Electrical System Questions???

[Duk]

Right-O, here we go with some questions that I hope you guys can help me with. 

1: With my intended rear mounted battery, I want to use a circuit breaker near the battery. So does anybody have any suggestions as to what sort of current draw the starter motor will have? IE, what sort of circuit breaker rating will I need???
Incidentally, I plan to follow Shiny's lead with how he integrated his new battery cable from the back of the car into the existing electrical system. I'll also have a new, heavier duty cable from my 120 amp alternator.

2: My car has 1 'New Era' dual relay for the headlights, mounted near where the battery was (passenger side) and there is some really ugly wiring (All of the headlight wiring is hideous and will be redone! It didn't even have plugs for the headlights, just individual crimp terminals for the individual spade terminals on the globes!!!  ) that goes underneath the bonnet catch panel, to the driver's headlight.
So I was thinking about running a power feed over to the driver's side in a similar (but MUCH neater manor), integrate it into the the power distribution post and run a separate 'New Era' dual relay for the driver's side headlight. Relay switching wires would be routed with the main power feed.
Now I will be redoing the wiring for the driver's side headlight anyway, but is it actually worth using an extra relay and running a new (chunky) power feed to the driver's side power distribution post???
Radiator fan will probably be powered from this PDP, too........... 

3: I want to use higher wattage globes and thought that using a DPDT change over relay wired into the high beam to actually switch off the low beam relay, would be a good idea to reduce thermal load on the headlights and current draw from the charging system (probably no drama with a 120 amp alternator, though).
Thoughts???

4: Apart from adding a starter motor solenoid relay, does anybody have any other suggestions for worthy electrical system upgrades?
My idea is to make the electrical system both reliable and as consistent in its performance as possible. Being neat and tidy is also a good idea  .

[shiny_car]

Firstly, some wiring general principles for anyone reading (which you probably already know, Duk):
*fuses can be within a range: minimum fuse is the amount of current expected to pass through the wire (eg: if supplying a 40A component, the smallest fuse you'd want to use is 40A); maximum fuse is determined by the gauge of wire, and thus up to the current handling rating of the wire (eg: 0awg (American Wire Gauge) is rated to 250~300A, so a 250A fuse is safe)
*whenever 'stepping down' wire gauge (eg: connecting 0awg to 4awg wire via a distribution block), you should add an additional fuse (eg: fused distribution block) if the upstream fuse is too big (eg: if using a 250A fuse for your 0awg this is 'too big' to safely protect 4awg wire, so you would also add something like a 120A fuse for the 4awg wire)

Approximate current ratings for common wire gauges:
0awg (~50mm^2) 250~300A
4awg (~20mm^2) 125~150A
8awg (~8mm^2) 60~80A
12awg (~3mm^2) ~30A

I've not seen an accurate specification of current draw for the starter motor in our cars. But I would expect the peak current draw to be over 200A, and probably around 100~150A 'continuous'. As such, I would recommend using 0awg from the battery in the boot to the engine bay, joined to the factory 2awg wire (2awg rated to ~200A). Thus, I would suggest a 200A circuit breaker/fuse near the battery in the boot.

Your alternator wire is probably going to be 4awg. Worth having a 120~150A fuse between this and the wire from the battery (eg: using a fused distribution block like I have).

I've used separate DPST relays for lowbeam and highbeam; each is supplied wire from the new distribution block via 30A fuses. I haven't rigged it up such that the lowbeam turns off when highbeam is activated. But sounds like a neat idea.

Do you use highbeam much? I very rarely use highbeam in any of our cars, let alone the 75 that I will hardly drive at night. If you do use highbeam a lot, then having the lowbeam filament turning off might avoid singing the headlight reflector.

I am satisfied that the power supply from the distribution block on the passenger side of the engine bay is fine to supply the headlight on the driver side. I've run wiring over the top of the radiator, keeping it a relatively short distance.

I recommend adding a 'groundwire kit'. Run various lengths of wire (eg: 8awg) from various points in the engine bay, to a solid, dependable ground spot. For example, I've run 8awg from the passenger side camcover, from the ignition coil bracket, and thermostat housing, on the passenger side (to the chassis...via my modified busbars). On the driver side, additional groundwires from the AAV, distributor, and AFM. Given electricity takes the 'path of least resistance', these should ensure no significant voltage drop and improve reliability. May even improve voltage and improve performance! Yeh, 0.01kW extra! 

[Duk]

Cheers for the input Shiny! 

[Al Campbell]

Circiut Breaker vs Fuse: Circuit breaker if you expect to reset it occaisionally or need to disconnect that cct. Fuse is cheaper (maybe at those ratings).

If you want thecircuit breaker as a battery isolator maybe instead use one of those battery post clamps that include a large knob so you can disconnect the wire without a spanner. But then thinking how often you work on an old ALFA flicking a cct brealer sounds good. Maybe I should shut up.

AL.

[Duk]

Big circuit breakers are pretty cheap these days. 
Certainly cheaper than you might first think.

[Duk]

Need some help.
My wiring is in a right old mess at the moment and it would be a PITA to try and attach a battery to the car, so can anyone tell me which of the headlight wires is the low beam and which is the high beam???

I'm fixing he abomination that is the headlight wiring in my car, adding a second dual relay (a previous owner had 1 'New Era' dual relay fitted but the installation was atrocious! So I'm adding a second New Era relay so it will have 1 relay for each beam) and need to know which wire is which so I can set up the change over relay (that will turn off low beam when high beam is switched on).

[four90s]

Duk,

I'm wrecking another 75 at the moment. I'll have a look at it tomorrow and give you a bell.

Cheers
Steve
Adelaide

[shiny_car]

*left low beam: grey/black
*left high beam: green/black

*right low beam: grey
*right high beam: green

[Duk]

Thanks guys. 

[four90s]

D'oh

Knew I'd forgotten to do something on the weekend!

Steve
Adelaide

[Duk]

While I'm doing horrible Alfa Romeo electrical system upgrades, does anyone know what sort of current draw the electric windows have?
I've been thinking that adding relays to each of the power windows, would be another worthy upgrade. And given you can get decent little dual DPDT relay boards (originally designed to be driven by TTL level signal but often rated to 12 volts) from eBay, it seams like a good idea.
However, these circuit board based relays are only rated to 10 amps.

[shiny_car]

This won't be very helpful! However, put it this way: the wiring diagram shows that all the wiring is 1.5mm^2 cross section. That equates to somewhere between 15~16awg wire. 16awg wire is rated to 15A 'continuous', there-abouts. One would expect the manufacturer to go overkill with the wiring to some degree, allowing for a margin of safety/reliability. Hence, 10A relays may be ok, but I obviously can't be sure for you! See, not very helpful!

Someone needs to use a clamp meter (ammeter) on the wiring to find out.  Can't help there either; I don't have one, and my car is in pieces! 

[Duk]

Food for thought, Shiny.
10 amps at 13.7 volts is (obviously) 137 watts of power. That seams reasonable, but doesn't allow for motor start up current draw. How much extra that is, is for someone else to say.
Kinda thinking that 10 amp PCB mounted relays wouldn't be suitable.
Maybe 2 relays in parallel for each direction. Probably still easier, better priced and more compact than using the typical Bosch style relays.