be needed anymore

THIS IS BASED on what you say about the fans load! Which I don't really is true! as b5blue says, the fans wire thickness will tell you the true more. If the fan loads is closer to 30 amps, one step less on the gauging charging network wiring could be more than enough.

on a next reply will post a diagram with what I would make for a regular fans setup not PCM controled, although depending on how the PCM fans system works could even work!

[Nacho-RT74]

this could be an option for a regular dual fan setup with a complementary activation of the second fan when A/C is turned on.

Relays ( 30 ) can be sourced either from Alt stud or batt, but if is sourced from batt, the fuse link ( or any other protection selected ) could be a weak point on a low charge batt stage. The wire to feed the fan relays can be even 12 gauge. Maybe 10, but no need for 8 there

[nitrousn]

I went with the Cold Case radiator, fans, and relay/wiring kit. Easy to wire. I also went with a trinary a/c switch. With this switch it had three functions. When the pressure drops (pumps down) to 30 psi, the trinary switch switches the a/c compressor clutch OFF (and the condenser fan is turned off).  Now, no cabin cooling.At about 200 psi, and above (to, about 400 psi) the trinary switch switches the a/c condenser  cooling .fan ON. At about 400 psi, the trinary switch switches the a/c compressor OFF, and turns on the condenser cooling fan. One it acts as the low pressure cut out, two as a fan control and a high pressure fan control. So with the a/c on the fans only work when the a/c pressures rise. Cruising with good air flow the pressure will be lower hence no fan running. Most systems are set to run the fans any time the compressor is on. I find that a waste. Granted at idle and low speeds the fan will run because the pressures will rise, however as speed increases there is no need for the fans to run as long as your cooling set up is adequate.

Switch  https://www.summitracing.com/parts/vta-11086-vus?seid=srese1&gclid=Cj0KCQjwtLT1BRD9ARIsAMH3BtXfplF-fmnrqHujzKKFgPBjIOcAd_fKHC4R7IwYa5wZaIo8u9UDCJsaAom4EALw_wcB

Fan control https://www.summitracing.com/parts/rad-ef-1

[Nacho-RT74]

The deal on the AC compressor function is also to keep engine cooler. As soon the compressor load is over the engine, engine will heat more, so will prevent that being one step forward, is not just about AC temperature into the cab. It can be either installed or not by preference. Engine temp will turn it on sooner or later without it anyway by the added load on engine.

I wired it handling negative to trig the second fan relay, but also can be wired to source positive straight to the fan. Just thought it would be easier and installed anywhere, no need to be side to side to the rest or get more wires to source it, being the ground anywhere into the car.

Override switch can be installed around too if wished. Didn't posted fuses but they can be installed too, maybe on the output to fans or the input to each relay, according with fan loads individually. The compressor clutch relay don't need fuse because is triggering the second fan relay, not sourcing it. Is just becoming the positive signal from clutch into a negative signal.

I'm showing a dual temp sensor switch which I think  have seen them available somewhere? If not, two sensor switches with dif rate temp can be used too.

It's also ilustrated for dual fans both single speed! To turn them on individually. Dual speed fans would need a diff wiring setup.

Nice control fan switch system kit! However from the distance it seems is just a "ready to go" system on what I already made but with just one temp function to turn it on. I went on the basic system without any central control system or PCM over fans. Of course control systems exist rated into $100-160 price rate, but on the cheap that's an option.

[Nacho-RT74]

I'm showing a dual temp sensor switch which I think  have seen them available somewhere? If not, two sensor switches with dif rate temp can be used too.

And yes, they exist... here are some examples, with turn on/off rates on each stage. Unfortunately these require to be wire grounded ( they are not chassis grounded ). Not hard but chasis grounded is cleaner.

[nitrousn]

The deal on the AC compressor function is also to keep engine cooler. As soon the compressor load is over the engine, engine will heat more, so will prevent that being one step forward, is not just about AC temperature into the cab. It can be either installed or not by preference. Engine temp will turn it on sooner or later without it anyway by the added load on engine.

Right the a/c system is on its own dependent on pressures. The main fan system is still operated by engine temperature.

[b5blue]

I'm recalling fan amp ratings are much higher for start up. I'd test by running an amp gauge in with battery and fan mocked up to get real world results. 

[Nacho-RT74]

 

I'm recalling fan amp ratings are much higher for start up. I'd test by running an amp gauge in with battery and fan mocked up to get real world results. 

just like giving throttle on a car...