Joined: Apr 2018 Posts: 191 Threads: 76
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Hi,
My Ulsteroid has a C35M dynamo and what I believe is a CF3 cut-out.
Neither the dynamo, cut out or switch panel incorporate a ½ charge resistor so at present I only get any charge in the winter position.
I’ve seen various suggestions of winding an open coil of resistance wire and attaching it between the dynamo terminals but it’s all a bit vague and having an exposed coil sound a bit vulnerable especially if it's not wound on a core.
Is there a proprietary wire wound resistor I could use and what sort of resistance / current capacity would I need?
Any suggestions would be much appreciated.
John.
Joined: Aug 2017 Posts: 610 Threads: 19
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Location: Hampshire UK
I second the advice for a metalclad 3 ohm resistor. To achieve its full 25 Watt power rating it is designed to be bolted to a flat heatsink. For the summer charge application I'd expect the dissipation to be only a few watts, so you should be OK just mounting it in air. From a mechanical point of view probably still best to bolt at least one end down to something firm. The metal cases are electrically insulated from the resistor.
Joined: Aug 2017 Posts: 1,462 Threads: 26
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Location: North Yorkshire
I've been using these since the mid 1990s with no problems at all. One of the bolts for the Patent Plate makes an ideal fixing behind the dashboard.
Steve
Joined: Jan 2019 Posts: 1,567 Threads: 20
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Location: Bala North Wales
Car type: 1933 RP Standard Saloon
Following advice on this forum given previously, I fitted a 100W 2 Ohm resistor, bolted to the bulkhead behind the Dash. £2.97 from fleabay. It cuts the charging rate exactly in half.
Joined: Dec 2017 Posts: 1,160 Threads: 68
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Location: Nottinghamshire. Robin Hood County
Car type: Austin Ruby Mk1 1935
03-08-2020, 05:05 PM
(This post was last modified: 03-08-2020, 05:09 PM by John Mason.)
I use a little Non to expensive electric box of tricks made by Ron Bailey a member of the PWA7C with instruction from him slight modifications are made to the wiring of the dynamo and the 3rd brush is removed. This allows for better charging of the battery with no requirement for Summer/Winter switching. I have had this for the last 6 years without any problems. The other benefit is that it charges faster and is kinder to the battery as it shuts off charge completely when the battery is full of charge
John Mason
Would you believe it "Her who must be obeyed" refers to my Ruby as the toy.
Joined: Jan 2019 Posts: 1,567 Threads: 20
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Location: Bala North Wales
Car type: 1933 RP Standard Saloon
I recall from my youth being told that a cold start using the starter took the dynamo between 5 and 10 minutes to bring the battery to full charge.
Bearing this in mind. when I first start the car, I use the full charge setting for ten minutes and then turn the switch to the half charge setting for the rest of the journey. After hot start, I switch to full charge for between 3 and 5 minutes and then go back to half charge.
I haven't had any battery problems so far.
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
03-08-2020, 08:52 PM
(This post was last modified: 03-08-2020, 08:56 PM by Bob Culver.)
The power dissipated is the volts dropped squared divided by the resistance ; so 10 watts should be far more than adequate. Someone here quite recently used a bulb so if you have lots of half dud ones could experiment.
The original fuse in the later cars is a mystery. It seems to only protect the resistor.
Dave T the resitor is not visible and my not be electrically connected . John Cornforths circuit diagram might be useful.