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+--- Thread: Converting cut out to 12v (/showthread.php?tid=8851)
Converting cut out to 12v - 12jslater - 31-08-2023
Before Anything is said I know 6v is fine however this a special so originality is off little concern, what value resistor do I use from the cutout to earth? I believe it’s around 30ohms but what would the wattage be?
Thank you!
RE: Converting cut out to 12v - John Cornforth - 31-08-2023
Hi
The shunt coil for a CFR2 should have a resistance of 33 to 39 ohms. Other 6V cutouts will be similar.
I suggest you measure yours with an ohmmeter between the +D and Earth terminals.
Add an equal value resistor between the cutout earth and the car earth and it will now pull-in at 13 +/- 0.4 volts rather than 6.5 +/- 0.2 volts.
You might need a couple of resistors in series to get the right value, e.g. a 33 ohm plus a 3.3 ohm to get 36.3 ohms.
The higher the value, the higher the pull-in voltage
The resistor will dissipate just over a watt, so a wirewound type rated at 2 watts or more will suit.
RE: Converting cut out to 12v - andrew34ruby - 31-08-2023
Or dispense with the cutout and use a diode to prevent the battery from draining through the dynamo. Purpose designed diodes are available or just use a couple of diodes in parallel, using diodes from an old alternator rectifier. Like this...
https://www.ebay.co.uk/itm/256080235299?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&mkscid=101&itemid=256080235299&targetid=1814673647262&device=c&mktype=pla&googleloc=1006766&poi=&campaignid=19089547614&mkgroupid=142438599285&rlsatarget=aud-1165553645405:pla-1814673647262&abcId=9303859&merchantid=6995734&gclid=Cj0KCQjw9MCnBhCYARIsAB1WQVXb4HuhXBfE3R0zvtpE5t7T8glFw1ZIW1HZCn1nPn-Vl391_6Bjau0aAoNdEALw_wcB
RE: Converting cut out to 12v - PaulS - 01-09-2023
The attached may be helpful.
I bought a repro Lucas 12v RB106 regulator and cut out, I disabled the regulator as it is not needed.
RE: Converting cut out to 12v - 12jslater - 04-09-2023
If I wanted to connect one of those alternator regulators how would I go about it? I’m not familiar with them?
RE: Converting cut out to 12v - andrew34ruby - 04-09-2023
(04-09-2023, 01:31 PM)12jslater Wrote: If I wanted to connect one of those alternator regulators how would I go about it? I’m not familiar with them?
I simply snipped a couple of separate diodes out of that pack, and joined them in parallel.
RE: Converting cut out to 12v - PaulS - 14-09-2023
Current through a 30ohm resistor I=V/R, 12/30 = 0.4 Amps max through the resistor.
Power = IV, 0.4 x12v = 4.8Watts, therefore a 10W wire wound resistor or a metal clad one mounted to the chassis should be good.
The resistor may already be included with the 12v cut-out.
RE: Converting cut out to 12v - John Cornforth - 14-09-2023
Hi PaulS
In the application discussed, the added 30 ohm resistor only has 6 volts (nominal) across it, the other 6 being dropped in the shunt coil. So that's 0.2 Amps and 1.2 watts dissipation in the resistor. If you assume 7 volts then the dissipation is 1.6 Watts.
I'm pretty sure that 12 volt versions of the cutout use a higher resistance shunt coil, presumably 120 ohms with twice as many turns of finer wire so that it works with 0.1 Amp.