VW 6v dynamo and Bosch cut out

Note!

· There’s no connection onto the D terminal of the SM5 panel

· 15 Ohm resistor fitted between the SH and IGN terminals

· Basic principle of this circuit can be applied to other A7 circuits.

Note!

· This circuit has a 20 amp fuse fitted to protect it from the rest of the system, this could be varied to suit your needs

· Note that this circuit controls the field at the ‘bottom’ or ‘earthy’ end of the circuit and the former third brush connection has to be made to the ‘live’ brush terminal.

· There is a current limiter fitted. I don’t know what the quoted value would limit the output to. Being a regulator for a bike this could be quite low. I’m not clever enough to work it all out and alternatives— can anybody help?

· Voltage is controlled by the three Zenner diodes and this is set at 15.9v in this circuit which seems a lot. I believe lead/acid batteries and modern Gel ones have slightly different preferred charging requirements. This can be accommodated with other voltage Zenners.

Positive earth

Negative earth

This circuit is an adaption of the positive earth one above to make it negative earth, thanks to Barry Riseley and Ron Hayhurst for their help. It’s drawn in a similar style to the one above.

 

Note!

· The circuit diodes and protecting fuse have greater values, these could be used in the positive earthed circuit as well.

· Note that this circuit controls the field at the ‘bottom’ or ‘earthy’ end of the circuit and the former third brush connection has to be made to the ‘live’ brush terminal.

· A similar comment to the above applies to the three Zenner diodes, choose the voltages to match your desired voltage.

This circuit was taken from another motorbike site. It was designed following the latest circuit designs for controlling alternators. It has a number of possibilities;

· The 470 Ohm potentiometer sets the required voltage, these can be tweaked to suit your needs and could even be set to suit a 6v application if the 13v diode was also changed to 6v. The original piece recommended a high quality trim pot for this, a Cermet or equivalent and to lock the adjustment once set with a blob of paint.

· Diode D2 was specified as 50v 6 amps. This may be OK for a bike but a car may need more, perhaps a 20 amp diode as the circuits above.

· Resistor R5 limits the circuit. Settings of 0.15 and 0.08 Ohms were quoted for 3 or 5 amps delivery. A car will want to draw more current than this so an even lower setting may be needed. Best way round this is to install a, say at least, 100 Ohm resistor in the circuit and then wrap some electric fire element around it in parallel as a low value resistor. Progressively trim the length to get the preferred setting.

· Resistor R2 should be selected to roughly match the resistance of the field windings and protect them from full voltage being applied.

· Transistor 2N3055 should be mounted on a heat sink.

· Note that this circuit controls the field at the ‘top’ or ‘live’ end of the circuit (hence the comment about R2 above) and the former third brush connection has to be made to the ‘earth’ brush terminal.