Replacing the old SEV Motorola alternator

The original alternator in the Volvo 122S in 1969 was a SEV Motorola 30 Amp one with an external regulator. When I rebuilt the engine I just cleaned it and refitted it. But I noticed after a while it couldn't really keep up with the power usage and the new battery was getting weaker. The alternator wasn't broken but I think it needed new brushes.

SEV Motorola alternator 30 Amp Volvo 122S

Wired Motorola alternator 30 Amp Volvo Amazon

Instead of rebuilding the Motorola alternator I decided to get a new stronger one. Also because I didn't like the fact that the little red amp light in the dash was always glowing a bit when driving with the lights or fan switched on.

Little red AMP light in dashboard Volvo 122S

When I took out the old Motorola alternator I only disconnected the external voltage regulator instead of taking it out..keeping the original look.

Disconnected Voltage regulator Volvo 122S 1969

The new (SCG) Alternator has an internal voltage regulator so it's easy to connect.

Installation instructions SCG 55 AMP alternator

I also used an extra negative wire as mentioned in the instructions, just to make sure it has a proper earth connection.

New SCG alternator connections
The black round part at the bottom is the voltage regulator

New SCG alternator Volvo B20 engine

Factory test results 12V/55A SCG Alternator

As you can see in the factory test results the alternator starts working at 1534 rpm (alternator rpm and not your engine rpm which is lower). Right click on an image to open it in a new window for max(100%) view.
I measured the alternator pulley diameter and the waterpump pulley diameter in order to calculate pulley ratio.

Alternator pulley approx. 74 mm
Waterpump pulley approx. 128 mm
Pulley ratio in my B20 engine: 128/74 = 1.73
The alternator starts working at 1534 rpm --> engine ca. 887 rpm (1534/1.73 = 887)
The B20 engine in my 122S is idling around 900-950 rpm, according to the factory test results the AMP output at idling speed is around 31-35 A, which is already more then the max output of the old Motorola alternator.

New alternator installed