Classic cars forum & vehicle restoration.

[jp928]

I have this dynamo running (believe its been refurbed), and it indicates 8-10A at a slightly fast idle. I have the 3rd brush as close to neg brush as I can get it. I believe that 10A will be more than will be good for the battery for any length of time. My central switch panel is marked Off (maggy shorted), On (running) and D(dynamo). The wiring diagram shows that charge should flow to battery (via the cutout) when the switch is on D, BUT, somebody in the past has bridged the switch so the D is always connected.
Question - I can readily remove the bridge, but is it good for the dynamo to break its connection to the battery? I was always told unloaded dynamos are not happy.
Note that I do not have any of the summer/winter switches , or any way to control the field current - the only wire coming out of the dynamo is positive charge, the 3rd brush internally feeds direct to field coils - I have 2 such dynamos off Rover 9s, both with single wires coming out.

thanks
jp

[Oldtimer]

Hi, I'm no expert but as you haven't had any other replies here goes!

I would agree that it's not ideal to run a three brush dynamo open circuit. Although the dynamo is giving 8-10 amps at a fast tick over as it speeds up the current will reduce, so leaving the link in and hence the dynamo permanently connected wouldn't, in my opinion, cause a problem.

Do you know if the car was originally fitted with a three brush dynamo or is it something that you or some previous owner has done?
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[jp928]

Thanks! According to the wiring diagram for the car of this year (26), a 3 brush is std. Its not wired according to the diagram though - that shows 3 leads ; it has only a single wire for +ve output, with the 3rd brush going directly to Field and then to ground - making it -ve earth by default. I guess my options are to leave it as is, and when I get to do some miles in it, see if the battery starts losing water, or think about a modern V/A regulator hidden somewhere. Losing a battery now and again will be a lot cheaper than pulling the dynamo out and modifying it!
thanks
jp