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I did a thorough search but want as best confirmation I can get that my 'plan' will work. Already installed an early 90's CS style 105 amp alternator. I plan on installing a Painless 70207 Auxiliary fuse block which has 3 ignition and 4 battery fuses (all 20 amp) On my '70 the wire from the horn block to starter is a straight shot. It does not go through the firewall then back out.
switched 1: HEI distributor
switched 2: electric fans (already have relays for fans just need switched and battery sources)
switched 3: future expansion (choke)
battery 1: electric headlight motors
battery 2: electric fans
battery 3: future expansion
battery 4 future expansion
The 'plan':
Step 1. Have custom positive battery cable made. 1 or 2 steps larger gauge with a pig tail extension to supply power to the Painless 70207. This wire will have a big 200? amp fuse near the battery
Step 2: Run heavy gauge wire from alternator to horn block'
Step 3. Run heavy gauge wire from horn block to starter. This wire will have a fuseable link like the original.
Q. Does it all sound reasonable?
Q. If not what changes should I make?
Q. Can a 2nd wire be piggybacked from alternator directly to starter (bypassing horn block) while leaving existing wires in place? (read on the 'net this was ok due to path of least resistance) IDK
Q. Are 20 amp fuses adequate?
I had made up a diagram for my car- and a few had asked for one-
***** DISCLAIMER- there are several ways to do it- I know- it worked for you...********
Nice clean set up- all the pieces are easily found and not expensive.
From the alternator to the starter- 6GU is fine- just make sure you are safe about it- away from heat- I recommend putting a protective cover -split loom is easy and inexpensive. Make sure you secure it. The lug on the alternator should fit snug around the terminal with no slop.
Just use the starter post as a terminal- and run a 6 or 8GU to the terminal post- I ran a bigger gauge as it is a GREAT place (easy access and current right to the starter) to jump the car.
Since you are not adding any extra loads on the stock wiring- no real need to beef it up.
Richard, your diagram looks very similar to what I have in mind. Is there any reason not to run the alternator wire directly to the battery? And is there any reason not to the accessory fuse block wire directly from the battery?
If the horn block is bypassed what should be done with original horn block to starter wire? Bend the ends back on itself and tape over?
Wire gauges sound good.... 1/0 battery pos and negs. 6gu alt to starter/battery.
Run a 6 gauge wire from the alternator to a terminal stud (or multi-terminal block if you want more connection points).
Run a 6 gauge from the terminal stud to the solenoid. Put a fusible link at the solenoid.
Run a 10 gauge wire from the terminal stud to the horn relay to power the original electrical parts. Put a fusible link at the terminal stud.
Run a 12 gauge wire from the terminal stud to the alternator voltage sensing terminal. Put a fusible link at the terminal stud.
Connect any new high power accessories to the terminal stud.
If you want even more power, then use 4 gauge instead of 6 gauge to wire the alternator and terminal stud.
Personally, I would not use that Painless fuse block as the power for fans. I have the 4 fuse version and I just don't think the fuse clips/build is heavy enough to reliably power 2 cooling fans. I'd just use a fusible link on the power wire to each fan relay. If you do want to try using it, use a 30A fuse for each fan.
Originally Posted by jim2527
Is there any reason not to run the alternator wire directly to the battery? And is there any reason not to the accessory fuse block wire directly from the battery?
When you have 1/0 battery cables, running a smaller gauge wire all the way to the battery will put more total resistance into that circuit then running the wire to the starter solenoid and using the bigger cable to complete the run. You can do it if you want, but there is no gain.
As for the alternator. You want the alternator to regulate the voltage of the power system in the car at the point where the main accessories are attached so things like the lights and cooling fans work at best efficiency. When you run separate wires from the alternator back to the battery and then forwards again to power accessories you will add resistance to the circuit from alternator to accessory. This means the battery voltage is higher than the accessory voltage and the alternator output voltage is even higher than the battery. It makes the alternator work harder since it's producing the same current at a higher voltage. The higher voltage may over-charge the battery a bit when the system has a heavy load on it.
Instead, run a short wire from the alternator to the accessories which makes the alternator more efficient. Then, the battery gets the accessory voltage minus whatever voltage drop occurs in the wire going to the battery.
Really the only big load you are adding is the Fans- adding a large wire from the alt to the battery isn't really needed in your car/system- you'd be better served just going with bigger wire.Like 4 GU alt to starter.
As you'll notice in my diagram-the power for the fans is not running through the accessory fusebox- as Peter stated the terminals are really not designed to handle that much current.
It looks to me the accessories you want to add are going to be under the hood. So putting at the battery doesn't make a lot of since- because you'd be running smaller gauge wire all the way up to the front of the car- adding resistance and less effectiveness of the battery's filtering- as noise can be picked on the way.
If you are doing a stereo amp -which will be in the back of the car- you'd want to just fuse at the battery- and not run the wires from the front to the back.
Keeping the OEM wire is fine- just leave it connected.
HOWEVER- doing this upgrade- the ammeter will not read correct. A voltmeter matching your green gauges is available from several venders.
IF the stock wiring is in pretty good shape, I would leave it alone, and run electric fans off their own fused main power wire off the alt out stud directly.....short as possible length.....the CONTROL of the relay coil is from the ignition/accessory power...other end of coil is to your control sw.....computer.....
headlights/etc all run off their own lead from the alt.....in stock form on my '72 it went from alt stud directly over to the horn relay/dist. block.....I ran that wire MY way down the valve cover with rest of the wiring, to firewall, then out to horn relay, nice heavy wire ~10 ga or so....
