Joined: Aug 2017 Posts: 217 Threads: 19
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A bit of a hornet's nest this one. When working well 6 volt systems are fine,but they seem to be at the limit of many tolerances and it would appear that it takes very little to cause system to malfunction. The conversion that I made to 12 volts has given no trouble at all in the last five years.
I converted my RP to 12 volts as I needed better lighting when driving to & from work,A VAST IMPROVEMENT. Better starting,acceleration under load,charge rate,can use LED bulbs and other accessories such as GPS CD's etc.
The conversion was easy.The existing 6 volt dynamo, modified to two brush operation, will easily produce the 12 volts required and the voltage control is by a electronic unit under the dash out of sight.A change of bulbs,coil,battery and you're done.Not a difficult job,control unit purchased from Dave Lindsley & cost in 2010 was £106.& includes instructions on dynamo mods, again very easy.A lot cheaper than fitting non standard looking parts.The only visual difference is the dynamo brush cover which I changed for some fine wire mesh to aid cooling. The only item that doesn't operate is the fuel gauge which didn't work on 6v either, I'm currently looking for a gauge to replace the dash instrument to match up with a modified "Mini" in tank sender,but will always rely on the dipstick method.( Copied from my reply on old forum pages".
Joined: Aug 2017 Posts: 121 Threads: 6
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Oops. Im currently running no volts to my lamps. They are not very good in the dark.
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
This topic is extensively covered on the old website. Several gave full details for simple conversions. Several more gave incomplete information so that the conversions seemed to effectively defy physical laws. Other conversions were more complex with (dubious) use of mechanical volt regulators, or more appropriate electronic regulators. As the original field winding is intended for just 4 or 5volts it is easy to cook. And, esp with the supplied field current not apparent on the ammeter, easy to exceed the safe total armature current and cook that too, as so many have been. Some 12v conversions I have seen are used for little more than ign current with the battery bench charged. Whatever, cars are rendered non standard and unless documented and kept with the car, become a puzzle for many, including auto electricians, already baffled by the 3rd brush. The most refined conversions as above combine 2 brush operation and electronic regulators, and the best of these have rewound field windings .
A major advantage of 12v is cheaper more readily available batteries and modern regulated bench chargers for.
As others have pointed out, many Sevens were used for general running including extensive at night. Modern brake lights and modern traffic holdups as at lights are a drain but the engine can be kept mildly revving. and headlamps turned off. A fundamental problem is that original 18w 6v headlamp bulbs are not available or considered too feeble so cars are run with larger bulbs. If ammeter max with lights off is limited to safe 8-10 amps the battery will then discharge at night. But you can still go a long way. (in emergency one lamp can be disconnected!)
For those with minimum electrical savvy much to be said for the original with charge rate kept within the recognised limit.
Joined: Aug 2017 Posts: 3,210 Threads: 100
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Location: Darkest Bedfordshire
I suggest the real problem with 6v is clapped out parts and amateur tinkering. I had my dynamo professionally overhauled by Wynalls longer ago than I can remember and it hasn't missed a beat since. I have just bought a new battery from Shield which has such a large capacity you scarcely need a dynamo anyway. The same company provides a modern, off the shelf trickle charger for same which will keep it in good shape. More expensive than 12v battery perhaps, but hardly enough to justify converting, in my humble opinion.
Joined: Aug 2017 Posts: 2,246 Threads: 33
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Location: Deepest Frogland 30960
Car type: 1933 RP Standard Saloon
On the subject of batteries. My car has an exide 80Ah 6v battery. I keep it topped up when not in use by connecting it to an accumate conditioner. When running I set the charge to winter for the first mile or so just to put back what was used up in starting and then run on summer setting with the 3rd brush set to give about 1amp. The battery was new in 2011.
Joined: Mar 2015 Posts: 5,186 Threads: 223
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Location: Scotchland
These batteries are excellent Bruce - by far the best performance I have experienced.
Joined: Dec 2017 Posts: 1,131 Threads: 66
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Location: Nottinghamshire. Robin Hood County
Car type: Austin Ruby Mk1 1935
I use the amber round dome shaped indicator lamps with 6 volt festoon bulbs on my Ruby fitted to brackets made from mild steel and bolted to the bumper bolts. I have no problems being seen indicating. I also have them wired via a relay so that both flashing indicators and original semaphores work together.
John Mason.
Joined: Aug 2017 Posts: 177 Threads: 1
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Like Bruce I have an Exide 80Ah of 2011,if you look after a battery and keep it fully charged it will last a good time.
Joined: Dec 2017 Posts: 1,131 Threads: 66
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Location: Nottinghamshire. Robin Hood County
Car type: Austin Ruby Mk1 1935
I use the amber round dome shaped indicator lamps with 6 volt festoon bulbs on my Ruby fitted to brackets made from mild steel and bolted to the bumper bolts. I have no problems being seen indicating. I also have them wired via a relay so that both flashing indicators and original semaphores work together.
John Mason.
