Dynamo

[rubyman]

Hi
Can any one tell me if a Lucas C35A dynamo is ok to replace a Lucas C35M dynamo on a Ruby mk 2





Thanks Graham

[Ian McGowan]

Yes. 
With a caveat that the C35A originally had the "summer charge" resistor incorporated in its internal wiring whilst the C35M had it externally. The internal resistance wire has often failed and you need to fit an external 3Ω resistor to take its place.

[Parazine]

Yes. 
With a caveat that the C35A originally had the "summer charge" resistor incorporated in its internal wiring whilst the C35M had it externally. The internal resistance wire has often failed and you need to fit an external 3Ω resistor to take its place.

Ian, I think the caveat applies to the CAV DEL dynamo (1928 - 31), which was a four pole machine of a different type. The C35A is identical to the C35M except that:

1) The brush holders are different,  hinged arms vs sliding on the later types.

2) I think the front bearing is different. In any case, the casing is different and the C35A requires that the long bolt into the crankcase is removed to allow the dynamo out. The C35M has the casing relieved so that this isn't necessary.

No reason why they cannot be interchanged otherwise, I had several of each type and some mixtures of types when I ran thirties cars and swapped them around incessantly.

[Robert Leigh]

Be careful setting the third brush. The C35M was rated at 11 amps, but the C35A is rated at only 9 amps. These figures are maximum output including ignition load which does not show on the ammeter. I suggest setting output to 7 - 8 amps showing on the ammeter with no other loads switched on.
Robert Leigh

[Ian McGowan]

Parazine is correct. The C35A had a small, cut-out style box in place of the C35M terminals, The little box contained the resistance and the field fuse.

[Bob Culver]

Hi Parazine

Amused by your last few words. Sums up Seven dynamo experiences of many. My car did a lot of running, including long night trips, with no working dynamo. I had a tech tutor with a Seven ditto. 
Batteries lasted about two years!

[Tony Press]

"Parazine is correct. The C35A had a small, cut-out style box in place of the C35M terminals, The little box contained the resistance and the field fuse."

According to that very useful 'Austin Seven Electrical Guide' by Harry Hales-

1931 Long Wheelbase cars were fitted with Lucas Dynamo C35 A fitted with a half charge resistor and field fuse in a pack on the body. When four speed cars were introduced the switch panel went from Lucas SM5 to SA1 with full and  half charge with cut out CF3. Around September 1933 the half charge resistor and fuse pack was moved to a new cutout type CFR.

When the 7 was changed to positive earth the Lucas Dynamo C35M with a cut out CFR2 was fitted.

Both the late 35A and all 35M had the resistor in the cutout and a plain bush at the distributor end.