Alternator alternatives

[jp928]

Along these lines....if I was to replace the 18ACR with an A127, where would be the easiest point to connect a cable from its B+ bolt to? Since the main battery feed from the bulkhead through bolt goes to the starter solenoid, would that big bolt be OK, using a ring terminal? How big a cable would be safe?
thanks

 

[PeterZRH]

Along these lines....if I was to replace the 18ACR with an A127, where would be the easiest point to connect a cable from its B+ bolt to? Since the main battery feed from the bulkhead through bolt goes to the starter solenoid, would that big bolt be OK, using a ring terminal? How big a cable would be safe?
thanks

The 18ACR and A127 have the same type of connector with two cables.

You can do it 2 ways.

1. Use the existing connector as one of the cables and add a second one to the starter. You might be able to get the spade into the terminal block. In my case I could not.

2. Run 2 new 8AWG cables to the pin of the floor. On my LHD these were exactly 6ft long. There are 2 spare grommets right next to where the main wiring loom goes through the bulkhead.

I did the second route and it leaves me the original alternator cable as a power feed for my electric PAS pump. In the unlikely even I want to revert it to original then nothing is cut.

The first picture shows the new cable below the main wiring loom
The second picture is the connection to the battery post (before wrapping)
3rd picture is old and new wiring.

 

[PeterZRH]

If you use 8AWG wire. Then the resistance is 0.0006282ohms per foot.

On a 6ft cable running 40amps (there are 2 of them to deal with a theoretical maximum of 80 amps)

You get using IR for voltage drop: 0.15V (~1% excellent)
Power lost using I^2R: 6W * 2 = 12W at maximum continuous load which across 6ft you'll barely feel any warmth. In reality the load on the alternator will be perhaps 10-15A amps rising to 25-30 on full beam.

 

[PeterZRH]

See the attached link, This is actually interesting as the quoted numbers are specifically for chassis wiring. I'd favour going one size up because my principle of DIY is everything you do *should* be better engineered and safer than original - both for your peace of mind and also for insurance purposes the weakest link shouldn't be anything you added.... In this you see 10AWG is fine for 55amps and hence you could use that. I think Lucas actually are not very generous with what they use looking at the original cables.

Electrical Wire Gauges

You'll consider the reason for the massively thick battery cable is not the maximum load it will be under - it's massively over specification for that. As the battery is in the boot and the cable run is long, the main reason is to avoid voltage drop.
I'd recommend also getting silicone insulated wire rather than PVC for your own jobs as it copes better with heat. You all know how old wiring looms lose their flexibility over time. That's PVC degrading.

 

[jp928]

Thanks, very helpful! Looking at that table, it lists AWG as solid wire - surely car wiring should be multi-stranded to provide enough flexibility for ease of installation, and resistance to vibration? Many car jumper cables I have seen look impressive, but on inspection they have very thick insulation over not much copper. I found some fine multi strand welding cable (70 sq mm section) and made my own jumpers, which are VERY flexible, and very effective.

 

[PeterZRH]

Thanks, very helpful! Looking at that table, it lists AWG as solid wire - surely car wiring should be multi-stranded to provide enough flexibility for ease of installation, and resistance to vibration? Many car jumper cables I have seen look impressive, but on inspection they have very thick insulation over not much copper. I found some fine multi strand welding cable (70 sq mm section) and made my own jumpers, which are VERY flexible, and very effective.

You are correct in that context that it will be stranded wire and that depends on the number of strands, therefore the original chassis wiring is even more weedy than I stated. 70mm2 welding cable is going to be overkill I'd think. Going up 2 gauges is enough looking at the figures. So 6AWG would be probably better for the 2 alternator wires but it'll be more than the OEM specs I'd think.

It's interesting reading US car forums, it seems stock truck alternator wiring with a 120amp alternator is 8 or even 10 AWG. This seems very small to me.

 

[jp928]

Peter,
is there anything wrong with connecting the std 3 pin connector to an A127 AND then running a separate cable from the B+ stud to the starter connection as well?