Fuse protection

[majicwrench]

Just to verify, went out and check my 72 spider. Dang, got a flat tire. But the headlight will NOT turn on unless you have the key in the "run" position. I did have my switch positions mixed up, if you leave headlight switch down, light come on and off with key. It all works just like 2081 says.

[racydave]

I ran a new circuit from the battery to the dash and provided a fuse (breaker) at the battery. The supply wire is insulated and isolated and runs most of my circuts with only two relays. One for the brown wire, the other is used for my ignition system. Basically, it leaves the alternator and starter unprotected.

[nalle]

Ok, Problem solved.
The main problem was that I was not the first electric engineer who tried to fix the problem .

It seems that somebody have had problems with the ignition swich and he (or she) has removed one wire and done an extra connection. Result was that in the "Black wire" flows almost all the current that spider needs and in the "brown wire" only the solenoid current. Now the currents are in balance, it is not exactly original wirering but it is fine for me.
I also add relays for the head lamps. The relays are installed above the fuse box. I made a small metal plate and screwed the relays on it.

Then the Black and brown wire fuse protection.
The fuses are only needed for short circuits eq. wire protection (not protecting any device).
On the other words fuses may be quite slow with small over currents (example 1,2-1,5x) so I will use MIDI-fuses.
The boxes are easy to install and I have good and steady wire connection with screws (no loose wires).
http://motonet.fi/fi/tuote/481755/DieselMIDIsulakerasia.
I will install the fuse somewhere next to motor.
And the fuses, 30 A is enough. As I measure currents max is 20 A/wire

[nalle]

One correction "the brown wire" will get 40 A fuse.
It's quite obvious that 30 A is enought but 40 A is more suitable.

[nalle]

here are the photos of my solution If somebody needs them.

Here are the relays:low, high and wipers. All relays get the power supply from Connector C17.
Control circuits (coil) low/high - original low/high supply to to lamps.
Wipers relay coil- any fuse base that gets power when ignition switch is turned.
All connctions can be done behind the fuse box, longest new wire is about 40 cm.


And here are my main fuses.

[spider2081]

neatly done. Thanks for the photos

[nalle]

some additional info:
Starter solenoid current (peak value) 17,5A.
So if you want to put a fuse there 25 A is fine (as Bosch recomends)
Current will stay at 17,5 A as long as solenoid is pulled.

Starter current (peak value) 243 A.
This is the zero-speed current (DC-motor is not a motor when n=0, it is a resitance, EMF=0V)
Current will go down after starter begins to rotate.
If we estimate that starter is 2kW and battery 12 V => 166A.
So if there is a need to put a fuse in battery line these are the current values what have to be fulfitted by the fuse.
And on the other hand it had to be calculated will the "big fuse " ever burn if there is "weak" ground fault in battery line.
But as i have said earlier it is really un common to have a battery fuse in a car.