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Thinking about trying 12V

My 6V battery is now 5 years old and has led a sheltered life being hooked up to an Accumate Battery Charger/Conditioner when parked in the garage. During the latter part of last year cold starting the Magneto engine in the Chummy was a painful experience. The sluggish starter could barely turn the engine over and battery power was gone after a few minutes. I would have thought the conditioner might have helped to prolong its useful life, but I'm not complaining after 5 years of use.
For some time I have been contemplating changing to 12V after first reading about the subject on this Forum and on the Cornwall A7 Club website Technical Pages. Recently as a trial I connected up a spare 12V battery to the Chummy terminals. The starter cranked like a modern and the engine burst into life. I am easily impressed.
I have spent most of today trailing through old posts on the Forum relating to 6V to 12V conversion and also revisiting the topic on the Cornwall Club website.
I also spent an hour in a cold garage tracking down a spare 12V Lucas Cutout Model CF1 Type BN. Inside the wound coil cover the points plate says model SB4 12V. This cutout is the same size and looks identical to the Chummy 6V Model CF1 whose points plate also says SB4 6V. The only other difference I can see is that the fuse box in 12V cutout has an extra E terminal in addition to the standard +D and A terminals.
My question is has anybody who has carried out a change from a 6V to a 12V system and used the 12V CF1 cutout had any problems with the charge rate of the 6V DFL dynamo? I have seen references to removing the third brush and also references to retaining the third brush but reducing the dynamo output.
I would be grateful for any comments before rushing out to try and find a Chummy size 12V battery and new bulbs.

Re: Thinking about trying 12V

This thread may help:

Re: Thinking about trying 12V

Hey Foxy, long time no speak, how's the vixen??

I have no experience of 12v conversion but suspect the extra E on the cutout is for an earth wire. It was most probably fitted to an Austin 12's wooden, and therefore non-earthing, bulkhead originally.

I have several bacon slicer starter motors that I know to work well and I have also just purchased two brand new batteries, it's a "loverly day" and I am working on the cars for all of it so why not (push?) start the Chummy and head over to try and solve the problem? However, if 12v is your prefered option, Malcolm Watts is your man!



Re: Thinking about trying 12V

When I converted to 12volt I used a an RB106 regulator but used the citout part only. Never had a problem. Dynamo will be OK but just adjust the 3rd brush to cope with its new environment. Batterywise look for a Spanish built Suziki Vitara battery


Re: Thinking about trying 12V

Quote: Red Fox

My question is has anybody who has carried out a change from a 6V to a 12V system and used the 12V CF1 cutout had any problems with the charge rate of the 6V DFL dynamo? I have seen references to removing the third brush and also references to retaining the third brush but reducing the dynamo output.

Yes and no. I was converting a later car (Ruby), but using the 12 volt equivalent of the original cut-out as you are. My problem was that the dynamo was producing too much charge, even with the third brush wound back. I presume the doubling of the voltage in the field circuit was overexciting the field magnetism and resulting in extra chrage.

The easiest answer to that one is to put extra resistance into the field circuit. Later cars like mine have a half charge setting which already does this. It is an easy job to add further resistance in - just make sure you buy a resistor rated to a high enough wattage with a decent heat sink, and site it somewhere where it gets enough airlow, otherwise that will melt too (though better than the dynamo melting). You can put a switch under the dash to bypass it when you have the headlamps on if you want.

Third brush removal only comes into it if you are fitting a "modern" 2 bobbin voltage regulator, such as that found on the Morris Minor. Since you have a proper 12 volt cutout, I would stick with it - a regulator would be a lot cheaper to buy if you were starting from scratch.

People who actually know something about elastic trickery may have more to add - these are just my layman's experiences.


Re: Thinking about trying 12V

I converted my 28 Top Hat to 12 Volts using Malcolm Watts Articles and Postings on this Site. I must say that has been entirely successful. I used a 6 volt CF1 cutout with a 33 ohm resistor from cut-out coil to earth as per the corwall site instructions. this resistor can be found in the back of later bakelite type cutout /regulators of lucas manufacture. I also put a similar resistor of about 1 ohm in the line to the field windings ,at the cut out junction. . a 2-3 ohm resistor was retained on the C35 type generator between F and D to give half charge facility. the generator was left as is with third brush undisturbed. It worked fine right from the start . I am running 60 /55 watt Halogen bulbs with the lights on I can balance the drain at 40 MPH in top gear. The lights are as good as a modern.!
I run the lights during the day if I am making a long journey, as I am producing 8-10 amps at 45 MPH. I have just done a trip of 1000 miles in the south island of New Zealand and the system performed without any trouble. I use a RIde on lawnmower battery which fits snugly in the original battery box. I would have no hesitation recommending this conversion, I believe in myself that it actually reduces the load and wear and tear on the generator, which can only be a good thing I am using a Narva 7" lamp kit which are available off the shelf here in N Z . They fit into the 28-31 headlamps perfectly , once the original clips are carefully removed. I glued them in a modern adhesive sealant. they have an inbuit side light bulb like the originals. The part number is 72038 C/W bulbs ad dust covers /Connectors. They are about 50 pound retail here in N Z