From: Las Vegas - Just stop perpetuating myths please.
Something I learned recently is that large wire from the horn relay to the starter solenoid (in parallel to the ammeter) works as a shunt for the ammeter in a current divider circuit. That wire has specific resistance by design and changing it's diameter or length will affect the ammeter calibration/readings.
Something I learned recently is that large wire from the horn relay to the starter solenoid (in parallel to the ammeter) works as a shunt for the ammeter in a current divider circuit. That wire has specific resistance by design and changing it's diameter or length will affect the ammeter calibration/readings.
Something I learned recently is that large wire from the horn relay to the starter solenoid (in parallel to the ammeter) works as a shunt for the ammeter in a current divider circuit. That wire has specific resistance by design and changing it's diameter or length will affect the ammeter calibration/readings.
Just something to be aware of if your ammeter no longer reads correctly.
I suggested replacing it with a Voltmeter.
The C3's ammeter isn't really one at all -but rather a sensitive voltmeter AKA galvanometer.
One lead senses the voltage at the starter solenoid - the other lead senses the voltage at the horn relay. The gauge just shows the difference in voltage between those two points. So the needle going positive indicates current is flowing to the battery. Negative is current going from the battery.
From: Las Vegas - Just stop perpetuating myths please.
Originally Posted by Big2Bird
Correct. However, you could find that value and use an external shunt. Just have to rearrange the ammeter leads.
Not that easy. The resistance of the ammeter plus its leads is matched to the shunt wire used in parallel as a current divider. Meaning you have to have the same proportional amount of current in each circuit path. If you change the resistance of the shunt wire you need to change the resistance of the ammeter plus its leads proportionally. Also the shunt wire resistance is tiny and not measurable with a normal hand held multimeter. You need a lab grade ohmmeter that can measure micro-ohms.
From: Las Vegas - Just stop perpetuating myths please.
Originally Posted by Richard454
.
The C3's ammeter isn't really one at all -but rather a sensitive voltmeter AKA galvanometer.
One lead senses the voltage at the starter solenoid - the other lead senses the voltage at the horn relay. The gauge just shows the difference in voltage between those two points. So the needle going positive indicates current is flowing to the battery. Negative is current going from the battery.
I was under that impression for a long time myself until someone measured his ammeter plus leads resistance for me. He found only 0.3 ohms revealing it's not a shunted voltmeter used as an ammeter like I had thought. Instead it's a shunted current divider ammeter and you can read about it in that Wikipedia link I posted. But a shunted parallel circuit ammeter using the shunt as a current divider has a tiny resistance in the order of 500 times less than the ammeter circuit path.
This has been misunderstood for too long - me included - and trying to get the word out there.
I was under that impression for a long time myself until someone measured his ammeter plus leads resistance for me. He found only 0.3 ohms revealing it's not a shunted voltmeter used as an ammeter like I had thought. Instead it's a shunted current divider ammeter and you can read about it in that Wikipedia link I posted. But a shunted parallel circuit ammeter using the shunt as a current divider has a tiny resistance in the order of 500 times less than the ammeter circuit path.
This has been misunderstood for too long - me included - and trying to get the word out there.
Thanks to everyone for giving sound advice. Its a real pain to find quality connectors and terminals. Everything local seems thin. As an example the O ring terminal from the donor alternator is 2X the thickness of my stock terminal and it crimps onto both the wire and insulation. Way too much running around. And more expensive tools I'll only use once. There's local car stereo joint that'll build cables.
I figured out how I'm going to wire it.... I suppose its similar to the diagram in post #2
Old wire from alternator to horn block will remain to power whatever normally is powered there.
Old horn block to starter wire will be disconnected at horn block and become the Painless fuse block battery lead (Painless recommends 10g)
New 8g wire will run from alternator directly to lug on starter.
New 1/0 battery cables and grounds.
From: Las Vegas - Just stop perpetuating myths please.
Originally Posted by Big2Bird
Like this?
Close but may need another digit to deal with resistance in the micro-ohms range. Also there is added resistance from mechanical contacts that has to be compensated for and I don't see many hobbies-ts able to do so.
I was under that impression for a long time myself until someone measured his ammeter plus leads resistance for me. He found only 0.3 ohms revealing it's not a shunted voltmeter used as an ammeter like I had thought. Instead it's a shunted current divider ammeter and you can read about it in that Wikipedia link I posted. But a shunted parallel circuit ammeter using the shunt as a current divider has a tiny resistance in the order of 500 times less than the ammeter circuit path.
This has been misunderstood for too long - me included - and trying to get the word out there.
Yes, the analog meter uses the current divider principal. However;
The movement of every analog meter made is controlled by the current flow through the meter, no matter what value the meter is reading. So, claiming the C3 ammeter is somehow different than the operation of any other analog meter is simply wrong. All analog meters provide some amount of load to the circuit they are attached to, because some amount of current always has to flow through the meter to make it read. The resistance of the meter GM used is much, much lower than a typical voltmeter used to measure the voltages of various circuits. However, the resistance of the wire being measured is much, much lower than the resistance of the ammeter circuit, hence the ability of the ammeter to work correctly despite having a low resistance.
Whatever, I agree with the others - when changing the alternator and wiring just convert to a voltmeter to eliminate the issue of trying to keep the ammeter working in some uncalibrated, wrong scale capacity.
Last edited by lionelhutz; Feb 2, 2019 at 11:26 PM.
Reason: spelling
Alternator wire upsizing...
