Re: Marelli generator advice, please
Pete,
Erik's message mentions a couple of important points that indicate the issue is the design of the electrical system and not a specific problem with his car. He says that "as I turn the lights etc on, the voltage drops to 12V, and the battery discharges eventually" and "the generator's max output, ca 22A, is only just enough to supply the ignition, lights and fan."
I believe both of his his statements are correct. Let's do some basic math, for driving WITH HEADLIGHTS ON HIGH BEAM (using wattages for the light bulbs from the Operator's manual):
Code:
+-------+---------+---------+---------+
| Qty | Watts | Tot W | Amps |
+-------------------------+-------+---------+---------+---------+
| Headlamp bulbs, outer | 2 | 40 | 80 | 6.7 |
+-------------------------+-------+---------+---------+---------+
| Headlamp bulbs, inner | 2 | 45 | 90 | 7.5 |
+-------------------------+-------+---------+---------+---------+
| Parking lights, front | 2 | 5 | 10 | 0.8 |
+-------------------------+-------+---------+---------+---------+
| Rear lights | 2 | 5 | 10 | 0.8 |
+-------------------------+-------+---------+---------+---------+
| License Plate light | 2 | 5 | 10 | 0.8 |
+-------------------------+-------+---------+---------+---------+
| Instrument lights | 4 | 2.5 | 10 | 0.8 |
+-------------------------+-------+---------+---------+---------+
| Ignition Coil | 1 | 30 | 30 | 2.5 |
+-------------------------+-------+---------+---------+---------+
| Fuel Pump | 1 | 20 | 20 | 1.7 |
+-------------------------+-------+---------+---------+---------+
| Temp & fuel gauge, etc. | 1 | 5 | 5 | 0.4 |
+-------------------------+-------+---------+---------+---------+
| Ventilator | 1 | 15 | 15 | 1.3 |
+-------------------------+-------+---------+---------+---------+
| 280 | 23.3 |
+=========+=========+
With the high beam on, the current drawn is in excess of what the generator can deliver. It gets worse. If we add some gizmo...
Use a period correct radio: add another 15 watts (1.3 Amps).
Use windshield wipers: add another 25 Watts (2.1 Amps).
Change Headlights to H4 lights: add another 40 Watts (3.3 Amps).
... we end up with a consumption of about 30 Amps. This means the battery drains at a rate of about 8 Amps per hour and a battery with a capacity of 50 Amp hours will drain completely in just over 6 hours.
With the high beam and gizmo off, the current drawn drops to about 16 Amps, which may be just about enough for the generator to produce enough voltage to charge the battery (charging the battery requires at least 13.2 Volts). This is consistent with the point Erik made.
Now, to put this in perspective: 1 horse power = 736 Watts. In other words, the generator delivers roughly 1/3 horse power. That was a lot at a time when many other cars had 6 Volt systems only. We've grown accustomed to an abundancre of power: Today, most modern car stereos consume about the amount of power that this generator could deliver then -- some consume even more.
Alternator, anyone?
Ruedi
